Tool Design Engineering

Die Casting History, Future and advantages

2009-03-23T23:54:00.000-07:00

History of Die Casting

The earliest examples of die casting by pressure injection - as opposed to casting by gravity pressure occurred in the mid-1800s. By 1892, commercial applications included parts for phonographs and cash registers, and mass production of many types of parts began in the early 1900s.
The first die casting alloys were various compositions of tin and lead, but their use declined
with the introduction of zinc and aluminum alloys in 1914. Magnesium and copper alloys quickly followed, and by the 1930s, many of the modern alloys still in use today became available.
The die casting process has evolved from the original low-pressure injection method to techniques including high-pressure casting at forces exceeding 4500 pounds per square inch squeeze casting and semi-solid die casting. These modern processes are capable of producing high integrity, near net-shape castings with excellent surface finishes.

Future of Die Casting

Refinements continue in both the alloys used in die casting
and the process itself, expanding die casting applications into almost every known market. Once limited to simple lead type, today's die casters can produce castings in a variety of complex shapes and sizes.

Advantages of die Casting

Die casting is an efficient, economical process offering a broader range of shapes and components than any other manufacturing technique. Parts have long service life and may be designed to complement the visual appeal of the surrounding part. Designers can gain a number of advantages and benefits by specifying die cast parts.

High-speed Production : Die casting provides complex shapes within closer tolerances than many other mass production processes. Little or no machining is required and thousands of identical castings can be produced before additional tooling is required.

Dimensional Accuracy and Stability : Die casting produces parts that are durable and dimensionally stable, while maintaining close tolerances. They are also heat resistant.

Strength and Weight : Die cast parts are stronger than plastic injection moldings having the same dimensions. Thin wall castings are stronger and lighter than those possible with other casting methods. Plus, because diecastings do not consist of separate parts welded or fastened together, the strength is that of the alloy rather than the joining process.

Multiple Finishing Techniques : Die cast parts can be produced with smooth or textured surfaces, and they are easily plated or finished with a minimum of surface preparation.

Simplified Assembly : Die castings provide integral fastening elements, such as bosses and studs. Holes can be cored and made to tap drill sizes, or external threads can be cast.

High pressure Die Casting Process

High pressure die casting is a manufacturing process in which molten metal (aluminum) is injected with a die casting machine under force using high speed and considerable pressure into a steel mold or die to form products. Die casting machines are typically rated in clamping tons
equal to the amount of pressure they can exert on the die. Machine sizes range from 400
tons to 4000 tons. Regardless of their size, the only fundamental difference in die casting machines is the method used to inject molten metal into a die. The two methods are hot chamber or cold chamber. A complete die casting cycle can vary from less than one second for small components weighing less than an ounce, to two-to-three minutes for a casting of several pounds, making die casting the fastest technique available for producing precise non-ferrous metal parts. Because of the excellent dimensional accuracy and the smooth surfaces, most high pressure die castings require no machining except the removal of flash around the edge and possible drilling and tapping holes. High pressure die casting production is fast and inexpensive relative to other casting processes.

There are several aluminum alloys with different mechanical properties and chemical breakdowns. Aluminium is used in 80-90% of the high pressure die casting alloys available in the world today. In many cases aluminum high pressure die casting can replace steel, increasing strength and reducing part weight. high pressure die casting parts are produced in small sizes of less than 30 gms up to large sizes.

This equipment consists of two vertical platens on which bolsters are located which hold the die halves. One platen is fixed and the other can move so that the die can be opened and
closed. A measured amount of metal is poured into the shot sleeve and then introduced into the mould cavity using a hydraulically-driven piston. Once the metal has solidified, the die is opened and the casting removed.In this process, special precautions must be taken to avoid too many gas inclusions which cause blistering during subsequent heat-treatment or welding of the casting product. Both the machine and its dies are very expensive, and for this reason pressure die casting is economical only for high-volume production.Thousands of high pressure die casting parts can be produced in a single day with the right die casting tooling and proper high pressure die casting part design. Production of quantities of 20,000 to 30,000 high pressure die casting parts a week in some cases. Most of the casting manufacturers are capable to design or work with buyer's designer to develop high volume high pressure die casting tooling.

High pressure die casting (HPDC) is a widely used manufacturing process for mass production of components of aluminium and magnesium alloys, such as automotive transmission housings and gearbox parts. Molten metal is injected at high speed (50 to 100 metres/sec) and under very high pressures into a die through a complex gate and runner system. The geometrical complexity of the die leads to strongly three-dimensional fluid flow. Within the die cavity, jetting and splashing results in liquid droplet and possibly atomised spray formation. Crucial to the production of homogeneous cast components with minimal entrapped voids
is the order in which the various parts of the die fill and the positioning of the gas exits. This is determined by the design of the gate configuration and the geometry of the die.

Basic functions of Die Casting

Hold molten metal in the shape of the desired casting. Provide a means for molten metal to get to a space where itwill be held to the desired shape. Remove heat from the molten metal and to allow the metal to solidify To provide for the removal of the casting.

Engineering Ferrous Metal

2009-03-16T01:14:00.000-07:00

Engineering Ferrous Metal

Use of Ferrous Metals in Precision Presswork & Tooling
All metals can be classified as Non ferrous metals and Ferrous metals. Ferrous metals are those metals which contain iron. They may have small amounts of other metals or other elements added, to give the required properties. All ferrous metals are magnetic and give little resistance to corrosion.
Most commonly used ferrous metals are Mild Steel, High Speed Steel, Stainless Steel, High Tensile Steel and Cast Iron.

Here are some ferrous metals with are used for tool making, manufacturing of pressed components and other industrial supplies.

Mild Steel:

It is the most commonly used ferrous metal. Its major properties are Toughness, high tensile strength and ductility. It contains 0.15 to0.30% carbon. Because of low carbon content it can not be hardened and tempered. It must be case hardened. It is normally used in manufacturing of girders, plates, nuts and bolts and other general purposes.

Cast Iron:

Cast iron is another example of commonly used ferrous metal. It is hard, brittle, strong, cheap, and self-lubricating ferrous metal. It is remelted pig iron with small amounts of scrap steel. It can be classified as Whitecast iron, grey cast iron, and malleable cast iron. It is normally used in the manufacturing of heavy crushing machinery. car cylinder blocks, vices, machine tool parts, brake drums, machine handle and gear wheels, plumbing fitments etc. Its an important ferrous metal in automotive pressing.

High Tensile Steel:

It is very strong and very tough ferrous metal and is exclusively used for manufacturing of Gears, shafts, engine parts etc. This is one of the most frequently used ferrous metals in industries because of its strength, hardness and toughness.

Stainless Steel

Its another very important ferrous metal. It comprises of 18% chromium, and 8% nickel. Its special characteristic is its strong resistance to corrosion. Its common uses are Kitchen draining boards, Pipes, cutlery and aircraft.

High Speed Steel

High speed steel is also a ferrous metal. It contains medium carbon, tungsten, chromium and vanadium. It can be hardened, tempered and can be brittle. Its special characteristic is that it retains hardness at high temperatures.

High Carbon Steel:

High Carbon Steel is a ferrous metal which contains of 0.70% to 1.40% carbon. The major characteristic is its hardness. It is the hardest of the carbon steels, but is less ductile, tough and malleable. It is used in making os Chisels, hammers, drills, files, lathe tools, taps and dies.

Medium Carbon Steels:

As the name says, this ferrous metal contains less Carbon contents, 0.30% to 0.70%. It is stronger and harder than mild steels, less ductile, tough and malleable. It is used in making metal ropes, wire, garden tools, springs etc.

Introduction to Manufacturing Techniques for composites

2009-03-11T21:14:00.000-07:00

Introduction to Manufacturing Techniques for composites

Every material possesses unique physical, mechanical, and processing characteristics and therefore a suitable manufacturing technique must be utilized to transform the material to the final shape. One transforming method may be best suited for one material and may not be an effective choice for another material. For example, wood is very easy to machine and therefore machining is quite heavily utilized for transforming a wooden block to its final shape. Ceramic parts are difficult to machine and therefore are usually made from powder using hot press techniques. In metals, machining of the blank or sheet to the desired shape using a lathe or CNC machine is very common. In metals, standard sizes of blanks, rods, and sheets are machined and then welded or fastened to obtain the final part. In composites, machining of standard-sized sheets or blanks is not common and is avoided because it cuts the fibers and creates iscontinuity in the fibers. Exposed and discontinuous fibers decrease the performance of the composites. Moreover, the ease of composites processing facilitates obtaining near net shape parts.
Composites do not have high pressure and temperature requirements for part processing as compared to the processing of metal parts using extrusion, roll forming, or casting. Because of this, composite parts are easily trans formed to near net shape parts using simple and low cost tooling. In certain applications such as making boat hulls, composite parts are made at room
temperature with little pressure. This lower energy requirement in the pro-cessing of composites as compared to metals offers various new opportuni-ties for transforming the raw material to near-net-shape parts. There are two major benefits in producing near-net- or net-shape parts. First, it minimizes the machining requirement and thus the cost of machining. Second, it minimizes the scrap and thus provides material savings. There are cases when machining of the composites is required to make holes or to create special features. The machining of composites requires a different approach than machining of metals.

Composite production techniques utilize various types of composite raw materials, including fibers, resins, mats, fabrics, prepregs, and molding compounds, for the fabrication of composite parts. Each manufacturing technique requires different types of material systems, different processing conditions, and different tools for part fabrication. Each technique has its own advantages and disadvantages in terms of processing, part size, part shapes, part cost, etc. Part production success relies on the correct selection of a manufacturing technique as well as judicious selection of processing parameters. The main focus of this chapter is to describe emerging and commercially available manufacturing techniques in the field of thermoset and thermoplastic based composite materials. Various composites manufacturing techniques are discussed in terms of their limitations, advantages, methods of applying heat and pressure, type of raw materials used, and other important parameters. The basic knowledge of these processes will help in selecting the right process for an application.

Manufacturing Process Selection Criteria

It is a monumental challenge for design and manufacturing engineers to select the right manufacturing process for the production of a part, the reason being that design and manufacturing engineers have so many choices in terms of raw materials and processing techniques to fabricate the part. This section briefly discusses the criteria for selecting a process. Selection of a process depends on the application need. The criteria for selecting a process depend on the production rate, cost, strength, and size and shape requirements of the part, as described below.

Production Rate/Speed

Depending on the application and market needs, the rate of production is different. For example, the automobile market requires a high rate of production, for example, 10,000 units per year (40 per day) to 5,000,000 per year (20,000 per day). In the aerospace market, production requirements are usually in the range of 10 to 100 per year. Similarly, there are composites manufacturing techniques that are suitable for low volume and high volume production environments. For example, hand lay-up and wet lay-up processes cannot be used for high volume production, whereas compression molding (SMC) and injection molding are used to meet high volume production needs.

Cost

Most consumer and automobile markets are cost sensitive and cannot afford higher production costs. Factors influencing cost are tooling, labor, raw materials, process cycle time, and assembly time. There are some composite processing techniques that are good at producing low cost parts, while others are cost prohibitive. Determining the cost of a product is not an easy task and requires a thorough understanding of cost estimating techniques. The cost of a product is significantly affected by production volume needs as well. For example, compression molding (SMC) is selected over stamping of steel for the fabrication of automotive body panels when the production volume is less than 150,000 per year. For higher volume rates, steel stamping is preferred.

Performance

Each composite process utilizes different starting materials and therefore the final properties of the part are different. The strength of the composite part strongly depends on fiber type, fiber length, fiber orientation, and fiber content (60 to 70% is strongest, as a rule). For example, continuous fiber composites provide much higher stiffness and strength than shorter fiber composites. Depending on the application need, a suitable raw material and thus a suitable composite manufacturing technique are selected.

Size

The size of the structure is also a deciding factor in screening manufacturing processes. The automobile market typically requires smaller sized components compared to the aerospace and marine industries. For small to medium sized components, closed moldings are preferred; whereas for large structures such as a boat hull, an open molding process is used.

Shape

The shape of a product also plays a deciding role in the selection of a production technique. For example, filament winding is most suitable for the manufacture of pressure vessels and cylindrical shapes. Pultrusion is very economical in producing long parts with uniform cross-section, such as circular and rectangular.

Design for manufacturing (DFM) in Composites

2009-03-11T21:03:00.000-07:00

Design for manufacturing (DFM) in Composites

DFM (design for manufacturing) can be defined as a practice for designing products, keeping manufacturing in mind. DFM starts by taking a plain sheet of paper and identifying a product’s functional, performance, and other requirements. It utilizes rules of thumb, best practices, and heuristics to design the part. Best practices for a highquality product design are to minimize the number of parts, create multifunctionality in the part, minimize part variations, and create ease of handling. DFM involves meeting the end use requirements with the lowest-cost design, material, and process combinations.

In the past, several product problems arose because of poor design. The designers were not aware of the various manufacturing techniques available on the market, nor the capabilities of each manufacturing technique. As a result, products were heavy, had many parts and thus many assembly operations, and resulted in poor quality and increased cost. To effectively design the product, manufacturing knowledge needs to be incorporated into product design. The designer should know how the process and design interact. In general, the real challenge in designing composite products is to develop a good understanding not only of engineering design techniques, but also of processing and material information.

The purpose of DFM is to:

• Narrow design choices to optimum design (Figure)
• Perform concept generation, concept selection, and concept improvement
• Minimize product development cycle time and cost
• Achieve high product quality and reliability
• Simplify production methods
• Increase the competitiveness of the company
• Have a quick and smooth transition from the design phase to the production phase
• Minimize the number of parts and assembly time
• Eliminate, simplify, and standardize whenever possible

DFM Implementation Guidelines

The main objective of DFM is to minimize the manufacturing information content in the product without sacrificing functional and performance requirements. DFM can also be applied for a product that is already in production or on the market. The main objective here will be to make the product more cost competitive. The following DFM guidelines are applicable to products made of composites, metals, and plastics.

Minimize Part Counts

There is good potential for part integration by questioning the need for separate parts. At General Motors, Ford, Chrysler, GE, IBM, and other companies, DFM strategies have reduced the total number of part counts by 30 to 60% in many product lines. Composite materials offer good potential for part integration. Minimization of part counts can result in huge savings by eliminating the need for assembly, inventory control, storage, inspection, transportation, and servicing. According to Huthwaite,3 “the ideal product has a part count of one.” In general, more than one part is needed if there is a relative motion requirement, a different materials requirement, a different manufacturing requirement, or an adjustment requirement. An example of part integration is the steel identification badge clip that has four different parts but can be replaced by a single injection molded plastic part. Another example is the monocoque composite bicycle frame. Do not perform part intergration if design becomes overly complex, heavy, or difficult to manufacture.

A typical automobile, airplane, or luxury yacht consists of thousands of parts to meet various functional or performance needs. For example, a Heloval 43-meter luxury yacht from CMN Shipyards is comprised of about 9000 metallic parts for hull and superstructure and over 5000 different types of parts for outfitting.

To determine if a part is a potential candidate for elimination, the following questions should be asked:
1. Do the parts move relative to each other?
2. Is there any need to make parts using a different material?
3. Will the part require removal for servicing or repair?
4. Will there be a need for adjustment?

If the answers to the above questions are “no,” then the part is a potential candidate for replacement. The following guidelines can be used to minimize the number of parts.
• Question and justify the need for a separate part. Ask the four
questions above; and if the answer is “no,” then redesign the prod-
uct by eliminating the separate part.
• Create multifunctionality features in the part.
• Eliminate any product feature that does not add any value for the
customer.
• Use a modular design.

Eliminate Threaded Fasteners

Avoid the use of screws, nuts, bolts, and other fasteners in the product. It is estimated that driving a screw into the product costs almost 6 to 10 times the cost of a screw. The use of fasteners increases inventory costs and add complexity in assembly. Fasteners are used to compensate for dimensional variation, to join two components, or for part disassembly. The use of fasteners creates the potential for a part to become loose during service. IBM has used this philosophy to redesign its printer, eliminating many screws and replacing them with snap fit assembly. The resulting design had 60% less parts and 70% reduced assembly time.
Snap fits are used with plastics or short fiber composite parts and provide ease of assembly due to the lack of any installation tool requirement. General concerns regarding the use of snap-fits include strength, size, servicing, clamp load, etc.

Minimize Variations

Part dimensional variation as well as property variation are the major sources of product defects and nonconformities. Try to use standard parts off the shelf and avoid the use of special parts. Eliminate part variations such as types of bushings or O-rings, seals, screws, or nuts used in one application. The same size would mean the same tool for assembly and disassembly. This guideline aims to reduce part categories and the number of variations in each category, thus providing better inventory control and part interchangeability.

Easy Serviceability and Maintainability

Design the product such that it is easy to access for assembly and disassembly. The part should be visible for inspection and have sufficient clearance between adjacent members for scheduled maintenance using wrench, spanner, etc.

Minimize Assembly Directions

For product assembly, minimize assembly direction. While designing the product, think about the assembly operations needed for various part attachments. It is preferable to use one direction; z-direction assembly operation allows gravity to aid in assembly. A one-direction assembly operation minimizes part movement as well as the need for a separate assembly station. It is better in terms of an ergonomics point of view as well.

Provide Easy Insertion and Alignment

When there are more than two parts in a product, the mating parts need to be brought close by performing insertion or alignment. Some guidelines for easy insertion and alignment are:

• Provide generous tapers, chamfers, and radii for easy insertion and assembly.
• Provide self-locating and self-aligning features where possible.
• Avoid hindrance and obstruction for accessing mating parts.
• Avoid excessive force for part alignment.
• Design parts to maintain location.
• Avoid restricted vision for part insertion or alignment.

Consider Ease for Handling

In an assembly plant, various parts are kept in separate boxes near the assembly station. Workers pick up those parts and assemble them using adhesive bonding or mechanical fastening or by slip fit or interference fit. Avoid using parts such as springs, clips, etc., which are easy to nest and become interlocked. It disrupts the assembly operation and creates irritation for the worker. For smooth assembly operation and ease of handling, parts should not be heavy and should not have many curves, thus reducing the potential for entanglement. To avoid physical fatigue of the worker, part and assembly locations should be easy to access. Parts should be symmetric to minimize handling and aid in orienting. Add features that help guide the part to its desired location. The following suggestions can improve part handling. These suggestions are more applicable for a high volume production environment.

• Minimize handling of parts that are sticky, slippery, fragile, or have sharp corners or edges.
• Keep parts within operator reach.
• Avoid situations in which the operator must bend, lift, or walk to get the part.
• Minimize operator movements to get the part. Avoid the need for two hands or additional help to get the part.
• Avoid using parts that are easy to nest or entangle.
• Use gravity as an aid for part handling.

Design for Multifunctionality

Once an overall idea of the product’s functions is gleaned, one can design individual components such that they provide maximum functionality. It is preferable to use molding operations that provide net shape or near netshape parts. For example, an injection molded composite housing part meets the structural requirement of the product and has built in features for alignment, self locating, mounting, and a bushing mechanism. This technique helps minimize the number of parts.

Design for Ease of Fabrication

In composite part fabrication, product design cannot be made effective without knowledge of the manufacturing operations. Each manufacturing process has its strengths and weaknesses. The product design should be tailored to reap the benefits of the selected manufacturing process. For example, if close tolerances are required on the inside diameter of a tube, then filament winding is preferred compared to a pultrusion process. The design should be simplified as much as possible because it helps in manufacturing and assembly and thus in cost savings. Workers and others who are dealing with the products can easily understand simplified design.

Prefer Modular Design

A module is a self contained component that is built separately and has a standard interface for connection with other product components. For example, a product that has 100 parts can be designed to have four or five modules.

Each module can be independently designed and improved without affecting the design of the other modules. Modular design is preferred because it helps in the final assembly, as well as in servicing where a defective module can be easily replaced by a new module. Modular design can be found in aerospace, automotive, computer, and other products. For example, steering systems, bumper beams, and chassis systems are separate modules designed, produced, and improved upon by independent organizations and assembled in the vehicle. In each of these modules, there are many other modules, which are again designed by various groups of the organization.

Design for Manufacturing of Composites

2009-03-11T20:54:00.000-07:00

Design for Manufacturing of Composites

Companies are constantly being challenged to find means to do things better, faster, and cheaper. Companies can no longer overdesign the product, nor can they afford a lengthy product development cycle time. The products can no longer be viewed individually, and designers can no longer pass the engineering concept to the manufacturing engineer for finding the ways to make it. The design engineer and manufacturing engineer need to work together to come up with a best design and manufacturing solutions for fabricating the products costeffectively. For example, if design and manufacturing engineers work separately to create the design of the outer body panels of automobiles, the manufacturing engineer will come up with a flat or square box-like product that is cheaper and quicker to make, but no one would buy it. On the other hand, the design engineer will come up with a design that is creative, eye-catching, and satisfies all customer needs and requirements, but it would be unaffordable. In either case, the product will not sell.

To be competitive, the product needs to be designed in a minimum amount of time, with minimum resources and costs. To meet current market needs, several philosophies, such as design for manufacturing, design for assembly, design for quality, design for life cycle, and concurrent design, are being developed. The primary aim of these philosophies is to think about the manufacturing, assembly, quality, or life-cycle needs during the design process. This is achieved by working concurrently in a concurrent engineering environment to avoid later changes in the design.

A product can be designed in many ways to meet functional, performance, and other requirements. Therefore, different organizations come up with different design concepts to meet the same application needs. The solution for an application depends on how the problem is defined to the designer as well as the knowledge and creativity of the designer. Because there are many design solutions to a problem, the question arises as to how to know which design is the best solution. It is also possible that there may be other designs that may be better than the realm of the designer. Design for manufacture is a tool that guides the designer in coming up with better design choices and then provides the optimum design. It is a tool for concept generation, concept approval, and concept improvement. It integrates processing knowledge into the design of a part to obtain maximum benefits and capabilities of the manufacturing method. To come up with the best design, the manufacturing engineer should have a good knowledge of the benefits and limitations of various composite manufacturing techniques. The team members should also be familiar with tools such as design for manufacturing (DFM), design for assembly (DFA), etc. for developing high-quality design. As compared to metals, composite materials offer the highest potential of utilizing DFM and part integration, and therefore can significantly reduce the cost of production.

Engineers utilizing isotropic materials such as aluminum and steel traditionally fabricate parts by first selecting raw materials from a design handbook based on performance requirements. Once the raw material is selected, the manufacturing process to fabricate the part is identified. This philosophy is not viable in the field of composite materials. With engineered composite materials, the material selection, design, and manufacturing processes all merge into a continuum philosophy embodying both design and manufacture in an integrated fashion. For example, a rod produced by filament winding, pultrusion, RTM, or braiding would impart distinct stiffness, damping, and mass characteristics due to different fiber and resin distributions and fiber volume fractions. Composites manufacturing processes create distinct microstructural properties in the product.

The best design example is Nature’s design in which different artifacts are grown in the entire system as a single entity. In contrast, engineers fabricate various parts and assemble them together. At present, we do not have biological manufacturing processes but we have plenty of opportunities for innovation by learning and imitating the no-assembly designs of the natural world.1 Designs in nature are strong but not necessarily stiff they are compliant. Nature tries to make the design compliant, whereas engineers traditionally make the structure and mechanism stiff. Ananthasuresh and Kota1,2 developed a one component plastic stapler in which they replaced the conventional steel stapler with no assembly design. Compliant mechanisms are single piece, flexible structures that deliver the desired motion by undergoing elastic deformation as opposed to rigid body motion.

Product Fabrication Needs in Composites

2009-03-10T06:04:00.000-07:00

Product Fabrication Needs in Composites

To make a part, the four major items needed are:

1. Raw material
2. Tooling/mold
3. Heat
4. Pressure

Depending on the manufacturing process selected, a suitable raw material is chosen and laid on the tool/mold. Then, heat and pressure are applied to transform the raw material into the final shape. Heat and pressure requirements are different for different material systems. Solid materials such as metals or thermoplastics require a large amount of heat to melt the material for processing, whereas thermosets require less heat. In general, the higher the melting temperature of a material, the higher the temperature and pressure required for processing. For example, steel, which melts at 1200°C, requires higher temperatures and pressures to process the part. Aluminum, which melts at around 500°C, requires less heat and pressure for transforming the shape as compared to steel processing. Thermoplastics have melting temperatures in the range of 100 to 350°C and therefore require lesser amounts of heat and pressure as compared to steel and aluminum. Thermosets are in the liquid state at room temperature and therefore are easy to form and process. Thermosets require heat for rapid curing of the material. The temperature requirement for thermosets depends on resin formulation and cure kinetics. In composites, fibers are not melted and thus heat is required for proper consolidation of the matrix materials only.

The higher pressure and temperature requirements during a manufacturing process need strong and heavy tools, which increase the cost of tooling. In addition to higher tooling costs, the higher pressure and temperature requirements mandate special equipment, which is another source of increased processing cost. For example, the higher pressure requirement during SMC molding requires large and bulky equipment and usually costs more than $1 million. The ideal manufacturing process will be the one that requires extremely low amounts of heat and pressure and is quick to process in order to obtain significant processing cost savings.

Every process requires a set of tools to transform the raw material to the final shape. Therefore, the success of a production method relies on the quality of the tool.

Manufacturing Process Selection Criteria of composites

2009-03-10T06:02:00.000-07:00

Manufacturing Process Selection Criteria of composites

It is a monumental challenge for design and manufacturing engineers to select the right manufacturing process for the production of a part, the reason being that design and manufacturing engineers have so many choices in terms of raw materials and processing techniques to fabricate the part. This section briefly discusses the criteria for selecting a process. Selection of a process depends on the application need. The criteria for selecting a process depend on the production rate, cost, strength, and size and shape requirements of the part, as described below.

Production Rate/Speed

Depending on the application and market needs, the rate of production is different. For example, the automobile market requires a high rate of production, for example, 10,000 units per year (40 per day) to 5,000,000 per year (20,000 per day). In the aerospace market, production requirements are usually in the range of 10 to 100 per year. Similarly, there are composites manufacturing techniques that are suitable for low-volume and high-volume production environments. For example, hand lay-up and wet lay-up processes cannot be used for high volume production, whereas compression molding (SMC) and injection molding are used to meet high-volume production needs.

Cost

Most consumer and automobile markets are cost sensitive and cannot afford higher production costs. Factors influencing cost are tooling, labor, raw materials, process cycle time, and assembly time. There are some composite processing techniques that are good at producing low-cost parts, while others are cost prohibitive. Determining the cost of a product is not an easy task and requires a thorough understanding of cost estimating techniques. The cost of a product is significantly affected by production volume needs as well. For example, compression molding (SMC) is selected over stamping of steel for the fabrication of automotive body panels when the production volume is less than 150,000 per year. For higher volume rates, steel stamping is preferred. Various cost-estimating techniques, as well as various parameters that affect the final cost of the products.

Performance

Each composite process utilizes different starting materials and therefore the final properties of the part are different. The strength of the composite part strongly depends on fiber type, fiber length, fiber orientation, and fiber content (60 to 70% is strongest, as a rule). For example, continuous fiber composites provide much higher stiffness and strength than shorter fiber composites. Depending on the application need, a suitable raw material and thus a suitable composite manufacturing technique are selected.

Size

The size of the structure is also a deciding factor in screening manufacturing processes. The automobile market typically requires smaller sized components compared to the aerospace and marine industries. For small to medium sized components, closed moldings are preferred; whereas for large structures such as a boat hull, an open molding process is used.

Shape

The shape of a product also plays a deciding role in the selection of a production technique. For example, filament winding is most suitable for the manufacture of pressure vessels and cylindrical shapes. Pultrusion is very economical in producing long parts with uniform cross section, such as circular and rectangular.

Introduction to Manufacturing Techniques of Composites

2009-03-10T05:48:00.000-07:00

Introduction to Manufacturing Techniques of Composites

Every material possesses unique physical, mechanical, and processing characteristics and therefore a suitable manufacturing technique must be utilized to transform the material to the final shape. One transforming method may be best suited for one material and may not be an effective choice for another material. For example, wood is very easy to machine and therefore machining is quite heavily utilized for transforming a wooden block to its final shape. Ceramic parts are difficult to machine and therefore are usually made from powder using hot press techniques. In metals, machining of the blank or sheet to the desired shape using a lathe or CNC machine is very common. In metals, standard sizes of blanks, rods, and sheets are machined and then welded or fastened to obtain the final part. In composites, machining of standard-sized sheets or blanks is not common and is avoided because it cuts the fibers and creates discontinuity in the fibers. Exposed and discontinuous fibers decrease the performance of the composites. Moreover, the ease of composites processing facilitates obtaining near net shape parts. Composites do not have high pressure and temperature requirements for part processing as compared to the processing of metal parts using extrusion, roll forming, or casting. Because of this, composite parts are easily transformed to near-net-shape parts using simple and low-cost tooling. In certain applications such as making boat hulls, composite parts are made at room
temperature with little pressure. This lower energy requirement in the processing of composites as compared to metals offers various new opportunities for transforming the raw material to near net shape parts.

There are two major benefits in producing near-net- or net-shape parts. First, it minimizes the machining requirement and thus the cost of machining. Second, it minimizes the scrap and thus provides material savings. There are cases when machining of the composites is required to make holes or to create special features. The machining of composites requires a different approach than machining of metals.

Composite production techniques utilize various types of composite raw materials, including fibers, resins, mats, fabrics, prepregs, and molding compounds, for the fabrication of composite parts. Each manufacturing technique requires different types of material systems, different processing conditions, and different tools for part fabrication. production success relies on the correct selection of a manufacturing technique as well as judicious selection of processing parameters. The main focus of this is to describe emerging and commercially available manufacturing techniques in the field of thermoset and thermoplastic based composite materials. Various composites manufacturing techniques are discussed in terms of their limitations, advantages, methods of applying heat and pressure, type of raw materials used, and other important parameters. The basic knowledge of these processes will help in selecting the right process for an application.

Composites Markets

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Composites Markets

There are many reasons for the growth in composite applications, but the primary impetus is that the products fabricated by composites are stronger and lighter. Today, it is difficult to find any industry that does not utilize the benefits of composite materials. The largest user of composite materials today is the transportation industry, having consumed 1.3 billion pounds of composites in 2000. Composite materials have become the materials of choice for several industries.

In the past three to four decades, there have been substantial changes in technology and its requirement. This changing environment created many new needs and opportunities, which are only possible with the advances in new materials and their associated manufacturing technology.
In the past decade, several advanced manufacturing technology and material systems have been developed to meet the requirements of the various market segments. Several industries have capitalized on the benefits of composite materials. The vast expansion of composite usage can be attributed to the decrease in the cost of fibers, as well as the development of automation techniques and high-volume production methods. For example, the price of carbon fiber decreased from $150.00/lb in 1970 to about $8.00/lb in 2000. This decrease in cost was due to the development of low-cost production methods and increased industrial use.
Broadly speaking, the composites market can be divided into the following industry categories: aerospace, automotive, construction, marine, corrosionresistant equipment, consumer products, appliance/business equipment, and others.

The Aerospace Industry

The aerospace industry was among the first to realize the benefits of composite materials. Airplanes, rockets, and missiles all fly higher, faster, and farther with the help of composites. Glass, carbon, and Kevlar fiber composites have been routinely designed and manufactured for aerospace parts. The aerospace industry primarily uses carbon fiber composites because of their high-performance characteristics. The hand lay-up technique is a common manufacturing method for the fabrication of aerospace parts; RTM and filament winding are also being used.
In 1999, the aerospace industry consumed 23 million pounds of composites, as shown in Figure 1.6. Military aircrafts, such as the F-11, F-14, F-15, and F-16, use composite materials to lower the weight of the structure. The composite components used in the above-mentioned fighter planes are horizontal and vertical stabilizers, wing skins, fin boxes, flaps, and various other structural components as shown in Table 1.3. Typical mass reductions achieved for the above components are in the range of 20 to 35%. The mass saving in fighter planes increases the payload capacity as well as the missile range.

The major reasons for the use of composite materials in spacecraft applications include weight savings as well as dimensional stability. In low Earthorbit (LEO), where temperature variation is from -100 to +100°C, it is imporant to maintain dimensional stability in support structures as well as in reflecting members. Carbon epoxy composite laminates can be designed to give a zero coefficient of thermal expansion. Typical space structures are tubular truss structures, facesheets for the payload baydoor, antenna reflectors, etc. In space shuttle composite materials provide weight savings of 2688 lb per vehicle.

The Automotive Industry

Composite materials have been considered the “material of choice” in some applications of the automotive industry by delivering high-quality surface finish, styling details, and processing options. Manufacturers are able to meet automotive requirements of cost, appearance, and performance utilizing composites. Today, composite body panels have a successful track record in all categories — from exotic sports cars to passenger cars to small, medium, and heavy truck applications. In 2000, the automotive industry used 318 million pounds of composites.
Because the automotive market is very cost-sensitive, carbon fiber composites are not yet accepted due to their higher material costs. Automotive composites utilize glass fibers as main reinforcements.

The Sporting Goods Industry

Sports and recreation equipment suppliers are becoming major users of composite materials. The growth in structural composite usage has been greatest in high-performance sporting goods and racing boats. Anyone who has visited a sporting goods store can see products such as golf shafts, tennis rackets, snow skis, fishing rods, etc. made of composite materials. These products are light in weight and provide higher performance, which helps the user in easy handling and increased comfort.
Total 1999 U.S. sports equipment shipment cost (including golf, hockey, basketball, baseball, tennis, etc.) was estimated to be $17.33 billion, as reported by the Sporting Goods Manufacturers Association (North Palm Beach, Florida). The market for recreational transport (bicycles, motorcycles, pleasure boats, RVs, snowmobiles, and water scooters) was estimated at $17.37 billion, up from 1998 sales of $15.39 billion. The total shipment for golf was $2.66 billion for 1999, including balls, clubs, and others, with a third of that amount attributed to golf clubs. The ice skates and hockey are estimated to $225 million, snowboards to $183 million, and snow skiing to about $303 million wholesale values in 1999. There are no statistics available that describe the amount of composites usage in the above sporting segments. In North Amer-
ica, 6 million hockey sticks are manufactured every year, with composites capturing 1 to 3% of this market (shafts retail for $60 to $150).4 The Kite Trade Association, San Francisco, estimated a total sale of $215 million in 1990 worldwide in kites, which are generally made by roll wrapping composite tubes or pultruded tubes. Composite bicycle frames and components repre-
sent half a million of these parts, or 600,000 lb of material worldwide in top of the line bicycles, which sell in the range of $3000 to $5000 per unit.

Marine Applications

Composite materials are used in a variety of marine applications such as passenger ferries, power boats, buoys, etc. because of their corrosion resistance and light weight, which gets translated into fuel efficiency, higher cruising speed, and portability. The majority of components are made of glass-reinforced plastics (GRP) with foam and honeycomb as core materials. About 70% of all recreational boats are made of composite materials according to a 361-page market report on the marine industry.5 According to this report total annual domestic boat shipments in the United States was $8.85 billion and total composite shipments in the boating industry worldwide is estimated as 620 million lbs in 2000.

Composites are also used in offshore pipelines for oil and gas extractions. The motivation for the use of GRP materials for such applications includes reduced handling and installation costs as well as better corrosion resistance and mechanical performance. Another benefit comes from the use of adhesive bonding, which minimizes the need for a hot work permit if welding is employed.

Consumer Goods

Composite materials are used for a wide variety of consumer good applications, such as sewing machines, doors, bathtubs, tables, chairs, computers, printers, etc. The majority of these components are short fiber composites made by molding technology such as compression molding, injection molding, RTM, and SRIM.

Construction and Civil Structures

The construction and civil structure industries are the second major users of composite materials. Construction engineering experts and engineers agree that the U.S. infrastructure is in bad shape, particularly the highway bridges. Some 42% of this nation’s bridges need repair and are considered obsolete, according to Federal Highway Administration officials. The federal government has budgeted approximately $78 billion over the next 20 years for major infrastructure rehabilitation. The driving force for the use of glass- and carbon-reinforced plastics for bridge applications is reduced installation, handling, repair, and life-cycle costs as well as improved corrosion and durability. It also saves a significant amount of time for repair and installation and thus minimizes the blockage of traffic.

Composite usage in earthquake and seismic retrofit activities is also booming. The columns wrapped by glass/epoxy, carbon/epoxy, and aramid/epoxy show good potential for these applications.

Industrial Applications

The use of composite materials in various industrial applications is growing. Composites are being used in making industrial rollers and shafts for the printing industry and industrial driveshafts for cooling-tower applications.

Filament winding shows good potential for the above applications. Injectionmolded, short fiber composites are used in bushings, pump and roller bearings, and pistons. Composites are also used for making robot arms and provide improved stiffness, damping, and response time.

Composites Product Fabrication

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Composites Product Fabrication

Composite products are fabricated by transforming the raw material into final shape using one of the manufacturing process

The products thus fabricated are machined and then joined with other members as required for the application. The complete product fabrication is divided into the following four steps:

1. Forming. In this step, feedstock is changed into the desired shape and size, usually under the action of pressure and heat. All the composites processing techniques described in Section 1.6 are in this category.

2. Machining. Machining operations are used to remove extra or undesired material. Drilling, turning, cutting, and grinding come in this category. Composites machining operations require different tools and operating conditions than that required by metals.

3. Joining and assembly. Joining and assembly is performed to attach different components in a manner so that it can perform a desired task. Adhesive bonding, fusion bonding, mechanical fastening, etc. are commonly used for assmbling two components. These operations are time consuming and cost money. Joining and assembly should be avoided as much as possible to reduce product costs.

4. Finishing. Finishing operations are performed for several reasons, such as to improve outside appearance, to protect the product against environmental degradation, to provide a wear-resistant coating, and/or to provide a metal coating that resembles that of a metal. Golf shaft companies apply coating and paints on outer composite shafts to improve appearance and look. It is not necessary that all of the above operations be performed at one manufacturing company. Sometimes a product made in one company is sent to another company for further operations. For example, an automotive driveshaft made in a filament winding company is sent to automakers (tier 1 or tier 2) for assembly with their final product, which is then sold to OEMs (original equipment manufacturers). In some cases, products such as golf clubs, tennis rackets, fishing rods, etc. are manufactured in one company and then sent directly to the distributor for consumer use.

Drawbacks of Composites

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Drawbacks of Composites

Although composite materials offer many benefits, they suffer from the following disadvantages:

1.The materials cost for composite materials is very high compared to that of steel and aluminum. It is almost 5 to 20 times more than aluminum and steel on a weight basis. For example, glass fiber costs $1.00 to $8.00/lb; carbon fiber costs $8 to $40/lb; epoxy costs $1.50/lb; glass/epoxy prepreg costs $12/lb; and carbon/epoxy prepreg costs $12 to $60/lb. The cost of steel is $0.20 to $1.00/lb and that of aluminum is $0.60 to $1.00/lb.

2. In the past, composite materials have been used for the fabrication of large structures at low volume (one to three parts per day). The lack of high-volume production methods limits the widespread use of composite materials. Recently, pultrusion, resin transfer molding (RTM), structural reaction injection molding (SRIM), compression molding of sheet molding compound (SMC), and filament winding have been automated for higher production rates. Automotive parts require the production of 100 to 20,000 parts per day. For example, Corvette volume is 100 vehicles per day, and Ford-Taurus volume is 2000 vehicles per day. Steering system companies such as Delphi Saginaw Steering Systems and TRW produce more than 20,000
steering systems per day for various models. Sporting good items such as golf shafts are produced on the order of 10,000 pieces per day.

3. Classical ways of designing products with metals depend on the use of machinery and metals handbooks, and design and data handbooks. Large design databases are available for metals. Designing parts with composites lacks such books because of the lack of a database.

4. The temperature resistance of composite parts depends on the temperature resistance of the matrix materials. Because a large proportion of composites uses polymer-based matrices, temperature resistance is limited by the plastics’ properties. Average composites work in the temperature range -40 to +100°C. The upper temperature limit can range between +150 and +200°C for high-temperature plastics such as epoxies, bismaleimides, and PEEK.

5. Solvent resistance, chemical resistance, and environmental stress cracking of composites depend on the properties of polymers. Some polymers have low resistance to solvents and environmental stress cracking.

6. Composites absorb moisture, which affects the properties and dimensional stability of the composites.

Special Features of Composites

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Special Features of Composites

Composites have been routinely designed and manufactured for applications in which high performance and light weight are needed. They offer several advantages over traditional engineering materials as discussed below.

1. Composite materials provide capabilities for part integration. Several metallic components can be replaced by a single composite component.

2. Composite structures provide in-service monitoring or online process monitoring with the help of embedded sensors. This feature is used to monitor fatigue damage in aircraft structures or can be utilized to monitor the resin flow in an RTM (resin transfer molding) process. Materials with embedded sensors are known as “smart” materials.

3. Composite materials have a high specific stiffness (stiffness to density ratio), Composites offer the stiffness of steel at one fifth the weight and equal the stiffness of aluminum at one half the weight.

4. The specific strength (strength-to-density ratio) of a composite material is very high. Due to this, airplanes and automobiles move faster and with better fuel efficiency. The specific strength is typically in the range of 3 to 5 times that of steel and aluminum alloys. Due to this higher specific stiffness and strength, composite parts are lighter than their counterparts.

5. The fatigue strength (endurance limit) is much higher for composite materials. Steel and aluminum alloys exhibit good fatigue strength up to about 50% of their static strength. Unidirectional carbon/epoxy composites have good fatigue strength up to almost 90% of their static strength.

6. Composite materials offer high corrosion resistance. Iron and aluminum corrode in the presence of water and air and require special coatings and alloying. Because the outer surface of composites is formed by plastics, corrosion and chemical resistance are very good.

7. Composite materials offer increased amounts of design flexibility. For example, the coefficient of thermal expansion (CTE) of composite structures can be made zero by selecting suitable materials and lay-up sequence. Because the CTE for composites is much lower than for metals, composite structures provide good dimensional stability.

8. Net-shape or near-net-shape parts can be produced with composite materials. This feature eliminates several machining operations and thus reduces process cycle time and cost.

9. Complex parts, appearance, and special contours, which are sometimes not possible with metals, can be fabricated using composite materials without welding or riveting the separate pieces. This increases reliability and reduces production times. It offers greater manufacturing feasibility.

10. Composite materials offer greater feasibility for employing design for manufacturing (DFM) and design for assembly (DFA) techniques. These techniques help minimize the number of parts in a product and thus reduce assembly and joining time. By eliminating joints, high-strength structural parts can be manufactured at lower cost. Cost benefit comes by reducing the assembly time and cost.

11. Composites offer good impact properties, as shown in Figures 1 and 2. Figure 1 shows impact properties of aluminum, steel, glass/epoxy, kevlar/epoxy, and carbon/epoxy continuous fiber
composites. Glass and Kevlar composites provide higher impact strength than steel and aluminum. Figure 2 compares impact properties of short and long glass fiber thermoplastic composites with aluminum and magnesium. Among thermoplastic composites, impact properties of long glass fiber nylon 66 composite (NylonLG60) with 60% fiber content, short glass fiber nylon 66 composite (NylonSG40) with 40% fiber content, long glass fiber polypropylene composite (PPLG40) with 40% fiber content, short glass fiber polypropylene composite (PPSG40) with 40% fiber content, long glass fiber PPS composite (PPSLG50) with 50% fiber content, and long glass fiber polyurethane composite (PULG60) with 60% fiber content are described. Long glass fiber provides three to four times improved impact properties than short glass fiber composites.

12. Noise, vibration, and harshness (NVH) characteristics are better for composite materials than metals. Composite materials dampen vibrations an order of magnitude better than metals. These characteristics are used in a variety of applications, from the leading edge of an airplane to golf clubs.

13. By utilizing proper design and manufacturing techniques, costeffective composite parts can be manufactured. Composites offer designfreedom by tailoring material properties to meet performance specifications, thus avoiding the over-design of products. This is achieved by changing the fiber orientation, fiber type, and/or resin systems.

14. Glass-reinforced and aramid-reinforced phenolic composites meet FAA and JAR requirements for low smoke and toxicity. This feature is required for aircraft interior panels, stowbins, and galley walls.

15. The cost of tooling required for composites processing is much lower than that for metals processing because of lower pressure and temperature requirements. This offers greater flexibility for design changes in this competitive market where product lifetime is continuously reducing.

Functions of Fibers and Matrix

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Functions of Fibers and Matrix

A composite material is formed by reinforcing plastics with fibers. To develop a good understanding of composite behavior, one should have a good knowledge of the roles of fibers and matrix materials in a composite. The important functions of fibers and matrix materials are discussed below.

The main functions of the fibers in a composite are:
• To carry the load. In a structural composite, 70 to 90% of the load is carried by fibers.
• To provide stiffness, strength, thermal stability, and other structural properties in the composites.
• To provide electrical conductivity or insulation, depending on the type of fiber used.
A matrix material fulfills several functions in a composite structure, most of which are vital to the satisfactory performance of the structure. Fibers in and of themselves are of little use without the presence of a matrix material or binder. The important functions of a matrix material include the following:
• The matrix material binds the fibers together and transfers the load to the fibers. It provides rigidity and shape to the structure.
• The matrix isolates the fibers so that individual fibers can act separately. This stops or slows the propagation of a crack.
• The matrix provides a good surface finish quality and aids in the production of net-shape or near-net-shape parts.
• The matrix provides protection to reinforcing fibers against chemical attack and mechanical damage (wear).
• Depending on the matrix material selected, performance characteristics such as ductility, impact strength, etc. are also influenced.

A ductile matrix will increase the toughness of the structure. For higher toughness requirements, thermoplastic-based composites are selected.

• The failure mode is strongly affected by the type of matrix material used in the composite as well as its compatibility with the fiber.

Conventional Engineering Materials

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Conventional Engineering Materials

There are more than 50,000 materials available to engineers for the design and manufacturing of products for various applications. These materials range from ordinary materials (e.g., copper, cast iron, brass), which have been available for several hundred years, to the more recently developed, advanced materials (e.g., composites, ceramics, and high-performance steels). Due to the wide choice of materials, today’s engineers are posed with a big challenge for the right selection of a material and the right selection of a manufacturing process for an application. It is difficult to study all of these materials individually; therefore, a broad classification is necessary for simplification and characterization.

These materials, depending on their major characteristics (e.g., stiffness, strength, density, and melting temperature), can be broadly divided into four main categories: (1) metals, (2) plastics, (3) ceramics, and (4) composites.

Each class contains large number of materials with a range of properties which to some extent results in an overlap of properties with other classes. For example, most common ceramic materials such as silicon carbide (SiC) and alumina (Al2O3) have densities in the range 3.2 to 3.5 g/cc and overlap with the densities of common metals such as iron (7.8 g/cc), copper (6.8 g/cc), and aluminum (2.7 g/cc). Table depicts the properties of some selected materials in each class in terms of density (specific weight), stiffness, strength, and maximum continuous use temperature. The maximum oper-rating temperature in metals does not degrade the material the way it degrades the plastics and composites. Metals generally tend to temper and age at high temperatures, thus altering the microstructure of the metals. Due to such microstructural changes, modulus and strength values generally drop. The maximum temperature cited in Table is the temperature at which the material retains its strength and stiffness values to at least 90% of the original values shown in the table.

Metals

Metals have been the dominating materials in the past for structural applications. They provide the largest design and processing history to the engineers. The common metals are iron, aluminum, copper, magnesium, zinc, lead, nickel, and titanium. In structural applications, alloys are more frequently used than pure metals. Alloys are formed by mixing different materials, sometimes including nonmetallic elements. Alloys offer better properties than pure metals. For example, cast iron is brittle and easy to corrode, but the addition of less than 1% carbon in iron makes it tougher, and the addition of chromium makes it corrosion-resistant. Through the principle of alloying, thousands of new metals are created.

Metals are, in general, heavy as compared to plastics and composites. Only aluminum, magnesium, and beryllium provide densities close to plastics. Steel is 4 to 7 times heavier than plastic materials; aluminum is 1.2 to 2 times heavier than plastics. Metals generally require several machining operations to obtain the final product.

Metals have high stiffness, strength, thermal stability, and thermal and electrical conductivity. Due to their higher temperature resistance than plastics, they can be used for applications with higher service temperature requirements.

Plastics

Plastics have become the most common engineering materials over the past decade. In the past 5 years, the production of plastics on a volume basis has exceeded steel production. Due to their light weight, easy processability, and corrosion resistance, plastics are widely used for automobile parts, aerospace components, and consumer goods. Plastics can be purchased in the form of sheets, rods, bars, powders, pellets, and granules. With the help of a manu-facturing process, plastics can be formed into near-net-shape or net-shape parts. They can provide high surface finish and therefore eliminate several machining operations. This feature provides the production of low-cost parts. Plastics are not used for high-temperature applications because of their poor thermal stability. In general, the operating temperature for plastics is less than 100°C. Some plastics can take service temperature in the range of 100 to 200°C without a significant decrease in the performance. Plastics have lower melting temperatures than metals and therefore they are easy to process.

Ceramics

Ceramics have strong covalent bonds and therefore provide great thermal stability and high hardness. They are the most rigid of all materials. The major distinguishing characteristic of ceramics as compared to metals is that they possess almost no ductility. They fail in brittle fashion. Ceramics have the highest melting points of engineering materials. They are generally used for high-temperature and high-wear applications and are resistant to most forms of chemical attack. Ceramics cannot be processed by common metallurgical techniques and require high-temperature equipment for fabrication. Due to their high hardness, ceramics are difficult to machine and therefore require net-shape forming to final shape. Ceramics require expensive cutting tools, such as carbide and diamond tools.

Composites

Composite materials have been utilized to solve technological problems for a long time but only in the 1960s did these materials start capturing the attention of industries with the introduction of polymeric-based composites. Since then, composite materials have become common engineering materials and are designed and manufactured for various applications including automotive components, sporting goods, aerospace parts, consumer goods, and in the marine and oil industries. The growth in composite usage also came about because of increased awareness regarding product performance and increased competition in the global market for lightweight components. Among all materials, composite materials have the potential to replace
widely used steel and aluminum, and many times with better performance. Replacing steel components with composite components can save 60 to 80% in component weight, and 20 to 50% weight by replacing aluminum parts. Today, it appears that composites are the materials of choice for many engi-neering applications.

THERMOFORMING

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Thermoforming is the art and science of forming commercial products by heat-
ing plastic sheet to a softened, pliable state, pressing the sheet against a cool mold, holding the formed sheet against the mold until rigid, and trimming the formed part from the web or skeleton surrounding it. Nearly all unfilled or un-reinforced thermoplastics are formed in this manner on conventional equipment. Newer forming technologies are used to form filled and reinforced thermoplas-tics and certain thermosetting polymers. In general, thermoforming is used when large surface area-to-wall thickness parts are needed, when rapid evaluation of product designs are sought, when very high production rates of thin-walled parts are desired, and when a few to a few hundred thick-walled parts are needed.

Although commercial thermoforming, sometimes called vacuum forming or swedging, was not developed until the 1870s, when cellulose nitrate was first cut into thin sheets, Egyptians, Pacific natives, and American Inuits formed naturally occurring tortoise sheet and tree bark or natural cellulose into bowls and boats long before then . In the 1870s, cellulose sheet was formed using metal molds and steam as the heating and forming medium . The earliest products were baby rattles, toys, mirror cases, and hairbrush backs. In the early 1900s, piano keys were drape-formed over captive wooden cores. In 1930, Fernplas Corp. patented a bottle fabri-cated from two thermoformed halves. Relief maps for the U.S. Coast and Geodetic Survey were thermoformed of cellulose acetate in the 1930s. The first automatic roll-fed thermoformer was sold by Clauss B. Strauch Co., in 1938, to manufacture cigarette tips and ice-cube trays. The heating, bending, and shaping of plastic sheet were taught in high school industrial art courses in the late 1930s .

The Second World War accelerated interest in thermoforming, with the demand for cast poly(methyl methacrylate) fighter/bomber windows, gun closure and windscreens .
By the mid-1950s, thermoformed blister packages and food containers of polystyrene were found in most grocery stores. In 1962, approximately 77,000 t of plastic was thermoformed in the United States. By 1998, approximately 2.9 million metric tons of plastic were thermoformed in North America . This is a sustained annual growth rate of about 10% over nearly four decades. An additional 4.55 million metric tons are thermoformed worldwide. The total world market is estimated to have a value of about US$ 35,000 million.

Thermoforming is typically bifurcated into thin-gauge thermoforming and heavy- or thick-gauge thermoforming. As seen in Table 1, thin-gauge thermo-forming uses sheet 1.5 mm or less in thickness, with its primary products be-ing packaging containers. Typical disposable products include blister packages, point-of-purchase containers, bubble packages, slip sleeve containers, auto/video cassette cases, hand and power tool cases, cosmetic cases, meat and poultry con-tainers, unit serving containers, convertible-oven food serving trays, wide-mouth jars, vending machine hot and cold drink cups, egg cartons, produce and wine bot-tle separators, medicinal unit dose portion containers, and form, fill, and seal (FFS) containers for foodstuffs, hardware supplies, medicine, and medicinal supplies.

Heavy-gauge thermoforming uses sheet 3 mm or more in thickness, with pri-mary products being permanent or industrial products. Typical products include equipment cabinets for medical and electronic equipment, tote bins, single and double deck pallets, transport trays, automotive inner-liners, headliners, shelves, instrument panel skins, aircraft cabin wall panels, overhead compartment doors, snowmobile and motorcycle shrouds, fairings and windshields, marine seating, locaters and windshields, golf cart, tractor, and RV shrouds, skylights, shutters, bath and tub surrounds, lavys, single- and double-wall shipping containers and pallets, storage modules, exterior signs, swimming and wading pools, landscap-ing pond shells, luggage, gun and gulf club cases, boat hulls, animal carriers, and seating of all types.

There is a growing but very still limited market for products formed from sheet between about 1.5 mm (thin-gauge) and 3.0 mm (heavy-gauge) thickness. Usually, products of this thickness are either too expensive to be disposable or too thin to be industrial or permanent products. One major application is in the manufacturing of very large volume drink cups (1/2 L or more).

Currently thin-gauge thermoforming accounts for about three-quarters of all sheet formed, in both tonnage and dollar volume. Thin-gauge thermoforming companies tend to be very large with broad spectra of products. Furthermore, companies that manufacture products may also do in-house thin-gauge thermo-forming for the packages for these products. Heavy-gauge thermoforming compa-nies tend to be small with narrow product lines. As a result, there are many more heavy-gauge thermoforming companies than thin-gauge thermoforming compa-nies. In 2001, it was estimated that there were about 500 heavy-gauge thermo-forming companies and less than 200 thin-gauge thermoforming companies in North America .

As outlined in Table 1, there are substantial differences in the characteristics of these two thermoforming categories. In addition to the sheet thickness crite-rion, there is a difference in the way the sheet is presented to the thermoforming machine. Thin sheet is usually delivered in rolls of up to 3000 m in length, weigh-ing up to 2300 kg and having diameters up to 1.5 m. The sheet is fed continuously into the thermoforming machines that are usually called roll-fed machines. Thick sheet is usually guillotine-cut to size and palletized. The individual sheets are then loaded manually or pneumatically into the thermoforming machines, known as cut-sheet machines.

Thermoforming is a competitive technology. In thin-gauge it competes with paper, paperboard, plastic-coated paper and paperboard, paper pulp, expanded polystyrene foam, aluminum foil, and roll-sheet steel. It also competes with plastics extrusion, compression molding, stretch-blow molding, injection molding, and injection-blow molding. In heavy-gauge, it competes with injection molding, rotational molding, blow molding, fiberglass-reinforced polyester resin spray-up molding and lay-up molding, compression molding, sheet compound molding, bulk compound molding, sheet metal forming, and metal die casting.

When compared to other technologies, thermoforming offers many advantages: there is a wide variety of polymers from which to choose; molds are singlesided and are thus less expensive than injection molds; the time from concept to final part acceptance is usually quite short; there are many available mold materials; aluminum—the mold material of choice—is lightweight, has a high thermal conductivity, is relatively inexpensive, and is easy to machine and cast; processing temperatures are low; processing pressures are very low; mold detail replication is good; part surface area-to-wall thickness is extremely high; and there are many excellent trimming techniques.

However, thermoforming has some serious limitations. Among others, the polymer of choice may not be extrudable or may sag too much during heating in the thermoforming machine; there is additional cost in producing sheet; the un-used portion of the sheet—the trim, web, or skeleton—must be recycled to keep sheet costs reasonable; because of the end-use of the product (medical, pharma-ceutical, foodstuffs), recycling of the trim may not be acceptable, it may not be possible to stretch the sheet sufficiently to achieve the desired part shape, part wall thickness is not well-controlled or predictable, and is not uniform across the part; wall thickness cannot be changed locally through design; surface texture may be required on both sides of the part; the part performance criteria may required reinforced or highly filled polymers; the part tolerance, edge radii, and draft angles may be unacceptably tight for the thermoforming process; and there may be other processes that are more economically attractive.

Temparature in Injectiopn moulding

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Temparature in Injectiopn moulding

1. Melt Temperature It should be noted that the melt temperature must not necessarily correspond to the barrel wall temperature set at the injectionmoulding machine. This difference is influenced by: a. Screw speed during metering b. Back pressure during metering
c. Residence time in the barrel d. Design and diameter of the screw
e. Viscosity of the melt f. Degree of wear of screw and barrel

A further temperature increase due to friction can be caused, in addition to the shearing of the screw, by a rapid melt flow through a small gate cross section (pin or film gates).
Grillamid, Grivory and Grilon injection moulding grades have excellent thermal stability. The relevant injection moulding material can be processed without problem at the maximum permissible melt temperature for parts with extended flow distances and small wall thicknesses. However, in such cases the influence of point’s a-f given above should be taken into consideration and monitored. Wear of screw and barrel wall have particularly disadvantageous effects. Leakage flow between the screw flight / barrel wall and nonreturn valve / thrust ring, results in quantities of melt remaining in the barrel for long periods of time.

Additional overheating of small amounts of metered melt in these areas of radial screw clearance is not registered by the melt temperature measurements (average temperatures). This in one reason why injection moulded parts produced at correct melt temperature settings
may exhibit discolouration or streaks caused by overheating. A low melt temperature is recommended when producing solid parts with large wall thickenesses, long cooling times and
short flow distances as this reduces thermal stressing of the melt. The choice of a lower melt temperature may also give improved surface quality of thick walled parts made of non-reinforced material.A range of melt temperatures is given in the tables on page 4 – 6. In addition the recommended melt temperatures and melting points are listed.

2. Barrel Temperatures The temperature settings of the heating barrel normally result in a profile where the temperature increases from feed hopper to nozzle. The choice of nozzle temperature is dependant on the design of nozzle used. It should be selected in such a way to avoid filament formation(stringing) at temperatures, which are too high, and cold slug formation at temperatures, which are too low. During long contact times between nozzle and mould, cooling of the nozzle tip from contact with the mould must be compensated by increasing
the nozzle temperature. A low temperature setting in zone 1 (feed zone), together with cooling of the hopper flange, prevents premature melting of the granules and therefore, promotes uniform and trouble free metering. Exceptions:Deviation from these rules is permissible when the maximum volume that can be metered by the plasticising unit has to be used within a short metering time (normally not exceeding 80% of maximum volume). In this case, a higher barrel temperature in the feed zone must be selected in order to create sufficient heat to allow the increased throughput. A temperature profile decreasing from hopper to nozzle is thus created. If production is interrupted, this temperature must be reduced immediately to normal levels in order to prevent melting of the granules in the hopper and feed zone,impeding or preventing restarting of production. Starting up of production runs requiring such high temperatures should be carried out with a normal temperature profile. The temperature in the feed zone is then increased during optimisation of the cycle time.

3. Mould Temperature The mould surface temperature is one of the decisive factors influencing the quality of parts made of Grillamid,Grivory or Grilon. Heating is carried out be a heating unit, which pumps water (up to 95° C, pressurised water up to 160° C) or oil (> 160° C) through heating channels in the mould. Water is preferable as use of a heating medium as it provides better and quicker heat transfer than oil. The heating systems are equipped with a control device, which maintains a constant mould surface temperature throughout production. The control tolerance should not exceed ± 3° C. Using Grilon injection moulding materials at high mould temperatures,parts are obtained which have a high degree of crystallinity and which exhibit excellent mechanical properties and have a low tendency to warp.Optical surface quality of parts made of glass reinforced Grillamid, Grivory and Grilon grades is achieved when mould temperatures above 80° C are used, following the recommendations in the temperature setting tab. If an injection-moulded part is to be sterilised with super heated steam (e.g. at 121° C), the mould temperature selected should be as high as possible. This reduces warping of the part during sterilizing to a minimum or may even prevent it.Large moulds should have separate heating circuits for ejector and nozzle areas. It is important to always have an even temperature distribution over the complete cavity surface of the mould.

The Basic Advantages and Uses of Acrylic Store Fixtures

2009-03-06T19:59:00.000-08:00

The Basic Advantages and Uses of Acrylic Store Fixtures

When you open a retail business, your inventory is critical, it is true, but your space and location of displays and store fixtures is equally important. Do not make the mistake of underestimating the importance of the brand image you can project to customers through the very floor space and fixtures in your store. Often, when you rent retail space, you also inherit lighting, displays and possibly even furniture. Some of these things may fit in with what you have in mind for your store's image. But if it doesn’t buy what you need to project the right image, it is worth the expense. When selecting store displays and store fixtures, there are certain things to consider:

The first and most important consideration is your image and your merchandise. If you are in the business of selling handmade folk art, for example, the displays and store fixtures you would need would be very different from that you would choose if you were selling electronic gadgets. You also need to consider optimum space usage to give your customers the most comfortable buying experience possible and guide them in an efficient pattern through your store. The final consideration is your budget. You have to find the middle path, allowing you to buy what you need, but keep your expenses low.

Your store fixtures can be your best salesmen, they can be customized to show your products perfectly, in the most attractive way, while attracting and keeping your clients’ attention. Consider the functionality in order to get the best store fixtures to aid your sales process. Figure out the specifications you need to create the perfect showcase, lighting, displays, etc for your retail store and then you can order exactly what you need, cutting out on wasted time and effort.

Think about your personal, and your staff’s selling style. Does it make more sense to have open front showcases that allow you to easily pick up merchandise to show clients or would you rather have rear access to the showcases to pick up merchandise from behind the counter? Do you want locked display cases to protect expensive merchandise or would you prefer open shelves so that your clients can pick up and handle the items before they buy? Do you need countertop and wall hanging display fixtures to show impulse items within reach at the register, or at eye level? Do you sell unusual or unique collectibles which need customized display and storage? Is it difficult to find a wooden box display case of the right size?

Wooden and other opaque kinds of shelving can throw shadows and hide the merchandise below eye level. Consider acrylic shelves to enable customers to see your merchandise better. Acrylic store fixtures are becoming more and more popular because of their superior durability, economy and convenience. These fixtures can be eye catching while they are subtle enough to let the product be the main focus. Acrylic, or acrylic thermoplastics are a kind of strong, stable, weather resistant and thermo formable synthetic material. The great advantage of using acrylic store fixtures is that the transparency, gloss and the dimensional shape of acrylics are almost totally unaffected even by years of exposure to the elements, to salt spray, or even corrosive atmospheres. They also withstand exposure to light very well, especially from fluorescent lamps, without any darkening or deterioration. The very low weights per square foot and the toughness of clear acrylic makes it ideal for many applications, even those that glass was formerly used for.

Acrylic store fixtures, signs, and P-O-P displays, are acrylic sheet products and offer UV resistance, with improved clarity, and ease adaptations, as well as good optical effects enhancing any retail environment. Acrylic mirrors are perfect for jewelry, glassware and artifact displays, being light weight and durable with a bright reflective finish. These unique properties of acrylic and acrylic store fixtures gives designers an enhanced flexibility of choices and styles for a variety of uses like P.O.P. displays, and store fixtures, like holders, sign holders, literature holders, cubes and risers, eyewear or jewelry displays, acrylic risers, bulk food dispensers, shelving, holders for menus, and trays. If you don't find exactly what you are looking for, custom acrylic fixtures are also available.

Injection moulding Process

2009-02-26T04:46:00.000-08:00

INTRODUCTION

Many of the things you own and come into contact with every day are made from plastics which have been injection moulded into shape. These things range in size from pens, up to computer and television cases. Many products have become very cheap and widely available because of the injection moulding 'revolution'. Injection moulding can produce very large or small products with great precision, in very large numbers, and at low cost.

Injection moulding is suitable processing method for following materials:

• Thermoplastics
• Elastomers
• Rubbers
• Thermosets
• Composites
• Foamed plastics

The most used materials are thermoplastics. Hence from here onwards injection moulding refers to thermoplastic injection moulding.

BASIC CONCEPT OF INJECTION MOULDING

The basic concept of injection moulding is the ability of a thermoplastic material to be softened by heating, formed under pressure, and hardened by cooling.

PRINCIPLE OF INJECTION MOULDING

Injection moulding, as its name suggests, involves injecting fused (softened) plastic into a mould. In an injection moulding machine, plastic granules are fed into a heated barrel. They are forced through this barrel either by a piston or a screw (similar to one in a mincing machine). The granules fuse together into a mass like soft chewing gum and this is forced from the end of the barrel into a metal mould.

The mould itself is made from two or more metal parts which fit tightly together leaving only a small hole for the fused plastic to enter. This hole is called the sprue entry. If you look at an injection moulded product carefully, you may see the point at which the plastic entered the mould. It will be a small mark where the sprue has been broken or cut off the moulding.

Advantages of Injection Moulding Process:
Parts can be produced in large volume at high production rates.
Process can be automated and hence increases in production
Relatively low labor cost per unit is obtainable.
Many different colors and finishes are available, and good decoration is possible.
Close dimensional tolerances can be maintained.
Parts can be molded with metallic and non-metallic inserts.
Parts can be molded in combination of plastics and additives such as fillers.
Molded parts require little or no finishing.
Minimal scrap loss result as runner, gate and rejection can regrind and reused.
Process creates consistent parts.
High return on investment.

Limitations of Injection Moulding Process:

High mold cost.
Moulding machine and auxiliary equipment cost are high.
Lack of knowledge about the fundamentals of process causes problem.
Lack of knowledge about the long term properties of the material may result in long term failure.
Process requires extremely high temperature.
Process requires extremely high clamping force.

INJECTION MOULDING PROCESS

In its broadest terms, thermoplastic injection moulding forms a part by forcing a liquid resin into a closed mould, under pressure, until the part has cooled or cured and can be ejected from the mould. This process consists of the following five distinct operations.
1. Feeding of raw materials
2. Plasticizing (mixing (mechanical work), external heating)
3. Injection (filling of the mould cavity)
4. Holding pressure
5. Cooling (cooling of the material in the mould cavity)
6. Ejection of the injection moulded part
The main factors in the injection moulding are the temperature and pressure history during the process, the orientation of flowing material and the shrinkage of the material. This means that the structure and the properties of injection moulded parts are inhomogeneous and the products have always internal stresses.

Feeding of Raw Material
First the molder receives plastic resin in the form of small chopped pellets. These are fed into the hopper of an injection-moulding machine, where they fall into an augur-type screw channel, which feeds the pellets forward inside the heated barrel.

Plasticizing

The cycle begins with the extruder plasticizing the resin and accumulating it in the forward section of the barrel. The heater bands maintain the melt's temperature as the shot it built up. The mould is closed. The cycle is typically timed so that there is minimal time between the closing of the mould and the next shot. Injection of the Resin into the Closed Mould.

Injection
After the mould closes, the screw (not rotating) pushes forward to inject melt into the cooled mould. The air inside the mould will be pushed out through small vents at the furthest extremities of the melt flow path.

Holding pressure

When the cavity is filled, the screw continues to push forward to apply a holding pressure. This has the effect of squeezing extra melt into the cavity to compensate for the shrinkage of the plastic as it cools. This holding pressure is only effective as long as the gate(s) remain open.

Cooling the Resin inside the Closed Mould
Cooling starts immediately when polymer mass flows into the mould cavity including the injection and holding phases, and continues after these too. Therefore the cooling time is the longest phase in the injection moulding process. Because the injection and holding phases are included in the cooling phase, they also effect on the cooling of the moulded part. Cooling time depends on the raw material, wall thickness of the part and the heat transfer capability of the mould. In order to have a nonporous and unstressed part the polymer melt should solidify uniformly.
Opening the Mould and Ejecting the Moulded part

Once the gate(s) freeze, no more melt can enter the mould and so the screw-back commences. At this stage the screw starts to rotate and draw in new plastic from the hopper. This is conveyed to the front of the screw but as the mould cavity is filled with plastic, the effect is to push the screw backwards. This prepares the next shot by accumulating the desired amount of plastic in front of the screw. At a pre-set point in time, the screw stops rotating and the machine sits waiting for the solidification of the moulding and runner system to be completed. When the moulding has cooled to a temperature where it is solid enough to retain its shape, the mould opens and the moulding is ejected. The mould then closes and the cycle is repeated.
THE PROTOMOLD PROCESS
At Protomold we have automated the process of designing and manufacturing molds based on customer supplied 3-D CAD part models. Due to this automation, we typically cut the lead time for the initial parts to one-third of conventional methods. Cost saving varies with the number of parts being produced, but Rapid Injection Molding may also have a substantial cost advantage in runs of up to thousands of parts.

The Protomold Rapid Injection Molding process gives design engineers a fast and affordable way to get real injection molded parts in prototype or low-volume quantities.
So from an overall market perspective we see Rapid Injection Molding as in between Rapid Prototyping and Conventional Injection Molding as illustrated in the figure.
THE INJECTION MOULDING PROCESS CYCLE

The typical process cycle time varies from several seconds to tens of seconds, depending on the part weight, part thickness, material properties, and the machine settings specific to a given process.

Process control of injection molding has a direct impact on the final part quality and the economics of the process. The various components of process control must be fully understood to maximize profit and part quality.
The various stages are:

Injection phase (filling phase)
Packing phase
Holding phase
Cooling phase

Fill time

At the beginning of the injection molding cycle (point 1), the mold has just closed and the molten polymer, which is maintained at a fairly uniform temperature inside the barrel of the injection machine, is forced to flow through the nozzle, runner, gate, and then into the cavity under controlled flow rate or pressure, depending on the control scheme of the injection unit. The fill time is defined as the time needed for the polymer to fill the entire cavity (duration between points 1 and 4.

Post-fill time
After the mold is completely filled (point 4), more material is packed into the cavity and the polymer continues to cool. The post-filling stage ends when the polymer temperature is sufficiently low and the part is rigid enough to be removed from the cavity without significant deformation (point 7). The post-fill time is defined as the time between the moment when the cavity is completely filled and the instant when the mold opens (duration between points 4 and 7).

Mold open time

The mold-opening stage begins when the mold is opened (point 7) and ends when the mold is closed (point 8) to start the next cycle. The mold-open time includes the time taken for mold opening and closing actions as well as part ejection (duration between points 7 and 8). Because this can be a significant portion of the cycle time in processes with extremely short cycles, each action of the mold clamp and ejection systems should be analyzed for possible time delays and wasted energy. During this stage, additional heat transfer occurs between the mold and ambient air.

To further illustrate the machine motion within the process cycle, the hydraulic (cylinder) and cavity pressure traces, screw position, and mold face separation position are shown below
1. Filling (injection stage) 2.Packing and cooling stage 3.Mold opening 4.Part ejection 5.Mold closing.

ULTRASONIC WELDING

2009-02-26T04:41:00.000-08:00

ULTRASONIC WELDING

When bonding material through ultrasonic welding, the energy required comes in the form of mechanical vibrations. The welding tool (sonotrode) couples to the part to be welded and moves it in longitudinal direction. Ultrasonic welding involves the use of high frequency sound energy to soften or melt the thermoplastic at the joint. Parts to be joined are held together under pressure and are then subjected to ultrasonic vibrations usually at a frequency of 20, 30 or 40 kHz.

Differences in the process for welding plastics and metals with ultrasonic

1. Anvil
2. Parts to be welded
3. Sonotrode
4. Ultrasonic oscillation

Ultrasonic welding of plastics

Oscillations are introduced vertically

Ultrasonic welding of plastics is a state-of-the-art technology that has been in use for many years. When welding thermoplastics, the thermal rise in the bonding area is produced by the absorption of mechanical vibrations, the reflection of the vibrations in the connecting area, and the friction of the surfaces of the parts. The vibrations are introduced vertically. In the contraction area, frictional heat is produced so that material plasticizes locally, forging an insoluble connection between both parts within a very short period of time.
The prerequisite is that both working pieces have a near equivalent melting point. The joint quality is very uniform because the energy transfer and the released internal heat remains constant and is limited to the joining area. In order to obtain an optimum result, the joining areas are prepared to make them suitable for ultrasonic bonding. Besides plastics welding, ultrasonic can also be used to rivet working parts or embed metal parts into plastic.
Benefits of the process include: energy efficiency, high productivity with low costs, ease of automated assembly line production and fast joining times.

Core and cavity generation method in injection mould design M. W. FU, J. Y. H. FUH and A. Y. C. NEE

2009-02-26T04:35:00.000-08:00

Core and cavity generation method in injection mould design M. W. FU, J. Y. H. FUH and A. Y. C. NEE

In a computer-aided injection mould design system, the generation of parting surfaces and the creation of core and cavity blocks is usually a bottleneck. The parting surfaces and core/cavity blocks are created based on the parting direction and parting lines. Here, the architecture of an injection mould design system is proposed on the basis of the practical information flow and processing steps in mould production lifecycle. In this architecture, the methodology to generate the parting surfaces and the core/cavity blocks is proposed. To generate the parting surfaces, the parting line edges are classified and the extruded directions specified to the different groups of parting line edges. Extruding the parting line edges to the boundary of the core/cavity-bounding box generates the parting surfaces. To create the core/cavity blocks, the Boolean regularized difference operation (BRDO) is used and the related algorithms are presented. The criterion to identify whether the undercut features need local tools for moulding is proposed. The case studies illustrate and validate the methodology to generate the parting surfaces and core/cavity blocks.

In injection mould design, the main design activities include the determination of parting direction, parting lines and surfaces, selection of mould types, cavity layout, gating, ejection, venting, heating/cooling types, mould materials, and the temperature control system. After the parting direction and lines are determined and the design scheme is decided, the rest of the detailed design activities mentioned above can proceed. Based on the known parting direction and parting lines, the methodologies related to the generation of parting surfaces and core/cavity blocks are presented.

To generate the core/cavity blocks automatically, two methods known as the Boolean-based approach (BBA) and the Euler-based approach (EBA. In BBA, the core/cavity blocks are generated using the Boolean regularized difference operation (BRDO) between the core/cavity bounding box and the moulding. In EBA, the Euler operation is the key process to generate the related core/ cavity block surfaces.

Generation of core/cavity blocks

Core and cavity blocks can be generated based on the following steps.
Step 1. Identify all the through-hole undercut features and `patch’ up all these features.
Step 2. Generation of a bounding box. The bounding box is defined as the material stock that fully contains the moulding with enough space for assembly of other components .Figure shows the bounding box of a moulding.
Step 3. Generation of parting surfaces and `sewing’ all the parting surfaces together.
Step 4. Subtracting the bounding box with the patched part solid by the BRDO and splitting the bounding box using the generated parting surfaces.
The procedures to generate the core and cavity blocks are shown in the figure . After patching all the through-hole features in Step 1, it is necessary to determine the maximum dimensions Lx, Ly and Lz of the moulding in X, Y, Z directions and the bounding box thicknesses a, b, c in three dimensions. The bounding box thicknesses can be determined based on the required mould strength and the moulding parameters. The final bounding box dimensions are (Lxa, Lyb, Lzc). In Step 3, the parting surfaces, generated based on the parting line edges, are sewn together. In the last step, the BRDO is performed between the bounding box and the patched moulding. After the operation, the bounding box has an empty space inside. The sewn parting surface is then used as the splitting surfaces to split the box into two mould halves. One is the core block; the other is the cavity block. The procedures are illustrated in figure.
In an injection mould, if the core and cavity blocks and their inserts cannot mould the undercut features, the incorporation of local tools in the mould structure will be needed. It is hence necessary to identify the undercut features that cannot be moulded by the core and cavity blocks based on the following equation:

Where is the undercut direction and is the parting direction. Above equation means that if the undercut direction is not in the parting direction, the undercut features will become the `real’ undercut features and local tools are needed. The method to generate the local tools is not covered here.

Conclusions
Here, the architecture of an injection mould design system is proposed based on the practical mould design procedures. An efficient methodology for the creation of parting surfaces and the creation of core/cavity blocks is presented according to the generated parting direction and parting lines. Three types of parting, namely flat, stepped or complex partings are proposed. To generate the core/cavity blocks, the Boolean regularized difference operation is adopted. Case studies are used to illustrate the procedures of the methodology and the related algorithms. The results have shown that the methodology is effective in providing a solution for the computer aided injection mould design system automatically to generate the parting surfaces and create the core and cavity blocks.

Decision criteria for computer-aided parting surface design by B Ravi and M N Srinivasan

2009-02-26T03:57:00.000-08:00

Decision criteria for computer-aided parting surface design by B Ravi and M N Srinivasan

A scientific approach is presented and the related logic developed for design of parting surfaces of patterns, moulds and dies used in the manufacture of cast, forged, injection-moulded and die-cast components. This has enabled computer-aided generation of parting surfaces and the determination of projected area, flatness and draw for a parting surface, identification of surfaces to which draft is provided, recognition of component segments causing undercuts, testing for dimensional stability, and location of flash, machined surfaces and feeders. Influencing criteria for parting-surface design have been formulated and developed into algorithms implemented on a personal computer. This approach greatly aids the engineer in rational decision making, paving the way for a systematized code for parting surface design.

Castings are manufactured by pouring molten alloys into various shaped mould assemblies. Moulds are in turn prepared by compacting sand around patterns in segments or halves, one each for the bottom and the top mould. A forged component is manufactured by compressing a heated blank between two shaped dies. In die-casting and plastic injection moulding the material is forced under high pressure into a cavity formed by bringing together two die-halves. In all these manufacturing processes, the design of patterns, moulds and dies, the crucial tooling, directly affects productivity and component quality. The most significant design aspect is the choice of the surface separating the two halves of the mould or die, referred to as the parting surface. A combination of several mechanical, metallurgical and process parameters influences parting-surface location, rendering the design exercise complex.

Decision criteria

Nine influencing parameters for decision making in parting-surface design for a component have been identified: projected area, flatness, draw, draft, undercuts, dimensional stability, flash, machined surfaces and directional solidification.

Projected area

To facilitate removal of the pattern from the mould or the manufactured component from the die, the cross-sectional area should gradually decrease from the parting surface to points farthest from the parting surface. The basal plane of an upright cone or the diametrical planes of a sphere satisfy this requirement. This condition is applicable to flat as well as irregular parting surfaces.

Flatness

Considering technological aspects such as side thrust, dimensional stability, sealing off, flash, and complexity in tooling and mould making, a flat parting surface is preferred over an irregular one.

Draw

Draw is the minimum distance through which a component is linearly translated in order to clear it from the mould. Design considerations such as application of draft to the vertical surfaces of mould and metallurgical and technological problems such as grain flow in forgings, flask size in castings and machine draw capability in injection moulding, as well as increase of cycle time and reduced productivity, are caused by deep draw.

Draft

A conical or pyramidal part is drawn along its axis from a mould with ease compared to a straight cylinder or rectangular part. Surface quality, interracial interaction between the pattern or component and the mould or die, the extent of draw and related factors also contribute to this effect. All such faces of the component that are parallel to the draw vector are given a small taper or draft to aid in easy withdrawal. Surfaces that are not parallel to the draw direction are considered to have a natural draft or form undercuts. Application of draft results in the alteration of the part geometry and additional machining may be required to restore the shape of the component.

Undercuts

Projections or recesses in the component unfavorably inclined with respect to the draw vector hinder the removal of the pattern from the mould or component from the die. It is not always possible to design the parting surface to avoid undercuts completely, so to overcome this, cores or other manufacturing devices like inserts and loose-pieces have to be incorporated. This directly affects the process cycle time and tooling and manufacturing costs.

Dimensional stability

Tile possibility of mismatch between the cope and drag portions of the mould or at the joint between two die halves, results in dimensional reliability across the parting surface being considerably lower compared to that in the portions of the mould lying on one side of the parting surface. Hence the parting surface is designed such that any two points between which high dimensional tolerance is required occur on the same side of it.

Flash

A material flowing into the gaps at the plane of separation of the two mould halves or the interface between mould and a core produces fin-like protrusions or flash. This is generally trimmed after manufacture. However, flash leaves surface imperfections, and in some cases trimming may not be feasible or economically viable. The designer may also specify certain surfaces to be free of flash. Such surfaces must not intersect the parting surface.

Location of surfaces to be machined

Critical surfaces of a cast component requiring machining are preferably located as the bottom or the vertical walls of the mould, which are relatively free of defects. In general, a casting may have several machined faces, all of which cannot be located as the bottom or vertical surfaces in the mould. When several alternative parting surfaces are considered, their relative merits are quantitatively assessed for location of machined surfaces using the criterion proposed below:
Feeders and directional solidification
Solidification of metal in a mould is accompanied by shrinkage, which can manifest in the form of micro pores or cavities. This is prevented by promoting controlled solidification initiating in thin sections to proceed towards thicker sections. The last freezing section is fed by a reservoir of molten metal (a feeder). This introduces definitive conditions on geometric interfaces and interactions between component sections, from which a number of design recommendations on variation of cross section and joining sections have emerged. Geometry of the casting and its disposition in the mould, particularly on access to the feeder, is considered an important parameter. The parting surface is chosen so that the hot spots (regions of mass concentration) are at the top of the casting.

Conclusion

A decision-making scheme on a scientific basis has been developed to assess the design of a parting surface for components manufactured in moulds or dies. Nine different criteria influencing the design have been identified and delineated to allow them to be analyzed by computer. The logic developed has been implemented in algorithms on a PC and tested on typical mechanical components.

An Intelligent Cavity Layout Design System for Injection Moulds by Weigang Hu and Syed Masood

2009-02-26T03:44:00.000-08:00

An Intelligent Cavity Layout Design System for Injection Moulds by Weigang Hu and Syed Masood

This paper presents the development of an Intelligent Cavity Layout Design System (ICLDS) for multiple cavity injection moulds. The system is intended to assist mould designers in cavity layout design at concept design stage. The complexities and principles of cavity layout design as well as various dependencies in injection mould design are introduced. The knowledge in cavity layout design is summarized and classified. The functionality, the overall structure and general process of ICLDS are explained. The paper also discusses such issues as knowledge representation and case-based reasoning used in the development of the system. The functionality of the system is illustrated with an example of cavity layout design problem.

Cavity Layout Design in Injection Moulds

Current practice for injection mould design, especially cavity layout design, depends largely on designers’ ex- pertinences and knowledge. It would therefore be desirable to use knowledge engineering, artificial intelligence and intelligent design techniques in generating an acceptable cavity layout design in injection mould accurately and efficiently. In mould design, most of patterns of cavity layout and rules and principles of cavity layout design can also be easily represented in the form of knowledge, which can be used in most of knowledge-based design systems.

For example, for the layout patterns shown in Fig, the criteria to select the suitable layout pattern for design are mainly dependent on working environments, conditions and requirements of customer and are mainly based on designer’s skill and experience. To make a choice of contradictory factors will rely obviously on designer’s knowledge and experiences. It is rather suitable for intelligent design techniques to be used in systems designed for such situations, especially for routine or innovation design.

Design of injection mould mainly involves consideration of design of the following elements or sub-systems

(1) Mould type

(2) Number of cavities

(3) Cavity layout
(4) Runner system
(5) Ejector system
(6) Cooling system
(7) Venting
(8) Mounting mechanism
Most of the elements are inter-dependent such that it is virtually impossible to produce a meaningful flow chart covering the whole mould design process. Some of the design activities form a complicated design network as shown in Fig.
Obviously, in injection mould design, it is difficult for designer to monitor all design parameters. Cavity design and layout directly affects most of other activities. The application of advanced knowledge based techniques to assist designer in cavity layout design at concept design stage will greatly assist in the development of a comprehensive computer-aided injection mould design and manufacturing system.

It is noted from Fig a number of different layout patterns are possible with multiple cavities inside a mould. Higher the number of cavities of mould, higher the productivity of the injection mould. But this may lead to difficulties with issues such as balancing the runners or products with the complicated cavity shapes, which in turn may lead to problems of mould manufacturability. It is also possible that the number of cavities and the pattern of cavity layout will influence the determination of parting line, type of gate, position of gate, runner system and cooling system. Most of the main activities of mould design are therefore linked to cavity layout design. Fig. 3.5 shows the relations between cavity layout design and other design activities. The cavity layout design problem therefore depends upon a number of functionalities of the overall mould design system, which includes:

(1) Definition of design specifications including analysis and description of characteristics of design problem
(2) Determination of mould type
(3) Determination of number of cavities
(4) Determination of orientation of product
(5) Determination of runner type and runner configuration
(6) Determination of type and position of gate
(7) Cavity layout conceptual design
(8) Evaluation of ejection ability, manufacturing
(9) Ability and economic performances
(10) Determination of cooling system
(11) Graphic results display and output

Relationship diagram between cavity layout design and other modules of mould.

Example of Application

An application example, “determination of cavity layout pattern” of the “conceptual design for cavity layout” provided by Intelligent Cavity Layout Design System
(ICLDS) is given below:
If the initial design conditions are:
(1) What type of mould is used? Two plate
(2) What type of runner is used? Cold runner
(3) How many cavities are there in mould?
(4) How long is it required for product to clear the moulding area? Small
(5) What shape of product does moulding make? Rectangle
Then the result is given by: (this is shown in Fig.) Pattern of cavity layout design is:
Y-Rectangular-Layout
The knowledge base is developed using features of ECLIPSE language, such as ‘defrelation’, ‘deftemplate’, ‘defruleset’, and ‘goal’ generation. Part of the program, which describes the overall format of knowledge base development, is listed below:
Conclusion
The problem of design of cavity layout in multiple cavity injection moulds has received relatively little attention in computer aided design support systems for injection moulding. A computer based design system will offer great savings in time and cost in arriving at the best possible layout from a number of alternatives. The development of Intelligent Cavity Layout Design System (ICLDS) is believed to be the first attempt in this direction using knowledge-based approach. The development of ICLDS for injection mould is based on RETE++ in Windows environment on PC. From a practical point of view, ICLDS can be used as a tool for designer to implement cavity layout design of injection mould at concept design stage. It provides a positive step towards the development of a fully automated injection mould design process from product model to mould manufacturing.

Polymeric Materials

2009-02-26T03:34:00.000-08:00

Polymeric Materials

Introduction
Joining together thousands of small molecular units known as monomers makes synthetic large molecules called Polymer. The process of joining the molecules is called polymerization and the number of these units in the long molecule is known as the degree of olymerization.

The words polymers and plastics are often taken as synonymous but in fact there is a distinction. The polymer is the pure material, which results from the process of polymerization and is usually taken as the family name for materials, which have long chain-like molecules (and this includes rubbers). Pure polymers are seldom used on and it is when additives are present that the term plastic is applied.

Classification of Polymeric Material
Polymers are classified as
• Thermosets
• Thermoplastics
Thermosets are cross-linking polymers in which the final macromolecules are formed by chemical reaction under the influence of heat and pressure. Once this reaction is complete, thermosets cannot be altered from this state by further application of heat and pressure. Phenol (PF), Urea (UF), Melamine (MF) formaldehyde resins, Polyester (UP) resins and epoxy (EP) resins are typical Thermosets.

Thermoplastics consist of long chain macromolecules, which are not interlinked. Their characteristics property is that they may be moulded when the temperature is increased beyond their softening range, and on cooling revert to the solid state in its new moulded shape. This process may be repeated indefinitely, but it is in fact limited by the ageing stability of the particular material. This means that after undergoing a certain number of processing operations, the original properties of the material are altered as a result of excess thermal stress. HDPE, LDPE, PP, PS, ABS, NYLON, PVC, PMMA, PBT, etc are thermoplastics.

Polymer Blends

By alloying of two polymers it is possible to get in one material advantage of two or more polymers. At present, the following alloys are available.

PVC / Acrylic	Tough with good flame and chemical resistance.
PVC / ABS	Easily processed with good impact and flame resistance.
PC / ABS	Hard with high heat distortion temperature and good notch impact strength.
ABS / Polysulphane	Less expensive than unmodified Polysulhone.
PPO / HIPS	Improved processability and reduced cost.
SAN / Olefin	Good weatherability.
Nylon / Elastomer	Improved notch impact strength.

General properties of plastic materials

Important characteristics of plastic materials to be considered while designing and manufacturing are:
1. Dimensional Stability: Dimensional stability is defined as the ability of a material to maintain its size and shape under various temperatures and stresses, which is necessary for satisfactory part performance in many applications. The complexity, size of the mould cavity and the tendency of the material being moulded to shrink as it cools in the mould determine the final dimensions of a moulded part.
2. Drying: Under adverse high humidity conditions or large temperature fluctuations from cold temperatures to hot temperatures, moisture pickup may occur and cause splay marks or bubble formation in formed parts. Drying the resin for about two hours at 71 - 82°C will eliminate condensed moisture on the granules and assure introduction of constant temperature granules to the fabrication equipment.
3. Compatibility: Equipment should be thoroughly purged with respective resins while fabricating. Few resins are physically compatible with themselves. Delaminating, streaking or haze will occur if incompatible resins are mixed with the material to be fabricated.
4. Outdoor Weatherability: Most of Plastics are not considered to be weather resistance plastics. Continuous long-term outdoor exposure results in both discoloration and reduction in strength and toughness properties. Weatherability can be improved by the addition of certain pigments or additives. Best results are obtained with finely dispersed carbon black or UV stabilizers.
5. Use of Regrind: Many thermoplastic resins can be reground for use as 100% regrind or blends of regrind resins with virgin resin. When you are fabricating with regrind resins, you need to use experienced judgment and screening. The use of degraded or contaminated regrind product may result in lower quality parts and performance.

Application of Plastics

Polymers will continue to replace other materials on an increasing scale. The polymers already perform satisfactorily in many applications previously employing metal, wood, paper, glass etc. Usage of polymers is already well established in Automobile, electronics, Telecommunication, Computer, Toys, Medical application, clock, house ware, plumbing, footwear, electrical switch gears, luggage, etc. New polymers with specific properties and applications are being developed. With the result, number of polymers with properties suitable for specific applications is now available.
Reasons for replacement of traditional materials:
• Availability of stronger, stiffer polymers.
• Development of processing techniques to exploit the properties,
• Design possibilities of plastics,
• Availability of accurate, meaningful data on the mechanical properties of polymers.
• Greater willingness on the part of engineers to consider plastics as raw materials in their own right, rather than substitute,
• Increasing awareness of the cost saving, energy saving, labor saving and ease of manufacturing technique.
It is not correct to say that PLASTICS will generally and universally replace all materials. Need for replacement of any part should arise from functional requirement, ease of fabrication, cost with out compromising functional needs, lower weight, lower energy requirement. New polymers with specific properties and applications are being developed.
The part should be designed with plastics material, by considering the
• Functional needs
• Service condition
• Mechanical loading and
• Duration of loading
• Polymer melt behavior ( flow, shrinkage, response to shearing )
• Strength of material Properties of plastics and
• Processing (conversion- fabrication) technique.

ASSEMBLY DEPARTMENT in Tool Design Engineering

2009-02-18T20:03:00.000-08:00

ASSEMBLY DEPARTMENT in Tool Design Engineering

TOOL ASSEMBLY:

We have now come to the stage in the manufacturing of the tool where the alignment between the core and cavity with respect to each other is done. The housing that mounts the cavity and the core is perfectly milled to the dimension of the inserts it houses, the housing in turn perfectly placed by maintaining similar pitches from the guiding elements thus aligning the two halves.

Equipment for assembly will include heavy handling devices such as cranes, trolleys etc. each part should be checked for fit with each meeting part that is course in cavities, guide pillar in bush, ejector pins in ejector holes, mechanical action of the tool that is opening and closing of the two halves, ejector assembly etc.

ASSEMBLY PROCEDURE:

The various stages involved in the assembly of the tool are as follows:

Finishing the impression
Aligning the core and cavity
Bedding down
Fitting the ejector system
Assemble the moving half
Assemble the fixed half
Water pooling circuit
Polishing, hardening and tryout

QUALITY CONTROL in Tool Design Engineering

2009-02-18T20:00:00.001-08:00

QUALITY CONTROL in Tool Design Engineering

Quality control is the entire collection of activities through which we achieve fitness for use.
It is a system of routine technical activities, to measure and control the quality of the inventory as it is being developed.

Objectives of quality control:

Evaluation of quality standard's of incoming material, product in actual manufacturing and of outcome product.
Judging the conformity of the process to the established standards and taking suitable action when deviations are noted.
Evaluation of the optimum quality obtainable under the given condition
To improve quality and productivity by the pre-control and experimentation.
Identify and address errors and omissions.
Provide routine and consistent checks to ensure data integrity, correctness, and completeness.

Quality assurance:

Quality Assurance covers all activities from design, development, production, installation, servicing and documentation. This introduced the rules: "fit for purpose" and "do it right the first time". It includes the regulation of the quality of raw materials, assemblies, products and components; services related to production; and management, production, and inspection processes.

One of the most widely used paradigms for QA management is the PDCA (Plan-Do-Check-Act) approach, also known as the Shewhart cycle.

Failure testing

A valuable process to perform on a whole consumer product is failure testing, the operation of a product until it fails, often under stresses such as increasing vibration, temperature and humidity. This exposes many unanticipated weaknesses in a product, and the data is used to drive engineering and manufacturing process improvements. Often quite simple changes can dramatically improve product service, such as changing to mould-resistant paint or adding lock-washer placement to the training for new assembly personnel.

Statistical control

Many organizations use statistical process control to bring the organization to Six Sigma levels of quality, in other words, so that the likelihood of an unexpected failure is confined to six standard deviations on the normal distribution. This probability is less than four one-millionths. Items controlled often include clerical tasks such as order-entry as well as conventional manufacturing tasks.

Traditional statistical process controls in manufacturing operations usually proceed by randomly sampling and testing a fraction of the output. Variances of critical tolerances are continuously tracked, and manufacturing processes are corrected before bad parts can be produced.

Company quality

During the 1980s, the concept of “company quality” with the focus on management and people came to the fore. It was realized that, if all departments approached quality with an open mind, success was possible if the management led the quality improvement process.
The company-wide quality approach places an emphasis on three aspects:-

1. Elements such as controls, job management, adequate processes, performance and integrity criteria and identification of records
2. Competence such as knowledge, skills, experience, qualifications
Soft elements, such as personnel integrity, confidence, organizational culture, motivation, team spirit and quality relationships.
The quality of the outputs is at risk if any of these three aspects are deficient in any way.
The approach to quality management given here is therefore not limited to the manufacturing theatre only but can be applied to any business activity:

• Design work
• Administrative services
• Consulting
• Banking
• Insurance
• Computer software
• Retailing
• Transportation

It comprises a quality improvement process, which is generic in the sense it can be applied to any of these activities and it establishes a behavior pattern, which supports the achievement of quality.

This in turn is supported by quality management practices which can include a number of business systems and which are usually specific to the activities of the business unit concerned.
In manufacturing and construction activities, these business practices can be equated to the models for quality assurance defined by the International Standards contained in the ISO 9000 series and the specified Specifications for quality systems.

Still, in the system of Company Quality, the work being carried out was shop floor inspection which did not control the major quality problems. This led to quality assurance or total quality control, which has come into being recently.

Total quality control:

Total Quality Control is the most necessary inspection control of all in cases where, despite statistical quality control techniques or quality improvements implemented, sales decrease.
The major problem which leads to a decrease in sales was that the specifications did not include the most important factor, “What the customer required”.
The major characteristics, ignored during the search to improve manufacture and overall business performance were:

• Reliability
• Maintainability
• Safety

As the most important factor had been ignored, a few refinements had to be introduced:

1. Marketing had to carry out their work properly and define the customer’s specifications.
2. Specifications had to be defined to conform to these requirements.
3. Conformance to specifications i.e. drawings, standards and other relevant documents, were introduced during manufacturing, planning and control.
4. Management had to confirm all operators are equal to the work imposed on them and holidays, celebrations and disputes did not affect any of the quality levels.
5. Inspections and tests were carried out, and all components and materials, bought in or otherwise, conformed to the specifications, and the measuring equipment was accurate, this is the responsibility of the QA/QC department.
6. Any complaints received from the customers were satisfactorily dealt with in a timely manner.
7. Feedback from the user/customer is used to review designs.
8. Consistent data recording and assessment and documentation integrity.
9. Product and/or process change management and notification.

PRACTICAL CONSIDERATIONS IN DEVELOPING QA/QC SYSTEMS:

Implementing QA/QC procedures requires resources, expertise and time. In developing any QA/QC system, it is expected that judgments will need to be made on the following:
Resources allocated to QC for different source categories and the compilation process;
Time allocated to conduct the checks and reviews of emissions estimates;
o Availability and access to information on activity data and emission factors, including data quality.
o Procedures to ensure confidentiality of inventory and source category information, when required.
o Requirements for archiving information.
o Frequency of QA/QC checks on different parts of the inventory.
o The level of QC appropriate for each source category.
o Whether increased effort on QC will result in improved emissions estimates and reduced uncertainties.
o Whether sufficient expertise is available to conduct the checks and reviews.

INSPECTION:

Inspection may be defined as the measurement of the dimensions / form / profile of the component as specified by the designer. The above described form of inspection is termed as Measurement, aided by instruments.

PURPOSE OF INSPECTION:

o By thorough inspection, we can detect faults at every manufacturing process and rectify them.
o To remove defective or incorrectly made parts as soon as fault occurs.
o It helps in building up the reputation of a firm or concern.
o It improves quality of the product.
o It reduces cost spent on scrap pieces and further process can be stopped if mistake is going on.
All parts are inspected in their respective stages while processing. This knows as stage inspection. It helps in rectifying the mistake occurred during each operation. Final inspection is one in which the product manufactured is inspected completely after completion of all final assembly.

INSPECTION CHECK LIST:

1) Check for the dimensional accuracy of the finished product.
2) Check for the surface finish of the finished product.
3) Check for damage, scratch and deformation accrued in the product.
4) Check for proper fractioning of the mould.
5) Check for proper assembly of the mould
6) Check for leakage in the cooling circuit.

MEASURING RANGE:

Range may be defined as the values (Min-Max value) for which the instrument can be used for measurement.

ACCURACY:

The closeness of the measured value with the true value of the measured quantity is termed as Accuracy.

PRECISION:

Precision may be defined as the responsibility of the measuring process; repeatability may be defined as the capability of the measuring process to indicate the same value for a measured quantity under different trials.

The different methods of measurement are listed below:

Direct Method of Measurement: The value of a quantity is obtained directly by comparing the unknown with a standard. Ex: scale, weighing instrument, vernier, and micrometer.
Indirect Method of Measurement: Several parameters of the measured directly and then the value is obtained by performing mathematical calculations. Ex: Density measurement by weighing the mass and measuring the geometrical dimensions.

Comparison Method of Measurement: Comparison of the measured quantity with known value of the same quantity with known value of the same quantity or another quantity. Ex: GO and NOGO gauges indicate whether the values are within the permissible range or not.
Some of the terms in the measurement process are explained below:

Basic Size: It can be defined as the size of a part in relation to which all limits of variation are determined.

Limits: These are the two extreme permissible sizes foe any dimension.

Tolerance: It is the difference between the high and low limits of size. It isnecessary to specify this because of the inaccuracies in the manufacturing process and reasonable inaccuracy in the workmanship. It can be Unilateral or Bilateral.

Allowance: An intentional difference between hole dimension and shaft dimension for any type of fit (clearance, Interference, Transition fit). Maximum allowance is obtained by subtracting the Min. shaft size with the largest hole size and Min. allowance is obtained by subtracting the largest shaft and the smallest hole size. The allowance is positive for clearance fit and negative for interference fit.

Deviation: Algebraic difference between actual and the basic size. Upper deviation is defined as the max. Limit of size and the corresponding basic size. Lower deviation is defined as the minimum limit of size and the corresponding basic size.

The following measuring instruments found at Inspection department:

Micrometer, Calipers, height gauge, Slip gauges, gauges, filler gauge, and magnifying lens, etc.
Precision Tools and Gages:

• Micrometers, Slide Calipers, Calipers, Dividers.
• Tool Sets, Squares, Protractors, Angle Measurements, Precision Rules, Straight Edges, Parallels.
• Electronic Data Collection Systems, Gage Amplifiers, Hardness & Surface Testers.
• Dial & Electronic Indicators & Gages, Height Gages, Depth Gages.
• Thread Gaging, Hole Gages, Slot Gages, Fixed Gage Standards.

DESIGN DEPARTMENT in Tool Design Engineering

2009-02-18T19:57:00.000-08:00

DESIGN DEPARTMENT in Tool Design Engineering

Tool design is a specialized area of manufacturing engineering which comprises the analysis, planning, design, construction and application of tools, methods and procedure necessary to increase manufacturing productivity.

To carry out these responsibilities, tool designer must have a working knowledge of machine shop practices, tool making procedure, machine tool design, manufacturing procedures and methods, as well as the more conventional engineering discipline of planning, designing, engineering graphics and drawing, and cost analysis.

RESPONSIBILITIES OF TOOL DESIGNERS:

Tool designers are responsible for a wide variety of special tools. Whether these tools are an end product or merely an aid to manufacturing, the tool designer must be familiar with the following:
Cutting tools, tool holder, cutting fluids, Machine tools, Jigs and fixture, Gauges and measuring instruments, Dies for sheet metal cutting and forming, Dies for forging, upsetting, cold finishing and extrusion, Fixtures and accessories for welding, riveting other mechanical testing.
It is the main organ of the industry. Quality of work done and hence the name & fame of the company depends largely on this section. Its functions can be enlisted as below.

• Collection of required technical data, study of component drawing etc.
• Design calculations are done and suitable assumptions are made.
• Design layout by considering cost effectiveness, machines available. It also includes Comparing new design with similar.
• Design review, design verification and changes if any will be implemented.
• Preparation of drawing and bill of materials.

OBJECTIVES OF TOOL DESIGN:

The main objective of tool design is to increase production while maintaining quality lowering costs

Therefore the tool designer must realize the following objectives:

• Reduce the overall cost of manufacturing a product by producing acceptable parts at the lower cost.
• Increase the production rate by designing tools that will produce parts and quickly possible.
• Maintain quality by designing tools, which will consistently produce parts with the required precision.
• Reduce the cost of special tooling by making every design as cost effective and efficient as possible.
• Design tool that will be safe and easy to operate.

CHECK POINTS IN MOLDING TOOL:

Mold halves fit only in one position.
Guide pins must be longer than highest part of the mold insert.
Horizontal matching faces at correct level.
Cavities polished in opening direction.
Surface finish/ polishing of cavity & core inserts.
Perfect matching of pins & inserts.
Are there sufficient ejector pins.
Ejector plates guided properly.
Sprue bush radius, taper & also finish of sprue taper.
Are hardened inserts/plates provided in back plate to avoid digging by
Cooling water connection flow & leakage.
Is there sufficient clearance between CAM and slide in closed position?
Are the guide pins longer than the CAM pins, so that they engage first?
Is the slide support hardened?
Gate and positions
STEPS IN DESIGN:
Gathering data’s and establishing design objectives.
Design proposals: Two or three alternate proposal may be discussed in detail before arriving at the final proposal.
Approval of concept design: This should be finalized with all concerned - customer, the tool room personnel and the production personnel.

Planning in Tool Design Engineering

2009-02-18T19:56:00.000-08:00

Planning in Tool Design Engineering

Planning is an essential activity in an organization and an important tool. Planning basically gives an idea of the following: what should be done, how should be done how should it to be done, who should do it, where it should be done. Thus process planning gives detailed planning of operations necessary to convert the raw material in to finished products. The work to be carried out at each stage is specified along with details of the equipment, tooling methods and procedures and number of personnel required for the operation. The operations are arranged in a sequence which is logical, economical and practical.

The operation sheet serves as medium of communication among the members of production team. Thus the process planning establishes an efficient sequence of operations, selection of proper equipment tools and specifies their operation in such a manner that the product will meet all requirement stipulated in the specification. At the same time the process will be performed at minimum cost and maximum productivity.

Before starting the actual production process planning is done. It gives the idea of sequence of operations, selection of machine, cost and time required, at the same time process will be performed with high percentage of material utilization. Planning is a primary function of human and material resources in an enterprise to realize maximum profits.

Process planning represents the link between engineering design and shop floor manufacturing. Since process planning determines how a part will be manufactured, it is the major determinant of manufacturing costs and profitability.

PLANNING CONSISTS OF FOLLOWING WORKS

1. Tool and high tech component: it involves job planning with effective utilization of machines available & using right tool for right operation.

2. Preparing process sheet: process sheet in forms the operations and machining conditions such as diameter of component, feed, speed, material setting g etc.

3. Job follows up: to follow up the progress of job in the shop floor.

4. Pre tooling: pre machining of the job in conventional machines to save the time of high tech machines.

5. Route card: route card is prepared to mention operations in sequence.

Principles of Process Planning

Establish Reference Datum Surfaces at Early Stage. For cubicle parts, first operation is generally machining the resting face, which can be used as datum for the subsequent operations. In cylindrical work pieces, the first operation is generally turning. The turned portion can be used as datum for subsequent operations.
Choose Economical Machining Process like turning which is cheaper than grinding.
Unimportant faces can be machined cheaply on shaping machines. It might be necessary to use milling for better finish and flatness. For perfect parallelism and high degree of surface finish it is necessary to use a costlier surface grinding operation. The size of the machine should also be commensurate with size of the work piece. It would be uneconomical to machine a small piece on a large machine.

Customer’s materials receive and issue procedure:

Check and ensure that a details like respective drawings, materials (if supplied by the customer). Special instructions, if any been received along with order confirmation copy for the work orders received from marketing department.
Check and ensure that materials received from the store are as per specification. Check and ensure that the correct material is issued to shop as per the specification and the color code.
Check and ensure that the test piece is included in with machined parts whiie carrying out the heat treatment operation.

Process planning - route card and job card preparation:

Check and ensure that the planning department will receive the approved for fabrication, Drawings including special instruction if any and all the required details.
Check and ensure that the process planning (consisting of process sheets, job cards and route cards) carried out for the parts which are to be processed in manufacturing.