Die Casting History, Future and advantages

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

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

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

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

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

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

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.