The critical items to be considered while designing a injection mould tool are
Ø Shrinkage.
Ø Draft angle.
Ø Selection of Parting Surface.
Ø Number of Cavities.
Ø Feed System.
Ø Cooling System.
Ø Ejection System.
Ø Venting.
In the simplest case a die consists of two halves into which the impression of the part to be moulded is cut. The mating surfaces of the die halves are accurately machined so that no leakage can occur at the split line. It may by seen that in order to facilitate mounting the mould in the machine and cooling and ejection of the moulding, several additions are made to the basic mould halves. Firstly, backing plates permit the mould to be bolted on to the machine platens. Secondly, channels are machined into the mould to allow the mould temperature to be controlled. Thirdly, ejector pins are included to that the moulded part can be freed from the mould. In most cases the ejector pins are operated by the shoulder screw hitting a stop when the mould opens. Two side cores are incorporated in fixed half as each component requires it. Two finger cams are provided in fixed half for the actuation of these side cores. The mould cavity is joined to the machine nozzle by means of the sprue. The sprue anchor pin then has the function of pulling the sprue away from the nozzle and ensuring that the moulded part remains on the moving half of the mould, when the mould opens. The impressions are joined to the sprue by runners - channels cut in core insert of the mould through which the plastic will flow without restriction. A narrow constriction between the runner and the impressions allows the moulding to be easily separated from the runner and sprue. This constriction is called the gate.
Fixed half and moving half
The various mould parts fall naturally into two section or halves. Hence that half attached to the stationary platen of the machine is termed the fixed half. The other half of the mould attached to the moving platen of the machine is known simply as the moving half.
Generally the core is situated in moving half and the overriding reason is, the molding, as it cools, will shrink on to the core and remain with it as the mould opens. This will occur irrespective of whether the core is in the fixed half or the moving half. However, this shrinkage on to the core means that some form of ejector system is almost certainly necessary. Motivation for this ejector system is provided if the core is in moving half. Moreover, in the case of single-impression basic mould, where a direct sprue feed to the underside of the molding is desired the cavity must be in the fixed half and core in the moving half.
Aluminum or aluminum is a silvery and ductile metal widely used for manufacturing components and parts in diverse industries. The metal is found primarily in bauxite ore and is known for its light weight and resistance to corrosion. Aluminum castings are used in the aerospace industry and very important in other areas of transportation and building.
Properties of Aluminum Alloy
Aluminum has a number of properties, which makes it suitable for being casted into unique
and complex shapes components and spare parts, which are further used in a number of industries. Some of the properties are:
Cobalt is a hard, lustrous, silver-gray metal, found in different ores. It is also used for preparing magnetic, wear-resistant, and high-strength alloys. The metal compounds are used in the production of inks, paints and varnishes.
The metal alloys are easily castable and the compositions are characterized with high carbon content & minimum silicon, both providing fluidity. Cobalt and its alloys have been used in demanding applications since a very long time and have contributed significantly to industrial products and processes.
Copper is a popularly used ductile metal with excellent electrical conductivity, and also finds extensive use as a thermal and electrical conductor, as a building material, and as an important component of various alloys.
There are numerous alloys of copper with important historical and contemporary uses. Casted copper alloys have high tensile and compressive strength, have good wear qualities when subjected to metal-to-metal contact, are easily machined, have good thermal and electrical conductivity, and high corrosion resistance for maximizing product performance. Some of the widely used alloys are:
· Bronze: An alloy of copper and tin
· Brass: An alloy of copper and zinc.
· Monel/ Cupronickel: An alloy of copper and nickel.
Properties of Copper
Copper has numerous properties, which makes it useful in various industrial applications. Some of the properties are:
Ø Malleable
Ø Ductile
Ø Good conductor of heat
Ø Good conductor of electricity-in pure state
Lead is a soft, heavy, toxic metal, bluish white in color when freshly cut but tarnishes to dull gray when exposed to air. The stable and heavy metal has a dull luster and is a dense, ductile, very soft, highly malleable, with poor electrical conductivity. This metal is highly corrosion resistant and this property, makes it useful for carrying corrosive liquids (e.g. sulfuric acid).
The metal is used in wide variety of industries as it can be easily casted or molded into different shapes & used as solder.
Magnesium is an abundantly found metal, silvery white in appearance, fairly strong and light in weight. The metal is protected by a thin layer of oxide which is hard to remove and it tarnishes slightly when exposed to air.
Magnesium alloys find applications in various industries as they meet the requirements for lightweight materials to operate under increasingly demanding conditions. These metal alloys have always been demanded by designers due to their low density, only two thirds that of aluminum. This has been a significant factor in the widespread use of casted and wrought magnesium alloy.
There have been quite a few developments in the recent years to improve the performance of these alloys used in different casting processes. Improvements in mechanical properties has made these alloys more in demand for specialty application areas like aerospace.
Magnesium Alloy Designation System
A standard system of alloy and temper designations, as given by the American Society for Testing and Materials (ASTM B 275) is explained in the following table:
Nickel is an alloy metal, silvery white in color that takes on a high polish. It belongs to the class of transition metals, and is hard and ductile. The metal is found combined with sulphur in millerite, with arsenic in the mineral niccolite, and with arsenic and sulphur in nickel glance.
It is pre-eminently an alloy metal, and its main use is in the nickel steels and nickel cast irons, of which there are large number of varieties. The metal is also widely used for many other alloys, such as nickel brasses and bronzes, and alloys with copper, chromium, aluminum, lead, cobalt, silver, and gold.
The metal is magnetic in nature, and is very frequently accompanied by cobalt, both being found in meteoric iron.
Refractory metals belong to a special class of metals that highly and exceptionally resistant to heat, wear, and corrosion. These properties make these reactive metals of use in various industrial applications.
Popular Refractory Metals:
Since these metals have a high melting point, the components are never fabricated by casting. Powder metallurgy process is used wherein the pure metal is compacted, heated using electric current, and further fabricated by cold working with annealing steps. Refractory metals can be molded and formed into wire, bars, ingots, sheets or foil.
Tin is one of the earliest metals discovered by human being. Tin is known for a low-melting point (450°F) and its fluidity. It's very easy to form tin alloy with other metals because of its softness and formability. The metal has a high boiling point and is nontoxic and solderable. The difference of temperature between melting and boiling points, which is important for castings, is greater than all other metals.
Different casting methods used for tin alloy casting are gravity die casting, pressure die casting, and centrifugal casting. As there is little or no shrinkage occurs on solidification, components produced by tin-alloy castings are sound and dimensionally accurate. The design of molds should be such that sufficient amount of metal is fed to inside corners of the mold cavity. Carbon-steel or rubber molds can be used as tin alloys have low-melting points.
Though, little bit expensive, tin is considered to be the perfect metal for casting. As the melting temperature is fairly low, simple molds, even molds made of special rubber can be used. Unlike lead, tin is non-toxic and it's shiny and doesn't tarnish.
Zinc alloys are nonferrous alloys and most commonly used in the manufacturing of die cast components. These components are produced with various compositions and grades. Zinc alloy components come with different shapes, dimensions, and features. There are very less amount of alloying elements in commercially pure, very low alloy or unalloyed zinc. Commercially, these (pure or unalloyed) zinc are used to galvanize metals and for other non-structural applications. Galvanizing iron to make it corrosion resistance is one classic example of this kind of use.
Dimensions and production processes are two things that should be analyzed properly before selecting zinc and zinc alloys.
Sand casting is one of the most popular and simplest types of casting that has been used for centuries. Sand casting allows for smaller batches to be made compared to permanent mold casting and a very reasonable cost. Not only does this method allow for manufacturers to create products for a good cost there are other benefits to sand casting such as there are very little size operations. From castings that fit in the palm of your hand to train beds (one casting can create the entire bed for one rail car) it can be done with sand casting. Sand casting also allows for most metals to be cast depending in the the type of sand used for the molds.
Sand casting requires a lead time of days for production at high output rates (1-20 pieces/hr-mold), and is unsurpassed for large-part production. Green (moist) sand has almost no part weight limit, whereas dry sand has a practical part mass limit of 2300-2700 kg. Minimum part weight ranges from 0.075-0.1 kg. The sand is bonded together using clays (as in green sand) or chemical binders, or polymerized oils (such as motor oil.) Sand in most operations can be recycled many times and requires little additional input.
