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.