High Pressure Die Casting(HPDC) is an efficient componentry manufacturing method for the production of various product forms with extremely quick casting possibilities coupled with a high pressure injection process.
The four main metal groups used with this technology are aluminum, zinc, magnesium and copper-base alloys.
- High pressure die casting can be divided into “cold-chamber” and “hot-chamber” processes.
- In the cold-chamber process, molten metal is metered into a cold chamber for each machine cycle (or shot).
- The molten metal is then forced by a single plunger through a narrow feeder channel (or gate), into the die cavity itself, by the application of pressures from 7 to 207 MPa.
- The metal solidifies rapidly because the die is water-cooled within a fraction of a second.
- Upon solidification, the dies are opened and the casting is removed using ejector pins.
- Most of the castings will have flash where the two die halves come together. This is usually removed in a trimming die.
- Hot-chamber die casting is limited to the low melting point magnesium and zinc alloys, where contamination by iron will be less extensive. A gooseneck shot sleeve is submerged in a heated pot of molten melt. A plunger descends and forces the molten metal into the die. As the piston retracts, the cylinder is filled with metal.
High-pressure die casting is a process in which molten metal is forced under pressure into a securely locked metal die cavity, where it is held by a powerful press until the metal solidifies. After solidification of the metal, the die is unlocked, opened, and the casting ejected. After removal of the casting, the die is closed and locked again for the next cycle. The injection of metal into the die cavity is completed in a fraction of a second. Often, while the molten metal is still held in the die, extremely high pressure is applied (called intensification pressure). This high pressure compresses any gas entrapped in the metal and feeds additional metal into the cavity to compensate for the shrinkage of the metal as it solidifies.
Two types of systems are used for injecting the molten metal into the die. The hot chamber system is used with metals such as zinc, magnesium, and lead. The injection system of a hot chamber machine is immersed in the molten metal bath of the melting furnace. As the shot plunger moves, it forces metal through the nozzle and into the die.
The cold chamber system is used for metals that melt at high temperatures, such as aluminum, brass, and magnesium. Magnesium parts can be produced using both systems, though usually small parts are produced in hot chamber machines and large parts in cold chamber machines since hot chamber machines are limited in size. There are also two injection systems used in the cold chamber process, horizontal and vertical injection.
In the cold chamber process, the molten metal is poured, by hand or by automatic means, into a port of the cold chamber sleeve. A hydraulically operated plunger advances through this steel sleeve, sealing off the port, and forcing the metal into the die at high speed and pressure. After solidification of the casting, the plunger is retracted, the die opened, the casting ejected, and the system is then ready for the next shot cycle. Higher pressure is used in this system than the hot chamber process. The production rate of a hot chamber machine is higher than that of a cold chamber machine because of the shorter time required during the pour operation.
Advantages of high pressure die casting
The advantages of high pressure die casting include higher production speeds when compared to the flow pouring under the effect of gravity.
Furthermore, the ability to produce flows of specific dimensions notably reduces processing operations.
The fusions have a good surface finish, which is a basic requisite for plating, and reduced thickness of the plate walls is made possible by reducing the overall weight of the fusion.
The moulds are durable, thus reducing unit cost prices and more complex parts can be manufactured, thus decreasing the number of components requested each time.