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Pressure Die Casting

Pressure die casting makes possible the economical quantity production of intricate castings at a rapid rate. Such castings, which may comprise various holes, recesses, screw threads, etc., are characterized by high dimensional accuracy, good surface finish, and economy of metal; they require little or no final machining.

Such a machine may be pneumatically operated or, more frequently, develop the pressure by the action of a ram. The casting metal for a cold-chamber machine is kept liquid in a holding furnace from which it is transferred to the pressure chamber which may be integral with the die or separate from it, by means of a scoop or a special automatic device and is forced into the die by means of a ram. Depending on the arrangement of the ram, a distinction can be made between Vertical (Fig.2) and horizontal (Fig.3) pressure die-casting machines.

The principle on which pressure die-casting processes are based consists in forcing molten metal into a mold under considerable pressure. The machines used for the purpose operate on one of two systems : hot-chamber machines i.e for metals with a low melting point and cold-chamber machines i.e for metals with a high melting point. In the first-mentioned type of machine (Fig.1) the metal is kept liquid in a crucible inside the machine, and the pressure chamber that delivers the metal into the die is located in the metal bath.

There are fully automatic machines which can turn out small zinc-alloy castings at a rate of more than 1500 cycles per hour. In pressure die casting, precision-made dies, sometimes of intricate multipart design and therefore very expensive, are employed, which are exposed to serve working conditions characterized by high pressures and a large number of successive variations in temperature. For the production of zinc and zinc-alloy castings the dies may be made of unalloyed steel; however, for aluminum, magnesium, copper and the alloys of these metals the dies are usually made of hot-work tool steel, which has greater durability.

The simplest machines are hand-operated, but fully automatic machines are more usually employed, which make possible high rates of production. A complete cycle of operations comprises closing the die, forcing the molten metal into it, withdrawing the cores, opening the die, ejecting the casting and shearing off the sprue, deburring the casting, and cleaning the die. The number of cycles per hour that a casting machine can attain will depend on the size and shape of the castings and on the casting metal used. Thus, with zinc alloys it is possible, within a given period of time, to produce about seven times the number of castings that can be made with brass.

A more recent development is vacuum die casting, which has hitherto been applied chiefly in the United States, Great Britain and Holland. It produces castings which have an even better surface finish than ordinary pressure die castings. There are two systems: either the die is enclosed within a hood which evacuates the air, or the holding furnace in which the casting metal is kept molten is so installed under the casting machine that on evacuation of the air from the die, the metal is sucked into the die and is compacted in it. A process for making iron castings based on this latter principle has been developed.

More and more customers are considering reduced fuel consumption when choosing a vehicle. This benefits their wallets as well as the environment.

Pressure die casting helps in that respect like no other process, since it offers vehicle manufacturers, and other companies searching for new kinds of components, the opportunity to harmonize functionality, performance, weight reduction, and aesthetics

This is a capability which nature exhibits admirably and has done so for millions of years. Yet, optimally designed components and products for today’s and tomorrow’s technology are just one of many reasons why automobile manufacturers and automotive suppliers, as well as companies in other industries, value working together with GF Automotive so highly.