Pressure-Die Casting

Pressure-Die Casting 

a method for the production of castings from nonferrous metal alloys and steels of some grades in press molds, which are filled with melt at high speed and under high pressure, as a result of which the melt acquires the shape of the casting. The method is used to produce parts for sanitary-engineering equipment, carburetors, and aluminum engine blocks. Casting is performed in casting machines with cold or hot molding chambers. The casting molds are usually called pressure dies and are made from steel. The shaping cavity of the mold corresponds to the outer surface of the casting, taking into account factors that affect dimensional precision. In addition, the pressure die contains movable metal cores (which form the interior cavities of the castings) and knockouts.

Casting in machines with cold molding chambers consists in the injection of the required quantity of melt manually or by means of a metering device. The melt flows from the molding chamber under the pressure of the compression piston into the shaping cavity of the tightly closed mold; the excess melt remains in the molding chamber as the compression residue and is removed. After the melt has hardened, the mold is opened, the cores are removed, and the casting is removed from the mold by the knockouts.

In machines with hot molding chambers, the melt flows from the crucible of the heating furnace into the molding chamber by gravity. Filling of the molding chamber is followed by the actuation of an automatic device (a time relay set for a fixed interval), and the piston begins to exert pressure on the liquid melt, which flows through the heated neck and gate sleeve under pressure through the sprues into the forming cavity of the mold and crystallizes. After a certain period of time, which is required for the formation of the casting, an automatic device operates, opening the mold, and the casting is removed by knockouts. The excess metal is cut off, the elements of the gating are removed, and the casting is then cleaned manually or mechanically. If necessary, heat treatment is performed.

Pressure-die casting is distinguished by high compression rates and high specific pressures (30–150 meganewtons per sq m, or 300–1,500 kilograms-force per sq cm) applied to the liquid melt in the mold. The quality of castings depends on a number of engineering and design factors, such as the selection of the alloy; the design of the casting, the gating and ventilation systems, and the mold; the temperature stability of the melt and the mold; and the evacuation of the mold to prevent the formation of pores. The method leads to high productivity and to good dimensional precision (precision classes 3–7), clarity of relief, and surface quality (precision classes 5–8 for aluminum castings weighing up to 45 kg). The productivity of the machines is one to 50 castings per minute. Multiple molds are also used, which make possible production of over 20 parts per casting cycle.

REFERENCES

Pliatskii, V. M. Tekhnologiia lit’a pod davleniem, 3rd ed. Moscow, 1957.
Bekker, M. B. Lit’e pod davleniem, 2nd ed. Moscow, 1973.

M. B. BEKKER