What is die casting and process.

DIE CASTING:

•        The die casting process uses steel dies into which metal is forced under pressure through a runner and gate to fill the dies. The pressure (70 to 5000 kg/cm²) is maintained while the casting solidifies after which the dies are separated, cores are withdrawn and the casting is ejected.

•        Metals and alloys that are die casted include zinc, aluminium, and magnesium, copper, lead and tin

•        Typical applications of die casting process include automobile components, household appliances, railway and aircraft fittings, bath room hardware, business machines, locks, pullers and many other similar parts.

DIE CASTING PROCESS:
A die casting process consists of the following steps:

(i) Closing the die halves

(ii) Clamping the die halves securely together

(iii) Forcing the liquid metal into the dies

(iv) Opening the die halves and

(v) Ejecting the casting

DIE CASTING MACHINES:

•       To be effective these machines should be strong and rigidly built to take up die weights and provide holding pressures against the pressure of the molten metal

•       The machine frame should hold the die halves rigidly in correct alignment

•       The die holding forces should be in excess of the maximum force developed by the molten metal to ensure leak proof joint in the dies

•        The die closing and locking arrangements generally used in the die casting machines include hydraulic, hydraulic mechanical or mechanical devices depending on the capacity of the machine

Advantages :

•  Advantages of die casting include excellent die life, high production rates, close dimensional tolerances, good details, and excellent surface finish of the castings

•  Die casting dies retain their accuracies for long production runs

•  Production rates vary- from 5 to 6 castings per minute with hot chamber machines to 2 to 3 castings per minute when cold chamber machine are used

•  Dimensional tolerances can be held to ± 0.075 mm.

•  Very thin sections can be cast and good surface finish obtained with excellent details.

Disadvantages :

•   High cost of dies and machines

•   Restriction on the size of the casting to about 100 kg for zinc alloys and 30 kg for aluminium alloys

•   Only certain non-ferrous metals can be economically die cast

•   Die casting products also are mechanically weaker because of the air entrapped during casting

•   The entrapped air makes die casting unsuitable for heat treatment. When these castings are heated for heat treatment the entrapped air expands causing blisters to be formed on the surface of the castings