High pressure die casting (Process Level 3)

Casting: die casting

In PRESSURE DIE CASTING, molten metal is injected under high pressure into a metal die through a system of sprues and runners and pressure is maintained during solidification. Afterwards, the die halves are opened and the casting is ejected. Because of the high pressures involved, the two die halves are held together by a high force and locked with toggle clamps. The dies are precision machined from heat resistant steel and are water-cooled. They often include several movable parts and are therefore complex and expensive.

Two types of die casting machines are used. In the 'hot chamber' or gooseneck process, the molten metal is held in a furnace in which a gooseneck chamber is submerged. Upon each cycle, the gooseneck is filled with metal which is then forced into the die. Because of the prolonged contact between the metal and the injection system, this process is restricted to zinc-base alloys. In the 'cold chamber' process (see figure above), metal is melted in a separate furnace and then transported to the die casting machine. The cold chamber process can be used for a variety of alloys. Because of internal porosity, die castings cannot be heat-treated. The process is very competitive for producing large quantities of thin-walled castings.