Q – WHAT IS DIE CASTING?
A – Die casting is a manufacturing process for producing accurately dimensioned, sharply defined,
smooth or textured-surface metal parts. It is accomplished by forcing molten metal under high
pressure into reusable metal dies. The process is often described as the shortest distance between
raw material and finished product. The term “die casting” is also used to describe the finished part.
The term “gravity die casting” refers to castings made in metal molds under a gravity head.
It is known as permanent mold casting in the U.S.A. and Canada. What we call “die casting” here
is known as “pressure die casting” in Europe.
HOW ARE DIE CASTINGS PRODUCED?
First, a steel mold capable of producing tens of thousands of castings in rapid succession must be
made in at least two sections to permit removal of castings. These sections are mounted securely
in a machine and are arranged so that one is stationary (fixed die half) while the other is
moveable (injector die half). To begin the casting cycle, the two die halves are clamped tightly
together by the die casting machine. Molten metal is injected into the die cavity where it
solidifies quickly. The die halves are drawn apart and the casting is ejected. Die casting dies
can be simple or complex, having moveable slides, cores, or other sections depending on the
complexity of the casting.
The complete cycle of the die casting process is by far the fastest known for producing precise
non-ferrous metal parts. This is in marked contrast to sand casting which requires a new sand mold
for each casting. While the permanent mold process uses iron or steel molds instead of sand,
it is considerably slower, and not as precise as die casting.
TYPES OF MACHINES FOR DIE CASTING
Regardless of the type of machine used, it is essential that die halves, cores and/or other
moveable sections be securely locked in place during the casting cycle. Generally, the clamping
force of the machine is governed by (a) the projected surface area of the casting
(measured at the die parting line) and (b) the pressure used to inject metal into the die.
Most machines use toggle type mechanisms actuated by hydraulic cylinders (sometimes air pressure)
to achieve locking. Others use direct acting hydraulic pressure. Safety interlock systems are used
to prevent the die from opening during the casting cycles.
Die casting machines, large or small, vary fundamentally only in the method used to inject molten
metal into the die. These are classified and described as either hot or cold chamber die casting