Injection molding is a process used to form products from plastic. The process
requires a mold, clamping component, injection unit, and some sort of plastic. As time has
advanced so has injection molding by developing new techniques and new products to aid
in the manufacturing of the injection molded parts.
Injection molding was used as early as the 1860's. It can be used to form many
different products. Whether the products are small, large, complex, or simple they can be
produced. Injection molding has derived from metal die casting. However, the polymer
can't just be poured into a mold, it has to be forced into the mold cavity. The polymer is
forced into the mold and pressure is held on it to avoid shrinkage in the mold cavity as it
cools. Injection molding is capable of producing a large number of parts with very high
precision. All thermoplastics except polytetraflouroethylene (PTFE), polyamides, and
some aromatic polyesters can be used by the injection molding machine. Some
thermosetting plastics can also be used.
The typical fabrication process can be done by one of two different types of
injection molding equipment. Either a plunger, or reciprocating screw type machine can
be used. The process starts by melting the polymer resin. Once the resin is melted, a mold
is placed in the clamping unit. The clamping unit is to hold the mold together.
The plunger or reciprocating screw then force the polymer resin into the mold. In the
plunger operated machine, the plunger is hydraulically operated. This forces the plastic
through a heated area, where it is then spread into a thin layer by the torpedo. Then the
melt comes to the nozzle and is injected into the mold. The reciprocating screw rotates,
this moves the polymer resin forward for injection. As the screw rotates it acts to melt,
mix, and pump the polymer to prepare it for injection. The reciprocating
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