Following are the various processes by which plastic parts
are manufactured.
Blow Moulding
The process of inflating a hot, hollow, thermoplastic preform inside a
closed mold so its shape conforms to that of the mold cavity.
Extrusion Moulding
Continuous section process by which parts are squeezed through a die and
cut to specified lengths.
Injection Moulding
High Volumes. Most popular plastics moulding process. Tooling costs are
usually high. Parts are formed by injecting soft or liquid material into a
mold under high pressures.
Pultrusion
Similar to extrusion moulding but with higher strength. Reinforcing
materials such as glass or other fibers are incorporated into the
extrusion. Materials are usually thermosets.
Rim Casting
Low volume parts. Expensive. Cure times are long. Chemically curing resins
are injected at low pressures.
Rotational Moulding
Large Parts. Items can be hollow, but generally for parts that form part
or all of a shell. Parts are formed by rotating a hollow tool with a
charge of powdered plastic inside. The tool is heated, then cooled, so the
plastic fuses to the inside of the tool, to form a shell.
Vacuum Forming and Thermoforming
Vacuum is used to make thicker parts such as keyboards. Thermoforming is
used to make thinner parts, primarily packaging. Tooling is fairly
inexpensive. Limited choice of materials. Parts are formed by heating a
sheet of plastic over a mold until it is soft, and then using a vacuum or
pressure to suck or push the sheet onto the mold, then allowing it to
cool.
