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Plastic
Parts
Most plastic components on the market today are injection
molded. Aninjection
molded plastic part is
created using an injection
molding machine,
which works by melting plastic pellets, and injecting them into a
mold.
Designing plastic
parts is a
complex process, and the manufacturing end of it must be taken into
account during the design phase. There are three elements of an
injection molded plastic part, the nominal wall, projections, and
holes and recesses.
The nominal wall refers to the wall thickness. The wall thickness
throughout the part should not vary by more than 10 percent. Varying
wall thicknesses in the injection molded plastic part are one of the
main causes of flawed product. In designing the part, one wishes to
avoid excessively thick walls, simply because thick walls use more
plastic, and are more expensive to produce. However, there is a
limit as to how thin the part can be as well. The strength of the
part is a function of the thickness, and the final use of the
product will determine the desired strength. Some specialized
injection molded plastic parts require reinforcement with glass or
carbon fibers.
A
projection is an element of the part that projects out of the
nominal wall, such as reinforcement ribs. The ribs must not be
thicker than the nominal wall, or else sink marks may result.
Recesses and holes also are a major design element, the location of
any holes or recesses may significantly affect the part's overall
strength. Trying to create a hole in the side of a part is
especially challenging, and the need for side holes should be
minimized in the initial design. |
