Plastics Design Guide

Plastic Part Design

To insure a quality final product, it is necessary to start out with quality components. Injection molded parts can be molded to a high quality standard by focusing on these areas of plastic technology:

1) Correct Part Design
2) Accurate Selection of Material
3) Proper Plastic Processing

Only by drawing on expertise from these three areas of plastic technology can a product designer create quality molded parts that maximize performance and are cost effective. The purpose of this design guide deals with the first of these three issues - part design.

Correct Part Design Guidelines

If there was only one rule for the injection molding process it would have to be "maintain uniform wall thickness". Here are some examples of problems associated with part designs that feature non-uniform wall thicknesses:

Sink marks due to uneven shrinkage Sink marks result from a wall yielding to the still shrinking interior mass.	Stress due to uneven shrinkage A part with non-uniform wall thickness will cool unevenly, resulting in high molded-in stress.
Voids due to uneven shrinkage The already cooled section will not yield to the shrinking action of the cooling interior mass causing voids in the thick portion of the part.	Warpage due to uneven shrinkage Concentrated stress at the junction of high & low shrinkage areas may cause a part to warp.