Plastic Molded Parts Design Guide
Designing for Maximum Quality, Engineering for Lowest Cost
Uniform Wall Thickness
Good injection molded part design relies on consistent wall thickness to minimize the potential for warped or distorted parts.
Avoiding Warp: In the design of parts to be injection molded, it is a good idea to
maintain consistent wall thickness and avoid thick areas whenever possible.
Avoid warp by minimizing: Warpage due to stresses in step transitions between
wall thicknesses can be improved through the use of a ramp. The use of gussets can be helpful to provide support in corners to avoid warping.
Avoiding Sink: The use of thinner, uniform wall thicknesses helps to avoid sink.
Rib-to-wall thickness ratios: To prevent sink, the thickness of the rib should be
about half the thickness of the wall.
Part Reinforcement and Draft
Proper use of draft and reinforcing fillets will aid in ejection, add rigidity to part ribs and strengthen the mold.
Rounding Corners: Avoid unnecessary stresses by rounding out corners
Include sufficient draft: Using at least 0.5 degrees on all “vertical” faces; 2
degrees works very well in most situations; 3 degrees is minimum for a shutoff (metal sliding on metal); 3 degrees is required for light texture; 5 or more degrees is required for heavy texture.
Use drafted shutoff surfaces: Draft results in improved mold shutoff surfaces.
Simple, Straight-Pull Parts
One of the primary characteristics of a “simple” injection molded part is that it does not have undercuts. To Consider using telescoping shutoffs to create through-holes, an equally functional redesigned part without undercuts can be molded using telescoping shutoffs.
The mold – Core-Cavity Approach
Consider core-cavity approaches when possible: As an alternative to deep ribs, consider using the illustrated type of core-cavity approach to producing a similar geometry.
CNC Milling Process
TIP uses CNC milling to produce its molds; part designs will benefit from the consideration of the mold-milling process.
Avoid fine details adjacent to deep walls: Drafted walls allow the use of shorter
tools, which results in greater milling accuracy and detail.
Radiused Corners: Some part corners will end up with a radius rather than a
Avoid deep & thin ribs if possible on rib design.
Part Ejection Considerations
Be aware of the need to accommodate ejection pins.
Choosing a Surface Finish
Keep in mind the relationships between surface finish, moldability, cost and lead time.
Choosing a Resin
Consider the mechanical characteristics, molding properties, and cost of the resin used. Designing for Maximum Quality, Engineering for Lowest Cost