 Plastic Molded Parts Design Guide
Designing for Maximum Quality, Engineering for Lowest Cost |
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Uniform Wall Thickness
Good injection molded part design relies on consistent wall thickness to minimize the potential for warped or distorted parts.
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Avoiding Warp:
In the design of parts to be injection molded, it is a good idea to
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maintain consistent wall thickness and avoid thick areas whenever possible.
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Avoid warp by minimizing: Warpage due to stresses in step transitions between
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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.
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Avoiding Sink:
The use of thinner, uniform wall thicknesses helps to avoid sink.
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Rib-to-wall thickness ratios: To prevent sink, the thickness of the rib should be
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about half the thickness of the wall. |
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Part Reinforcement and Draft
Proper use of draft and reinforcing fillets will aid in ejection, add rigidity to part ribs and strengthen the mold.
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Rounding Corners: Avoid unnecessary stresses by rounding out corners |
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Include sufficient draft:
Using at least 0.5 degrees on all "vertical" faces;
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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. |
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Use drafted shutoff surfaces: Draft results in improved mold shutoff surfaces. |
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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 produce 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.
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Avoid
fine details adjacent to deep walls: Drafted walls
allow the use of shorter |
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tools, which results in greater
milling accuracy and detail. |
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Radiused Corners:
Some part corners will end up with a radius rather than a |
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sharp edge. |
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Avoid deep & thin ribs if possible on rib design. |
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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.
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