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Plastic Injection Molding Design Considerations
Apr 23, 2009

Plastic Injection Molding Design Guidelines

Use an approximately uniform wall thickness throughout your design.

Keep walls thin - typically between 1/32" and 1/10". This allows for proper cooling and reduces cost by minimizing use of material. Thin walls also reduce problems with material shrinkage. Although some unevenness will occur due to shrinkage, walls as thick as 1/5" can be used. Keep wall thickness at least wall length / 50. Keep 90 deg walls under 0.25" high. Keep thickness of ejection pin surface wall at least .07".

To strengthen parts, instead of using thicker walls, use additional structures such as ribs. Use fillets at the base of ribs.

When using a rib make it about half the main wall thickness. 

Round corners and edges wherever possible.

For easy release of the part from the mold, add a slight taper to the sides (typically ~ 2 deg) - especially for textured walls and walls higher than 0.25".

Avoid shapes that are impossible to remove from the mold.  Lighter colors hide flow patterns better than dark colors. Choose the right material from the table. Drawing dimensions should be of the final part - material shrinkage will automatically be considered in the design of the mold. Use raised text instead of recessed text when possible. Where walls meet at a 90 angle, round inside and outside to at least .05" radius - sharper outside corners can create molding problems and sharper inside corners will increase tooling cost. Keep holes at least .015" from edges. It should not be possible to fully hide a 0.3" diameter ball anywhere inside the material.