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Design Guidelines

Uniform wall thickness
Consistent wall thickness for plastic parts to minimize the potential for warped or distortion.

Sink Marks
Wall Thickness by Material Guideline
Avoid Warping
Rib/Boss to Wall Thickness Ratio
Part Draft on Plastic Injection Molds


Sink Marks
As the plastic in the mold cools from the outside it can cause pulling on outer walls resulting in sink marks. Thinner wall thickness will help to prevent this. Where possible always try to design a part with thinner and consistent wall sections to minimize warp and sink marks.


Wall Thickness by Material Guideline
The proper material selection for your desired part thickness can also help. See table below for injection moldable material selection and recommended wall sections for your molding project.

  ABS 0.045 - 0.140
  Acetal 0.030 - 0.120
  Acrylic 0.025 - 0.500
  Liquid crystal polymer 0.030 - 0.120
  Long-fiber reinforced plastics 0.075 - 1.000
  Nylon 0.030 - 0.115
  Polycarbonate 0.040 - 0.150
  Polyester 0.025 - 0.125
  Polyethylene 0.030 - 0.200
  Polyphenylene sulfide 0.020 - 0.180
  Polypropylene 0.025 - 0.150
  Polystyrene 0.035 - 0.150
  Polyurethane 0.080 - 0.750

Fiber reinforced plastic allows for larger thicker parts

Part Warp In addition, because thinner sections will freeze faster than thicker sections there is also the possibility of stresses building up between thick & thin sections, resulting in part warp.

Avoid Warping
1. Reducing transitions between Thick and thin sections.
2. use gussets and ribs instead of thick sections.

Even small transitions like this can cause warp


Rib/Boss to Wall Thickness Ratio
Ribs and Bosses protruding from wall thickness should follow this rule of thumb.

60% of wall thickness.

Tip: Reduce the Boss diameter and strengthen with ribs



Part Draft on Plastic Injection Molds
Plastic parts should be designed with draft to prevent sticking and ejector pin push marks on the show surface during the molding process. Also, an adequate amount of draft is needed for surfaces that will be textured. Don't forget ribs should not exceed 60% of wallthickness.