Injection molded parts are made of thermoplastics, a polymer that turns into liquid when heated then turns back to solid when cooled.
Carefull thoughts on the following elements shall be considered for the design of plastic injection molded part.
Wall Thickness
As much as possible use a uniform wall thickness. If you must change the wall thickness, change it gradually to avoid warping.
If the strength is not compromised, design the part with minimal wall thickness to allow faster cooling time and cycle time.
Draft angles
Draft angle is necessary for easy removal of molded part from the mold. Draft angle should be applied in the direction of draw from the cavity and core.
Parts with textured surface require greater draft angle in order to avoid scratches on the textured surface as the part is being removed from the mold. 1 to 3 degrees normally applies to moderately matte or sand-blasted surfaces and 3 to 5 degrees for roucher surface.
But for smaller precision molded parts, it is sometime unnecessary to include draft angles as long as the cavity and core are highly polished.
Corner Radius
Apply radius on corners as much as possible. A proper radius size is not less than the wall thickness of the part.
Radius reduces the stress on the corner thus reducing the warpage compared to corners without radius.
Rib
Apply rib instead of using thicker wall thickness. Uneven cooling of thick wall will lead to uneven shrinkage inside and outside the wall. This could cause warpage and sinkmark due to internal stress. Applying rib will help improve the rigidity and geometric integrity of the molded part. It also improves the cooling time.
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