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Sink & Warp

insert molding

Careful consideration should always be taken to part design and the chosen material, as both play significant roles in sink & warp of injection molded plastic parts.

Avoiding Sink in Plastic Parts

  • Coring out thick sections will help to reduce the potential for shrink
  • Design your parts with ribs & bosses that are no greater than 60% of your nominal wall thickness.

Walls that are designed too thick or too thin can lead to cosmetic defects in final parts and should be reduced if not eliminated all together.

Variations of shrinkage in materials can lead to warp, distortion and dimensional issues with injection molded parts.

As the plastic material cools, the molecules that make it up move closer together.

If the cooling rate is different, such as thinner or thicker walls the stress caused by cooling can lead to the material wanting to warp.

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 thicknesses to minimize warp and sink marks.

When considering materials look for stable materials that capture all of the properties your product requires and has low shrink rates to ensure better, more consistent plastic parts.

Careful consideration to part and mold design must be addressed in order to create high quality ,consistent plastic parts and at Xcentric we provide you with the tools and experience to reduce or eliminate potential cosmetic or structural defects of your plastic custom parts.