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Designing to Reduce Plastic Shrinkage and Warpage

All injection moulding parts shrink, however it’s understanding is the cause of this. In this article we’ll be highlighting how to reduce and control shrinkage and warping and why it’s important to do so.

 

Shrinkage

 

Shrinkage is the reduction in size of the injection moulding part as it cools. Different plastics shrink more than others  and other plastics can shrink in different directions. If any element of the part shrinks at a different rate, then it creates internal stress, if the stress exceeds the part’s structural integrity then the injection moulding part will warp.

 

  1. Regional – one area or region shrinks more than the other
  2. Thickness – this happens when one side of the cross-section is different to the other and therefore one side can shrink more.
  3. Directional – shrinkage can happen parallel and perpendicular to the material’s orientation or direction of flow.
  4. In-plane Vs. Thickness – Polymers typically shrink in the thickness direction rather than the plane of the surface.

 

Warpage

 

Warping is a distortion in the intended shape of the injection moulding part that occurs during cooling, it can make the parts twist, fold, bend and bow. Warping is a direct result of shrinkage, but variations in wall thickness and improperly gated parts can also cause a component to warp.

 

How to reduce and control shrinkage and warp

 

  • Avoid non-uniform wall thickness
  • Pack the cavity after filling and use a proper packing pressure level
  • Balance the filling pattern
  • The cooling system should apply uniform cooling across both the thickness and throughout the part

 

When designing for injection moulding, the amount of shrinkage needs to be accurately predicted and this can be determined by part size and resin selection in some cases. It is also important to consider the shrink of the resin when designing the injection moulding part.

 

Our in-house team of specialists can help you design and fine-tune the shrinkage of your injection moulding parts by adjusting the density of the material and considering the above factors. Get in touch today to discuss your requirements, our team will be more than happy to help, advise and quote.

 

 

 

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Looking for more information? Check out our blog, News & Views for useful articles, tips and tricks on plastic injection moulding.