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Design Essentials for Plastic Injection Moulding

Before any type of production begins, it’s important to consider the design elements of a part. Through doing so, you may improve the moulding, reduce costs and limit the chances of production issues.


To achieve a properly designed injection moulding part, you need to apply draft to your design.

Draft will help release the part from its mould with less drag of the part’s surface. You should apply 1 degree of draft per 25mm of cavity depth. Depending on the material selected and the moulds capability, this size may still not be sufficient.

 At CJ Tool and Mouldings, we use analytics to individually look at each part feature and put it in comparison to our toolset. We can then identify where increased draft and thickness may be required.

Wall thickness

Controlling wall thickness whilst designing a part is beneficial when managing cosmetics, weight and strength. If your part is too thick you may see areas that have sunk, warped or become pockets of air. You can avoid this through the attached wall thickness guidelines.

Coring Out and Rabbing

If a part is correctly designed it should contain ribs and supporting gussets. These will increase strength and will help reduce or remove cosmetic defects like warp, sink and voids. Be careful to watch out for rib-to-wall thickness ratios, the rib should be about half of the thickness of the wall.


Core-cavity may also be referenced as A and B sides or top and bottom halves of a mould. Through using a core-cavity approach to part design, you’ll be able to save time manufacturing and save money whilst improving the overall cosmetics as well. This design technique requires the outside and inside walls to be drafted so they’re parallel to one another. Using this method, you’ll keep a consistent wall thickness.

 For more information on our design services, click here. Should you need some advice or would like a quote, our friendly team are always happy to help. For our specialist advice, please contact CJ Tool and Mouldings today on 01384 378 866 or read our latest articles for further tips and advice on plastic injection moulding.

Added: 27 Mar 2018 09:09

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