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Design Considerations for Injection Moulding: Coring and Drafts

Before undertaking any injection moulding project you should consider Coring and Drafts whilst at the design stages.




Drafts are vital to improving mouldability of a plastic part. The draft angles anticipate shrinkage during the cooling process. When a part is being released from the mould, draft angles reduce friction between the walls of the part and the mould making as clean a release as possible. – Even ribs, bosses, depressions and holes must have a draft. Without them an injection moulding part can expect to see surface defects as well as an unsuccessful ejection from the mould tool.


Benefits of adding draft:


  • Reduced risk of damage to injection moulding part
  • Reduced wear and tear and chances of damage
  • A uniformed smooth and unscratched surface finish
  • Overall cooling time by lessening the need for unconventional ejection setups
  • Reduction in overall injection moulding production cost




Coring is the removal of excess material from the cross section of a moulded part to achieve a more uniform wall thickness. A uniform wall thickness is desired when it comes to plastic injection moulding. To help achieve uniform wall thickness, thick wall areas of the component may need to be cored. This is because Coring reduces the wall thickness to avoid sink marks and saves on weight and cost. Coring out a thick piece will not only reduce the injection moulding manufacturing costs but also improve its look and performance without influencing other important dimensions


Benefits of coring:


  • Reduced wall thickness
  • Reduced sink marks
  • Reduced manufacturing cost through saved weight
  • Improved uniform and performance


After analysing the thickness of your part, if too thick you are suggested to core out to avoid sink marks. CJ Tool & Mouldings can best advise you when it comes to designing for plastic injection moulding, Get in touch with our team of experts today! 


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Our team will be more than happy to help, advise and quote for your requirements.

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