In Pursuit Of The Perfect Injection Moulded Part 3 – Warping

It is very easy to make expensive errors when it comes to injection moulding. Quality issues in injection-moulded products can range from minor surface defects to more serious problems that can affect the safety, performance and function of the product. They can be caused by problems related to the moulding process, material use, tooling design or a combination of all three.

This is the third on our series of posts where we look at a number of issues that can affect the quality of the end product and some of the common remedies. This post is about Warping.


Plastic Injection Moulding - WarpingWarping is deformation that can occur in injection moulded products when different parts of a component shrink unevenly. Just as wood can warp when it dries unevenly, plastic and other materials can warp during the cooling process when uneven shrinkage puts undue stress on different areas of the moulded part. This undue stress results in bending or twisting of the finished part as it cools. This is evident in a part that’s meant to lie flat but leaves a gap when laid on a flat surface.

Causes and prevention of warping in moulded parts

One of the main causes for warping in injection-moulded plastic and similar materials is that cooling happens too quickly. Often excessive temperature or low thermal conductivity of the molten material can worsen the problem. Other times mould design can contribute to warping when the walls of the mould are not of uniform thickness—shrinkage increases with wall thickness. Here are some common ways to prevent warping in your moulded parts:

  • Ensure the cooling process is gradual and long enough to prevent uneven stresses on the material
  • Lower the temperature of the material or mould
  • Try switching to a material that shrinks less during cooling (e.g. particle-filled thermoplastics shrink much less than semi-crystalline materials or unfilled grades)

Redesign the mould with uniform wall thickness and part symmetry to ensure greater stability in the part during cooling.

Patterson & Rothwell are a Plastic Injection Moulding Company based in the North West of England, UK producing goods for many business sectors. Our ethos is to offer our customers a professional yet flexible approach and of course provide attention to detail at every stage. Please contact us if you wish to discuss any Plastic Injection Moulding Project.