In Pursuit Of The Perfect Injection Moulded Part 6 – Weld Lines

Weld Lines

Weld lines can appear on the surface of a moulded part where the molten material has converged after splitting off into two or more directions in a mould. The hair-like weld line is the result of weak material bonding, which lowers the strength of the part.

Common causes of weld lines and how to prevent them

In Pursuit Of The Perfect Injection Moulded Part - Weld Lines

Two or more fronts of polymer or other molten material need to maintain a certain temperature when colliding.  Otherwise, they become partially solidified and won’t sufficiently bond where they meet, resulting in weld lines. Common remedies for weld lines in moulded parts include:

  • Increase material temperature to prevent partial solidification
  • Raise injection speed and pressure to limit cooling before the material has filled the mould
  • Redesign the mould to eliminate partitions
  • Switch to a material with a lower melting temperature or viscosity to allow faster flow and prevent early 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.