In Pursuit Of The Perfect Injection Moulded Part 11 – Flash


Flash is an excess of moulding material that appears as a thin lip or protrusion at the edge of a component. Flash appears because material has flowed outside of the intended flow channels and into the space between the tooling plates or at the injector. pin.

Flash is usually subtle but might be considered a major defect if particularly obvious on a product. The process for reworking a moulded product with flash often includes trimming the excess material.

Common causes of flash and prevention in moulded products

In Pursuit Of The Perfect Injection Moulded Part - Flash

A poorly-designed or worn and degraded mould tool is the most common contributor to flash. Excessively high mould temperature or injection pressure can also cause flash. Material flowing through the mould cavities can force its way between plates when plate clamping force is inadequate. Common methods for addressing flash in moulded products include:


  • Retool or redesign the mould if plates don’t fit together properly or allow material to flow outside the channel
  • Increase plate clamping force to confine material flow to the channel
  • Adjust mould temperature, injection pressure and ventilation to improve material flow


It’s easy to follow a path that makes an injection mould tool cheaper to manufacture. But once you have a defect built into the tool created by cost cutting it becomes very expensive to fix the problem afterwards. It’s so much cheaper to make it right first time around and in our experience it’s better to bite the bullet. By all means if the part can live with a design change that makes tooling cheaper to do then that’s fine. But if it means your part can suffer from any points we have covered in our series it needs serious consideration. A £70,000 tool (that makes 1 million parts a year) that with a tweak here and a tweak there could become £50,000 is tempting. The downside is we have slowed it down by 10 seconds per cycle. This alone adds £20,000 to our part costs per year. Well your short term saving doesn’t look so good in year 2.

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.