Glossary
Flash — definition
A thin film of metal squeezed out along the parting line when the die does not close perfectly tight.
Flash forms where the two die halves meet, around slide cores and at ejector pins. A little flash is normal; a lot of flash is a symptom.
The most common causes are clamping force too low for the projected area of the part, wear in the parting line, or excessive injection pressure.
Flash has to be removed during fettling, and that is manual work costing money per part. As the tool wears, flash increases — and with it the post-processing across the life of the series. It is one of the costs most often underestimated in the costing.