A weakness or visible flaw created when two or more flow paths meet and converge while filling a plastic part.
Meld lines can be caused by holes or inserts in the part, multiple injection gates, or variable wall thickness where hesitation or race tracking can occur.
A meld line is typically formed by parallel flows. Weld lines are formed by flows meeting at higher angles, often head on.
Meld lines tend to be less weak than weld lines. The quality of the meld line is dependent on the material type, the type and amount of fillers, and the pressure and temperature at the meld line.