The weld lines in Plastic Injection Molding refer to the surface defect caused by the two streams being welded together.

Causes: If there are holes, inserts, or multi-gate injection molding methods in the fabricated parts or the wall thickness of the parts is uneven, weld lines may be generated.
Remedies:
Material: Increase the fluidity of plastic melt
Mold Design:
(1) Change the position of the gate
(2) Add a venting slot
Process:
(1) Increase the melt temperature
(2) Reduce the amount of release agent