The weld line is due to the fact that the forepart of the melt resin（raw material for plastic injection molding） from different directions is cooled and the bond is not fully fused. Generally speaking, it mainly affects the appearance, painting and electroplating. In severe cases, the strength of the product is affected (especially when the fiber reinforced resin is used). The following improvements can be made：
1.Adjust forming conditions to improve fluidity. For example, increase resin temperature, mould temperature, injection pressure and speed, etc.
2.Adding an exhaust groove and setting a push rod at the place where the weld mark occurs are also conducive to exhaust.
3.Minimize the use of release agent.
4.Set up the process spills and act as the place where the weld marks occur. After forming, cut them off and remove them.