Welding Line is refers to the slim line disappear in which the plastic raw material melting and collecting.

Why it happens?
1. Insufficient liquidity of melting raw materials
2. Have air or volatile component
3. Release agent or colorant
4. Defect of mold design

How to improve?
1. Change raw material to better liquidlity
2. Check and improve the air venting, decrease the injection speed
3. Use less release agent or use non-silicone release agent
4. Change sprue position and product thickness