Formation and Mitigation of Weld Lines in Injection Molding
Release time:
2025-07-03
In the cavity of molten plastic, a linear weld line is formed due to the inflow of air pockets, incoherent flow patterns, and interruptions in the flow of filling material in a multi-strand form. Additionally, a weld seam may occur when the gate jet is filled, and the strength of the weld joint is significantly reduced. The main reasons are as follows:
Aspects of processing:
- If the injection pressure and speed are too low, and the barrel and mold temperatures are too low, the melt may cool prematurely upon entering the mold, resulting in a weld seam.
- If the injection pressure and speed are too high, it can cause jetting and result in a weld seam.
3. The speed should be increased, and the back pressure should be raised to reduce the melt viscosity and increase the product density.
4. The plastic material must be thoroughly dried, and the use of recycled material should be minimized, Excessive or poor-quality release agent can also cause weld seams.
5. The clamping force should be reduced to facilitate better venting.
2. Aspects of the mold:
1. lf the gate is too large, its size should be reduced or it should be positioned as close as possible to the weld line location. For multi-cavity molds, gates should be arranged symmetrically.
2. The exhaust channels at the weld line are insufficient. The venting system should be improved to allow air to escape.
3. lf the runner is too large or the gate size is improper, the gate location should be modified to prevent the melt from flowing around the core. The use of inserts should also be minimized.4. The wall thickness is either too large or too small. The part design should be modified to ensure uniform wall thickness.
5. lf necessary, a cold slug well or a weld line relocation feature should be added to move the weld line to a less critical area.
3. Plastic material aspects:
1. Suitable lubricants or stabilizers should be added to plastics with poor flow properties or low thermal stability.
2. lf the plastic contains excessive impurities, it should be replaced with a higher-quality material.
Related news
2025-07-03
Share