In Vietnamese injection molding factories, the application of new technologies is common in the molding process. One of the key issues is the formation of weld lines in plastic products. Weld lines occur when molten resin from different directions does not fully merge during the injection process. Since the resin flows do not mix at the weld points, the lower the temperature, the more visible the weld lines become, and the strength is reduced accordingly.
Conversely, higher temperatures result in stronger adhesion. In addition, the adhesion at the weld points depends on the pressure applied; lower holding pressure leads to weaker fusion and reduced strength. The weld point is not only where resin flows meet but can also be the end of the flow. If there is no proper venting at the weld line location, trapped gases can cause defects in both appearance and strength.
Improvement Measures:
- Increase resin temperature, mold temperature, as well as injection pressure and speed.
- Pay attention to venting on the parting surface, and add inserts or ejector pins at the weld line location to aid in venting.
- Select a reasonable gate location, and ideally, conduct a mold flow analysis before mold design.
- Add extra overflow channels for removing cold material, which can be cut off after molding.
- Widen and shorten the runner system as much as possible to improve resin flow.
- For matte surface products, choosing a rougher texture can help improve the appearance of weld lines.
DAYIN Plastic Products Co., Ltd. is a high-tech enterprise specializing in product research, design, manufacturing, and sales services, providing one-stop solutions. Founded in 1989, the company excels in mold making, injection molding, post-processing, and electronic assembly. In addition to contract manufacturing, we also develop proprietary products that support direct private label production for clients. The company has a 50,000-square-meter production facility, 30 years of mold development experience, over 50 R&D personnel, and more than 100 injection molding machines, all dedicated to delivering high-quality manufacturing services to our customers.