Solutions for Weld Lines in Precision Injection Molding
During precision injection molding, if the leading edges of two or more streams of molten material have cooled before they meet, preventing complete fusion, a linear groove is created at the junction, forming a weld line.
Generally, weld lines are easily caused in precision injection molding. The reasons for this problem in precision injection molding are summarized as follows:
I. Cause: Poor mold venting. First, check if the melt or other materials have solidified, and whether there are foreign objects at the gate to prevent blockage of the mold vents.
Solution: If carbonization points still appear after removing the blockage, add vents at the mold joint, or reposition the gate, or appropriately reduce the clamping force and increase the venting gap to accelerate the merging. In terms of process operation, measures such as lowering the material and mold temperatures, shortening the high-pressure injection time, and reducing the injection pressure can also be taken.
II. Cause: Improper use of release agents in precision injection molding.
Solutions: 1. **Solution:** In precision injection molding, only a small amount of mold release agent is typically applied evenly to areas that are difficult to peel off, such as loose threads. In principle, the amount of mold release agent should be minimized.
2. **Cause:** The temperature of the material in the precision injection mold is too low. Low-temperature molten material has poor flow distribution and convergence properties, easily forming weld marks. If fine weld lines appear on the inner and outer surfaces of the plastic part in the same location, it is usually due to weld failure caused by excessively low material temperature.
3. **Solution:** The temperature of the barrel and nozzle can be appropriately increased, or the spraying time can be extended to raise the material temperature. Simultaneously, the throughput of coolant in the mold should be controlled to appropriately increase the temperature of the three-color vertical injection mold. Typically, the strength of the weld seam in the plastic part is poor. If localized heating is applied to the corresponding part of the automotive injection mold where weld marks have appeared, and the local temperature of the welded portion of the molded part increases, the strength of the welded portion of the plastic part will usually increase.
4. **Cause:** The precision injection mold design is unreasonable.
Solution: Poor welding can occur if the walls of plastic parts are too thin or too thick, or if inserts are too large. When designing the plastic body structure, ensure that the thinnest part of the plastic component is greater than the minimum wall thickness allowed during molding. Furthermore, minimize the use of inserts, and ensure the wall thickness is as uniform as possible.
HUIWEN Professional Injection Plastic Parts,like Household appliances plastic parts, Automotive Plastic parts, agricultural tools plastic parts, medical equipment plastic parts, toys plastic parts, food bottles, boxes, buckets and so on.
