In precision injection molding, when two or more strands of melt fill the cavity, if the front part of the two or more strands of melt have cooled down when they meet, so that they can not fully fuse, a linear groove is created at the confluence, forming a weld line.

In general, precision injection mold machining is easy to cause weld marks. The reasons for this problem are summarized as follows:

First, the reason is: the mold exhaust is bad. First, check whether the melt or other objects are solidified, and whether there are foreign bodies at the gate to prevent blockage of the mold vents.

Solution: If the carbonization point is still present after removal of the plug, a vent should be added at the mold joint, or by relocating the gate, or by properly reducing the clamping force and increasing the exhaust clearance to achieve a re-closed accelerated confluence. In the process operation, we can also take measures to reduce the material temperature and mold temperature, shorten the high-pressure injection time, reduce the injection pressure and so on.

Two, reason: precision injection mold processing release agent improper use.

Solution: In precision injection mold processing and molding, usually only a small amount of demoulding agent is uniformly coated in the parts that are not easy to peel off, such as thread, in principle, the amount of demoulding agent should be reduced as much as possible.

3. Reasons: The temperature of the materials processed by the precision injection mold is too low, and the diversion convergence performance of the low-temperature molten materials is poor, so it is easy to form welding marks. If the inner and outer surfaces of the plastic parts produce fine lines in the same place, the welding usually fails because the material temperature is too low.

Solution: Increase the temperature of barrel and nozzle properly, or prolong the injection time to increase the temperature of material. At the same time, the throughput of coolant in the mold should be controlled to properly increase the temperature of the three-color vertical injection mold. Usually, the strength of the plastic parts at the weld is poor. If local heating is carried out on the corresponding parts of the automobile injection mold which produces weld marks and the local temperature of the welded parts of the molded parts increases, the strength of the welded parts of the plastic parts usually increases.

Four, reason: the precision injection mold design is unreasonable.

Solution: If the wall thickness of plastic parts is too thin or too thick, and the plug-in is too large, it will lead to poor welding. In designing the main structure of the plastics, it should be ensured that the thinnest part of the plastic parts must be greater than the minimum wall thickness allowed during molding. In addition, the use of inserts should be minimized and the wall thickness should be as uniform as possible.