Defects And Solutions For Injection Molding

- Jul 13, 2018-

9. Jet flow pattern

The jet pattern is a trace of a meandering curve from the gate along the flow direction. It is caused by the excessive injection speed of the resin from the gate. Therefore, expanding the cross section of the burnt or lowering the injection speed is an optional measure. In addition, by increasing the temperature of the mold, the cooling rate of the resin in contact with the surface of the cavity can be slowed down, which also has a good effect in preventing the formation of the surface-hardened skin at the initial stage of filling.

The warpage and deformation of the injection product is a very difficult problem. Mainly from the mold design, the adjustment effect of the molding conditions is very limited. The causes and solutions for warpage and deformation can be referred to the following:

(1) When deformation is caused by residual stress caused by molding conditions, stress can be relieved by lowering the injection pressure, increasing the mold and making the mold temperature uniform, increasing the resin temperature, or annealing.

(2) When the stress is deformed due to poor mold release, it can be solved by increasing the number or area of the push rod and setting the draft angle.

(3) Since the cooling method is not suitable, and the cooling is not uniform or the cooling time is insufficient, the cooling method and the cooling time can be adjusted. For example, a cooling circuit can be placed as close as possible to the deformation.

(4) For the deformation caused by the molding shrinkage, it is necessary to correct the design of the mold. Among them, the most important thing is to make the wall thickness of the product consistent. Sometimes, in the case of a last resort, the mold must be trimmed in the opposite direction by measuring the deformation of the product.

A resin with a large shrinkage ratio is generally a crystalline resin (such as polyacetal, nylon, polypropylene, polyethylene, and PET resin) than a non-crystalline resin (such as PMMA resin, polyvinyl chloride, polystyrene, ABS resin). And AS resin, etc.) have large deformation. In addition, since the glass fiber reinforced resin has fiber orientation, the deformation is also large.