The occurrence of deformation, bending and twisting of injection molded products is mainly due to the fact that the shrinkage rate of the flow direction during plastic molding is larger than that of the vertical direction, so that the shrinkage rates of the parts are different and warped, and it is inevitable due to injection filling. There is a large internal stress remaining inside the part to cause warpage, which is a manifestation of deformation caused by high stress orientation.

The mold design determines the warpage tendency of the part. It is very difficult to suppress this tendency by changing the molding conditions. The problem must be solved from the injection molding part structure and mold design and improvement.

A. Mold aspect

1. The thickness and quality of the parts should be uniform.

2. The design of the cooling system should make the temperature of each part of the mold cavity uniform; the pouring system should make the flow symmetry to avoid warping caused by different flow direction and shrinkage rate, and appropriately thicken the shunt and main flow of the hard part. Road, try to eliminate the density difference, pressure difference, temperature difference in the cavity.

3. The transition zone and corner of the part should be round enough to have good release property, such as increasing the draft angle and improving the polishing of the die face. The ejector system should be balanced.

4. The exhaust should be good.

5. Increase the wall thickness of the part or increase the anti-warpage direction, and strengthen the rib to enhance the anti-warping ability of the part.

6. The strength of the material used in the mold is sufficient.

2. Plastics

The crystal type has a greater chance of warping deformation than the amorphous plastic, and the crystal type plastic can correct the warpage deformation by utilizing a crystallization process in which the crystallinity decreases as the cooling rate increases and the shrinkage rate becomes smaller.

Processing aspects

1. The injection pressure is too high, the holding time is too long, the melt temperature is too low, and the speed is too fast, which will cause an increase in internal stress and warpage.

2. The mold temperature is too high, and the cooling time is too short, so that the parts during demolding are overheated and the ejection deformation occurs.

3. Reduce the screw speed and back pressure and reduce the density to reduce the generation of internal stress while maintaining a low amount of charge.

4. If necessary, the mold can be soft-shaped for the parts that are easy to warp and deform, or annealed after demolding.