Analysis and solution of the causes of warpage deformation of injection molding products

April 12, 2019

Analysis and solution of the causes of warpage deformation of injection molding products

 

The deformation, bending and twisting of the product are mainly caused by the fact that the shrinkage rate of the flow direction during the molding of the plastic is larger than that of the vertical direction, so that the shrinkage of the parts is different and the warpage is different, and the parts are inevitably in the case of injection molding. The internal internal residual stress causes warpage, which is the manifestation of deformation caused by high stress orientation. Therefore, fundamentally speaking, the mold design determines the warping tendency of the part. It is very difficult to suppress the tendency by changing the molding conditions. Finally, the problem must be solved from the mold design and improvement. This phenomenon is mainly caused by the following aspects:
 

1. Mold aspect:
(1) The thickness and quality of the parts should be uniform.
(2) The design of the cooling system is to make the temperature of each part of the mold cavity uniform. The pouring system should make the flow symmetry avoid the warpage caused by the different flow direction and shrinkage rate, and properly thicken the shunt and main flow which are difficult to form part. Road, try to eliminate the density difference, pressure difference, temperature difference in the cavity.
(3) The transition zone and corner of the workpiece should be sufficiently rounded and have good demolding properties, such as increasing the demoulding margin 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 direction of warping resistance, and strengthen the rib to enhance the anti-warping ability of the part.
(6) The strength of the material used in the mold is insufficient.

 

2. Plastics:
The crystal form has more chance of warpage deformation than the amorphous plastic, and the crystal type plastic can be used to correct the warpage deformation by using a crystallizing process in which the crystallinity decreases as the cooling rate increases and the shrinkage rate becomes smaller.

 

3. Processing:
(1) The injection pressure is too high, the holding time is too long, and the melt temperature is too low. The speed is too fast, which causes the internal stress to increase 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) Reducing the screw speed and the back pressure reduction density while maintaining the minimum charge amount to limit the generation of internal stress.
(4) If necessary, the mold can be softly shaped or demoulded after the mold is easily warped and deformed.

 

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