Causes Of Warpage Of Injection Molded Products
The deformation, bending and twisting of injection molded products are mainly caused by 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 ratio of the parts is different and warped, and it is inevitable in the injection molding. There is a large internal stress remaining inside the piece to cause warpage, which is a 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 this 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) 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, and the pouring system should make the flow symmetry avoid the warpage caused by the different flow direction and shrinkage rate, and appropriately thicken the shunting channel and the mainstream 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 warpage 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.
The crystal type has more chance of warping deformation than the amorphous plastic, and the crystal type plastic can be used to correct the warpage deformation by using a crystallization process in which the crystallinity decreases as the cooling rate increases and the shrinkage rate becomes smaller.
(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 at the time of 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 soft-shaped or demoulded after the mold is easily warped and deformed.