The deformation, bending, and twisting of injection moulding products are mainly caused by the shrinkage rate in the flow direction of the plastic moulding being greater than that in the vertical direction, which causes the shrinkage rate of the parts to warp in different directions. In addition, due to the large internal stress that inevitably remains inside the parts during injection moulding, warping is caused. These are all manifestations of deformation caused by high-stress orientation. Therefore, fundamentally speaking, mould design determines the warping tendency of the parts. It is challenging to suppress this tendency by changing the moulding conditions. The ultimate solution to the problem must start with mould design and improvement. The following aspects mainly cause this phenomenon:
1. 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 material flow symmetrical to avoid warping due to the flow direction, shrinkage rate is different, appropriate thickening of the difficult to mold part of the manifold, the main stream channel, as far as possible to eliminate the difference in density within the cavity, the difference in pressure, the difference in temperature.
(3) The transition area and corners of the thickness of the parts should be rounded enough to have good mold release, such as increasing the mold release margin, improving the polishing of the mold surface, and the ejector system should be balanced.
(4) Exhaust should be good.
(5) Increase the wall thickness of the part or increase the direction of warpage resistance, by reinforcing bars to enhance the warpage resistance of the part.
(6) Insufficient strength of the material used in the mold.
2. Plastics:
Crystalline than non-crystalline plastics appear warping deformation opportunities, coupled with crystalline plastics can be used to correct warping deformation of the crystallization process as the crystallinity with the cooling rate increases and decreases, shrinkage becomes smaller.
3. Processing:
(1) injection pressure is too high, the holding time is too long, the melt temperature is too low too fast will cause an increase in internal stress and warpage deformation.
(2) The mold temperature is too high, and the cooling time is too short, so that when the mold is removed from the part overheating and ejection deformation.
(3) Reduce the screw speed and back pressure to reduce the density to limit the generation of internal stress while keeping the low limit of charging volume.
(4) If necessary, the parts that are prone to warping and deformation can be softly shaped in the mold or demolded after demolding.
Our company----Hongke Mould has specialised in plastic mould and injection moulding for over 15 years, and mainly engaged in
Medical Plastic Mould,
Aero Injection Mould, Auto Plastic Mould, etc. Feel free to reach out for a free quotation.
