Methods of eliminating deformation of products

- May 13, 2019-


I. Causes of deformation
The shape of the 1-1 product, especially the residual stress caused by the relationship between the forming shrinkage and the thickness of the product.
1-2 Residual stress due to molding conditions
Residual stress generated when 1-3 is demolded
1-4 Deformation due to insufficient cooling time
II. Linked knowledge
The deformation of the 2-1 product(warping, bending, small wrinkles) is the same as the cause of the crack. That is, the residual internal stress in the product. The forming setting conditions shall be set in the direction of eliminating the internal stress of the product. That is, after increasing the temperature of the cartridge and mold temperature, the pressure of the injection should not be too high under the condition of material fluidity.
In order to reduce the residual internal stress, annealing is performed, that is, at a thermal deformation temperature of less than 10 degrees, heating for more than 2 hours has the effect of eliminating the internal stress. However, this method of annealing is not commonly used due to high costs.
2-3 If the cooling water hole of the mold can not evenly cool the product, residual stress will also occur, which means that the cooling water hole can not be too shallow.
III. Solutions.
3-1 Instant: Full cooling and curing(extended cooling time timer) in the mold to increase the temperature of the cartridge and reduce the injection pressure.
3-2 Short term: to make the mold cooling homogenize.
3-3 Long-term: Avoid the difference in the thickness of the product, set the gate(1-1) where the thickness of the product is large, and the straight line is prone to warping to make a large R curve(Figure A). The reversible bending die of the product(Figure B) increases the number of top rods and increases the demoulding slope.
Fourth, differences in materials:
4-1 Crystalline materials(polyethylate, polypropyl, polyformaldehyde, nylon) have a large shrinkage rate, and they are prone to bias. Non-crystalline materials(polyphenylene, ABS) can easily cause residual stress.
References:
After 5-1 molding, it is maintained at room temperature with a correction device, which can slightly prevent deformation, but can not have too much expectation.
5-2 In thin box molding, bending caused by the forming temperature is common in thermal expansion alone. (Figure C)