Reasons and solutions for warping of four injection molded parts

1. Insufficient or uneven cooling
When ejected before complete cooling, the pushing force of the ejector pin often causes deformation of the formed part, so reluctantly demolding without sufficient cooling can cause deformation. The countermeasure is to fully cool the mold cavity and wait for complete hardening before ejecting. It can also reduce the mold temperature and extend the cooling time.
However, some molds have insufficient local cooling and sometimes cannot prevent deformation under normal forming conditions. In this situation, consideration should be given to changing the path of cooling water, the position of cooling water channels, or adding cooling tip holes, especially considering the use of air cooling instead of water cooling.
2. Caused by the top rod
Some parts have poor demolding performance, resulting in deformation due to forced demolding with a top bar. For plastic parts that are not easily deformed, cracks may occur instead of deformation.
For ABS and polystyrene parts, this deformation is manifested by the whitening of the pushed part (referring to cracking, cracking, microcracking, and whitening). The elimination method is to improve the polishing of the mold and make it easy to demould, and sometimes the use of demolding agents can also improve demolding. The most fundamental improvement method is to grind the core, reduce demolding resistance, or increase the draft angle, and add ejector rods in areas that are difficult to eject, while changing the ejection method is more important.
3. Caused by forming strain
The deformation caused by forming strain is mainly caused by the differences in direction of forming shrinkage and changes in wall thickness. Therefore, increasing the mold temperature, increasing the melt temperature, reducing injection pressure, and improving the flow conditions of the pouring system can all reduce the difference in shrinkage rate in direction.
However, it is often difficult to correct by simply changing the forming conditions. In this case, it is necessary to change the position and number of gates, such as injecting from one end when forming long rods. Sometimes it is necessary to change the configuration of the cooling water channel; Longer thin pieces are more prone to deformation, and sometimes it is necessary to change the local design of the parts by setting reinforcing ribs on the back of the upturned side. Using auxiliary tools for cooling to correct this deformation is mostly effective.
When correction is not possible, it is necessary to modify the design of the mold. The most important thing is to ensure that the wall thickness of the product is consistent. In the last resort, the mold had to be corrected in the opposite direction by measuring the deformation of the product.
4. Crystalline plastic
Resins with higher shrinkage are generally crystalline resins (such as polyoxymethylene, nylon, polypropylene, polyethylene, and PET resins) that exhibit greater deformation than non crystalline resins (such as PMMA resin, polyethylene, polystyrene, ABS resin, and AS resin). Additionally, due to the fiber orientation of glass fiber reinforced resins, deformation is also significant. Due to the narrow temperature range of the melting point, most deformation occurs and is often difficult to correct.
The crystallinity of crystalline plastics varies with different cooling rates, namely, sharp cooling reduces crystallinity and reduces molding shrinkage, while slow cooling increases crystallinity and molding shrinkage. The special correction method for deformation of crystalline plastics is to utilize this property. The actual correction method used is to create a certain temperature difference between the dynamic and static models. By adopting a temperature that causes strain on the other side of the warp, deformation can be corrected.
Sometimes the temperature difference can reach over 20 ℃, but it must be evenly distributed. It must be pointed out that when designing crystalline plastic molded parts and molds, if special measures are not taken to prevent deformation in advance, the parts will become unusable due to deformation, and only if the molding conditions meet the above requirements, deformation cannot be corrected in most cases.
Method for warping of Jiaozheng products:
If the product taken out of the mold needs to be corrected, the simple method is to place the product to be corrected on the correction tool and add a heavy object to the warped area, but the weight of the heavy object must be clearly determined and the position it is placed in. Alternatively, place the warped product on a straightener and place it in hot water near the product's deformation temperature, simply straightening it by hand.
But it should be noted that the temperature of hot water should not be too high, otherwise it will cause more severe deformation of the product. After warping correction, no spots should be left on the product.