Causes of warpage, bending and distortion of injection molded parts and solvent method

Causes of warpage, bending and distortion of injection molded parts and solvent method

1. Insufficient or uneven cooling

When the ejector is not completely cooled, the pushing force of the ejector rod often deforms the molded part, so the forced demoulding without sufficient cooling will produce deformation. The solution is to cool the die cavity sufficiently and eject it after complete hardening. It can also reduce the mold temperature and prolong the cooling time.
However, the local cooling of some molds is not enough, and deformation can not be prevented sometimes under the normal forming conditions. In this case, it should be considered to change the path of cooling water, the position of cooling water channel or add cooling tip hole, especially the way of air cooling instead of water cooling.
2. Caused by ejector pin
Some parts have poor demoulding performance, and deformation is caused by forced demoulding with ejector pin. For plastic parts which are not easy to deform, cracks are produced instead of deformation. For ABS and polystyrene parts, the deformation is shown by the whitening of the pushed part (refer to cracking, cracking, microcracking and whitening). Sometimes the mold release agent can be improved and eliminated easily.
The most fundamental improvement method is to grind the core, reduce the demoulding resistance, or increase the draft angle, and add a ejector pin at the difficult ejection position, and changing the ejection mode is more important.
3. It is caused by forming strain
The deformation caused by forming strain is mainly caused by the difference of forming shrinkage direction and the change of wall thickness. Therefore, increasing the mold temperature, increasing the melting temperature, reducing the injection pressure and improving the flow conditions of the gating system can reduce the difference of shrinkage in the direction. However, it is difficult to correct the problem only by changing the molding conditions, so it is necessary to change the location 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 channel; long sheet parts are easier to deform, and sometimes it is necessary to change the local design of the parts, and to set stiffeners on the back of the upwarped side. It is effective to use auxiliary cooling tools to correct the deformation. If it cannot be corrected, the design of the die must be corrected.
Among them, the most important thing is to make the wall thickness of the products consistent. In the case of no alternative, only by measuring the deformation of the product, in the opposite direction to correct the mold.
4. Crystalline plastics
The resin with higher shrinkage rate, generally crystalline resin (such as polyoxymethylene, nylon, polypropylene, polyethylene and PET resin, etc.) has greater deformation than non crystalline resin (such as PMMA resin, polyethylene, polystyrene, ABS resin and as resin). In addition, due to the fiber orientation of glass fiber reinforced resin, the deformation is also large.
Due to the narrow range of melting point temperature, most of them produce deformation, which is difficult to correct. The crystallinity of crystalline plastics changes with the cooling rate, that is, the crystallinity decreases rapidly and the molding shrinkage decreases, while the crystallinity increases and the molding shrinkage increases with slow cooling. This property is used to correct the deformation of crystalline plastics.
In fact, the correction method used is to make the dynamic and static mold have a certain temperature difference. The deformation can be corrected by taking the temperature that strain the other side of the warpage. Sometimes the temperature difference is as high as 20 ℃, but it must be very evenly distributed. It must be pointed out that if special measures are not taken in advance to prevent deformation, the parts will not be able to be used due to deformation, and only the molding conditions can meet the above requirements, the deformation can not be corrected in most cases.
5. Warping method of Jiaozheng products
If the products taken out from the mold are to be corrected, the simple way is to put the products to be corrected on the correction tools, and add heavy objects to the warped places, but it must be determined clearly that the weight of the heavy objects is the same as the position.
Or put the warped products on the straightener and put them into the hot water near the thermal deformation temperature of the products, and straighten them by hand. However, the temperature of hot water should not be too high, otherwise the deformation of products will be more serious. After warping correction, no mark should be left on the product.