Large flat plastic parts have a large area, and the shrinkage is also large. Due to the severe molecular orientation of large plastic parts, and the uneven cooling of the mold, the shrinkage of the plastic parts in different directions appears inconsistent, which leads to the phenomenon of deformation and distortion easily after injection molding of thin and large flat plastic parts. Sometimes a large plane injection molded part is designed with supporting ribs on one side, at this time the injection part must also be bent toward the side with supporting rib.
It is indeed a difficult problem to completely solve the deformation problem of large flat plastic parts. Some more effective measures are summarized in production to improve the deformation problem.
1, Change the mold to a multi-point gate (usually all three-plate molds). It is best to reach 4 or more for large flat plastic parts with a clamping force of 24t or more. This can reduce the degree of molecular orientation and reduce the inconsistency of the contraction in each direction.
2, Properly increase the mold temperature. ABS plastic is usually kept above 60 ℃ to reduce the cooling rate of plastic parts and reduce the deformation caused by excessively fast cooling. At the same time, it can reduce the degree of molecular orientation.
3, The most important one is to increase the injection or holding pressure, and greatly extend the injection time or holding pressure time, so that the size of the injection molded part is increased, and the amount of shrinkage is reduced, so the degree of deformation will be obvious improve. Therefore, prolonging the time of injection or holding pressure (such as prolonging 10 to 15s) has become an important method commonly used to solve the deformation problem.
4, If the above three measures fail to achieve the desired effect, only the method of demoulding and stereotypes is adopted. Because this process is more difficult to use, it is necessary to pay attention to the following tips.
First of all, the plastic parts should be demolded early, and then while the plastic parts are still at a high temperature, they are placed on the workbench for fixture shaping. Note that the design of the shaping fixture needs to be appropriate. At the same time, the degree of springback of the plastic parts must also be considered. Usually, the rebound will basically stop after 12h, and the lower the demolding temperature, the greater the springback.
The last thing to emphasize is that you must pay attention to the packaging and placement of injection molded parts. This is indeed very important, otherwise all the above efforts will be abandoned. Under normal circumstances, the injection molded parts can be packed on the side, of course, the form of placement should be determined according to the shape of the injection molded parts. Never allow plastic parts to squeeze each other, or allow a part of an injection molded part to float, otherwise the injection molded part will deform after a few days.
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