In production, it is common for PVC cartoon ornaments to have their heads or hands and feet twisted from the neck position that connects their bodies. In addition to design and material issues, injection molding is also a significant cause. Sometimes, within the same set of molds, there are several identical injection molded parts, some of which are constantly twisted while others are easily broken. Even for injection molded parts with the same cavity, there may be situations where they are sometimes twisted continuously and sometimes easily broken. Therefore, injection molding technology and production control have become quite important.
In the production process, it is first necessary to ensure that the molten adhesive has sufficient temperature, and appropriate foot back pressure and molten adhesive time should be applied to make the molten adhesive mature and have good fluidity. Otherwise, it is an unmelted glue that is enough to make the connection easily break.
Secondly, as long as the product structure allows, try to increase the transition angle of the connection, preferably reaching R1.0mm or larger, so that when the melt passes through the corner, there will be no eddy currents caused by the skin. Meanwhile, adding transition fillets can also prevent stress concentration and increase the tensile strength of the joint.
The third is to control the injection speed, which is the most crucial point. When adjusting the machine, a lower speed must be used to ensure that the molten liquid flows smoothly from the end of the mushroom to the cavity of the head or hands and feet. The reason for skinning is that when the melt flows from the small end to the large end, the volume suddenly changes and eddy currents are generated. Therefore, reducing the injection speed can reduce the energy required to generate eddy currents. In addition, due to the good transition angle, the glue can smoothly pass through the connection without generating eddy currents, thus achieving the goal of eliminating the skin.
However, continuing to shoot at a slow speed will definitely lead to misalignment. Therefore, after the glue flows through the joint, the second stage of accelerated injection must be started immediately.
In addition, in production, there are often many identical injection parts in a set of molds. At this point, this problem is usually solved, while another problem is caused by the inconsistent injection speed of each cavity. Therefore, when producing several identical injection parts in the same set of molds, it is necessary to adjust the injection speed of each cavity to achieve balance, ensuring that the injection speed and starting point of each cavity can be consistent, thereby achieving the goal of simultaneously eliminating skin.
