How to solve the stress mark problem from the perspective of design and process
On injection molding products, especially those made of ABS, PP, and PC, you will often see shiny stress marks on the surface of the products, including ejector stress marks, insert stress marks, and thickness difference stress marks.
These shiny and whitish marks are the result of injection internal stress, and internal stress is nothing more than orientation stress and cooling shrinkage stress. Irregular stress marks near the gate are typically caused by orientation stress, while thickness difference is the result of orientation and shrinkage stress, and ejector and oblique pin stress marks are caused by more factors.
In general, as the holding pressure and time increase during the injection molding process, the first to start are the thickness difference stress marks, ejector oblique pin stress marks, then the thickness difference stress marks, and finally the irregular stress marks near the gate (white and shiny when viewed from the side), which of course also depends on the specific structure of the product and the pouring position.
Therefore, when these stress marks appear, it is most important to reduce the holding pressure and holding time. If you understand this, it is more effective to modify the product design and injection mold design from here than to adjust the molding.
1. Product design:
The overall thickness is too thin or the thickness at the end of the flow is too thick, resulting in excessive filling pressure and holding pressure, and it is necessary to add glue or steal meat at the end of the flow. That is to say, when the holding pressure is reduced, see if the shrinkage can be improved by stealing meat. If not, glue should be added to the large surface;
Try to avoid the difference in meat thickness. If there is, it needs to be differentiated;
Avoid making the rib of the male mold too large, resulting in rib stress marks on the female mold.
2. Injection mold design:
The gate is too small or the number is too small, and the distribution is uneven;
The loose mold matching of the movable parts or the unreasonable water channel configuration leads to high mold temperature.
3. Injection molding conditions:
Reasonably set the holding pressure and time (lower);
Increase or decrease the mold temperature (increase can improve filling and reduce the holding pressure; decrease makes the texture surface shiny and the surface and stress marks close. Generally speaking, lowering the mold temperature is the most choice)
