How to solve the shrinkage problem of injection molding

How to solve the shrinkage problem of plastic injection molding?

With the continuous improvement of plastic injection molding, it is imperative to improve product quality in order to minimize the shrinkage of plastic injection molding.

In the thicker parts of the plastic injection molded part, the shrinkage formed at the ribs or protrusions is more severe than that of the adjacent parts, because the cooling rate of the thicker area is much slower than that of the surrounding area. The difference in cooling rate results in the formation of depressions at the connecting surface, which are known as shrinkage marks. This defect severely restricts the design and molding of plastic products, especially large thick-walled products such as beveled cabinets and display housings for televisions. In fact, shrink marks must be eliminated on products with strict requirements such as household appliances, while plastic toys and other products with low surface quality requirements are allowed to have plastic processing shrink marks.

There may be one or more reasons for plastic injection molding shrinkage marks, including processing methods, part geometry, material selection, and plastic mold design. The geometry and material selection are usually determined by the raw material supplier and are not easy to change. However, there are many factors related to mold design in mold manufacturers that may affect the shrinkage of plastic injection molding. The cooling runner design gate type and gate size may have multiple effects. For example, small gates such as tube gates cool much faster than tapered gates. Premature cooling at the gate will reduce the filling time in the cavity, thereby increasing the chance of shrinkage marks. For molding workers, adjusting processing conditions is a way to solve the shrinkage problem of plastic processing. Filling pressure and time significantly affect shrinkage. After the part is filled, the excess material continues to be filled into the cavity to compensate for the shrinkage of the material. Too short a filling stage will result in increased shrinkage, which will eventually produce more or larger shrinkage marks.

This method of solving the shrinkage of plastic injection molding may not reduce the shrinkage mark to a satisfactory level, but the molding worker can adjust the filling conditions to improve the shrinkage mark. Another method is to modify the mold. A simple solution is to modify the conventional core hole, but this method cannot be expected to be suitable for all resins. In addition, the gas-assisted method can also solve the shrinkage problem of plastic injection molding.