How to solve shrinkage problem of plastic injection molding

Introduction

With the continuous improvement of Automobile injection molding technology, it is imperative to minimize the shrinkage problem of plastic injection molding and improve product quality.

Solution

The shrinkage formed in the thicker parts of plastic injection molding parts, such as ribs or protrusions, is more serious than that in adjacent positions. This is because the cooling rate of the thicker areas is much slower than that of the surrounding areas. The different cooling rates lead to depressions at the connection surface, which are familiar shrinkage marks. This defect seriously limits the design and molding of plastic products, especially large thick-walled products such as the beveled casing of TV sets and the casing of monitors. In fact, shrinkage marks must be removed on products with strict requirements such as daily electrical appliances, while plastic shrinkage marks are allowed for some products with low surface quality requirements such as plastic toys.

Causes of shrinkage marks in plastic injection molding

Shrinkage marks in plastic injection molding may be caused by one or more reasons, including processing methods, part geometry, material selection, and plastic mold design. Geometry and material selection are usually determined by the raw material supplier and are not easy to change. However, there are many factors on the mold design side that may affect the shrinkage process of Automobile injection molding. Cooling runner design Gate type and gate size may have a variety of effects. For example, a small gate such as a tube gate cools much faster than a conical gate. Premature cooling at the gate will reduce the filling time in the cavity, thereby increasing the chance of shrinkage marks. For molders, adjusting processing conditions is a way to solve the problem of shrinkage in plastic processing. Filling pressure and time significantly affect shrinkage. After the part is filled, excess material continues to fill the cavity to compensate for the shrinkage of the material. Filling the phase too short will lead to increased shrinkage, and ultimately more or larger shrinkage marks will be produced.

Conclusion

This method of solving shrinkage in plastic injection molding may not reduce shrinkage marks to a satisfactory level by itself, but molders can adjust filling conditions to improve shrinkage marks. 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 applicable to all resins. In addition, the gas-assisted method can also solve the shrinkage problem of plastic injection molding.