Methods for addressing the symptoms and root causes of shrinkage in precision castings

Methods for addressing the symptoms and root causes of shrinkage in precision castings

In the practice of precision casting production, it is found that a certain part of a product has shrinkage or looseness. In most cases, process designers may consider insufficient filling and the simplest way is to add a gate at that position. There are two situations: one is to solve the problem, which is called a cure for the root cause; Another situation is that the problem is not solved and may become more serious, which I call symptomatic treatment.

The root cause is to solve the problem and find the root cause of the problem; However, addressing the symptoms is not finding the correct way to solve the problem. From the perspective of casting solidification theory, in order to obtain castings with dense structure, two problems must be solved: one is shrinkage, and the other is solidification conditions, or in other words, heat dissipation. In the actual production of investment casting, it is necessary to have a profound understanding of the shrinkage and porosity problems that occur in the product. Whether it is a shrinkage problem or a heat dissipation problem, or both, only by truly controlling the pulse of the casting can practical problems be truly solved.

So how to determine whether it is a shrinkage problem or a heat dissipation problem?

There is actually a very simple principle: the thickness of the precision casting mold shell. In areas with thick mold shells, heat dissipation is definitely not good, especially in areas such as corners, narrow grooves, and inner cavities; The insufficient filling can actually be simply judged by the size and length of the gate. Of course, in actual production, it can sometimes be very complex and requires certain experience and testing methods to carry out. So, when shrinkage and porosity occur in castings, it is necessary to consider solving the problem from two aspects. 1、 Supplementing and shrinking; 2、 Heat dissipation. After adding a gate, if the heat dissipation is good, the gate can completely solve the problem, which is equivalent to treating the root cause of traditional Chinese medicine; Simply adding a gate at the corresponding position due to shrinkage is equivalent to treating the symptoms of Western medicine.

Precision machining