The so-called investment casting process is simply to use fusible materials (such as wax or plastics) to make fusible models (for short, fusible models or models), coated with a number of layers of special refractory coatings, after drying and hardening to form a whole shell, then use steam or hot water to melt the model from the shell, and then put the shell in sand. In the box, dry sand moulding is filled around it. Finally, the castings are put into the calciner and roasted at high temperature (for example, when the high strength shell is used, the shell after demoulding can be directly roasted instead of moulding). After roasting, the castings are obtained by pouring molten metal into the castings.
The dimension accuracy of investment casting is high, generally up to CT4-6 (sand casting is CT10-13, die casting is CT5-7). Of course, due to the complex process of investment casting, there are many factors affecting the dimension accuracy of investment casting, such as shrinkage of die material, deformation of investment mould, linear change of shell during heating and cooling, shrinkage rate of alloy and so on. In the solidification process, the deformation of castings and so on, so the dimensional accuracy of ordinary investment casting is higher, but its consistency still needs to be improved (the size consistency of castings with medium and high temperature wax is much higher).
When pressing the melting die, the high surface finish of the cavity is used, so the surface finish of the melting die is also higher. In addition, the shell is made of a refractory coating made of a special high temperature binder and refractory material, which is coated on the melting die. The inner surface of the cavity directly contacted with the molten metal has a high smoothness. Therefore, the surface finish of investment castings is higher than that of ordinary castings, generally up to Ra.1.6-3.2 um.