Due to the complex investment casting process of stainless steel precision castings, there are many factors that affect the dimensional accuracy of the castings, such as the shrinkage of the mold material, the deformation of the investment mold, the linear change of the shell during the heating and cooling process, the shrinkage rate of the alloy, and In the solidification process, the deformation of the castings, etc., so the dimensional accuracy of ordinary investment castings is relatively high, but its consistency still needs to be improved (the dimensional consistency of castings using medium and high temperature waxes should be improved a lot).
When pressing the investment mold, a pressure type with a high surface finish of the cavity is used, so the surface finish of the investment mold is also relatively high. In addition, the shell is made of a refractory coating made of a high-temperature-resistant special adhesive and refractory material, which is coated on the investment mold, and the inner surface of the cavity that is in direct contact with the molten metal has a high smoothness. Therefore, the surface finish of investment castings is higher than that of general castings, generally reaching Ra.1.6~3.2μm.
The biggest advantage of investment casting is that because investment castings have high dimensional accuracy and surface finish, machining work can be reduced. It is enough to leave a little machining allowance on the parts with higher requirements, and even some castings only Leave a grinding and polishing allowance, and it can be used without mechanical processing. It can be seen that the use of investment casting method can save a lot of machine tool equipment and processing man-hours, and greatly save metal raw materials.
Another advantage of the investment casting method is that it can cast complex castings of various alloys, especially high-temperature alloy castings. For example, the blade of a jet engine, its streamlined profile and cooling cavity, can hardly be formed by machining technology. Production with investment casting process can not only achieve mass production, ensure the consistency of castings, but also avoid the stress concentration of residual knife marks after machining.