The dimensional accuracy of investment castings is relatively 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 that affect the dimensional accuracy of castings, such as the shrinkage of mold materials, deformation of investment molds, changes in the amount of wire in the shell during heating and cooling, shrinkage of alloys, and deformation of castings during solidification. Therefore, although the dimensional accuracy of ordinary investment castings is relatively high, its consistency still needs to be improved (the dimensional consistency of castings using medium and high temperature wax materials should be much improved).
When pressing the investment mold, a die with 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 special high-temperature resistant binder and refractory materials, 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 finish. Therefore, the surface finish of investment castings is higher than that of general castings, generally up to Ra.1.6~3.2μm.
The biggest advantage of investment casting is that since investment castings have high dimensional accuracy and surface finish, mechanical processing can be reduced. Only a small amount of machining allowance is required for parts with higher requirements on the parts. Some castings can even be used without mechanical processing with only grinding and polishing allowances. It can be seen that the use of investment casting can save a lot of machine tools and processing time, 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 streamlined outer contour and cooling inner cavity of the blade of a jet engine are almost impossible to form with mechanical processing technology. The production of investment casting technology can not only achieve mass production and ensure the consistency of castings, but also avoid the stress concentration of residual knife marks after mechanical processing.
