Stainless steel casting is not only suitable for casting of various types and alloys, but also has higher dimensional accuracy and surface quality of castings than other casting methods. Even complex, high-temperature resistant and difficult-to-process castings that are difficult to cast by other casting methods can be cast by investment casting.
The so-called investment casting process is simply to use fusible materials (such as wax or plastic) to make a fusible model (referred to as “investment model or mold”), apply several layers of special refractory coating on it, and wait for the blank to dry and harden to form an integral shell. Then use steam or hot water to melt the melt in the shell, and then put the mold sand into the shell, and the dry sand fills the surrounding of the mold. Finally, put the mold into the roasting furnace for high-temperature roasting (if a high-strength shell is used, the shell after demolding can be directly roasted without molding). After roasting, pour the molten metal into the mold or shell to obtain the casting.
The dimensional accuracy of investment casting is relatively high, generally up to CT4-6 (sand casting can reach CT10-13, and die casting can reach CT5-7). Of course, due to the complexity of the investment casting process, there are many factors that affect the dimensional accuracy of castings. Such as shrinkage and deformation of investment casting materials, linear changes in the shell during heating and cooling, and alloy shrinkage and deformation during solidification of castings. Therefore, although ordinary-sized investment castings have high precision, they still need to improve consistency (the dimensional consistency of wax castings at medium and high temperatures should be much higher).
When die-casting investment castings, a die with a high surface finish of the cavity is used, so the surface finish of the investment casting is also required to be high. In addition, the shell is coated with a refractory coating composed of a high-temperature resistant special binder and a refractory material on the investment casting, and the surface finish of the cavity in direct contact with the molten metal is high. Therefore, the surface finish of the investment casting is higher than that of ordinary castings, generally up to Ra.1.6~3.2μm.
The biggest advantage of investment casting is that due to the high dimensional accuracy and high surface finish of investment casting, the workload of mechanical processing can be reduced, and only a small amount of machining allowance is required for high-requirement parts. Some castings are even left only for grinding and polishing, and can be used without mechanical processing. It can be seen that the use of investment casting can greatly save machine tools and processing time, as well as 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 contours and cooling cavities of jet engine blades are difficult to form using machining technology. The use of investment casting technology can not only achieve mass production and ensure the consistency of castings, but also avoid the stress concentration of residual cutting lines after machining.
