The development history of stainless steel precision casting

The practical application of modern investment casting methods in industrial production was in the 1940s. The development of aviation jet engines at that time required the manufacture of heat-resistant alloy parts with complex shapes, precise dimensions and smooth surfaces, such as blades, impellers, and nozzles. Since the heat-resistant alloy materials are difficult to machine and the shapes of the parts are so complex that they cannot or are difficult to manufacture by other methods, it is necessary to find a new precise molding process, so the lost wax casting handed down from ancient times is used for reference. With the improvement of modern investment casting methods, important development has been achieved on the basis of ancient craftsmanship. Therefore, the development of the aviation industry has promoted the application of investment casting, and the continuous improvement and perfection of investment casting has also created favorable conditions for the aviation industry to further improve its performance. my country began to apply investment casting to industrial production in the 1950s and 1960s. Since then, this casting process has been developed, and has been widely used in aviation, automobiles, machine tools, ships, internal combustion engines, gas turbines, telecommunication instruments, weapons, medical equipment and knives and other manufacturing industries. It is also used for arts and crafts. manufacture. The so-called investment casting process, simply put, is to use fusible materials (such as wax or plastic) to make a fusible model (referred to as investment mold or model), and coat it with several layers of special refractory coatings, which are dried and hardened. After forming an integral mold shell, the mold is melted from the mold shell with steam or hot water, and then the mold shell is placed in a sand box, filled with dry sand molding around it, and finally the mold is placed in a roasting furnace for high temperature. Roasting (for example, when a high-strength mold is used, the mold shell after demolding can be directly fired without molding), after the mold or mold is fired, molten metal is poured into it to obtain a casting. The dimensional accuracy of investment castings is relatively high, generally reaching CT4-6 (CT10~13 for sand casting and CT5~7 for die casting). Of course, due to the complex process of investment casting, there are many factors that affect the dimensional accuracy of castings, such as mold The shrinkage of the material, the deformation of the investment mold, the linear change of the shell during heating and cooling, the shrinkage rate of the alloy, and the deformation of the casting during the solidification process, etc., so the dimensional accuracy of ordinary investment castings is high, but its Consistency still needs to be improved (castings with medium and high temperature waxes are much more dimensionally consistent). When pressing the investment mold, the mold 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 high temperature-resistant special binder and refractory paint prepared from refractory materials, which is coated and hung 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 due to the high dimensional accuracy and surface finish of investment castings, machining work can be reduced, but only a small amount of machining allowance can be left on the parts with higher requirements, and even some castings only Leave grinding, polishing allowance, can be used without machining. It can be seen that the use of investment casting method can save a lot of machine tool equipment 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 superalloy castings. For example, the blade of a jet engine has a streamlined outline and an inner cavity for cooling, which can hardly be formed by machining. The investment casting process can not only achieve mass production and ensure the consistency of castings, but also avoid the stress concentration of residual knife lines after machining.