Investment casting, also known as lost wax casting, includes processes such as pressing wax, wax repairing, tree forming, dipping, wax melting, molten metal casting and post-processing. Lost wax casting is to use wax to make a wax mold of the part to be cast, and then coat the wax mold with mud, which is a mud mold. After the clay mold is dry, put it in hot water to melt the inner wax mold. Take out the clay mold that has melted the wax mold and then bake it into a pottery mold. Once roasted. Generally, the pouring port is left when the mud mold is made, and then the molten metal is poured from the pouring port. After cooling, the required parts are made. So, what are the advantages of investment 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 the heating and cooling process, the shrinkage rate of the alloy, and the deformation of the casting during the solidification process, etc., so the dimensional accuracy of ordinary lost wax investment castings is high, but its The accuracy still needs to be improved (the dimensional accuracy of castings using medium and high temperature waxes is much improved).
When pressing the investment mold, a mold 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 high temperature-resistant special binder and refractory paint made of refractory material, which is painted 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 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 need to be left. Grinding and 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. Using the investment casting process to produce can not achieve mass production, which ensures the integrity of the castings, and avoids the stress concentration of residual knife lines after machining.