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, 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 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.
The first process of investment casting production is to manufacture the investment mold. The investment mold is used to form the model of the cavity in the refractory shell. Therefore, in order to obtain castings with high dimensional accuracy and surface finish, the investment mold itself should have a high size first. Precision and surface finish. In addition, the performance of the investment mold itself should also make the subsequent processes such as forming shells as simple and easy as possible. In order to obtain the investment mold with the above-mentioned high quality requirements, in addition to having a good pressing shape (the mold for pressing the investment mold), it is also necessary to select the appropriate molding material (referred to as the mold material) and a reasonable molding process.
