Investment casting process introduction

When wax is used to make the pattern, investment casting is also called "lost wax casting". Investment casting refers to making a pattern with fusible raw materials, coating the surface of the pattern with several layers of refractory materials to make a shell, and then melting the pattern to expel the shell, so as to obtain a casting without a parting surface, which can be filled with sand and poured after high-temperature roasting. Because the pattern is generally made of wax material, investment casting is often called "lost wax casting".

The alloys that can be produced by investment casting include carbon steel, alloy steel, heat-resistant alloy, stainless steel, compact alloy, permanent magnet alloy, bearing alloy, copper alloy, aluminum alloy, titanium alloy and ductile iron.

The shape of investment castings is generally complex, the minimum diameter of the hole that can be cast on the casting can reach 0.5mm, and the minimum wall thickness of the casting is 0.3mm. In production, some parts that were originally composed of several parts can be designed as a whole part by changing the structure of the parts and directly cast by investment casting, so as to save processing time and metal material consumption and make the part structure more reasonable.

The weight of investment castings is mostly a few tenths of a Newton (from a few grams to more than ten kilograms, generally not more than 25 kilograms). It is more troublesome to produce too heavy castings by investment casting.

The process of investment casting is relatively complex and difficult to control. The materials used and consumed are relatively expensive. Therefore, it is suitable for the production of small parts with complex shapes, high precision requirements, or difficult to carry out other processing, such as turbine engine blades. Introduction to investment casting

The dimensional accuracy of investment castings is relatively high, generally up to CT4-6 (sand casting is CT10~13, die casting is CT5~7). Although the process of investment casting is complicated, there are many factors that affect the dimensional accuracy of castings, such as the shrinkage of mold materials, deformation of investment molds, linear quality changes of mold shells during heating and cooling, shrinkage rate 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 needs to be improved a lot).

When pressing the investment mold, a mold with high surface brightness of the cavity is used, so the surface brightness of the investment mold is also relatively high. In addition, the mold shell of engineering vehicle parts 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 surface brightness of the cavity directly in contact with the molten metal is high. Therefore, the surface brightness of investment castings is higher than that of ordinary castings, generally up to Ra.1.6~3.2μm.

The biggest advantage of investment casting is that because investment castings have high dimensional accuracy and surface brightness, marine parts can reduce machining work, just leave a small amount of machining allowance on the parts with higher requirements, and even some castings only leave grinding and polishing allowances, and can be used without machining. It can be seen that the use of investment casting can greatly save machine tool equipment and processing time, and greatly save metal raw materials.

Another advantage of investment casting 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 jet engine blades are almost impossible to form by machining technology. The production of investment casting technology can not only achieve batch production, ensure the consistency of castings, but also avoid the stress concentration of residual knife marks after machining.