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What is investment precision casting?

What is investment precision casting?What is investment precision casting?

Lost wax casting is now called investment precision casting. It is a casting process with little or no cutting. It is an excellent process technology in the casting industry, and its application is very wide. It is not only suitable for casting of various types and alloys, but also produces castings with higher dimensional accuracy and surface quality than other casting methods, and even other casting methods are difficult to cast, complex, high temperature resistant, and not easy to process castings. Can be cast by investment casting.

Investment casting is developed on the basis of ancient wax casting. As an ancient civilization, China was one of the countries that used this technology earlier. As far back as hundreds of years BC, the ancient Chinese working people created this lost wax casting technology, which was used to cast various fine patterns and characters. Zhong Ding and utensils, such as Zunhou Yi’s tomb in spring and autumn. The base of Zenghou Yi’s tomb is a series of intertwined dragons, which are connected end to end and staggered up and down to form a multi-layer moire pattern hollowed out in the middle. These patterns are difficult to manufacture by ordinary casting techniques, but cast by the lost wax The process can use the characteristics of paraffin that is not strong and easy to engrave. You can use common tools to carve out the paraffin crafts that are the same as the Zenghouyi Tomb Zun tray you want to get, and then add a pouring system, paint, dewaxing, pouring You can get a beautiful Zunhou Yi tomb Zunhou.

The practical application of modern investment casting methods in industrial production was in the 1940s. At that time, the development of aviation jet engines required the manufacture of heat-resistant alloy parts such as blades, impellers, and nozzles with complex shapes, precise dimensions, and smooth surfaces. Because heat-resistant alloy materials are difficult to machine, the shape of the parts is complex, making it impossible or difficult to manufacture by other methods. Therefore, we need to find a new precision molding process, so we learn from the lost wax casting passed down in ancient times. Improvement, modern investment casting methods have achieved important development 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 improvement of investment casting has also created favorable conditions for the aviation industry to further improve performance.

China began to use investment casting in industrial production in the 1950s and 1960s. Since then, this advanced casting process has been greatly developed, and it has been widely used in manufacturing industries such as aviation, automobiles, machine tools, ships, internal combustion engines, gas turbines, telecommunications equipment, weapons, medical equipment, and knives. Manufacture of fine arts.

The so-called investment casting process is simply to use fusible materials (such as wax or plastic) to make a fusible model (abbreviated as investment model or model), coated with several layers of special refractory coating on it, after drying and hardening After forming an integral mold shell, use steam or hot water to melt the model from the mold shell, and then put the mold shell in the sand box, fill it with dry sand molding, and finally put the mold into the roaster. Roasting (if high-strength mold shell is used, the mold shell after demolding can be directly fired without molding), after the mold or mold shell is roasted, molten metal is poured into it to obtain a casting.

The dimensional accuracy of investment castings is high, generally up to CT4 ~ 6 (CT10 ~ 13 for sand casting and CT5 ~ 7 for die casting). Of course, due to the complicated 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 mold shell during heating and cooling, the shrinkage rate of the alloy, and the deformation of the casting during the solidification process, so although the dimensional accuracy of the ordinary investment casting is high, but its Consistency still needs to be improved (consistency of castings using medium and high temperature wax materials is much improved).

When the investment mold is pressed, 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 mold shell is made of a high-temperature special adhesive and a refractory paint made of refractory material and coated on the investment mold. The surface of the mold cavity that is in direct contact with the molten metal has a high surface finish. Therefore, the surface finish of investment castings is higher than that of general castings, generally up to Ra.1.6 ~ 3.2μm.

The biggest advantage of investment casting is that because investment casting has a high dimensional accuracy and surface finish, it can reduce mechanical processing work, but only a small amount of machining allowance is required on the higher parts of the part, even some castings only Leave the grinding and polishing allowances, and can be used without mechanical processing. It can be seen that the investment casting method can save a lot of machine tool equipment and processing time, and save a lot of 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 blade of the jet engine, its streamlined outline and cooling cavity, can hardly be formed by mechanical processing technology.

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