Medical investment machine castings, is a kind of less cutting or no cutting casting technology, which is an excellent technology in the casting industry, and it is widely used. 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. Even the complicated, high temperature resistant and difficult to process castings which are difficult to be cast by other casting methods can be cast by medical investment machine castings.
Medical investment machine castings is developed on the basis of ancient wax casting. As an ancient civilization country, China is one of the earliest countries to use this technology. As far back as several hundred years BC, the ancient working people of our country created this lost wax casting technology, which was used to cast products such as bells, tripods and utensils with various fine patterns and characters, such as the zunpan in the tomb of Zeng Hou Yi in the spring and Autumn period. The base of the zunpan in the tomb of Marquis Yi of Zeng is made up of several intertwined dragons, which are connected end to end and interlaced up and down, forming a multi-layer moire pattern with hollowed out middle. It is difficult to make these patterns by ordinary casting process, but the wax loss casting process can take advantage of the characteristics of paraffin wax, which has no strength and is easy to carve, With ordinary tools, we can carve out the same paraffin crafts as the tomb zunpan of Marquis Yi of Zeng, and then add the pouring system, paint, dewaxing, pouring, we can get the exquisite tomb zunpan of Marquis Yi of Zeng.
It was in the 1940s that modern investment casting method was applied in industrial production. At that time, the development of Aerojet engine required the manufacture of heat-resistant alloy parts with complex shape, accurate size and smooth surface, such as blades, impellers and nozzles. Because heat resistant alloy materials are difficult to machine and the shape of parts is complex, it is impossible or difficult to manufacture by other methods. Therefore, it is necessary to find a new precision molding process. Therefore, drawing lessons from the lost wax casting handed down from ancient times, through the improvement of materials and technology, the modern investment casting method has obtained important development on the basis of ancient technology. Therefore, the development of aviation industry promotes the application of investment casting, and the continuous improvement and perfection of investment casting also creates favorable conditions for further improving the performance of aviation industry.
Investment casting has been used in industrial production since 1950s and 1960s in China. Since then, this advanced casting technology has been greatly developed, and has been widely used in aviation, automobile, machine tool, ship, internal combustion engine, gas turbine, telecommunication equipment, weapons, medical equipment, cutting tools and other manufacturing industries, as well as in the manufacturing of Arts and crafts.
The so-called medical investment machine castings process is to make a fusible mold (investment mold or mold for short) from fusible materials (such as wax or plastic), coat it with several layers of special refractory coating, form an integral mold shell after drying and hardening, melt the mold from the mold shell with steam or hot water, and then put the mold shell in the sand box, and fill the dry sand around it for molding, Finally, the mold is put into the baking furnace and roasted at high temperature (for example, when the high strength shell is used, the demoulded shell can be roasted directly without molding). After the mold or shell is roasted, the molten metal is poured into it to obtain the casting.
The dimensional accuracy of medical investment machine castings is high, generally up to ct4-6 (ct10-13 for sand casting and ct5-7 for die casting). Of course, due to the complex process of medical investment machine castings, there are many factors affecting the dimensional accuracy of castings, such as shrinkage of mold material, deformation of medical investment machine castings, linear variation of shell during heating and cooling, shrinkage of alloy and deformation of casting during solidification, Therefore, although the dimensional accuracy of ordinary medical investment machine castings is high, its consistency still needs to be improved (the dimensional consistency of castings with medium and high temperature wax materials needs to be improved a lot).
When pressing the investment mold, the mold with high cavity surface finish is used, so the surface finish of the investment mold is also relatively high. In addition, the shell is made of refractory coating made of high temperature resistant special binder and refractory materials, which is coated on the investment mold. The surface finish of the cavity directly contacting with the molten metal is high. Therefore, the surface finish of medical investment machine castings is higher than that of ordinary castings, generally up to RA. 1.6 ~ 3.2 μ m.
The biggest advantage of medical investment machine castings is that because investment casting has high dimensional accuracy and surface finish, it can reduce the machining work, just leave a little machining allowance in the parts with high requirements, and even some castings only leave grinding and polishing allowance, which can be used without machining. It can be seen that the medical investment machine castings method can save a lot of machine tools, processing time and metal raw materials.
Another advantage of medical investment machine castings is that it can cast complex castings of various alloys, especially superalloy castings. For example, the blade of jet engine can hardly be formed by machining. Medical investment machine castings process can not only achieve mass production, ensure the consistency of castings, but also avoid the stress concentration of residual knife marks after machining.