Investment casting is a revival of an ancient craft
Lost wax method casting is now called investment casting, is a little cutting or no cutting casting process, is an excellent technology in the casting industry, its application is very wide. It is not only suitable for casting of various types and alloys, but also can produce castings with higher dimensional accuracy and surface quality than other casting methods.
Investment casting was developed on the basis of ancient wax casting. As an ancient civilization, China is one of the early countries to use this technology. As far back as hundreds of BC, the ancient Chinese laboring people created this lost wax casting technology, which was used to cast zhong ding and other articles with various fine patterns and characters, such as the tomb of zeng hou yi in the spring and autumn period. Tomb statue of plate base for multiple mutually intertwined dragons, they end to end, staggered up and down, form the middle hollow out layers of moire pattern, these designs using ordinary casting process are hard to make out, and with the method of lost wax casting process, can make use of the characteristics of paraffin wax no strength, easy to carve, carved with ordinary tools can and to be the tomb of paraffin wax material arts and crafts of the plates, then additional gating system, coating, dewaxing, pouring, can be beautiful tomb statue of plate.
The practical application of modern investment casting method in industrial production was in the 1940s. The development of aero-jet engines at that time required the manufacture of heat-resistant alloy parts with complex shapes, sizes and smooth surfaces, such as blades, impellers and nozzles. Due to heat resistant alloy materials difficult to machining, complex shape parts, so that can't or difficult to use other methods, therefore, need to find a new molding process, then draw lessons from the ancient tradition of lost wax casting, after improvement of materials and technology, modern investment casting method on the basis of ancient technology for the development of the important. Therefore, the development of 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 the performance.
China began to use investment casting in industrial production in the 1950s and 1960s. Since then, the great development of this advanced casting technology has been widely used in the manufacturing industry of aviation, automobile, machine tools, ships, internal combustion engines, gas turbines, telecommunications instruments, weapons, medical instruments and knives, as well as in the manufacturing of arts and crafts.
So-called investment casting process, simply be with fusible materials (such as wax material or plastic) into the meltability model (referred to as "investment pattern or model), on which the coated with several layers of tailor-made refractory coating, after drying and hardening type to form a whole shell, reoccupy steam or hot water from the melt in the shell model, and then put type shells in the sand, dry sand by filling in all round its modelling, the high-temperature roasting cast into the furnace (such as high strength shell, can need not modelling and will release the shell directly after roasting), cast type or shell after roasting, in casting pouring molten metal.
Size precision investment castings, general of CT4-6 (sand casting is CT10 ~ 13, die-casting is CT5 ~ 7), of course, due to the complexity of investment casting process, factors influencing the dimension accuracy of castings is more, such as mold material shrinkage and deformation of casting, shell in the process of heating and cooling line quantity change, alloy of shrinkage and deformation of castings in the solidification process, so the average size although higher precision investment castings, but still need to improve the consistency (in medium and high temperature of the wax casting size consistency to improve a lot).
When pressing the mold, the cavity surface finish is high pressure, therefore, the surface finish of the mold is also relatively high. In addition, the shell by high temperature resistance of the special binder and refractory materials made of refractory coating coated and hung on the investment model, and direct contact with the molten metal cavity inside the surface finish is high. Therefore, the surface finish of investment castings is higher than that of ordinary castings, generally up to Ra.1.6~3.2 m.
The advantage of investment casting is due to the investment casting has a high dimensional accuracy and surface finish, so can reduce the machining work, only in the parts of the higher requirements to leave a little processing allowance, or even some castings only left polishing, polishing allowance, can be used without mechanical processing. It can be seen that the investment casting method can save a lot of machine tools and processing time, greatly saving 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 jet engine, its streamline profile and cooling with the cavity, with the mechanical processing process almost impossible to form. The production by investment casting process can not only achieve batch production and ensure the consistency of casting, but also avoid the stress concentration of the residual blade after machining.