Investment casting has the following advantages: the investment casting has high dimensional accuracy and surface finish, and the size accuracy is generally CT4-6 (is CT10-13, die casting is CT5-7). The design is flexible, which provides sufficient freedom for the structural design of castings, and can produce highly complex castings through foam plastic block combination. At low temperature, the mold material is harmless to the environment, and the recovery rate of used sand is more than 95%. At the same time, investment casting has the following disadvantages: high cost of raw materials, high cost of castings; complex process, long process, long production cycle (4-15 days); generally, the performance of castings is not high.
In order to occupy a part of the aviation aluminum casting market, the American Howmet aluminum casting company began to develop a series of rapid solidification investment casting technologies to manufacture high-strength thin-wall aluminum alloy castings in the 1980s, and has achieved success. It has developed a rapid solidification technology applicable to thin and thick wall castings, which is called Sophia process . The basis of Sophia process is to control the cooling parameters effectively and repeatedly. The molten metal can solidify at a much higher cooling rate than the traditional investment. It can also ensure that the casting is well filled, the grain is refined, the structure is dense, and has excellent static and dynamic properties. Compared with the common investment casting process, the relationship between the wall thickness and the dendrite spacing of the castings in Sophia process.
The alloys commonly used in investment casting are A357, A356, c355 and A201. The mechanical properties of the castings produced by Howmet aluminum casting company in the United States can be achieved. The castings for Boeing aircraft doors and aircraft boxes are produced by Sophia process.
Generally speaking, great progress has been made in the research and production of complex, thin-walled and precision aluminum alloy castings in China, especially the foundry technology of sand mold aluminum alloy castings has reached the world’s synchronous level, but the gap with the world’s highest level in the development of metal mold, gypsum mold, investment casting and other technologies and equipment is also narrowing.