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     The application mechanism of "expansion and shrinkage complementary precision forming" was proposed. The original thermal variable speed coating process was created. The technology of high temperature resistant coating sand was invented with cheap desert silica sand as raw material to replace expensive zircon sand as investment casting material, which solved the production problem of complex thin-wall precision casting in China, More than 90% of the key castings of automobile engine in China are produced by "Renchuang coated sand" technology.