Precision Casting Process Is The Original?
Modern investment casting process in industrial production has been the practical application of the nineteen forties. At that time, the development of jet engines required the manufacture of heat-resistant alloy parts with complicated shapes, precise dimensions and smooth surfaces such as blades, impellers and nozzles. Because the heat-resistant alloy material is difficult to machine, the shape of the parts is so complex that it can not or can not be easily manufactured by other methods. Therefore, it is necessary to find a new precision molding process, so draw lessons from the ancient lost wax casting, Process improvement, modern precision casting methods in the ancient process based on the important development. Therefore, the development of aviation industry has promoted the application of precision casting, while the continuous improvement and improvement of precision casting has also created favorable conditions for the aviation industry to further improve its performance.
China is in the last century, the fifties and sixties began to use precision casting for industrial production. Since then this advanced precision casting process has been tremendous development, one after another in the aviation, automotive, machine tools, ships, internal combustion engines, gas turbines, telecommunications equipment, weapons, medical equipment and knives and other manufacturing industries are widely used, but also for Manufacture of arts and crafts.
The so-called precision casting process, simply put it is made of fusible material (such as wax or plastic) fusible model (referred to as melt or model), coated with several layers of special fire-resistant coating, after drying and hardening to form After a monolithic shell is formed, the model is then melted from the shell with steam or hot water, the shell is then placed in a sandbox, and the shell is filled with dry sand. The model is then placed in a roaster and calcined at high temperature (Such as the use of high-strength shell, you can not model and will be demolded after the direct roasting shell), mold or shell after firing, in which the molten metal casting castings obtained.
Investment Castings high dimensional accuracy, generally up to CT4-6 (sand casting for the CT10 ~ 13, die-casting CT5 ~ 7), of course, due to the complexity of the precision casting process, casting dimensional accuracy factors, such as mold The shrinkage of the material, the deformation of the mold, the change of the line volume of the shell during heating and cooling, the shrinkage rate of the alloy and the deformation of the casting during the solidification process, etc. Although the dimensional accuracy of the ordinary investment casting is relatively high, Consistency still needs to be improved. (Consistency of castings with medium and high temperature waxes should be much improved.)
Molding press, the cavity surface finish with high pressure, therefore, the surface finish of the investment is relatively high. In addition, the shell is made of high temperature resistant special binder and refractory coating made of refractory coating coated on the melt made of the molten metal in direct contact with the cavity surface finish. Therefore, the investment casting surface finish than the average casting precision, generally up to Ra.1.6 ~ 3.2μm.
The biggest advantage of precision casting is due to the investment casting has a high dimensional accuracy and surface finish, so it can reduce the machining work, but in the parts require higher parts to leave a little allowance, and even some of the cast only Polishing, polishing allowance, you can use without machining. Thus, the use of precision casting method can save a lot of machine tools and processing hours, substantial savings of metal raw materials.
Another advantage of precision casting method is that it can be precision casting of various alloys of complex castings, in particular, can be precision cast superalloy casting. Such as jet engine blades, its streamlined profile and the cooling cavity, using mechanical processing is almost impossible to form. With precision casting process can not only do mass production, ensure the consistency of the casting, but also to avoid residual machining after machining stress concentration.