Precision casting parts pouring methods and precautions

　　Precision casting parts refers to the casting of dimensional accuracy, surface quality, internal quality and performance requirements are very high, usually used in aviation, aerospace, military, energy and other high-end fields. In the precision casting process, pouring methods and technology selection and mastery is the key, the following on this point to expand the discussion.
　　
　　First, the pouring method
　　
　　1, vacuum casting method: vacuum casting is cast under vacuum conditions. Vacuum casting can greatly reduce the casting surface oxidation, improve casting quality. Vacuum casting under the casting solidification speed is faster, can be effective casting porosity, cracking and other defects and micro-organizational unevenness.
　　
　　2, pressure casting method: pressure casting method refers to the casting, after a certain amount of pressure, the liquid metal is forced into the mold cavity. Pressure casting mainly includes high-pressure casting and gravity casting. Pressure casting through the pressure to implement the force, so that the liquid metal flow more smoothly, reduce gas inclusions, improve the quality of castings.
　　
　　3, low-pressure casting method: low-pressure casting method refers to the use of hydraulic pressure and the principle of inertia, the molten metal from below to join the closed expansion type sand mold, and apply a certain pressure. Low-pressure casting can eliminate the liquid metal in the liquid surface of the gas inclusions, casting surface smoothness is relatively high, molding quality is better.
　　
　　4, precision gypsum casting method: precision gypsum casting method is a new type of casting process. In this process, the main use of gypsum mixtures to manufacture casting, making the casting surface in high contrast under the special light irradiation can be clearly presented. This method can achieve different surface quality and precision by different gypsum.
　　
　　Second, casting precautions
　　
　　1、Choose suitable casting method: Different metal materials, shapes and precision requirements should be chosen as suitable casting method, and do not change the casting method arbitrarily.
　　
　　2、Casting design should be reasonable: casting should have enough cooling time. Appropriately increase the cooling time of the casting, so that the casting in the process of solidification and shrinkage effectively reduce the melt in the longitudinal shrinkage stress, so as to avoid casting defects. At the same time, the casting performance is also very important, the main attention to tensile strength and compression capacity.
　　
　　3, strict control of casting temperature: control the casting temperature and casting weight ratio is very critical, too high or too low casting temperature will lead to casting defects. According to different casting materials, choose the appropriate casting temperature.
　　
　　4、Preparation treatment for casting shape: The preparation treatment of casting is a very important part, which can effectively control the generation of defects. For example, because the longitudinal shrinkage force is larger in resin casting, it is necessary to correct the longitudinal shrinkage trend through pre-pressing.
　　
　　5, strict control of dimensional tolerances: precision casting pitch tolerance is usually required between 0.15 ~ 0.5mm. Therefore, it is necessary to strictly declare and control the dimensional tolerance in the casting process.
　　
　　Summarize
　　
　　In a word, precision casting is inseparable from each other from time to time methods and matters of attention. According to different casting materials and performance requirements, choose the appropriate casting method, and strictly comply with the casting process, so as to avoid casting defects, to achieve the purpose of ensuring the precision and quality of castings.