What affects the machining accuracy of castings？

1.The influence of the structure of precision castings：a. The casting wall is thick and the shrinkage rate is large; the casting wall is thin and the shrinkage rate is small. b. The free shrinkage rate is large, and the hindered shrinkage rate is small.
2.The influence of precision casting material: a. The higher the carbon content in the material, the smaller the linear shrinkage rate, and the lower the carbon content, the greater the linear shrinkage rate. b. The casting shrinkage rate of common materials is as follows: casting shrinkage rate K=(LM-LJ)/LJ100%, LM is the cavity specification, LJ is the casting specification. K is affected by the following reasons: wax mold K1, casting structure K2, alloy type K3, pouring temperature K4.
3.Influence of Mold Making on Line Shrinkage of Precision Castings: a. The influence of wax injection temperature, wax injection pressure, and holding time on the specifications of the investment mold is the most significant effect on the injection wax temperature. In addition, it is the injection wax pressure. The holding time has little effect on the final specifications of the investment mold after the investment mold is formed. b.The linear shrinkage of wax (mold) material is about 0.9-1.1%.c. When the investment mold is stored, it will further shrink, and its shrinkage value is about 10% of the total shrinkage. However, after 12 hours of storage, the investment mold specification is generally stable. d. The radial shrinkage rate of the wax mold is only 30-40% of the shrinkage rate in the longitudinal direction, and the influence of the wax injection temperature on the free shrinkage rate is far greater than the impact on the hindered shrinkage rate (the suitable wax injection temperature is 57-59 ° C, the temperature The higher the contraction, the greater the contraction).
4.The influence of shell material: Zircon sand, zircon powder, Shangdian sand and Shangdian powder are used, because of their small expansion coefficient, only 4.610-6/℃, so they can be ignored.
5.Influence of Shell Roasting:Due to the small expansion coefficient of the shell, when the shell temperature is 1150°C, it is only 0.053%, so it can be ignored.
6.Influence of casting temperature: The higher the pouring temperature, the greater the shrinkage, and the lower the pouring temperature, the smaller the shrinkage, so the pouring temperature should be appropriate.