The following are several factors that can cause dimensional accuracy defects in precision casting:
1. Influence of casting structure. Casting wall thickness, shrinkage, casting wall thin, shrinkage; Free shrinkage rate is big, hinder shrinkage rate is small.
2. Influence of casting material. The higher the carbon content in the material, the smaller the linear shrinkage, and the lower the carbon content, the larger the linear shrinkage. The casting shrinkage of common materials is K=(lm-lj)/LJ×100%, LM is the cavity size, LJ is the casting size, K is affected by the factors of wax model K1, casting structure K2, alloy type K3, casting temperature K4.
3. Influence of mold making on casting line shrinkage. The influence of ejection temperature, ejection pressure and holding time on the investment mold size was most obvious in the ejection temperature, followed by the ejection pressure. The linear shrinkage rate of wax (mold) material is about 0.9-1.1%. The shrinkage value is about 10% of the total shrinkage. However, after 12 hours, the investment size is basically stable. The radial shrinkage rate of the wax mold is only 30-40% of the shrinkage rate in the length direction, and the influence of ejection temperature on the free shrinkage rate is far greater than that on the hindered shrinkage rate (the optimal ejection temperature is 57-59℃, and the higher the temperature, the greater the shrinkage).
4. The influence of shell making materials is zirconium sand, zirconium powder, shangdian sand and shangdian powder. The expansion coefficient is small, only 4.6×10-6/℃, so it can be neglected.
5. Due to the small expansion coefficient of molded shell, when the temperature of molded shell is 1150℃, it is only 0.053%, so it can be neglected.
6, the influence of casting temperature, the higher the casting temperature, the larger the shrinkage rate, the lower the casting temperature, the smaller the shrinkage rate, so the casting temperature should be appropriate.