The following factors can cause dimensional precision defects of precision casting:

1. Influence of casting structure. Casting wall thickness, high shrinkage, thin casting wall, low shrinkage; Large free shrinkage, small hindrance shrinkage.

2. Influence of casting material. The higher the carbon content in the material, the smaller the linear shrinkage rate, the lower the carbon content, and the larger the linear shrinkage rate. The casting shrinkage rate of common materials is K=(lm-lj)/LJ * 100%, LM is the cavity size, LJ is the casting size, K is affected by the wax mold K1, casting structure K2, alloy type K3, casting temperature K4.

3. Influence of mold making on shrinkage of casting line. The influence of injection temperature, injection pressure and holding time on the size of investment mold is most obvious, followed by injection pressure. The holding time has little influence on the final size of investment mold after molding. The linear shrinkage of wax (mold) material is about 0.9-1.1%; During storage, shrinkage will be further generated, and the shrinkage value is about 10% of the total shrinkage. However, after 12 hours of storage, the size of the investment mold is basically stable. Wax models of radial shrinkage rate was only about the length direction shrinkage rate of 30-40%, shooting wax temperature effect on the free shrinkage rate is much greater than stuck to the influence of shrinkage (optimum temperature for 57 ℃, 59 - the higher the temperature the greater the shrinkage).

4, the influence of the shell making materials, the use of zircon sand, zircon powder, sand, powder, because of its small expansion coefficient, only 4.6 x 10-6 / ℃, thus can be neglected.
5, the influence of the type of shell roasting, due to the shell of the small expansion coefficient, when the shell temperature of 1150 ℃, is only 0.053%, so also is negligible.
6, casting temperature, casting temperature, the higher the shrinkage rate, the lower the casting temperature, the smaller the shrinkage rate, so the casting temperature should be appropriate.