The following are several factors that can cause dimensional accuracy defects in precision casting:

1. The influence of casting structure. The casting wall is thick, the shrinkage rate is large, the casting wall is thin, and the shrinkage rate is small; the free shrinkage rate is large, and the hindering shrinkage rate is small.

2. The influence of casting material. 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; the casting shrinkage rate of common materials is casting shrinkage rate K=(LM-LJ)/LJ×100%, LM Is the cavity size, LJ is the size of the casting, and K is affected by the wax mold K1, the casting structure K2, the alloy type K3, and the pouring temperature K4.

3. The influence of mold making on the linear shrinkage of castings. The wax injection temperature, wax injection pressure, and pressure holding time have the most obvious influence on the investment size. The wax injection temperature is the most obvious, followed by the wax injection pressure. The pressure holding time has little effect on the final size of the investment after the investment is formed; The linear shrinkage rate of (mold) material is about 0.9-1.1%; when the investment mold is stored, it will shrink further, and its shrinkage value is about 10% of the total shrinkage, but after 12 hours of storage, the investment size is basically stable; The radial shrinkage rate of the wax mold is only 30-40% of the lengthwise shrinkage rate. The wax injection temperature has a far greater influence on the free shrinkage rate than the hindered shrinkage rate (the best wax injection temperature is 57-59°C, the higher the temperature The greater the high shrinkage).

4. The influence of shell-making materials is to use zircon sand, zircon powder, Shangdian sand, and Shangdian powder. Because of its small expansion coefficient, only 4.6×10-6/℃, it can be ignored.

5. The effect of molding shell firing is that due to the small expansion coefficient of the molding shell, when the temperature of the molding shell is 1150℃, it is only 0.053%, so it can be ignored.

6. ​​The influence of the casting temperature, the higher the casting temperature, the greater the shrinkage rate, and the lower the casting temperature, the smaller the shrinkage rate, so the casting temperature should be appropriate.