In general, the dimensional accuracy of precision castings is influenced by various factors such as casting structure, casting material, mold making, shell making, roasting, pouring, etc. Any unreasonable setting or operation of any link can cause changes in the shrinkage rate of the casting, resulting in deviations from the required dimensional accuracy of the casting. The following are factors that can cause dimensional accuracy defects in precision castings:

(1) The influence of casting structure: a. Casting wall thickness, high shrinkage rate, casting wall thickness, low shrinkage rate. b. The free shrinkage rate is high, while the obstructed shrinkage rate is low.

(2) The influence of casting material: a. The higher the carbon content in the material, the smaller the linear shrinkage rate, and the lower the carbon content, the larger the linear shrinkage rate. b. The casting shrinkage rate of common materials is as follows: casting shrinkage rate K=(LM-LJ)/LJ × 100%, LM is the cavity size, and LJ is the casting size. K is influenced by the following factors: wax mold K1, casting structure K2, alloy type K3, and pouring temperature K4.

(3) The influence of mold making on the shrinkage rate of castings: a. The wax injection temperature, wax injection pressure, and holding time have a significant impact on the size of the investment mold, with wax injection temperature being the most important factor, followed by wax injection pressure. Holding time has little effect on the final size of the investment mold after ensuring its formation. b. The linear shrinkage rate of wax (mold) material is about 0.9-1.1%. c. When the investment mold is stored, further shrinkage will occur, with a shrinkage value of about 10% of the total shrinkage. However, after 12 hours of storage, the size of the investment mold is basically stable. d. The radial shrinkage rate of wax molds is only 30-40% of the longitudinal shrinkage rate, and the effect of wax injection temperature on the free shrinkage rate is much greater than that on the hindered shrinkage rate (the optimal wax injection temperature is 57-59 ℃, and the higher the temperature, the greater the shrinkage).

(4) The influence of shell making materials: The use of zircon sand, zircon powder, Shangdian sand, and Shangdian powder can be ignored due to their small expansion coefficient of only 4.6 × 10-6/℃.

(5) The influence of shell roasting: Due to the small expansion coefficient of the shell, when the shell temperature is 1150 ℃, it is only 0.053%, so it can also be ignored.

(6) The influence of casting temperature: The higher the casting temperature, the greater the shrinkage rate, and the lower the casting temperature, the smaller the shrinkage rate. Therefore, the casting temperature should be appropriate.