In general, the dimensional accuracy of 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 castings, resulting in deviations between the dimensional accuracy of castings and requirements. The following are the factors that can cause dimensional accuracy defects in castings:

(1) The impact of casting structure: a Casting wall thickness, high shrinkage rate, thin casting wall, low shrinkage rate. b. The free shrinkage rate is high, while the hindered 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. 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)/LJ × 100%, LM is the cavity size, and LJ is the casting size. K is affected 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 linear shrinkage rate of castings: a. The effect of wax injection temperature, wax injection pressure, and holding time on the size of the investment mold is more obvious than that of wax injection temperature, followed by wax injection pressure. Holding time has little effect on the size of the investment mold after it is formed. 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 length direction shrinkage rate, and the impact of wax injection temperature on the free shrinkage rate is much greater than on the hindered shrinkage rate (wax injection temperature is 57-59 ℃, the higher the temperature, the greater the shrinkage).