Precision control in precision casting process

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

1. Influence of casting structure. Casting wall thickness, large shrinkage, thin casting wall, small shrinkage; The free shrinkage is large, and the hindered shrinkage is small.

2. The influence of casting material. The higher the carbon content in the material, the smaller the linear shrinkage, and the lower the carbon content, the greater 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, and K is affected by wax mold K1, casting structure K2, alloy type K3, and pouring temperature K4.

3. The influence of mold making on the linear shrinkage of castings. The influence of wax injection temperature, wax injection pressure and holding time on the size of the investment mold is obvious with wax injection temperature * * *, followed by wax injection pressure. The holding time has little influence on the final size of the investment mold after ensuring the investment molding; The linear shrinkage of wax (mold) is about 0.9-1.1%; When the investment mold is stored, it will further shrink, and its shrinkage value is about 10% of the total shrinkage. However, after 12 hours of storage, the size of the investment mold is basically stable; The radial shrinkage rate of wax mold is only 30-40% of the shrinkage rate in the length direction. The influence of wax injection temperature on the free shrinkage rate is far greater than that on the blocked shrinkage rate (* * * The wax injection temperature is 57-59 ℃, and the higher the temperature, the greater the shrinkage rate).

4. Due to the influence of shell making materials, zircon sand, zircon powder, Shangdian sand and Shangdian powder are used. Because of their small expansion coefficient, they are only 4.6 × 10-6/℃, so it can be ignored.

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

6. The higher the pouring temperature is, the greater the shrinkage is. The lower the pouring temperature is, the smaller the shrinkage is. Therefore, the pouring temperature should be appropriate.