What are the factors that affect the dimensional accuracy of precision castings?

Under ordinary circumstances, the dimensional accuracy of compact castings is affected by the layout of the castings, casting materials, mold making, shell making, baking, pouring and other factors. The setting and improper operation of any link among them will shorten the compact castings. The rate has changed, causing errors in the dimensional accuracy of castings and requirements. The following are the main reasons for the shortcomings of the dimensional accuracy of compact castings:

What are the factors that affect the dimensional accuracy of precision castings?

(1) The effect of compact casting material: a. The higher the carbon content in the material, the smaller the line shortening rate, and the lower the carbon content, the greater the line shortening rate. b. The forging shortening rate of common materials is as follows: Casting shortening rate K=(LM-LJ)/LJ×100%, LM is the cavity size, LJ is the casting size. K is affected by the following factors: wax mold K1, casting layout K2, alloy type K3, pouring temperature K4.

(2) The influence of mold making on the shortening rate of compact castings: a. The influence of wax injection temperature, injection pressure, and pressure holding time on the investment size is the most important in the wax injection temperature, followed by the wax injection pressure and the pressure holding time After guaranteeing that the investment mold is formed, it has little effect on the final size of the investment mold. b. The line shortening rate of wax (mold) material is about 0.9-1.1%. c. When the investment is deposited, there will be further shortening, and its shortening value is about 10% of the total shortening, but when it is deposited for 12 hours, the investment size remains unchanged. d. The radial shortening rate of the wax model is only 30-40% of the shortening rate of the length target. The wax injection temperature has a far greater influence on the free shortening rate than the hindered shortening rate (the best wax injection temperature is 57-59 ℃, the higher the temperature, the greater the shortening).

(3) The influence of the compact casting layout: a. The casting wall is thick and the shortening rate is large, and the casting wall is thin and the shortening rate is small. b. Freedom shortening rate is large, obstacle shortening rate is small.

(4) The influence of shell baking: Because the shrinkage coefficient of the shell is small, when the shell temperature is 1150℃, it is only 0.053%, so it can be ignored.

What are the factors that affect the dimensional accuracy of precision castings?

(5) The influence of casting temperature: the higher the casting temperature, the greater the shortening rate, and the lower the casting temperature, the smaller the shortening rate, so the casting temperature should be appropriate.

(6) The influence of shell-making materials: zircon sand, zircon powder, Shangdian sand, Shangdian powder are used. Because of their small shrinkage coefficient, only 4.6×10-6/℃.