Under normal circumstances, the precision of the specifications of Dongguan precision casting castings is affected by many factors such as casting structure, casting materials, mold making, shell making, firing, pouring, etc. The setting and actual operation of all stages are unscientific. The shrinkage rate of the casting causes a change, causing errors in the precision of the casting specifications and the regulations. The following are the factors that can lead to the shortcomings of the precision of high-precision casting specifications:
(1) The influence of casting structure: a. Casting wall thickness, large shrinkage rate, thin casting wall, small shrinkage rate. b. The random shrinkage rate is large, and the blocking shrinkage rate is small.
(2) The influence of casting material: a. The higher the carbon content in the raw material, the smaller the linear shrinkage rate, and the lower the carbon content, the greater the linear shrinkage rate. b. The forging shrinkage rate of common materials is below: forging shrinkage rate K=(LM-LJ)/LJ×100%, LM is the die specification, and LJ is the casting specification. K is affected by the following factors: wax mold K1, casting structure K2, aluminum alloy type K3, pouring temperature K4.
(3) The influence of mold making on the linear shrinkage rate of castings: a. The influence of wax injection temperature, wax injection working pressure, and pressure holding time on the investment specifications is the most significant of the wax injection temperature, followed by the wax injection working pressure, and The pressing time has little effect on the final specifications of the investment mold after ensuring that the investment mold is formed. b. The linear shrinkage rate of wax (mold) material is about 0.9-1.1%. c. When the investment mold is stored, it will further cause the collapse, and the collapse value is about 10% of the total pressure strength, but after 12 hours of storage, the investment specifications are stable. d. The axial shrinkage rate of the wax mold is only 30-40% of the long and short azimuth shrinkage rate. The wax injection temperature has a far greater impact on the random shrinkage rate than the resistance shrinkage rate (the best wax injection temperature is 57-59 ℃, the higher the temperature, the greater the shrinking).
(4) The influence of shell-making raw materials: zircon sand, zircon powder, Shangdian sand, and Shangdian powder are selected, and the coefficient of thermal expansion is small, only 4.6×10-6/℃, so it can be ignored.
(5) The influence of the mold shell burning: Because the thermal expansion coefficient of the mold shell is small, when the mold shell temperature is 1150 ℃, it is only 0.053%, so it can be ignored.
(6) The influence of casting temperature: the higher the pouring temperature, the greater the shrinkage rate, and the lower the pouring temperature, the smaller the shrinkage rate, so the pouring temperature is as much as possible.