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

Edit:Xiangyang Liqiang Machinery Co., Ltd.UpDate:2020-05-07

Precision casting is a very common forging method. Today, everyone is talking about the reasons for the harm to the precision of precision casting specifications.

Under normal circumstances, the precision of precision casting specifications is compromised by many factors such as casting structure, casting material, mold making, shell making, firing, pouring and so on. In all of them, setting and actual operation are not scientific. It changes the shrinkage rate of castings and causes errors in the precision of casting specifications and regulations. The following are elements that endanger the precision of precision casting specifications.

1. The hazards of casting structure: casting wall thickness, large shrinkage rate, thin casting wall, small shrinkage rate; large random shrinkage rate, small blocking shrinkage rate.

2. The hazards of casting materials: the higher the carbon content in the raw materials, the smaller the linear shrinkage rate, and the lower the carbon content, the greater the linear shrinkage rate. The forging shrinkage rate of common materials is below: forging shrinkage rate K=(LM-LJ)/LJ×100%, LM is the specification of the die, and LJ is the specification of the casting. K is affected by the following elements: wax mold K1, casting structure K2, aluminum alloy type K3, pouring temperature K4.

3. The hazards of mold making to the shrinkage rate of castings: wax injection temperature, wax injection working pressure, and curing time have the most significant damage to investment specifications, followed by wax injection working pressure. Ensure that the final specifications of the investment mold are not harmful after the investment is formed.

4. The hazards of shell-making raw materials: zircon sand, zircon powder, Shangdian sand, and Shangdian powder are used, because their thermal expansion coefficient is small, only 4.6×10-6/℃, so they can be ignored.

5. The hazard 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 hazard 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 good as possible.

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