Criterion for Contraction Behavior of the Casting

The precise contraction rate achieved by accurately determining the contraction behavior of castings is an essential aspect to enhancing casting dimensional accuracy. In this study, the contraction process of the L-shaped Al-5%Cu ZL205A alloy castings was investigated to explore the criteria for the contraction behavior of the castings. To acquire the precise contraction rate, a novel approach for the evaluation of contraction behavior was proposed based on the envelope density and contraction center. The results indicate that, when the line between any point of the casting and the contraction center passes through the sand mold, the contraction behavior of the casting is hindered contraction. Otherwise, it is free contraction. Correspondingly, the contraction center is the center of mass in the casting. In addition, the contraction behavior and the envelope density determine the contraction rate of the casting. For castings with envelope issues, if the contraction behavior is hindered contraction, the contraction rate of the casting is computed through the envelope density; otherwise, the contraction rate of the casting is free contraction rate. The results show that the envelope density ρ' of 2.114 g/cm³ is the critical value between free contraction and hindered contraction for L-shaped Al-5%Cu ZL205A alloy castings.