Prediction of Shrinkage Allowance Coefficient of Investment Castings Based on Geometric Parameters

Investment casting technology has been increasingly applied in the aerospace field due to its advantages, but investment castings inevitably undergo shrinkage deformation due to the principles of casting. However, the allocation of shrinkage allowance coefficient is not reasonable. The casting sizes are severely deviating from tolerances and the mold needs to be repaired repeatedly. In addressing the problem, the paper discussed the geometric correlation of casting shrinkage deformation and established prediction models for shrinkage allowance coefficient. First, casting experiments and simulations were conducted for H-shaped castings. And the measured pattern allowance coefficients aligned with the simulation results, verifying the reliability of the simulation. Then, the distribution trend of shrinkage along the casting geometric contour was analyzed, and the complex dependence of casting dimensional shrinkage changes on the geometry was discussed. Finally, the paper identified the key geometric parameters that affect shrinkage of each region. And the shrinkage prediction modeling of castings based on geometric parameters was realized. Compared with the conventional constant value for pattern allowance coefficients, the accuracy of the predicted value in assigning shrinkage allowance has been improved by 30.4 pct. The regression model has a good predictive effect on the measured values. The research is beneficial to the dimensional accuracy control in casting production. It can also provide a theoretical basis for the development of shrinkage deformation control technology for complex shape investment castings.