Determination of pattern allowances for steel castings using the finite element inverse deformation analysis

In recent years, the development of computational models to predict casting distortions has led to improvements in efficiency and accuracy over traditional pattern design that relies on shrink rules. Unfortunately, the determination of pattern dimensions using computer simulation remains a trial-and-error process that requires several design iterations. In this study, the finite element inverse deformation analysis is utilized to calculate the pattern geometry in a single iteration for a plastically deformed (i.e., distorted) body. This method is evaluated through a loop test, for which an inverse simulation is performed first to calculate the pattern shape. This configuration is then used as the input geometry for a forward simulation, which is shown to successfully recover the original as-cast shape used for the inverse analysis. Through this sequence, the inverse deformation method is shown to be a viable technique for the determination of pattern allowances in production castings.