Non-proportional Shrinkage Compensation

Shrinkage and warpage is a leading fact in casting. It is common to compensate shrinkage by scaling the tool by a certain percentage. The transformed 3D CAD model of a final product is used for tool generation. The transformations of CAD model include 3D scaling or external surface offset. Both methods are proportional and uniform in all three axes, and they are already included in a vast variety of CAD software packages. The shrinkage and warpage process, however, is not necessarily uniform, and some portions of a product can have different shrinkage ratio. Therefore, it is necessary to introduce the new CAD transformation technique: non-proportional 3D scaling. This paper deals with estimation of 3D function that should be used to transform the 3D CAD model of a tool, in order to obtain the optimum result. The casting tool and sample castings are measured on a coordinate measuring machine, and these measurement results are used to estimate the shrinkage percentage needed for different parts of a CAD model.