Dimensional Prediction: Trials Research

摘要

One of the many hallmarks of investment casting is the ability to manufacture very complex components with high dimensional accuracy. While the end user of the component provides detailed drawings and precise dimensions which are expected to be present in the manufactured part, the foundry must ensure that the casting process steps that lead to the final part shape properly capture various expansion and contraction allowances due to changes in wax shape, strength of the shell and contraction of the cast component during cooling. The application of standard shrink allowance suggestions and rules for these complex castings requires a high level of accumulated experience from the wax tooling and process designers in order to achieve a cast shape that nears the required dimensions. In order to achieve higher accuracy in developing a proper set of wax tooling to achieve the required casting dimensions, casting simulation can be used to quantitatively and accurately identify the dimensional changes during the full wax injection to cast production process, and enable engineers to provide the proper shape that leads to an accurate component shape. By achieving dimensional accuracy, time and cost savings will be attained by removing the need for straightening / hot pressing, reduction of scrap due to warpage, and reduction of material and labor by eliminating unnecessary machining stock, among other corrective measures. While the bulk of methodology to study various modes of deformation is currently available in capable simulation tools, such as ESI’s ProCAST Casting Simulation software, a significant amount of input data in the form of wax and shell material property data has not been developed to allow for such simulation-based dimensional investigations. This discussion identifies the sources of distortion during the full casting process, describes current dimensional allowance methods, summarizes previous simulation work in this area, and proposes a methodology for using simulation to develop wax tooling shapes that account for dimensional changes through the full process.