Superplastic forming with ceramic lost-wax dies

Superplastic forming of metal sheet, using gas pressure at elevated temperature at low strain rates, has been performed with ceramic dies formed using lost-wax techniques, which are utilised commonly in the manufacture of investment-casting moulds. In the case of superplastic forming, low die-loading and, commonly, low production volumes would permit the use of such disposable ceramic shell dies. Although care must be taken with these shell dies due to their limited mechanical strength, their use gives added flexibility to the process: this includes the production of re-entrant forms with good surface finish which would normally lead to considerable problems with conventional metal tooling. The evaluation of ceramic die material is reported here, together with the results of forming trials using lost-wax ceramic dies for a simple re-entrant shape.