J. G. Schroth, GM Research and Development Center, Warren, MI; R. H. Hammar, General Motors Corporation, Warren, MI

Summary:

Quick Plastic Forming (QPF) is a high temperature blow forming process for aluminum sheet that is carried out at higher strain rates than those typically used for superplastic forming. The relatively short cycle times and large “press-open time-fractions” of the QPF process require significant attention to thermal control of the press/tooling system in order to maintain the process temperature within an acceptable range. A dynamic equilibrium is ultimately produced in which the temperatures at the working tool face undergo short-time-scale changes while the majority of the tool volume maintains a relatively stable temperature distribution. Careful attention to the insulation system and to the type, number, and placement of heating elements within the tool is required to obtain the desired thermal uniformity. The requirements for fast tool changes in a multi-product press line drive additional tool design considerations. Insulation amount and packaging have been optimized to minimize energy use and to maintain an acceptable temperature at the surface of the tool package while minimizing tool package size. Elements of load-bearing and peripheral insulation systems will be described. Thermal analyses of alternate press/tooling configurations will be presented to differentiate the characteristics of heated QPF tools and typical heated SPF press systems. Details of alternate heater configurations and their influence on the thermal distribution within a tool system will be explored.