Method and apparatus for regulating preselected loads on forming dies

Abstract

An improvement to an apparatus for and method of making structures from at least one workpiece is disclosed. The prior art apparatus and method comprised a pair of dies which were clamped about the periphery of the at least one workpiece creating a gap therebetween. A pair of non-inflatable platens were then used to apply a force against the pair of dies further clamping the workpiece in place. The die assembly and workpiece were then heated to forming temperatures and thereafter the workpiece was formed within the pair of dies by fluid under pressure. Typically the forming was Superplastic Forming or Superplastic Forming/Diffusion Bonding. The improvement to the apparatus and method comprises providing an inflatable platen between one of the dies and one of the non-inflatable platens, adapted to regulate the force applied by said pair of dies to said at least one workpiece. A sensor, mounted within the gap is adapted to sense changes in the dimensions of the actual gap and provide a first output signal proportional thereto during the forming of the structure. A signal generator is provided for producing a second output signal proportional to a preferred gap dimension that is produced when said force is the minimum amount necessary for forming the at least one workpiece into the structure. A control system is provided to regulate the pressure level within the inflatable platen, and, therefore, the force applied to the pair of dies, using the first and second output signals such that the actual gap substantially equals the preferred gap during forming. In an alternate embodiment, a buffer platen is placed between the die assembly and inflatable platen to isolate the inflatable platen from the heat.