Method of superplastically forming and braze bonding a structure

Abstract

A process for forming single piece metal alloy panel structures includes both superplastic forming and braze bonding steps, and is particularly adapted to superplastically formable materials which are not particularly diffusion bondable, such as aluminum alloys. The process involves constructing a worksheet assembly from a plurality of worksheets which are associated with a brazing alloy capable of brazing the worksheets. At least two of the worksheets are joined in facing contact with each other by welding in a preselected pattern. The perimeter of the joined worksheets is then sealed, with the provision of means for permitting the admission of pressurized gas therebetween, after which the worksheet assembly is placed in a forming die. The actual structure forming process begins by heating the die and its associated worksheet assembly to a temperature suitable for superplastic forming, and simultaneously applying gas pressure at the means for admission of pressurized gas. The pressurized gas is applied to cause expansion of the sheets until the desired geometry of the structure has been attained. Following the superplastic forming step, the structure is braze bonded by ensuring that the die temperature is at or above the minimum brazing temperature of the brazing alloy for a specified period of time, thereby bonding at least some of the contacting surfaces of the structure together.