Abstract: The invention relates to a device for forming and welding blanks in a material able to become superplastic, of the type comprising cooperating dies between which such blanks are placed, which dies are respectively mounted on a lower frame and on an upper frame of the device.The device according to the invention is remarkable in that the lower frame is constituted of a base and of a vertically movable part carrying a die, in that an inflatable bladder is interposed between the base and the movable part of the lower frame, in that a mechanical a lock is provided for connecting together the the base and the upper frame, when the latter is in low position, and in that, in the low and locked position of the upper frame with respect to the base of the lower frame, cooperation of the dies is achieved by controlling the bladder.