Method of manufacturing an article by diffusion bonding and superplastic forming

A method of manufacturing an article by diffusion bonding and superplastic forming comprising the steps of:—

• a) providing at least a first metal workpiece and a second metal workplace, the first metal workpiece having a first surface and a second surface, the second metal workpiece having a third surface and a forth surface,
• b) applying stop off material to prevent diffusion bonding in a predetermined pattern on the first surface of the first metal workpiece, the predetermined pattern being spaced from the edges of the first surface of the first metal workplace,
• c) applying stop off material to prevent diffusion bonding in a predetermined position on the first surface of the first metal workpiece or the third surface of the second metal workpiece, the predetermined position extending from the predetermined pattern of stop of material on the first surface of the first metal workpiece towards one edge of the first surface of the first metal workpiece,
• d) providing a recess in a second predetermined position on the first surface of the first metal workpiece, the second surface of the first metal workpiece, the third surface of the second metal workpiece or the fourth surface of the second metal workpiece, the recess extending towards the same edge of the first metal workpiece or a corresponding edge of the second metal workpiece,
• e) assembling at least the first metal workpiece and the second metal workpiece in a stack such that the first surface of the first metal workpiece faces the third surface of the second metal workpiece and the recess in the second predetermined position on the first surface of the first metal workplace, the second surface of the first metal workpiece, the third surface of the second metal workpiece or the fourth surface of the second metal workpiece is aligned with the stop off material arranged in the predetermined position on the first surface of the first metal workpiece,
• f) sealing the edges of the first metal workpiece to the edges of the second metal workplace to form a sealed assembly,
• g) evacuating the sealed assembly,
• h) heating and externally pressurising the sealed assembly to diffusion bond the first and second metal workpieces together in areas other than the predetermined pattern and predetermined position to form a sealed integral structure,
• i) connecting an inflation pipe to the stop off material in the first predetermined position on the first surface of the first metal workpiece of the sealed integral structure,
• j) heating and internally pressurising the sealed integral structure to cause the first metal workpiece, or the second metal workpiece, where the stop off material was arranged in the predetermined position and the recess was arranged in the second predetermined position, to be hot formed to create an inflation passage within the sealed integral structure,
• k) heating and internally pressurising the sealed integral structure to cause the first metal workpiece and/or the second metal workpiece where the stop off material was arranged in the predetermined pattern to be superplastically formed to create a hollow metal article.