Metal fusion bonding – Process – With shaping
Reexamination Certificate
1998-09-23
2001-07-24
Ryan, Patrick (Department: 1725)
Metal fusion bonding
Process
With shaping
C228S118000, C228S190000, C228S193000
Reexamination Certificate
active
06264091
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of manufacturing an article by diffusion bonding, and particularly relates to a method of manufacturing an article by superplastic forming and diffusion bonding.
BACKGROUND OF THE INVENTION
It is known to manufacture hollow metallic articles by superplastic forming and diffusion bonding metal workpieces. These metal workpieces include elementary metal, metal alloys, intermetallic materials and metal matrix composites. At least one of metal workpieces must be capable of superplastic extensions.
In one known process of diffusion bonding the surfaces of the workpieces to be joined are cleaned. The workpieces are arranged in a stack and the edges of the workpieces are welded together, except for an aperture where a pipe is welded to the workpieces, to form a sealed assembly. The interior of the sealed assembly is evacuated and the pipe is sealed. The sealed assembly is placed in a pressure vessel and is heated and pressed to diffusion bond the workpieces together to form an integral structure. Diffusion bonding occurs when two mating surfaces are pressed together under temperature, time and pressure conditions that allow atom interchange across the interface such that the interface effectively ceases to exist.
In one known process of superplastic forming and diffusion bonding the surfaces of the workpieces to be jointed are cleaned, and at least one surface of one or more of the workpieces is coated in preselected areas with a material to prevent diffusion bonding. The workpieces are arranged in a stack and the edges of the workpieces are welded together, except for an aperture where a pipe is welded to the workpieces, to form a sealed assembly. The pipe enables a vacuum, or inert gas pressure, to be applied to the interior of the sealed assembly. The sealed assembly is placed in an autoclave and heated so as to “bake out” the binder from the material used to prevent diffusion bonding. The sealed assembly is then evacuated and the pipe is sealed. The sealed assembly is placed in a pressure vessel and is heated and pressed to diffusion bond the workpieces together to form an integral structure. Diffusion bonding occurs when two mating surfaces are pressed together under temperature, time and pressure conditions that allow atom interchange across the interface. The first pipe is removed and a second pipe is fitted to the diffusion bonded assembly at the aperture where the first pipe was located. The integral structure is located between two appropriately shaped dies and is placed within an autoclave. The integral structure and dies are heated and pressurised fluid is supplied through the second pipe into the interior of the integral structure to cause at least one of the workpieces to be superplastically formed to produce an article, or component, matching the shape of the dies.
In another known process of diffusion bonding the surfaces of the components to be joined are cleaned. The components are arranged in a stack and the stack is placed in a metal bag, the metal bag is sealed except for an aperture where a pipe is welded to the metal bag, to form a sealed assembly. The interior of the sealed assembly is evacuated and the pipe is sealed. The sealed assembly is placed in a pressure vessel and is heated and pressed to diffusion bond the components and metal bag together to form an integral structure. Diffusion bonding occurs when two mating surfaces are pressed together under temperature, time and pressure conditions that allow atom interchange across the interface such that the interface effectively ceases to exist.
In these known methods of diffusion bonding and superplastic forming it is essential that there is a vacuum in the sealed assembly in order to ensure that a satisfactory diffusion bond is formed between the workpieces, or components, and that the vacuum is maintained in the sealed assembly when they are subsequently heated and pressed together during the diffusion bonding process.
The heat and pressure applied during diffusion bonding causes the pipe to collapse, but the end of the pipe joined to the sealed assembly is supported by the joint. It is often necessary to use large internal diameter pipes, particularly for the manufacture of large articles, to provide sufficient gas conductance at reduced pressure for good evacuation of the sealed assembly prior to diffusion bonding. These large internal diameter pipes have thin walls. A problem associated with the diffusion bonding process is that the temperature and pressure applied during the diffusion bonding process is likely to cause the walls of the pipes to be sucked back into the sealed assembly because of the vacuum in the sealed assembly. If the walls of the pipe are sucked back there is a possibility that the pipe will burst and thus the vacuum in the sealed assembly will be lost. This means that diffusion bonding of the workpieces, or components, will not occur.
SUMMARY OF THE INVENTION
The present invention seeks to provide a novel method of manufacturing an article by diffusion bonding which reduces, or overcomes, the above mentioned disadvantages.
Accordingly the present invention provides a method of manufacturing an article by diffusion bonding at least two metal workpieces, or at least two metal components, comprising the steps of:
(a) assembling the at least two metal workpieces, or at least two metal components, into a stack relative to each other so that the surfaces are in mating contact,
(b) sealing the edges of the at least two metal workpieces, or at least two metal components, together, except for an aperture where a pipe is to be inserted, joining a pipe to the stack to provide a sealed assembly, joining the pipe to the stack such that the axis of the pipe is arranged at an angle of at least 45° to the axis of the aperture,
(c) evacuating the interior of the sealed assembly via the pipe,
(d) sealing the pipe with at least one seal,
(e) applying sufficient heat and pressure across the thickness of the at least two metal workpieces, or at least two metal components, to diffusion bond the at least two metal workpieces, or at least two metal components, together to form an integral structure.
The sealing of the edges of the at least two metal workpieces, or at least two metal components, may be by welding the edges of the at least two metal workpieces, or at least two metal components, together. Alternatively the sealing of the edges of the at least two metal workpieces, or at least two metal components, may be by placing the at least two metal workpieces, or at least two metal components, in a metal bag.
Preferably the pipe is joined to the stack such that the axis of the pipe is arranged at an angle of at least 60° to the axis of the aperture, more preferably the pipe is joined to the stack such that the axis of the pipe is arranged at an angle of 90° to the axis of the aperture.
If the pipe has a diameter less than the aperture, the method comprises sealing the aperture to the outer periphery of a ring and sealing the pipe to the inner periphery of a ring.
Preferably the method comprises before the metal workpieces are stacked together, applying a stop off material to preselected areas of at least one of the surfaces of at least one of the at least two metal workpieces to prevent diffusion bonding at the preselected areas, before the pipe is sealed placing the sealed assembly in an oven, heating the sealed assembly while it is within the oven to evaporate volatile binder from the stop off material and continuously evacuating the sealed assembly to remove volatile binder from between the at least two metal workpieces of the sealed assembly, after the integral structure is formed heating the integral structure and internally pressurising the integral structure to cause some of the preselected areas of at least one of the metal workpieces to be superplastically formed to produce an article of predetermined shape.
The article may be a fan blade, a compressor blade, a fan duct outlet guide vane or a heat exchanger component.
Preferably
Manelli Denison & Selter PLLC
Pittman Zidia
Rolls-Royce plc
Ryan Patrick
Taltavull W. Warren
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