Method of manufacturing an article by superplastic forming and diffusion bonding

• US 5,323,536 A
• Filed: 08/06/1993
• Issued: 06/28/1994
• Est. Priority Date: 08/14/1992
• Status: Expired due to Fees

• Current Assignee: Rolls-Royce PLC (Rolls-Royce Holdings Plc)
• Original Assignee: Rolls-Royce PLC (Rolls-Royce Holdings Plc)
• Inventors: Richardson, Brian, Fowler, John O.
• Primary Examiner(s): Ramsey, Kenneth J.
• Application Number:
  US08/102,809
• Time in Patent Office: 326 Days
• Field of Search: 228/157, 228/193, 228/265, 228/172, 228/262.71, 29/889.72
• US Class Current: 29/889.72
• CPC Class Codes: B21D 26/055 Blanks having super-plastic properties
• CPC Class Codes: B23K 20/002 specially adapted for particular articles or work B23K20/129 takes precedence
• CPC Class Codes: Y10T 29/49339 Hollow blade

Abstract

A plurality of workpieces are assembled into a stack. Two of the workpieces are machined on one surface at predetermined positions from the edges of the workpieces. The workpieces are stacked so that the machined surfaces of the workpieces face away from each other. Two workpieces are provided with a stop off material on one of their surfaces to prevent diffusion bonding at predetermined positions. The edges of the workpieces are welded together and a pipe is welded to the stack to interconnect with the stop off material to form a sealed assembly. The workpieces are diffusion bonded together. The integral structure formed is heated and opposite ends of the integral structure are twisted relatively to contour the integral structure to a predetermined shape. The integral structure is heated and the machined portions on the workpieces are isothermally forged and then the twisted integral structure is internally pressurised to superplastically form one workpiece to produce an article, eg a fan blade.

Claims

1. A method of manufacturing an article by superplastic forming and diffusion bonding at least two workpieces comprising the steps of:

(a) forming a first workpiece which has a flat surface,

(b) forming a second workpiece which has a flat surface, the first and second workpieces defining the outer profile of the finished article,

(c) machining a portion of a surface of at least the first workpiece at a predetermined distance from at least a portion of the periphery of the first workpiece, the said surface being opposite to the flat surface of the first workpiece,

(d) applying a stop off material to prevent diffusion bonding to preselected areas of at least one of the flat surfaces of at least one of the at least two workpieces,

(e) assembling the at least two workpieces into a stack relative to each other so that the flat surfaces are in mating abutment,

(f) applying heat and pressure across the thickness of the at least two workpieces to diffusion bond the at least two workpieces together in areas other than the preselected areas to form an integral structure,

(g) applying heat and pressure to the integral structure to isothermally forge the machined portion on the first workpiece which forms part of the integral structure to substantially produce the required finished peripheral shape and dimensions of the finished article,

(h) heating the integral structure and internally pressurising it to cause the preselected areas of at least one of the workpieces to be superplastically formed to produce an article of predetermined shape,

(i) finish machining the article to remove excess material from the isothermally forged peripheral shape to produce the finished article.

2. A method as claimed in claim 1 further comprising machining a portion of a surface of the second workpiece at a predetermined distance from at least a portion of the periphery of the second workpiece, the said surface being opposite to the flat surface of the second workpiece, applying heat and pressure on the integral structure to isothermally forge the machined portions on the first and second workpieces which form part of the integral structure to substantially produce the required finished peripheral shape and dimensions of the finished article.

3. A method as claimed in claim 1 wherein after diffusion bonding the stack of workpieces and before superplastically forming the integral structure, heating the integral structure and applying loads to opposite ends of the integral structure to twist one end relative to the other end to contour the integral structure to a predetermined shape.

4. A method as claimed in claim 3 wherein after twisting the integral structure and before superplastic forming the integral structure, internally pressurising the contoured integral structure to break the adhesive bond between the stop off material and the at least one workpiece in the preselected areas.

5. A method as claimed in claim 4 wherein after internally pressurising the integral structure to break the adhesive bond and before internally pressurising the integral structure to superplastically form at least one workpiece, sequentially evacuating and supplying inert gas to the interior of the integral structure to remove oxygen from the interior of the integral structure.

6. A method as claimed in claim 5 wherein the step of sequentially evacuating and supplying inert gas to the interior of the integral structure to remove oxygen is performed a plurality of times.

7. A method as claimed in claim 1 wherein the isothermal forging and superplastic forming steps are performed sequentially in a single die.

8. A method as claimed in claim 7 comprising internally pressurising the contoured integral structure to break the adhesive bond between the stop off material and the at least one workpiece in the preselected areas before the contoured integral structure is isothermally forged.

9. A method of manufacturing an article by superplastic forming and diffusion bonding at least two workpieces comprising the steps of:

(a) forming a first workpiece which has a flat surface,

(b) forming a second workpiece which has a flat surface, the first and second workpieces defining the outer profile of the finished article,

(c) machining a portion of a surface of at least the first workpiece at a predetermined distance from at least a portion of the periphery of the first workpiece, the said surface being opposite to the flat surface of the first workpiece,

(d) applying a stop off material to prevent diffusion bonding to preselected areas of at least one of the flat surfaces of at least one of the at least two workpieces,

(e) assembling the at least two workpieces into a stack relative to each other so that the flat surfaces are in mating abutment,

(f) sealing the edges of the at least two workpieces together, except where a pipe is to be inserted, and joining a pipe to the stack to provide a sealed assembly,

(g) sequentially evacuating the interior of the sealed assembly and supplying inert gas to the interior of the sealed assembly through the pipe to remove oxygen from the interior of the sealed assembly,

(h) placing the sealed assembly in an oven while continuously evacuating the sealed assembly,

(i) heating the sealed assembly while it is within the oven to evaporate volatile binder from the stop off material while continuously evacuating the sealed assembly to remove the volatile binder from between the at least two workpieces of the sealed assembly,

(j) sealing the pipe,

(k) applying heat and pressure across the thickness of the at least two workpieces to diffusion bond the at least two workpieces together in areas other than the preselected areas to form an integral structure,

(l) applying heat and pressure to the integral structure to isothermally forge the machined portion on the first workpiece which forms part of the integral structure to substantially produce the required finished peripheral shape and dimensions of the finished article,

(m) heating the integral structure and internally pressurising it to cause the preselected areas of at least one of the workpieces to be superplastically formed to produce an article of predetermined shape,

(n) finish machining the article to remove excess material from the isothermally forged peripheral shape to produce the finished article.

10. A method as claimed in claim 9 further comprising machining a portion of a surface of the second workpiece at a predetermined distance from at least a portion of the periphery of the second workpiece, the said surface being opposite to the flat surface of the second workpiece, applying heat and pressure on the integral structure to isothermally forge the machined portions on the first and second workpieces which form part of the integral structure to substantially produce the required finished peripheral shape and dimensions of the finished article.

11. A method as claimed in claim 9 wherein after diffusion bonding the stack of workpieces and before superplastically forming the integral structure, heating the integral structure and applying loads to opposite ends of the integral structure to twist one end relative to the other end to contour the integral structure to a predetermined shape.

12. A method as claimed in claim 11 wherein after twisting the integral structure and before superplastic forming the integral structure, internally pressurising the contoured integral structure to break the adhesive bond between the stop off material and the at least one workpiece in the preselected areas.

13. A method as claimed in claim 12 wherein after internally pressurising the integral structure to break the adhesive bond and before internally pressurising the integral structure to superplastically form at least one workpiece, sequentially evacuating and supplying inert gas to the interior of the integral structure to remove oxygen from the interior of the integral structure.

14. A method as claimed in claim 11 wherein the integral structure is heated to a temperature of 800°

C. for twisting the opposite ends of the integral structure.

15. A method as claimed in claim 11 wherein before the opposite ends of the integral structure are twisted, heating the integral structure and applying a load to one end of the integral structure to camber said end.

16. A method as claimed in claim 11 comprising holding one end of the integral structure stationary and rotating the other end of the integral structure to twist the integral structure.

17. A method as claimed in claim 9 wherein before the pipe is sealed, cooling the sealed assembly whilst the sealed assembly is continuously evacuated.

18. A method as claimed in claim 17 comprising cooling the sealed assembly to ambient temperature.

19. A method as claimed in claim 13 wherein the step of sequentially evacuating and supplying inert gas to the interior of the integral structure to remove oxygen is performed a plurality of times.

20. A method as claimed in claim 9 comprising welding the edges of the workpieces together.

21. A method as claimed in claim 9 wherein the step of sequentially evacuating the interior of the sealed assembly and supplying inert gas to the interior of the sealed assembly through the pipe to remove oxygen from the interior of the sealed assembly is performed a plurality of times.

22. A method as claimed in claim 9 wherein where the workpieces are made of a titanium alloy, heating the workpieces to a temperature equal to, or greater than, 850°

C. and applying a pressure equal to, or greater than, 20×

10⁵ Nm^-2 to diffusion bond the workpieces together to form an integral structure.

24. A method as claimed in claim 9 comprising heating the integral structure to a temperature equal to, or greater than, 850°

C. to superplastically form the integral structure.

25. A method as claimed in claim 24 wherein the integral structure is heated to a temperature between 900°

C. and 950°

C.

26. A method as claimed in claim 9 wherein the integral structure is heated to a temperature of 920°

C. and is isothermally forged at a pressure of up to 16×

10⁶ Nm^-2.

27. A method as claimed in claim 9 wherein the machining of the surfaces of the first, or second, workpieces comprises milling, electrochemical machining, chemical machining or electro discharge machining.

28. A method as claimed in claim 9 wherein the finish machining comprises cutting and finish grinding.

29. A method as claimed in claim 9 wherein the article is a vane manufactured from two workpieces by machining a first portion of the first workpiece at a predetermined distance from a first edge of the first workpiece, machining a second portion of the first workpiece at a predetermined distance from a second opposite edge of the first workpiece, machining a first portion of the second workpiece at a predetermined distance from a first edge of the second workpiece, machining a second portion of the second workpiece at a predetermined distance from a second opposite edge of the second workpiece, assembling the first and second workpieces into a stack such that the flat surfaces are in abutment and the first edges of the workpieces are adjacent each other, the first edges of the workpieces correspond to the leading edge of the vane and the second edges of the workpieces correspond to the trailing edge of the vane.

30. A method as claimed in claim 9 wherein the article is a blade manufactured from three workpieces by machining a first portion of the first workpiece at a predetermined distance from a first edge of the first workpiece, machining a second portion of the first workpiece at a predetermined distance from a second opposite edge of the first workpiece, machining a first portion of the second workpiece at a predetermined distance from a first edge of the second workpiece, machining a second portion of the second workpiece at a predetermined distance from a second opposite edge of the second workpiece, assembling the first, second and third workpieces into a stack such that the flat surface of the first workpiece is in abutment with one flat surface of the third workpiece and the flat surface of the second workpiece is in abutment with an opposite flat surface of the third workpiece, the first edges of the workpieces are adjacent each other, the first edges of the workpieces correspond to the leading edge of the blade and the second edges of the workpieces correspond to the trailing edge of the blade.

31. A method as claimed in claim 9 wherein the article is a vane manufactured from two workpieces by machining a first portion of the first workpiece at a predetermined distance from a first edge of the first workpiece, machining a second portion of the first workpiece at a predetermined distance from a second opposite edge of the first workpiece, assembling the first and second workpieces into a stack such that the flat surfaces are in abutment and the first edge of the first workpiece corresponds to the leading edge of the vane and the second edge of the first workpiece corresponds to the trailing edge of the vane.

32. A method as claimed in claim 9 wherein the article is a blade manufactured from three workpieces by machining a first portion of the first workpiece at a predetermined distance from a first edge of the first workpiece, machining a second portion of the first workpiece at a predetermined distance from a second opposite edge of the first workpiece, assembling the first, second and third workpieces into a stack such that the flat surface of the first workpiece is in abutment with one flat surface of the third workpiece and the flat surface of the second workpiece is in abutment with an opposite flat surface of the third workpiece, the first edge of the first workpiece corresponds to the leading edge of the blade and the second edge of the first workpiece corresponds to the trailing edge of the blade.

33. A method as claimed in claim 9 comprising machining the first or second workpiece centrally of the surface opposite to the flat surface to vary the mass distribution of the first or second workpiece.

34. A method as claimed in claim 9 comprising performing the isothermal forging and superplastic forming steps sequentially in a single die.

35. A method as claimed in claim 34 comprising internally pressurising the contoured integral structure to break the adhesive bond between the stop off material and the at least one workpiece in the preselected areas before the contoured integral structure is isothermally forged.

23. A method as claimed in 22 wherein the workpieces are heated to a temperature between 900°

C. and 950°

C. and the pressure applied is between 20×

10⁵ Nm^-2 and 30×

10⁵ Nm^-2.

36. A method of manufacturing an article comprising the steps of:

(a) producing a plurality of stackable workpieces comprising at least first and second workpieces, the first and second workpieces each having at least one flat surface and a surface intended to form the outside of the finished article, any further workpieces in said plurality of workpieces having two flat surfaces for abutting flat surfaces on the other workpieces,

(b) machining at least a portion of at least one of the surfaces intended to form the outside of the finished article to predefine an edge portion of the finished article,

(c) applying a stop off material to preselected areas of preselected flat surfaces of the workpieces,

(d) assembling the workpieces into a stack so that the flat surfaces of adjacent workpieces are in mating abutment,

(e) applying heat and pressure across the stack of workpieces to diffusion bond the workpieces together in areas of the flat surfaces other than the preselected areas where the stop off was applied, thereby forming an integral structure,

(f) applying heat and pressure to the integral structure to isothermally forge the machined portion on the at least one of the surfaces of the workpieces intended to form the outside of the finished article which form part of the integral structure to substantially produce the required finished peripheral shape and dimensions of the finished article,

(g) heating the integral structure and internally pressurising it to cause the preselected areas of at least one of the workpieces to be superplastically formed to produce an article of predetermined shape,

(i) finish machining the article to remove excess material from the isothermally forged peripheral shape to produce the finished article.