Airfoil fabrication

• US 4,042,162 A
• Filed: 07/11/1975
• Issued: 08/16/1977
• Est. Priority Date: 07/11/1975
• Status: Expired due to Term

• Current Assignee: Allison Engine Company, Inc. (Rolls-Royce Holdings Plc)
• Original Assignee: General Motors Corporation (General Motors Company)
• Inventors: Meginnis, George B., Sodeberg, Earl W.
• Primary Examiner(s): Smith, Al Lawrence
• Assistant Examiner(s): Ramsey, K. J.
• Application Number:
  US05/595,025
• Time in Patent Office: 767 Days
• Field of Search: 29/156.8 R, 29/156.8 B, 29/156.8 H, 29/156.8 P, 29/447, 29/448, 228/193, 228/194, 228/195, 228/106, 228/127, 228/173, 228/243, 228/212, 228/213
• US Class Current: 228/106
• CPC Class Codes: B23K 20/00 Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
• CPC Class Codes: B23K 20/02 by means of a press ; Diffusion bonding B23K20/001, B23K20/04 take precedence
• CPC Class Codes: B23K 20/14 Preventing or minimising gas access, or using protective gases or vacuum during welding formed by material interposed between workpieces B23K20/18
• CPC Class Codes: B23K 2101/001 Turbines
• CPC Class Codes: F01D 5/182 Transpiration cooling
• CPC Class Codes: Y10T 29/49341 with cooling passage

Abstract

A method of bonding a laminated porous sheath to a cast strut includes the step of performing a compressible pad to have a plurality of closely spaced grooves on one surface thereon and a plurality of spaced apart lands on the opposite face thereof; locating a preformed porous laminate sheath over the outer surface of a cast strut and laser welding it thereto and thereafter assembling the preformed compressible pad to locate the plurality of grooves thereon in overlying relationship to a plurality of airflow openings in the porous laminated sheath and with ribs on either side of the grooves being located in juxtaposed relationship with the outer surface of the porous laminated sheath for uniformly distributing a load thereto; locating the preassembled casting, sheath and compressible pad within a contoured opening formed by a three piece pressure block fixture and applying a predetermined pressure to the assembled parts while subjecting them to a predetermined bond temperature while applying a vacuum.

Claims

1. A method for bonding a laminated structure to a cast airfoil strut comprising:

preforming a cast airfoil strut to have a leading edge, a trailing edge and first and second walls joining the leading edge to the trailing edge and the walls having cooling passages therethrough, preforming a laminated metallic sheath having an exterior surface and an inner surface each with a plurality of pin hole openings formed therein for communicating the wall cooling passages in the cast airfoil strut with the exterior surface of the sheath, wrapping said sheath by locating its inner surface over the first and second walls of said cast airfoil strut from the leading edge to the trailing edge and tack welding a portion thereon to the leading edge of said cast airfoil strut, preforming one side of a compressible pressure pad with a plurality of ribs and grooves each formed on the one side to extend completely across one length of the pad, preforming the opposite side of the compressible pressure pad to have a plurality of spaced apart separate lands, wrapping the pressure pad on the outer surface of the laminated metallic sheath to locate the plurality of ribs and grooves in contact across the full planar extent of the exterior surface of the laminated sheath including the full height thereof, thereafter placing the wrapped compressible pressure pad, laminated sheath and cast airfoil strut between the contoured pressure blocks and applying a predetermined load to deform the separate lands and to press the plurality of ribs thereon against the exterior surface of the laminated sheath for distributing load to the laminated sheath without deformation thereof, applying a vacuum to the pressure loaded pieces and maintaining a bonding temperature thereon, directing outgas flow from between the cast airfoil strut and laminated sheath outwardly along the grooves formed in the one side of the compressible pad along the full height of the cast airfoil strut during the bonding operation, the inner surface of the laminated sheath being bonded to the outer surface of the cast airfoil strut by the pressure directed thereagainst across the grooved surface of the pressure pad without interruption of the gas flow through the grooves.

2. A process for diffusion bonding a thin metallic porous laminated sheath to an airfoil casting having a leading edge, a trailing edge and first and second surfaces joining the leading and trailing edges, by means of a plurality of contoured pressure blocks having a cavity therein comprising the steps of;

wrapping the metallic porous laminated sheath on the outer surface of the casting completely across the first and second surfaces from the leading to trailing edge, tacking a predetermined segment of the metallic sheath to the casting, preforming a compression pad with an inner and outer surface to have a plurality of transverse ribs and grooves formed longitudinally and completely across an inner surface portion thereof and to further have a separate plurality of compressible lands on the outer surface thereof, positioning the ribs and grooves on the inner surface in overlaying juxtaposed relationships with the outer surface of the wrapped metallic laminated porous sheath to provide communication between the grooves and pores in the metallic porous laminated sheath for outgasing of air trapped between the casting and sheath, supporting the compressible lands on the outer surface of the compression pad along the contour of the pressure blocks and applying pressure from the blocks thereagainst to produce deformation of the lands on the compressible pad, and a transfer of loading through the ribs of the pad against the outer surface of the metallic porous sheath to maintain the metallic sheath in intimate contact with the outer surface of the casting for a predetermined bond period, maintaining the pressure block cavity under vacuum to draw air from between the sheath and the pad along the full longitudinal interface therebetween, concurrently maintaining an elevated temperature during maintenance of the vacuum to produce a bonded interface between the inner surface of the laminated sheath and the casting without deformation of the laminated sheath.

3. A method for thermally bonding a metallic sheath on the outer surface of a casting of the type having a plurality of ribs formed thereon with transverse openings in communication with a plurality of valleys between each of the grooves and wherein the metallic sheath includes inner and outer surfaces with a plurality of pin point openings therein to communicate the valleys with the exterior surface of the metallic sheath comprising:

the steps of wrapping the metallic sheath on the outer surface of the casting to maintain the inner surface thereof in intimate contact with each of the ribbed outer surface portions of the casting, preforming a pressure relief and compression pad with an inner and outer surface and of a softer material than that of the sheath and including a plurality of outgas grooves and ribs on the inner surface thereof with each rib and groove extending completely across the longitudinal extent of the pad, also preforming the pad to have a plurality of reinforcing ribs, and a plurality of spaced lands on the outer surface, locating the grooves in the inner surface of the pad to produce a predetermined spacing therebetween to locate an outgas groove in communication will all the pin point openings of the sheath when the pad is in place thereon, placing the wrapped pad, sheath and casting within spaced-apart pressure blocks with a cavity therebetween with the spaced lands on the outer surface of the pad being located in alignment with an inner surface of the pressure blocks, applying a predetermined load to the blocks sufficient to produce a controlled deformation of each of the spaced lands on the outer surface of the compression pad while distributing a bonding pressure through the ribs on inner surface of the compression pad across the full outer planar extent of the metallic sheath, maintaining a vacuum on the cavity between the pressure blocks to draw gas from the pad and sheath along the full longitudinal interface therebetween through the grooves and concurrently maintaining the compressed parts under an elevated temperature to produce a diffusion bond between the outer ribs surface of the casting and the inner surface of the metallic sheath.