초록 ▼

A method for cold working metal structures. A compound indenter is used to produce deformation in a workpiece, to provide a selected beneficial residual stress profile, to provide improved fatigue life structures with minimal manufacturing steps. A compound indenter deforms a workpiece, resulting in

A method for cold working metal structures. A compound indenter is used to produce deformation in a workpiece, to provide a selected beneficial residual stress profile, to provide improved fatigue life structures with minimal manufacturing steps. A compound indenter deforms a workpiece, resulting in dimples therein. A relatively uniform beneficial residual stress profile is provided at the surface and at the midplane of apertures in a workpiece, so as to improve overall fatigue life. A compound indenter tool having a first, elongate indenter with a shaped indenter surface portion, and a second shaped indenter surrounding the first indenter and forming an annular shoulder recessed from the surface portion of the first indenter, is used. Optionally, a foot having a bottom portion is used to confiningly surround an indenter during application of deforming force to the surface of a workpiece, to prevent deformation of adjacent workpiece surface.

대표청구항 ▼

The invention claimed is: 1. A method for working a bounding portion of material in a structure, said bounding portion adjacent a pre-selected location for an opening through said structure, in order to provide residual compressive stresses in said bounding portion for improving the fatigue life of

The invention claimed is: 1. A method for working a bounding portion of material in a structure, said bounding portion adjacent a pre-selected location for an opening through said structure, in order to provide residual compressive stresses in said bounding portion for improving the fatigue life of said structure, said method comprising: providing a first compound indenter, said first compound indenter comprising a first indenter surface portion, said first indenter surface portion adapted to impact said structure at pre-selected surface locations adjacent said pre-selected location for said opening through said structure, and a second indenter surface portion, said second indenter surface portion adapted to impact said structure at pre-selected surface locations adjacent said pre-selected location for said opening through said structure; said first indenter surface portion spaced apart from said second indenter surface portion; and indenting said pre-selected surface location of said structure with said first compound indenter to provide said residual compressive stresses in bounding portion of material. 2. The method as set forth in claim 1, further comprising removal of a selected portion of material from said structure, said selected portion of material removed from said structure having an outer border portion, said outer border portion located at or adjacent to said pre-selected surface location on said structure having been impacted by said first indenter surface portion and said second indenter surface portion of said first compound indenter, so that said bounding portion of material expands transversely to said outer border portion of said selected portion of material removed from said structure. 3. A method for working a bounding portion of material in a structure, said bounding portion adjacent a pre-selected location for an opening through said structure, in order to provide residual compressive stresses in said bounding portion for improving the fatigue life of said structure, said method comprising: providing a first compound indenter, said first compound indenter comprising: a first indenter surface portion, said first indenter surface portion adapted to deform said structure at pre-selected surface locations adjacent said pre-selected location for said opening through said structure, and a second indenter surface portion, said second indenter surface portion adapted to deform said structure at pre-selected surface locations adjacent said pre-selected location for said opening through said structure; said first indenter surface portion spaced apart from said second indenter surface portion; and deforming said pre-selected surface location of said structure with said first compound indenter to provide residual stress in said bounding portion of material, wherein said bounding portion is adjacent to said pre-selected location for said opening through said structure. 4. The method as set forth in claim 3, further comprising removal of a selected portion of material from said structure, said selected portion of material removed from said structure having an outer border portion, said outer border portion located at or adjacent to said pre-selected surface location on said structure having been deformed by said first indenter surface portion and said second indenter surface portion of said first compound indenter, so that said bounding portion of material expands transversely to said outer border portion of said selected portion of material removed from said structure. 5. The method as set forth in claim 1 or claim 3, wherein said first compound indenter comprises a dynamic indenter. 6. The method as set forth in claim 2 or claim 4, wherein removal of said selected portion of material from said structure defines an elongated recessed portion. 7. The method as set forth in claim 6, wherein said elongated recessed portion comprises a closed end portion. 8. The method as set forth in claim 2 or claim 4, wherein removal of said selected portion of material from said structure defines a through passageway. 9. A method of manufacturing a joint which includes overlapping at least first and second structural members, said method comprising: (a) contacting a preselected portion of said first structural member with a first compound indenter at a pressure greater than the yield point of the composition of said structural member to deform a portion of said first structural member in a manner so as to impart a pre-selected residual stress at a location at or near a selected location for a first fastener aperture through said first structural member, and wherein said residual compressive force is substantially uniform along the entire length of sidewall portions of said first fastener aperture; (b) machining said first structural member to define said first fastener aperture via sidewall portions resulting from said machining; (c) providing in said second structural member, a second fastener aperture defined by second sidewall portion; (d) inserting a fastener through said first and said second fastener apertures; (e) securing said fastener. 10. The method of claim 9, further comprising the step of applying force or displacement to said fastener to seat said fastener within said first and said second fastener apertures. 11. The method of claim 10, wherein the step of seating said fastener further comprises deforming an end portion of said fastener in order to secure and retain said fastener against said first structural member. 12. The method as set forth in claim 9, wherein the depth of indentation on the obverse and the reverse side is different. 13. The method as set forth in claim 9, further comprising, post indentation, the step of drilling a hole into or through said workpiece. 14. The method as set forth in claim 13, wherein said step of drilling comprises a drilling step selected to provide a finished hole selected from the group consisting of (a) straight through hole, (b) stepped hole, (c) a blind hole, (d) a countersink hole, (e) a non-round or non-circular hole. 15. The method as set forth in claim 14, further comprising the step of threading the hole. 16. The method as set forth in claim 9, further comprising (a) contacting a preselected portion of said second structural member with a first compound indenter at a pressure greater than the yield point of the composition of said second structural member to deform a portion of said second structural member in a manner so as to impart a pre-selected residual stress at a location at or near a selected location for said second fastener aperture through said second structural member, and wherein said residual compressive force is substantially uniform along the entire length of sidewall portions of said second fastener aperture. 17. The method as set forth in claim 13, wherein said step of drilling comprises a drilling step selected to provide a finished hole selected from the group consisting of (a) straight through hole, (b) stepped hole, (c) a blind hole, (d) a countersink hole, and (e) a non-round or non-circular hole. 18. A method for manufacturing a workpiece for having an enhanced fatigue life structure, said workpiece having a first surface, a second surface, a thickness of material therebetween, and at least a first pre-selected location at which a hole having an edge location is to be fabricated in said workpiece, said method comprising: (a) securing said workpiece at a first working location, said first working location suitable for press forming work on said workpiece; (b) deforming a pre-selected location on said workpiece by indenting said workpiece at said pre-selected location with a compound indenter having a first indenter surface portion and a second indenter surface portion, said first indenter surface portion spaced apart from said second indenter surface portion. to create residual compressive stresses through said thickness of said material of said workpiece along said hole edge location; and (c) machining an aperture in said workpiece to provide said hole in said workpiece. 19. The method of claim 18, wherein the deformation of said workpiece results in a residual compressive stress along said hole edge location through said material thickness of said workpiece, from said first surface of said workpiece to said second surface of said workpiece. 20. The method of claim 18, further comprising the steps of: (a) determining desired application of stress and strain in said workpiece during said indentation step, by using finite-element analysis of the workpiece and the relationship of residual stress as a function of the material of the workpiece as well as of the applied force and indenter shape; and (b) selecting an appropriate indenter shape and applied force to form the workpiece while avoiding surface upset on the workpiece. 21. The method as set forth in claim 1, or in claim 3, or in claim 9, or in claim 18, wherein said first compound indenter further comprises a first foot portion. 22. The method as set forth in claim 21, wherein said first foot portion applies a load to said workpiece sufficient to substantially avoid surface upset in said workpiece. 23. The method as set forth in claim 22, wherein said load applied to said workpiece is applied prior to impacting or deforming said workpiece. 24. The method of claim 18, wherein said method of manufacturing involves advancing said workpiece incrementally in a machine to position said workpiece to the repetitive action of one or more selected compound indenters, to thereby create desirable residual compressive stress at a plurality of pre-selected locations, and machining an aperture at a plurality of said pre-selected locations, so as to provide a plurality of holes in said workpiece each having improved fatigue life by virtue of having residual compressive stress along at least a portion of an edge wall of said hole. 25. The method as set forth in claim 24, wherein said residual compressive stress is provided along the entire hole edge wall throughout the thickness of said workpiece between said first surface and said second surface. 26. A joint comprising: (a) a stack of structural members including: (1) a first member having a body made of material having a bounding portion of material substantially perpendicular to a first fastener aperture in which the first fastener aperture defined by a first edge wall portion is conditioned by the method of claim 1, or of claim 3, or of claim 18, wherein said bounding portion of the material provides a residual, radially inward, substantially uniform compressive stress to the first edge wall portion, and (2) a second member having a second fastener aperture defined by a second edge wall portion, said second fastener aperture aligned with said first fastener aperture; and (b) an interference fit fastener including a shank portion, said shank portion located adjacent said first fastener aperture and adjacent said second fastener aperture, and wherein said first fastener aperture provides residual compressive stresses around said shank. 27. A method for manufacturing a workpiece for having an enhanced fatigue life structure, said workpiece of the type having a first surface, a second surface, a thickness of material therebetween, and at least a first pre-selected location at which a hole having an edge location is to be fabricated in said workpiece, said method comprising: (a) securing said workpiece at a first working location, said first working location suitable for press forming work on said workpiece; (b) deforming a preselected location on said workpiece by indenting said workpiece at said preselected location with a compound indenter defined by a first indenter surface portion spaced apart from a second indenter surface portion, to create residual compressive stresses through said thickness of said material of said workpiece along said desired hole edge location; (c) machining an aperture in said workpiece to provide said hole in said workpiece; (d) wherein the deformation of said workpiece results in a predetermined zero hoop stress profile, after reaming, substantially as set forth in FIG. 10. 28. A method for making a thick metal part in which holes are to be fabricated at predetermined locations, said part having first and second surfaces and a thickness of material therebetween, said method comprising the steps of: (a) providing a thick metal plate (b) applying a controlled strain and/or stress rate at at least one of said predetermined locations at which holes are to be formed, by indenting said part with a compound indenter, said indenter of the type having a primary indenter, a secondary indenter, a tertiary indenter, and a foot, by actuating a ram against said first surface of said part; and (c) machining the indented part to remove material to shape a hole and thus convert the thick metal plate into a finished part. (d) wherein the manufacture forming greatly reduces the handling necessary by allowing said hole to be fabricated by a single drilling operation to provide a hole in a desired configuration in the finished part. 29. The method of claim 28, wherein forming occurs with the zero hoop stress relationship as a function of dimple depth substantially as set forth in FIG. 10. 30. The method as set forth in claim 28, wherein said foot applies a load to said workpiece sufficient to substantially avoid surface upset in said workpiece. 31. A joint comprising: (a) a stack of structural members including: (1) a first member having a body made of material in which a first fastener aperture defined by a first edge wall portion is conditioned by the method of claim 9, or of claim 28 to have a residual, radially inward compressive stress adjacent the first edge wall portion, and wherein said first member has a first surface which is substantially perpendicular to said first edge wall portion of said first fastener aperture; (2) a second member having a second fastener aperture defined by a second edge wall portion, said second fastener aperture aligned with said first fastener aperture; and (b) an interference fit fastener including a shank portion, said shank portion located adjacent said first fastener aperture and adjacent said second fastener aperture, and wherein said first fastener aperture provides residual compressive stresses around said shank. 32. The joint as set forth in claim 31, wherein said second edge wall portion in said second member is conditioned to have radially inward compressive residual stress. 33. The joint as set forth in claim 31, wherein said interference fit fastener comprises a flush type rivet further comprising a countersunk portion, and wherein said residual compressive stress is applied through said body of said first member along said countersunk portion of said rivet. 34. The joint as set forth in claim 33, wherein said interference fit fastener comprises a rivet having a straight shank portion, and wherein said residual compressive stress is applied substantially uniformly through said body of said first member along said first edge wall portion. 35. A joint comprising: (a) a stack of structural members comprising (1) a first member having a body made of material in which a first fastener aperture defined by a first edge wall portion is conditioned by the method of claim 1, or of claim 3, or of claim 9, or of claim 18, or of claim 28, to have a residual, radially inward compressive stress, and wherein said first member has a first surface which is substantially perpendicular to said first edge wall portion of said first fastener aperture; (2) a second member having a second fastener aperture defined by a second edge wall portion, said second fastener aperture aligned with said first fastener aperture; and (b) one or more fasteners, said one or more fasteners securely affixing said first member to said second member. 36. The joint as set forth in claim 34, wherein said second edge wall portion in said second member is conditioned to have radially inward compressive residual stress. 37. The joint as set forth in claim 31, wherein said joint further comprises, between said first and said second members, a sealing compound. 38. The joint as set forth in claim 31, wherein said joint further comprises, between said first and said second members, a cured sealant. 39. The joint as set forth in claim 31, wherein said joint further comprises, between said first and said second members, a bonding compound. 40. The joint as set forth in claim 31, wherein said joint comprises two members. 41. The joint as set forth in claim 31, said joint comprises at least three members. 42. A metal plate structure that is manufactured for enhanced fatigue life, said structure having a first surface, a second surface, a thickness of material therebetween, and at least a first preselected location at which a hole having an edge location is to be fabricated, said metal plate structure having a bounding area adjacent said edge location, said metal plate structure manufactured using a method comprising: (a) securing said metal plate structure at a first working location, said first working location suitable for press forming work on said metal plate structure; (b) indenting a pre-selected location on said metal plate structure by indenting said metal plate structure at said preselected location with a compound indenter, in said bounding area a substantially uniform residual compressive stresses through said thickness of said material of said metal plate structure along said hole edge location; (c) machining an aperture in said metal plate structure to provide said hole in said metal plate structure; and (d) wherein said metal plate structure has a first surface which is substantially perpendicular to said hole edge location. 43. The metal plate structure as set forth in claim 42, wherein said metal plate structure is manufactured by a method wherein said deformation of said metal plate structure in a predetermined zero hoop stress profile, after reaming, substantially as set forth in FIG. 10. 44. The metal plate structure as set forth in claim 42, wherein said metal plate structure is manufactured by a method wherein said deformation of said metal plate structure results in a residual compressive stress along said hole edge location through said material thickness of said metal plate structure, from a first surface of said metal plate structure to a second surface of said metal plate structure. 45. An article of manufacture comprising: a finished metal part, said finished metal part comprising a metal plate having first and second surfaces and a thickness of material therebetween, said metal plate having predetermined locations at which holes are fabricated therein, said metal part comprising material bounding the predetermined locations, wherein said material bounding the predetermined locations provides a radially inward compressive stress toward the predetermined locations, said metal plate manufactured according to a method comprising the steps of: (a) providing the metal plate; (b) applying a controlled strain and/or stress rate at, at least one of said predetermined locations at which holes are to be formed, by indenting said metal plate with a compound indenter, said indenter of the type having a primary indenter, a secondary indenter, a tertiary indenter, and a foot, by actuating a ram against said first surface of said metal plate; (c) machining the indented metal plate to remove material to shape a hole having an edge wall portion, and thus convert the metal plate into a finished metal part; and (d) wherein said holes are fabricated by a single drilling operation to provide a hole in a desired configuration in said finished metal part, and (e) wherein said first surface is substantially perpendicular to said edge wall portion. 46. The part of claim 45 wherein the finished metal part comprises aluminum. 47. A method of manufacturing a joint which includes overlapping at least first and second structural members, said method comprising: (a) contacting a pre-selected portion of said first structural member with a first compound indenter at a pressure greater than the yield point of the composition of said first structural member to deform a portion of said first structural member in a manner so as to impart a pre-selected residual compressive stress at a location at or near a selected location for a first fastener aperture through said first structural member, and wherein said pre-selected residual compressive stress is substantially uniform along the entire length of sidewall portions of said first fastener aperture; (b) machining said first structural member to define said first fastener aperture via sidewall portions resulting from said machining; (c) providing in said second structural member, a second fastener aperture defined by second sidewall portion; (d) inserting a fastener through said first and said second fastener apertures; and (e) securing said fastener to said first and to said second structural members, to for a workpiece comprising a secure, fastened joint between said overlapping first and second structural members. 48. The method as set forth in claim 47, wherein said first structural member comprises a first obverse side, and wherein said second structural member comprises a first reverse side, and further wherein the depth of indentation on the obverse side and the depth of an indentation on the first reverse side is different. 49. The method as set forth in claim 47, further comprising, contacting a pre-selected portion of said second structural member with a first compound indenter at a pressure greater than the yield point of the composition of said second structural member to deform a portion of said second structural member in a manner so as to impart a pre-selected residual compressive stress at a location at or near a selected location for said second fastener aperture through said second structural member, and wherein said pre-selected residual compressive stress is substantially uniform along the entire length of sidewall portions of said second fastener aperture. 50. A method for making a thick metal part in which holes are to be fabricated at predetermined locations, said part having first and second surfaces and a thickness of material therebetween, said method comprising the steps of: (a) providing a thick metal plate; (b) applying a controlled strain and/or stress rate at, at least one of, said predetermined locations at which holes are to be formed, by indenting said part with a compound indenter, said indenter of the type having a primary indenter, a secondary indenter, a tertiary indenter, and a foot, by actuating a ram against said first surface of said part; (c) machining the indented part to remove material to shape a hole and thus convert the thick metal plate into a finished part; and (d) wherein the manufacture forming greatly reduces the handling necessary by allowing said hole to be fabricated by a single drilling operation to provide a hole in a desired configuration in the finished part. 51. The method as set forth in claim 50, wherein said foot applies a load to said part sufficient to substantially avoid surface upset in said part.