Metal fusion bonding – Process – Using dynamic frictional energy
Reexamination Certificate
2002-08-12
2004-08-24
Stoner, Kiley (Department: 1725)
Metal fusion bonding
Process
Using dynamic frictional energy
C244S119000, C244S13500B, C428S615000
Reexamination Certificate
active
06779707
ABSTRACT:
REFERENCE TO A “MICROFICHE APPENDIX”
Not applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the manufacture of aircraft, space vehicles and the like wherein panels are connected using friction stir welding. More particularly, the present invention relates to the construction of aircraft, space vehicles and the like wherein an improved method enables stringer stiffened panels to be joined with friction stir lap welds, in replacement of the traditional riveting practice.
2. General Background of the Invention
Friction stir welding (FSW) is a solid state joining process developed by The Welding Institute (TWI), Cambridge, England and described in U.S. Pat. No. 5,460,317, incorporated herein by reference. Compared with traditional fusion welding processes, it offers simplified processing, improved mechanical properties, diminished weld defect formation, equivalent corrosion resistance, and reduced distortion, shrinkage, and residual stresses. Using conventional milling equipment with a backside anvil support, a non-consumable, cylindrical pin tool is rotated and plunged into the butt or lap joint of the material to be welded. Pin tools are specifically designed for a given alloy and gauge. Also incorporated herein by reference are U.S. Pat. No. 5,718,366 and all references disclosed therein. The following additional references of possible interest are incorporated herein by reference: U.S. Pat. Nos. 3,853,258, 3,495,321, 3,234,643, 4,087,038, 3,973,715, 3,848,389; British Patent Specification No. 575,556; SU Patent No. 660,801; and German Patent No. 447,084. Publications that discuss friction stir welding include “New Process to Cut Underwater Repair Costs”, TWI Connect, No. 29, January 1992; “Innovator's Notebook”, Eureka Transfer Technology, October 1991, p. 13; “Repairing Welds With Friction-Bonded Plugs”, NASA Tech. Briefs, September 1996, p. 95; “Repairing Welds With Friction-Bonded Plugs”, Technical Support Package, NASA Tech. Briefs, MFS-30102; “2195 Aluminum-Copper-Lithium Friction Plug Welding Development”, AeroMat '97 Abstract; “Welding, Brazing and Soldering”, Friction welding section: “Joint Design”, “Conical Joints”, Metals Handbook: Ninth Edition Vol. 6, p. 726. A publication authored by applicants is entitled “Friction Stir Welding as a Rivet Replacement Technology”; Brian Dracup and William Arbegast; SAE Aerofast Conference, Oct. 5, 1999.
BRIEF SUMMARY OF THE INVENTION
The present invention provides an improved method of constructing structures such as aircraft using friction stir welding, to thereby replace the traditional riveting practice of previously unweldable aluminum alloys. Possible applications include the intertank of the External Tank of the Space Shuttle and airplane manufacturing.
Friction Stir Welding is a Solid State joining process that now allows the welding of previously unweldable aluminum alloys. Traditionally, these aluminum alloys have found use only in mechanically joined structures such as in aircraft and space vehicles. The present invention provides a method of joining overlapped panels using friction stir welding, replacing the traditional riveting practice The method of the present invention is a viable, and cost reducing alternative to aluminum riveted structures.
The present invention features a non-consumable friction stir weld pin tool (see
FIGS. 1-4
) that is preferably constructed of H13 tool steel. The tool is rotated, plunged, and traversed along the stringer flanges of a stringer-skin panel to produce a friction stir lap weld. The tool is preferably tilted at an angle of about 2½ degrees.
As the pin tool initially plunges into the weld jointline, the material is frictionally heated and plasticized at a temperature below that of the alloy's melting temperature and typically within the material's forging temperature range. When the metal becomes sufficiently soft and plastic, and the appropriate penetration depth has been reached, the tool is traversed along the weld line. As the tool is traversing, metal flows to the back of the pin tool where it is extruded/forged behind the tool. It then consolidates and cools under hydrostatic pressure conditions [2-8].
Unlike fusion welding processes in which there are numerous inputs to the welding schedule, friction stir welding requires only three: spindle speed (RPM), travel speed (IPM), and the penetration depth of the tool in the material (heel plunge or penetration ligament). Penetration depth can be monitored either through load control or displacement [9].
The present invention thus discloses a method and apparatus that uses a friction stir welding tool that fully penetrates through the top sheet and partially penetrates into the bottom sheet. The material around the pin tool is frictionally heated, plasticized, and extruded/forged to the back of the pin where it consolidates and cools under hydrostatic pressure conditions.
Friction stir lap welding stringer-skin panels will eliminate the inter-rivet buckling commonly seen on mechanically joined structures and consequently, increase the buckling strength of the vehicle. In addition, the present invention enables simpler processing as compared with the traditional riveting practice by replacing any touch labor required with an automated process. Eliminating the rivets and other associated parts will also reduce quality control and material handling issues. Consequently, friction stir welding will increase production build rates and reduce production costs. Overall vehicle weight will also be decreased by eliminating the rivets and their associated parts.
REFERENCES:
patent: 3234643 (1966-02-01), Hollander
patent: 3495321 (1970-02-01), Shaff et al.
patent: 3848389 (1974-11-01), Gapp et al.
patent: 3853258 (1974-12-01), Louw et al.
patent: 3973715 (1976-08-01), Rust
patent: 4087038 (1978-05-01), Yagi
patent: 5460317 (1995-10-01), Thomas et al.
patent: 5718366 (1998-02-01), Colligan
patent: 5813592 (1998-09-01), Midling et al.
patent: 5862975 (1999-01-01), Childress
patent: 5975406 (1999-11-01), Mahoney et al.
patent: 6045027 (2000-04-01), Rosen et al.
patent: 6050474 (2000-04-01), Aota et al.
patent: 6053391 (2000-04-01), Heideman et al.
patent: 6070784 (2000-06-01), Holt et al.
patent: 6105902 (2000-08-01), Pettit
patent: 6247633 (2001-06-01), White et al.
patent: 6247634 (2001-06-01), Whitehouse
patent: 6328261 (2001-12-01), Wollaston et al.
patent: 6450394 (2002-09-01), Wollaston et al.
patent: 477084 (1929-05-01), None
patent: 575566 (1946-02-01), None
patent: WO 98/58759 (1998-12-01), None
patent: 411047959 (1999-02-01), None
patent: 660-801 (1979-05-01), None
“New Process to Cut Underwater Repair Costs”, TWI Connect, No. 29, Jan. 1992.
“Innovator's Notebook”, Eureka Transfer Technology, Oct. 1991, p. 13.
“Repairing Welds with Friction-Bonded Plugs”, NASA Tech Briefs, Sep. 1996, p. 95.
“Repairing Welds with Friction-Bonded Plugs”, Technical Support Package, NASA Tech. Briefs, MFS-30102.
“2195 Aluminum-Cooper-Lithium Friction Plug Welding Development”, AeroMat '97 Abstract.
“Welding, Brazing and Soldering”, Friction Welding Section: “Joint Desing”, “Conical Joints”, Metals Handbook: Ninth Edition, vol. 6, pp. 719-738.
Why aren't Airplanes Welded?, Bob Irving, Welding Journal, Jan. 1997, pps 31-41 and drawing.
Arbegast William J.
Dracup Brian J.
Garvey, Jr. Charles C.
Garvey, Smith, Nehrbass & Doody LLC
Lockheed Martin Corporation
Nehrbass Seth M.
Stoner Kiley
LandOfFree
Friction stir welding as a rivet replacement technology does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Friction stir welding as a rivet replacement technology, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Friction stir welding as a rivet replacement technology will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3305108