Metal fusion bonding – Process – Using dynamic frictional energy
Reexamination Certificate
2000-04-10
2001-07-03
Ryan, Patrick (Department: 1725)
Metal fusion bonding
Process
Using dynamic frictional energy
C228S119000, C228S203000, C228S112100, C029S402010, C029S402180
Reexamination Certificate
active
06253987
ABSTRACT:
REFERENCE TO A “MICROFICHE APPENDIX”
Not applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to friction welding. More particularly, the present invention provides an improved method and apparatus of friction plug welding that employs a specially configured pull plug that enhances bonding and that is suitable for flight hardware usage.
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. Also incorporated herein by reference are U.S. Pat. No. 5,718,366 and all references disclosed therein. The following references are also 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; German Patent No. 447,084, “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.
Friction plug welding (FPW), also referred to as plug welding and friction taper plug welding (FTPW), is a process in which initial defective weld material is located, removed and replaced by a tapered plug, which is friction welded into place. This process is similar to friction stud welding, in which a plug is welded to the surface of a plate, end of a rod, or other material. The primary difference is that FPW is designed to replace a relatively large volume of material containing a defect whereas friction stud welding is a surface-joining technique.
Friction plug welding could be used to repair weld defects in a wide variety of applications; however, it would most likely be used where weld strength is critical. This is due to the fact that manual weld repairs result in strengths much lower than original weld strengths, as opposed to friction plug welds (FPWs) whose typical mechanical properties exceed that of the initial weld. In applications where high strength is not required, manual welding would be less expensive and would not require specialized equipment.
An extension of FPW is known as stitch welding or friction tapered stitch welding (FTSW) and has been developed to repair defects longer than what a single plug can eliminate. Stitch welding is the linear sequential welding of several plugs such that the last plug weld partially overlaps the previous plug. Defects of indefinite length can be repaired with this process, limited only to the time and cost of performing multiple plug welds. These welds have undergone the same testing procedures as single FPWs, including NDI and destructive evaluation. The strengths for stitch welds are similar to those for single plug welds.
Stagger stitch welding is a process best defined as stitch welding in a non-linear fashion. Areas wider than one plug length can be completely covered by staggering plugs side to side as they progress down the length of an initial weld. This process is being developed for plug welds whose minor diameter is on the crown side of the initial weld, and where replacement of the entire initial weld is desired.
While friction plug welding might be a preferred method of repairing defects or strengthening initial welds, there are some applications where heretofore it has been extremely difficult to use friction plug welding. The main cause is due to the logistics of setting up the equipment and/or support tooling to perform friction plug welding, and the geometry of the workpiece to be welded.
BRIEF SUMMARY OF THE INVENTION
The present invention provides an improved method and apparatus for friction plug welding an article using a plug that has an improved configuration and geometry that facilitates a good weld when the plug is pulled.
With previous pull plug designs (which typically did not include an angular transition), the plug top usually did not weld to the plate top in 0.385″ gage plate. This lack of bonding resulted in penetrant, x-ray defects, and ultrasonic indications at the plug top, ultimately leading to a reduction in tensile strength. Since a friction pull plug welding (FPPW) process that produces defects would not be considered for usage on flight hardware, the defects along the interface have to be eliminated.
The “Top Hat” plug design of the present invention ensures complete bonding between the plug and the plate on the inside skin line (ISL) side of the weld. The top hat achieves this improvement through a combined effect of supplying additional material to frictionally heat at the plug top end portion, as well as providing additional radial and axial pressure at plug top. Overall weld quality is significantly improved with the addition of the “Top Hat” to a plug, through the elimination of all top side defects as characterized through NDE evaluation (Dye Penetrant, X-Ray, and Ultrasonic), and through a higher tensile strength weld interface.
Listed below are typical and exemplary dimensions of a “top hat” plug design; a {fraction (3/16)}″ radius is utilized in the curved annular surface transition from the plug body to the “top hat”; the plug top hat has a diameter of 1.250″ to 1.480″ extending out from the body by 0.050″ to 0.250″; the plug hat has a thickness of 0.020″, however the thickness can range up to 0.100″ thick.
The present invention includes a method of friction plug welding an article, comprising several stages. Preferably, the first stage is making a hole (that is preferably tapered) in the article to be welded. Machining a tapered hole is not necessarily required in friction plug push welding where (in certain situations generally characterized when the article to be welded is softer (having lower hardness) relative to the harder (having higher hardness) plug) the plug will form a hole, self bore or embed into the material either while rotating or not. A tapered plug is inserted through the tapered hole. The plug is then attached to a chuck of a rotary tool or like motor which can both pull on the tapered plug and rotate it. Some connector or connection means, such as threads, key grooves, flats, or locking retention interface, are provided on the tapered plug to facilitate pulling the plug with the rotary tool.
The second stage, or heating cycle is always required to weld the plug to the article. This stage preferably consists of rotating the plug while pulling (placing the plug in tension axially) into intimate contact with the hole's surface, or region surrounding the hole. The typical axial load exerted on the plug during the heating phase is between about 1000 pounds and 20,000 pounds, preferably between about 6000 pounds and 18,000 pounds, more preferably 10,000 pounds to 16,000 pounds, and most preferably 12,500 pounds to 15,000 pounds.
Other forms of heating may also be utilized, including but not limited to, using electricity to assist in the heating process, or vibrational energy such as oscillatory rotation rather than the preferred method of continuous rotation, or lateral, axial or some combination thereof, rapid displacement (such as ultrasonic welding) to impart sufficient energy to assist in the heating the weldment. The plug (preferably tapered, with a taper the same as or preferably different from the taper of the hole (if it is tapered), and rotating the plug relative to the part while moving the plug in the direction such to make contact with the hole's surface, until contact is made, and forcing the plug into the surface of the hole by pulling on the plug (imposing a tensile for
Cantrell Mark A.
Coletta Edmond R.
Cooke Colleen P.
Garvey, Smith, Nehrbass & Doody LLC
Lockheed Martin Corporation
Ryan Patrick
LandOfFree
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