FSW tool design for thick weld joints

Details FSW tool design for thick weld joints FSW tool design for thick weld joints

1998-04-30

2001-05-08

Ryan, Patrick (Department: 1725)

Metal fusion bonding

Including means to provide heat by friction between...

C228S112100, C156S073500, C411S412000

Reexamination Certificate

active

06227430

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to friction stir welding, and more particularly, to friction stir welding tool designs and a method for forming thick friction stir weld joints.
BACKGROUND OF THE INVENTION
Friction stir welding (FSW) is a relatively new welding process for joining together parts of materials such as metals, plastics, and other materials that will soften and commingle under applied frictional heat to become integrally connected. A detailed description of the FSW apparatus and process may be found in Patent Publications WO 93/10935 and WO 95/26254; and U.S. Pat. No. 5,460,317, all of which are hereby fully incorporated by reference. One of the useful apparatus for FSW is shown in
FIGS. 1A and 1B
. As shown, two parts, exemplified by plates
10
A′ and
10
B′, are aligned so that the edges of the plates to be welded together are held in direct contact on a backing plate
12
′. An FSW tool W has a shoulder
14
′ at its distal end, and a nonconsumable welding pin
16
′ extending downward centrally from the shoulder. As the rotating tool W′ is brought into contact with the interface between plates
10
B′ and
10
A′, the rotating pin
16
′ is forced into contact with the material of both plates, as shown. The rotation of the pin in the material and rubbing of the shoulder against the upper surface of the material produce a large amount of frictional heating of both the welding tool and the plate interface. This heat softens the material of the plates in the vicinity of the rotating pin and shoulder, causing commingling of material which, upon hardening, forms a weld. The tool is moved longitudinally along the interface between plates
10
A′ and
10
B′, thereby forming an elongate weld along the interface between the plates. The welding tool's shoulder
14
′ prevents softened material from the plates from escaping upward, and forces the material into the weld joint. When the weld is completed, the welding tool is retracted.
Nonconsumable welding pin
16
′ can have a threaded surface. When a pin with a threaded surface is used, the pin is typically rotated in a negative direction, i.e., in a screwing-out direction, to enhance shearing of workpiece material into particles. This occurs because a threaded pin rotated in a positive direction, i.e., in a screwing-in direction, tends not to generate enough frictional heat to form a satisfactory FSW. A pin rotated in a negative direction, however, encounters greater resistance than a pin without threads or a pin rotated in a screwing-in direction, and thus requires a greater vertical load to drive the pin into workpieces. As the thickness of the workpieces that are welded together increases, the thickness of the weld joint increases. In order to form thicker weld joints, the FSW pin must penetrate more deeply into the workpieces, and a vertical load applied to drive the pin must be increased accordingly. There is a limit, however, to the amount of vertical load that can be applied to the FSW tool, and thus a limit to the depth the pin can be driven into workpieces. A need exists for a friction stir welding tool design that is suitable for penetrating farther into workpieces to form a thicker weld joint without overloading the tool.
SUMMARY OF THE INVENTION
The present invention provides a novel pin design for a friction stir welding (FSW) tool that enables the pin to penetrate more deeply into workpieces that require such penetration to form satisfactory weld joints. The design of the pin includes features that cooperate with the rotation of the pin to complement the vertical load, and encourage penetration of the pin into the workpieces. A pin formed in accordance with the present invention includes threads on its surface that are of a positive hand, termed “positive threads”. The term “positive threads” means threads provided on a pin that screw in to draw the pin into workpieces when the pin is rotated. Conversely, the term “negative threads” means threads on a pin that screw out to oppose drawing-in of the pin when the pin is rotated.
One embodiment of the pin design includes negative threads at its distal and proximal ends, and positive threads between the ends. As the pin is rotated and plunged into workpieces, the negative threads on the pin enhance shearing of workpiece material into particles, while the positive threads on the same pin encourage penetration of the pin into the workpieces. Another embodiment of the pin design includes a combination of positive threads and flat surfaces. In both embodiments, the positive threads complement the vertical load required to drive the pin into workpieces. Accordingly, the pin design of the present invention allows the pin to penetrate more deeply into workpieces to form a thicker weld joint without overloading the welding tool.
Preferably, the pin diameter is decreased from its proximal end to its distal end, either discretely in steps or linearly in a tapering manner, to further ease penetration of the pin. The decrease in diameter further reduces the amount of transverse welding load required to traverse the pin along the workpieces interface to form an elongate weld.
The invention also provides a method of forming thicker friction stir weld joints by reducing the amount of vertical welding load required to drive a welding pin more deeply into workpieces. The method includes providing a FSW tool pin having positive threads and either negative threads or flat surfaces, and rotating and driving the pin into workpieces while the positive threads cooperate with the rotation of the pin to complement the vertical load required to drive the pin.


REFERENCES:
patent: 310229 (1885-01-01), Seely
patent: 4018132 (1977-04-01), Abe
patent: 4144110 (1979-03-01), Luc
patent: 4534690 (1985-08-01), Barth
patent: 4907989 (1990-03-01), Huska
patent: 4959241 (1990-09-01), Thomas et al.
patent: 5098237 (1992-03-01), Harker
patent: 5262123 (1993-11-01), Thomas et al.
patent: 5460317 (1995-10-01), Thomas et al.
patent: 5469617 (1995-11-01), Thomas et al.
patent: 5624067 (1997-04-01), Harwig et al.
patent: 5718366 (1998-02-01), Colligan
patent: 6029879 (2000-02-01), Cocks
patent: 6053391 (2000-04-01), Heideman et al.
patent: 2 306 366 (1997-05-01), None
patent: WO 93/10935 (1993-06-01), None
patent: WO 95/26254 (1995-10-01), None
TWI Bulletin, “Friction stir—where we are, and where we're going . . . ”, Thomas, Dawes, Gittos, Andrews, May/Jun. 1998.*
Rockwell Science Center, “Friction Stir Welding”, Deinken, Jul. 20, 1999.*
Kaiser Aluminum & Chemical Corporation, Metals Research, Henry Yang, “Hot Friction Stir Welding of Aluminum Alloys”, Jan. 10, 1998.*
Thomas, W.M., et al., “Emergent Friction Joining Technologies for the Non-ferrous Casting Industry,” TWI, BCIRA International Conference, 1996, pp. 30-1 through 30-12.

Affiliated with

Also associated with

Rating

FSW tool design for thick weld joints does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with FSW tool design for thick weld joints, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and FSW tool design for thick weld joints will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2534239