Tapered friction stir welding tool

Details Tapered friction stir welding tool Tapered friction stir welding tool

2002-05-07

2003-12-30

Elve, M. Alexandra (Department: 1725)

Metal fusion bonding

Including means to provide heat by friction between...

Means to rotate one surface relative to the other about a...

C228S002100, C228S112100, C228S114500

Reexamination Certificate

active

06669075

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed generally toward friction stir welding and, more particularly, toward an improved tool for use in friction stir welding processes.
BACKGROUND OF THE INVENTION
Friction stir welding is a process that makes use of frictional heat, which includes the heat generated between a rotating, non-consumable pin and workpieces and the heat generated as a result of plastic work from the workpiece material being strained and mixed, to weld the workpieces together. The produced frictional heat plasticizes the workpiece materials and consolidates them to create one piece of material where there were originally two. Friction stir welding is used for joining together various parts of materials, such as metals, plastics, and other materials that will soften and consolidate under applied frictional heat to become integrally connected. While friction stir welding has been commonly applied to butt joints and corner joints, it can also be applied to lap joints and other types of joints, as well as for eliminating or closing cracks in a given material and for joining together two sides of a material to form a hollow section, such as a tube.
A prior art apparatus for friction stir welding is shown generally in FIG.
1
. The apparatus
10
is rotatable about an axis
12
, and includes a support body
14
and a non-consumable pin
16
extending from a distal end of the support body
14
. As shown in
FIG. 1
, two workpieces
18
and
20
are aligned so that the edges of the workpieces to be welded together are held in direct contact at an interface
22
. As the rotating apparatus
10
is brought into contact with the interface
22
between the workpieces
18
and
20
, the rotating pin
16
is forced into contact with the material of both workpieces
18
and
20
, as shown in FIG.
1
. The pin
16
is inserted into the material of the workpieces
18
and
20
until a flat shoulder
24
at the distal end of the support body
14
contacts the upper surface of the workpieces
18
and
20
. As the apparatus
10
is moved through the material, the rotation of the pin
16
in the material and the rubbing of the flat shoulder
24
against the upper surface of the workpieces
18
and
20
, as well as the resultant plastic work from the workpiece material being strained and mixed, produces a large amount of frictional heat in the vicinity of the workpiece interface
22
. This frictional heat softens the material of the workpieces
18
and
20
in the vicinity of the rotating pin
16
and shoulder
24
creating a plasticized region and causing commingling of the material which, upon hardening, forms a weld
26
. As the apparatus
10
is moved longitudinally along the interface
22
, the weld
26
is formed along the interface
22
between the workpieces
18
and
20
, thereby joining the workpieces
18
and
20
together. The flat shoulder
24
of the support body
14
prevents softened material from the workpieces from escaping upward, and forces the material into the plasticized region. When the weld is completed, the apparatus
10
is removed.
Prior art friction stir welding tools require minimal differences in workpiece thickness across the weld joint. Thus, fluctuations in the thickness of the workpieces at their interface may compromise the integrity of the weld formed by friction stir welding processes. Similarly, prior art friction stir welding tools require that the position of the tool be precisely controlled relative to the upper surface of the workpieces in order to generate sufficient frictional heat to adequately plasticize the material. Failure to generate sufficient frictional heat will also compromise the integrity of the weld joint.
Additionally, for prior art bobbin-type friction stir welding tools, the pin and back shoulder must be precisely controlled relative to the back surface of the workpieces. Thus, the pin must be independently movable axially relative to the front shoulder, e.g., support body
14
, of the friction stir welding tool.
The present invention is directed toward overcoming one or more of the above-mentioned problems.
SUMMARY OF THE INVENTION
A friction stir welding tool is provided, according to the present invention, for joining together workpieces utilizing friction stir welding processes. The inventive tool includes a support body rotatable about a first axis and having a distal end defining a shoulder. A rotatable pin extends from the distal end of the support body downward from the shoulder. The shoulder of the support body includes at least one section that is tapered, with the taper extending downward toward the pin.
In one form of the present invention, the shoulder includes a face having at least one groove formed therein. The at least one groove may include either a spiral formed groove or a plurality of concentric grooves formed in the face of the shoulder.
In another form of the present invention, the shoulder includes a substantially flat section and a tapered section having a taper extending downward toward the pin. The substantially flat and tapered sections are concentric and displaced radially from the pin to the outer edge of the support body. Preferably, the substantially flat section is provided adjacent the pin, and the tapered section is provided adjacent the outer edge of the support body. However, an opposite arrangement of the sections may be utilized.
In yet another form of the present invention, the shoulder includes first and second tapered sections. The first tapered section has a first taper extending downward toward the pin. The first taper is formed at a first angle referenced from a plane perpendicular to the first axis. The second tapered section has a second taper also extending downward toward the pin. The second taper is formed at a second angle, greater than the first angle, referenced from a plane perpendicular to the first axis. The first and second tapered sections are concentric and displaced radially from the pin to the outer edge of the support body. Preferably, the first tapered section is provided adjacent the pin, and the second tapered section is provided adjacent the outer edge of the support body. However, an opposite arrangement of the sections may be utilized.
In still another form of the present invention, the shoulder additionally includes a third tapered section having a third taper extending downward toward the pin. The third taper is formed at a third angle, different than the first and second angles, referenced from a plane perpendicular to the first axis. The first, second and third tapered sections are concentric and displaced radially from the pin to the outer edge of the support body. Preferably, the second angle is greater than both the first and third angles, with the first tapered section provided adjacent the pin, the third tapered portion provided adjacent the outer edge of the support body, and the second tapered section provided between the first and third tapered sections However, alternate arrangements of the sections may be utilized.
The third angle may be greater than or equal the first angle. In a further form of the present invention, the first angle is substantially 0°, such that the first tapered portion is substantially flat.
In an additional form of the present invention, each of the first, second, and third tapered sections includes a face having at least one groove formed therein. The at least one groove formed in each of the first, second and third section faces may include either a spiral formed groove or a plurality of concentric grooves. In one form, the grooves are formed normal to the respective planes of the first, second and third section faces.
In an alternate embodiment of the present invention, the friction stir welding tool further includes a bottom support member connected to a distal end of the pin, such that the pin is disposed between the support body and the bottom support member. In this embodiment, the inventive tool is configured as a bobbin-type friction stir welding tool. The bottom support member is also rotatable a

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