Metal fusion bonding – Process – Using dynamic frictional energy
Reexamination Certificate
2000-02-29
2001-05-29
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
Using dynamic frictional energy
C228S002100
Reexamination Certificate
active
06237835
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to friction stir welding and, more particularly, relates to backing up a weld joint during friction stir welding.
BACKGROUND OF THE INVENTION
Friction stir welding is a relatively new process using a rotating tool, which includes a threaded pin or probe attached to a concave shoulder, to join in a solid state two workpieces or to repair cracks in a single workpiece. At present, the process is applied almost exclusively in straight-line welds. For example, such a process is described in U.S. Pat. No. 5,460,317 to Thomas et al., the contents of which are incorporated herein by reference. As shown in
FIG. 1A
, during friction stir welding, the probe
10
of the rotating tool
12
is plunged into a workpiece or between two workpieces
14
by a friction stir welding machine (not shown) to produce the required resistance force to generate sufficient frictional heating to form a region of plasticized material. As shown in
FIG. 1B
, the tool
12
is typically tilted approximately 3° relative to the workpiece or workpieces
14
such that the trailing edge of the concave shoulder
16
is thrust into and consolidates the plasticized material. Upon solidification of the plasticized material, the workpieces
14
are joined along the weld joint
18
. The magnitude of force exerted by the friction stir welding tool
12
must be maintained above a prescribed minimum in order to generate the required frictional heating.
To prevent deformation of a workpiece by the force exerted by the friction stir welding tool
12
and maintain dimensional tolerances, the workpiece
14
must have support
15
behind the weld joint. Additionally, because the frictional heat generated by the welding tool plasticizes the material within the weld joint, the plasticized material must be constrained to prevent the material from flowing out of the weld joint and also must be consolidated to minimize porosity and provide a weld joint having the desired surface finish. When friction stir welding relatively flat workpieces, the weld joint can be supported by a continuous planar surface, such as a steel plate, positioned underneath the workpieces to be joined.
When friction stir welding large workpieces or workpieces having curvilinear geometries, providing adequate support to the weld joint becomes problematic because the amount of support material necessary and/or the curvilinear geometry makes it more difficult and expensive to provide a continuous support surface. Such welds are often necessary when fabricating military and commercial aircraft and rocket fuel tanks. In certain instances, a built-up structure, commonly referred to as “tooling,” can be secured to the interior surfaces of the workpieces prior to friction stir welding. However, weight restrictions and/or design parameters often require a finished assembly having a smooth interior surface. As such, the tooling must be removed, for example, by machining, which is time consuming and labor intensive and increases the manufacturing cost of the finished assembly.
Thus, there is a need for an improved backing device for weld joints formed by friction stir welding large workpieces or workpieces having curvilinear geometries. The backing device should be capable of effectively supporting a weld joint and constraining the plasticized material within the weld joint during friction stir welding. Additionally, the backing device should be easily adaptable to varying workpiece geometries and sizes.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and an associated method for backing up weld joints formed by friction stir welding. The self-backing friction stir welding tool includes a rotatable shoulder adapted to at least partially engage the weld joint. The backing device also includes a probe having first and second ends and an intermediate portion therebetween. At least a portion of the intermediate portion of the probe is capable of frictionally engaging the workpiece to form the weld joint. The first end of the probe defines a backing member, at least a portion of which engages the weld joint opposite the rotatable shoulder. Advantageously, the second end of the probe is adapted to rotatably and axial translatably communicate with the rotatable shoulder to thereby rotate the probe and urge the backing member toward the weld joint, thus constraining the plasticized material within the weld joint. According to one embodiment, the shoulder defines a threaded aperture and the probe defines a plurality of threads that are in rotatable and axial translatable communication with the threaded aperture of the shoulder to thereby rotate the probe and urge the backing member toward the weld joint. The backing member can be contoured to correspond to the contour of the workpiece.
The backing member can include an anchor, such as a ball joint, and a support member, at least a portion of which engages the weld joint opposite the rotatable shoulder. Advantageously, the support member defines a recess for receiving the anchor and wherein the anchor urges the support member toward the workpiece and maintains the support member in this position. In one embodiment, the recess of the backing member includes a plurality of thrust bearings to rotatably receive the anchor. The support member can include at least one pair of rollers that are rotatable such that the support member is movable relative to the workpiece.
The backing device can also include a carriage that defines an aperture therethrough for rotatably mounting the rotatable shoulder at an angle relative to the workpiece. The carriage can include at least one pair of rollers that are rotatably secured to the carriage such that the carriage is movable relative to the workpiece.
The present invention also provides an apparatus for friction stir welding a weld joint in a workpiece. According to one embodiment, the friction stir welding device includes a milling machine having a spindle in rotatable communication with a shoulder adapted to at least partially engage the weld joint formed in the workpiece to consolidate the plasticized material within the weld joint. The friction stir welding device also includes a probe having first and second ends and an intermediate portion therebetween. At least a portion of the intermediate portion of the probe is capable of frictionally engaging the workpiece to form the weld joint. The first end of the probe defines a backing member, at least a portion of which engages the weld joint opposite the shoulder. Advantageously, the second end of the probe is adapted to rotatably and axial translatably communicate with the rotatable shoulder to thereby rotate the probe and urge the backing member toward the weld joint. According to one embodiment, the shoulder defines a threaded aperture and the probe defines a plurality of threads that are in rotatable and axial translatable communication with the threaded aperture of the shoulder to thereby rotate the probe and urge the backing member toward the weld joint. The backing member can be contoured to correspond to the contour of the workpiece.
The backing member can include an anchor, such as a ball joint, and a support member, at least a portion of which engages the weld joint opposite the rotatable shoulder. Advantageously, the support member defines a recess for receiving the anchor and wherein the anchor urges the support member toward the workpiece and maintains the support member in this position. In one embodiment, the recess of the backing member includes a plurality of thrust bearings to rotatably receive the anchor. The support member can include at least one pair of rollers that are rotatable such that the support member is movable relative to the workpiece.
The friction stir welding device can also include a carriage that defines an aperture therethrough for rotatably mounting the rotatable shoulder at an angle relative to the workpiece. The carriage can include at least one pair of rollers that are rotatable such that the carriage is movable relative to the workp
Litwinski Edward
Syms Bert E.
Alston & Bird LLP
Dunn Tom
Stoner Kiley
The Boeing Company
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