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Tool and apparatus for friction stir welding

Tool and apparatus for friction stir welding description/claims

This application is a continuation of U.S. application Ser. No. 10/991,578 filed Nov. 18, 2004, which is a divisional of U.S. application Ser. No. 10/237,506 filed Sep. 9, 2002, which claimed the benefit of U.S. Provisional Application No. 60/376,758 filed Apr. 29, 2002, all of which are hereby incorporated herein in their entirety by reference.

1. Field of the Invention

The present invention relates to friction welding and, more specifically, to backing up a weld joint during friction stir welding.

2. Description of Related Art

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.

Another problem that has been encountered with friction stir welding occurs when joining workpieces formed of different materials having different material properties, such as solidus temperature, hardness, and/or thermal conductivity. The “solidus” temperature of a particular alloy is the temperature below which only a solid is stable. The different material properties can require that the friction stir welding tool be rotated within each workpiece at different rotational speeds and/or have different rates of tool advance through the workpieces, which can complicate the friction stir welding process and can limit the types of materials that can be joined. For example, when friction stir welding workpieces with different solidus temperatures, the friction stir welding tool will plasticize the workpiece with the lower solidus temperature first, such that the workpiece with the higher solidus temperature may not be sufficiently plasticized to be mixed with the other workpiece, as is necessary to form a strong weld joint.

Thus, there is a need for an improved friction stir welding tool for forming weld joints between large workpieces or workpieces having curvilinear geometries. The tool should be capable of effectively supporting a weld joint and constraining the plasticized material within the weld joint during friction stir welding and should be easily adaptable to varying workpiece geometries and sizes. In addition, the tool should allow for friction stir welding workpieces having different material properties.

The present invention provides a tool for forming a friction stir weld joint in a workpiece. According to one embodiment of the present invention, the tool includes a rotatable pin having first and second ends and defining a stirring portion therebetween structured to frictionally engage the workpiece so as to at least partially form the friction stir weld joint. The tool includes a rotatable first shoulder defining an aperture therethrough structured to slidably receive the first end of the pin. The tool also includes a second shoulder defining an aperture structured to receive the second end of the pin such that the pin extends between the first and second shoulders and such that the second shoulder is in rotatable communication with the pin. The first shoulder is structured to rotate independently of the pin and the second shoulder. In one embodiment, the first and second shoulders are structured to opposingly support the workpiece during friction stir welding. In another embodiment, the second shoulder defines a plurality of fins adapted to transfer heat away from the weld joint.

According to another embodiment of the present invention, the tool includes a rotatable pin having first and second ends and defining a stirring portion therebetween structured to frictionally engage the workpiece so as to at least partially form the friction stir weld joint. The tool includes a rotatable first shoulder defining an aperture therethrough structured to slidably receive the first end of the pin. The tool also includes a second shoulder defining an aperture structured to receive the second end of the pin such that the pin extends between the first and second shoulders and such that the second shoulder is in rotatable communication with the pin. At least one of the first and second shoulders has a surface defining at least one raised portion structured to frictionally engage the workpiece so as to at least partially form the friction stir weld joint. The first and second shoulders are structured to opposingly support the workpiece during friction stir welding. In one embodiment, the first shoulder is structured to rotate independently of the pin and the second shoulder. In another embodiment, the second shoulder defines a plurality of fins adapted to transfer heat away from the weld joint.

According to another embodiment of the present invention, the tool includes a rotatable pin having first and second ends and defining a stirring portion therebetween structured to frictionally engage the workpiece so as to at least partially form the friction stir weld joint. The tool includes a rotatable first shoulder defining an aperture therethrough structured to slidably receive the first end of the pin. The tool also includes a second shoulder defining an aperture structured to receive the second end of the pin such that the pin extends between the first and second shoulders and such that the second shoulder is in rotatable communication with the pin. The second shoulder defines a plurality of fins adapted to transfer heat away from the weld joint. In one embodiment, the first and second shoulders are structured to opposingly support the workpiece during friction stir welding. In another embodiment, the first shoulder is structured to rotate independently of the pin and the second shoulder.

The stirring portion of the pin can comprise a variety of configurations. For example, in one embodiment, the stirring portion of the pin defines at least one planar surface. In another embodiment, the stirring portion of the pin defines at least one threaded surface and at least one planar surface. In still another embodiment, the stirring portion of the pin comprises a first threaded surface having threads oriented in a first direction and a second threaded surface having threads oriented in a second direction, and wherein the first direction is different from the second direction.

The first and second shoulders each has a surface structured to frictionally engage the workpiece to thereby at least partially form the friction stir weld joint. For example, in one embodiment, at least one of the surfaces of the first and second shoulders is threaded. In another embodiment, at least one of the surfaces is convex. In still another embodiment, at least one of the surfaces is concave. In yet another embodiment, at least one of the surfaces defines at least one raised portion structured to frictionally engage the workpiece.

The pin can be connected to the second shoulder in a variety of different ways. For example, in one embodiment, at least a portion of the second end of the pin is threaded. Similarly, at least a portion of the aperture of the second shoulder is threaded so as to threadably receive the second end of the pin. In another embodiment, the second end of the pin has a polygonal configuration and the aperture of the second shoulder has a polygonal configuration corresponding to the configuration of the second end of the pin.

The present invention also provides an apparatus for forming a friction stir weld joint in a workpiece. According to one embodiment, the apparatus includes a machine having a spindle defining a rotatable inner portion and a rotatable outer portion. The apparatus includes a friction stir welding tool. In one embodiment, the friction stir welding tool includes a pin having first and second ends and defining a stirring portion therebetween structured to frictionally engage the workpiece so as to at least partially form the friction stir weld joint. The first end of the pin is in rotatable communication with the inner portion of the spindle. The friction stir welding tool includes a first shoulder defining an aperture therethrough structured to slidably receive the first end of the pin. The first shoulder is in rotatable communication with the outer portion of the spindle. The friction stir welding tool also includes a second shoulder defining an aperture structured to receive the second end of the pin such that the pin extends between the first and second shoulders and such that the second shoulder is in rotatable communication with the pin. The first shoulder is structured to rotate independently of the pin and the second shoulder. As described above, many variations and modifications of the friction stir welding tool and first and second shoulders are possible.

The present invention also provides a method of friction stir welding a workpiece. According to one embodiment of the present invention, the method comprises positioning first and second shoulders adjacent the workpiece. Each of the first and second shoulders has a surface structured to frictionally engage the workpiece. A pin is connected to the first and second shoulders so that the pin extends therebetween. The pin defines a stirring portion structured to frictionally engage the workpiece. Thereafter, the first shoulder is rotated at a first angular velocity and the pin and the second shoulder are rotated at a second angular velocity different from the first angular velocity so that at least a portion of each of the pin, first shoulder, and second shoulder frictionally engages the workpiece to thereby form a friction stir weld joint. The stirring portion of the pin can be moved through the workpiece along a predetermined path.

According to another embodiment of the present invention, the method includes positioning first and second shoulders adjacent the workpiece. Each of the first and second shoulders has a surface structured to frictionally engage the workpiece. A pin is connected to the first and second shoulders so that the pin extends therebetween. The pin defines a stirring portion structured to frictionally engage the workpiece. The first shoulder is rotated. Concurrently with the first rotating step, the pin and the second shoulder are rotated independently of the first shoulder so that at least a portion of each of the pin, first shoulder, and second shoulder frictionally engages the workpiece to thereby form a friction stir weld joint. For example, the first and second rotating steps can include rotating the first shoulder at a first angular velocity and the pin and the second shoulder at a second angular velocity, wherein the second angular velocity is different from the first angular velocity. As used herein, “angular velocity” includes both a speed component and a direction component. The direction component is positive for motion following the “right hand rule,” i.e., counter-clockwise motion, and is negative for motion in the opposite direction, i.e., clockwise motion. The stirring portion of the pin can be moved through the workpiece along a predetermined path.

• Provisional Patent
• Utility Patent

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