Patent Application
20050121497
1) Field of the Invention
The present invention relates to friction welding and, more specifically, to a tool and method for forming lap joints by friction stir welding.
2) Description of Related Art
Friction stir welding is a process in which a rotating tool, such as a pin or probe, is urged into and/or through a workpiece, e.g., to join multiple structural members of the workpiece in a solid state or to repair cracks in a workpiece. As shown in
Friction stir welding has been demonstrated to be a successful joining method for forming typical butt joints. When forming a butt joint, the pin of the tool is inserted into the workpiece to extend substantially parallel to the interface between the structural members. Thus, the pin makes contact with the workpiece throughout the interface and mixes the material at the interface. During formation of a lap joint, however, the pin is typically inserted in a direction substantially perpendicular to the interface between the structural members. That is, as illustrated in
In addition, friction stir welding of lap joints often results in a “thinning” of one or both of the structural members 20, 22 adjacent to the weld joint 26. Thinning generally refers to a condition in which the interface 24 between the members 20, 22 of a workpiece is deformed, i.e., either lifted or lowered toward the outer surface of a respective one of the members 20, 22. The thickness of the respective member 20, 22, as measured between the interface 24 and the outer surface of the member, is reduced, and the member 20, 22 is therefore subject to an increased risk of failure when stressed.
Conventional friction stir welding tools and methods have been shown to form weld joints in which the material of the workpiece is plasticized and mixed, and the resulting grain structure in the weld joint is refined. However, a need continues to exist for an improved friction stir weld tool and method for sufficiently mixing and refining the workpiece throughout a lap joint. Preferably, the tool and method should be capable of forming a lap joint, in which the joint extends substantially perpendicular through the interface.
The present invention provides a rotatable tool for friction stir welding a workpiece and an associated apparatus and method. The tool includes a first pin portion that extends from a shoulder and second pin portion that extends from the first pin portion. Advantageously, the first pin portion defines a contour surface opposite the shoulder. The contour surface, which mixes the material of the workpiece during welding, can increase the mixing of the material at the interface, thereby increasing the strength of the joint. The tool can also reduce the deformation of the interface. The workpiece can be formed of materials such as aluminum, aluminum alloys, titanium, titanium alloys, copper, copper alloys, magnesium, magnesium alloys, and ferrous alloys.
According to one embodiment of the present invention, the second pin portion extends longitudinally from the contour surface of the first pin portion and the second pin portion has a width in a transverse direction that is smaller than a width of the first pin portion. The contour surface of the first pin portion defines at least one ridge extending in a spiral configuration, e.g., in a continuous spiral configuration from the second pin portion to an outer diameter of the contour surface. The first pin portion can define a cylindrical outer surface, the contour surface can be parallel to the shoulder, and the second pin portion can be tapered in the longitudinal direction away from the contour surface. Further, the second pin portion can define at least one feature extending radially therefrom, such as a generally helical thread extending from an outer surface of the second pin portion.
According to another embodiment, the present invention provides an apparatus for forming a friction stir weld lap joint in a workpiece including first and second structural portions in a lap configuration and defining an interface therebetween. The apparatus includes a rotatable tool that has a shoulder, from which the first and second pin portions extend longitudinally. An actuator is connected to the tool and configured to rotate the tool and urge the tool in a longitudinal direction substantially perpendicular to the interface so that the shoulder is urged against the workpiece. Thus, the first pin portion pin extends at least partially through the first structural portion, and the second pin portion extends at least partially through the second structural portion. The first and second pin portions plasticize a portion of the workpiece and form a friction stir weld lap joint therein. According to one aspect, the first pin portion defines a length in the longitudinal direction that corresponds substantially to a thickness of the first structural portion of the workpiece. Thus, when the shoulder is urged against the first structural portion, the contour surface can be disposed, e.g., within about 0.050 inch, or within about 0.030 inch, from the interface.
The present invention also provides a method for forming a friction stir weld lap joint in a workpiece. The method includes positioning at least one structural member in an overlapping configuration to define an interface between first and second structural portions, rotating the friction stir welding tool, and urging the tool in a longitudinal direction substantially perpendicular to the interface. Thus, the pin extends through the interface. In particular, the first portion of the pin extends longitudinally from the shoulder at least partially through the first structural portion, and the second portion of the pin extends longitudinally from the contour surface of the first pin portion at least partially through the second structural portion. The pin portions thereby plasticize a portion of the workpiece and form a friction stir weld joint therein. The contour surface can be urged to a position near the interface, e.g., within about 0.050 inch from the interface or within about 0.030 inch from the interface.
The foregoing and other advantages and features of the invention, and the manner in which the same are accomplished, will become more readily apparent upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings, which illustrate preferred and exemplary embodiments, but which are not necessarily drawn to scale, wherein:
The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.
Referring now to the drawings and, in particular, to
The structural members 152, 154 can be formed of a variety of materials including, but not limited to, aluminum, aluminum alloys, titanium, titanium alloys, steel, and the like. Further, the workpiece 150 can include members of similar or dissimilar materials, for example, structural members 152, 154 formed of different alloys of a base metal, including alloys that are unweldable or uneconomical to join by conventional fusion welding techniques. Unweldable materials, when joined by conventional fusion welding techniques, produce relatively weak weld joints that tend to crack during weld solidification. Such materials include aluminum and some aluminum alloys, particularly AA series 2000 and 7000 alloys. The use of friction stir welding permits workpieces 150 formed of unweldable materials to be securely joined. Friction stir welding also can be used to securely join weldable materials to other weldable and to unweldable materials. Thus, the materials that form the workpiece 150 can be chosen from a wider variety of light weight, high strength metals and alloys, thereby facilitating reduction of the overall weight of the workpiece 150 and a structural assembly formed therefrom.
The workpiece 150 formed according to the methods of the present invention can be used in a variety of applications, including, for example, frames, panels, skins, airfoils, and the like for aeronautical and aerospace structures such as aircraft and spacecraft, for marine vehicles, automobiles, and the like, as well as for other applications outside of the transportation industry. The friction stir weld joints can be used for joining large workpieces and workpieces having curvilinear geometries. In some applications, the structural members 152, 154 are joined in geometrical configurations that make difficult, or prevent, access to the opposing sides of the workpiece 150. For example, the structural members 152, 154 can be joined to form a partially or fully closed body such as a tube or an airplane wing.
As illustrated in
The tool 110 can also define a shank 114 or other connection portion that can be engaged by a chuck, spindle, or other member of the actuator 140. The actuator 140 can be any of various types of actuating devices, including electric, hydraulic, or pneumatic devices. For example, the actuator 140 can be part of a machine, such as a milling machine or a drill, that is structured for rotating and moving the friction stir welding tool 110. The actuator 140 can be operated manually, but preferably is operated by a computer, microprocessor, microcontroller or other controller, which can be programmed to operate according to a schedule such as a schedule stored in or created by a computer software program.
The shoulder 112 is structured to be urged against the workpiece 150 so that the pin portions 120, 130 are inserted into the workpiece 150, e.g., into the lap interface 156 as shown in
The urging force of the shoulder 112 against the workpiece 150 can be opposed by an anvil or other support device (not shown) positioned opposite the shoulder 112 or by a second shoulder connected to the pin portions 120, 130 and positioned opposite the workpiece 150. Thus, the workpiece 150 can be “sandwiched” between the shoulder 112 and the additional shoulder or support device during friction stir welding. Advantageously, the shoulder 112 and the second shoulder or other support device can create a seal that prevents the plasticized material from being extruded therefrom. Thus, planar or otherwise desired contours can be formed on the opposing sides of the workpiece 150 at the weld joint. The rotating friction stir welding tool 110 can be moved through the workpiece 150 along a predetermined path to thereby form an elongate weld joint. Thus, the material of the workpiece 150 can be mixed by the pin portions 120, 130, and the grain size of the material can be refined, possibly improving the material properties of the material at the joint.
The pin portions 120, 130 stir, or mix, the plasticized material of the workpiece 150 during welding. Advantageously, the surface 122 of the first pin portion 120 opposite the shoulder 112 is contoured and thus facilitates the mixing of the plasticized material. For example, as shown in
During friction stir welding with the tool 110 of the present invention, the contour surface 122 of the first pin portion 120 can assist in plasticizing and dispersing the material of the workpiece 150. In particular, the contour surface 122 can increase the mixing of the material at the interface 156 to improve the quality of the resulting joint. According to one embodiment of the invention, the tool 110 can be structured so that the contour surface 122 is disposed proximate to the interface 156 during welding. That is, the first pin portion 120 can have a length L that corresponds to a thickness T of the first structural member 152 so that the contour surface 122 is disposed proximate to the interface 156 when the shoulder 112 is urged against the workpiece 150. More particularly, the first pin portion 120 can be about as long as the thickness T of the first structural member 152 or slightly longer or slightly shorter than the thickness T of the first structural member 152. The length L of the first pin portion 120 is generally measured between the shoulder 112 and the contour surface 122, including the ridge 124 as shown in
For example,
Similarly,
It is appreciated that the friction stir weld tool 110 can be moved through the workpiece 150 along a path that defines the desired configuration of the friction stir weld joint 160. The path of the tool 110 and, hence, the joint 160 can be formed in any desired configuration in the workpiece 150. In addition, the joint 160 can extend from an edge of the workpiece 150, i.e., by configuring the tool 110 at an edge of the workpiece 150, rotating the tool 110, and urging the tool 110 against and through the workpiece 150. Thus, the shoulder 112 contacts the surface of the workpiece 150, thereby constraining the axial movement of the plasticized material of the workpiece 150, and the pin portions 120, 130 plasticize and mix the material of the workpiece 150. Alternatively, the weld joint 160 can begin or end at a point inward from the edge of the workpiece 150, e.g., by urging, or “plunging,” the tool 110 into the workpiece 150 at the start of the weld joint 160, and/or subsequently retracting the tool 110 therefrom after welding.
Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
