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Friction stir nut and method of joining therewithRelated Patent Categories: Metal Fusion Bonding, Process, Using Dynamic Frictional Energy (i.e., Friction Welding)Friction stir nut and method of joining therewith description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060175381, Friction stir nut and method of joining therewith. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] The present disclosure relates generally to friction stirring and a method of joining therewith, particularly to a friction stir nut and a friction stir rivet nut, and a method of joining therewith. [0002] Friction stir welding (FSW) is a method used to join metal workpieces that generally uses a cylindrical shouldered tool with a profiled pin that is rotated at the joint line between two workpieces while being traversed along the joint line. The rotary motion of the tool generates frictional heat that serves to soften and plasticize the workpieces. As the pin moves laterally, the softened material, contributed by both workpieces, intermingles in the wake of the traversing pin and cools and hardens due to the absence of further frictional stirring, creating a bond between the two workpieces. [0003] Recent advances in friction stir processes have extended the FSW technique to friction stir riveting (FSR), where a stir rivet is rotated and advanced into an arrangement of workpieces to be joined such that the material of the workpieces plasticizes around the rivet during the friction stirring, and then hardens around the rivet when the body of the rivet stops rotating and the workpieces and rivet are allowed to cool. [0004] Both of the aforementioned processes result in a bonded workpieces. However, in some instances it may be desirable to both bond the workpieces and provide a means for receiving additional hardware. Accordingly, there is a need in the art to further advance the technology of friction stir bonding in a manner that offers opportunities for the addition of supplementary features and capabilities through the use of additional hardware at the point of bonding. BRIEF DESCRIPTION OF THE INVENTION [0005] Embodiments of the invention include a friction stir nut suitable for friction stir welding to a workpiece via a mandrel tool. The friction stir nut includes a body, a cap, and an anti-rotation feature. The body has an elongated cylindrical shank extending between a first end and a second end, the cap being disposed at the second end, and the anti-rotation feature being disposed at the cap, at an outer surface of the body, or at both. The body and cap have a blind axial hole extending from the first end to the second end, the first end being blind and the second end being open. The outer surface of the first end has a flat surface oriented substantially perpendicular to the axis of the shank, and the body has a cylindrical wall thickness suitable for receiving internal threads. In response to the mandrel tool friction stir welding the friction stir nut to the workpiece and then the mandrel tool being extracted from the friction stir nut, uniform internal threads result at the body, and the anti-rotation feature bonds to the workpiece by metallurgical bonding, mechanical bonding, or both. [0006] Other embodiments of the invention include a friction stir rivet nut suitable for friction stir welding to a workpiece via a mandrel tool. The friction stir rivet nut includes a body, a cap, and an anti-rotation feature. The body has an elongated cylindrical shank extending between a first end and a second end, a first portion proximate the first end, and a second portion proximate the second end. The first portion has a first nominal cylindrical wall thickness, and the second portion has a second nominal cylindrical wall thickness that is less than the first nominal cylindrical wall thickness. The cap is disposed at the second end, and the anti-rotation feature is disposed at the cap, at an outer surface of the body, or at both. The body and cap have a blind axial hole extending from the first end to the second end, the first end being blind and the second end being open. The first end has internal threads, and the outer end surface of the first end has a flat surface oriented substantially perpendicular to the axis of the shank. [0007] Further embodiments of the invention include a method of friction stir welding an embodiment of the aforementioned friction stir rivet nut to workpieces via a mandrel. The mandrel is threadably engaged with the rivet nut, the rivet nut is positioned at a point of engagement of the workpieces, the mandrel is rotated about its rotational axis, and the rivet nut driven toward and into the workpieces such that resultant frictional heating between the rivet nut and the workpieces causes the materials of the workpieces to soften at a process temperature thereby providing a friction stirred displaceable path for the rivet nut to traverse. The rivet nut is driven along the displaceable path until the cap is seated against or partially into the workpieces. Further rotation of the mandrel is stopped and the workpieces and rivet nut are allowed to cool below the process temperature, thereby permitting the softened workpieces to harden. The mandrel is axially loaded with sufficient force such that the second portion of the body buckles at an opposite side of the workpieces to that of the cap, and the mandrel is rotationally extracted such that uniform internal threads result at the first portion. BRIEF DESCRIPTION OF THE DRAWINGS [0008] Referring to the exemplary drawings wherein like elements are numbered alike in the accompanying Figures: [0009] FIGS. 1 and 2 depict in cross section longitudinal view exemplary friction stir rivet nuts in accordance with embodiments of the invention; and [0010] FIGS. 3A-F depict an exemplary friction stir riveting method in accordance with embodiments of the invention. DETAILED DESCRIPTION OF THE INVENTION [0011] Embodiments of the invention disclose a friction stir nut and a friction stir rivet nut having a body with an elongated cylindrical shank and a cap at one end. The body and cap have an axial blind hole extending from the cap (the open end) to the end of the shank (the blind end). The outer end of the body at the blind end has a flat surface that engages the workpieces to be joined, thereby providing a friction stir surface that has a reduced tendency to undesirably displace the softened friction stirred material sideways in the joint between the workpieces. The shank of the body may have internal threads in place prior to friction stir welding, or may have a suitable wall thickness for receiving internal threads via a tapping operation during and/or subsequent to friction stir welding. In a friction stir nut, the nominal cylindrical wall thickness of the body may be uniform, whereas in a friction stir rivet nut, the nominal cylindrical wall thickness is reduced in a region proximate the cap, thereby enabling a pulling operation on the body to buckle the cylindrical wall of the body on an opposite side of the workpieces to that of the cap. The method of joining two or more workpieces using the friction stir nut or friction stir rivet nut may be accomplished in the absence of a preexisting hole in the workpieces to be joined. [0012] FIG. 1 depicts a cross section view of an exemplary embodiment of a friction stir nut 100 having a body 105 with an elongated cylindrical shank (generally depicted by numeral 105) extending between a first end 110 and a second end 115, and a cap 120 at the second end 115. As used herein, reference numeral 100 refers to both a friction stir nut and a friction stir rivet nut, with the distinction between the two being more specifically described later. The body 105 and/or cap 120 may have anti-rotation features, such as scallops 125, projections 130, recesses 135, through holes 140 (best seen by referring to FIG. 2), or any combination of the foregoing. While the shapes of the anti-rotation features are depicted circular, they may be of any shape suitable for the purposes disclosed herein, such as geometrical indentation recesses and associated geometrical elevated features from a knurling operation for example. Accordingly, a combination of projections 130 and recesses 135 is herein considered representative of a knurl. While FIGS. 1 and 2 depict anti-rotation features 130, 135 and 140 only in certain areas, it will be appreciated that these features may be uniformly placed around the body 105 and cap 120, may be non-uniformly placed, may be all of one type, or may be of mixed types. For example, the anti-rotation features at the cap 120 may include one or multiple scalloped sections 125 at the perimeter of the cap 120, projections 130 at the underside of the cap 120, recesses 135 at the underside of the cap 120, and/or through-holes 140 at the cap. Similarly, the anti-rotation features at an outer surface of the body 105 may include one or multiple projections 130, recesses 135, and/or a knurl 130, 135. The body 105 and cap 120 have a blind axial hole 145 extending from the first end 110 to the second end 115, the first end 110 being blind and the second end 115 being open. The outer end surface of the first end 110 has a flat surface 150 oriented substantially perpendicular to the axis 155 of the shank 105. In an embodiment, the flat surface 150 of rivet nut 100 is flat to within plus-or-minus two degrees of perpendicular relative to axis 155. [0013] Referring now to FIGS. 1 and 2 in combination, body 105 has a cylindrical wall thickness "t" suitable for receiving internal threads 160, which may be cut into body 105 prior to friction stir welding, or cut via a tapping operation during or subsequent to friction stir welding, which will be discussed in more detail later. As can be seen in FIG. 2, the flat surface 150 may only be a portion of the available flat surface from outside diameter D of body 105. In an embodiment, the flat surface 150 has a diameter equal to or greater than about 80% of diameter D. [0014] In an embodiment of a friction stir rivet nut 100, where it is desirable for the body to buckle during a pulling operation thereby providing a rivet-like compressive load on the workpieces, the body 105 includes a first portion 165 and a second portion 170. The first portion 165 has a first nominal cylindrical wall thickness "t" suitable for receiving internal threads, and the second portion 170 has a second nominal cylindrical wall thickness "d" that is less than the first nominal cylindrical wall thickness, thereby resulting in the second portion 170 having a compressive strength that is less than the compressive strength of the first portion 165. The first portion 165 is proximate the first end 110 and the second portion 170 is proximate the second end 115. In response to a mandrel tool 210, best seen by referring to FIG. 3, friction stir welding the friction stir rivet nut 100 to the workpieces 200, and then the mandrel tool 210 being pulled (see description relating to FIG. 3D), the second portion 170 of the body 105 buckles at an opposite side of the workpiece to that of the cap 120. As will now be appreciated, a friction stir rivet nut differs from a friction stir nut by the presence of the second portion 170 having a nominal wall thickness "d" that is allowed to buckle to provide a rivet-like compressive load on the workpieces 200. [0015] Referring now to FIGS. 3A-F, six exemplary frames of a method for friction stir welding a friction stir rivet nut 100 to workpieces 200 via a mandrel tool 210 are depicted. Workpieces 200 may be a sheet 202 placed on top of a tubular structure 204 for example, may be a single part for example, may be a solid block of metal such as aluminum for example, or may be any other set of materials desired to be and suitable to be friction stir welded using a friction stir nut or friction stir rivet nut 100. In all embodiments of FIGS. 3A-F, workpieces 200 are supported in a suitable fashion. [0016] In FIG. 3A, the mandrel 210 is threadably engaged with the rivet nut 100 and positioned at the desired point of engagement with the workpieces 200. While not shown, it will be appreciated that mandrel 210 is connected to a rotary machine for providing the desired rotation and driving action for friction stir welding. In an embodiment, mandrel 210 is driven at a rotational speed of about 12,000 revolutions per minute (rpm), and at an axial downward speed of about 12 millimeters per minute (mm/min). [0017] In FIG. 3B, mandrel 210 is rotated 215 about its rotational axis, which is the same as axis 155, and the rivet nut 100 is driven toward and into the workpieces 200 such that resultant frictional heating between the rivet nut 100 and the workpieces 200, and more particularly frictional heating initiated by the friction stir interaction between the flat surface 150 of the rivet nut 100 and the workpieces 200, causes the materials of the workpieces 200 to soften at a friction stir process temperature, thereby providing a friction stirred displaceable path for the rivet nut 100 to traverse. In an embodiment, the friction stir process temperature is greater than 20 deg-C. and less than or equal to the melt temperature of the workpieces 200. Where the workpieces 200 are aluminum, the process temperature is less than or equal to about 660 deg-C., for example, and in an embodiment where the workpieces 200 are thermoplastic, the process temperature is less than the melt temperature of the respective thermoplastic. The rivet nut 100 is driven along this displaceable path until the cap 120 is seated against or partially embedded into the workpieces 200. In this manner of friction stirring, the rivet nut 100 may be driven into workpieces 200 absent a preexisting hole in the workpieces 200. While it may be possible to rotate and drive rivet nut 100 at sufficient speed and rate to cause melting of workpieces 200, it is contemplated that rotating and driving rivet nut 100 to cause softening of workpieces 200 is sufficient for producing a suitable joint. In an embodiment, mandrel 210 is rotated at a speed of about 12,000 rpm and is driven at a rate of equal to or greater than about 6 mm/min and equal to or less than about 150 mm/min. However, it is contemplated that rotational speeds of equal to or less than about 12,000 rpm may be suitable for the purposes disclosed herein. As a result of the rotational speed in combination with the drive rate, the friction heating initiated between the flat surface 150 of rivet nut 100 and the surface of workpiece 202, a friction stir process temperature is established that results in the softening of workpieces 200, and preferably but not necessarily results in softening without melting. As discussed previously, the process temperature is that temperature between room temperature and the melt temperature of workpieces 200 at which the workpieces 200 are soft enough to provide a displaceable friction stir path for rivet 100 to traverse. In an embodiment, the process temperature is substantially less than the melt temperature of rivet nut 100. [0018] In an embodiment, and with reference still to FIG. 3B, mandrel 210 drives rivet nut 100 toward workpieces 200 until the underside of cap 120 is in loaded contact with the topside surface of workpiece 202, resulting in friction stirring and partial penetration of cap 120 into the surface of workpiece 202, holds the 12,000 rpm rotation of mandrel 210 for a defined period of time, such as two seconds for example, and then stops further rotation to allow workpieces 200 and rivet nut 100 to cool below the process temperature. During the cooling, the softened workpieces 200 harden. [0019] In an alternative embodiment, mandrel 210 is held at the 12,000 rpm rotation for a defined period of time subsequent to the underside of cap 120 being seated against the topside surface of workpiece 202, and is then stopped to allow workpieces 200 and rivet nut 100 to cool below the process temperature. [0020] In FIG. 3C, rotation of the mandrel 210 is stopped to allow the workpieces 200 and rivet nut 100 to cool below the process temperature, thereby permitting the softened workpieces 200 to harden. During the hardening phase, the flowable friction stir material that has flowed into and around the anti-rotation features 125, 130, 135, 140 of rivet nut 100 also hardens, thereby providing a mechanical engagement between rivet nut 100 and workpieces 200 that resists an applied torque on rivet nut 100 about axis 155. Continue reading about Friction stir nut and method of joining therewith... Full patent description for Friction stir nut and method of joining therewith Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Friction stir nut and method of joining therewith patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Friction stir nut and method of joining therewith or other areas of interest. ### Previous Patent Application: Self-assembly method, opal, photonic band gap, and light source Next Patent Application: Tool geometries for friction stir spot welding of high melting temperature alloys Industry Class: Metal fusion bonding ### FreshPatents.com Support Thank you for viewing the Friction stir nut and method of joining therewith patent info. 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