Friction stir nut and method of joining therewith

Abstract

A friction stir nut is disclosed. 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 and/or an outer surface of the body. 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 a mandrel tool friction stir welding the friction stir nut to a workpiece and then being extracted, uniform internal threads result at the body. The anti-rotation feature bonds to the workpiece by metallurgical bonding and/or mechanical bonding.

1 . A friction stir nut suitable for friction stir welding to a workpiece via a mandrel tool, the friction stir nut comprising: 
 a body having an elongated cylindrical shank extending between a first end and a second end;    a cap at the second end; and    an anti-rotation feature at the cap, at an outer surface of the body, or at both;    wherein 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 having a flat surface oriented substantially perpendicular to the axis of the shank;    wherein the body has a cylindrical wall thickness suitable for receiving internal threads; and    wherein 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.    
   
   
       2 . The friction stir nut of  claim 1 , wherein: 
 the body comprises a first portion and a second portion;    the first portion has a first nominal cylindrical wall thickness suitable for receiving internal threads;    the second portion has a second nominal cylindrical wall thickness that is less than the first nominal cylindrical wall thickness;    the first portion is proximate the first end and the second portion is proximate the second end; and    in response to the mandrel tool friction stir welding the friction stir nut to the workpiece and then the mandrel tool being pulled, the second portion of the body buckles at an opposite side of the workpiece to that of the cap.    
   
   
       3 . The friction stir nut of  claim 2 , wherein: 
 in response to the mandrel tool being inserted into the body, internal threads are received at the first portion; and    in response to the mandrel tool being extracted from the friction stir nut, uniform internal threads result at the first portion.    
   
   
       4 . The friction stir nut of  claim 1 , wherein: 
 the anti-rotation feature at the cap comprises a scalloped section at the perimeter of the cap, a projection at the underside of the cap, a recess at the underside of the cap, a through-hole at the cap, or any combination comprising at least one of the foregoing features.    
   
   
       5 . The friction stir nut of  claim 1 , wherein: 
 the anti-rotation feature at an outer surface of the body comprises a projection, a recess, a knurl, or any combination comprising at least one of the foregoing features.    
   
   
       6 . The friction stir nut of  claim 1 , further comprising: 
 internal threads at the body.    
   
   
       7 . The friction stir nut of  claim 1 , wherein: 
 the body and cap comprise an iron-based alloy.    
   
   
       8 . The friction stir nut of  claim 1 , wherein: 
 the body and cap comprise a material having a higher melting point than that of the material of the workpiece.    
   
   
       9 . The friction stir nut of  claim 1 , wherein: 
 the flat surface oriented substantially perpendicular to the axis of the shank is perpendicular to within plus-or-minus two degrees thereof.    
   
   
       10 . The friction stir nut of  claim 9 , wherein: 
 the flat surface has a diameter equal to or greater than about 80% of the outside diameter of the first end of the body.    
   
   
       11 . The friction stir nut of  claim 2 , wherein: 
 the second portion has a compressive strength less than the compressive strength of the first portion.    
   
   
       12 . A friction stir rivet nut suitable for friction stir welding to a workpiece via a mandrel tool, the friction stir rivet nut comprising: 
 a body having an elongated cylindrical shank extending between a first end and a second end, the body comprising a first portion proximate the first end and a second portion proximate the second end, the first portion having a first nominal cylindrical wall thickness, the second portion having a second nominal cylindrical wall thickness that is less than the first nominal cylindrical wall thickness;    a cap at the second end; and    an anti-rotation feature at the cap, at an outer surface of the body, or at both;    wherein 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 having internal threads, the outer end surface of the first end having a flat surface oriented substantially perpendicular to the axis of the shank.    
   
   
       13 . The friction stir rivet nut of  claim 12 , wherein: 
 in response to the mandrel tool friction stir welding the friction stir rivet nut to the workpiece and then the mandrel tool being pulled, the second portion of the body buckles at an opposite side of the workpiece to that of the cap.    
   
   
       14 . The friction stir rivet nut of  claim 12 , wherein: 
 in response to the mandrel tool friction stir welding the friction stir rivet nut to the workpiece and then the mandrel tool being extracted from the friction stir rivet nut, uniform internal threads result at the body, and the anti-rotation feature bonds to the workpiece by metallurgical bonding, mechanical bonding, or both.    
   
   
       15 . The friction stir rivet nut of  claim 12 , wherein: 
 the anti-rotation feature comprises a recess, a projection, a hole, or any combination comprising at least one of the foregoing features.    
   
   
       16 . A method of friction stir welding a friction stir rivet nut to workpieces via a mandrel, comprising: 
 threadably engaging the mandrel with the rivet nut, the rivet nut comprising: a body having a first end and a second end and a cap at the second end, the body having a first portion proximate the first end and a second portion proximate the second end, the first portion having a first nominal cylindrical wall thickness suitable for receiving internal threads, the second portion having a second nominal cylindrical wall thickness that is less than the first nominal cylindrical wall thickness, the outer end of the first end having a flat surface that extends over equal to or greater than about 80% of the effective outer diameter of the first end;    positioning the rivet nut at a point of engagement of the workpieces;    rotating the mandrel about its rotational axis, driving the rivet nut 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, and driving the rivet nut along the displaceable path until the cap is seated against or partially into the workpieces;    stopping further rotation of the mandrel and allowing the workpieces and rivet nut to cool below the process temperature, thereby permitting the softened workpieces to harden;    axially loading the mandrel 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    rotationally extracting the mandrel such that uniform internal threads result at the first portion.    
   
   
       17 . The method of  claim 16 , wherein the rivet nut further comprises an anti-rotation feature at the cap, at an outer surface of the body, or at both, the method further comprising: 
 in response to the mandrel being rotationally extracted from the rivet nut, the workpieces being held together at the point of engagement by the stirred, intermingled materials of the workpieces, the differential thermal contraction of the workpieces and the rivet nut, the mechanical interference between the anti-rotation feature and the workpieces, the mechanical loading between the buckled second portion of the body and the workpieces, or any combination comprising at least one of the foregoing.    
   
   
       18 . The method of  claim 16 , wherein: 
 the rotating comprises rotating the mandrel at equal to or less than about 12,000 revolutions per minute; and    the driving comprises driving the rivet nut at a rate equal to or greater than about 6 millimeters per minute and equal to or less than about 150 millimeters per minute.    
   
   
       19 . The method of  claim 16 , wherein the causing the materials of the workpieces to soften at a process temperature comprises: 
 causing the materials to soften at a process temperature that is substantially lower than the melting temperature of the rivet nut.    
   
   
       20 . The method of  claim 16 , wherein the driving the rivet nut into the workpieces comprises: 
 driving the rivet nut absent a preexisting hole in the workpieces.    
   
   
       21 . The method of  claim 16 , wherein: 
 the resultant frictional heating is initiated by the friction stir interaction between the flat surface of the first end of the rivet nut and the workpieces; and    the driving displaces material of the workpieces along the displaceable path in such a manner as to reduce the tendency for the displaced material to penetrate the region between the workpieces as the rivet nut is driven into the workpieces.