Abstract:
A friction stir weld tool sleeve is supported by an underlying support pin. The pin material is preferably selected for toughness and fracture characteristics. The pin sleeve preferably has a geometry which employs the use of an interrupted thread, a plurality of flutes and/or eccentric path to provide greater flow through. Paddles have been found to assist in imparting friction and directing plastic metal during the welding process.

Description:
STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein was made in part by an employee of the United States Government and may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to friction stir welding pin-tools, and more particularly to pin design and the pin surface geometry which engages a workpiece. 
   2. Description of Related Art 
   Friction Stir Welding (FSW) is a solid-state welding process that uses a non-consumable rotating pin-tool to make linear welds. Typical pin-tools consist of a cylindrical “shoulder” and a smaller diameter protruding “pin”. The process is initiated by plunging the rotating pin-tool into a weld joint until the shoulder is in intimate contact with the surface of the work piece. After the pin-tool has reached its final plunge depth a dwell-time is initiated wherein the material surrounding the pin-tool is heated by friction and plastic deformation. Travel is initiated after sufficient dwell-time, and the weld is created by literally stirring plasticized material together under compressive forces generated by the tool shoulder. Finally, the weld is concluded by halting travel and withdrawing the rotating pin-tool from the work piece. 
   Friction stir welding (FSW) is a relatively new technology but because of its broad applicability in the welding industry (as a replacement for fusion welding processes) it is the focus of significant research and development. The process is still in its infancy and has already been implemented in several production applications in the aerospace, automotive, rail, and trucking industries. 
   Accordingly, improvements in pin-tool design are believed to be important to provide industry with quality tools so that FSW will be an attractive option for manufacturers and metal workers. 
   Several patent applications have been filed, and some patents granted on friction stir welding tools. U.S. Patent Application Publication No. US 2002/0011509 shows a probe for friction stir welding having a shank, a shoulder and a pin-tool. No pin sleeves are shown or described in this reference. U.S. Patent Application Publication No. US 2002/0179682 shows a method and apparatus for joining work pieces by friction welding comprising a rotatable shaft which is biased toward a workpiece to plasticize an engaged area of the workpiece. A sleeve element moves toward the workpiece as the shaft is removed in order to push plasticized material back into the workpiece. 
   U.S. Patent Application Publication No. US 2002/0014516 shows a friction stir welding tool comprising a probe including a shank, shoulder and a pin disposed through the shoulder and into the shank, wherein the pin and the shoulder at least include a coating comprised of a super abrasive material, and having a collar around a portion of the shoulder and the shank to thereby prevent movement of the shoulder relative to the shank, and incorporating thermal management by providing a thermal flow barrier between the shoulder and the shank, and between the collar and the tool. 
   U.S. Patent Application Publication No. US 2001/0004989 shows a friction stir welding tool having a cylindrical body and at least one flash cutter formed integrally to the cylindrical body of the tool. 
   Other patents and applications showing FSW technology include U.S. Pat. No. 6,543,670 showing an interface preparation for weld joints, U.S. Patent Application Publication No. US 2001/0040179 showing a friction agitation joining apparatus for joining a plurality of abutted members, U.S. Pat. No. 5,875,953 showing a method and apparatus for effecting interference fit of two parts by accelerating the part or parts, U.S. Pat. No. 5,460,317 showing friction welding utilizing a number of differently shaped pin-tools, U.S. Pat. No. 6,367,681 showing a friction stir welding apparatus and method with a fairly typical stir welding tool, U.S. Pat. No. 6,516,992 showing one embodiment having a threaded pin-tool, U.S. Pat. No. 6,230,957 showing a method of using friction stir welding to repair weld defects and to help avoid weld defects in intersecting welds, U.S. Pat. No. 206,268 showing a friction stir welding pin-tool with internal flow channels, U.S. Pat. No. 5,971,251 showing a method of welding a terminal to a flat flexible cable, U.S. Pat. No. 6,325,273 showing a friction welding apparatus and method showing one or more metal with a spaced apart probes having a crescent shaped cross-section, U.S. Pat. No. 6,299,048 showing a pin-tool having threaded exterior surfaces, U.S. Pat. No. 6,264,088 showing pin-tools having a threaded exterior surface, U.S. Pat. No. 6,227,430 showing a friction stir weld tool for thick weld joints having four sections of thread tapers, U.S. Pat. No. 6,053,391 showing a friction stir welding tool having a unique thread configuration, U.S. Pat. No. 6,029,879 showing a probe having both right-handed and left-handed threads, U.S. Pat. No. 5,893,507 showing an auto-adjustable pin-tool for friction stir welding with what appears to be a traditional pin-tool, U.S. Pat. No. 5,713,507 showing a programmable friction stir welding process with a pin depth sensor, U.S. Pat. No. 6,138,895 showing a manual adjustable probe tool for friction stir welding, U.S. Pat. No. 6,302,315 showing a friction stir welding machine and method having a threaded pin-tool shown in FIG. 5, U.S. Pat. No. 3,822,821 showing a friction welding apparatus which includes a carrier member to receive a component to be friction welded to the workpiece, U.S. Pat. No. 5,718,366 showing a friction stir welding tool for welding variable thickness workpieces, U.S. Pat. No. 6,050,475 showing a method and apparatus for controlling downforce during friction stir welding, and finally, U.S. Pat. No. 5,697,544 showing an adjustable pin-tool for friction stir welding. 
   Foreign patents have also been filed for friction stir weld improvements. FIG. 2D of Great Britain Patent No. GB 2 306 366 shows a probe having a plurality of projections for mixing plasticized material. European Patent Application No. EP 0 810 055 as well as PCT Patent Application WO 02/070186 also show friction stir welding pin-tool. 
   While many improvements have been initiated, none are believed to satisfactorily address pin-tool strength, durability, wear resistance and stress management. 
   SUMMARY OF THE INVENTION 
   As can be seen from the prior art, there exists a need for a FSW tool which provides a tool pin design allowing for greater traverse speeds and an increased tool life. 
   Another object is to provide for an ability to operate at higher temperature and torque load. 
   Another object is to provide a FSW pin-tool to handle high start up torque. 
   Another object is to provide improved wear characteristics of FSW pin-tools. 
   Accordingly, the present invention provides a friction stir weld pin-tool which is supported by an underlying support pin. The pin material is preferably selected for toughness and fracture characteristics. The pin has a geometry which advantageously connects with an external sleeve. Although external sleeves can take a variety of geometries, the presently preferred geometry employs the use of one of an interrupted thread, an odd number of flutes, and/or an eccentric path to provide greater thru-flow. Abrasive surface geometries may also be utilized. Furthermore, paddles on an exterior surface of the sleeve may also be utilized to advantageously stir plastic metal during the welding process. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings in which: 
       FIG. 1  shows a side plan view of a body for use in FSW process with integral shoulder and smaller diameter protruding support pin; 
       FIGS. 2A-D  shows four presently preferred cross-sectional configurations for the support pin shown in  FIG. 1 ; 
       FIGS. 3A-H  shows alternatively preferred pin sleeve embodiments; 
       FIGS. 4A  and B are top plan views of an even number of flutes illustrating the concepts of up-milling and down-milling; 
       FIG. 5  shows a swath path for a four fluted work pin; 
       FIG. 6  shows the swath path of a three fluted tool; 
       FIG. 7  shows a bottom plan view of a pin-tool connected in accordance with the presently preferred embodiment; and 
       FIG. 8  shows a side perspective view of the presently preferred embodiment of the pin-tool connected to the shaft of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows a tool body with integral shoulder  10  and integral smaller diameter protruding support pin  12  in accordance with the presently preferred embodiment of the present invention. While tool bodies with integral shoulders have been known in the art, the support pin  12  is believed to be new. The body, shoulder and pin  10 ,  11  and  12  rotate together about rotational axis  64 . The pin  12  is selected from material for toughness, fracture, wear resistance, and other characteristics. The pin  12  may have a coating and/or sleeve intermediate the pin  12  and any of the alternatively preferred embodiments of tool sleeves as shown in  FIGS. 3A-3H . The currently preferred embodiment of a tool sleeve is illustrated in  FIGS. 7 and 8  as sleeve  14  connected to pin  12 . 
     FIG. 2  shows cross section embodiments taken along the line A-A of  FIG. 1 . These or other cross sectional embodiments could also be utilized. Any of the planar segments shown may be useful to prevent rotation of sleeve  14  relative to pin  12 . Sleeves such as those shown in  FIGS. 3A-3H  or in the preferred embodiment shown in  FIGS. 6 ,  7  and  8  are connected to pin  12  as shown in  FIGS. 7 and 8 . The body  10  has a shoulder  11 . The pin  12  has proximal end  13  and distal end  15 . The sleeve  14  has proximal end  17  and distal end  19 . 
     FIG. 4  shows what machinists typically call “up-milling” and “down-milling.” In any slotted cutting operation, where the tool is completely engaged in the material, both conditions exist simultaneously. It can be understood in that in this scenario there is an opposite piece of material opposite the workpiece from material as shown in  FIGS. 4   a  and  4   b . Accordingly, as the blades  18  rotate with the shaft  10  shown in  FIG. 1 , when a first blade contacts the workpiece  20  as shown in  FIG. 4A , an opposite blade in an even number configuration contacts a second workpiece  22  as shown in  FIG. 4B . The terms “advancing side” and “retreating side” refer to the up-milling and down-milling sides without identifying the tool action itself since the tool continues to rotate about the axis of the shaft  10 . 
   In the tool design, as represented by the swath path  FIG. 5 , having an even number of flutes such as four, continuous threads a smooth surface, a “nipping action” can occur where a flow of material “thru” or the tools&#39; cutting volume. In  FIG. 5  the tool is rotating clockwise and is being fed up the longitudinal axis  24  so that the direction of feed is established. This represents the workpieces passing about and below the tool which are not shown in  FIG. 5 . The swath path of the tool is shown. 
   The apparent swath path of a four bladed tool is represented at  FIG. 5 . Namely, area  26  is the apparent swath of the first flute which pinches at point  28  before the apparent swath path of the second flute  30  is commenced. The apparent swath path of the third flute  32  continues until reaching the pinching point  34  before beginning the apparent swath path of fourth flute  36 . Fourth flute  36  is on the advancing side (upmilling) while first flute  26  is on the retreating side or downmilling side. As can be seen from this diagram and understood by one skilled in the art, the pinching points  28 , and  34  are undesirable since they block the flow of material at these points. 
   However, when using an odd number of flutes as shown in  FIG. 6 , the pinching action does not occur on opposite portions of axis  38  at the pinching points  28 , and  24  opposite one another about the axis of rotation  40  as shown in  FIG. 5 . By utilizing a three fluted tool, a single pinching point  42  may occur relative to axis of rotation  44  of axes  46  and  48 . Since there are not a number of evenly spaced flutes, there is not a corresponding pinch point opposite the axis of rotation  44  from the pinch point  42 . A similar result can be had with an interrupted thread, a smooth pin with an eccentric path such as caused by the tilting of the tool relative to the workpieces and for the flattening of a side of the pin engaging the workpieces. A much greater thru flow can be had than with the even sided design as shown in  FIG. 5 .  FIG. 6  shows the presently preferred embodiment having a plurality of paddles  50  disposed on threads  52  which wind about the sleeve  14 . The paddles  50  are disposed with the threads  52  on exterior surface  60  of the sleeve  14 . The paddles  50  interrupt threads  52  as shown in the preferred embodiment. The paddles have a forward planar face  62  which is preferably either substantially perpendicular to the threads or parallel to and contained in a plane intersecting the shaft axis  64 . The paddles  50  are preferably odd in number and as they are substantially evenly spaced about the exterior surface of the sleeve  14 . The sleeve  14  preferably tapers from its proximal end  17  to its distal end  19 . The paddles  50  may have a planar back  66  which extends from distal end  68  of planar face to threads  52 . The sleeve is connected to a pin  12  as shown in  FIG. 7 .  FIG. 8  shows the shoulder. This design is believed to enhance the formation of the nugget at all speeds, and permits higher transverse speeds without danger of shearing the pin-tool. 
   As can be seen in  FIGS. 7 and 8  the sleeve  14  has a bore which cooperates with pin  12  so that sleeve  14  is locked on the pin  12 . The pin  12  has been selected for its toughness, temperature and load characteristics. The pin  12  has been manufactured to support a sleeve  14  like a cover which is inserted over the supporting pin  12 . The construction of the sleeve  14  preferably out of rhenium or other wear-resistant material has been preferably chosen for its ability to withstand temperatures and compressive wear. The sleeve  14  preferably includes the use of threads, flutes, and/or abrasives in order to engage material being joined by a friction stir welding technique. A compressive fit may be utilized to join the pin  12  to the sleeve  14  in conjunction with slotted key way and/or riding surfaces to support and attach the pin  12  to sleeve  14 . These may be coated to provide satisfactory thermal characteristics. Internal sleeves with satisfactory thermal characteristics may be utilized as liners in interior coatings intermediate the pin  12  and sleeve  14 . In other embodiments the sleeve  14  may be fabricated directly onto the underlying support pin  12  via other methods. 
   Numerous alterations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to the preferred embodiment of the invention which is for purposes of illustration only and not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.