Patent Publication Number: US-2022234132-A1

Title: Systems and methods for internal channel formation within a workpiece

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Application No. 63/141,883 filed Jan. 26, 2021 and entitled “Systems and Methods for Internal Channel Formation with a Workpiece,” which is hereby incorporated herein by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND 
     Friction stir welding is a solid-state process whereby two or more workpieces are joined together through heat and pressure generated by the engagement of a specially designed welding tool. A friction stir welding tool includes a pin that is inserted into the joint (of the two workpieces) and a shoulder that is applied against an upper surface of the workpieces. The pin and shoulder rotate while in contact with the workpieces to generate sufficient friction to weld the work pieces to one another during operations. Similarly, friction stir processing involves passing a friction stir welding tool through a single workpiece to modify the microstructure and/or the form of the workpiece without joining it to other workpieces. 
     BRIEF SUMMARY 
     Some embodiments disclosed herein are directed to a method of forming an internal channel within a workpiece. In some embodiments, the method includes (a) rotating a tool about a central axis. The tool includes a shoulder, a pin extending axially from the shoulder, and a flange mounted to the pin that is spaced from the shoulder along the central axis. In addition, the method includes: (b) moving the tool across the workpiece in a radial direction with respect to the central axis during (a); (c) engaging the shoulder of the tool with an outer surface of the workpiece during (a) and (b); (d) submerging the pin and the flange within the workpiece during (a) and (b); and (e) forming the internal channel with the flange during (a) and (b). 
     Some embodiments disclosed herein are directed to a tool for forming an internal channel within a workpiece. In some embodiments, the tool includes a tool body including a central axis and a shoulder, and a pin projected outward from the shoulder along the central axis. The pin includes a flange that is axially spaced from the shoulder along the central axis, and the shoulder includes a plurality of spiral grooves. 
     Some embodiments disclosed herein are directed to the shoulder includes a plurality of spiral grooves. The workpiece includes a first surface, a second surface opposite the first surface, and a groove extending into the first surface that extends across the workpiece. In some embodiments, the method includes (a) rotating a tool about a central axis. The tool includes a shoulder, a pin extending axially from the shoulder, and a flange mounted to the pin that is spaced from the shoulder along the central axis. In addition, the method includes: (b) inserting the tool into the workpiece from the first surface such that the flange is positioned between the first surface and the second surface; (c) moving the tool across the workpiece along the groove in a radial direction with respect to the central axis; (d) engaging the shoulder of the tool with the first surface of the workpiece during (c); and (e) forming the internal channel with the flange during (c) and (d). 
     Embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical characteristics of the disclosed embodiments in order that the detailed description that follows may be better understood. The various characteristics and features described above, as well as others, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes as the disclosed embodiments. It should also be realized that such equivalent constructions do not depart from the spirit and scope of the principles disclosed herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of various exemplary embodiments, reference will now be made to the accompanying drawings in which: 
         FIG. 1  is a perspective view of a tool performing a friction stir processing operation to form an internal channel within a workpiece according to some embodiments; 
         FIG. 2  is a side, cross-sectional view of the tool performing the friction stir processing operation of  FIG. 1  according to some embodiments; 
         FIGS. 3 and 4  are perspective views of a tool that may be used to perform the friction stir processing operation of  FIG. 1  according to some embodiments; 
         FIGS. 5 and 6  are perspective views of the tool body of the tool in  FIGS. 3 and 4  according to some embodiments; 
         FIGS. 7 and 8  are perspective views of the pin and the flanges of the tool of  FIGS. 3 and 4  according to some embodiments; 
         FIGS. 9, 10, and 11  are perspective views of pins and flanges that may be used with the tool of  FIGS. 3 and 4  according to some embodiments; 
         FIG. 12  is an exploded perspective view of a tool that may be used to perform the friction stir processing operations of  FIG. 1  according to some embodiments; 
         FIG. 13  is a side cross-sectional view of the tool of  FIG. 12  according to some embodiments; 
         FIG. 14  is a side cross-sectional view of a tool body of the tool of  FIG. 12  according to some embodiments; 
         FIG. 15  is an end view of the tool body of  FIG. 14  according to some embodiments; 
         FIG. 16  is an end view of the tool body of  FIG. 14  according to some embodiments; 
         FIG. 17  is a side view of a pin of the tool of  FIG. 12  according to some embodiments; 
         FIG. 18  is a side cross-sectional view of the pin of  FIG. 17  according to some embodiments; 
         FIG. 19  is an end view of the pin of  FIG. 17  according to some embodiments; 
         FIG. 20  is a cross-sectional view of a workpiece that may undergo the friction stir processing operation of  FIG. 1  according to some embodiments; and 
         FIG. 21  is a plot showing travel speeds for a tool during the friction stir processing operation according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion is directed to various exemplary embodiments. However, one of ordinary skill in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment. 
     The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness. 
     In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection of the two devices, or through an indirect connection that is established via other devices, components, nodes, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a given axis, while the terms “radial” and “radially” generally mean perpendicular to the given axis. For instance, an axial distance refers to a distance measured along or parallel to the axis, and a radial distance means a distance measured perpendicular to the axis. Further, when used herein (including in the claims), the words “about,” “generally,” “substantially,” “approximately,” and the like mean within a range of plus or minus 10%. 
     As previously described, friction stir processing is a process whereby the microstructure and/or form of a workpiece is modified via frictional engagement with a rotating tool. In some instances, one may wish to form an internal channel within a workpiece that may receive a flow of fluids (e.g., air, water, refrigerant) during operations. For instance, one may wish to form an internal channel in a heat exchange device, such as a cooling plate. In other instances, internal channels may provide a conduit for cabling (e.g., electrical cables, fiber optic cables), or may receive injectable materials (e.g., polymers) that modify one or more characteristics of a workpiece (e.g., elasticity, stiffness, etc.). 
     Accordingly, embodiments described herein include tools and related methods for forming internal channels within a workpiece. Embodiments of the tools disclosed herein may include a bobbin configuration having two opposing surfaces separated along a cylinder or pin that is aligned with a central axis of the tool. During operations, one of the surfaces is submerged within the material of the workpiece as the tool is rotated about the central axis, so as to form the internal channel. Through use of the embodiments disclosed herein, internal channels may be formed within a workpiece that are sealed from the outside environment by the monolithic, one-piece material of the workpiece itself. 
     Referring now to  FIGS. 1 and 2 , welding tool  10  for forming an internal channel  50  within a workpiece  60  according to some embodiments is shown. The workpiece  60  may comprise a wide variety of materials, such as, a metal (e.g., aluminum, aluminum alloys, titanium, titanium alloys, steel, copper, magnesium, magnesium alloys, ferrous alloys), or a non-metal (e.g., polymers). 
     The tool  10  comprises a tool body  14  that is engaged with a rotational driver  12  (e.g., a chuck of a drill press, lathe, computer numerical control (CNC) machine, or other rotatable piece of equipment). The tool body  14  includes a central, longitudinal axis  15 . During operations, the rotational driver  12  rotates the tool body  14  about axis  15  while engaging tool body  14  with workpiece  60  so as to form a deformed region  55  within the workpiece  60  that includes the internal channel  50  as described in more detail below. 
     As best shown in  FIG. 2 , tool body  14  includes a first or upper end  14   a  and a second or lower end  14   b  opposite upper end  14   a . A radially extending shoulder  20  is defined on lower end  14   b . Shoulder  20  may include a number of configurations and shapes in various embodiments such as, flat, tapered, convex, concave, etc. Shoulder  20  may be referred to herein as an “inner flange” of tool  10 . 
     In addition, a pin  30  extends axially from lower end  14   b . Specifically, pin  30  includes a first or an upper end  30   a  that is inserted into lower end  14   b  of tool body  14  and a second or lower end  30   b  extended or projected axially away from lower end  14   b  of tool body  14  along axis  15 . 
     An outer flange  32  is formed on lower end  30   b  of pin  30 . Flange  32  may have a maximum radial width W 32  that is larger than a maximum radial width W 30  of the pin  30 . The radial widths W 32 , W 30  may be measured along the radial direction of axis  15 . The outer flange  32  and shoulder  20  (or “inner flange  20 ”) are axially spaced from one another along axis  15  via pin  30  so that tool  10  may have a bobbin configuration as generally noted above. 
     Flange  32  includes a first or upper surface  40 , a second or lower surface  42 , and a radially outer surface  44  extending axially between upper surface  40  and lower surface  42 . In some embodiments, the upper surface  40  and/or lower surface  42  may be planar and may extend radially with respect to axis  15 . In some embodiments, upper surface  40  and/or lower surface  42  may comprise a number of different shapes or configurations. For instance, in some embodiments, as described in more detail below, upper surface  40  may be frustoconical in shape, or may have other concave or convex curvatures. In addition, in some embodiments, lower surface  42  may be hemispherical, concave, convex, conical, frustoconical, etc. 
     Referring again to  FIGS. 1 and 2 , during operations, the rotational driver  12  rotates tool  10  about axis  15 , while tool body  14 , pin  30 , and flange  32  are engaged with workpiece  60  to form deformed region  55  and channel  50 . In particular, shoulder  20  is engaged with an upper surface  62  of workpiece  60  while pin  30  and flange  32  are inserted within and engaged with workpiece  60 . Workpiece  60  may include a lower surface  64  that is opposite the upper surface  62 , and the pin  30  and flange  32  may be inserted within workpiece  60  such that flange  32  is positioned between the upper surface  62  and lower surface  64 . As a result, the upper surface  40  of flange  32  may act as an additional shoulder that is spaced from shoulder  20  along axis  15  and that bears against the material of the workpiece  60  during operations. 
     As the tool  10  is rotated about axis  15 , the tool  10  is moved in a radial direction with respect to axis  15  along the workpiece  60  (e.g., parallel with upper surface  62 ). As a result, during operations, the axis  15  is oriented perpendicularly or normally to the upper surface  62  of workpiece  60 ; however, it should be appreciated that axis  15  may not be perpendicular to the upper surface  62  of workpiece  60  in some embodiments. 
     The material forming workpiece  60  is heated by the frictional engagement of shoulder  20 , pin  30 , and flange  32  so that the material of workpiece  50  softens and opens to allow progression of the tool  10  (particularly pin  30  and flange  32 ) into the workpiece  60 . In addition, as the tool  10  advances through workpiece  60  in the radial direction, the softened material of workpiece  60  may flow around the pin  30  and flange  32 , between the shoulder  20  and upper surface  40  of flange  32  to re-close the opening behind the tool  10  (with respect to the direction of travel of the tool  10 ), thereby leaving a region of deformed material  55 . However, as the tool  10  progresses radially across the workpiece  60 , the material may not re-fill the cavity formed by flange  32 , so that channel  50  is formed within the deformed material  55 . During these operations, the material of workpiece  60  within the deformed region  55  may be pinched and compressed between the shoulder  20  and upper surface  40  of flange  32  in the axial direction with respect to axis  15 . 
     Within the deformed region  55 , the frictional engagement of the shoulder  20 , pin  30 , and flange  32  may refine the metallurgical grain size of the material of workpiece  60 , such that the deformed region  55  may be strengthened adjacent the internal channel  50  relative to the properties of the bulk material of workpiece  60 . In some embodiments, deformed region  55  may have an average metallurgical grain size which is between about 25% and about 75% smaller than an average metallurgical grain size within workpiece  60 , outside of deformed region  55 . 
     It should also be appreciated that the internal channel  50  formed using tool  10  may be seamless, such that the channel is free of seams that are generally parallel to the longitudinal axis of the channel. Such seams may be expected in channels formed by, for example, joining two separate workpieces (whereby the channel is formed along the line of engagement between the two workpieces). 
     In some embodiments, the channel  50  may be non-linear or may include non-linear (e.g., curved) sections or portions. In particular, the tool  10  may be moved along workpiece  60  in a plane that is radial to the axis  15  along a non-linear (e.g., curved) path to thereby result in a non-linear channel  50 . 
     Referring now to  FIGS. 3-8 , in some embodiments, tool body  14  may include a plurality of facets  16  formed thereon. During operations, teeth or other features on the rotational driver  12  ( FIGS. 1 and 2 ) may engage with facets  16  to drive rotation of tool body  14  about axis  15 . 
     In addition, in some embodiments shoulder  20  may include a number of shapes, contours, or other features. For instance, in some embodiments, shoulder  20  may comprise a plurality of first or inner spiral grooves  22 , and a plurality of second or outer spiral grooves  24 . As best shown in  FIG. 5 , a threaded bore  26  extends axially into tool body  14  from lower end  14   b  along axis  15 . Threaded bore  26  threadably receives pin  30  therein during operations. The outer spiral grooves  24  may extend to the radially outer edge of shoulder  20 , and inner spiral grooves  22  may be positioned radially inside of outer spiral grooves  24 . The inner spiral grooves  22  may spiral toward the axis  15  in a first direction, and the outer spiral grooves  24  may spiral toward the axis  15  in a second direction that is opposite the first direction. 
     Referring still to  FIGS. 3-8 , pin  30  and flange  32  may also may include a number of shapes, contours, or other features. For instance, lower surface  42  of flange  32  includes a plurality of spiral grooves  34  that spiral away from the central axis  15  along the same direction as the plurality of inner grooves  22  on shoulder  20  (e.g., along the “first direction” as noted above). The radially outer surface  44  includes a plurality of radially extending notches or recesses  36 . Each notch  36  may align with one of the grooves  34 . As best shown in  FIGS. 4 and 8 , the upper surface  40  of flange  32  may also include a plurality of spiral grooves  38  that spiral in toward the axis  15  along a direction that is opposite the first direction of the spiral grooves  34 . Thus, the spiral grooves  38  may spiral into the axis  15  along the same direction as the outer spiral grooves  24  on shoulder  20  (e.g., along the “second direction” as noted above). In some embodiments, the upper surface  40  of flange  32  is frustoconical in shape. As a result, the spiral grooves  38  may each extend along a conical helix path. In addition, each notch  36  may also align with one of the grooves  38 . 
     Pin  30  may comprise a helical thread  31  that may threadably engage within the threaded bore  26  in shoulder  20  to connect the pin  30  and flange  32  to tool body  14 . In some embodiments, pin  30  and flange  32  may be formed of one monolithic one-piece body (e.g., via casting, molding, machining, or other suitable process(es)). In some embodiments, the axial length of pin  30  from the shoulder  20 , and thus the axial distance between shoulder  20  and flange  32  may be adjustable (e.g., via a linear actuator, threaded engagement or disengagement of pin  30  in bore  26 ) so as to adjust a depth of the channel  50  within the workpiece  60  during operations. 
     In some embodiments, flange  32  may be selectively expanded or extended during operations so as to vary a size and shape of the channel  50  during operations. For instance, flange  32  may be axially expanded (e.g., at or along lower surface  42  and/or upper surface  40 ) to increase an axial length of flange  32  during operations. In some embodiments, flange  32  may be expandable in a radial direction (e.g., at or along radially outer surface  44 ) during operations. For instance, in some embodiments the flange  32  may comprise a plurality of axially extending segments that are circumferentially spaced about axis  15 . The segments may be rearranged (and/or replaced) to selectively increase or decrease a radial width (e.g., radial width W 32  in  FIG. 2 ) during operations. Without being limited to this or any other theory, the axial and/or radial expansion of flange  32  may allow the formation of a channel  50  with varying cross-sectional area. 
     During the operations described above to form channel  50  within workpiece  60  ( FIGS. 1 and 2 ), the interaction of the notches  36  and spiral grooves  22 ,  24 ,  34 ,  38  with the material forming the workpiece  60  may cause the material of the workpiece  60  to flow around the shoulder  20 , pin  30 , and flange  32  to form the channel  50  as generally described above. Specifically, as shown in  FIG. 3 , the tool body  14  may be configured to rotate about axis  15  in a direction  17  that is generally aligned with the directions of spiral grooves  22 ,  34  and opposite the directions of spiral grooves  24 ,  38 . 
     During operations, the directions of the spiral grooves  34  on lower surface  42  of flange  32  may move material of the workpiece  60  away from central axis  15 , and the spiral grooves  38  on upper surface  40  may move material of workpiece  60  axially away from flange  32  and toward shoulder  20  so as to form channel  50  when tool  10  is rotated about axis  15  in direction  17 . In addition, the direction of the helical thread  31  on pin  30  may also act to move material of the workpiece  60  axially away from flange  32  to facilitate formation of channel  50  as tool  10  is rotated about axis  15  in direction  17 . 
     More particularly, grooves  34  are oriented such that when the tool is rotated in direction  17 , material of deformed region  55  tends to move outward radially along surface  42  towards outer surface  44 . Recesses  36  may then direct the material toward surface  40 , where grooves  38  direct the material toward threads  30 . Thereafter, threads  30  tend to promote a continuation of flow of material toward shoulder  20 , where grooves  22  engage the material to move it radially outward away from pin  30 . This general path of material flow promotes the evacuation of material of deformed region  55  to form channel  50 . Finally, during rotation of tool  10  in direction  17 , grooves  24  tend to oppose grooves  22  to contain the material along the outer periphery of shoulder  20  to help consolidate the material in the upper portion of channel  50  and thereby close and seal the outer surface of channel  50 . 
     Referring now to  FIG. 9 , an embodiment of a pin  130  and flange  132  is shown that may be used with tool body  14  in some embodiments. In describing the features of pin  130  and flange  132 , like reference numerals will be used to identify parts of pin  130  and flange  132  that are shared with the pin  30  and flange  32  described above. Moreover, the focus of the following description will be on the features of pin  130  and flange  132  that are different from pin  30  and flange  32 , respectively. 
     In particular, pin  130  includes a plurality of circumferentially adjacent, parallel helicoidal surfaces  136  extending from upper surface  40  of flange  132 , toward upper end  30   a . As shown in  FIG. 9 , the helicoidal surfaces  136  may not extend fully to upper end  30   a  and may terminate at a point positioned axially between upper end  30   a  and lower end  30   b.    
     In addition, upper surface  40  of flange  132  includes a plurality of facets  142  that extend from pin  132  to the radially outer surface  44 . As shown in  FIG. 9 , in some embodiments, the radially outer surface  44  may be cylindrical in shape, and the lower surface  42  may be planar or flat; however, any suitable shape or features may be included on these surfaces in various embodiments (e.g., notches  36 , grooves  34 ). As is also shown in  FIG. 9 , each of the facets  142  is aligned with a corresponding one of the helicoidal surfaces  136  at the interface of the pin  130  and upper surface  40  of flange  132 . 
     Referring now to  FIG. 10 , another embodiment of a pin  230  and flange  232  is shown that may be used with tool body  14  in some embodiments. Generally speaking, pin  230  and flange  232  are generally the same as the pin  130  and flange  132  shown in  FIG. 9  and described above, except that pin  230  includes the thread  31  that was previously described above for pin  30  ( FIGS. 7 and 8 ). The thread  31  may extend through the helicoidal surfaces  136 . 
     Referring now to  FIG. 11 , another embodiment of pin  330  and flange  332  is shown that may be used with tool body  14  in some embodiments. Generally speaking, pin  330  and flange  332  are generally the same as the pin  230  and flange  232  shown in  FIG. 10  and described above, except that radially outer surface  44  of flange  332  include an additional helical thread  334  that extends between upper surface  40  and lower surface  42 . 
     Referring now to  FIGS. 12 and 13 , an embodiment of a tool is shown that may be used in place of tool of  FIGS. 1 and 2  for carrying out a friction stir processing operation according to some embodiments. Specifically, the tool of  FIGS. 12 and 13  includes a tool body  414  and pin  430  that may be used in place of tool body  14  and pin  30 , respectively, to form channel  50  in  FIGS. 1 and 2  according to some embodiments. 
     Referring now to  FIGS. 12-14 , the tool body  414  includes a central, longitudinal axis  415 . During operations, tool body  414  is rotated about axis  415  in a rotational direction  417  (e.g., a counter clockwise direction when viewing tool body  414  from lower end  414   b  along axis  415 ) while engaging tool body  414  and pin  430  with workpiece  60  so as to form a deformed region  55  within the workpiece  60  that includes the internal channel  50  as previously described ( FIG. 1 ). Tool body  414  includes a first or upper end  414   a  and a second or lower end  414   b  opposite upper end  414   a . In addition, tool body  414  may include a plurality of facets  16  formed thereon as previously described above for tool body  14  ( FIG. 3 ). 
     A radially extending shoulder  420  is defined on lower end  414   b . Shoulder  420  may include a number of configurations and shapes in various embodiments such as, flat, tapered, convex, concave, etc. Shoulder  420  may be referred to herein as an “inner flange” of tool  10  ( FIG. 1 ). In some embodiments, the shoulder  420  may comprise a planar, radially oriented (or extending) surface. A frustoconical surface or chamfer  423  may extend circumferentially about shoulder  420  with respect to axis  415 . 
     A bore  424  extends axially into shoulder  420  at lower end  414   b  along axis  415 . As best shown in  FIG. 14 , bore  424  includes an annular shoulder  426  that extends circumferentially about axis  415 , and a set of threads  428  axially spaced from shoulder  426 . The annular shoulder  426  may be spaced axially between the shoulder  420  (and lower end  414   b ) and the threads  428 . Because bore  424  includes threads  428  it may be referred to herein as a “threaded bore.” 
     Referring now to  FIGS. 12 and 15 , shoulder  420  may comprise a plurality of spiral grooves  422 . As best shown in  FIG. 15 , the outer spiral grooves  422  may extend from the frustoconical surface  423  (and therefore from the radially outer edge of shoulder  420 ) across shoulder  420  to the bore  424 . In some embodiments (e.g., such as in the embodiment of  FIGS. 12 and 15 ), the spiral grooves  422  may spiral radially inward toward the axis  415  from frustoconical surface  423  along a circumferential direction  421  that is opposite from the rotational direction  417  of tool body  414 . Referring briefly to  FIG. 16 , in some embodiments, the spiral grooves  422  may spiral radially inward toward the axis  415  from frustoconical surface  423  along a circumferential direction  425  that is aligned with (or the same as) the rotational direction  417  of tool body  414 . 
     Referring again to  FIGS. 12 and 13 , pin  430  is threadably coupled to tool body  414 . Specifically, pin  430  is threadably engaged with threads  428  within bore  424  such that pin  430  extends along axis  415  during operations. 
     Referring now to  FIGS. 17 and 18 , pin  430  includes a central or longitudinal axis  435 , a first or upper end  430   a , and a second or lower end  430   b  opposite upper end  430   a . An outer flange  432  is formed on lower end  430   b . In addition, threads  438  extend helically about pin  430  (with respect to axis  435 ) from upper end  430   a . Further, an annular shoulder  436  is positioned axially between flange  432  and threads  438  along axis  435 . The annular shoulder  436  may include a first or upper radial surface  436   a  and a second or lower radial surface  436   b  axially spaced from upper radial surface  436   a . The lower radial surface  436   b  is positioned axially between flange  432  and upper radial surface  436   a  with respect to axis  435 . 
     Flange  432  includes a first or upper surface  440 , a second or lower surface  442 , and a radially outer surface  444  extending axially between upper surface  440  and lower surface  442 . The lower surface  442  may be planar and may extend radially with respect to axis  435 . Conversely, the upper surface  440  may be frustoconical or convexly curved, but may generally extend inward toward axis  435  from (or proximate to) radially outer surface  444 . 
     Referring now to  FIG. 19 , a recess  460  extends axially inward along axis  435  from lower surface  442 . The recess  460  terminates at a planar, radially extending surface  462  that is axially recessed into lower end  430   b  and lower surface  442  along axis  435 . In addition, a plurality of spiral grooves  443  extend radially inward (or toward axis  435 ) from radially outer surface  444  toward recess  460 . The spiral grooves  443  spiral radially inward toward the central axis  435  and the recess  460  along a circumferential direction  437  that is aligned with (or the same as) the as the rotational direction  417 . During operations, the recess  460  may collect softened material of the workpiece (e.g., workpiece  60 ) that is then directed radially outward from the recess  460  toward radially outer surface  444  via the plurality of spiral grooves  443 . 
     Referring back to  FIGS. 17 and 18 , a plurality of helical grooves  446  are formed in the radially outer surface  444 . Generally speaking, the helical grooves  446  may each extend in a clockwise direction about axis  435  as the helical grooves  446  advance axially from the lower surface  442  to the upper surface  440  and when pin  430  is viewed along axis  435  from lower end  430   b . Stated differently, the helical grooves  446  may extend circumferentially about axis  435  along a circumferential direction that is opposite the rotational direction  417  when moving axially from lower surface  442  to upper surface  440 . 
     An additional helical groove  452  extends about pin  430  axially from upper surface  440  to annular shoulder  436 . The helical groove  452  may extend in the same direction as the helical grooves  446 . Thus, the helical groove  452  may extend circumferentially about axis  435  along a circumferential direction that is opposite the rotational direction  417  when moving axially from upper surface  440  to annular shoulder  436 . 
     Referring now to  FIGS. 12 and 17 , a plurality of flats or facets  454  are formed on pin  430  axially between upper surface  440  of flange  432  and annular shoulder  436 . Thus, the flats  454  may extend through and interfere with the helical groove  452 . The plurality of flats  454  may be uniformly circumferentially spaced about axis  435 . The flats  454  may comprise planar surfaces that extend axially between upper surface  440  of flange  432  and annular shoulder  436 . Thus, in some embodiments (e.g., such as the embodiment of  FIGS. 12 and 17 ), there are a total of three (3) flats  454  that are spaced approximately 120° apart from one another about axis  435 . However, there may be different numbers of flats  454  in other embodiments (e.g., such as two flats  454  spaced approximately 180° apart about axis  435 , four flats  454  spaced approximately 90° apart about axis  435 , etc.). 
     Referring again to  FIGS. 12 and 13 , threads  438  are engaged with threads  428  within recess  424  on tool body  414  so that central axis  435  is aligned (and is co-axial with) central axis  415 . Threaded advancement of pin  430  into recess  424  proceeds until annular shoulder  436  on pin  430  engages or abuts with the annular shoulder  426  within recess  424 . Specifically, the upper radial surface  436   a  of annular shoulder  436  engages or abuts with annular shoulder  426  within recess  424 . In some embodiments, the lower radial surface  436   b  of annular shoulder  436  is flush or co-planar with shoulder  420  on tool body  414 . Conversely, in some embodiments, the lower radial surface  436   b  of annular shoulder  436  is recessed axially within (or axially projected from) shoulder  420  on tool body  414  along axes  415 ,  435 . 
     Without being limited to this or any other theory, the engagement between annular shoulder  436  on pin  430  and the annular shoulder  426  within recess  424  may reduce a tension borne by the threads  438 ,  428 . Thus, the positive engagement between annular shoulders  436 ,  426  may prevent or reduce shearing of the threads  426 ,  436  even when relatively high torsion loads are transferred to the pin  430  and/or tool body  414  during the friction stir welding operations described herein. 
     Referring now to  FIGS. 1, 2, 12, and 13 , during operations rotational driver  12  is engaged with tool body  414  as previously described. Thereafter the tool body  414  and pin  430  are rotated about the aligned axes  415 ,  435  via the rotational driver  12  in the rotational direction  417 . The rotating tool body  414  and pin  430  are then engaged with the workpiece  60  to form the region of deformed material  55  and the channel  50  as previously described. More particularly, the rotating tool body  414  and pin  430  are traversed across workpiece  60  in a radial direction with respect to the axes  415 ,  435 , while the flange  432  of pin  430  is positioned between the upper surface  62  and lower surface  64  of workpiece  60 . 
     The interaction of spiral grooves  443 ,  422 , helical grooves  446 ,  452 , and flats  454  with the material forming the workpiece  60  may cause the material of the workpiece  60  to flow around shoulder  420 , pin  430 , and flange  432  to form channel  50  as previously described. Specifically, the directions of spiral grooves  443  and helical grooves  446 ,  452  relative to rotational direction  417  may move material of the workpiece  60  radially outward from axes  435 ,  415  along lower surface  442  of flange  432  and axially upward along radially outer surface  444  and pin  430  toward lower surface  436   b  of annular shoulder  436 . Thereafter, the material of workpiece  60  may interact with the spiral grooves  422  formed on shoulder  420  of tool body  414 . Referring briefly again to  FIG. 15 , for embodiments having spiral grooves  422  spiraling radially inward toward axis  415  along the circumferential direction  421 , the material may be restricted from moving radially outward from shoulder  420  via the spiral grooves  422  so that the captured or retained material may better seal the upper end of channel  50  (e.g., along the upper surface  62  of workpiece  60 ). Referring briefly again to  FIG. 16 , for embodiments having spiral grooves  422  spiraling radially inward toward axis  415  along the circumferential direction  425 , the material of the workpiece  60  may be directed radially outward or away from the axes  415 ,  435  along shoulder  420 . The choice between the two directions (e.g., circumferential directions  421 ,  425 ) of spiral grooves  422  shown in  FIGS. 15 and 16  may be made based on a variety of factors such as, for instance the material forming workpiece  60 , the speed of rotation (e.g., along rotational direction  417 ), the speed of the radial movement of the tool body  414  and pin  430 , etc. 
     Referring now to  FIG. 20 , an embodiment of workpiece  560  that may serve as the workpiece  60  shown in  FIGS. 1 and 2  is shown. In some embodiments, workpiece  560  may be pre-worked, formed, milled, etc. in order to facilitate the formation of channel  50  ( FIGS. 1 and 2 ). As with workpiece  60 , workpiece  560  may include a first or upper surface  562 , and a second or lower surface  564  opposite upper surface  562 . A groove  566  may be cut or milled into the upper surface  562  that is extends part-way through the workpiece  560  (i.e., the groove  566  may not extend completely through to the lower surface  564 ). The groove  566  may extend to a depth D 566  measured perpendicularly from the upper surface  562 . In some embodiments, the groove  566  may extend less than half-way through thickness of the workpiece  560  (i.e., the depth D 566  is less than half the total distance between the upper surface  562  and lower surface  564 ), or less than a third of the way through the thickness of the workpiece  560  (i.e., the depth D 566  is less than a third of the total distance between the upper surface  562  and lower surface  564 ). In some embodiments, the depth D 566  of the groove  566  may have a magnitude that is equal to or less than the axial distance between the upper surface  440  and the lower radial surface  436   b  ( FIGS. 17 and 18 ). The groove  566  may define the path of the eventual internal channel (e.g., channel  50  in  FIGS. 1 and 2 ) that is to be formed in workpiece  560  via interaction with tool  10  as previously described. 
     In addition, a recess  568  extends into workpiece  560  from upper surface  562  that is adjacent the groove  566 . In some embodiments, recess  568  may be spaced from groove  566  (e.g., such as shown in  FIG. 20 ). However, in some embodiments, recess  568  may be contiguous with groove  566 . Like the groove  566 , the recess  568  extends part-way through the workpiece  560 . The recess  568  may extend to a depth D 568  measured perpendicularly from the upper surface  562 . The depth D 568  may define a maximum depth of the internal channel that may be formed by interaction of the tool  10  with the workpiece  560  (channel  50  in  FIGS. 1 and 2 ). The depth D 568  may be greater than the depth D 566 . 
     Referring now to  FIGS. 1, 2, and 20 , during operations for forming an internal channel  50  within workpiece  560 , the flange  32  of tool  10  may be inserted into the recess  568  and then rotated about axis  15 . The depth D 568  of recess  568  may be such that the shoulder  20  of tool  10  is separated from the upper surface  562  of workpiece  560  when the flange  32  is initially inserted within recess  568  and engaged with a terminal surface  569  therein. However, after tool  10  reaches a suitable rotational speed, the flange  32  maybe plunged slightly into the terminal surface  569  of the recess  568  so that shoulder  20  brought into contact with upper surface  562 . In some embodiments, the tool  10  is rotated in place about axis  15  after initial contact is formed between shoulder  20  and the upper surface  562 . When tool  10  engages with the workpiece  560 , the local temperature within the workpiece  560  surrounding tool  10  may increase to form a so-called “thermal plume” within workpiece  560  about the tool  10 . The thermal plume may allow for flow or movement of material via interaction with tool  10  (including flange  32  and shoulder  20 ) as previously described. Once a sufficient thermal plume is initiated, the rotating tool  10  may be traversed (e.g., radially with respect to axis  15 ) along the line of groove  566  to thereby form an internal channel  50 . 
     Without being limited to this or any other theory, the groove  566  may provide sufficient space along upper surface  562  to allow material of workpiece  560  that is displaced by pin  30  (including flange  32 ) and shoulder  20  to form a top or ceiling of the channel  50  along upper surface  562 . Thus, the groove  566  may be placed along workpiece  560  for all or most of the length of channel  50  in some embodiments. 
     Referring still to  FIGS. 1 and 2 , during the above-described operations to form an internal channel  50  within a workpiece  60 , the travel speed of the tool  10  through the workpiece  60  may be adjusted throughout the process to ensure formation of a sealed internal channel  50 . As previously described, when tool  10  engages with the workpiece the local temperature within the workpiece surrounding the tool  10  may increase to form a thermal plume to facilitate movement of the material forming the workpiece about the tool  10  as previously described. Thus, at the initial stages of the friction stir processing operation to form the internal channel (e.g., channel  50 ), the travel speed of the tool  10  through the workpiece  60  may be progressively increased from a relatively low speed to a final target speed so as to first establish and thereafter maintain the thermal plume around the tool  10  within the workpiece  60 . 
     For instance, reference is now made to  FIG. 21  which shows a plot  600  of various travel speed profiles  602 ,  604 ,  606 ,  608 ,  610  for a tool  10  that is forming an internal channel  50  within a workpiece  60  according to some embodiments. Each of the profiles  602 ,  604 ,  606 ,  608 ,  610  has a different final target speed for the tool  10  through the workpiece  60 . Specifically, the profile  602  has a target travel speed of 5 inches per minute (ipm), the profile  604  has a target travel speed of 10 ipm, the profile  606  has a target travel speed of 15 ipm, the profile  608  has a target travel speed of 20 ipm, and the profile  610  has a target travel speed of 25 ipm. However, while the profiles  602 ,  604 ,  606 ,  608 ,  610  have different, final target speeds, each increases the rate of travel for the tool  10  from a relatively low rate up to the final target speed so as to establish and then maintain the thermal plume within the workpiece  60  and thereby form the internal channel  50 . 
     The embodiments described herein include systems and methods for forming internal channels within a workpiece. Through use of the embodiments disclosed herein, internal channels may be formed within a workpiece that are effectively sealed along the length of the channel from the outside environment by the monolithic, one-piece material of the workpiece itself. 
     While exemplary embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.