Patent Publication Number: US-2023146110-A1

Title: Friction based additive manufacturing systems and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Application 63/270,470, filed on Oct. 21, 2021, the content of which is hereby incorporated in its entirety. 
    
    
     BACKGROUND 
     Solid-phase thermo-mechanical processes are used for additive manufacturing and repair. Additive friction stir deposition allows for dense material deposition, refined and equiaxed grains, and minimal distortion of the substrate. However, current additive friction stir deposition methods and other solid-phase additive manufacturing methods have limited capabilities. Depositing large deposits requires reloading of feed rods and constant attention from a user during the deposition process. In addition, known tools for additive friction stir deposition require non-circular feed rods to avoid rotational slipping of the feed rod with respect to the tool. 
     Thus, a need exists for improved systems for solid-phase additive manufacturing and/or additive friction stir deposition. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Example features and implementations are disclosed in the accompanying drawings. However, the present disclosure is not limited to the precise arrangements and instrumentalities shown. 
         FIG.  1    is a cross-sectional view of a system for friction based additive manufacturing. 
         FIG.  2    is a partial, detailed perspective view of a tool head, an actuator, and feed materials of the system of  FIG.  1   . 
         FIG.  3    is a partial, detailed cross-sectional view of the tool head, actuator, and feed materials shown in  FIG.  2    as taken along the  3 - 3  line. 
         FIG.  4    is a detailed perspective view of the actuator shown in  FIG.  1   . 
         FIG.  5    is another detailed perspective view of the actuator shown in  FIG.  1   . 
         FIG.  6    is a detailed perspective view of the spools, actuator motor, and tool motor of the system in  FIG.  1   . 
         FIG.  7    is a detailed perspective view of the spacer of the system shown in  FIG.  1   . 
         FIG.  8    is an end view of the tool head shown in  FIG.  1   . 
         FIG.  9    is an end view of a tool head according to another implementation. 
         FIG.  10    is an end view of a tool head according to another implementation. 
         FIG.  11    is a front view of another system for friction based additive manufacturing. 
         FIG.  12    is a perspective view of a system for friction based additive manufacturing according to another implementation. 
         FIG.  13    is a partial, detailed, cross-sectional view of the system in  FIG.  12    as taken along the  13 - 13  line. 
         FIG.  14    is a cross-sectional view of a tool, tool head, coupling collar, and actuator according to another implementation. 
         FIG.  15    is a perspective view of the tool, tool head, coupling collar, and actuator shown in  FIG.  14   . 
         FIG.  16    is an end view of the tool head and coupling collar shown in  FIG.  14   . 
     
    
    
     DETAILED DESCRIPTION 
     The devices, systems, and methods described herein include a system for high shear continuous solid-phase deposition of material without solid-liquid-solid phase transformations. 
     According to various implementations, the system includes a tool defining a feed channel that allows for the continuous deposit of feed material while preventing melting when cladding, repairing, or depositing the feed material (e.g., in one or more layers) onto a substrate. The feed material (e.g., feed rod or feed wire) is rotated by a tool head of the tool about a central axis of the tool head adjacent the substrate. The outlet opening of the feed channel is offset from the central axis of the tool head, which allows for the use of circular feed rods or feed wires. The tool head includes one or more channels. The tool head may define more channels to increase deposition rate and reduce localized stresses in the tool, or the tool may define fewer channels to increase resolution and decrease the size of the deposition, according to some implementations. In addition, having the outlet opening of the feed channel(s) be offset from the central axis of the tool head eliminates the need for co-dependent rotation of the feed rod or feed wire and the tool head. In other words, the feed rod or feed wire can rotate about its own axis (or not) independently of the rotation of the tool head about its central axis. 
     According to various implementations, a system for friction based additive manufacturing is disclosed herein. The system includes a tool head and an actuator. The tool head includes a central axis, a first end, and a second end opposite and spaced apart from the first end along the central axis. The tool head defines a feed channel that extends between openings defined by the first end and the second end. The opening defined by the second end is offset from the central axis. The tool head is configured to rotate about the central axis. The actuator is configured to urge a feed material through the feed channel in a direction from the first end to the second end of the tool. The actuator is disposed adjacent the first end of the tool, and a second end of the tool is configured for being disposed adjacent a substrate onto which the feed material is being friction stir deposited. 
     In some implementations, the actuator engages an external perimetrical surface of the feed material to urge the feed material toward the substrate. Engaging the external perimetrical surface allows for more uniform processing and controlled conditions in depositing the feed material onto the substrate. As used herein, perimetrical surface refers to the external surface of the feed material as viewed through a radial cross-section of the feed material, regardless of the radial cross-sectional shape of the feed material. For example, for a feed material having a circular radial cross-sectional shape, the external perimetrical surface refers to the external circumferential surface of the feed material. 
     In some implementations, the force of the actuator on the feed material is controlled (e.g., by controlling the speed of rotation of the actuator and/or by controlling a downward force on the actuator) to control the feed rate of the feed material through the tool head and onto the substrate and to control a height of the layer of feed material being deposited. 
     According to various implementations, a method of friction based additive manufacturing is disclosed herein. The method includes (1) providing a tool including a central axis, a first end, and a second end opposite and spaced apart from the first end along the central axis, the tool defining a feed channel that extends between openings defined by the first end and the second end, the opening defined by the second end being offset from the central axis, and wherein the tool further comprises an actuator that is disposed adjacent the first end of the tool; (2) disposing a portion of a feed material through the feed channel; (3) actuating the actuator such that the actuator urges the feed material through the feed channel in a direction from the first end to the second end of the tool; and (4) rotating the tool about the central axis and moving the tool through a plane that is parallel to a substrate onto which the feed material is being friction stir deposited by the tool. 
       FIG.  1    shows an implementation of a system  100  for friction based additive manufacturing that includes a tool  105  comprising a tool head  110  and a spacer  180 , an actuator  150 , and two spools  174 ,  176  of feed material  144 ,  146 , according to one implementation of the aspects described herein. For example, the system  100  is an additive friction stir deposition system. As used herein, the term feed material includes, but is not limited to, feed rods or feed wires. 
     As shown in  FIGS.  1  and  2   , the tool head  110  includes a cylindrically shaped outer wall  112 , a central axis  114 , a first end  116 , and a second end  118  opposite and spaced apart from the first end  116  along the central axis  114 . The outer wall  112  extends between the first end  116  and the second end  118 . The outer wall  112  of the tool head  110  includes a tool engagement portion  123  that extends axially from the first end  116  to a plane P that extends orthogonal to the central axis  114  between the first end  116  and the second end  118 . The tool engagement portion  123  defines two flat portions  120  that each extend axially from the first end  116  to the plane P and two shoulders  121  that extend transversely from the flat portions  120  to the outer wall  112  in plane P. The flat portions  120  are diametrically opposed and lie in planes parallel to each other. A cross-sectional shape of the tool engagement portion  123  as viewed in plane P (or a plane extending through the tool engagement portion that is parallel to plane P) corresponds to the cross-sectional shape of an inner wall  111  of a cavity  107  of a tool  105  as viewed in a plane that is perpendicular to a central axis of the tool  105 . In particular, the cross-sectional shape of the inner wall  111  of the tool  105  has two arcuate shaped wall portions and two flat wall portions that correspond to the cross-sectional shape of the tool head  110  as viewed in plane P described above. The ends of the arcuate shaped wall portions of the inner wall  111  extend between the ends of the two flat wall portions of the inner wall  111  such that the arcuate shaped wall portions are diametrically opposed, and the flat wall portions are diametrically opposed. 
     The tool engagement portion  123  is configured for engaging the inner wall of the cavity  107  of the tool  105  via a friction fit and not rotating relative to the tool  105  when the tool  105  is rotated about the central axis  114  of the tool head  110 . Set screws may be inserted radially through the tool to engage the tool head to prevent the tool head from being unintentionally removed relative to the tool. The tool head  110  is removable from the tool  105  such that another tool head can replace it when the tool head  110  is damaged or has deposits on it that compromise its effectiveness (e.g., to mitigate cross-contamination between different deposited materials). 
     In other implementations, the tool head and the tool may be coupled by other suitable mechanisms such that movement of the tool head relative to the tool is prevented and rotation of the tool is translated to the tool head. For example,  FIG.  14 - 16    illustrate an example implementation of a coupling collar  608  that couples the tool  605  and the tool head  610 . In this implementation, a portion of the tool head  610  does not engage within a cavity of the tool  605 . A first surface  616  of the tool head  610  is axially abutted against a second surface  607  of the tool  605  that faces the first surface  616  of the tool head  610 . An inner wall  609  of the coupling collar  608  slides over and engages at least a portion of the external surfaces of the tool head  610  and the tool  605  that face the inner wall  609  such that the coupling collar  608  surrounds the abutting surfaces of the tool head  610  and tool  605 . At least one set screw  625  is engaged radially through the coupling collar  608  to abut the tool  605 , and at least one set screw  626  is engaged radially through the coupling collar  608  to abut the tool head  610 . As shown in  FIGS.  15  and  16   , diametrically opposed set screws  625 ,  626  are engaged through the coupling collar  608  to engage the tool  605  and the tool head  610 , respectively. The set screws  625 ,  626  prevent movement of the tool  605  and tool head  610  relative to each other. In other implementations (not shown), screws that extend through at least a portion of the tool and/or tool head, bolts, or other suitable fasteners may be used instead of set screws to couple the tool and the tool head to each other and/or to the coupling collar. 
     The tool head material selected has a hardness that is greater than the hardness of the feed material to be deposited. For example, to deposit lightweight alloys, like aluminum or magnesium alloys, a harder tool head material, such as tool steel, is appropriate. Whereas, for steels, nickel-based alloys, high entropy alloys, or titanium alloys, a harder tool head material, such as tungsten-rhenium or tungsten-lanthanide, helps to extend tool life, minimizing wear of the tool material being deposited with the feed material that is fed through the tool head. 
     The tool head  110  defines a first feed channel  122  and a second feed channel  132 . Each channel  122 ,  132  extends along a channel axis that is offset from the central axis  114 . The first end  116  of the tool head  110  defines a first feed channel inlet  124  to the first feed channel  122  and a second feed channel inlet  134  to the second feed channel  132 . The first end  116  of the tool head  110  also defines an actuator recess  138  disposed between the first feed channel inlet  124  and the second feed channel inlet  134  and coaxial with the central axis  114 . The second end  118  of the tool head  110 , which is shown in detail in  FIG.  2   , defines a first feed channel outlet  126  to the first feed channel  122  and a second feed channel outlet  136  to the second feed channel  132 . The first feed channel  122  and the second feed channel  132  extend along axes that are parallel to the central axis  114 . The first feed channel  122  and the second feed channel  132  are diametrically opposed to each other. 
     Although the implementation shown in  FIGS.  1  and  2    defines two feed channels  122 ,  132 , in other implementations, the tool head defines one or more feed channels, wherein the opening defined by the second end is offset from the central axis. And, although the implementation in  FIGS.  1  and  2    shows the channel axes of the feed channels equally spaced from each other about the central axis of the tool head, in other implementations, the channel axes of the feed channels are unequally spaced from each other about the central axis of the tool head. For example, in the implementation shown in  FIG.  8   , the tool head  210  defines three feed channels  222 ,  232 ,  242  having channel axes that are equally spaced about the central axis  214  of the tool head  210 . 
     Although the implementation shown in  FIGS.  1 ,  2 , and  8    shows a cylindrically shaped tool head, the tool head may have any elongated solid shape (e.g., elliptical, prismatic, or any solid shape having straight and/or curved surfaces) that allows it to be used with the system. For example, in the implementation shown in  FIG.  10   , the tool head  310  is a triangular prism that defines three feed channels  322 ,  332 ,  342  that are equally spaced from each other about the central axis  314 . 
     Although the implementations shown in  FIGS.  1 - 2 ,  8 ,  9 , and  10    show channels having a circular cross-sectional shape as viewed in a plane perpendicular to the central axis of the tool, in other implementations, the feed channels may have any suitable cross-sectional shape (e.g., elliptical, polygonal, or any closed shaped having straight and/or curved lines) as viewed in a plane perpendicular to the central axis of the tool head that corresponds to the cross-sectional shape of the feed material. 
     To operate the tool head  110 , a first feed material  144  is disposed within the first feed channel  122  and a second feed material  146  is disposed within the second feed channel  132 . Both the first feed material  144  and the second feed material  146  are fed through the tool head  110  such that the feed material enters the respective inlet and exits the respective outlet. Because the material is fed through the first end  116  of the tool head  110  and exits from the second end  118  of the tool head  110 , a user is not required to continually stop and feed the feed material through the second end  118  of the tool head  110 , as in known tools. In some implementations, the feed material is a spooled feed material, discrete rods, strips of material, or any suitable feed material for friction stir welding that can be continuously top fed into the tool. 
     In the implementation shown in  FIG.  1   , the cross-section of the feed material  144 ,  146  is circular, however, in other implementations, the cross-section of the feed material is polygonal or any other suitable closed shape. In  FIG.  1   , the first feed material  144  and the second feed materials  146  are the same, although, in other implementations, the first feed material and the second feed material are different. In some implementations, the feed materials include combinations of similar and dissimilar materials, such as aluminum and aluminum alloys, magnesium and magnesium alloys, steels, stainless steels, multi-principal element alloys or high entropy alloys, titanium and titanium alloys, copper and copper alloys, nickel based super alloys, and metal matrix composites. 
     As shown in  FIG.  3   , the actuator  150  includes a threaded drive mechanism  152  (also referred to herein as a threaded drive gear or threaded screw gear), a drive shaft  154 , and a bearing  160 . The threaded drive gear  152  is at least partially disposed within the actuator recess  138  and has a threaded outer surface  162  as shown in  FIGS.  3 - 5   . A first end  164  of the threaded drive gear  152  defines a hexagonal opening and channel  166  and a conical recess  168  axially adjacent the hexagonal channel  166 . 
     The drive shaft  154  includes a first end  156  and a second end  158  opposite and spaced apart from the first end  156 . The first end  156  of the drive shaft  154  is coupled to an actuator motor  157  that rotates the drive shaft  154 . The second end  158  of the drive shaft  154  includes a hexagonal portion  170  and a conically shaped portion  171  axially adjacent thereto that corresponds to the shape of the hexagonal channel  166  and conical recess  168  of the first end  164  of the threaded drive gear  152 . 
     The bearing  160  is a spherical bearing and is coupled to the second end  165  of the threaded drive gear  152 . The bearing  160  engages a conically shaped floor  140  of the actuator recess  138  of the tool head  110 . Rotation of the drive shaft  154  causes rotation of the threaded drive gear  152  upon the bearing  160 . 
     The outer surface  162  of the threaded drive gear  152  extends partially into the first feed channel  122  and the second feed channel  132  such that the outer surface  162  of the threaded drive gear  152  contacts a portion of an external perimetrical surface  145  of the first feed material  144  that is disposed within the first feed channel  122  and a portion of an external perimetrical surface  147  of the second feed material  146  that is disposed within the second feed channel  132 . When the threaded drive gear  152  is driven by the drive shaft  154 , the outer surface  162  of the threaded drive gear  152  engages the external perimetrical surfaces of the feed materials  144 ,  146  (e.g., the external circumferential surfaces of the circular feed materials  144 ,  146  shown in  FIGS.  1  and  2   ) to cause the feed materials  144 ,  146  to be urged from the first end  116  to the second end  118  of the tool head  110 . 
     To cause deposition of the feed material  144 ,  146  onto the substrate  11 , the threaded drive gear  152  rotates, urging the feed material  144 ,  146  through the second end  118  of the tool head  110  as the tool head  110  rotates. As shown in  FIG.  1   , the tool  105  has deposited two full layers of feed material  144 ,  146  onto the substrate  11  and is in the process of depositing a third layer. 
     As shown in  FIGS.  1  and  6   , the tool head  110  is coupled to the tool  105 , and the tool  105  is rotated by a tool motor  133 . In the implementation shown, the tool  105  is coupled to the tool motor  133  through a drive belt  131 , which transfers rotational force to the tool  105  such that the tool rotates the tool head  110  about the central axis  114 . The tool motor  133  and the actuator motor  157  are driven independently of each other in the implementations shown, but in other implementations, the tool motor and the actuator motor may be driven together via a transmission arrangement. The tool motor and actuator motor may also be coupled through a linkage or gear or belt type drivetrain system. 
     The ratio of the speeds of rotation of the threaded drive gear  152  and the second end  118  of the tool head  110  influences the material deposition rate and the heat input to the tool head  110 . For example, the greater the speed of rotation of the threaded gear drive  152  relative to the speed of rotation of the tool head  110 , the more feed material is pushed out of the tool head  110 . In addition, if the tool head  110  and the threaded drive gear  152  are rotating in the same direction, the speed of rotation of the threaded drive gear  152  is greater than or equal to the speed of rotation of the tool head  110 . However, if the directions of rotation of the tool head  110  and the threaded drive gear  152  are opposite, the speed of rotation of the threaded drive gear  152  can be greater than or less than or equal to the speed of rotation of the tool head  110 . The second end  118  of the tool head  110  is configured to be disposed adjacent a substrate onto which the feed materials  144 ,  146  are being friction stir deposited. 
     A length of the threaded portion of the threaded drive gear  152  is selected based on the compressive force desired for imparting onto the feed materials. For example, a longer threaded portion of the threaded drive gear  152  results in more compressive force onto the feed materials. 
     The spools  174 ,  176  each have a central axis that is coaxial with the central axis  114  of the tool head  105 . The spools  174 ,  176  are coupled around the tool  105  with bearings  175 ,  177 , respectively, disposed between the spools  174 ,  176  and the tool  105 , as shown in  FIG.  1   . Rotation of the threaded gear drive  152  causes tension in the feed material  144 ,  146 , which pulls the feed material  144 ,  146  through the tool  105  from the spools  174 ,  176  (e.g., through radial openings defined in the tool  105  or through an opening(s) defined by the end of the tool  105  opposite the tool head  110 ) and urges the feed material  144 ,  146  through the tool  105  and tool head  110  for depositing onto the substrate  11  adjacent the second end  118  of the tool head  110 . 
     The spacer  180  is configured for being disposed within the cavity  107  of the tool  105  to keep the feed materials  144 ,  146  and the drive shaft  154  for the threaded gear drive  152  separated within the tool  105 . The spacer  180  includes a first end  186 , a second end  188  opposite and spaced apart from the first end  186  along a central axis  184 , and an outer surface  182  that extends between the first end  186  and the second end  188 . The outer surface  182  of the spacer  180  includes two flat surfaces  190  diametrically opposed from each other and two arcuate shaped surfaces  191  diametrically opposed from each other. The flat surfaces  190  and the arcuate shaped surface  191  define a perimetrical shape that corresponds to the cross-sectional shape of the inner wall  111  of the tool  105  as viewed through a plane perpendicular to the central axis of the tool  105 , which allows the spacer  180  to be inserted and held via a friction fit within the tool  105 . 
     The spacer  180  defines a first feed material opening  192 , an actuator opening  194 , and a second feed material opening  196  that extend from the first end  186  to the second end  188  of the spacer  180  parallel to the central axis  184  of the spacer  180 . The spacer  180  is disposed within the system  100  adjacent (e.g., axially adjacent and spaced apart from) the first end  116  of the tool head  110  such that the spacer  180  straightens the feed material  144 ,  146  before it reaches the tool head  110  and maintains the alignment of the actuator  150 . 
     Another implementation of a system for friction based additive manufacturing  400  is shown in  FIG.  11   . The system  400  also includes a tool head  410  and an actuator  450 . The system  400  shown in  FIG.  11    is similar to the system  100  described above in relation to  FIG.  1   , except that the spooled feed materials each have a central axis within a plane R that is transverse (e.g., perpendicular) to the central axis  414  of the tool head  410 . Furthermore, instead of the threaded drive gear  152  of  FIG.  1   , the actuator  450  shown in  FIG.  11    includes a set of pinch rollers  472 . The set of pinch rollers  472  includes a pair of pinch rollers associated with each feed material to urge the respective feed material through the tool head  410 . For example, the implementation shown in  FIG.  11    includes a first feed material  444  and a second feed material  446 . A first pair of pinch rollers are associated with the first feed material  444 , and a second pair of pinch rollers are associated with the second feed material  446 . The first pair of pinch rollers includes first pinch roller  474  that rotates about rotational axis  475  and second pinch roller  486  that rotates about rotational axis  477 . The second pair of pinch rollers includes third pinch roller that rotates about a rotational axis that is coaxial to rotational axis  477  and fourth pinch roller  478  that rotates about rotational axis  479 . The third pinch roller is not shown in  FIG.  11    because it is disposed behind the second pinch roller  486  in the view shown in  FIG.  11   . The pinch rollers are spaced apart from the first end  416  of the tool head  410  such that the rotational axis  477  of the second pinch roller  486  and the rotational axis of the third pinch roller are perpendicular to the central axis  414  of the tool head  410 . The rotational axis  475  of the first pinch roller  474  is parallel to the rotational axis  477  of the second pinch roller  486 , and the rotational axis of the third pinch roller is parallel to the rotational axis  479  of the fourth pinch roller  478 . In the implementation shown, the first rotational axis  475  and the fourth rotational axis  479  are also parallel to each other. The first and fourth pinch rollers  474 ,  478  are spaced apart from the second pinch roller  486  and the third pinch roller, respectively, such that the first and second pinch rollers  474 ,  486  define a first feed material gap  498 , and the third and fourth pinch rollers  478  define a second feed material gap  499 . The first and fourth pinch rollers  474 ,  478  also include a threaded outer surface (not shown) that contacts the external perimetrical surface of the first and second feed material  444 ,  446 , respectively, when the first and second feed materials  444 ,  446  are disposed within the first feed material gap  498  and the second feed material gap  499 , respectively. The second pinch roller  486  is idle while the first pinch roller  474  is driven (e.g., by a first actuator motor (not shown)) to rotate clockwise to urge the first feed material  444  through the first feed channel. Similarly, the third pinch roller is idle while the fourth pinch roller  478  is driven (e.g., by a second actuator motor (not shown)) to rotate counterclockwise to urge the second feed material  446  through the second feed channel. The feed materials  444 ,  446  are urged through the respective channels in a direction from the first end  416  to the second end  418  of the tool head  410 . The feed materials  444 ,  446  may be urged through the respective channels one at a time or simultaneously. The driven pinch rollers may be rotated at the same speed if the feed rates for the respective feed materials are the same. Or, the driven pinch rollers may be rotated at different speeds if the feed rates for the respective feed materials are different. 
     In other implementations, a block or other structure may be disposed between the first roller and fourth roller instead of the second and/or third pinch rollers, and the structure provides a counter pressure to the feed material being engaged by the first roller and/or the fourth roller such that the first and fourth rollers are able to engage the circumferential surface of the respective feed material and urge the respective feed material through the tool head. 
     The ratio of the speeds of rotation of the rollers  472  and the second end  418  of the tool head  410  influences the material deposition rate and the heat input to the tool head  410 . For example, the greater the speed of rotation of the rollers  472  relative to the speed of rotation of the tool head  410 , the more feed material is pushed out of the tool head  410 . The second end  418  of the tool head  410  is configured to be disposed adjacent a substrate onto which the feed materials  444 ,  446  are being friction stir deposited. 
     In another implementation, the second and third pinch rollers include a threaded outer surface and the first and fourth pinch rollers are idle with the second and third pinch rollers being driven to rotate and urge the first and second feed materials through the tool head in a direction from the first end to the second end of the tool head. In another implementation, the pinch rollers are not threaded. In other implementations, the actuator includes two or more rotating or idle pinch rollers. In some implementations, the actuator includes one, two, three, or any suitable number of pinch rollers that are threaded. Although the third pinch roller rotates about a rotational axis that is coaxial to the rotational axis  477  of the second pinch roller  486  in  FIG.  11   , in some implementations, the second pinch roller rotates about a rotational axis that is not coaxial to the rotational axis of the third pinch roller. 
     However, in other implementations (not shown), any orientation of the central axis of each spool can be used in combination with any type of actuator for urging the feed material through the tool head. For example, the rollers  472  may be used with spools oriented like spools  174 ,  176  shown in  FIGS.  1  and  6   , and the actuator  150  may be used with the spools oriented like spools  484 ,  476  shown in  FIG.  11   . 
       FIGS.  12  and  13    illustrate another implementation of a system  500 . The system  500  includes a tool head  510  that defines a channel  522  that extends between the first end  516  and the second end  518  of the tool head  510 . The opening  524  to the channel  522  defined by the first end  516  is coaxial with the central axis  514  of the tool head  510 , but the channel  522  bends within the tool head  510  and the opening  526  defined by the second end  518  is offset from the central axis  514  of the tool head  510 . Having an offset opening in the second end  518  allows the feed material  544  being urged through the channel  522  to be offset from the central axis  514  where it is being deposited onto the substrate, which prevents the tool head  510  from rotating about a central axis of the feed material  544 . The feed material  544  is spooled around spool  574  and fed into the opening  524  to the channel  522  defined by the first end  516  of the tool head  510  by rollers  572 . The first end  516  of the tool head  510  is engaged within a tool  505  that rotates the tool head  510  about its central axis. The tool  505  is rotated by a tool motor (not shown), which is separate from the actuator motor that drives the rollers  572 . 
     During an extrusion period, the feed material is being pushed out at a certain rate by the actuator as the tool is moved laterally relative to the substrate to create a layer of deposition of a certain height. During a dwell period, the feed material is frictionally engaged with the substrate and the tool head is rotated to generate and build up head in the feed material, but the tool head may not be moved laterally relative to the substrate. In some implementations, during the dwell period, the actuator (e.g., the threaded drive gear  152  or rollers  472  described in the above implementations) may be stationary or rotated at a speed that is less than the speed of rotation of the actuator during an extrusion period. In addition, the speed of rotation of the actuator may be adjusted relative to the speed of rotation of the tool head depending on whether a dwell or extrusion period is desired. For example, the speed of rotation of the actuator may be controlled to be equal to or less the speed of rotation of the tool head during a dwell period. The speed of rotation of the actuator may be controlled to be greater than the speed of rotation of the tool head during an extrusion period. 
     In other implementations, the actuator includes a push rod that engages an axial end of a feed rod having a discrete length (e.g., not a continuously fed wire). In implementations in which the tool head defines more than one feed channel, the actuator may include feed material engaging legs corresponding to the number of feed channels that can be axially pushed against the axial end of each feed rod. The feed material engaging legs may be pushed individually (e.g., at different forces and/or rates) or together. The feed material engaging legs are pushed against the axial ends of the respective feed material by a linear actuator, such as a rack and pinion, cam lever, impending rollers, impeding gears, electro-mechanical actuator, and hydraulic actuator. To control movement of the legs individually, a linear actuator may be configured to act on each leg individually (e.g., by using multiple linear actuators or by using a linear actuator capable of acting on the legs individually). And, in some implementations in which the legs are pushed together, a linear actuator may act on a single push leg that is coupled to the legs of the push rod. 
       FIG.  14    illustrates an example implementation in which the actuator  650  includes a push rod that has a push leg  652  and one or more feed material engaging legs  654 ,  656  that extend axially from a central body  653 . The push leg  652  extends axially from the central body  653  in a first axial direction, and the feed material engaging legs  654 ,  656  extend axially from the central body  653  in a second axial direction that is opposite the first axial direction. The number of feed material engaging legs  654 ,  656  corresponds with the number of channels defined within the tool  605  and/or tool head  610  through which feed rods  644 ,  646  may be disposed. A distal end  657  of the push leg  652  extends out of the tool  605  and an axial force in direction F is applied to the distal end  657  of the push leg  652  to push the feed material engaging legs  654 ,  656  into contact with the feed rods  644 ,  646  in each channel defined by the tool head  610  and out of the tool head  610  onto the substrate. 
     In other implementations, the actuator includes a paddle wheel that pushes discrete or continuous feed material through the tool by rotating fins about an axis, wherein the fins engage the axial ends or the external perimetrical surfaces of the feed material, pushing the feed material through the tool head as the fins rotate about the axis. In yet another implementation, the actuator includes a linear actuator that linearly pushes discrete or continuous feed material through the tool. In other implementations, the actuator includes a screw feed drive, pinch rollers, paddle wheel, or linear actuators in any suitable combination for urging the feed material from the first end to the second end of the tool. 
     In another implementation, a method of friction based additive manufacturing is disclosed herein. The method may be used for additive friction stir deposition, for example. The method includes providing a tool head including a central axis, a first end, and a second end opposite and spaced apart from the first end along the central axis, the tool defining a feed channel that extends between openings defined by the first end and the second end, and the opening defined by the second end is offset from the central axis of the tool, and wherein the tool further comprises an actuator that is disposed adjacent the first end of the tool, disposing a portion of a feed material through the feed channel, actuating the actuator such that the actuator urges the feed material through the feed channel in a direction from the first end to the second end of the tool, and rotating the tool about the central axis and moving the tool through a plane that is parallel to a substrate onto which the feed material is being friction stir deposited by the tool. 
     In some implementations, the feed channel comprises a first feed channel and a second feed channel, the outlet of each feed channel being parallel to and offset from the central axis of the tool, wherein the feed material comprises a first feed material and a second feed material, and wherein disposing a portion of the feed material comprises disposing a portion of the first feed material through the first feed channel and disposing a portion of the second feed material through the second feed channel. 
     A number of implementations have been described. The description in the present disclosure has been presented for purposes of illustration but is not intended to be exhaustive or limited to the implementations disclosed. It will be understood that various modifications and variations will be apparent to those of ordinary skill in the art and may be made without departing from the spirit and scope of the claims. Accordingly, other implementations are within the scope of the following claims. The implementations described were chosen in order to explain the principles of the systems and methods claimed herein and their practical applications, and to enable others of ordinary skill in the art to understand the systems and methods for various implementations with various modifications as are suited to the uses contemplated. 
     The terminology used herein is for the purpose of describing particular implementations only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, operations, elements, components, and/or groups thereof.