Abstract:
A friction stir welding apparatus has a novel tool-in-tool construction where a friction stir welding pin tool extends through a center bore of a friction stir welding shoulder tool and is moveable axially and rotationally relative to the shoulder tool. The pin tool and shoulder tool both have their own dedicated tool holders and spindles that enable the tools to rotate and move axially relative to each other and enable easy replacement of each of the tools.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     (1) Field of the Invention  
         [0002]     The present invention pertains to a friction stir welding apparatus in which a friction stir welding pin tool is received in a center bore of a friction stir welding shoulder in a tool-in-tool arrangement.  
         [0003]     (2) Description of the Related Art  
         [0004]     Friction stir welding is a recently developed method of welding that involves joining two sheets of metal along a weld line without fusing the metal of the sheets and without the use of welding filler materials. The welds are created by the combination of frictional heating of the metal by a rotating tool and mechanically deforming the metal with the rotating tool. The tool is typically constructed of a metal that is harder than the metal being friction stir welded. The tool has a cylindrical section with a circular distal end surface. The circular distal end surface of the tool is typically known as the “shoulder surface” of the tool. A smaller cylindrical section projects outwardly from the center of the tool distal end surface. The smaller cylindrical section or probe is typically referred to as the “pin” of the tool. The junction between the pin and the shoulder surface forms the “shoulder” of the tool.  
         [0005]     In the friction stir welding process, the stir welding tool is rotated and pressed into a butt joint or lap joint or other similar type of joint, between the two pieces of metal being joined. The two pieces of metal must be rigidly pressed together before the welding operation. The pin penetrates into the metal of the joint and the shoulder surface rubs the top surfaces of the two pieces of metal over the joint. The rotation of the tool shoulder surface and pin generates friction heat in the joint. The friction heat generated causes the metal along the joint to soften without reaching the melting point of the metal. The softening of the metal allows the friction stir welding tool to be moved along the weld line of the joint. The softened metal is transferred from the leading edge of the rotating tool to the trailing edge of the tool, forming a solid phase bond between the two pieces of metal along the weld joint. As the weld is completed, the tool shoulder and pin sections are withdrawn from the two pieces of metal. To avoid leaving a hole in the weld by the withdrawal of the pin from the welding joint, the friction stir welding tool can have a pin that is retracted into the shoulder section of the tool, leaving a flat shoulder surface at the distal end of the tool that leaves behind an integral weld between the two pieces of metal.  
         [0006]     The prior art friction stir welding tools are mounted on machines similar to milling machines. Such a machine rotates the tools about their center axes, moves the tools axially toward and away from the materials being welded, and moves the materials laterally when making the weld. In retractable pin stir welding tools, the pin is mounted inside the shoulder and is operatively connected with the shoulder by an actuator that selectively extends the pin a set distance from the shoulder end surface during the welding operation, and retracts the pin into the shoulder end surface at the completion of the welding operation. The pin tool actuator is typically contained inside the shoulder tool and the shoulder and pin assembly is rotated together by a spindle. The shoulder and pin assembly is removably connected to the spindle and moves with the spindle relative to the pieces of material being welded during the welding operation.  
         [0007]     Due to the existing designs of friction stir welding machine spindles and the present techniques of installing retractable pin and shoulder friction stir welding tools on the spindles, maintaining a tight tolerance between the pin and shoulder tools is impractical. The tolerances between prior art pin and shoulder tools are low, and therefore the run-out tolerance or the close fit between the pin and shoulder is generally very poor. This results in inaccurate welds produced by the tools. In addition, the time required to change the pin and shoulder friction stir welding tools in a spindle in the current configuration of friction stir welding machines is very slow and costly.  
       SUMMARY OF THE INVENTION  
       [0008]     The friction stir welding apparatus of the invention provides a novel tool-in-tool holding system that, when combined with an electromechanical coaxial spindle design of a stir welding machine, is ideal for the production friction stir welding process. The apparatus of the invention comprises a friction stir welding pin tool that is mounted through a center bore of a friction stir welding shoulder tool. The coaxial mounting of the two tools enables both the pin tool and shoulder tool to be engaged and held by two separate standard commercially available tool holders. This facilitates the installation and removal of each of the pin and shoulder tools from the friction stir welding apparatus, and thereby increases the available production time of the apparatus.  
         [0009]     The shoulder tool holder is modified to allow the pin tool to extend through both the shoulder tool center bore and the shoulder tool holder. The use of two separate holders for the pin and shoulder tools utilizes the overall accurate positioning of the pin and shoulder spindles of the apparatus. The use of two off-the-shelf tool holders for holding the pin and shoulder tools separately is a unique alternative to the prior art method of holding the prior art friction stir welding pin and shoulder assemblies that allows for tighter welding process tolerances, decreases the run-out of the pin tool and shoulder tool, and allows for shorter, predictable tool changes and more accurate friction stir welds. Pin tool and shoulder tool changes are predictable, man-hours are decreased, tool accuracy and tool relationships are very accurate, welding tolerances are increased and are more predictable. In addition, the wear and tear on expensive spindles is decreased because the run-out of the friction stir welding pin tool and shoulder tool is reduced.  
         [0010]     The friction stir welding apparatus of the invention makes use of a conventional machine employed in friction stir welding operations, such as a milling machine. The milling machine is modified with a pair of separate spindle assemblies in lieu of the single spindle assembly of the conventional milling machine. The two spindle assemblies include a dedicated pin tool spindle and a dedicated shoulder tool spindle that are contained in a spindle casing of the machine in axially aligned and spaced positions. The pin tool spindle and the shoulder tool spindle rotate independently of each other and can be controlled to rotate at the same or different rates of rotation, and in the same or different directions of rotation. As in the conventional friction stir welding apparatus, the machine can be controlled to move the two spindles together toward and away from the materials to be welded, and the machine can be controlled to move the materials laterally relative to the machine.  
         [0011]     The friction stir welding apparatus also includes a friction stir welding pin tool and pin tool holder, and a friction stir welding shoulder tool and shoulder tool holder.  
         [0012]     The friction stir welding pin tool has a generally cylindrical length with opposite proximal and distal ends, and opposite proximal and distal end surfaces. The pin tool has a center axis that is also the center axis of the tool-in-tool apparatus. The pin tool proximal end is removably attached to the pin tool spindle by the pin tool holder. The opposite distal end and distal end surface of the pin tool function as the projecting pin in the friction stir welding process.  
         [0013]     The friction stir welding shoulder tool as a length with opposite proximal and distal ends and opposite proximal and distal end surfaces. A hollow center bore extends entirely through the length of the friction stir welding shoulder tool. The center bore extends through the opposite proximal and distal end surfaces of the shoulder tool. The shoulder tool holder removably attaches the shoulder tool to the shoulder tool spindle. The shoulder tool holder also has a center bore that is aligned with the shoulder tool center bore when the shoulder tool is engaged by the shoulder tool holder.  
         [0014]     With the friction stir welding pin tool held to the pin tool spindle by the pin tool holder, and with the friction stir welding shoulder tool held to the shoulder tool spindle by the shoulder tool holder, the pin tool extends axially through the center bore of the shoulder tool holder and through the center bore of the shoulder tool. Rotation of the pin tool spindle and the shoulder tool spindle rotates both the pin tool and shoulder tool in the same or opposite directions, and at the same or different rates of rotation. In addition, relative axial movement between the pin tool spindle and the shoulder tool spindle moves the pin tool axially through the center bore of the shoulder tool. This enables the distal end of the pin tool to be extended outwardly from the distal end of the shoulder tool to produce the relatively positioned pin and shoulder surfaces used in the friction stir welding processes, and enables the retraction of the pin into the shoulder tool surface when the welding process is completed.  
         [0015]     The tool-in-tool arrangement of the pin tool and shoulder tool enables the use of separate spindles and separate tool holders for the friction stir welding tools. This also enables reduced tolerances between the tools that produces better friction stir welds, and enables easier replacement of the two tools that reduces man-hours and downtime of the friction stir welding apparatus. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     Further features of the invention are set forth in the following detailed description of the preferred embodiment of the invention and in the drawing figures wherein:  
         [0017]      FIG. 1  is a perspective view of a portion of a conventional machine, such as a milling machine, that has been modified to house the tool-in-tool friction stir welding apparatus of the present invention;  
         [0018]      FIG. 2  is a cross section of a portion of the machine shown in  FIG. 1  taken along the line  2 - 2  of  FIG. 1 ;  
         [0019]      FIG. 3  is an exploded view of the component parts of the tool-in-tool friction stir welding apparatus of the invention; and  
         [0020]      FIG. 4  is a partial cross section of the friction stir welding apparatus of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]      FIG. 1  shows a portion of a conventional friction stir welding machine  12 , for example a milling machine, that has been modified by the tool-in-tool apparatus of the present invention to perform friction stir welding operations. Because various types of milling machines exist and their constructions are well known, the component parts of the machine  12  shown in  FIG. 1  will not be described in detail. The machine  12  includes a spindle carriage  14  that supports the friction stir welding tool-in-tool apparatus of the invention over materials to be welded (not shown). As is conventional, the machine  12  is capable of moving the materials to be welded laterally relative to the spindle carriage  14  in performing the welding operation. The spindle carriage  14  suspends a spindle housing  16  from pivot assemblies  18 . The spindle housing  16  contains the friction stir welding tool-in-tool apparatus of the invention. The connection of the spindle housing  16  to the carriage  14  by the pivot assemblies  18  enables the entire spindle housing to be pivoted by the machine about a horizontal axis that extends through the pivot assemblies.  
         [0022]      FIG. 2  shows a cross section view through a lower portion of the spindle housing  16  of  FIG. 1 .  FIG. 2  shows the modifications made to the conventional machine  12  for the apparatus of the invention. The machine  12  has been modified by replacing the single spindle assembly of the conventional machine with a pair of separate spindle assemblies  22 ,  24 . The two spindle assemblies include a dedicated pin tool spindle  22  and a dedicated shoulder tool spindle  24 . Both spindle tools  22 ,  24  are contained in the spindle housing  16  and operate in the same manner as conventional spindles. The two spindles  22 ,  24  are axially aligned and spaced from each other in the spindle housing  16 . Conventional controls are used to control the operation of the pin tool spindle  22  and shoulder tool spindle  24 . The pin tool spindle  22  and shoulder tool spindle  24  are controlled to rotate independently of each other, and are controlled to rotate at the same or different rates of rotation. In addition, the two spindles  22 ,  24  are controlled to rotate in the same or different directions of rotation. As in the conventional stir friction welding apparatus, the machine  12  can be controlled to move the spindle carriage  14  and the two spindles  22 ,  24  toward and away from the materials to be welded, and laterally relative to the materials to be welded. In addition, the machine  12  and control system are modified to move the two spindles  22 ,  24  toward and away from each other.  
         [0023]     A pin tool  28  of the friction stir welding apparatus of the invention is operatively connected to the pin tool spindle  22 . The pin tool  28  has a generally cylindrical length with opposite proximal  32  and distal  34  end portions with respective proximal  36  and distal  38  end surfaces. The pin tool  28  has a center axis  42  that is also the center axis of the pin tool spindle  22  and the shoulder tool spindle  24 . The pin tool  28  has a generally cylindrical exterior surface  44  along its length. The pin tool circumference tapers down to a reduced diameter at the distal end portion  34  of the tool. The distal end portion  34  at the distal end surface  38  of the pin tool function as the pin of the friction stir welding apparatus of the invention.  
         [0024]     A pin tool holder  46  operatively connects the pin tool  28  to the pin tool spindle  22  for rotation of the pin tool with the spindle. The pin tool holder  44  is a conventional holder, for example a standard HSK E-40 tool holder or other equivalent holder that removably attaches the pin tool  28  to the pin tool spindle  22  without the use of separate fasteners. The pin tool holder  46  engages around the exterior surface of the pin tool at the proximal end portion  32  and engages inside the pin tool spindle  22  in attaching the pin tool to the spindle in a conventional manner. With the pin tool  28  removably attached to the pin tool spindle  22 , the pin tool rotates with the rotation of the pin tool spindle and moves axially with axial movements of the pin tool spindle.  
         [0025]     The shoulder tool  48  of the invention receives the pin tool  28 . The shoulder tool  48  has a length with opposite proximal  52  and distal  54  end portions at respective proximal  56  and distal  58  end surfaces of the tool. A hollow interior bore  62  extends through the length of the shoulder tool  48  and emerges from the opposite proximal end surface  56 , and distal end surface  58  of the tool. The center bore  62  has a center axis that is coaxial with the pin tool center axis  42 . The pin tool  28  is mounted in the shoulder tool center bore  62  with the proximal end portion  32  of the pin tool projecting from the shoulder tool  48 . This enables attachment of the pin tool holder  46  to the pin tool proximal end portion  32 . The pin tool  28  is mounted in the shoulder tool center bore  62  for relative rotational movement of the two tools and for relative axial movement of the two tools. The mounting of the pin tool  28  in the shoulder tool center bore  62  enables a close tolerance between the cylindrical exterior surface of the pin tool  28  and the cylindrical interior surface of the shoulder tool bore  62 . The shoulder tool distal end surface  58  functions as the shoulder surface during friction stir welding operations performed by the apparatus, and the juncture between the shoulder tool distal end surface  58  and the distal end portion  34  of the pin tool  28  defines the shoulder of the friction stir welding apparatus.  
         [0026]     The shoulder tool holder  66  is a modified conventional tool holder, for example a modified HSK A-100 tool holder. The shoulder tool holder  66  is modified with a center bore  68  that matches the diametric dimensions of the shoulder tool center bore  62 . This enables the pin tool  28  to pass entirely through the shoulder tool holder  66  and the shoulder tool  48  and to move freely, with minimal run-out or tolerance between the shoulder tool and the pin tool. The modified shoulder tool holder  66  also removably attaches the shoulder tool  48  to the shoulder tool spindle  24  without the use of separate fasteners.  
         [0027]     With the friction stir welding pin tool  28  held to the pin tool spindle  22  by the pin tool holder  46 , and with the friction stir welding shoulder tool  48  held to the shoulder tool spindle  24  by the shoulder tool holder  66 , the pin tool  28  extends axially through the center bore  68  of the shoulder tool holder and through the center bore  62  of the shoulder tool. Rotation of the pin tool spindle  22  and the shoulder tool spindle  24  rotates both the pin tool  28  and the shoulder tool  48  in the same or opposite directions, and at the same or different rates of rotation. In addition, relative axial movement between the pin tool spindle  22  and the shoulder tool spindle  24  moves the pin tool  28  axially through the shoulder tool center bore  62 . This enables the distal end surface  38  of the pin tool to be extended outwardly from the distal end surface  58  of the shoulder tool to produce the relatively positioned pin and shoulder surfaces used in the friction stir welding process. Movement of the pin tool spindle  22  relative to the shoulder tool spindle  24  also enables the retraction of the pin tool distal end portion  34  into the shoulder tool center bore  62  with the pin tool distal end surface  38  being retracted to the shoulder tool distal end surface  58  when the welding process is completed.  
         [0028]     The tool-in-tool arrangement of the pin tool and shoulder tool enables the use of separate spindles and separate tool holders for the friction stir welding tools. This enables reduced tolerances between the tools that produces better friction stir welds, and enables easier replacement of the two tools that reduces man-hours and downtime of the friction stir welding apparatus.  
         [0029]     Although the apparatus of the invention has been described above by reference to a particular embodiment, it should be understood that variations and modifications could be made to the apparatus without departing from the intended scope of the following claims.