Abstract:
A friction stir welding apparatus and a method of operating the friction stir welding apparatus are disclosed. The friction stir welding apparatus includes a rotary tool whose extremity constitutes a probe, a retaining arm which supports the rotary tool, and a roller provided at a position of the retaining arm opposite the rotary tool. The method includes adjusting the retaining arm so as to position workpieces between the rotary tool and the roller while adjusting the roller to turn in a direction where a joint line of the workpieces extends, rotating the rotary tool and lowering the probe until the probe presses the workpieces, gradually inserting the probe into the joint line, and moving the probe along the joint line.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the foreign priority benefit under Title 35, United States Code, §119(a)-(d) of Japanese Patent Applications No. 2006-024028 filed on Feb. 1, 2006 in the Japan Patent Office, the disclosure of which is herein incorporated by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a friction stir welding apparatus and a method of operating a friction stir welding apparatus. The Friction stir welding apparatus is usually attached to a distal end of an arm of an articulated robot. 
   In recent years, friction stir welding has been widely used as a joint technology without causing a deformation of workpieces to be joined together due to heat generating in the welding process. Friction stir welding is a joining process for joining two members (workpieces) together along a joint line at a joint region (butted region) of the two workpieces by rotating and pressing a rotary tool against the joint region and gradually inserting the same into the joint line, so that the material of the workpieces undergoes plastic deformation under the rotating force of the rotary tool, allowing the rotary tool to move along the joint line to thereby join the two workpieces together. 
   A friction stir welding apparatus is known, for example, by Japanese Laid-open Patent Application No. 2002-103061. This friction stir welding apparatus includes a retaining arm, to which a rotary tool and a receiving table are fixed in a position opposite to each other. The retaining arm of the friction stir welding apparatus is attached to a distal end of an arm of an articulated robot (hereinafter referred to as a robot arm) so that the friction stir welding apparatus is movable in three-dimensional directions through the robot arm. Meanwhile, workpieces are set on a work table, whose lower surface is provided with feed rollers. The friction stir welding apparatus is operated such that after the upper surface of the receiving table is adjusted to come into contact with the rollers so that the reaction force is applied to the friction stir welding apparatus, the rotary tool which is rotating is pressed against and inserted into the workpieces and then moved along the joint line of the workpieces, to thereby join the two workpieces together. 
   According to this friction stir welding apparatus, since the receiving table is fed by the feed rollers of the work table, the receiving table is capable of moving only in the feeding direction of the feed rollers during the welding process of the workpieces. Therefore, if the workpieces are joined together along a joint line extending in two or more directions, it is necessary to change the direction of the workpieces and set them on the work table whenever the direction of the joint line changes. This requires much time and labor, and thus increases the production cost in the end. 
   With the foregoing drawback of the prior art apparatus in view, the present invention seeks to provide a friction stir welding apparatus and a method of operating a friction stir welding apparatus, which can be readily used with workpieces to be welded along a joint line extending in two or more directions. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of the present invention, there is provided a friction stir welding apparatus comprising: a rotary tool whose extremity constitutes a probe; a retaining arm which supports the rotary tool; and a roller provided at a position of the retaining arm opposite the rotary tool. 
   According to a second aspect of the present invention, there is provided a method of operating a friction stir welding apparatus, which comprises: a rotary tool whose extremity constitutes a probe; a retaining arm which supports the rotary tool; and a roller provided at a position of the retaining arm opposite the rotary tool. The method comprises the steps of: adjusting the retaining arm so as to position workpieces between the rotary tool and the roller while adjusting the roller to turn in a direction where a joint line of the workpieces extends; rotating the rotary tool and lowering the probe until the probe presses the workpieces; gradually inserting the probe into the joint line; and moving the probe along the joint line. 
   With these constructions, after the roller comes into contact with the lower surface of the work table (or workpiece(s) per se) onto which workpieces are set, the rotary tool is rotated and the probe is lowered until it presses the workpieces. The rotation of the rotary tool makes the material of the workpieces soften and allows the probe to be gradually inserted into the joint line at the joint region or the butted region of the workpieces. The probe is then moved along the joint line of the workpieces, so that the workpieces are joined together. Since the roller is provided on the retaining arm, it is possible to move the retaining arm relative to the work table in any arbitrary directions. Therefore, the friction stir welding apparatus and the method of operating the friction stir welding apparatus according to the present invention do not require setting the workpieces on the work table in conformity with the direction of the rollers of the work table whenever the direction of the joint line changes, which makes it possible to use with workpieces to be welded along a joint line extending in any directions. 
   In the aforementioned friction stir welding apparatus and method, the roller may be a caster roller attached to a rotary shaft member which rotates about an identical axis with a rotation axis of the rotary tool. 
   With this construction, since the direction of the roller can be changed by turning the rotary shaft member, it is possible to change the traveling direction of the retaining arm without requiring an adjustment of the retaining arm. This enables the friction stir welding apparatus and the method of operating the friction stir welding apparatus to be readily used with workpieces to be welded along a joint line extending in two or more directions. 
   In the aforementioned friction stir welding apparatus and method, the retaining arm may be attached to a distal end of a robot arm, which is movable in three-dimensional directions. 
   With this construction, even if the joint line of the workpieces extends along an uneven and stepped surface, manipulating the robot arm makes it possible to follow the retaining arm along the joint line. Therefore, it is possible to continuously join the workpieces together along the joint line. 
   In the aforementioned friction stir welding apparatus and method, the retaining arm may be of a C-shaped form. 
   With this construction, it is possible to effectively arrange the rotary tool and the roller in a position opposite to each other. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aspects of the present invention will become more apparent by describing in detail illustrative, non-limiting embodiment thereof with reference to the accompanying drawings, in which: 
       FIG. 1  is a perspective view of a general-purpose articulated robot, to which is attached a friction stir welding apparatus according to one embodiment of the present invention; 
       FIG. 2A  is a front view of the friction stir welding apparatus, illustrating a state before the welding process is performed, and  FIG. 2B  is a front view of the friction stir welding apparatus, illustrating a state during the welding process; 
       FIG. 3  is an enlarged perspective view of the friction stir welding apparatus, illustrating main parts during the welding process; 
       FIG. 4A  is a front view of the friction stir welding apparatus, illustrating a state when the welding process is initiated, and  FIG. 4B  is a front view of the friction stir welding apparatus, illustrating a state during the welding process; and 
       FIG. 5  is a front view of a friction stir welding apparatus according to a modified embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   One preferred embodiment of the present invention will be described with reference to the accompanying drawings. 
   As seen in  FIG. 1 , a friction stir welding apparatus  1  is attached to a general-purpose articulated robot  10  and is movable in three-dimensional directions. At first, the articulated robot  10  will be described below. 
   Articulated Robot 
   The articulated robot  10  includes a turn table  11 , and first, second and third arms (robot arm)  12 ,  13 ,  14  which are in this order joined together from the turn table  11  toward the distal end of the robot arm. 
   The turn table  11  is attached to a base  15  installed on the installation surface and rotatable around an axis substantially extending in the direction perpendicular to the base  15 . The first arm  12  is attached to the turn table  11  through a first shaft member  16   a  which is pivotally supported on the turn table  11 . The first arm  12  is therefore rotatable around the axis of the first shaft member  16   a . The second arm  13  is attached to the first arm  12  through a second shaft member  16   b  which is pivotally supported on the first arm  12 . The second arm  13  is therefore rotatable around the axis of the second shaft member  16   b . The third arm  14  is attached to the second arm  13  through a third shaft member  16   c . The third arm  14  is therefore rotatable around the axis of the third shaft member  16   c . The third arm  14  is also rotatable relative to the axis substantially orthogonal to the axis of the third shaft member  16   c . A retaining arm  2  of the friction stir welding apparatus  1  is attached to the distal end of the third arm  14 . 
   Likewise any known conventional articulated robot, according to the articulated robot  10  as constructed above, when the first shaft member  16   a , the second shaft member  16   b , the third shaft member  16   c , and the turn table  11  are driven by a hydraulic system (not shown), each of the first to third arms  12 - 14  operates so that the friction stir welding apparatus  1  attached to the distal end of the third arm  14  is movable in three-dimensional directions. 
   Friction Stir Welding Apparatus 
   With reference to  FIGS. 2A and 2B , the friction stir welding apparatus  1  will be described. In this preferred embodiment, the position of the friction stir welding apparatus  1  as shown in  FIGS. 2A and 2B  is considered as a reference position, in which the distal end of the rotary tool faces downward, and upward and downward directions are defined based on this reference position. 
   As seen in  FIG. 2A , the friction stir welding apparatus  1  includes a retaining arm  2 , a rotary tool  3  supported on the retaining arm  2 , a drive unit  4  for driving the rotary tool  3 , and a roller member  5  supported on the retaining arm  2 . 
   The retaining arm  2  is an arm member in the shape of a letter C as seen from the front. The rotary tool  3  is arranged at the upper part of the retaining arm  2 , and the roller member  5  is arranged at the lower part of the retaining arm  2 . The rotary tool  3  and the roller member  5  are positioned opposite to each other. 
   The rotary tool  3  is a tool for joining workpieces W 1 , W 2  together. The rotary tool  3  includes a cylindrical body portion  31 , and a probe  32  coaxially extending from the extremity of the body portion  31 . The body portion  31  is coupled to the drive unit  4  to be described later. The probe  32  is a pin-shaped member having a diameter smaller than the body portion  31 , and the outer periphery of the probe  32  provides a threaded screw. The length of the probe  32  is substantially the same as the thickness of the work piece W 2 . The body potion  31  and the probe  32  are made of a material which is harder than the workpieces W 1 , W 2  and having a heat-resistant property for resisting frictional heat caused by the friction stir welding process. 
   The drive unit  4  is arranged at an upper inner side of the retaining arm  2 , and includes a pressing drive unit  41  for moving the rotary tool  3  toward and away from the workpieces W, W 2 , and a rotary drive unit  42  for rotating the rotary tool  3 . 
   The pressing drive unit  41  is mounted on a mount bracket B 1  fixed to the upper part of the retaining arm  2 . The pressing drive unit  41  includes a servo motor  41   a , a ball screw  41   b , a slide-guide rail  41   c , and a slide table  41   d.    
   Torque of the servo motor  41   a  is transmitted to the ball screw  41   b  through a drive belt V. The ball screw  41   b  is a mechanism which converts the torque of the servo motor  41   a  into the axial pushing force and then transmits the axial pushing force to the slide table  41   d . The slide-guide rail  41   c  is a rail for guiding the slide table  41   d . The slide-guide rail  41   c  is attached to the mount bracket B 1  and the supporting portion B 2 , and extends in parallel with the ball screw  41   b . The slide table  41   d  is supported through a nut (not shown), which is threadedly engageable with the ball screw  41   b , over the ball screw  41   b  and the slide-guide rail  41   c . The rotary tool  3  is further attached to the slide table  41   d  through the rotary drive unit  42 . 
   In the pressing drive unit  41 , when the servo motor  41   a  is driven and the ball screw  41   b  rotates, this rotating force of the ball screw  41   b  is transmitted to the slide table  41   d  as the axial pushing force to thereby move the slide table  41   d  in one direction along the slide-guide rail  41   c . The slide table  41   d  moves up and down when the ball screw  41   b  is rotated in the clockwise and counterclockwise directions. Therefore, the rotary tool  3  can be moved in the directions toward and away from the workpieces W 1 , W 2 . 
   The rotary drive unit  42  consists of a servo motor, and is attached to the slide table  41   d . The rotary shaft of the servo motor as the rotary drive unit  42  is coupled with the rotary tool  3  so that when the rotary drive unit  42  is driven, the rotary tool  3  rotates. 
   The roller member  5  supports a load (pressing force), which is applied by the rotary tool  3  to the workpieces W 1 , W 2  during the welding process, from the lower side of the work table T to be fixed to a predetermined position. The roller member  5  also guides the movement of the retaining arm  2 . The roller member  5  is a so-called caster including a rotary shaft member  51 , and a caster roller (roller)  52  attached to the rotary shaft member  51 . 
   The rotary shaft member  51  includes a shaft main body  51   a , and a roller holder  51   b  provided at the upper part of the shaft main body  51   a . The shaft main body  51   a  is mounted on the retaining arm  2  in such a manner as to be coaxial with (the axis of the shaft main body  51   a  is identical with) and rotatable with the rotation axis of the rotary tool  3 . The rotary shaft member  51  extends along the same axis as that of the rotary tool  3 , so that the load from the rotary tool  3  can be linearly received by the rotary shaft member  51 . Further, turning the rotary shaft member  51  allows the caster roller  52  to be directed to any arbitrary directions. The roller holder  51   b  is a U-shaped member for rotatably supporting therein the caster roller  52 . 
   The caster roller  52  includes a roller shaft  52   a  orthogonal to the axis of the rotary shaft member  51 , and a roller body  52   b  integral with the roller shaft  52   a . Both ends of the roller shaft  52   a  are supported by the roller holder  51   b . The roller body  52   b  is a cylindrical member whose roller surface faces toward the rotary tool  3 , and the roller shaft  52   a  penetrates through the center of the roller body  52   b . The roller body  52   b  rotates around the axis of the roller shaft  52   a  to guide the retaining arm  2  along the work table T. The width of the roller body  52   b  can be modified when necessary in accordance with the load applied from the rotary tool  3 . 
   Workpieces W 1 , W 2   
   Workpieces W 1 , W 2  (members to be joined together along the joint line) will be described below. The workpieces W 1 , W 2  are members, for example, made of aluminum alloy. The workpiece W 1  is a longitudinal member whose cross-section is trapezoidal. The workpiece W 2  is a thin plate-like member which is pressed into the shape to cover the upper surface of the workpiece W 1 . The workpieces W 1 , W 2  are placed one on top of another and set on (fixed to) the work table T. The workpieces W 1 , W 2  are welded by the friction stir welding apparatus  1 . 
   Operation of Friction Stir Welding Apparatus 
   With reference to the drawings, the operation of the friction stir welding apparatus  1  will be described. In the following description, an explanation will be given of the case in which the workpieces W 1 , W 2  are joined together along the joint line L 1  as shown in  FIG. 3 . In order to move the friction stir welding apparatus  1  along a predetermined locus, the movement of the articulated robot  10  is programmed (taught) in advance in accordance with shapes of the workpieces W 1 , W 2 . 
   At first, as seen in  FIG. 1 , the articulated robot  10  is operated to move the friction stir welding apparatus  1 . To be more specific, as seen in  FIG. 2A , the retaining arm  2  is moved and positioned for the workpieces W 1 , W 2  to be set on the work table T between the rotary tool  3  and the roller member  5 . The roller body  52   b  of the roller member  5  is then moved to come into contact with the lower surface of the work table T. During this time, the roller body  52   b  of the roller member  5  is adjusted to turn in the direction where the joint line L 1  of the workpieces W 1 , W 2  extends. 
   The pressing drive unit  41  is driven while driving the rotary drive unit  42  and thus rotating the rotary tool  3 . The rotary tool  3  then lowers while rotating, so that the probe  32  presses the workpieces W 1 , W 2 . As seen in  FIG. 2B , the workpieces W 1 , W 2  are softened by frictional heat caused by the rotation of the rotary tool  3 , and the probe  32  of the rotary tool  3  is gradually inserted into the softened area of the workpiece W 2  that is positioned above the workpiece W 1 . The probe  32  then reaches a region adjacent to the joint region of the workpieces W 1 , W 2 . During this time, the work table T is supported by the roller member  5  positioned below the work table T. Since the work table T is supported by the roller member  5 , a sufficient reaction force can be obtained from below the work table T against the pressing force of the probe  32 . According to the friction stir welding apparatus  1 , even if an increased load is applied from the rotary tool  3  to the workpieces W 1 , W 2 , the reaction force can be adjusted at the pressing drive unit  41 . 
   As seen in  FIG. 3 , the probe  32  of the rotary tool  3  is then moved along the joint line L 1  of the workpieces W 1 , W 2  while the probe  32  which is rotating is inserted into the workpiece W 2 . The movement of the probe  32  can be facilitated because the roller body  52   b  of the roller member  5  turns. Rotating and moving the probe  32  along the joint line L 1  enables the material of the workpieces W 1 , W 2  to be plasticized in a region adjacent to the joint region of the workpieces W 1 , W 2  due to frictional heat generated between the probe  32  and the material of the workpieces W, W 2 . Therefore, the workpieces W 1 , W 2  are joined together along the joint line L 1 . 
   According to the friction stir welding apparatus  1 , even if a joint line of workpieces extends along an uneven and stepped surface, it is possible to continuously join the workpieces together along the joint line. For example, the friction stir welding apparatus  1  is able to join the workpieces W 1 , W 2  together along the joint line L 2  as shown in  FIG. 3 . 
   As shown in  FIG. 4A , the position of the retaining arm  2  is adjusted so that the line connecting the rotary tool  3  and the roller member  5  becomes substantially orthogonal to the joint region of the workpieces W 1 , W 2 . Thereafter, the probe  32  of the rotary tool  3  that is rotating is gradually inserted into the joint line L 2  ( FIG. 3 ) in the joint region of the workpieces W 1 , W 2  while supporting the lower surface of the work table T by the roller member  5 . Next, as shown in  FIG. 4B , while positioning the workpieces W 1 , W 2  between the rotary tool  3  and the roller member  5 , the rotary tool  3  is moved along the joint line L 2  as shown in  FIG. 3 . During this time, the tilt angle of the retaining arm  2  is adjusted through the articulated robot  10  so that a load from the rotary tool  3  constantly acts in the direction orthogonal to the joint line L 2 . Further, the vertical movement distance of the rotary tool  3  is adjusted through the pressing drive unit  41  so that the insertion depth of the probe  32  into the workpiece W 2  is kept constant. Therefore, the workpieces W 1 , W 2  are highly accurately joined together along the joint line L 2 . The pressing force of the rotary tool  3  against the workpieces W 1 , W 2  is controlled, for instance, by detecting the reaction force applied to the rotary tool  3  with the use of a pressure sensor, and by controlling the servo motor  41   a  based on this detected value. 
   According to the friction stir welding apparatus  1 , the following advantages can be obtained. 
   In the friction stir welding apparatus  1 , the roller member  5  is provided on the retaining arm  2 . Therefore, unlike the conventional arrangement in which the work table is provided with rollers, the retaining arm  2  can be moved in any arbitrary directions relative to the work table T. Therefore, the friction stir welding apparatus  1  does not require setting the workpieces W 1 , W 2  in conformity with the direction of the rollers of the work table T whenever the direction of the joint line L 2  changes, which makes it possible to use with workpieces to be welded along a joint line extending in any directions (two or more directions) on a plane. 
   In the friction stir welding apparatus  1 , even if the joint line L 2  extends along an uneven and stepped surface, manipulating the robot arm  10  makes it possible to follow the retaining arm  2  along the joint line L 2 . Especially, since the roller member  5  is provided on the retaining arm  2 , the roller member  5  tilts in such a manner as to follow the tilting movement of the retaining arm  2 . This makes it possible to generate a sufficient reaction force from below the workpieces W 1 , W 2 . Therefore, even if the workpieces W 1 , W 2  extend in three-dimensional directions, the workpieces can be continuously and highly accurately joined together along the joint line L 2 . 
   While a friction stir welding apparatus according to the present invention has been described in detail with reference to the preferred embodiment thereof, the present invention is not limited to this specific embodiment and various changes and modifications may be made without departing from the scope of the attached claims. 
   In the above preferred embodiment, the rotary shaft member  51  of the roller member  5  is coaxial with (on the same axis with) the rotation axis of the rotary tool  3  (see  FIG. 2A ). However, the tool center line Al of the rotary tool  3  (i.e., axis of the rotary tool  3 ) and the roller center line A 2  of the caster roller  52  may be slightly offset from each other such as shown in  FIG. 5 . To be more specific, the roller holder  51   c  of the rotary shaft member  51  may support the roller shaft  52   a  at a position slightly more inward of the retaining arm  2  when compared with the arrangement described in the above preferred embodiment. This enables the roller member  5  to always follow the joint line L 2  in the traveling direction. Therefore, notwithstanding any complicated shape of the joint line L 2 , the workpieces W 1 , W 2  can be joined together to provide a high-quality welding. 
   In the above preferred embodiment, the workpieces W 1 , W 2  are both made of the same kind of material such as aluminum alloy. However, the friction stir welding apparatus  1  can be applicable to other workpieces made of the same material other than aluminum alloy or different kinds of materials. 
   In the above preferred embodiment, the workpieces W 1 , W 2  are joined together while they are superposed one on top of another. However, the friction stir welding apparatus  1  can be applicable to other workpieces whose end surfaces are butted together. 
   In the above preferred embodiment, the workpieces W 1 , W 2  are set on the work table T and the work table T is supported from the lower surface side. However, the workpieces W 1 , W 2  may be directly supported from the lower surface side thereof. 
   In the above preferred embodiment, the roller member  5  is a so-called caster roller. However, the roller body  52   b  may be directly fixed to the retaining arm  2 . In this configuration, the direction of the retaining arm  2  is adjusted when necessary in accordance with the direction of the joint line during the welding process. 
   In the above preferred embodiment, the friction stir welding apparatus  1  is attached to the distal end of the robot arm so as to be movable in three-dimensional directions. However, the friction stir welding apparatus  1  may be attached to equipment which allows two-dimensional movement on a plane. 
   Further, in the above preferred embodiment, the retaining arm  2  is provided with one roller member  5 . However, two or more roller members  5  may be provided.