Patent Publication Number: US-2022226927-A1

Title: Method for producing hollow container

Description:
TECHNICAL FIELD 
     The present invention relates to a method for producing a hollow container. 
     RELATED ART 
     For example, Patent Document 1 discloses an invention to perform friction-stir joining on a pair of metal members having a plate shape, with use of a rotary tool. In the invention, an auxiliary member softer than the metal members is interposed therebetween, and the rotary tool is inserted into the auxiliary member to perform friction stirring. Performing friction-stir joining on metal members having high hardness severely damages the rotary tool so that tool cost is increased. However, with the invention, the rotary tool is inserted into the soft auxiliary member to perform friction-stir joining so that the metal members having high hardness are suitably joined to each other. 
     RELATED ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Japanese Patent Application Publication No. 2007-83242 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the conventional joining method, a stirring pin of the rotary tool has a columnar shape, to have a problem that the stirring pin is not easily inserted into the auxiliary member. Further, friction stirring is performed with a shoulder of the rotary tool kept in contact with the metal members, to have a large load reacting on a friction stirring device. 
     In view of such problems, the present invention is intended to provide a method for producing a hollow container using a joining method, with which metal members having high hardness are suitably joined to each other. 
     To solve the problems described above, the present invention provides a method for manufacturing a hollow container with use of a rotary tool including a tapered stirring pin, the method including: preparing a first metal member having a concave portion which is formed by a bottom and a peripheral wall extending from a peripheral edge of the bottom, a second metal member having a concave portion which is formed by a bottom and a peripheral wall extending from a peripheral edge of the bottom, and an auxiliary member having a frame shape; butting, in which an end surface of the peripheral wall of the first metal member and an end surface of the peripheral wall of the second metal member are faced with each other, the auxiliary member is interposed in a gap between the end surfaces, the end surface of the peripheral wall of the first metal member is butted against one side surface of the auxiliary member to form a first butted portion, and the end surface of the peripheral wall of the second metal member is butted against the other side surface of the auxiliary member to form a second butted portion; and joining, in which the rotating rotary tool is inserted only through an external surface of the auxiliary member and is relatively moved along the first butted portion and the second butted portion, with only the stirring pin contacting the auxiliary member and an outer peripheral surface of the stirring pin slightly contacting the first and second metal members, to join the first metal member to the second metal member via the auxiliary member, wherein the first metal member, the second metal member, and the auxiliary member are made of aluminum or an aluminum alloy, and the first metal member and the second metal member have higher hardness than the auxiliary member, and the end surface of the peripheral wall of at least one of the first metal member and the second metal member has an inclined surface to face outward, and the auxiliary member has an inclined surface, which is tapered from the external surface toward an internal surface, on at least one side surface. 
     Further, a method for manufacturing a hollow container with use of a rotary tool including a tapered stirring pin, the method including: preparing a first metal member having a concave portion which is formed by a bottom and a peripheral wall extending from a peripheral edge of the bottom, a second metal member having a concave portion which is formed by a bottom and a peripheral wall extending from a peripheral edge of the bottom, and an auxiliary member having a frame shape; butting, in which an end surface of the peripheral wall of the first metal member and an end surface of the peripheral wall of the second metal member are faced with each other, the auxiliary member is interposed in a gap between the end surfaces, the end surface of the peripheral wall of the first metal member is butted against one side surface of the auxiliary member to form a first butted portion, and the end surface of the peripheral wall of the second metal member is butted against the other side surface of the auxiliary member to form a second butted portion; and joining, in which the rotating rotary tool is inserted only through an external surface of the auxiliary member and is relatively moved along the first butted portion and the second butted portion, with only the stirring pin contacting the auxiliary member and an outer peripheral surface of the stirring pin slightly contacting the first and second metal members, to join the first metal member to the second metal member via the auxiliary member, wherein the first metal member, the second metal member, and the auxiliary member are made of aluminum or an aluminum alloy, and the first metal member and the second metal member have higher hardness than the auxiliary member, and the end surfaces of the peripheral walls of the first metal member and the second metal member have inclined surfaces to face outward, and the auxiliary member has inclined surfaces, which are tapered from the external surface toward an internal surface, on both side surfaces. 
     Further, the present invention provides a method for manufacturing a hollow container with use of a rotary tool including a tapered stirring pin, the method including: preparing a first metal member having a concave portion which is formed by a bottom and a peripheral wall extending from a peripheral edge of the bottom, a second metal member having a concave portion which is formed by a bottom and a peripheral wall extending from a peripheral edge of the bottom, and an auxiliary member having a frame shape; butting, in which an end surface of the peripheral wall of the first metal member and an end surface of the peripheral wall of the second metal member are faced with each other, the auxiliary member is interposed in a gap between the end surfaces, the end surface of the peripheral wall of the first metal member is butted against one side surface of the auxiliary member to form a first butted portion, and the end surface of the peripheral wall of the second metal member is butted against the other side surface of the auxiliary member to form a second butted portion; and joining, in which the rotating rotary tool is inserted only through an external surface of the auxiliary member and is relatively moved along the first butted portion and the second butted portion, with only the stirring pin contacting the auxiliary member and an outer peripheral surface of the stirring pin slightly contacting the first and second metal members, to join the first metal member to the second metal member via the auxiliary member, wherein the first metal member, the second metal member, and the auxiliary member are made of aluminum or an aluminum alloy, and the first metal member and the second metal member have higher hardness than the auxiliary member, the end surface of the peripheral wall of at least one of the first metal member and the second metal member has an inclined surface to face outward, and the auxiliary member has an inclined surface, which is tapered from the external surface toward an internal surface, on at least one of the side surfaces, and has a protrusion, which extends on at least one of the side surfaces side, on the internal surface. 
     Further, the present invention provides a method for manufacturing a hollow container with use of a rotary tool including a tapered stirring pin, the method including: preparing a first metal member having a concave portion which is formed by a bottom and a peripheral wall extending from a peripheral edge of the bottom, a second metal member having a concave portion which is formed by a bottom and a peripheral wall extending from a peripheral edge of the bottom, and an auxiliary member having a frame shape; butting, in which an end surface of the peripheral wall of the first metal member and an end surface of the peripheral wall of the second metal member are faced with each other, the auxiliary member is interposed in a gap between the end surfaces, the end surface of the peripheral wall of the first metal member is butted against with one side surface of the auxiliary member to form a first butted portion, and the end surface of the peripheral wall of the second metal member is butted against the other side surface of the auxiliary member to form a second butted portion; and joining, in which the rotating rotary tool is inserted only through an external surface of the auxiliary member and is relatively moved along the first butted portion and the second butted portion, with only the stirring pin contacting the auxiliary member and an outer peripheral surface of the stirring pin slightly contacting the first and second metal members, to join the first metal member to the second metal member via the auxiliary member, wherein the first metal member, the second metal member, and the auxiliary member are made of aluminum or an aluminum alloy, and the first metal member and the second metal member have higher hardness than the auxiliary member, the end surfaces of the peripheral walls of the first metal member and the second metal member have inclined surfaces to face outward, and the auxiliary member has inclined surfaces, which are tapered from the external surface toward an internal surface, on both of the side surfaces, and has a protrusion, which extends on at least one of the side surfaces side, on the internal surface. 
     The method for manufacturing a hollow container uses the rotary tool including the tapered stirring pin, which is easily inserted into the auxiliary member. Further, only the stirring pin is inserted into the auxiliary member so that a load reacting on a friction stirring device is reduced. Further, the rotary tool is inserted into the auxiliary member which is softer than the first metal member and the second metal member, to allow the rotary tool to have a longer service life. Still further, the stirring pin is slightly brought in contact with the first metal member and the second metal member, so that joining strength is increased. 
     Further, when the protrusion, which extends on at least one side surface side, is provided on the internal surface of the auxiliary member, the auxiliary member is prevented from coming off at a time of friction stirring. Accordingly, the auxiliary member is prevented from being displaced with respect to the first metal member and the second metal member, to perform friction-stir joining more suitably. 
     Further, in the joining step, the rotary tool is desirably moved over an entire outer peripheral surfaces of the first metal member and the second metal member. With this setting, a hollow container has increased sealing property. 
     Further, the present invention provides a method for manufacturing a hollow container with use of a rotary tool including a tapered stirring pin, the method including: preparing a first metal member having a concave portion which is formed by a bottom and a peripheral wall extending from a peripheral edge of the bottom, a second metal member having a plate shape, and an auxiliary member having a frame shape; butting, in which an end surface of the peripheral wall of the first metal member and a peripheral edge on an internal surface of the second metal member are faced with each other, the auxiliary member is interposed in a gap between the end surface and the peripheral edge, the end surface of the peripheral wall of the first metal member is butted against one side surface of the auxiliary member to form a first butted portion, and the peripheral edge on the internal surface of the second metal member is butted against the other side surface of the auxiliary member to form a second butted portion; and joining, in which the rotating rotary tool is inserted only through an external surface of the auxiliary member and is relatively moved along the first butted portion and the second butted portion, with only the stirring pin contacting the auxiliary member and an outer peripheral surface of the stirring pin slightly contacting the first and second metal members, to join the first metal member to the second metal member via the auxiliary member, wherein the first metal member, the second metal member, and the auxiliary member are made of aluminum or an aluminum alloy, and the first metal member and the second metal member have higher hardness than the auxiliary member, and at least one of the end surface of the peripheral wall of the first metal member and the peripheral edge on the internal surface of the second metal member has an inclined surface to face outward, and the auxiliary member has an inclined surface, which is tapered from the external surface toward an internal surface, on at least one side surface. 
     Further, the present invention provides a method for manufacturing a hollow container with use of a rotary tool including a tapered stirring pin, the method including: preparing a first metal member having a concave portion which is formed by a bottom and a peripheral wall extending from a peripheral edge of the bottom, a second metal member having a plate shape, and an auxiliary member having a frame shape; butting, in which an end surface of the peripheral wall of the first metal member and a peripheral edge on an internal surface of the second metal member are faced with each other, the auxiliary member is interposed in a gap between the end surface and the peripheral edge, the end surface of the peripheral wall of the first metal member is butted against one side surface of the auxiliary member to form a first butted portion, and the peripheral edge on the internal surface of the second metal member is butted against the other side surface of the auxiliary member to form a second butted portion; and joining, in which the rotating rotary tool is inserted only through an external surface of the auxiliary member and relatively moved along the first butted portion and the second butted portion, with only the stirring pin contacting the auxiliary member and an outer peripheral surface of the stirring pin slightly contacting the first and second metal members, to join the first metal member to the second metal member via the auxiliary member, wherein the first metal member, the second metal member, and the auxiliary member are made of aluminum or an aluminum alloy, and the first metal member and the second metal member have higher hardness than the auxiliary member, and the end surface of the peripheral wall of the first metal member and the peripheral edge on the internal surface of the second metal member have inclined surfaces to face outward, and the auxiliary member has inclined surfaces, which are tapered from the external surface toward an internal surface, on both side surfaces. 
     Further, the present invention provides a method for manufacturing a hollow container with use of a rotary tool including a tapered stirring pin, the method including: preparing a first metal member having a concave portion which is formed by a bottom and a peripheral wall extending from a peripheral edge of the bottom, a second metal member having a plate shape, and an auxiliary member having a frame shape; butting, in which an end surface of the peripheral wall of the first metal member and a peripheral edge on an internal surface of the second metal member are faced with each other, the auxiliary member is interposed in a gap between the end surface and the peripheral edge, the end surface of the peripheral wall of the first metal member is butted against one side surface of the auxiliary member to form a first butted portion, and the peripheral edge on the internal surface of the second metal member is butted against the other side surface of the auxiliary member to form a second butted portion; and joining, in which the rotating rotary tool is inserted only through an external surface of the auxiliary member and is relatively moved along the first butted portion and the second butted portion, with only the stirring pin contacting the auxiliary member and an outer peripheral surface of the stirring pin slightly contacting the first and second metal members, to join the first metal member to the second metal member via the auxiliary member, wherein the first metal member, the second metal member, and the auxiliary member are made of aluminum or an aluminum alloy, and the first metal member and the second metal member have higher hardness than the auxiliary member, and at least one of the end surface of the peripheral wall of the first metal member and the peripheral edge on the internal surface of the second metal member has an inclined surface to face outward, and the auxiliary member has an inclined surface, which is tapered from the external surface toward an internal surface, on at least one side surface, and has a protrusion, which extends on the at least one side surface side, on the internal surface. 
     Further, the present invention provides a method for manufacturing a hollow container with use of a rotary tool including a tapered stirring pin, the method including: preparing a first metal member having a concave portion which is formed by a bottom and a peripheral wall extending from a peripheral edge of the bottom, a second metal member having a plate shape, and an auxiliary member having a frame shape; butting, in which an end surface of the peripheral wall of the first metal member and a peripheral edge on an internal surface of the second metal member are faced with each other, the auxiliary member is interposed in a gap between the end surface and the peripheral edge, the end surface of the peripheral wall of the first metal member is butted against one side surface of the auxiliary member to form a first butted portion, and the peripheral edge on the internal surface of the second metal member is butted against with the other side surface of the auxiliary member to form a second butted portion; and joining, in which the rotating rotary tool is inserted only through an external surface of the auxiliary member and is relatively moved along the first butted portion and the second butted portion, with only the stirring pin contacting the auxiliary member and an outer peripheral surface of the stirring pin slightly contacting the first and second metal members, to join the first metal member to the second metal member via the auxiliary member, wherein the first metal member, the second metal member, and the auxiliary member are made of aluminum or an aluminum alloy, and the first metal member and the second metal member have higher hardness than the auxiliary member, and the end surface of the peripheral wall of the first metal member and the peripheral edge on the internal surface of the second metal member have inclined surfaces to face outward, and the auxiliary member has inclined surfaces, which are tapered from the external surface toward an internal surface, on both of the side surfaces, and has a protrusion, which extends on at least one of the side surfaces side, on the internal surface. 
     The method for manufacturing a hollow container uses the rotary tool including the tapered stirring pin, which is easily inserted into the auxiliary member. Further, only the stirring pin is inserted into the auxiliary member so that a load reacting on a friction stirring device is reduced. Still further, the rotary tool is inserted into the auxiliary member which is softer than the first metal member and the second metal member, to allow the rotary tool to have a longer service life. Yet further, the stirring pin is slightly brought in contact with the first metal member and the second metal member, so that joining strength is increased. 
     Further, when the protrusion, which extends on at least one side surface side, is provided on the internal surface of the auxiliary member, the auxiliary member is prevented from coming off at a time of friction stirring. Accordingly, the auxiliary member is prevented from being displaced with respect to the first metal member and the second metal member, to perform friction-stir joining more suitably. 
     Further, in the joining step, the rotary tool is desirably moved over around the first metal member and the second metal member. With this setting, a hollow container has increased sealing property. 
     Further, when the first metal member and the second metal member are made of a cast material, and the auxiliary member is made of an expansile material, the cast materials are suitably joined to each other. 
     Advantageous Effects of the Invention 
     With the method for producing a hollow container according to the present embodiment, metal members having high hardness are suitably joined to each other to form a hollow container. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of components in a preparing step of a method for producing a hollow container according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view of an auxiliary member according to the first embodiment, in an unprocessed state; 
         FIG. 3  is a cross-sectional view of the components in a butting step of the method for producing a hollow container according to the first embodiment; 
         FIG. 4  is a cross-sectional view of the components in a joining step of the method for producing a hollow container according to the first embodiment; 
         FIG. 5  is a perspective view of the components in the joining step of the method for producing a hollow container according to the first embodiment; 
         FIG. 6  is a cross-sectional view of components in a butting step of the method for producing a hollow container according to a second embodiment of the present invention; 
         FIG. 7  is a cross-sectional view of components in a butting step of the method for producing a hollow container according to a third embodiment of the present invention; 
         FIG. 8  is a cross-sectional view of the components in a joining step of the method for producing a hollow container according to the third embodiment; 
         FIG. 9  is a perspective view of components in a preparing step of the method for producing a hollow container according to a fourth embodiment of the present invention; 
         FIG. 10  is a cross-sectional view of the components in a joining step of the method for producing a hollow container according to the fourth embodiment; 
         FIG. 11  is a perspective view of the components in the joining step of the method for producing a hollow container according to the fourth embodiment; 
         FIG. 12  is a perspective view of components in a preparing step of the method for producing a hollow container according to a fifth embodiment of the present invention; 
         FIG. 13  is a perspective view of the auxiliary member according to the fifth embodiment, in an unprocessed state; 
         FIG. 14  is a cross-sectional view of the components in a butting step of the method for producing a hollow container according to the fifth embodiment; 
         FIG. 15  is a cross-sectional view of the components in a joining step of the method for producing a hollow container according to the fifth embodiment; 
         FIG. 16  is a perspective view of the components in the joining step of the method for producing a hollow container according to the fifth embodiment; 
         FIG. 17  is a cross-sectional view of components in a butting step of the method for producing a hollow container according to a sixth embodiment of the present invention; 
         FIG. 18  is a cross-sectional view of components in a butting step of the method for producing a hollow container according to a seventh embodiment of the present invention; 
         FIG. 19  is a cross-sectional view of the components in a joining step of the method for producing a hollow container according to the seventh embodiment; 
         FIG. 20  is a perspective view of components in a preparing step of the method for producing a hollow container according to an eighth embodiment of the present invention; 
         FIG. 21  is a cross-sectional view of the components in a joining step of the method for producing a hollow container according to the eighth embodiment; and 
         FIG. 22  is a perspective view of the components in the joining step of the method for producing a hollow container according to the eighth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     A description is given of a first embodiment of the present invention with reference to the drawings as appropriate. A method for producing a hollow container according to the first embodiment includes a preparing step, a butting step, and a joining step. As illustrated in  FIG. 5 , in the present embodiment, friction-stir joining is performed on a first metal member  1  and a second metal member  2  to produce a hollow container  100 . 
     In the description below, an “outer surface” is a surface opposite to an “inner surface”. Further, in the description below, an “outer peripheral surface” is a surface opposite to an “inner peripheral surface”. Still further, an “external surface” is a surface opposite to an “internal surface”. 
     As illustrated in  FIG. 1 , in the preparing step, the first metal member  1 , the second metal member  2 , and an auxiliary member  10  are prepared. 
     The first metal member  1  and second metal member  2  are metal members having a square plate shape. The first metal member  1  and second metal member  2  have the same thickness as each other. The first metal member  1  and second metal member  2  are not particularly limited as long as the members are made of metals to be frictionally stirrable, and may be made of aluminum or an aluminum alloy, for example. In the present embodiment, cast material is used for the first metal member  1  and second metal member  2 , and the cast material is an aluminum alloy such as JISH5302 ADC12 (Al—Si—Cu series alloy). 
     The first metal member  1  has, on a center portion of an inner surface  1   c  thereof, a concave portion  1   f  formed by a square bottom  1   d  and a peripheral wall  1   e , which has a square tube shape and extends from a peripheral edge of the bottom  1   d.    
     The second metal member  2  has, on a center portion of an inner surface  2   c  thereof, a concave portion  2   f  formed by a square bottom  2   d , and a peripheral wall  2   e , which has a square tube shape and extends from a peripheral edge of the bottom  2   d.    
     As illustrated in  FIG. 3 , the first metal member  1  has an end surface  1   a  of the peripheral wall  1   e  formed into an inclined surface to face outward (toward an end surface  2   a  of the peripheral wall  2   e  of the second metal member  2 ). The second metal member  2  has the end surface  2   a  of the peripheral wall  2   e  formed into an inclined surface to face outward (toward the end surface  1   a  of the peripheral wall  1   e  of the first metal member  1 ). 
     Thus, the end surface  1   a  and end surface  2   a  are inclined surfaces to face each other so as to be further away from each other with an increasing distance from inner peripheral surfaces  1   h ,  2   h  toward outer peripheral surfaces  1   g ,  2   g  of the peripheral walls  1   e ,  2   e . Inclination angles of the end surfaces  1   a ,  2   a  are the same as each other with respect to an imaginary orthogonal plane orthogonal to the outer peripheral surface  1   g  of the peripheral wall  1   e.    
     As illustrated in  FIG. 1 , the auxiliary member  10  is a member having a substantially square frame shape, to be interposed between the first metal member  1  and second metal member  2 . The auxiliary member  10  is made of a metal having hardness lower than the first metal member  1 . The auxiliary member  10  is formed of expansile material, which is an aluminum alloy such as JIS A1050, A1100, A6063. 
     As illustrated in  FIG. 2 , the auxiliary member  10  is formed of an elongated member  15  which is an extruded member having a substantially trapezoidal shape in cross section. The elongated member  15  has four notches  15   a  in a surface to form an inner periphery of the auxiliary member  10  at intervals in a longitudinal direction (see  FIG. 3 ). The elongated member  15  is bent orthogonally at the notches  15   a  and both ends of the elongated member  15   a  are butted to form the auxiliary member  10  having a square frame shape, as illustrated in  FIG. 1 . Note that the auxiliary member  10  having a flame shape may be formed by die casting, for example. 
     As illustrated in  FIG. 3 , the auxiliary member  10  includes a main body  11  having a trapezoidal shape in cross section and a protrusion  12  protruding inward from an inner peripheral surface  10   d  of the main body  11 . 
     The main body  11  includes an outer peripheral surface (external surface)  10   a , side surfaces  10   b  and  10   c , and an inner peripheral surface (internal surface)  10   d . The side surfaces  10   b ,  10   c  are inclined surfaces to come closer with each other with an increasing distance from the outer peripheral surface  10   a  (toward the inner peripheral surface  10   d ). That is, the side surfaces  10   b ,  10   c  of the auxiliary member  10  are inclined surfaces tapered from the outer peripheral surface  10   a  toward the inner peripheral surface  10   d . Inclination angles of the side surfaces  10   b ,  10   c  are the same as the inclination angles of the end surfaces  1   a ,  2   a  which face the side surfaces  10   b ,  10   c , respectively. 
     The protrusion  12  has a rectangular shape in cross section which is wider than the inner peripheral surface (internal surface)  10   d  of the main body  11 . The protrusion  12  is formed to have a predetermined shape in a circumferential direction of the auxiliary member  10 . 
     As illustrated in  FIG. 3 , in the butting step, the first metal member  1  is butted against the second metal member  2 , having the auxiliary member  10  therebetween. In the butting step, the end surface  1   a  of the first metal member  1  is arranged to face the end surface  2   a  of the second metal member  2 . Further, the auxiliary member  10  is arranged between the end surfaces  1   a ,  2   a , to be interposed in a gap between the end surfaces  1   a ,  2   a.    
     The end surface  1   a  of the first metal member  1  is butted against the side surface  10   b  of the auxiliary member  10  so as to substantially surface-contact with each other, to form a butted portion J 1 . The end surface  2   a  of the second metal member  2  is butted against the side surface  10   c  of the auxiliary member  10  so as to substantially surface-contact with each other, to form a butted portion J 2 . The outer peripheral surface (external surface)  10   a  of the auxiliary member  10  is flush with the outer peripheral surface  1   g  of the first metal member  1  and the outer peripheral surface  2   g  of the second metal member  2 . The inner peripheral surface  10   d  of the auxiliary member  10  is flush with the inner peripheral surface  1   h  of the first metal member  1  and the inner peripheral surface  2   h  of the second metal member  2 . Further, the protrusion  12  is locked to the inner peripheral surface  1   h  of the first metal member  1  and the inner peripheral surface  2   h  of the second metal member  2 , respectively. 
     As illustrated in  FIG. 4 , a rotary tool F includes a base F 1  and a stirring pin F 2 . The rotary tool F is made of tool steel, for example. The base F 1  is a portion connected to a rotation shaft of a friction stirring device. The stirring pin F 2  extends downward from the base F 1  to have a tapered shape. The stirring pin F 2  has, at a tip thereof, a flat surface F 3  perpendicular to a central axis for rotation. The flat surface F 3  is formed to have a size slightly larger than the inner peripheral surface (internal surface)  10   d  of the auxiliary member  10 . 
     A taper angle of an outer peripheral surface of the stirring pin F 2  is the same as each of the inclination angles of the end surface  1   a  of the first metal member  1  and the end surface  2   a  of the second metal member  2 . That is, a cross-sectional shape of the stirring pin F 2  in a lateral view is substantially the same as a cross-sectional shape of the main body  11  of the auxiliary member  10 . 
     A spiral groove is formed in the outer peripheral surface of the stirring pin F 2 . In the present embodiment, the rotary tool F is rotated clockwise so that the spiral groove is formed counterclockwise from a base end toward a tip. Note that, in a case where the rotary tool F is rotated counterclockwise, a spiral groove is formed clockwise from the base end toward the tip. Accordingly, plastically fluidized metal is guided by the spiral groove to move toward the tip, which prevents generation of burrs. The rotary tool F may be attached to an arm robot including a rotation driver at a tip thereof, for example. 
     As illustrated in  FIG. 4 , in the joining step, friction-stir joining is performed on the first metal member  1  and second metal member  2 , with use of the rotary tool F. In the joining step, the stirring pin F 2  of the rotary tool F being rotated clockwise is inserted into the center in a width direction of the outer peripheral surface (external surface)  10   a  of the main body  11  of the auxiliary member  10 . 
     In the joining step, the outer peripheral surface of the stirring pin F 2  may not be brought in contact with the end surface  1   a  of the first metal member  1  and the end surface  2   a  of the second metal member  2 . However, in the present embodiment, the stirring pin F 2  is relatively moved along the auxiliary member  10 , with the outer peripheral surface of the stirring pin F 2  being slightly in contact with both the end surfaces  1   a ,  2   a . A contact margin between the outer peripheral surface of the stirring pin F 2  and the end surfaces  1   a ,  2   a  may be appropriately set to be less than 1.0 mm, for example. 
     In the joining step, only the stirring pin F 2  is brought in contact with the first metal member  1 , the second metal member  2 , and the auxiliary member  10 , and friction stirring is performed with a part of the stirring pin F 2 , which is continuous with the base end, exposed on the outside of the first metal member  1  and second metal member  2 . The flat surface F 3  of the stirring pin F 2  is inserted to a deep position as far as the flat surface F 3  does not protrude from the inner peripheral surface  1   h  of the first metal member  1  and the inner peripheral surface  2   h  of the second metal member  2 . 
     As illustrated in  FIG. 5 , the rotary tool F is relatively moved along the auxiliary member  10  over entire outer peripheral surfaces of the peripheral walls  1   e ,  2   e  of the first metal member  1  and second metal member  2 . At this time, a start position is overlapped with an end position in the joining step. When reaching the end position, the rotary tool F is removed from the auxiliary member  10 . As described above, friction-stir joining is performed on the butted portions J 1 , J 2  simultaneously in one step. A plasticized region W is formed in a track of the rotary tool F. 
     Friction-stir joining is performed on the peripheral wall  1   e  of the first metal member  1  and the peripheral wall  2   e  of the second metal member  2  so that the concave portion  1   f  of the first metal member  1  and the concave portion  2   f  of the second metal member  2  are coupled with each other. This forms the hollow container  100  having an inner space therein defined by both the concave portions  1   f ,  2   f.    
     According to the method for producing the hollow container  100  of the present embodiment described above, the rotary tool F including the tapered stirring pin F 2  is used as illustrated in  FIG. 4  to facilitate inserting the stirring pin F 2  into the outer peripheral surface (external surface)  10   a  of the auxiliary member  10 . Further, only the stirring pin F 2  is inserted into the auxiliary member  10  and friction stirring is performed with a part of the stirring pin F 2 , which is continuous with the base end, exposed, so that a load reacting on the friction stirring device is reduced. 
     Further, the rotary tool F is inserted into the auxiliary member  10  which is softer than the first metal member  1  and second metal member  2 , so that a service life of the rotary tool F is prolonged. Still further, the stirring pin F 2  is only slightly brought in contact with the first metal member  1  and second metal member  2 , so that a large amount of hard metal forming the first metal member  1  and second metal member  2  is prevented from being mixed into the auxiliary member  10 . Therefore, joining strength is further increased. 
     Further, the end surface  1   a  of the first metal member  1  and the end surface  2   a  of the second metal member  2  are formed into the inclined surfaces, so that the stirring pin F 2  is prevented from greatly coming in contact with the first metal member  1  and second metal member  2 . Still further, in the present embodiment, the taper angle of the stirring pin F 2  is substantially the same as (substantially in parallel with) the inclination angles of the end surfaces  1   a ,  2   a  so that friction stirring is performed in a well-balanced manner end-to-end in a height direction. 
     Further, when a length of material to be joined by friction-stir joining is long, the auxiliary member  10  is also formed long, accordingly. In such a case, friction-stir joining may result in the auxiliary member  10  coming off. However, according to the present embodiment, the auxiliary member  10  includes the protrusion  12  which is locked to the inner peripheral surfaces  1   h ,  2   h  so that the auxiliary member  10  is prevented from coming off. Accordingly, the auxiliary member  10  is prevented from being displaced with respect to the first metal member  1  and second metal member  2 , so that friction-stir joining is performed more suitably. 
     Note that, in the present embodiment, the protrusion  12  is set to lock to both the first metal member  1  and second metal member  2 . However, the protrusion  12  may be locked to at least one of the first metal member  1  and second metal member  2 , in order to prevent the auxiliary member  10  from coming off. 
     Second Embodiment 
     Next, a description is given of a method for producing a hollow container according to a second embodiment of the present invention.  FIG. 6  is a cross-sectional view of components in a butting step of the method for producing a hollow container according to the second embodiment of the present invention. 
     The method for producing a hollow container of the second embodiment includes a preparing step, the butting step, and a joining step. The second embodiment mainly differs from the first embodiment on the point that an auxiliary member  10 A has a different shape. In the present embodiment, the description is focused on difference from the first embodiment. 
     As illustrated in  FIG. 6 , the first metal member  1  and second metal member  2  are the same as those in the first embodiment. The auxiliary member  10 A is formed with the main body  11  having a trapezoidal shape in cross section. That is, the auxiliary member  10 A of the second embodiment is configured without the protrusion  12  of the auxiliary member  10  (see  FIG. 3 ) of the first embodiment. 
     In the butting step, as in the first embodiment, the first metal member  1  and the second metal member  2  are butted against the auxiliary member  10 A from both sides. The end surface  1   a  of the first metal member  1  is butted against the side surface  10   b  of the auxiliary member  10  to form the butted portion J 1 . The end surface  2   a  of the second metal member  2  is butted against the side surface  10   c  of the auxiliary member  10  to form the butted portion J 2 . 
     In the joining step, friction-stir joining is performed on the butted portions J 1 , J 2  with use of the rotary tool F, as in the first embodiment. 
     The second embodiment described above achieves substantially the same effects as the first embodiment. Further, the auxiliary member  10 A of the second embodiment has a trapezoidal shape in cross section so that the auxiliary member  10 A is easily made of extruded protrusion material. 
     Third Embodiment 
     Next, a description is given of a method for producing a hollow container according to a third embodiment of the present invention.  FIG. 7  is a cross-sectional view of components in a butting step of the method for producing a hollow container according to the third embodiment of the present invention.  FIG. 8  is a cross-sectional view of the components in a joining step of the method for producing a hollow container according to the third embodiment of the present invention. 
     The method for producing a hollow container according to the third embodiment includes a preparing step, the butting step, and the joining step. The third embodiment mainly differs from the first embodiment on the point that an auxiliary member  10 B has a different shape. In the present embodiment, the description is focused on difference from the first embodiment. 
     In the preparing step, a first metal member  1 B, the second metal member  2 , and the auxiliary member  10 B are prepared. The end surface  1   a  of the first metal member  1 B is perpendicular to the outer peripheral surface  1   g  and the inner peripheral surface  1   h . The second metal member  2  is the same as that in the first embodiment. 
     The auxiliary member  10 B of the third embodiment includes a main body  11 B having a trapezoidal shape in cross section and the protrusion  12  protruding inward from the inner peripheral surface  10   d  of the main body  11 B. 
     The main body  11 B has the outer peripheral surface (external surface)  10   a , the side surfaces  10   b ,  10   c , and the inner peripheral surface (internal surface)  10   d . The side surface  10   b  is perpendicular to the outer peripheral surface  10   a . The side surface  10   c  is inclined to taper with an increasing distance from the outer peripheral surface  10   a . An inclination angle of the side surface  10   c  is the same as that of the end surface  2   a  of the second metal member  2 . The protrusion  12  is the same as that in the first embodiment. Note that the protrusion  12  may not be formed in the auxiliary member  10 B of the third embodiment. 
     In the butting step, the first metal member  1 B and second metal member  2  are butted against the auxiliary member  10 B. The end surface  1   a  of the first metal member  1 B is butted against the side surface  10   b  of the auxiliary member  10 B to form the butted portion J 1 . The end surface  2   a  of the second metal member  2  is butted against the side surface  10   c  of the auxiliary member  10 B to form the butted portion J 2 . The outer peripheral surface (external surface)  10   a  of the auxiliary member  10  is flush with the outer peripheral surface  1   g  of the first metal member  1  and the outer peripheral surface  2   g  of the second metal member  2 . The inner peripheral surface (internal surface)  10   d  of the auxiliary member  10 B is flush with the inner peripheral surface  1   h  of the first metal member  1  and the inner peripheral surface  1   h  of the second metal member  2 . 
     As illustrated in  FIG. 8 , in the joining step, friction-stir joining is performed with use of the rotary tool F. In the third embodiment, only the stirring pin F 2  of the rotary tool F is inserted into the auxiliary member  10 B and is relatively moved along the auxiliary member  10 B, with a part of the stirring pin F 2 , which is continuous with the base end, exposed, to perform friction-stir joining on the butted portions J 1 , J 2 . 
     Further, in the third embodiment, friction stirring is performed, with the outer peripheral surface of the stirring pin F 2  being slightly in contact with the end surface  1   a  of the first metal member  1  and the end surface  2   a  of the second metal member  2  while a central axis for rotation Z of the stirring pin F 2  being inclined toward the second metal member  2 . 
     Note that an inclination angle of the rotary tool F may be set appropriately, but is preferably set such that the outer peripheral surface of the stirring pin F 2  is in parallel with the end surface  1   a  of the first metal member  1 B and the end surface  2   a  of the second metal member  2 . 
     The method for producing a hollow container according to the third embodiment described above also achieves substantially the same effects as the first embodiment. Further, in the third embodiment, the end surface  1   a  of the first metal member  1 B is not required to be an inclined surface, resulted in reduction in time and labor. 
     Fourth Embodiment 
     Next, a description is given of a method for producing a hollow container according to a fourth embodiment of the present invention.  FIG. 9  is a perspective view of components in a preparing step of the method for producing a hollow container according to the fourth embodiment of the present invention.  FIG. 10  is a cross-sectional view of the components in a joining step of the method for producing a hollow container according to the fourth embodiment.  FIG. 11  is a perspective view of the components in the joining step of the method for producing a hollow container according to the fourth embodiment. 
     The method for producing a hollow container according to the fourth embodiment includes a preparing step, a butting step, and the joining step. The fourth embodiment mainly differs from the first embodiment on the point that a first metal member  1 C, a second metal member  2 C, and an auxiliary member  10 C each have a different shape. In the present embodiment, the description is focused on difference from the first embodiment. 
     As illustrated in  FIG. 9 , the first metal member  1 C in the fourth embodiment has, on a center portion of the inner surface  1   c  thereof, the concave portion  1   f  formed by the bottom  1   d  in a circular shape and the peripheral wall  1   e , which has a cylindrical shape, extending from the peripheral edge of the bottom  1   d.    
     The second metal member  2 C in the fourth embodiment has, on a center portion of the inner surface  2   c  thereof, the concave portion  2   f  formed by the bottom  2   d  in a circular shape and the peripheral wall  2   e , which has a cylindrical shape, extending from the peripheral edge of the bottom  2   d.    
     The auxiliary member  10 C in the fourth embodiment is a member having a circular frame shape, which is interposed between the first metal member  1 C and second metal member  2 C. 
     As illustrated in  FIG. 10 , in the butting step, the auxiliary member  10 C is interposed between the end surface  1   a  of the first metal member  1 C and the end surface  2   a  of the second metal member  2 C to form the butted portions J 1 , J 2 . 
     In the joining step, substantially as in the first embodiment, only the stirring pin F 2  is brought in contact with the first metal member  1 C, the second metal member  2 C, and the auxiliary member  10 C, and friction stirring is performed, with a part of the stirring pin F 2 , which is continuous with the base end, exposed on the outside of the first metal member  1 C and second metal member  2 C. Then, as illustrated in  FIG. 11 , the rotary tool F is relatively moved along the auxiliary member  10 C over the entire outer peripheral surfaces of the peripheral walls  1   e ,  2   e  of the first and second metal members  1 C,  2 C. The plasticized region W is formed in a track of the rotary tool F. 
     Friction-stir joining is performed on the peripheral wall  1   e  of the first metal member  1 C and the peripheral wall  2   e  of the second metal member  2 C so that the concave portion  1   f  of the first metal member  1 C and the concave portion  2   f  of the second metal member  2 C are coupled with each other. This forms a hollow container  200  in a cylinder shape, having an inner space therein defined by both the concave portions  1   f ,  2   f.    
     The method for producing a hollow container according to the fourth embodiment described above also achieves substantially the same effects as the first embodiment. 
     Fifth Embodiment 
     A description is given of a fifth embodiment of the present invention with reference to the drawings as appropriate. A method for producing a hollow container according to the fifth embodiment includes a preparing step, a butting step, and a joining step. As illustrated in  FIG. 16 , in the present embodiment, friction-stir joining is performed on the first metal member  1  and a second metal member  20  to produce a hollow container  300 . 
     In the description below, the “outer surface” is a surface opposite to the “inner surface”. Further, in the description below, the “outer peripheral surface” is a surface opposite to the “inner peripheral surface”. Still further, in the description below, the “external surface” is a surface opposite to the “internal surface”. 
     As illustrated in  FIG. 12 , in the preparing step, the first metal member  1 , the second metal member  20 , and an auxiliary member  30  are prepared. 
     The first metal member  1  and second metal member  20  are metal members each having a square plate shape. The first metal member  1  and second metal member  20  are not particularly limited as long as the members are made of metals to be frictionally stirrable. For example, aluminum or an aluminum alloy may be used therefor. In the present embodiment, cast material is used for the first metal member  1  and second metal member  20 , and the cast material is an aluminum alloy such as JIS H5302 ADC12 (Al—Si—Cu series alloy). 
     The first metal member  1  has, on a center portion of the inner surface  1   c  thereof, the concave portion  1   f  formed by the square bottom  1   d  and the peripheral wall  1   e , which has a square tube shape and extends from the peripheral edge of the bottom  1   d.    
     The second metal member  20  has a rectangular plate shape. The second metal member  20  has a peripheral edge  20   d  of an internal surface  20   b  inclined so as to become thinner toward an outer peripheral surface  20   c . The peripheral edge  20   d  has an inclined surface formed over an entire periphery thereof. 
     As illustrated in  FIG. 14 , the first metal member  1  has the end surface  1   a  of the peripheral wall  1   e  inclined in a direction so as to be further away from the second metal member  20  toward the outer peripheral surface  1   g . That is, the end surface  1   a  of the first metal member  1  and the peripheral edge  20   d  of the second metal member  20  are inclined so as to be further away from each other with an increasing distance from the inner peripheral surface  1   h  toward the outer peripheral surface  1   g . Inclination angles of the end surface  1   a  and the peripheral edge  20   d  are the same as each other with respect to an imaginary orthogonal plane orthogonal to the outer peripheral surface  1   g  of the peripheral wall  1   e.    
     As illustrated in  FIG. 12 , the auxiliary member  30  is a member having a substantially square frame shape, to be interposed between the first metal member  1  and second metal member  20 . The auxiliary member  30  is made of a metal having hardness lower than the first metal member  1 . The auxiliary member  30  is formed of expansile material, which is an aluminum alloy such as JIS A1050, A1100, A6063. 
     As illustrated in  FIG. 13 , the auxiliary member  30  is formed of the elongated member  15  which is an extruded member having a substantially trapezoidal shape in cross section. The elongated member  15  has the four notches  15   a  in a surface to form an inner periphery of the auxiliary member  30  at intervals in a longitudinal direction (see  FIG. 14 ). The elongated member  15  is bent orthogonally at the notches  15   a  and both ends of the elongated member  15   a  are butted to form the auxiliary member  30  having a square frame shape, as illustrated in  FIG. 12 . Note that the auxiliary member  30  having a flame shape may be formed by die casting, for example. 
     As illustrated in  FIG. 14 , the auxiliary member  30  includes a main body  31  having a trapezoidal shape in cross section and a protrusion  32  protruding inward from an inner peripheral surface (internal surface)  30   d  of the main body  31 . 
     The main body  31  includes an outer peripheral surface (external surface)  30   a , side surfaces  30   b  and  30   c , and the inner peripheral surface (internal surface)  30   d . The side surfaces  30   b ,  30   c  are inclined surfaces to come closer with each other with an increasing distance from the outer peripheral surface  30   a  (toward the inner peripheral surface  30   d ). That is, the side surfaces  30   b ,  30   c  of the auxiliary member  30  are inclined surfaces which are tapered from the outer peripheral surface  30   a  toward the inner peripheral surface  30   d . Inclination angles of the side surfaces  30   b ,  30   c  are the same as the inclination angles of the end face  1   a  and the peripheral edge  20   d , respectively facing the side surfaces  30   b ,  30   c.    
     The protrusion  32  has a rectangular shape in cross section which is wider than the inner peripheral surface (internal surface)  30   d  of the main body  31 . The protrusion  32  is formed to have a predetermined shape in a circumferential direction of the auxiliary member  30 . 
     As illustrated in  FIG. 14 , in the butting step, the first metal member  1  is butted against the second metal member  20 , having the auxiliary member  30  therebetween. In the butting step, the end surface  1   a  of the first metal member  1  and the peripheral edge  20   d  of the second metal member  20  are arranged to face each other. Further, the auxiliary member  30  is interposed in a gap between the end surface  1   a  and the peripheral edge  20   d.    
     The end surface  1   a  of the first metal member  1  is butted against the side surface  30   b  of the auxiliary member  30  so as to substantially surface-contact with each other, to form a butted portion J 11 . The peripheral edge  20   d  of the second metal member  20  is butted against the side surface  30   c  of the auxiliary member  30  so as to substantially surface-contact with each other, to form a butted portion J 12 . The outer peripheral surface (external surface)  30   a  of the auxiliary member  30  is flush with the outer peripheral surface  1   g  of the first metal member  1  and an outer peripheral surface  20   c  of the second metal member  20 . The inner peripheral surface  30   d  of the auxiliary member  30  is flush with the inner peripheral surface  1   h  of the first metal member  1 . Further, the protrusion  32  is locked to the inner peripheral surface  1   h  of the first metal member  1 . 
     As illustrated in  FIG. 15 , the rotary tool F includes the base F 1  and the stirring pin F 2 . The rotary tool F is made of tool steel, for example. The base F 1  is a portion connected to the rotation shaft of the friction stirring device. The stirring pin F 2  extends downward from the base F 1  to have a tapered shape. The stirring pin F 2  has, at the tip thereof, the flat surface F 3  perpendicular to a central axis for rotation. The flat surface F 3  is formed to have a size slightly larger than the inner peripheral surface  30   d  of the auxiliary member  30 . 
     A taper angle of the outer peripheral surface of the stirring pin F 2  is the same as each of the inclination angles of the end surface  1   a  of the first metal member  1  and the peripheral edge  20   d  of the second metal member  20 . That is, a cross-sectional shape of the stirring pin F 2  in a lateral view is substantially the same as a cross-sectional shape of the main body  31  of the auxiliary member  30 . 
     The spiral groove is formed in the outer peripheral surface of the stirring pin F 2 . In the present embodiment, the rotary tool F is rotated clockwise so that the spiral groove is formed counterclockwise from the base end toward the tip. Note that, in a case where the rotary tool F is rotated counterclockwise, a spiral groove is formed clockwise from the base end toward the tip. Accordingly, plastically fluidized metal is guided by the spiral groove to move toward the tip, which prevents generation of burrs. The rotary tool F may be attached to an arm robot including a rotation driver at a tip thereof, for example. 
     As illustrated in  FIG. 15 , in the joining step, friction-stir joining is performed on the first metal member  1  and second metal member  20 , with use of the rotary tool F. In the joining step, the stirring pin F 2  of the rotary tool F being rotated clockwise is inserted into the center in a width direction of the outer peripheral surface (external surface)  30   a  of the auxiliary member  30 . 
     In the joining step, the outer peripheral surface of the stirring pin F 2  may not necessarily be brought in contact with the end surface  1   a  of the first metal member  1  and the peripheral edge  20   d  of the second metal member  20 . In the present embodiment, the stirring pin F 2  is relatively moved along the auxiliary member  30 , with the outer peripheral surface of the stirring pin F 2  being slightly in contact with both the end surface  1   a  and the peripheral edge  20   d . A contact margin between the outer peripheral surface of the stirring pin F 2 , and the end surface  1   a  and the peripheral edge  20   d  may be appropriately set to be less than 1.0 mm, for example. 
     In the joining step, only the stirring pin F 2  is brought in contact with the first metal member  1 , the second metal member  20 , and the auxiliary member  30 , and friction stirring is performed, with a part of the stirring pin F 2 , which is continuous with the base end, exposed on the outside of the first metal member  1  and second metal member  20 . The flat surface F 3  of the stirring pin F 2  is inserted to a deep position as far as the flat surface F 3  does not protrude from the inner peripheral surface  1   h  of the first metal member  1 . 
     As illustrated in  FIG. 16 , the rotary tool F is relatively moved along the auxiliary member  30  over an entire peripheral wall  1   e  of the first metal member  1  and the outer peripheral surface  20   c  of the second metal member  20 , to overlap a start position with an end position. When reaching the end position, the rotary tool F is removed from the auxiliary member  30 . Thus, friction-stir joining is performed on the butted portions J 11 , J 12  simultaneously in one step. The plasticized region W is formed in the track of the rotary tool F. 
     Friction-stir joining is performed on the peripheral wall  1   e  of the first metal member  1  and the second metal member  20 , and this forms the hollow container  300 , having an inner space therein defined by the concave portion  1   f.    
     According to the method for producing the hollow container  300  of the present embodiment described above, the rotary tool F including the tapered stirring pin F 2  is used as illustrated in  FIG. 15  to facilitate inserting the stirring pin F 2  into the outer peripheral surface (external surface)  30   a  of the auxiliary member  30 . Further, only the stirring pin F 2  is inserted into the auxiliary member  30  and friction stirring is performed with a part of the stirring pin F 2 , which is continuous with the base end, exposed, so that a load reacting on the friction stirring device is reduced. 
     Further, the rotary tool F is inserted into the auxiliary member  30  which is softer than the first metal member  1  and second metal member  20 , so that a service life of the rotary tool F is prolonged. Still further, the stirring pin F 2  is only slightly brought in contact with the first metal member  1  and the second metal member  20 , so that a large amount of hard metal forming the first metal member  1  and second metal member  20  is prevented from being mixed into the auxiliary member  30 . Therefore, joint strength is further increased. 
     Further, the end surface  1   a  of the first metal member  1  and the peripheral edge  20   d  of the second metal member  20  are formed into inclined surfaces, so that the stirring pin F 2  is prevented from greatly coming in contact with the first metal member  1  and second metal member  20 . Still further, in the present embodiment, the taper angle of the stirring pin F 2  is substantially the same as (substantially in parallel with) the inclination angles of the of the end surface  1   a  and the peripheral edge  20   d  so that friction stirring is performed in a well-balanced manner end-to-end in a height direction. 
     Further, when a length of material to be joined by friction-stir joining is long, the auxiliary member  30  is also formed long, accordingly. In such a case, friction-stir joining may result in the auxiliary member  30  coming off. However, according to the present embodiment, the auxiliary member  30  includes the protrusion  32  which is locked to the inner peripheral surface  1   h  of the peripheral wall  1   e  so that the auxiliary member  30  is prevented from coming off. Accordingly, the auxiliary member  30  is prevented from being displaced with respect to the first metal member  1  and second metal member  20 , so that friction-stir joining is performed more suitably. 
     Sixth Embodiment 
     Next, a description is given of a method for producing a hollow container according to a sixth embodiment of the present invention.  FIG. 17  is a cross-sectional view of components in a butting step of the method for producing a hollow container according to the sixth embodiment of the present invention. 
     The method for producing a hollow container of the sixth embodiment includes a preparing step, the butting step, and a joining step. The sixth embodiment mainly differs from the first embodiment on the point that an auxiliary member  30 A has a different shape. In the present embodiment, the description is focused on difference from the fifth embodiment. 
     As illustrated in  FIG. 17 , the first metal member  1  and second metal member  20  are the same as those in the fifth embodiment. The auxiliary member  30 A includes the main body  31  having a trapezoidal shape in cross section. That is, the auxiliary member  30 A of the sixth embodiment is configured without the protrusion  32  of the auxiliary member  30  (see  FIG. 14 ) of the fifth embodiment. 
     In the butting step, as in the fifth embodiment, the first metal member  1  and the second metal member  2  are butted against the auxiliary member  30 A from both sides. The end surface  1   a  of the first metal member  1  is butted against the side surface  30   b  of the auxiliary member  30  to form the butted portion J 11 . The peripheral edge  20   d  of the second metal member  20  is butted against the side surface  30   c  of the auxiliary member  30  to form the butted portion J 12 . 
     In the joining step, friction-stir joining is performed on the butted portions J 11 , J 12  with use of the rotary tool F, as in the fifth embodiment. 
     The sixth embodiment described above achieves substantially the same effects as the fifth embodiment. Further, the auxiliary member  30 A of the sixth embodiment has a trapezoidal shape in cross section, so that the auxiliary member  30 A is easily made by extruded protrusion. 
     Seventh Embodiment 
     Next, a description is given of a method for producing a hollow container according to a seventh embodiment of the present invention.  FIG. 18  is a cross-sectional view of components in a butting step of the method for producing a hollow container according to the seventh embodiment of the present invention.  FIG. 19  is a cross-sectional view of the components in a joining step of the method for producing a hollow container according to the seventh embodiment of the present invention. 
     The method for producing a hollow container according to the seventh embodiment includes a preparing step, the butting step, and the joining step. The seventh embodiment mainly differs from the fifth embodiment on the point that an auxiliary member  30 B has a different shape. In the present embodiment, the description is focused on difference from the fifth embodiment. 
     As illustrated in  FIG. 18 , in the preparing step, the first metal member  1 , a second metal member  20 B, and the auxiliary member  30 B are prepared. The first metal member  1  is substantially the same as that in the fifth embodiment. The second metal member  20 B does not have any inclined surface formed at the peripheral edge  20   d  of the internal surface  20   b.    
     The auxiliary member  30 B of the seventh embodiment includes a main body  31 B having a trapezoidal shape in cross section and the protrusion  32  protruding from the inner peripheral surface  30   d  of the main body  31 B. 
     The main body  31 B has the outer peripheral surface (external surface)  30   a , the side surfaces  30   b ,  30   c , and the inner peripheral surface (internal surface)  30   d . The side surface  30   c  is perpendicular to the outer peripheral surface  30   a . The side surface  30   b  is inclined to taper with an increasing distance from the outer peripheral surface  30   a . An inclination angle of the side surface  30   c  is the same as that of the end surface  1   a  of the first metal member  1 . The protrusion  32  is substantially the same as that in the fifth embodiment. 
     In the butting step, the first metal member  1  and second metal member  20 B are butted against the auxiliary member  30 B. The end surface  1   a  of the first metal member  1  is butted against the side surface  30   b  of the auxiliary member  30 B to form the butted portion J 11 . The peripheral edge  20   d  of the second metal member  20 B is butted against the side surface  30   c  of the auxiliary member  30 B to form the butted portion J 12 . The outer peripheral surface (external surface)  30   a  of the auxiliary member  30  is flush with the outer peripheral surface  1   g  of the first metal member  1  and the outer peripheral surface  20   c  of the second metal member  20 B. The inner peripheral surface (internal surface)  30   d  of the auxiliary member  30 B is flush with the inner peripheral surface  1   h  of the first metal member  1 . 
     As illustrated in  FIG. 19 , in the joining step, friction-stir joining is performed with use of the rotary tool F. In the seventh embodiment, only the stirring pin F 2  of the rotary tool F is inserted into the auxiliary member  30 B and is relatively moved along the auxiliary member  30 B, with a part of the stirring pin F 2 , which is continuous with the base end, exposed, to perform friction-stir joining on the butted portions J 11 , J 12 . 
     Further, in the seventh embodiment, friction stirring is performed, with the outer peripheral surface of the stirring pin F 2  being slightly in contact with the end surface  1   a  of the first metal member  1  and the peripheral edge  20   d  of the second metal member  20 B while the central axis for rotation Z of the stirring pin F 2  being inclined toward the bottom  1   d  of the first metal member  1 . 
     Note that the inclination angle of the rotary tool F may be set appropriately, and is preferably set such that the outer peripheral surface of the stirring pin F 2  is in parallel with the end surface  1   a  of the first metal member  1  and the peripheral edge  20   d  of the second metal member  20 B. 
     The method for producing a hollow container according to the seventh embodiment described above also achieves substantially the same effects as the fifth embodiment. Further, in the seventh embodiment, the peripheral edge  20   d  of the second metal member  20 B is not required to be an inclined surface, resulted in reduction in time and labor. Note that the protrusion  32  may be omitted. 
     Eighth Embodiment 
     Next, a description is given of a method for producing a hollow container according to an eighth embodiment of the present invention.  FIG. 20  is a perspective view of components in a preparing step of the method for producing a hollow container according to the eighth embodiment of the present invention.  FIG. 21  is a cross-sectional view of the components in a butting step of the method for producing a hollow container according to the eighth embodiment.  FIG. 22  is a perspective view of the components in the butting step of the method for producing a hollow container according to the eighth embodiment. 
     The method for producing a hollow container according to the eighth embodiment includes the preparing step, the butting step, and the joining step. The eighth embodiment mainly differs from the fifth embodiment on the point that the first metal member  1 C, a second metal member  20 C, and an auxiliary member  30 C have different shapes. In the present embodiment, the description is focused on difference from the fifth embodiment. 
     As illustrated in  FIG. 20 , the first metal member  1 C in the eighth embodiment has, on a center portion of the inner surface  1   c  thereof, the concave portion  1   f  formed by the bottom  1   d  in a circular shape and the peripheral wall  1   e , which has a cylindrical shape, extending from the peripheral edge of the bottom  1   d.    
     The second metal member  20 C of the eighth embodiment has a circular-plate shape. The peripheral edge  20   d  of the internal surface  20   b  of the second metal member  20 C is inclined so as to become thinner toward the outer peripheral surface  20   c . The peripheral edge  20   d  has an inclined surface formed over an entire periphery thereof. 
     The auxiliary member  30 C in the eighth embodiment is a member having a circular frame shape, which is interposed between the first metal member  1 C and second metal member  20 C. The auxiliary member  30 C has a trapezoidal shape, tapered inward, in cross section. 
     As illustrated in  FIG. 21 , in the butting step, the auxiliary member  30 C is interposed between the end surface  1   a  of the first metal member  1 C and the peripheral edge  20   d  of the second metal member  20 C to form the butted portions J 1 , J 2 . The butted portion J 11  is a portion where the end surface  1   a  of the first metal member  1 C is butted against the side surface  30   b  of the auxiliary member  30 C. The butted portion J 12  is a portion where the peripheral edge  20   d  of the second metal member  20 C is butted against the side surface  30   c  of the auxiliary member  30 C. 
     In the joining step, substantially as in the fifth embodiment, only the stirring pin F 2  is brought in contact with the first metal member  1 C, the second metal member  20 C, and the auxiliary member  30 C, and friction stirring is performed with a part of the stirring pin F 2 , which is continuous with the base end, exposed on the outside of the first metal member  1 C and second metal member  20 C. Then, as illustrated in  FIG. 22 , the rotary tool F is relatively moved along the auxiliary member  30 C over the entire outer peripheral surfaces of the first metal member  1 C and second metal member  20 C. The plasticized region W is formed in a track of the rotary tool F. 
     Friction-stir joining is performed on the peripheral wall  1   e  of the first metal member  1 C and the peripheral edge  20   d  of the second metal member  20 C, and this forms a cylindrical hollow container  400  having an inner space formed by the concave portion  1   f.    
     The method for producing a hollow container according to the eighth embodiment described above also achieves substantially the same effects as the fifth embodiment. 
     EXPLANATION OF REFERENCE SYMBOLS 
     
         
         
           
               1 : first metal member (first embodiment, seventh embodiment);  1 B: first metal member (third embodiment);  1 C: first metal member (fourth embodiment, eighth embodiment);  1   a : end surface (inclined surface);  2 : second metal member;  2 C: second metal member (fourth embodiment);  2   a : end surface (inclined surface);  10 : auxiliary member;  10   a : outer peripheral surface (external surface);  10   b : inner peripheral surface (internal surface);  10 A: auxiliary member (second embodiment);  10 B: auxiliary member (third embodiment);  10 C: auxiliary member (fourth embodiment);  12 : protrusion;  20 : second metal member (fifth embodiment);  20   b : internal surface;  20   d : peripheral edge;  30 : auxiliary member (fifth embodiment);  30 A: auxiliary member (sixth embodiment);  30 B: auxiliary member (seventh embodiment);  30 C: auxiliary member (eighth embodiment);  32 : protrusion; J 1 : butted portion; J 2 : butted portion; J 11 : butted portion; J 12 : butted portion; F: rotary tool; F 2 : stirring pin