Abstract:
In the present invention, a method for joining members involves preparing a steel component having a bottom wall in which a hole is provided, and a hollow aluminum pipe. The aluminum pipe is slipped through the hole in the steel component and passed through the bottom wall, rubber is inserted into the interior of the aluminum pipe, and the rubber is compressed in the direction of the axis (L) of the aluminum pipe and induced to distend towards the outside from the inside. As a result of the foregoing, at least a section of the aluminum pipe slipped through the hole is induced to undergo expansion and is joined by clinching to the bottom wall. This method for joining members reduces the load on the members, improves the joint strength, and enables two members to be joined at reduced cost.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to methods for joining members. 
       BACKGROUND ART 
       [0002]    In order to achieve weight reduction and improved safety in automobiles, high-strength steel sheets composed of so-called high-tensile steel are used. Although effective for weight reduction and improved safety, such high-tensile steel is still heavy compared with low specific gravity materials, such as aluminum. Moreover, high-tensile steel is problematic in terms of low formability due to its high strength, increasing forming load, and also low dimensional accuracy. In order to solve these problems, a multi-material process that involves using a steel component together with an extruded product, a molded product, or a press-formed product that use aluminum, which has lower specific gravity than steel sheets, has been performed in recent years. 
         [0003]    A problem with this multi-material process is in the joining of the steel component and the aluminum component. In the welding technology typified by spot-welding, fragile intermetallic compounds (IMC) occur at the interface between the steel sheet and the aluminum sheet. Thus, joining techniques, such as an electromagnetic-forming joining technique, a screw-fastening technique typified by bolts and nuts, a friction-stir welding (FSW) technique, a riveting technique, a self-piercing-riveting (SPR) technique, a mechanical clinching technique, and a bonding technique, are put to practical use. 
         [0004]    A clinching process based on electromagnetic forming involves inserting a solenoid forming coil into a pipe-shaped component fitted to a counterpart component and causing induced current to occur in the pipe serving as a conductor in accordance with a changing magnetic field occurring as a result of applying impulse current to the coil. An electromagnetic force is generated between the magnetic field caused by primary current in the coil and the induced current flowing oppositely in the circumferential direction of the pipe, and the pipe receives an outward force and thus expands, thereby becoming clinched to the counterpart component. This joining method is suitable for copper and aluminum, which have high electric conductivity, and is put to practical use in some techniques for joining together automobile components. 
         [0005]    Patent Literature 1 discloses a clinching technique based on electromagnetic forming for performing a multi-material process. In Patent Literature 1, a bumper reinforcement member formed of a metallic material that is hollow in cross section is caused to expand by electromagnetic forming and is engaged with holes provided in a bumper stay composed of an aluminum alloy so as to be joined thereto. 
       CITATION LIST 
     Patent Literature 
       [0006]    PTL 1: Japanese Unexamined Patent Application Publication No. 2007-284039 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    As in Patent Literature 1, electromagnetic forming is suitable for clinching a hollow component composed of copper or aluminum having high electric conductivity to a counterpart component, and a circular shape is preferred due to this joining mechanism. 
         [0008]    However, the joining technique based on electromagnetic forming requires that the inner diameter of the solenoid coil to be used be smaller than that of the aluminum component (i.e., aluminum pipe). When the diameter of a coil is to be reduced when joining together small-diameter components, there are problems in terms of difficulties in manufacturing of the coil, as well as performance and durability thereof. With regard to difficulties in manufacturing, it is difficult to form a conductor into the shape of a coil, leading to stricter limitations with respect to the material and the cross-sectional shape of the conductor. In addition, the conductor cross-sectionally deforms when being formed into the shape of a coil. Moreover, a new capital investment becomes necessary, such as requiring a large-capacity high-voltage capacitor. Furthermore, the joining is not possible if the aluminum component has an angular cross-sectional shape, a hole, or a slit. 
         [0009]    An object of the present invention is to provide a method for joining members, by which two members can be joined together at low cost while reducing the load on the members and increasing the joint strength. 
       Solution to Problem 
       [0010]    The present invention provides a joining method including: preparing a first member and a hollow second member, the first member having a first section provided with a first hole; fitting the second member into the first hole in the first member so as to cause the second member to extend through the first section; inserting an elastic body into the second member; and compressing the elastic body in a direction of an axis of the second member so as to cause the elastic body to expand from an inner side toward an outer side, and thus causing at least a part of the second member fitted in the first hole to expand so as to become clinched to the first section. 
         [0011]    According to this method, the elastic body is caused to expand outward so that the second member expands uniformly, thereby preventing local deformation and reducing the load on the members. This is because the second member can be uniformly deformed by utilizing the properties in which the elastic body compressed in the direction of the axis expands uniformly from the inner side toward the outer side. Therefore, fit accuracy can be improved, thereby achieving increased joint strength. Moreover, this is an easier method, as compared with an electromagnetic forming method or other machining methods. An electromagnetic forming method is usable only on electrically conductive materials and has limitations with respect to cross-sectional shapes and dimensions depending on coils to be used. In contrast, this method is not dependent on materials and has no limitations related to cross-sectional shapes and dimensions. Moreover, since the method is executable in a facility that applies a compressive force to the elastic body, an electrical facility that requires a large-capacity capacitor is not necessary. Consequently, the two members can be joined together at low cost. 
         [0012]    Furthermore, a shape of the first hole in the first member may be analogous to a cross-sectional shape of the part of the second member fitted in the first hole. 
         [0013]    According to this method, the first member and the second member have shapes analogous to each other so that the joining process can be performed by causing the second member to expand uniformly, thereby preventing local load from occurring in the first member and the second member. 
         [0014]    Furthermore, an outer-frame mold may be disposed at the outer side of the second member, and at least a part of the second member may be formed to extend along the outer-frame mold so as to become clinched. 
         [0015]    According to this method, the second member can be deformed to a freely-chosen shape by using outer-frame molds with various inner-surface shapes. The deformation shape can be appropriately selected in view of, for example, component performance and can be set in accordance with the intended purpose. 
         [0016]    Furthermore, an outer-frame mold may be disposed at the outer side of the second member, and clinching may be performed while partially limiting expansion of the second member by using the outer-frame mold. 
         [0017]    According to this method, by disposing the outer-frame mold, an expanding region of the second member is regulated, so that the expanding region can be controlled with high accuracy. This expanding region refers to a region in which the second member expands outward. 
         [0018]    Furthermore, the second member may also be compressed in the direction of the axis when the elastic body is compressed. 
         [0019]    According to this method, the second member is also compressed in the direction of the axis so as to assist with outward expansion of the second member. Specifically, together with the expanding force applied by the elastic body from the inner side of the second member, the second member can be expanded more reliably, thereby enabling clinching. 
         [0020]    Furthermore, an edge of the first hole may be burred. 
         [0021]    According to this method, the edge of the hole in the first member is burred so that the strength of the hole and the first section of the first member can be increased. Consequently, the first member can be prevented from deforming, the second member can be prevented from being damaged, and the joint strength between the two members can be increased. 
         [0022]    Furthermore, a surface different from a surface provided with the first hole may have a bead section protruding in the direction of the axis, and clinching may be performed by including the bead section. 
         [0023]    According to this method, because clinching is performed by including the bead section, the two members can be fixed to each other more securely, and the joint strength therebetween can be further increased. In particular, in a case where the second member has a circular cross-sectional shape, the second member can be prevented from rotating relative to the first member. 
         [0024]    Furthermore, the first member may include a second section having a second hole and may be clinched to the second member at the first hole and the second hole. 
         [0025]    According to this method, clinching is performed at two locations so that the joint strength can be further increased, as compared with the case where clinching is performed at a single location. 
         [0026]    Furthermore, the elastic body may be split at a joining section between the first member and the second member. 
         [0027]    According to this method, the elastic body is split at the joining section so that deformation of the joining section of the first member can be prevented. Specifically, the elastic body is split such that the elastic body is not disposed near the joining section, whereby the second member does not receive an expanding force from the elastic body near the joining section and thus does not expand near the joining section. Consequently, the first member does not receive a force from the second member near the joining section, so that the shape of the joining section can be maintained. 
         [0028]    Furthermore, a plate may be inserted between split pieces of the elastic body. 
         [0029]    According to this method, the plate exists in the joining section so that deformation of the joining section of the first member can be prevented more reliably. Because the plate does not expand even by receiving a compressive force in the direction of the axis, an expanding force is not applied to the joining section, so that the joining section can maintain its original shape more reliably. 
         [0030]    Furthermore, the second member may include an outer wall provided with a partition wall therein and extending in the direction of the axis, and clinching may be performed by inserting a plurality of the elastic bodies in spaces partitioned by the partition wall. 
         [0031]    According to this method, because the clinching process is performed by using the plurality of elastic bodies, concentration of stress caused by deformation can be prevented, so that the load on the first member and the second member can be reduced. 
         [0032]    Furthermore, the second member may include an end surface inclined relative to the axis, and opposite end surfaces of the elastic body in the direction of the axis may be parallel to the inclined surface. 
         [0033]    Accordingly, this method can be used for clinching the first member and the second member together in an inclined state, which is often seen from a practical standpoint. In particular, opposite end surfaces of the elastic body are given the same angle as the joining angle, so that the elastic body expands uniformly, whereby the second member can be expanded uniformly. 
         [0034]    Furthermore, the first member may include an upright wall parallel to the axis, and clinching may be performed while restraining deformation of the upright wall by using a fixation jig. 
         [0035]    According to this method, deformation of the first member is restrained by the jig, so that deformation of the first member caused by expansion of the second member can be suppressed. 
       Advantageous Effects of Invention 
       [0036]    According to the present invention, the second member is caused to expand uniformly by causing the elastic body to expand from the inner side toward the outer side, thereby preventing local deformation and reducing the load on the members. Therefore, fit accuracy can be improved, thereby achieving increased joint strength. Moreover, since this is an easier method, as compared with an electromagnetic forming method or other machining methods, the two members can be joined together at low cost. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0037]      FIG. 1A  is a perspective view of a channel-type steel component having a circular hole and an aluminum pipe having a circular cross-sectional shape. 
           [0038]      FIG. 1B  is a perspective view of the steel component and the aluminum pipe in  FIG. 1A  in a clinched state. 
           [0039]      FIG. 2A  is a cross-sectional view illustrating a state before a clinching process according to a first embodiment of the present invention. 
           [0040]      FIG. 2B  is a cross-sectional view illustrating a state where the clinching process according to the first embodiment of the present invention is being performed. 
           [0041]      FIG. 2C  is a cross-sectional view illustrating a state after the clinching process according to the first embodiment of the present invention. 
           [0042]      FIG. 2D  is a cross-sectional view illustrating a state where a rubber piece is being pulled out after the clinching process according to the first embodiment of the present invention. 
           [0043]      FIG. 3A  is a cross-sectional view illustrating a state before the clinching process when a rubber piece according to a modification of the first embodiment of the present invention is a fluid sealing member. 
           [0044]      FIG. 3B  is a cross-sectional view illustrating a state after the clinching process when the rubber piece according to the modification of the first embodiment of the present invention is a fluid sealing member. 
           [0045]      FIG. 4A  is a perspective view of a steel component having a circular hole and an aluminum pipe having a rectangular cross-sectional shape. 
           [0046]      FIG. 4B  is a perspective view of a steel component having a rectangular hole and an aluminum pipe having a circular cross-sectional shape. 
           [0047]      FIG. 5A  is a cross-sectional view of an example of a joining section of a steel component having undergone a burring process. 
           [0048]      FIG. 5B  is a cross-sectional view of another example of a joining section of a steel component having undergone a burring process. 
           [0049]      FIG. 5C  is a cross-sectional view of another example of a joining section of a steel component having undergone a burring process. 
           [0050]      FIG. 6A  is a perspective view of a joining section of a steel component having a circular hole having undergone a burring process. 
           [0051]      FIG. 6B  is a perspective view of a joining section of a steel component having a rectangular hole having undergone a burring process. 
           [0052]      FIG. 7A  is a cross-sectional view illustrating a state before a clinching process performed by using an outer-frame mold according to a second embodiment of the present invention. 
           [0053]      FIG. 7B  is a cross-sectional view illustrating a state after the clinching process performed by using the outer-frame mold according to the second embodiment of the present invention. 
           [0054]      FIG. 8A  is a perspective view of an aluminum pipe formed into a cylindrical tube shape. 
           [0055]      FIG. 8B  is a perspective view of an aluminum pipe formed into a hexagonal tube shape. 
           [0056]      FIG. 8C  is a perspective view of an aluminum pipe formed into a cross tube shape. 
           [0057]      FIG. 9A  is a cross-sectional view illustrating a state before a clinching process performed by disposing a rubber piece only near a joining section in accordance with a third embodiment of the present invention. 
           [0058]      FIG. 9B  is a cross-sectional view illustrating a state after the clinching process performed by disposing the rubber piece only near the joining section in accordance with the third embodiment of the present invention. 
           [0059]      FIG. 10A  is a cross-sectional view illustrating a state before a clinching process in which an aluminum pipe is partially expanded by using an outer-frame mold according to a modification of the third embodiment of the present invention. 
           [0060]      FIG. 10B  is a cross-sectional view illustrating a state after the clinching process in which the aluminum pipe is partially expanded by using the outer-frame mold according to the modification of the third embodiment of the present invention. 
           [0061]      FIG. 11A  is a cross-sectional view illustrating a state before a clinching process performed by using a truncated-cone-shaped indenter according to a fourth embodiment of the present invention. 
           [0062]      FIG. 11B  is a cross-sectional view illustrating a state after the clinching process performed by using the truncated-cone-shaped indenter according to the fourth embodiment of the present invention. 
           [0063]      FIG. 12A  is a cross-sectional view illustrating a state before a clinching process performed by compressing an aluminum pipe according to a fifth embodiment of the present invention in an axial direction. 
           [0064]      FIG. 12B  is a cross-sectional view illustrating a state after the clinching process performed by compressing the aluminum pipe according to the fifth embodiment of the present invention in the axial direction. 
           [0065]      FIG. 13A  is a cross-sectional view illustrating a state before a clinching process performed by using an indenter equipped with an outer frame in accordance with a modification of the fifth embodiment of the present invention. 
           [0066]      FIG. 13B  is a cross-sectional view illustrating a state after the clinching process performed by using the indenter equipped with the outer frame in accordance with the modification of the fifth embodiment of the present invention. 
           [0067]      FIG. 14A  is a perspective view of a steel component having a circular hole and an aluminum pipe having a circular cross-sectional shape when the two are clinched together at two locations in accordance with a sixth embodiment of the present invention. 
           [0068]      FIG. 14B  is a perspective view of a steel component having a rectangular hole and an aluminum pipe having a rectangular cross-sectional shape when the two are clinched together at two locations in accordance with the sixth embodiment of the present invention. 
           [0069]      FIG. 15A  is a perspective view of a hat-channel-type steel component having a circular hole and an aluminum pipe having a circular cross-sectional shape when the two are clinched together at two locations in accordance with a modification of the sixth embodiment of the present invention. 
           [0070]      FIG. 15B  is a perspective view of a hat-channel-type steel component having a rectangular hole and an aluminum pipe having a rectangular cross-sectional shape when the two are clinched together at two locations in accordance with a modification of the sixth embodiment of the present invention. 
           [0071]      FIG. 16  is a cross-sectional view illustrating a state where the clinching process in  FIGS. 15A and 15B  is being performed. 
           [0072]      FIG. 17A  is a cross-sectional view illustrating a state after the clinching process in  FIG. 16A . 
           [0073]      FIG. 17B  is a cross-sectional view illustrating a state after the clinching process in  FIG. 16A  is performed by partial expansion. 
           [0074]      FIG. 18A  is a cross-sectional view illustrating a state after a steel component and an aluminum pipe are clinched together at surfaces having bead sections in accordance with a modification of a seventh embodiment of the present invention. 
           [0075]      FIG. 18B  is a cross-sectional view taken along line XVIII-XVIII in  FIG. 18A . 
           [0076]      FIG. 19  is a cross-sectional view illustrating a state after a clinching process performed by using split rubber pieces according to an eighth embodiment of the present invention. 
           [0077]      FIG. 20A  is a cross-sectional view illustrating a state after a clinching process performed by inserting a plate between split rubber pieces in accordance with a modification of the eighth embodiment of the present invention. 
           [0078]      FIG. 20B  is a cross-sectional view illustrating a state after a clinching process performed by using a rubber piece with a different hardness at a joining section in accordance with a modification of the eighth embodiment of the present invention. 
           [0079]      FIG. 21A  is a perspective view illustrating a state before a resinous tube component and an aluminum pipe according to a ninth embodiment of the present invention are clinched together. 
           [0080]      FIG. 21B  is a perspective view illustrating a state after the resinous tube component and the aluminum pipe in  FIG. 21A  are clinched together. 
           [0081]      FIG. 22A  is a cross-sectional view illustrating the state before the resinous tube component and the aluminum pipe in  FIG. 21A  are clinched together. 
           [0082]      FIG. 22B  is a cross-sectional view illustrating the state after the resinous tube component and the aluminum pipe in  FIG. 21A  are clinched together. 
           [0083]      FIG. 23  is a perspective view of a steel bumper beam and an aluminum stay according to a tenth embodiment of the present invention. 
           [0084]      FIG. 24A  is a cross-sectional view of a bulging jig according to the tenth embodiment of the present invention. 
           [0085]      FIG. 24B  is a cross-sectional view of a steel bumper beam and an aluminum stay having the bulging jig inserted therein, according to the tenth embodiment of the present invention. 
           [0086]      FIG. 25A  is a cross-sectional view illustrating a state before a clinching process according to the tenth embodiment of the present invention. 
           [0087]      FIG. 25B  is a cross-sectional view illustrating a state after the clinching process according to the tenth embodiment of the present invention. 
           [0088]      FIG. 26A  is a cross-sectional view illustrating a state where the bulging jig has been removed after the clinching process according to the tenth embodiment of the present invention. 
           [0089]      FIG. 26B  is a cross-sectional view taken along line XXVI-XXVI in  FIG. 26A . 
           [0090]      FIG. 27A  is a perspective view of an aluminum pipe according to an eleventh embodiment of the present invention. 
           [0091]      FIG. 27B  is a cross-sectional view illustrating a state before a clinching process, taken along line XXVI-XXVI in  FIG. 27A . 
           [0092]      FIG. 27C  is a cross-sectional view illustrating a state after the clinching process, taken along line XXVI-XXVI in  FIG. 27A . 
           [0093]      FIG. 27D  is a plan view of the aluminum pipe and rubber pieces according to the eleventh embodiment of the present invention. 
           [0094]      FIG. 27E  is a plan view of the aluminum pipe and rubber pieces with a different shape, according to the eleventh embodiment of the present invention. 
           [0095]      FIG. 27F  is a plan view of the aluminum pipe, rubber pieces, and L-shaped angles according to the eleventh embodiment of the present invention. 
           [0096]      FIG. 28A  is a cross-sectional view illustrating a state before a clinching process according to a twelfth embodiment of the present invention. 
           [0097]      FIG. 28B  is a cross-sectional view illustrating a state after the clinching process according to the twelfth embodiment of the present invention. 
           [0098]      FIG. 29A  is a plan view illustrating a state before and after a clinching process according to a thirteenth embodiment of the present invention. 
           [0099]      FIG. 29B  is a plan view illustrating a state before and after the clinching process according to the thirteenth embodiment of the present invention. 
           [0100]      FIG. 29C  is a front view illustrating a state before the clinching process according to the thirteenth embodiment of the present invention. 
           [0101]      FIG. 29D  is a front view illustrating a state after the clinching process when a fixation jig according to the thirteenth embodiment of the present invention is not used. 
           [0102]      FIG. 29E  is a front view illustrating a state after the clinching process when the fixation jig according to the thirteenth embodiment of the present invention is used. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0103]    Embodiments of the present invention will be described below with reference to the appended drawings. In the following description, terms that express directions and positions (such as “upper side” and “lower side”) are sometimes used, but these terms are used for providing an easier understanding of the present invention and are not to limit the technical scope of the invention. Furthermore, the following description merely relates to examples of embodiments of the present invention and is not intended to limit the application or the purpose of the invention. 
         [0104]    Although materials of individual components are exemplified in the embodiments described below, the materials of the components in all of the embodiments are particularly not limited to the exemplified materials, and the present invention is applicable to arbitrary materials. 
       First Embodiment 
       [0105]    A method for joining a steel component (first member)  10  and an aluminum pipe (second member)  20  together by clinching will be described with reference to  FIGS. 1A to 2D . 
         [0106]    As shown in  FIG. 1A , the steel component  10  is composed of high-tensile steel and has a shape of a channel. The steel component  10  includes a bottom wall (first section)  11 , two side walls  12  and  13  extending vertically upward from the base wall  11 , and upper walls  14  extending horizontally outward from the two side walls  12  and  13 . The bottom wall  11  is provided with a hole (first hole)  15  in which the aluminum pipe  20  is fittable. The aluminum pipe  20  is composed of an aluminum alloy, has a hollow and circular cross-sectional shape, and extends along an axis L. The axis L extends through the center of the aluminum pipe  20  and through the center of the hole  15  in the steel component  10 . 
         [0107]    As shown in  FIG. 1B , with regard to the aluminum pipe  20  and the steel component  10 , the aluminum pipe  20  expands from the inner side toward the outer side so that an upper edge  21  thereof in the drawing is pressed and bent, whereby the aluminum pipe  20  becomes clinched to the hole  15  in the steel component  10 . The hole  15  in the steel component  10  preferably has a shape analogous to the cross-sectional shape of the aluminum pipe  20  and a size that is as small as possible within a range in which the aluminum pipe  20  is fittable therein. 
         [0108]    The steel component  10  and the aluminum pipe  20  are clinched together in accordance with the following procedure. 
         [0109]    As shown in  FIGS. 2A to 2D , the steel component  10  and the aluminum pipe  20  are clinched together by using a rubber piece (elastic body)  30 . 
         [0110]    First, as shown in  FIG. 2A , the aluminum pipe  20  is fitted into the hole  15  in the steel component  10 , the rubber piece  30  is inserted into the aluminum pipe  20 , and the components are set in a pressing device  40 . Alternatively, the aluminum pipe  20  may be fitted into the hole  15  in a state where the rubber piece  30  is inserted in the aluminum pipe  20 . The pressing device  40  includes an indenter  43  and a strike plate  42 . The indenter  43  has a flat lower surface and uses the lower surface to press against the steel component  10  or the rubber piece  30 . The strike plate  42  has a flat upper surface, and the steel component  10  and the rubber piece  30  are placed on the upper surface. The rubber piece  30  has a columnar shape with a diameter that allows it to be insertable into the aluminum pipe  20 , and has an overall length that is larger than that of the aluminum pipe  20 . Therefore, when in the set state, the rubber piece  30  partially protrudes from the upper end of the aluminum pipe  20 . Thus, when the pressing device  40  begins pressing such that the strike plate  42  and the indenter  43  relatively approach each other, the rubber piece  30  is pressed first. However, the rubber piece  30  does not necessarily have to protrude from the upper end of the aluminum pipe  20 , and may alternatively be flush with the upper end of the aluminum pipe  20  or be accommodated therein. 
         [0111]    Next, as shown in  FIG. 2B , the pressing device  40  applies a compressive external force to the rubber piece  30  along the axis L. The rubber piece  30  dimensionally enlarges in the diameter direction as its size decreases along the axis L. Accordingly, the rubber piece  30  is caused to elastically deform (expand) outward from the axis L, thereby causing the aluminum pipe  20  to expand. Then, as shown in  FIG. 2C , the aluminum pipe  20  is further expanded by being further compressed by the pressing device  40 . At the same time, the upper edge  21  in the drawing is pressed and bent toward the steel component  10 , so that the aluminum pipe  20  becomes clinched to the steel component  10 . 
         [0112]    After the clinching process, the rubber piece  30  from which the compressive force of the pressing device  40  has been removed restores its original shape with its own elastic force, as shown in  FIG. 2D , so that the rubber piece  30  can be readily removed from the aluminum pipe  20 . 
         [0113]    According to this method, the rubber piece  30  is expanded outward so that the aluminum pipe  20  expands uniformly, thereby preventing local deformation and reducing the load on the members  10  and  20 . This is because the aluminum pipe  20  can be uniformly deformed by utilizing the properties in which the rubber piece  30  compressed along the axis L expands uniformly from the inner side toward the outer side. Therefore, fit accuracy can be improved, thereby achieving increased joint strength. Moreover, this is an easier method, as compared with an electromagnetic forming method or other machining methods. 
         [0114]    An electromagnetic forming method is usable only on electrically conductive materials and has limitations with respect to cross-sectional shapes and dimensions depending on coils to be used. In contrast, this method is not dependent on materials and has no limitations related to cross-sectional shapes and dimensions. Moreover, since the method is executable in a facility that applies a compressive force to the rubber piece  30 , an electrical facility that requires a large-capacity capacitor, as in the electromagnetic forming method, is not necessary. 
         [0115]    According to this method, two members can be joined together, so that a multi-material process can be readily executed at low cost. Therefore, as described above, this method can be used on members composed of various materials other than the two components composed of high-tensile steel and an aluminum alloy. The same applies to the subsequent embodiments. 
         [0116]    The material used as the rubber piece  30  to be inserted into the aluminum pipe  20  is preferably, for example, urethane rubber, chloroprene rubber, CNR rubber (chloroprene rubber+nitrile rubber), or silicon rubber. Moreover, it is preferable that the rubber piece  30  have a Shore A hardness of 30 or higher. 
         [0117]    A member to be inserted into the aluminum pipe  20  is not limited to the rubber piece  30 . For example, as shown in  FIGS. 3A and 3B , a fluid sealing member  32  having gas or liquid sealed therein may be used in place of the rubber piece  30 . Other members that expand outward in accordance with a compressive force so as to expand the aluminum pipe  20  are also usable. It is preferable that the member deforms uniformly like the rubber piece  30  when expanding outward in response to a compressive force. 
         [0118]    Furthermore, as shown in  FIGS. 4A and 4B , the shape and size of the hole  15  provided in the bottom wall  11  of the steel component  10  do not have to be analogous to the cross-sectional shape of the aluminum pipe  20  to be fitted thereto. Specifically, a steel component  10  having a circular hole  15  and an aluminum pipe  20  having a rectangular cross-sectional shape may be clinched together as in  FIG. 4A , or a steel component  10  having a rectangular hole  15  and an aluminum pipe  20  having a circular cross-sectional shape may be clinched together as in  FIG. 4B . 
         [0119]    Furthermore, as shown in  FIGS. 5A to 5C , a burring process (flange-up process) may be performed on the hole  15  for preventing deformation of the steel component  10 , for reducing damages to the aluminum pipe  20 , and for increasing the clinching strength. Conceivable shapes obtained as a result of the burring process include, for example, various cross-sectional shapes shown in  FIGS. 5A to 5C . In  FIG. 5A , a shoulder section  15   a  has a large radius. In  FIG. 5B , the shoulder section  15   a  is chamfered. In  FIG. 5C , a rolling process is employed. Accordingly, even in a case where the steel component  10  has high strength, cracking of the steel component  10  as a result of machining can be effectively prevented. 
         [0120]    The burring process may be performed in the upward direction or the downward direction in the drawings. Preferably, as indicated by a two-dot chain line in  FIG. 2A , the burring process is performed in the downward direction in the drawing such that a part that is bent as a result of the burring process does not appear on the top surface of the steel component  10 . 
         [0121]    As shown in  FIGS. 6A and 6B , there are various conceivable shapes, such as a circular shape (see  FIG. 6A ) or a rectangular shape (see  FIG. 6B ), for the hole  15  that is to undergo the burring process. In particular, in a case where the hole  15  is polygonal, corner sections  15   b  may be cut out, and only straight side sections  15   c  may be bent upward, as shown in  FIG. 6B , so that the corner sections  15   b  can be prevented from cracking. 
       Second Embodiment 
       [0122]    A joining method according to this embodiment shown in  FIGS. 7A and 7B  is similar to that in the first embodiment in  FIGS. 2A to 2D  except for a feature related to an outer-frame mold  41 . Therefore, parts identical to those in the configuration shown in  FIGS. 2A to 2D  will be given the same reference signs, and descriptions thereof will be omitted. 
         [0123]    As shown in  FIG. 7A , in this embodiment, the steel component  10  and the aluminum pipe  20  are clinched together by using the outer-frame mold  41 . The outer-frame mold  41  has a cylindrical shape concentric with the aluminum pipe  20 . The outer-frame mold  41  is disposed between the strike plate  42  and the steel component  10  and at the outer side of the aluminum pipe  20 . When set in the pressing device  40 , the aluminum pipe  20  and the outer-frame mold  41  have a gap therebetween. By applying pressure using the indenter  43  in this state, the aluminum pipe  20  can conform to the shape of the inner surface of the outer-frame mold  41  when the aluminum pipe  20  expands, as shown in  FIG. 7B . 
         [0124]    According to this method, as shown in  FIGS. 8A to 8C , the inner surface of the outer-frame mold  41  may have various polygonal shapes, such as a hexagonal shape (see  FIG. 8B ) or a cross shape (see  FIG. 8C ), in addition to the cylindrical shape (see  FIG. 8A ). With regard to these shapes, an appropriate shape can be selected in view of, for example, component performance. For example, if the aluminum pipe  20  is a bumper stay, which is one of automobile components, the inner surface of the outer-frame mold  41  may be given small recesses and protrusions so that these small recesses and protrusions are transferred onto the aluminum pipe  20 , thereby achieving enhanced performance for absorbing impact energy in the event of a collision. 
       Third Embodiment 
       [0125]    A joining method according to this embodiment shown in  FIGS. 9A to 10B  is similar to that in the first embodiment in  FIGS. 2A to 2D  except for a feature related to an expanding region  22  of the aluminum pipe  20 . Therefore, parts identical to those in the configuration shown in  FIGS. 2A to 2D  will be given the same reference signs, and descriptions thereof will be omitted. 
         [0126]    As shown in  FIG. 9A , in this embodiment, the rubber piece  30  to be inserted into the aluminum pipe  20  is reduced in length, such that the rubber piece  30  is disposed only near the joining section of the aluminum pipe  20 . Moreover, the strike plate  42  has a columnar protrusion  42   a  extending upward. The protrusion  42   a  is inserted into the aluminum pipe  20  and supports the rubber piece  30 . In other words, the lower end of the rubber piece  30  is in contact with the upper end of the protrusion  42   a,  and the upper end of the rubber piece  30  is in contact with the lower end of the indenter. 
         [0127]    According to this method, an outward expanding force does not act on the part where the rubber piece  30  is not disposed. Thus, as shown in  FIG. 9B , the expanding region  22  of the aluminum pipe  20  is limited, so that the aluminum pipe  20  and the steel component  10  can be clinched together by causing only the region near the joining section of the aluminum pipe  20  to expand. Selection of whether the aluminum pipe  20  is to be substantially entirely deformed as in the first and second embodiments described above or whether the aluminum pipe  20  is to be partially deformed as in this embodiment may be made, as appropriate, based on, for example, the relationship with the component performance. 
         [0128]    As shown in  FIGS. 10A and 10B , a cylindrical outer-frame mold  44  that regulates expansion of the aluminum pipe  20  may be disposed therearound. The outer-frame mold  44  has, at the upper end thereof, a large-diameter section  44   a  with a large inner diameter near the joining section so as to expand only near the joining section. The inner diameter excluding that of the large-diameter section  44   a  is substantially equal to the outer diameter of the aluminum pipe  20 . Therefore, by using the outer-frame mold  44 , the expanding region  22  can be controlled with high accuracy such that the aluminum pipe  20  expands only near the joining section. 
       Fourth Embodiment 
       [0129]    A joining method according to this embodiment shown in  FIGS. 11A and 11B  is similar to that in the third embodiment in  FIGS. 10A and 10B  except for a feature related to the shape of the indenter  43 . Therefore, parts identical to those in the configuration shown in  FIGS. 10A and 10B  will be given the same reference signs, and descriptions thereof will be omitted. 
         [0130]    As shown in  FIG. 11A , the indenter  43  included in the pressing device  40  according to this embodiment has a downwardly-tapered truncated-cone shape and has a protrusion  43   a  and a brim  43   b.  Sometimes, a high forming force is required for expanding the edge  21  of the aluminum pipe  20  protruding upward from the steel component  10 , and there are cases where the clinching is insufficient with the deformation of the rubber piece  30  alone or the durability of the rubber piece  30  may become a problem due to large deformation thereof. In such cases, the method according to this embodiment is effective. 
         [0131]    As shown in  FIG. 11B , at the final stage of the forming process, the upper edge  21  of the aluminum pipe  20  protruding upward from the steel component  10  is pressed and expanded outward directly by the protrusion  43   a  of the indenter  43  without the intervention of the rubber piece  30 , and is further bent toward the steel component  10 . This enables more secure clinching. Moreover, the durability of the rubber piece  30  is improved since excessive load does not act on the rubber piece  30 . 
       Fifth Embodiment 
       [0132]    A joining method according to this embodiment shown in  FIGS. 12A and 12B  is similar to that in the first embodiment in  FIGS. 2A to 2D  except for a feature related to the shapes of the indenter  43  and the strike plate  42 . Therefore, parts identical to those in the configuration shown in  FIGS. 2A to 2D  will be given the same reference signs, and descriptions thereof will be omitted. 
         [0133]    As shown in  FIG. 12A , in this embodiment, the strike plate  42  includes a columnar protrusion  42   a  extending upward and a brim  42   b  provided around the protrusion  42   a.  The indenter  43  includes a columnar protrusion  43   a  extending downward and a brim  43   b  provided around the protrusion  43   a.  The protrusions  42   a  and  43   a  are inserted in the aluminum pipe  20 . 
         [0134]    As shown in  FIG. 12B , when performing pressing, the brims  42   b  and  43   b  come into contact with the respective ends of the aluminum pipe  20 . Thus, the brims  42   b  and  43   b  apply compressive forces along the axis L onto the aluminum pipe  20 . 
         [0135]    According to this method, the aluminum pipe  20  is also compressed along the axis L so as to assist with outward expansion of the aluminum pipe  20 . Specifically, together with the expanding force applied by the rubber piece  30  from the inner side of the aluminum pipe  20 , the aluminum pipe  20  can be expanded more reliably, thereby enabling clinching. 
         [0136]    As shown in  FIGS. 13A and 13B , it is also effective to dispose an outer frame  45  at the outer side of a part of the aluminum pipe  20  that is not to be expanded (i.e., the edge  21  in this embodiment). The outer frame  45  is cylindrical and is disposed around the edge  21  of the aluminum pipe  20 . By disposing the outer frame  45 , deformation of the edge  21  of the aluminum pipe  20  is regulated, so that a shape according to the intended use can be obtained. 
       Sixth Embodiment 
       [0137]    A joining method according to this embodiment shown in  FIGS. 14A to 17B  is similar to that in the first embodiment in  FIGS. 2A to 2D  except for a feature related to the number of joining sections. Therefore, parts identical to those in the configuration shown in  FIGS. 2A to 2D  will be given the same reference signs, and descriptions thereof will be omitted. 
         [0138]    As shown in  FIG. 14A , in this embodiment, the steel component  10  and the aluminum pipe  20  are clinched together at two locations. The steel component  10  includes a bottom wall  11 , an upper wall (second section)  14  disposed parallel to the bottom wall  11 , and two side walls  12  and  13  connecting these walls, all of which constitute a closed cross section. The bottom wall  11  is provided with a hole  15  (first hole). The upper wall  14  is provided with a hole  17  (second hole). As shown in  FIG. 14B , the aluminum pipe  20  is clinched to these two holes  15  and  17 . 
         [0139]      FIG. 16  is a cross-sectional view during a clinching process. In the clinching process performed on the two holes  15  and  17 , the indenter  43  is used to press and bend the edge  21  of the aluminum pipe  20  toward the steel component  10  as in the first embodiment, and the aluminum pipe  20  is further expanded so as to be clinched to the upper hole  17  in the drawing. The aluminum pipe  20  is clinched to the lower hole  15  in the drawing by being simply expanded. 
         [0140]    By performing clinching at two locations as in this embodiment, the joint strength can be further increased, as compared with the case where clinching is performed at a single location. In particular, the clinching method using the rubber piece  30  is the same as the case where clinching is performed at a single location in terms of the facility used, and is thus effective since the method can easily be used when performing clinching at a plurality of locations. 
         [0141]    The shape of the steel component  10  or the aluminum pipe  20  when performing clinching at two locations is not limited to the above. For example, the steel component  10  may have a hat-channel shape, as shown in  FIGS. 15A and 15B , or another shape. 
         [0142]    Furthermore, as shown in  FIG. 17A , the entire aluminum pipe  20  may be freely expanded when performing the clinching process. By using the outer-frame mold  44  described with reference to  FIGS. 7A and 7B , only the regions of the aluminum pipe  20  near the joining sections may be clinched by being expanded, as shown in  FIG. 17B . 
       Seventh Embodiment 
       [0143]    A joining method according to this embodiment shown in  FIGS. 18A and 18B  is similar to that in the sixth embodiment in  FIG. 16  except for features related to joining locations and bead sections  12   a  and  13   a.  Therefore, parts identical to those in the configuration shown in  FIG. 16  will be given the same reference signs, and descriptions thereof will be omitted. 
         [0144]    As shown in  FIGS. 18A and 18B , in the steel component  10  according to this embodiment, the two side walls  12  and  13  are respectively provided with the bead sections  12   a  and  13   a.  The bead sections  12   a  and  13   a  are inward protrusions and extend along the axis L. The aluminum pipe  20  is entirely clinched to the hole  15  in the bottom wall  11  and to the bead sections  12   a  and  13   a  of the two side walls  12  and  13 . 
         [0145]    As shown in  FIG. 18B , the aluminum pipe  20  and the steel component  10  are clinched together by including the bead sections  12   a  and  13   a  of the side walls  12  and  13  so that the joint strength can be further increased. Moreover, because the aluminum pipe  20  and the steel component  10  are clinched together by including the bead sections  12   a  and  13   a,  rotation of the aluminum pipe  20  relative to the steel component  10  can be regulated. Accordingly, the bead sections  12   a  and  13   a  are effective for preventing the aluminum pipe  20  from rotating. Alternatively, for preventing the aluminum pipe  20  from rotating, it is also effective to give the edge of the hole  15  a cutout shape or a shape other than the circular shape. 
       Eighth Embodiment 
       [0146]    A joining method according to this embodiment shown in  FIG. 19  is similar to that in the seventh embodiment in  FIG. 18A  except for a feature related to split rubber pieces  30 . Therefore, parts identical to those in the configuration shown in  FIG. 18A  will be given the same reference signs, and descriptions thereof will be omitted. 
         [0147]    As shown in  FIG. 19 , in this embodiment, the rubber piece  30  is split near the hole  15 . According to this method, the rubber piece  30  is split at the hole  15 , that is, at the joining section, so that deformation of the hole  15  and the bottom wall  11  of the steel component  10  can be prevented. Specifically, because the rubber piece  30  is split, an expanding force is not applied to the hole  15 , so that the hole  15  and the bottom wall  11  can maintain their original shapes. 
         [0148]    Furthermore, as shown in  FIGS. 20A and 20B , it is preferable that a tabular plate  31  be inserted between the rubber pieces  30  split at the joining section and inserted in the aluminum pipe  20 . The plate  31  may be composed of metal or resin so long as it is strong enough not to deform in response to a compressive force received from the rubber piece  30 , and preferably has a thickness of 15 mm or smaller. 
         [0149]    According to this method, the plate  31  exists in the joining section so that deformation of the hole  15  and the bottom wall  11  of the steel component  10  can be prevented more reliably. Because the plate  31  does not expand, an expanding force is not applied to the hole  15 , so that the hole  15  and the bottom wall  11  can maintain their original shapes. 
         [0150]    As an alternative to  FIG. 20A  in which the rubber piece  30  is split and the plate  31  is disposed between the split pieces, a rubber piece  30  partially composed of a different material may be used, as in  FIG. 20B . In  FIG. 20B , the rubber piece is a non-split single piece but has a high-hardness section  30   a  near the joining section. Specifically, the rubber piece  30  has a high hardness only in a part thereof near the joining section. Thus, this high-hardness section  30   a  has a function similar to that of the plate  31 , so that the hole  15  and the bottom wall  11  can maintain their original shapes. 
       Ninth Embodiment 
       [0151]    A joining method according to this embodiment shown in  FIGS. 21A to 22B  is similar to that in the fifth embodiment in  FIGS. 9A and 9B  except that the steel component  10  is replaced with a cylindrical resinous tube component  50 . Therefore, parts identical to those in the configuration shown in  FIGS. 9A and 9B  will be given the same reference signs, and descriptions thereof will be omitted. 
         [0152]    As shown in  FIGS. 21A and 21B , in this embodiment, the cylindrical resinous tube component  50  having a flange at the upper end thereof and the aluminum pipe  20  are clinched together. Like the resinous tube component  50 , the target member does not have to be tabular or be composed of metal. As mentioned above, the aluminum pipe  20  deforms outward in response to a compressive force applied along the axis L from the rubber piece  30  so as to expand. Therefore, this method is not limited to be used on electrically conductive materials, as in the electromagnetic forming method, and can also be used on resin materials, and the shape is not limited to the tabular shape. 
         [0153]      FIGS. 22A and 22B  are cross-sectional views illustrating states before and after the resinous tube component and the aluminum pipe in  FIG. 21A  are clinched together. As shown in  FIGS. 22A and 22B , the aluminum pipe  20  is clinched to the cylindrical resinous tube component  50  by being expanded at the opposite ends thereof. 
       Tenth Embodiment 
       [0154]    An example in which the present invention is applied to a bumper, which is one of automobile components, will now be described. 
         [0155]    As shown in  FIG. 23 , a cylindrical aluminum stay (second member)  120  is clinched to a closed-cross-section steel bumper beam (first member)  110  having a partition  111  in the middle. The steel bumper beam  110  has openings  113  and  113  at opposite sides thereof. The openings  113  and  113  are separated from each other by the partition  111 . For illustrative purposes, a top plate  114  (see  FIG. 26A ) of the steel bumper beam  110  is shown in a removed state in  FIG. 23 . As shown in  FIG. 24A , for the implementation, a bulging jig  150  including a round-rod-shaped rubber piece  130 , a tabular steel plate  131 , and a narrow round rod  140  composed of steel is used. A through-hole  112  into which the narrow round rod  140  is insertable is provided in the middle of the rubber piece (elastic body)  130  and the tabular plate  131 . One end of the round rod  140  is provided with a brim  141  for preventing the rubber piece  130  from falling out. The rubber piece  130  is split into two, one of which is provided with a countersunk hole  132  to which the brim  141  of the round rod  140  is fittable. The tabular plate  131  is placed on the rubber piece  130  with the countersunk hole  132  facing downward, the other rubber piece  130  is placed thereon, and the round rod  140  is subsequently inserted from below. The plate  131  has a circular shape with an outer diameter of φ83.5 mm and a thickness of 10 mm. The rubber pieces  130  used are composed of urethane rubber and have a circular shape with an outer diameter of φ83.5 mm, a length of 50 mm, and a Shore A hardness of 90. 
         [0156]      FIG. 24B  illustrates a state where the aluminum stay  120  is fitted in the hole (hole)  112  (see  FIG. 23 ) provided in the steel bumper beam  110 , and the aforementioned bulging jig  150  is inserted in the aluminum stay  120 . As shown in  FIG. 23 , the steel bumper beam  110  is processed into a closed-cross-sectional shape having a partition  111  in the middle by roll-forming a 1470-MPa-class cold-rolled steel plate having a thickness of 1.4 mm and has a circular hole  112  having an outer diameter of φ90.2 mm formed in the joining section with the aluminum stay  120 . In this case, the partition  111  in the middle is partially removed. The aluminum stay  120  is formed of a circular pipe composed of an aluminum alloy A6063 and having a thickness of 3 mm, an outer diameter of φ90 mm, and a length of 150 mm. 
         [0157]    Next, a clinching process shown in  FIGS. 25A and 25B  will be described.  FIG. 25A  illustrates a state where the steel bumper beam  110 , the aluminum stay  120 , and the bulging jig  150  are set on a lower mold  152 , and a presser jig  151  is disposed thereon. This state is set in the pressing device  40  (see  FIGS. 2A to 2D ), and a slide having the presser jig  151  set thereon is lowered so as to apply a compressive force to the rubber pieces  130 . In this case, pressure along the axis L of the aluminum pipe  20  is not applied, as shown in  FIGS. 9A and 9B . 
         [0158]      FIG. 25B  illustrates a state where the slide is at the bottom dead center. The rubber pieces  130  are compressed by the presser jig  151  so as to expand in the horizontal direction, thereby bulge-forming the aluminum stay  120 . Because the tabular plate  131  is inserted, the joint surface of the steel bumper beam  110  does not receive an excessive force so that undesired deformation is suppressed, whereby a clinching process with high fit accuracy is completed. 
         [0159]      FIGS. 26A and 26B  illustrate the steel bumper beam  110  and the aluminum stay  120  upon completion of the clinching process.  FIG. 26A  is a cross-sectional view of the steel bumper beam  110  and the aluminum stay  120  in a clinched state, and  FIG. 26B  is a cross-sectional view taken along line XXVI-XXVI. This embodiment is characterized in that the joint strength is high since clinching can be achieved at the middle partition  111  in addition to clinching at the hole  112  provided in the steel bumper beam  110  due to expansion of the aluminum stay  120  caused by the rubber pieces  130  shown in  FIG. 26B . 
       Eleventh Embodiment 
       [0160]    A joining method according to this embodiment shown in  FIGS. 27A to 27F  is similar to that in the fifth embodiment in  FIGS. 9A and 9B  except that the aluminum pipe  20  has a partition wall  23  therein and a plurality of rubber pieces  30  are inserted in the aluminum pipe  20 . Therefore, parts identical to those in the configuration shown in  FIGS. 9A and 9B  will be given the same reference signs, and descriptions thereof will be omitted. 
         [0161]    As shown in  FIG. 27A , the aluminum pipe  20  according to this embodiment has outer walls  24  extending along the axis L and having a rectangular shape in cross section and the partition wall  23  provided inside the outer walls  24 . The space inside the aluminum pipe  20  is divided into four spaces by the partition wall  23  having a cross shape in plan view. By providing the partition wall  23  in this manner, the strength of the aluminum pipe  20  can be increased. The cross-sectional shape is not limited to the rectangular shape and may be a freely-chosen shape. 
         [0162]    As shown in  FIGS. 27B and 27C , the indenter  43  according to this embodiment is provided with a cutout  43   c  in conformity to the shape of the partition wall  23 . By providing the cutout  43   c,  the clinching process can be completed without interference with the aluminum pipe  20  even when the rubber pieces  30  are pressed. 
         [0163]    Accordingly, because the clinching process is performed by using the plurality of rubber pieces  30  (i.e., four in this embodiment), concentration of stress caused by deformation can be prevented, so that the load on the steel component  10  and the aluminum pipe  20  can be reduced. 
         [0164]    The shape of each rubber piece  30  according to this embodiment is not limited in particular. For example, as shown in  FIG. 27D , the corners of the four inserted rubber pieces  30  may be round-chamfered so as to reduce the load on the corners of the aluminum pipe  20 , thereby preventing cracking and damaging. As shown in  FIG. 27E , C-chamfering may be performed, similarly to round-chamfering. As shown in  FIG. 27F , although the shape of the four inserted rubber pieces  30  is columnar, steel L-shaped angles  46  may be disposed along the partition wall  23  within the aluminum pipe  20 . Consequently, the load on the partition wall  23  can be reduced, thereby suppressing deformation. 
       Twelfth Embodiment 
       [0165]    A joining method according to this embodiment shown in  FIGS. 28A and 28B  is similar to that in the fifth embodiment in  FIGS. 9A and 9B  except that the steel component  10  and the aluminum pipe  20  are joined together in an inclined state. Therefore, parts identical to those in the configuration shown in  FIGS. 9A and 9B  will be given the same reference signs, and descriptions thereof will be omitted. 
         [0166]    As shown in  FIGS. 28A and 28B , the aluminum pipe  20  according to this embodiment has an end surface  25  inclined relative to the axis L. The steel component  10  is bent and is placed on an inclined surface  42   c.  The aluminum pipe  20  is placed on the inclined surface  42   c  in a state where the inclined end surface  25  is in contact therewith, and is clinched to the steel component  10 . Therefore, the steel component  10  and the aluminum pipe  20  are clinched together in an inclined state. Opposite end surfaces  30   b  and  30   c  of the rubber piece  30  according to this embodiment are formed and disposed parallel to the inclined end surface  25  of the aluminum pipe  20 . A pressing surface  43   d  of the indenter  43  is also formed parallel to the end surfaces  30   b  and  30   c  of the rubber piece  30 . 
         [0167]    Accordingly, this method can be used for clinching the steel component  10  and the aluminum pipe  20  together in an inclined state, which is often seen from a practical standpoint. Specifically, the opposite end surfaces  30   b  and  30   c  of the rubber piece  30  are given the same angle as the joining angle, so that the rubber piece  30  expands uniformly, whereby the aluminum pipe  20  can be expanded uniformly. 
       Thirteenth Embodiment 
       [0168]    A joining method according to this embodiment shown in  FIGS. 29A to 29D  is similar to that in the fifth embodiment in  FIGS. 9A and 9B  except that the steel component  10  is joined in a state where deformation thereof is restrained by a fixation jig  47 . Therefore, parts identical to those in the configuration shown in  FIGS. 9A and 9B  will be given the same reference signs, and descriptions thereof will be omitted. 
         [0169]    As shown in  FIGS. 29A and 29B , the steel component  10  according to this embodiment has a bottom wall  11  and an upright wall  18  extending along the axis L from the bottom wall  11 . The cross-sectional shape of the aluminum pipe  20  before the clinching process is not particularly limited and may be circular (see the dashed line in  FIG. 29A ) or rectangular (see the dashed line in  FIG. 29B ). The fixation jig  47  for suppressing deformation is provided at the outer side of the steel component  10 . The fixation jig  47  is disposed along the upright wall  18  and is fixed from the directions of the arrows in the drawings so as not to move outward. Although the fixation jig  47  used in this embodiment is tabular, the shape of the fixation jig  47  is not limited to this shape and may alternatively be a freely-chosen shape that can suppress deformation. 
         [0170]    As shown in  FIGS. 29C to 29E , in a case where the fixation jig  47  is not provided, the steel component  10  may deform in a warping manner when clinching is performed (see  FIG. 29D ). However, with the fixation jig  47 , deformation of the steel component  10  is restrained, so that deformation, such as warping, of the steel component  10  caused by expansion of the aluminum pipe  20  can be suppressed (see  FIG. 29E ). 
       REFERENCE SIGNS LIST 
       [0171]      10  steel component (first member) 
         [0172]      11  bottom wall (first section) 
         [0173]      12 ,  13  side wall 
         [0174]      12   a,    13   a  bead section 
         [0175]      14  upper wall (second section) 
         [0176]      15  hole (first hole) 
         [0177]      15   a  shoulder section 
         [0178]      15   b  corner section 
         [0179]      15   c  straight side section 
         [0180]      17  hole (second hole) 
         [0181]      18  upright wall 
         [0182]      20  aluminum pipe (second member) 
         [0183]      21  edge 
         [0184]      22  expanding region 
         [0185]      23  partition wall 
         [0186]      24  outer wall 
         [0187]      25  end surface 
         [0188]      30  rubber piece (elastic body) 
         [0189]      30   a  high-hardness section 
         [0190]      30   b,    30   c  end surface 
         [0191]      31  plate 
         [0192]      32  fluid sealing member 
         [0193]      40  pressing device 
         [0194]      41  outer-frame mold 
         [0195]      42  strike plate 
         [0196]      42   a  protrusion 
         [0197]      42   b  brim 
         [0198]      42   c  inclined surface 
         [0199]      43  indenter 
         [0200]      43   a  protrusion 
         [0201]      43   b  brim 
         [0202]      43   c  cutout 
         [0203]      43   d  pressing surface 
         [0204]      44  outer-frame mold 
         [0205]      44   a  large-diameter section 
         [0206]      45  outer frame 
         [0207]      46  L-shaped angle 
         [0208]      47  fixation jig 
         [0209]      50  resinous tube component 
         [0210]      110  steel bumper beam (first member) 
         [0211]      111  partition 
         [0212]      112  hole (hole) 
         [0213]      113  opening 
         [0214]      114  top plate 
         [0215]      120  aluminum stay (second member) 
         [0216]      130  rubber piece (elastic body) 
         [0217]      131  plate 
         [0218]      132  countersunk hole 
         [0219]      140  round rod 
         [0220]      141  brim 
         [0221]      150  bulging jig 
         [0222]      151  presser jig 
         [0223]      152  lower mold