Patent Publication Number: US-2005115456-A1

Title: Structural body of railway car and joint structure for friction stir welding

Description:
The present application is based on and claims priority of Japanese patent applications No. 2003-357266 filed on Oct. 17, 2003 and No. 2004-46171 filed on Feb. 23, 2004, the entire contents of which are hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the invention  
      The present invention relates to a structural body of a railway car formed by joining extruded shape members or hollow shape members via friction stir welding, and further relates to a joint structure for friction stir welding suitable for application to the structural body of a railway car.  
      2. Description of the related art  
      In general, the car body of a railway car, that is, the structural body of a railway car is structured as illustrated in  FIG. 4 . In  FIG. 4 , a structural body  1  of a railway car is composed of side constructions  2  corresponding to both side walls of the structural body, end constructions  3  corresponding to the ends in the traveling direction of the car body, a roof construction  4  corresponding to the upper surface thereof, and an under frame  5  corresponding to the lower surface thereof. In recent years, such a structural body  1  of a railway car is mainly formed using extruded shape members made of aluminum alloy, wherein plural extruded shape members are joined together by friction stir welding. Each extruded shape member forming the structural body of the railway car is composed of a flat panel portion constituting the outer surface of the car body and a rib functioning as a reinforcement member for the flat panel portion. Further, each extruded shape member is formed in a flat-panel shape, but it is also possible to adopt a hollow extruded shape member in which two flat panels are connected via trusses.  
      The art of forming a structural body of a railway car via friction stir welding is disclose, for example, in Japanese Patent Publication Laid-Open No. 11-314173.  
      FIGS.  5 (A) through  5 (C) are explanatory views showing a joint structure for friction stir welding according to the prior art.  
      Two extruded shape members  10  and  20  to be joined together by friction stir welding are disposed with their joining ends butted against one another to form a joining surface  30  of a joint portion.  
      At the joining end of a first extruded shape member  10  is formed a protrusion  12  that projects from the upper surface of the extruded shape member  10  toward the direction from which a tool  50  for friction stir welding is to be inserted.  
      An upper surface  14  of the protrusion  12  is formed as a flat plane, and a side surface  13  of the protrusion  12  is connected to the upper surface  11  of the flat panel portion of the extruded shape member  10  via a small arc R 1 .  
      Similarly, a protrusion  22  is formed to the joining end of a second extruded shape member  20  that projects from the upper surface  21  of the flat panel portion. The upper surface  24  of the protrusion  22  is also formed as a flat plane, and the side surface  23  of the protrusion  22  is connected to the upper surface  21  of the flat panel portion of the extruded shape member  20  via a connecting portion having a small arc R 1 .  
      The friction stir welding tool  50  has a small diameter portion  52  at an end thereof, the center of the small diameter portion  52  being positioned to correspond to the joining surface  30  when carrying out friction stir welding ( FIG. 5 (A)).  
      The joint portion of the extruded members  10  and  20  being welded together has a flat surface  40  formed as the upper surface, and weld flashes B 1  remain on both sides of the flat surface  40  ( FIG. 5 (B)). The weld flashes B 1  are then cut and removed to finish the formation of the joint portion ( FIG. 5 (C)).  
      The upper surface  42  of the joint portion is projected than the upper surfaces  11  and  21  of the two extruded shape members  10  and  20  being joined together, by which a stepped portion is formed.  
      This stepped portion constitutes a notch  41 .  
      In such a joint portion, it is advantageous to increase the plate thickness compared to that of the flat panel portion, so as to compensate for the deterioration of strength at the joining portion. That is, the plate thickness of the flat panel portion of the extruded shape member should be reduced as much as possible in order to reduce the weight of the structural body of the railway car while assuring necessary strength. Therefore, if the plate thickness of the joining ends of the extruded shape members is the same as the plate thickness of the flat panel portion, it may not be possible to ensure sufficient strength due to the deterioration in strength at the joints. Therefore, it is considerable to increase the plate thickness at the joint portion compared to the plate thickness at the flat panel portion. Therefore, as shown in  FIG. 5 (B), in removing the weld flashes B 1  at the joint portion, portions of the protrusions  12  and  22  are left remaining to assure the plate thickness of the joint portion as shown in  FIG. 5 (C). However, the notch  41  of the protrusion remaining on the joint portion may cause stress concentration to occur when flexural stress or the like is applied to the extruded shape members  10  and  20 .  
     SUMMARY OF THE INVENTION  
      The object of the present invention is to provide a structural body of a railway car and a joint structure for friction stir welding suitably applied to the structural body of a railway car, that solve the problems mentioned above.  
      In order to achieve the object, the structural body of a railway car and the joint structure for friction stir welding according to the present invention comprise, as basic components, a protrusion that projects from the upper surface of the flat panel portion of the extruded shape member toward the direction from which a tool for friction stir welding is to be inserted, and a connecting portion formed between a side surface of the protrusion and the upper surface of the extruded shape member composed of an arc having a large curvature formed to the surface of the extruded shape member and an arc having a small curvature formed near the side surface of the protrusion, wherein the extruded shape members are used as outer panels of the structural body of the railway car with the side provided with the protrusions of the shape members disposed to face the inner side of the car body.  
      According to the present invention, a structural body of a railway car formed by joining plural extruded shape members via friction stir welding characterizes in that each extruded shape member subjected to friction stir welding formed of a flat panel and a rib; a protrusion is formed to a joining end of the flat panel, the protrusion projecting from an upper surface of the flat panel toward a direction from which a friction stir welding tool is to be inserted; a connecting portion is formed between a side surface of the protrusion and the upper surface of the flat panel, the connecting portion composed of an arc with a large curvature formed near the upper surface of the flat panel and an arc with a small curvature formed near the side surface of the protrusion; wherein the extruded shape members are used as outer panels of the structural body of a railway car with the side of the extruded shape members having the protrusion facing an inner side of the car body.  
      According further to the present invention, a structural body of a railway car formed by joining plural extruded shape members via friction stir welding characterizes in that each extruded shape member subjected to friction stir welding is formed of a flat panel and a rib; a protrusion is formed to a joining end of the flat panel, the protrusion projecting from an upper surface of the flat panel toward a direction from which a friction stir welding tool is to be inserted; a connecting portion is formed between a side surface of the protrusion and the upper surface of the flat panel, the connecting portion composed of an ellipse; wherein the extruded shape members are used as outer panels of the structural body of a railway car with the side of the extruded shape members having the protrusion facing an inner side of the car body.  
      According to another aspect of the present invention, a structural body of a railway car formed by joining plural extruded hollow shape members via friction stir welding characterizes in that each extruded hollow shape member subjected to friction stir welding is formed of two flat panels and trusses; a protrusion is formed to a joining end of at least one of the two flat panels, the protrusion projecting from an upper surface of the flat panel toward a direction from which a friction stir welding tool is to be inserted; a connecting portion is formed between a side surface of the protrusion and the upper surface of the flat panel, the connecting portion composed of an arc with a large curvature formed near the upper surface of the flat panel and an arc with a small curvature formed near the side surface of the projection; wherein the extruded hollow shape members are used as outer panels of the structural body of a railway car with the side having the protrusion facing an inner side of the car body.  
      According to yet another aspect of the present invention, a structural body of a railway car formed by joining plural extruded hollow shape members via friction stir welding characterizes in that each extruded hollow shape member subjected to friction stir welding is formed of two flat panels and trusses; a protrusion is formed to a joining end of at least one of the two flat panels, the protrusion projecting from an upper surface of the flat panel toward a direction from which a friction stir welding tool is to be inserted; a connecting portion formed between a side surface of the protrusion and the upper surface of the flat panel, the connecting portion composed of an ellipse; wherein the extruded hollow shape members are used as outer panels of the structural body of a railway car with the side having the protrusion facing an inner side of the car body.  
      According to the present invention, a joint structure for friction stir welding suitably applied to the structural body of a railway car and formed to an end of an extruded shape member to be subjected to friction stir welding comprises a protrusion projecting from an upper surface of the extruded shape member toward a direction from which a friction stir welding tool is to be inserted; and a connecting portion formed between a side surface of the protrusion and the upper surface of the extruded shape member, the connecting portion composed of an arc with a large curvature formed near the upper surface of the extruded shape member and an arc with a small curvature formed near the side surface of the projection.  
      Furthermore, a joint structure for friction stir welding suitably applied to the structural body of a railway car and formed to an end of an extruded shape member to be subjected to friction stir welding comprises a protrusion projecting from an upper surface of the extruded shape member toward a direction from which a friction stir welding tool is to be inserted; and a connecting portion formed between a side surface of the protrusion and the upper surface of the extruded shape member, the connecting portion formed of an ellipse.  
      Furthermore, the above-mentioned extruded shape member is a hollow shape member of a structural body of a car having a structure in which two flat panels are connected via trusses, and at least the joint structure for friction stir welding disposed on the inner side of the car body is equipped with a connecting portion.  
      Since the structural body of a railway car and the joint structure for friction stir welding according to the present invention comprises the above features, it is possible to assure a sufficient plate thickness at the joint portion, and the height differences between the joining surface from which the weld flash generated during friction stir welding is removed and the upper surface of the extruded shape member are connected via an arc having a large curvature. Therefore, the present structure enables to prevent concentration of stress to the area with the height differences. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an explanatory view showing embodiment 1 of the present invention;  
       FIG. 2  is an explanatory view showing embodiment 2 of the present invention;  
       FIG. 3  is an explanatory view showing embodiment 3 of the present invention;  
       FIG. 4  is an explanatory view of a structural body of a railway car; and  
       FIG. 5  is an explanatory view of a joint structure according to the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The embodiments of the present invention will now be explained with reference to the drawings.  
      [Embodiment 1] 
      FIGS.  1 (A) through  1 (C) are explanatory views illustrating embodiment 1 of the present invention.  
      Two extruded shape members  100  and  120  to be joined via friction stir welding are placed so that joining ends thereof are butted against one another, forming a joining surface  140  of the joint portion.  
      A joining end of the first extruded shape member  100  is provided with a protrusion  110  formed to protrude from an upper surface of a flat panel portion of the extruded shape member  100  toward the direction from which a tool  50  for friction stir welding is to be inserted.  
      The upper surface  114  of the protrusion  110  is formed as a flat surface, and a side surface  112  of the protrusion  110  is connected to the upper surface  102  of the flat panel portion of the extruded shape member  100  via a connecting portion having a first arc R 2  and a second arc R 3 . The first arc R 2  has a small curvature and the second arc R 3  has a large curvature.  
      Similarly, a joining end of the second extruded shape member  120  is provided with a protrusion  130  formed to protrude from an upper surface of a flat panel portion of the extruded shape member  120  toward the direction from which a tool  50  for friction stir welding is to be inserted.  
      The upper surface  134  of the protrusion  130  is formed as a flat surface, and a side surface  132  of the protrusion  130  is connected to the upper surface  122  of the flat panel portion of the extruded shape member  120  via a connecting portion having a first arc R 2  and a second arc R 3 . The first arc R 2  has a small curvature and the second arc R 3  has a large curvature. These extruded shape members  100  and  120  are used as the outer panels of the structural body of the railway car, with the side having the protrusions  110  and  130  disposed to face the inner side of the car body.  
      The friction stir welding tool  50  has a small diameter portion  52  formed at an end thereof, and the center of the small diameter portion  52  is placed to correspond to the joining surface  140  when performing friction stir welding ( FIG. 1 (B)).  
      The joint portion formed between the extruded shape members  100  and  120  being joined has a flat surface  150  formed to the upper surface thereof and weld flashes B 1  formed at both ends of the flat surface  150 . The weld flashes B 1  are cut and removed, and a joint portion is completed ( FIG. 1 (C)).  
      When utilizing the extruded shape members  100  and  120  as the outer panels of the structural body of the railway car, the surface having the protrusions  110  and  130  is disposed to face the inner side of the car body. The plate thickness T excluding the joining portion between the extruded shape members  100  and  120  is set to a predetermined thickness to ensure necessary strength as the outer panel of the structural body of the railway car. This plate thickness T must be thick enough to ensure a plate thickness Tc of a joining portion determined considering the strength deterioration of the portion being subjected to friction stir welding, so if the flat surface having no protrusions  110  and  130  formed is disposed as the outer surface of the car body, the thickness T must be thicker than the thickness required to ensure the necessary strength as the outer plate. However, as shown in  FIG. 1 (C), by shaping protrusions  110  and  130  while leaving the portion corresponding to arc R 3  to remain, the plate thickness required to compensate for the deterioration of strength at the joining portion can be reserved by this portion. Therefore, the plate thickness T excluding the joining portion can be set to the thickness required to ensure necessary strength as the outer panel of the structural body of the railway car, and so it is possible to reduce the weight of the extruded shape members  100  and  120 . In other words, the weight of the whole structural body of the railway car can be cut down. If the appearance of the surface disposed as the outer side of the car body corresponding to the friction stir welded portion is not good when the surface having protrusions  110  and  130  of the extruded shape members  100  and  120  is positioned to face the inner side of the car body, it may be possible to provide protrusions having small heights to the surface of the extruded shape members  100  and  120  opposite to the surface having protrusions  110  and  130 , which is the surface disposed as the outer side of the car body, and to remove the protruded portions after completing welding to create a smooth finished surface.  
      According to the structure described above, the plate thickness Tc at the joining portion is finished so that the arc R 3  of protrusions  110  and  130  are left remaining, so that sufficient plate thickness Tc can be ensured without causing any stress concentration. Therefore, since it is not necessary to set the plate thickness T excluding the joining portions of the extruded shape members  100  and  130  to a thickness more than what is required as the outer panel of the structural member of the railway car, it becomes possible to reduce the overall weight of the structural body of the railway car.  
      [Embodiment 2] 
      FIGS.  2  (A) through  2  (C) are explanatory views illustrating embodiment 2 of the present invention.  
      The two extruded shape members  200  and  220  to be joined via friction stir welding are placed so that joining ends thereof are butted against one another, forming a joining surface  240  of the joint portion.  
      A joining end of the first extruded shape member  200  is provided with a protrusion  210  formed to protrude from an upper surface of a flat panel portion of the extruded shape member  200  toward the direction from which a tool  50  for friction stir welding is to be inserted.  
      The upper surface  214  of the protrusion  210  is formed as a flat surface, and a side surface  212  of the protrusion  210  is connected to the upper surface  202  of the flat panel portion of the extruded shape member  200  via a connecting portion composed of a portion of an ellipse D 1 . The portion of an ellipse D 1  is formed so that the portion near the flat panel has a large curvature and the portion near the side surface  212  of the protrusion  210  has a small curvature.  
      Similarly, a joining end of the second extruded shape member  220  is provided with a protrusion  230  formed to protrude from an upper surface of a flat panel portion of the extruded shape member  220  toward the direction from which a tool  50  for friction stir welding is to be inserted.  
      The upper surface  234  of the protrusion  230  is formed as a flat surface, and a side surface  232  of the protrusion  230  is connected to the upper surface  222  of the flat panel portion of the extruded shape member  220  via a connecting portion composed of a portion of an ellipse D 1 . The portion of an ellipse D 1  is formed so that the portion near the flat panel has a large curvature and the portion near the side surface  212  of the protrusion  210  has a small curvature.  
      These extruded shape members  200  and  220  are used as the outer panels of the structural body of the railway car, with the side having the protrusions  210  and  230  disposed to face the inner side of the car body.  
      The friction stir welding tool  50  has a small diameter portion  52  formed at an end thereof, and the center of the small diameter portion  52  is placed to correspond to the joining surface  240  when performing friction stir welding ( FIG. 2 (B)).  
      The joint portion formed between the extruded shape members  200  and  220  being joined has a flat surface  250  formed as the upper surface and weld flashes B 1  formed at both ends of the flat surface  250 . The weld flashes B 1  are cut and removed, and the formation of a joint portion is completed ( FIG. 2 (C)).  
      According to the structure described above, the plate thickness at the joining portion is finished so that the portions of an ellipse D 1  formed to the protrusions  210  and  230  are left to remain, so that sufficient plate thickness can be ensured without causing any stress concentration. Therefore, since it is not necessary to set the thickness of the plate thickness T excluding the joining portions of the extruded shape members  200  and  230  to more than what is required as the outer panel of the structural member of the railway car, it becomes possible to reduce the weight of the entire structural body of the railway car.  
      [Embodiment 3] 
      FIGS.  3 (A) through  3 (D) illustrate embodiment 3 of the present invention.  
      The present embodiment illustrates an example for forming a side construction of a railway car using hollow shape members made of aluminum alloy.  
      A first hollow extruded shape member  400  constituting a joint portion is structured so that its cross-sectional shape is hollow, having two parallel flat panels  410  and  420  connected via trusses  460 .  
      A second hollow extruded shape member  500  is also structured so that its cross-sectional shape is hollow, having two parallel flat panels  510  and  520  connected via trusses  560 .  
      A first flat panel  410  of the first hollow extruded shape member  400  is disposed to face an inner side S 1  of the railway car body, with a protrusion  430  formed at the joining end thereof. A connecting portion between the protrusion  430  and the first flat panel  410  is composed of an arc R 2  having a small curvature and an arc R 3  having a large curvature, as explained in embodiment 1.  
      Similarly, a first flat panel  510  of the second hollow extruded shape member  500  is disposed to face an inner side S 1  of the railway car body, with a protrusion  530  formed at the joining end thereof. A connecting portion between the protrusion  530  and the first flat panel  510  is composed of an arc R 2  having a small curvature and an arc R 3  having a large curvature, as explained in embodiment 1.  
      A second flat panel  420  of the first hollow extruded shape member  400  is disposed to face an outer side S 2  of the railway car body, with a protrusion  440  formed at the joining end thereof. The protrusion  440  and the flat panel  420  are connected via a corner portion C 1 .  
      A second flat panel  520  of the second hollow extruded shape member  500  is disposed to face an outer side S 2  of the railway car body, with a protrusion  540  formed at the joining end thereof. The protrusion  540  and the flat panel  520  are connected via a corner portion C 2 .  
      The end portions of the first hollow extruded shape member  400  and the second hollow extruded shape member  500  are engaged with one another via tapered surfaces T 1  and T 2 .  
      Thus, gaps G 1  and G 2  are formed to butted portions between the first hollow member  400  and the second hollow member  500 .  
      Friction stir welding is carried out having the center of the small diameter portion  52  of the friction stir welding tool  50  placed to substantially correspond to the center of gaps G 1  and G 2 .  
      During welding, the pressing force applied by the friction stir welding tool is mainly received by a truss  560  having high rigidity of the second hollow extruded shape member.  
       FIG. 3 (B) illustrates a state in which a joint surface  600  facing the inner side S 1  of the car body and a joint surface  650  facing the outer side S 2  of the car body are joined by friction stir welding.  
      Weld flashes B 1  are formed on both sides of joint surfaces  600  and  650 .  
       FIG. 3 (C) illustrates a state in which the weld flashes are removed through processing performed to the joint surface  600  facing the inner side S 1  of the car, thereby finishing a joint surface  610 .  
      The joint surface  610  constitutes a surface projected from the flat panel  410  of the first hollow extruded shape member and the flat panel  510  of the second hollow extruded shape member, similar to embodiment 1, and the connecting portion is connected via an arc R 3  having a large curvature, so that there will be no stress concentration. Since an interior decoration is applied to the side construction facing the inner side S 1  of the car, there is no problem even if the joint surface  610  remains protruded. Moreover, since the joint surface  610  forms a surface projected from the flat panel  410  of the first extruded hollow shape member and the flat panel  510  of the second extruded hollow shape member, it becomes possible to ensure a sufficient plate thickness at the joints, and thus there is no need to increase the thickness of the flat panels  410  and  510 , so the weight of the entire structural body of the railway car can be reduced advantageously.  
       FIG. 3 (D) illustrates a state in which the joint surface  660  facing the outer side S 2  of the car is processed to complete a joint surface  670  forming the same plane as the flat panel  420  of the first hollow extruded shape member and the flat panel  520  of the second hollow extruded shape member.  
      Since the outer side S 2  of the car body is finished as a flat plane, stress concentration will not occur, and a side construction having an improved appearance can be obtained.  
      Further, it is of course possible to apply the ellipse-shaped connection described in embodiment 2 to the protrusion of the joint surface facing the inner side S 1  of the car.