Friction stir bonding method

The end of a face plate 11 of a hollow member 10 is abutted against the end of a face plate of a hollow member 20 . The end of a face plate 21 is stacked to a protrusion 15 . A small-diameter portion 52 of a rotary tool 50 is inserted to the abutted area, and the tool 50 is moved along the abutted region while being rotated in the right direction observed from the large-diameter portion 51 . The direction of movement is from the front of the drawing of FIG. 1 toward the far end thereof. In FIG. 1 , the pressure of mobilized metal is greater in the right side of the axial center of the rotary tool. The thickness of the member from the tip of the inserted small-diameter portion 51 to the hollow areas 10 b and 10 a is thicker at the right side. Accordingly, the thickness of the member is greater at the right side of the tool where the pressure is higher, thus preventing metal from flowing out into the hollow region 10 a . Since the member positioned to the left side of the tool is thinner, the weight of the bonded member is reduced.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS One embodiment of the present invention will now be explained with reference to FIGS. 1 through 4 . A body 500 of a railroad car comprises a side structure 501 constituting the side surfaces, a roof structure 502 constituting the roof, an underframe 503 constituting the floor, and an end structure 504 constituting the longitudinal edge portions of the car. The side structure 501 , the roof structure 502 and the underframe 504 are each formed by bonding plural extruded members 10 , 20 . The longitudinal direction (the extruded direction) of the extruded members 10 , 20 are arranged to the longitudinal direction of the car body 500 . The extruded members 10 , 20 are hollow members made of aluminum alloy. The structure of the hollow members 10 , 20 constituting the side structure 501 will now be explained. The hollow members constituting the other areas are similarly formed. The hollow member 10 ( 20 ) comprises two substantially parallel face plates 11 ( 21 ), 12 ( 22 ), and a plural number of connecting plates 13 ( 23 ) connecting the two face plates. The connecting plates 13 ( 23 ) are each tilted against the face plates 11 ( 21 ) and 12 ( 22 ). In other words, the face plates 11 ( 21 ), 12 ( 22 ) and the connecting plates 13 ( 23 ) constitute a truss. A connecting plate 14 ( 24 ) formed to the end portion of the hollow member 10 ( 20 ) in the width direction is orthogonal to the face plates 11 , 12 ( 21 , 22 ). The outer surface of the joint between the connecting plate 14 and the face plate 11 ( 12 ) is a convex portion for receiving the face plate 21 ( 22 ) of the hollow member 20 . The end portion of the hollow member 10 is stacked on the face plates 21 , 22 of the hollow member 20 . The ends of the face plates 11 , 12 are each provided with a protrusion 15 for supporting the face plate 21 or 22 . The protrusion 15 is protruded from the connecting plate 14 . The protrusion 15 is connected to the concave portion. The end of the face plates 11 , 12 ( 21 , 22 ) are each provided with a convex portion 17 ( 27 ) extending outward from the outer surface of the hollow members 10 , 20 (protruded outward in the direction of thickness). The end surface of the face plates 11 , 21 ( 21 , 22 ) and the convex portion 17 ( 27 ) is formed along the direction of thickness of the hollow member 10 ( 20 ). The end surface of the face plates 11 , 21 and the convex portion 17 (in other words, the convex portion close to the face plates 11 , 12 ) is positioned near the center of thickness of the connecting plate 14 . The end surface of the face plate 11 ( 12 ) and the convex portion 17 of the hollow member 10 is abutted against the end surface of the face plate 21 ( 22 ) and the convex portion 27 of the hollow member 20 . The face plate 11 ( 12 ) and the face plate 21 ( 22 ) are positioned along the same face, and the protruded margin of the convex portions 17 and 27 are equal. The width of the two convex portions 17 , 27 are equal. The width of the two convex portions is greater than the diameter of the large-diameter portion 51 of the rotary tool 50 . The metal forming the convex portions 17 , 27 is used as the source material for filling the gap of the abutted portions. Upon bonding, the two hollow members 10 , 20 are fixed on a base 100 . Reference number 101 refers to a groove to which the convex portions 17 , 27 formed to the lower surface is inserted. The rotary tool 50 comprises a large-diameter portion 51 and a small-diameter portion 52 mounted on the end of the large-diameter portion 51 . The small-diameter portion 52 is equipped with a screw. Upon bonding, the rotary tool 50 is inserted to the abutted portions. The bottom area of the large-diameter portion 51 is positioned within the convex portions 17 , 27 . The small-diameter portion 52 is inserted to the abutted portions between the face plates 11 and 21 . The lower end of the small-diameter portion 52 is somewhat inserted to the protrusion 15 . While rotating the rotary tool 50 , the tool is moved along the joint line of the abutted portions. After inserting the rotary tool 50 to the area to be bonded, the rotary tool 50 is moved from the closer side of the drawing of FIG. 1 to the farther side thereof. In FIG. 2 , which is a plan view of FIG. 1 , arrow A shows the direction of movement of the rotary tool 50 , and arrow B shows the direction of rotation of the rotary tool 50 . The screw of the small-diameter portion 52 is a left-hand screw. When observing the small-diameter portion 52 from the large-diameter portion 51 , the rotational direction of the rotary tool 50 is rightward (clockwise). When looking forward from the rotary tool 50 toward the direction of movement, the protrusion 15 is positioned to the right from the center of axis of the rotary tool 50 , as shown in FIG. 1 . After the friction stir bonding of the upper surface shown in FIG. 3 is finished, the hollow members 10 , 20 are reversed, and friction stir bonding is similarly performed to the other side. The pressure provided to the metal material of the joint portion mobilized by the rotary tool 50 is greater in the right side of the axial center of the rotary tool 50 than the left side thereof in the direction of movement of the rotary tool 50 . The right-hand rotation of the rotary tool 50 is considered to cause this phenomenon, the rotation pushing the material existing in front of the rotary tool 50 that has not yet been bonded toward the right side of the tool. In FIG. 1, a hollow area 10 b , 10 a exists on the left and right sides of the connecting plate 14 . The distance from the tip of the small-diameter portion 15 inserted to the joint portion to the left and right hollow areas 10 b , 10 a is set so that the distance from the tip to the protrusion 15 existing in the right side is greater than to the left side. Since the protrusion 15 must support the face plate 21 , the thickness of the protrusion is relatively thick. Therefore, the thickness of the area of the member receiving higher pressure is designed thicker. The mobilized metal will not flow out into the hollow area 10 a because of this thickness of the protrusion 15 , and therefore, no hole will be generated within the joint portion. On the other hand, the pressure provided to the left side of the rotary tool 50 is relatively low compared to the right side thereof. The reason for this is considered to be because no unbonded metal exists behind the rotary tool 50 . Since the left side of the axial center of the rotary tool receives small inner pressure, the thickness of the member measured from the tip of the small-diameter portion 52 to the hollow portion 10 b of the left side of the connecting plate 13 can be reduced. This enables to lighten the weight of the hollow member 10 . The “thickness of the member beginning from the tip of the inserted small-diameter portion 52 to the hollow portions 10 b or 10 a ” will now be explained with reference to FIG. 1 . The thickness of the metal needed in order to prevent the flow-out of metal at the side receiving higher pressure is set as R. Thickness R is necessary t the right side of the axial center of the small-diameter portion 52 measured from the tip of the portion 52 . In other words, the member on the right of the small-diameter portion 52 must have a thickness of radius R centering at the right-end corner of portion 52 . The term “thickness of the member beginning from the tip of the inserted small-diameter portion 52 to the hollow portion lob” refers to the thickness in the horizontal direction as well. The thickness of the member to the left of the axial center of the small-diameter portion 52 is smaller than thickness R. We will now consider a comparison example, where the direction of the screw and the rotating direction of the rotary tool 50 is the same as the above-mentioned embodiment, but the position of the hollow members 10 and 20 are opposite, or in other words, the protrusion 15 is protruded toward the left side of the rotary tool 50 . In this case, the thinner member is positioned to the right side of the rotary tool 50 where the pressure is higher, so the mobilized metal material flows out into the hollow space. Therefore, a hole may be generated within the joint portion. Moreover, when the stacked area of the protrusion 15 and the face plate 21 are placed to the left side of the small-diameter portion, the stacked surface near the joint portion may be knuckled toward the large-diameter portion 51 of the rotary tool 50 , generating a notch. However, if the stacked area is positioned to the right side thereof, the stacked area exists where the pressure is high, and therefore reduces the possibility of generating a notch. In other words, the area having a greater thickness measured from the tip of the small-diameter portion 52 to the surface of the member opposite the large-diameter portion 51 should be placed where the pressure is higher. The high-pressure region exists at the right side of the rotary tool 50 when observing the tool from behind the direction of movement, if the direction of rotation of the rotary tool 50 is right-hand rotation when observing the tool from the large-diameter portion 41 . If the screw of the small-diameter portion 52 is a right-hand screw, and if the direction of rotation of the rotary tool 50 is left-handed (counterclockwise), the hollow members 10 and 20 should be oppositely assembled, so that the protrusion 15 is positioned to the left of the axial center of the rotary tool 50 . FIG. 5 shows the present bonding method applied to bond non-hollow members. The face plates 12 , 22 and connecting plates 14 , 24 are removed from the hollow members 10 and 20 of FIG. 2 . The back surface of the joint portion is mounted on a flat base 105 . The technical scope of the present invention is not limited to the terms used in the claims or in the summary of the present invention, but is extended to the range in which a person skilled in the art could easily substitute based on the present disclosure. According to the friction stir bonding of the present invention, a lightweight bond having good characteristics is provided.