Friction stir welding method and composite body produced thereby

Abstract: A composite body and its manufacturing method, the composite body having first and second members (31,32), each having a structure comprising spaced first and second face webs (33,34) which provide opposite exterior faces of the member and at least one cross-web (35,36) connecting said face webs, said first and second members being shaped and adapted so as to be assembled together in a joining arrangement in which respective edges (34a) of said first face webs (34) are mutually adjacent for direct connection to each other while said second face webs (33) are mutually spaced apart by a gap, said edges (34a) of said first face webs (34) being joined by a weld bead (45) formed by friction stir welding, and said second face webs (33) being connected by a third member (60) welded to both said second face webs and bridging across said gap between them.

Description: The present invention relates to a friction welding method that is suitably applied to panel welding used, for example, in aluminum alloys railway cars and buildings. A two-face structure (panel) for railway cars using hollow shape members is disclosed in Japanese Patent Laid-Open No. 246863/1990, and another using laminated panels such as honeycomb panels is disclosed in Japanese Patent Laid-Open No. 106661/1994. Another example is disclosed in EP-A-0579500, in which laser beam welding is used to form a composite body from two honeycomb members. The laser beam is passed through a gap formed by the members at one side of the body to be formed, to weld the members at the opposite side. The gap is then closed by laser beam welding. Thus the two laser beam welding operations are performed from one side only of the body. Friction stir welding is performed by rotating a round tool inserted in a joint region to heat and plasticize the joint region thus forming a weld. This welding is applied to a butt joint and a lap joint. This is described in wo 93/10935 (which is the same as wo 0615480B1 and the Published Japanese Translation of PCT Patent Application from another country No. 505090/1995) and the Welding & Metal Fabrication, January 1995, pp. 13-16. Reference should be made to these documents for explanation of friction stir welding, which is employed in the present invention. In friction stir welding, the reaction of the plasticized metal being extruded from immediately beneath the rotating tool (round rod) to the surface during the welding results in a downward force acting on the joint region. Thus, when this welding method is applied to a two-face structure (panel), this downward force causes the joint material at the joint region to flow downward, deforming the joint. This makes it impossible to produce a satisfactory weld. Two-face structures (panels) include hollow shape members made of extruded aluminum alloy and honeycomb panels. Joining such panels has been accomplished by MIG welding and TIG welding. When the friction welding is applied to such a joint, the joint is bent down or the material in the joint region is forced to flow down by a downward force produced during the friction welding. Therefore, there is now proposed a method of forming a composite body, by friction stir welding, in which welding may be carried out from only one side of the body. The invention provides a method as set out in claim 1. The present invention further provides a composite body having friction stir weld joints, as set out im claim 8. The present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a vertical cross section of one construction using friction stir welding. Figure 2 is a vertical cross section of Figure 1 after friction welding. Figure 3 is a vertical cross section of another construction including friction stir welding. Figure 4 is a vertical cross section of Figure 3 after friction welding. Figure 5 is a vertical cross section of another construction including friction stir welding. Figure 6 is a vertical cross section of Figure 5 after friction welding. Figure 7 is a vertical cross section of still another construction including friction stir welding. Figure 8 is a vertical cross section of Figure 7 after friction welding. Figure 9 is a vertical cross section showing the procedure of friction welding of an embodiment of this invention. Figure 10 is a perspective view of a structural body of a railway car. Figures 1 to 8 show constructions formed by friction stir welding and are included by way of explanation. The construction shown in Figure 1 has a joint configuration of abutting type between hollow shape members 31, 32 as panels. The hollow shape members 31, 32 have vertical plates 36, 36 at their ends in the width direction. Before the welding, the vertical plates 36, 36 are disposed immediately beneath a rotary tool 50. The vertical plates 36, 36 are opposed to each other in contact. If they are spaced apart, the distance is small and approximately 1 mm. On the extension of the interface between the vertical plates 36, 36 lies the center of a projection 52. The vertical plates 36, 36 have a stiffness strong enough to sustain the downward force mentioned earlier. The vertical plates 36 are perpendicular to two plates 33, 34. The hollow shape members 31, 32 are formed by extruding aluminum alloy. The upper and lower faces of the hollow shape member 31 are flush with the corresponding upper and lower faces of the hollow shape member 32. That is, the hollow shape members 31, 32 have the same thickness. This is true also of the succeeding constructions described below. During the friction welding, the boundary 53 between a large-diameter portion 51 and the projection 52 of a small-diameter portion of the rotary tool 50 is situated above the upper surfaces of the hollow shape members 31, 32. Numeral 35 designates a plurality of members that are arranged in trusses to connect the two plates 36, 36. The hollow shape members 31, 32 each have bilaterally symmetrical end portions. The hollow shape members 31, 32 are mounted on a bed (not shown) and fixed immovably. The bed also lies under the vertical plates 36, 36. Friction stir welding is performed by rotating the tool 50, plunging the projection 52 into the joint region of the hollow shape members 31, 32, and moving the projection 52 along the joint region. The rotating center of the projection 52 is between the two vertical plates 36, 36. Figure 2 shows the two panels after they are friction-welded. Reference number 45 denotes the shape of a weld bead after welding. On the extension of the border line between the vertical plates 36, 36 is situated the width center of the weld bead 45. The bead 45 lies in an area on the extension of the thickness of the vertical plates 36, 36. The depth of the weld bead 45 is determined by the height of the projection 52 at the lower end of the rotary tool 50 inserted in the joint region. With this construction, because the vertical plates 36, 36 perpendicular to the plates 33, 34 sustain the vertical force produced during the friction welding, the joint region does not bend, offering a satisfactory joint as shown in Figure 2. The vertical plate 36 is made vertical to the plates 33, 34 as much as possible. The vertical plate 36 may be holed for a lighter weight. This is true also of the succeeding constructions and the embodiment shown in Figure 9. Welding of the lower side is done by turning the hollow shape members upside down. The construction of Figure 3 has a vertical plate 36 at the end of one hollow shape member 31 but not at the opposing end of the other hollow shape member 32. Corners in the vertical direction of the vertical plate 36 of the hollow shape member 31 are recessed so as to receive the ends of projecting pieces 38, 38 of the hollow shape member 32. These recessed portions are open in a direction of thickness of the hollow shape member 31 and in a direction perpendicular to the thickness direction (toward the hollow shape member 32 side). When the projecting pieces 38 are placed (superposed) on the recessed portions, there is actually a clearance between them although they are in contact with each other in the figure. There is also a gap between the front ends of these members (i.e., between the projecting pieces 38, 38 and the corners 33a, 34b). The abutting joint portions on the upper face side of the two hollow shape members 31, 32 and the vertical plate 36 are situated directly below the center of the rotary tool 50. The rotating center of the projection 52 of the welding tool 50 is disposed on an extension of the centre line of the thickness of the vertical plate 36. That is, the joint region of the plate 33 (34) and plate 33 (34) is situated on the extension of the center line of the thickness of the vertical plate 36. The corners 33b, 34b extending from the plates 33, 34 to the recessed portions lie on an extension of the center line of the thickness of the vertical plate 36. Considering the gap between the corners 33b, 34b and the projecting pieces 38, the corners 33b, 34b are situated slightly to the left of the extension of the center line of the thickness of the vertical plate 36. The vertical plate 36 has a rigidity to support the downward force. The horizontal gap between the front ends of the projecting pieces 38 and the hollow shape member 31 is similar to that shown in Figure 1. The height of the projection 52 of the welding tool 50 is approximately equal to the thickness of the projecting piece 38. The region that is plastic and fluid extends below the projecting piece 38, and comes to have an area larger than the diameter of the projection 52, and the two hollow shape members 31, 32 are friction-welded. It is desirable that the friction weld be so formed as to extend beyond the contact area between the underside of the projecting piece 38 and the vertical plate 36. Figure 4 shows the state of the joint after being welded. The weld bead 45 is formed such that the width center of the weld bead 45 is situated on an extension of the thickness center of the vertical plate 36. To support the vertical force, it is desirablethat the rotating center of the tool 50 be located on the extension of the center line of the thickness of the vertical plate 36. To make the quantity of joint of the left and right hollow shape members 31, 32 equal, it is desirable that the corners 33b, 34b be situated on the extension of the thickness center line of the vertical plate 36. While the projection 52 of the tool 50 should preferably be placed in the range between extension lines of thickness of the vertical plate 36, the thickness of the vertical plate 36 is determined by the vertical force, the position of the projection 52 and the strength of the vertical plate 36. Hence, there may be a case that the thickness of the plate 36 is smaller than the diameter of the projection 52. In view of the possible errors of the position of the rotary tool 50 and those of the corners 33b, 34b, it is desirable that the corners 33b, 34b be positioned in the range between extension lines of thickness of the vertical plate 36, and at least a part of the projection 52 of the tool 50 be situated in the range. This arrangement enables the vertical plate 36 to receive at least a part of the vertical force, substantially preventing the deformation of the joint. As a result, a satisfactory joint can be formed. When the bead 45 is taken as a reference, although the bead 45 is slightly larger than the projection 52, the same as above can be said. This is true also of the other constructions here described. Compared with the case of Figure 1, this joint configuration can minimize the surface sink of the joint region even when the horizontal gap between the projecting piece 38 and the hollow shape member 31 is large. As a result, the joint has a good appearance and requires a reduced amount of putty for painting. This is because the gap between the two members is terminated at a depth equal to the thickness of the projecting piece 38. It is also considered that this joint configuration can reduce the weight. Further, because one of the hollow members is fitted into the other, the positioning in the height direction of the two members can be accomplished easily. The ends of the hollow shape member 31 are bilaterally symmetrical in shape. The hollow shape member 32 are also bilaterally symmetrical. Alternatively, the hollow shape member 31 has one end shaped as shown in Figure 3 and the other end shaped like the end of the hollow shape member 32 of Figure 3. In the construction of Figure 5, there is virtually no vertical plate 36 immediately below the corners 33b, 34b of the recessed portion of the hollow shape member 31. The right end of the vertical plate 36 lies on the extension of the corners 33b, 34b. On this extension is the rotating center of the tool 50. The end portion of the hollow shape member 31 is given a rigidity to sustain the vertical force by making the lower projecting piece 37 at the joint thicker and increasing the size of the arcs extending from the front ends of the projecting pieces 37 to the plate 36. The projecting pieces 38 of the other hollow shape member 32 are received in the recessed portions of the projecting pieces 37, as in the preceding construction of Figure 3. The second hollow shape member 32 has a vertical plate 36 near the projections 38 for connecting the upper and lower plates 33, 34. This arrangement prevents the joint region from being defective even when there is no vertical plate 36 directly below the corners of the recessed portions. It is noted, however, that below the range of bead 45 there is a vertical plate 36 of the panel 31. Figure 6 shows the state after welding. In the construction of Figure 5, the plate 36 of the hollow shape member 32 may be removed. Figure 7 shows another construction, a variation of the preceding construction of Figure 5, in which the joint region of the two hollow shape members 31, 32 is provided with raised portions 37a, 38a protruding outside. This makes the joint region thick. The heights of the raised portions 37a, 38a are equal. Other parts are similar to those of Figure 5, except that the vertical plate 36 and the projections 37 are slightly thinner. With this configuration, if there is a gap between the raised portions 37a and 38a before welding, the gap is filled with the material of the raised portions 37a, 38a, when welded, improving the appearance and reducing the amount of putty required. In conventional welded joints, the weld bead has a sink corresponding to the volume of the lost material 41 that has flowed down by the downward force. In the joint configuration of Figure 7, the rotary tool 50 plasticizes the raised portions 37a, 38a and forces them downward making up for the lost volume of the material 41. Thus, formation of sink can be prevented, providing a satisfactory welded joint. Figure 8 shows the shape of bead 45 after welding. After welding, unnecessary parts, if any, are cut off as shown. The raised portions 37a, 38a can also be applied to Figure 1, 3 and 5 and to the subsequent embodiment, shown in Figure 9. Figure 9 shows a construction which is an embodiment according to the present invention which allows welding at the upper and lower faces from only one side. The ends of the hollow shape members 31, 32 on the lower side have projecting pieces 34a, 34a protruding flush with the lower plates 34, 34 greatly toward the opposing hollow shape member sides. The front ends of the projecting pieces 34a, 34a are virtually in contact with each other. The front ends of the upper plates 33, 33 are back from the front ends of the lower plates 34a, 34a. The front ends of the upper plates 33, 33 are connected to the lower plates 34, 34 through the vertical plates 36, 36. The vertical plates 36, 36 are connected to intermediate portions of the lower plates 34. The top portions of the vertical plates 36, 36 are provided with recessed portions 39, 39 that receive a joint 60. When mounted on the recessed portions 39, 39, the upper surface of the joint 60 is flush with the upper face of the upper plates 33, 33. The distance between the two vertical plates 36, 36 is long enough for the rotary tool 50 to be inserted and is as short as possible. The relation between the vertical plates 36 and the recessed portions 39 is the same as explained in the constructions of Figure 5 and Figure 7. The welding procedure will be described below. In the state of Figure 9(A), the front ends of the lower plates 34a, 34a are welded by the rotary tool 50. At this time, the hollow shape members 31, 32, including the joint region of the plates 34a, 34a, are mounted on a bed. The upper surface of the bed (that backs the bead) is flat. The height of the projection 52 of the rotary tool 50 is smaller than the thickness of the plates 34a, 34a. This design ensures that the bottom surface after welding is flat. Thus, the bottom side can easily be used as an outer surface of the structure of a railway car or a building (the outer surface being the surface on which no decorative plate is mounted). Generally, the upper face of the friction welded joint tends to be uneven (at a boundary portion 51). Next, as shown in Figure 9(B), the joint 60 is mounted between the two hollow shape members 31, 32. The joint 60 is T-shaped in vertical cross section. When both ends of the joint 60 are placed on the recessed portions 39, 39, the lower end of a vertical portion 61 has a clearance between it and the weld bead on the lower plate. The vertical portion 61 may be omitted. Next, as shown in Figure 9(C), the joint portion between the joint 60 and the hollow shape member 31 is friction-welded by the rotary tool 50. The rotary tool 50 need not be the same as used in Figure 9(A). Then, as shown in Figure 9(D), the joint portion between the joint 60 and the hollow shape member 32 is friction-welded by the rotary tool 50. This procedure allows the welding to be performed from one side and eliminates the need to invert the body to be welded, therefore decreasing the time required for assembly of the body, and even increasing the precision of assembly. Figure 10 shows an example of an application of this embodiment of the present invention to the structural body of a railway car. The structural body has side bodies 101, a roof body 102, a floor body 103, and gable bodies 104 at the ends in the longitudinal direction. The side bodies 101 and the roof body 102 include panels 31, 32, whose long sides are oriented in the longitudinal direction of the car. The joining between the side bodies 101 and the roof body 102 and between the side bodies 101 and the floor body 103 is accomplished by MIG welding. The roof body 102 and the side bodies 101 are often shaped into arcs in cross section. The panels 31, 32 of Figure 9 may be combined in a mirror-image arrangement. The end of the projecting plate 34a of each panel is placed on the recessed portion 39 of the plate 33 of the other panel. This obviates the use of the joint 60 and allows the simultaneous friction welding of the joint region both from above and below. The plates 33, 34a can be provided with raised portions, as shown in Figure 7.

Claims: A method of joining first and second members (31, 32), each having a structure comprising spaced first and second face webs (33, 34) which provide opposite exterior faces of the member and at least one cross-web (35, 36) connecting said face webs, said first and second members being shaped and adapted so as to be assembled together in a joining arrangement in which respective edges of said first face webs (34) are mutually adjacent for direct connection to each other while said second face webs (33) are mutually spaced apart in order to allow access to said adjacent edges of said first face webs from the interior sides thereof, the method comprising the steps of (i) assembling said first and second members (31, 32) in said joining arrangement, (ii) carrying out a welding operation to join said adjacent edges of said first face webs from the interior sides thereof, and (iii) after step (ii), connecting said second face web (33) of said first and second members, characterised in that in step (ii) the welding operation is friction stir welding and step (iii) is carried out by friction stir welding a third member (60) to both said second face webs (33) of said first and second members so that said third member (60) bridges across the gap between said second face webs. A method according to claim 1, wherein in each of said first and second members, at least one said cross-web (35, 36) joins said second face web (33) at the zone (39) thereof to which said third member (60) is welded. A method according to claim 2, wherein in each of said first and second members, said face webs (33, 34) are parallel and one said cross-web (36) is perpendicular to said face webs and joins said second face web (33) at said zone to which said third member (60) is welded. A method according to any one of claims 1 to 3, wherein said third member (60) is T-shaped in cross-section, the leg of the T-shape being supported by said first face webs (34) in the assembled state. A method according to any one of claims 1 to 4, wherein the zones (39) of said second face webs (33) of said first and second members, at which said third member is joined, have rebates formed by re-entrant angles which receive respective edge portions of said third member (60). A method according to claim 5, wherein in each of said first and second members, a said cross-web (36) thereof is connected to said second face web thereof at the zone (39) thereof to which said third member (60) is welded, and extends perpendicularly to said second face web as seen in cross-section of the member so that the friction stir welding location of the second face web (33) and the third member (60) is at least partly aligned with the direction of the cross-web (36). A method according to any one of claims 1 to 6, wherein the first, second and third members are part of a railway car structure, and the exterior face of said first face webs (34) of said first and second members constitute an exterior face of the railway car structure. A composite body having first and second members (31, 32), each having a structure comprising spaced first and second face webs (33, 34) which provide opposite exterior faces of the member and at least one cross-web (35, 36) connecting said face webs, said first and second members being shaped and adapted so as to be assembled together in a joining arrangement in which respective edges (34a) of said first face webs (34) are mutually adjacent for direct connection to each other while said second face webs (33) are mutually spaced apart by a gap, said edges (34a) of said first face webs (34) being joined by a weld and said second face webs are connected at said gap; characterised in that said weld is formed by friction stir welding, and said second face webs (33) are connected by a third member (60) which is friction stir welded to both said second face webs and bridges across said gap between them. A composite body according to claim 8, wherein in each of said first and second members, at least one said cross-web (35, 36) joins said second face web (33) at the zone (39) thereof to which said third member (60) is welded. A composite body according to claim 8 or claim 9, wherein in each of said first and second members, said face webs (33, 34) are parallel and one said cross-web (36) is perpendicular to said face webs and joins said second face web (33) as the zone thereof to which said third member is welded. A composite body according to any one of claims 8 to 10, wherein said third member (60) is T-shaped in cross-section, the leg of the T-shape being supported by said first face webs (34). A composite body according to any one of claims 8 to 11, wherein in each of said first and second members, a said cross-web (36) thereof is connected to said second face web at the zone thereof to which said third member (60) is welded, and extends perpendicularly to said second face web as seen in cross-section of the member so that the friction stir welding location of the second face web (33) and the third member (60) is at least partly aligned with the direction of the cross-web (36). A composite body according to any one of claims 8 to 12, which is a railway car structure and wherein the exterior face of said first face webs (34) of said first and second members constitute an exterior face of the railway car structure.

Inventors: AOTA KINYA, ISHIMARU YASUO, TAKENAKA TSUYOSHI, AOTA, KINYA, ISHIMARU, YASUO, TAKENAKA, TSUYOSHI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1997
Main classification: B23K20
IPC codes: B61D17, E04C2, B23K33, B23K20