Friction stirring-welding method

Abstract

A friction stirring-welding method capable of increasing the welding strength of a lap joint. A welding tool ( 1 ) comprises a small diameter projected part ( 2 ) at the tip of a shoulder ( 3 ). The welding tool is press-fitted to the upper plate ( 4 ) of the lap joint while being rotated. By a friction stirring action, an upper plate side welding boundary surface ( 6 ) plastically flows, a surface oxidation film on a lapped surface is peeled off, and the boundary surface is activated to provide an excellent welding part. Also, since the welding tool is formed in a shape having the small diameter semispherical projected part ( 2 ) at the tip thereof, the thickness ( 12 ) of an upper plate welding part is increased, and a lap joint part with high welding strength can be provided.

1 . A friction stir welding method for a lap joint, in which a plurality of members are lapped and a welding tool is pressed into one of the members, while being rotated, to cause friction stir to achieve welding, characterized in that the method comprises using, as the welding tool, a welding tool having a small diameter projected part at a tip end of a shoulder, and pressing the projected part and the shoulder of the welding tool into one of the members.  
   
   
       2 . The friction stir welding method according to  claim 1 , characterized in that the small diameter projected part is semispherical in shape.  
   
   
       3 . The friction stir welding method according to  claim 2 , characterized in that a recess is provided on the shoulder around the projected part.  
   
   
       4 . The friction stir welding method according to  claim 1 , characterized in that an outer peripheral surface of a tip end of the shoulder of the welding tool is inclined to define an inclined surface.  
   
   
       5 . The friction stir welding method according to  claim 1 , characterized in that an outer peripheral surface of a tip end of the shoulder of the welding tool is rounded.  
   
   
       6 . The friction stir welding method according to  claim 1 , characterized in that the welding tool is pressed into one of the members and a welding boundary surface is activated and welded by plastic flow, in which such pressing causes the one of the members to be discharged to an outer periphery of the welding tool.  
   
   
       7 . A friction stir welding method for a lap joint, in which a plurality of members are lapped and a welding tool is pressed into one of the members, while being rotated, to cause friction stir to achieve welding, characterized in that a tip end of the welding tool is semispherical in shape.  
   
   
       8 . The friction stir welding method according to  claim 7 , characterized in that only a part of the semispherical shaped portion of the welding tool is pressed into the one of the members to make a contact angle between the welding tool and a surface of the one of the members an acute angle.  
   
   
       9 . The friction stir welding method according to  claim 7 , characterized in that the welding interface is activated and welded by causing the one of the members to undergo plastic flow.  
   
   
       10 . A friction stir welding method for a lap joint, in which a plurality of members are lapped and a welding tool is pressed into one of the members, while being rotated, to cause friction stir to achieve welding, characterized in that a tip end of the welding tool is flat and an outer peripheral surface thereof is rounded.  
   
   
       11 . The friction stir welding method according to  claim 10 , characterized in that the whole of the flat portion of and only a part of the rounded portion of the welding tool are pressed into the one of the members.  
   
   
       12 . The friction stir welding method according to  claim 10 , characterized in that a welding interface is activated and welded by causing the one of the members to undergo plastic flow.  
   
   
       13 . The friction stir welding method according to  claim 1 , characterized in that the welding tool is pressed into the one of the members to cause friction stir of the member and then pulled out to perform spot welding.  
   
   
       14 . The friction stir welding method according to  claim 1 , characterized in that the welding tool is moved in a direction of welding in a state, in which the welding tool is pressed into the one of the members.  
   
   
       15 . The friction stir welding method according to  claim 1 , characterized in that lapped surfaces of the plurality of members are coated with soft metal.  
   
   
       16 . The friction stir welding method according to  claim 15 , wherein the soft metal is any one of nickel, zinc, and copper.  
   
   
       17 . The friction stir welding method according to  claim 1 , characterized in that a trapezoidal member is provided on a surface of the one of the members on that side, into which the welding tool is pressed, to prevent an indentation produced due to pressing of the welding tool.  
   
   
       18 . The friction stir welding method, according to  claim 1 , characterized in that one of the members is provided on a lapped surface thereof with a groove, another of the members is provided on a lapped surface thereof with a projected part, and the projected part is fitted into and welded to the groove.  
   
   
       19 . A friction stir welding apparatus that rotates a welding tool to cause friction stir to weld a plurality of members, characterized in that a tip end surface of the welding tool defines a convex-shaped and curved surface.  
   
   
       20 . A friction stir welding apparatus that rotates a welding tool to cause friction stir to weld a plurality of members, characterized in that the welding tool comprises, at a central portion of a tip end thereof, a projected part having a smaller diameter than that of the welding tool and a tip end of the projected part defines a curved surface.  
   
   
       21 . A friction stir welding apparatus that rotates a welding tool to cause friction stir to weld a plurality of members, characterized in that the welding tool comprises, at a central portion of a tip end thereof, a projected part and a recess is formed around the projected part.  
   
   
       22 . A friction stir welding apparatus that rotates a welding tool to cause friction stir to weld a plurality of members, characterized in that the welding tool comprises a tip end shaped to be trapezoidal in cross section transverse to an axial direction thereof.