Mash seam welding process and mash seam welding apparatus

Abstract

Mash seam welding process and apparatus, wherein two plate-like workpieces having different thickness values are fed and guided by a guiding device such that a length W H of contact of the thick plate-like workpiece with one of two roller electrodes is smaller than a length W M of contact of the thin plate-like workpiece with the other roller electrode. In this arrangement, the amount of mashing of the thick plate-like workpiece by the roller electrode is made larger than that of the thin plate-like workpiece by the other roller electrode, so that an interface of the two plate-like workpieces is positioned intermediate between the pair of roller electrodes, whereby a weld nugget formed intermediate between the roller electrodes extends across the interface, permitting the weld to have a sufficient strength owing to a nugget ratio, which is a ratio of a width dimension W N of the weld nugget in the direction of the interface to a width dimension W G of the interface.

We claim: 
     
       1. A mash seam welding process of continuously welding a first plate-like workpiece and a second plate-like workpiece having a smaller thickness than said first plate-like workpiece, at overlapping portions of .Iadd.said .Iaddend.first and second plate-like workpieces, by applying a welding current between a pair of roller electrodes disposed rotatably about respective axes thereof, to thereby form a .[.weld.]. .Iadd.welding .Iaddend.nugget at an interface of said overlapping portions while said overlapping portions are squeezed by said pair of roller electrodes, wherein .Iadd.a surface area of contact of one of said pair of roller electrodes with said first plate-like workpiece is made smaller than a surface area of contact of the other of said pair of roller electrodes with said second plate-like workpieces, so that .Iaddend.an amount of mashing of said first plate-like workpiece by .Iadd.said .Iaddend.one .[.of said pair of.]. roller .[.electrodes.]. .Iadd.electrode .Iaddend.is made larger than that of said second plate-like workpiece by .[.the.]. .Iadd.said .Iaddend.other .[.of said pair of.]. roller .[.electrodes.]. .Iadd.electrode.Iaddend.. .[.2. A mash seam welding process according to claim 1 wherein a surface area of contact of said one roller electrode with said first plate-like workpiece is made smaller than a surface area of contact of said other roller electrode with said second plate-like 
     
     
        workpiece..].3. A mash seam welding process according to claim 1, wherein a length of contact of said one roller electrode with said first plate-like workpiece in an axial direction of said pair of roller electrodes is made smaller than that of said other roller electrode with 
     
     
        said second plate-like workpiece in said axial direction. 4. A mash seam welding process according to claim 1, wherein said one roller electrode located on the side of said first plate-like workpiece has a smaller diameter than said other roller electrode located on the side of said second plate-like workpiece. .[.5. A mash seam welding process of continuously welding a first plate-like workpiece and a second plate-like workpiece having a smaller thickness than said first plate-like workpiece, at overlapping portions of said first and second plate-like workpieces, by applying a welding current between a pair of roller electrodes disposed rotatably about respective axes thereof, to thereby form a weld nugget at an interface of said overlapping portions while said overlapping portions are squeezed by said pair of roller electrodes, said process comprising: feeding a pair of plate-like workpieces at a speed of 20 m/min. or higher while said plate-like workpieces are squeezed by said pair of roller electrodes..]..[.6. A mash seam welding process of continuously welding a first plate-like workpiece and a second plate-like workpiece having a smaller thickness than said first plate-like workpiece, at overlapping portions of said first and second plate-like workpieces, while said overlapping portions of said first and second plate-like workpieces are squeezed by a pair of roller electrodes disposed rotatably about respective two parallel axes thereof, said process comprising:   a welding step of continuously welding said first and second plate-like workpieces by applying a welding current between said pair of roller electrodes, to thereby form a weld nugget at an interface of said overlapping portions while said overlapping portions are squeezed by said pair of roller electrodes; and   a preliminary treatment step of squeezing a welding portion of said first plate-like workpiece between upper and lower roller dies of a presser roller device thereby to reduce the thickness of said welding portion of   
     
     
        said first plate-like workpiece, prior to said welding step..].7. A mash seam welding apparatus for continuously welding a first plate-like workpiece and a second plate-like workpiece having a smaller thickness than said first plate-like workpiece, at overlapping portions of said first and second plate-like workpieces, by applying a welding current between a pair of roller electrodes disposed rotatably about respective axes thereof, to thereby form a weld nugget at an interface of said overlapping portions while said overlapping portions are squeezed by said pair of roller electrodes, said mash seam welding apparatus comprising: said pair of roller electrodes being biased toward each other and having a same diameter; and   a guiding device for guiding said first and second plate-like workpieces such that said two plate-like workpieces overlap each other with a predetermined lap amount, while said first and second plate-like workpieces are fed toward said pair of roller electrodes, so that said overlapping portions of said first and second plate-like workpieces are squeezed by said pair of roller electrodes such that a surface area of contact of one of said pair of roller electrodes with said first plate-like workpiece is smaller than a surface area of contact of the other of said pair of roller electrodes with said second plate-like   
     
     
        workpiece. 8. A mash seam welding .[.process.]. .Iadd.apparatus .Iaddend.according to claim 7, wherein said guiding device guides said first and second plate-like workpieces such that a length of contact of said one roller electrode with said first plate-like workpiece in an axial direction of said pair of roller electrodes is smaller than that of said other roller electrode with said second plate-like workpiece in said axial 
     
     
        direction. 9. A mash seam welding .[.process.]. .Iadd.apparatus .Iaddend.according to claim 8, wherein said pair of roller electrodes have respective outer circumferential contact surfaces and are disposed such that widthwise centerlines of said outer circumferential contact .[.surf aces.]. .Iadd.surfaces .Iaddend.are substantially aligned with each other, and wherein said guiding device guides said first and second plate-like workpieces such that an edge of said first plate-like workpiece is located between a widthwise end of said outer circumferential contact surface of said one roller electrode on the side of said first plate-like workpiece and said widthwise centerline of said outer circumferential contact surface of said one roller electrode, while an edge of said second plate-like workpiece is located at an widthwise end of said outer circumferential contact surface of said other roller electrode on the side 
     
     
        of said first plate-like workpiece. 10. A mash seam welding apparatus according to claim 8, wherein said pair of roller electrodes have respective outer circumferential contact surfaces, respectively, and are disposed such that widthwise centerlines of said outer circumferential contact surfaces are offset from each other by a predetermined distance in an axial direction of said pair of roller electrodes, and wherein said guiding device guides said first and second plate-like workpieces such that a centerline of overlapping edge portions of said first and second plate-like workpieces is substantially aligned with said widthwise centerline of said outer circumferential contact surface of said one 
     
     
        roller electrode. 11. A mash seam welding apparatus according to claim 8, wherein said pair of roller electrodes have respective outer circumferential contact surfaces, respectively, said outer circumferential contact surface of said one roller electrode located on the side of said first plate-like workpiece having a smaller width dimension than that of said outer circumferential contact surface of said other roller electrode located on the side of said second plate-like workpiece, said pair of roller electrodes being disposed such that widthwise centerlines of said outer circumferential contact surfaces are substantially aligned with each other, and wherein said guiding device guides said first and second plate-like workpieces such that a centerline of overlapping edge portions of said first and second plate-like workpieces is substantially aligned with said widthwise centerlines of said outer circumferential contact surfaces of said pair of roller electrodes. .[.12. A mash seam welding apparatus according to claim 7, wherein said one roller electrode located on the side of said first plate-like workpiece has a smaller diameter than said other roller electrode located on the side of said second plate-like workpiece..]..[.13. A mash seam welding apparatus according to claim 7, further comprising a feeding device for feeding said first and second plate-like workpieces at a speed of 20 m/min. or higher while said first and second plate-like workpieces are squeezed by said first and second 
     
     
        roller electrodes..].14. A mash seam welding apparatus for continuously welding a first plate-like workpiece .[.(12 H ).]. and a second plate-like workpiece .[.(12 M ).]. having a smaller thickness than said first plate-like workpiece, at overlapping portions of said first and second plate-like workpieces, by applying a welding current between a pair of roller electrodes .[.(20).]. disposed rotatably about respective axes .[.(C3).]. thereof, to thereby form a weld nugget .[.(N).]. at an interface .[.(G).]. of said overlapping portions while said overlapping portions are squeezed by said pair of roller electrodes, said mash seam welding apparatus comprising: said pair of roller electrodes being biased toward each other and having a same diameter;   a guiding device for guiding said first and second plate-like workpieces such that said first and second plate-like workpieces overlap each other with a predetermined lap amount, while said first and second plate-like workpieces are fed toward said pair of roller electrodes, so that said overlapping portions of said first and second plate-like workpieces are squeezed by said pair of roller electrodes such that .Iadd.a surface area of contact of one of said pair of roller electrodes with said first plate-like workpiece is made smaller than a surface area of contact of the other of said pair of roller electrodes with said second plate-like workpiece, so that .Iaddend.an amount of mashing of said first plate-like workpiece by .Iadd.said .Iaddend.one .[.of said pair of.]. roller .[.electrodes.]. .Iadd.electrode .Iaddend.is made larger than that of said second plate-like workpiece by .[.the.]. .Iadd.said .Iaddend.other .[.of said pair of.]. roller .[.electrodes.]. .Iadd.electrode.Iaddend.; and   a feeding device for feeding said first and second plate-like workpieces at a speed of 20 m/min. or higher while said overlapping portions are   
     
     
        squeezed by said pair of roller electrodes. .[.15.  A mash seam welding apparatus for continuously welding a first plate-like workpiece and a second plate-like workpiece having a smaller thickness than said first plate-like workpiece, at overlapping portions of said first and second plate-like workpieces, while said overlapping portions of said first and second plate-like workpieces are squeezed by a pair of roller electrodes disposed rotatably about respective two parallel axes thereof, said mash seam welding apparatus comprising: a work feeding device for feeding said first and second plate-like workpieces in a predetermined feeding direction;   a welding portion for continuously welding said first and second plate-like workpieces by applying a welding current between said pair of roller electrodes, to thereby form a weld nugget at an interface of said overlapping portions, while said first and second plate-like workpieces are fed by said work feeding device and squeezed by said pair of roller electrodes; and   a preliminary treatment device comprising a presser roller device including upper and lower dies disposed upstream of said welding portion, for squeezing the portion of said first plate-like workpiece which overlaps said second plate-like workpiece, between said upper and lower roller dies thereby to reduce the thickness of said portion of said first plate-like   
     
     
        workpiece..]..Iadd.16.  A mash seam welding apparatus for continuously welding a first plate-like workpiece and a second plate-like workpiece having a smaller thickness than said first plate-like workpiece, at overlapping portions of said first and second plate-like workpieces, by applying a welding current between a pair of roller electrodes disposed rotatably about respective axes thereof, to thereby form a weld nugget at an interface of said overlapping portions while said overlapping portions are squeezed by said pair of roller electrodes, said mash seam welding apparatus comprising: said pair of roller electrodes being biased toward each other, one of said pair of roller electrodes located on the side of said first plate-like workpiece having a smaller diameter than that of the other of said pair of roller electrodes located on the side of said second plate-like workpiece; and   a guiding device for guiding said first and second plate-like workpieces such that said two plate-like workpieces overlap each other by a predetermined lap amount, while said two plate-like workpieces are fed toward said pair of roller electrodes, so that said overlapping portions of said first and second plate-like workpieces are squeezed by said pair of roller electrodes such that a surface area of contact of said one roller electrode with said first plate-like workpiece is smaller than a surface area of contact of said other roller electrode with said second plate-like workpiece..Iaddend.