Mash seam welding process and mash seam welding apparatus

Abstract

PCT No. PCT / JP96 / 00410 Sec. 371 Date Dec. 24, 1996 Sec. 102(e) Date Dec. 24, 1996 PCT Filed Feb. 23, 1996 PCT Pub. No. WO96 / 26037 PCT Pub. Date Aug. 29, 1996Mash 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 WH of contact of the thick plate-like workpiece with one of two roller electrodes is smaller than a length WM 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 WN of the weld nugget in the direction of the interface to a width dimension WG of the interface.

Description

FIELD OF THE ARTThis invention relates to a mash seam welding process and a mash seam welding apparatus for continuously welding together two plate-like workpieces by overlapping the workpieces at their edges and applying a welding current between a pair of roller electrodes while the overlapping edge portions of the two plate-like workpieces are squeezed to be mashed, by and between the pair of roller electrodes.BACKGROUND TECHNOLOGYHigh-speed welding is possible by mash seam welding in which two plate-like workpieces are continuously welded together at their overlapping edge portions while the edge portions are squeezed to be mashed by and between a pair of roller electrodes, with a welding current being applied between the pair of roller electrodes. Since the mash seam welding is suitable for mass production, it is widely employed in production lines for steel plates, automobiles, etc.In the mash seam welding described above, the two plate-like workpieces are positioned relative ...

AI Technical Summary

Benefits of technology

In the present process in which the amount of mashing of the first thick plate-like workpieces by the first plate-like workpieces is larger than that of the second thin plate-like workpiece, the position of the interface of the two plate-like workpieces is shifted to a position intermediate between the pair of roller electrodes, so that the weld nugget formed at the position intermediate between the pair of roller electrodes extends across the above-indicated interface, permitting a sufficient weld strength.

It is also preferable that the pair of plate-like workpieces are fed at a speed of 20 m / min. or higher while the plate-like workpieces are squeezed by the above-indicated pair of roller electrodes. In this arrangement in which the welding speed is increased, the contact resistance of the pair of roller electrodes and the two plate-like workpieces is made higher than the specific resistance of the plate-like workpieces, so that the weld nugget formed within the two plate-like workpieces is formed along the interface, with a result of an increase in the nugget ratio, permitting the weld to have a sufficient strength even where the pair of roller electrodes have different surface areas of contact with the two plate-like workpieces having different thickness values.

The above object may also be achieved according to another aspect of the invention, which provides a mash seam welding process of continuously welding a first plate-like workpiece and a second plate-like workpiece which has a smaller thickness than the first plate-like workpiece and which overlaps the first plate-like workpiece, while overlapping portions of the two plate-like workpieces are squeezed a pair of roller electrodes disposed rotatably about respective two parallel axes thereof, the process comprising: a welding step of continuously welding the two plate-like workpieces by applying a welding current between a pair of roller electrodes, to thereby form a weld nugget at an interface of the two plate-like workpieces, while the two plate-like workpieces are squeezed by the pair of roller electrodes; and a preliminary treatment step of reducing the thickness of a welding portion of the first plate-like workpiece, prior to the welding step. In this arrangement, the thickness of the welding portion of the first thick plate-like workpiece is first reduced, so as to reduce the thickness difference with respect to the welding portion of the second thin plate-like workpiece, so that the weld nugget formed at the position intermediate between the pair of roller electrodes extends across the interface of the two plate-like workpieces, permitting the weld to have a sufficient strength.

In the present apparatus wherein the surface area of contact of one of the above-indicated pair of roller electrodes with the first plate-like workpiece is made smaller than that of the other roller electrode with the second plate-like workpiece, the amount of mashing of the first thick plate-like workpiece is made larger than that of the second thin plate-like workpiece when the pair of plate-like workpieces are squeezed and mashed by the pair of roller electrodes. Accordingly, the position of the interface of the two plate-like workpieces is shifted to a position intermediate between the pair of roller electrodes, so that the weld nugget formed at the position intermediate between the pair of roller electrodes extends across the above-indicated interface, permitting a sufficient weld strength.

It is also preferable that the apparatus further comprises a feeding device for feeding the pair of plate-like workpieces at a speed of 20 m / min. or higher while the pair of plate-like workpieces are squeezed by the pair of roller electrodes. In this arrangement, the feeding device for feeding the plate-like workpieces permits a high welding speed, and causes a higher resistance of contact of the pair of roller electrodes with the two plate-like workpieces than the specific resistance of the plate-like workpieces, whereby the nugget ratio of the weld nugget formed along the interface of the two plate-like workpieces is increased, advantageously permitting a sufficient weld strength.

The above object may also be achieved according to a further aspect of the invention, which provides a mash seam welding apparatus for continuously welding a first plate-like workpiece and a second plate-like workpiece which has a smaller thickness than the first plate-like workpiece and which overlaps the first plate-like workpiece, while the overlapping portions of the two plate-like workpieces are squeezed by a pair of roller electrodes disposed rotatably about respective two parallel axes thereof, characterized by comprising: a work feeding device for feeding the two plate-like workpieces in one direction; a welding portion for continuously welding the two plate-like workpieces by applying a welding current between a pair of roller electrodes, to thereby form a weld nugget at an interface of the two plate-like workpieces, while the two plate-like workpieces are fed by the work feeding device and squeezed by the pair of roller electrodes; and a preliminary treatment device disposed upstream of the welding portion, for reducing the thickness of a welding portion of the first plate-like workpiece. In this arrangement wherein the thickness of the welding portion of the first thick plate-like workpiece is reduced prior to the welding by the pair of roller electrodes, the thickness difference of the welding portion of the first thick plate-like workpiece with respect to that of the second thin plate-like workpiece is reduced, so that the weld nugget formed intermediate between the pair of roller electrodes extends across the interface of the two plate-like workpieces, advantageously permitting a sufficient weld strength.

Problems solved by technology

Accordingly, it is difficult to form the weld nugget N in alignment with the interface G of the two plate-like workpieces 12.sub.H, 12.sub.M, and is therefore difficult to obtain the desired weld strength in some cases.

While it is of course possible to increase the nugget ratio R.sub.N indicated above by increasing the amount of the welding current to thereby form a large weld nugget N, an increase in the nugget ratio R.sub.N leads to easy occurrence of cracking on the surfaces of the plate-like workpieces due to enlargement of the weld nugget N which undergoes rapid volumetric expansion.

This cracking may develop into rupture in a subsequent press-forming process, for example.

In view of this, the application of the mash seam welding is conventionally limited to the workpieces whose thickness ratio is not larger than a predetermined upper limit, for example, about 1.5, and the mash seam welding is not conventionally practiced where the thickness ratio of the workpieces exceeds the upper limit.

Therefore, this process has a drawback that the operation efficiency is inevitably lowered.

Further, where the two plate-like workpieces are positioned relative to each other by using guide rollers while the workpieces are fed toward the roller electrodes, there is a drawback that the above seam welding process using the shim cannot be practiced.

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