| 摘要 |
PURPOSE:To prevent the occurrence of a dent on the metal plate surface and to form a satisfactory joining part on the joining part interface by concentrating an applied electric current on the inside of an annular projection and applying the current in a specific short time. CONSTITUTION:The annular projection 15 provided at a joining place of a first metal plate 1a to be joined to a second metal plate 1b is formed so that its cross section in the diametrical direction is formed of a projecting curved surface and closed curved lines to form the outside periphery and inside periphery of a rising part of the projecting curved surface do not have an inflection point. Further, a shape of the projecting curved surface is formed so that the apex 18 of the projecting curved surface is located at the inside from the central position between the closed curved lines 16 and 17 of the outside periphery and inside periphery and its height (h) is maintained constant extending over the entire periphery. The first metal plate 1a is brought into contact with the second metal plate 1b and pressed against each other via said annular projection 15 and the current with the pulse-height time <=3 mm/sec is applied to the annular projection 15 and the first metal plate 1a can be joined to the second metal plate 2b.
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