Patent ID: 7385157

Claim:
A method of welding overlapping regions of sheets, each having a base metal covered with a layer of a metal whose melting point is lower than the melting point of the base metal, to each other by applying laser beams to the overlapping regions, comprising the steps of: positioning a holding mechanism having a continuously moving contact portion directly above a portion of the overlapping regions of the sheets so as to make contact with a top one of the sheets, the position of the continuously moving contact portion of the holding mechanism being offset to one side of a welding region of the sheets, and being disposed at all times near a first laser beam and ahead of a second laser beam with respect to a moving direction of the holding mechanism; positioning and holding the welding region of the sheets with the holding mechanism, and applying the first laser beam to the sheets near the contact portion of the holding mechanism to heat the sheets for thereby spacing the sheets apart from each other by a first predetermined distance (H); applying the second laser beam to the region of the sheets where the sheets are spaced apart from each other by the first predetermined distance (H), thereby to weld the sheets to each other, the region where the second laser beam is applied being spaced apart from said first laser beam by a second predetermined distance (S 2 ) in a direction orthogonal to the moving direction of the holding mechanism, and setting an amount of heat applied by said first laser beam, a moving speed of said first laser beam, and a focused spot diameter of said first laser beam to keep the sheet irradiated with said first laser beam in an unmelted state, wherein the contact portion of the holding mechanism and the first and second laser beams move continuously and simultaneously in the moving direction across a surface of at least one of the sheets, with the second laser beam following behind the contact portion.