Patent ID: 6693254
Filing Date: 2004-02-17
Classification: B23K

Abstract:
Method for laser welding of two or more metal sheets which are overlapped with each other, wherein at least one of the sheets has a protective layer on its surface in contact with another sheet, said layer being made of a material having a vaporization temperature lower than the melting temperature of the metal forming the sheet,wherein the sheets to be welded are clamped with each other during the welding operation with the aid of clamping means which are moveable between an inoperative condition and an operative condition to press the overlapped sheets against each other, and wherein welding is carried out by directing a laser beam at the welding area of the clamped overlapped sheets, wherein: at least one of the sheets is shaped or arranged such that when the clamping means are brought from their inoperative condition to their operative condition, in which the clamping means press the sheets against each other, said at least one of the sheets will undergo an elastic deformation from a rest condition in which a gap is defined between this sheet and the adjacent sheet, to a deformed condition in which this gap is nullified and the sheets are completely in contact with each other at the welding area, and in that before welding is carried out the clamping means are controlled according to the following sequence of stages: in a first stage the clamping means are brought from their inoperative condition to their operative condition so as to ensure the complete contact of the sheets to be welded due to said elastic deformation, in a second stage the clamping means are moved back towards their inoperative condition, through a predetermined limited length, so as to create again a gap having substantially predetermined dimensions between the sheets to be welded by exploiting the elastic return of the sheet which is elastically deformed during the first stage, the clamping means are kept in the condition reached thereby during welding so that the vapours of protective material which are generating during welding can escape through said gap.