Abstract: A process for controlling the weldability of a sheet (1) of the composite metal sheet type having a layer (7) which is interposed between two metal facing sheets (3,5) and comprises a polymer (8) having a filler of conductive particles (9). This process comprises measuring by means of a signal of given frequency f applied to two electrodes (11,13) disposed in facing relation to each other, each electrode being in contact with a corresponding metal facing sheet (3,5), the voltage/current phaseshift .phi. due to the resistive and capacitive properties of the composite sheet (1). The response of the composite sheet (1) to this signal corresponds to that of an equivalent parallel RC circuit. Thereafter, the mass fraction of the conductive particles (9) is calculated from the value of .phi.. By comparing the determined mass fraction with prefixed thresholds, the weldability and the vibration-damping capacity of the composite sheet (1) are evaluated.

Abstract: The subject of the present invention is a method for butt welding metal sheets (1, 2) by means of a laser beam, characterized in that a lateral pressure F directed towards the joint plane (3) of the metal sheets (1, 2) is exerted on the metal sheets (1, 2) to be welded in order that the contact pressure between the said metal sheets, at any point in the region of the joint plane (3), lies between 0.05 times the elastic limit of the metal sheet (1 or 2) having the lower elastic limit and the buckling pressure of the metal sheet (1 or 2) having the minimal buckling pressure and a welded seam is produced in the region of the joint plane (3) by local melting of the said metal sheets (1, 2) by means of the laser beam.The subject of the invention is also a welding device for implementing this method.

Abstract: The subject of the invention is a method for butt welding at least two metal sheets of different thicknesses, by means of a laser beam. The method consists in bringing the metal sheets into contact at their lateral faces to be butt jointed, in directing the laser beam towards the thicker metal sheet so that the vertical axis X--X passing through the focal point P of the laser beam on the said metal sheet is at a defined distance from the joint plane of the metal sheets and in making a welded joint at the butt jointed lateral faces by local melting of the said metal sheets by means of a laser beam.