Method and a device for the welding of two parts to be joined made of thermoplastic synthetic materials along a weld seam by means of laser

A method for welding two parts to be joined made of thermoplastic synthetic materials along a weld seam by a laser, wherein a laser beam generated by the laser is controlled in its beam direction within an operating field by a control method with control data corresponding to the weld seam course to be produced,

• the laser beam comprising a beam dimension in the region around its focus causing the welding, which is smaller in a joint plane than a target width of the weld seam to be produced, and is dependent upon at least one of an angle of incidence of the laser beam on the joint plane a and a position of the focus relative to the joint plane, and
• wherein the laser beam is displaced in a first movement component in a principal forward-feed direction along a track of the weld seam to be produced, and in a second, oscillating movement component superimposed over the former in order to cover the weld-seam width transversely to the principal forward-feed direction with an oscillation amplitude width,
• wherein the control method comprises adjusting the oscillation amplitude width in inverse dependence upon the beam dimension in the joint plane in such a manner that the width of the beam field scanned by the laser beam in the transverse direction relative to the principal forward-feed direction corresponds to the target width of the weld seam.