Method for welding sheet metal parts

A method for butt welding of adjacent edges (4, 5) of flat metal blanks (1, 2) in a welding machine, comprising:

• providing two flat metal blanks (1, 2) to be welded together;
• placing the two metal blanks (1, 2) on a conveyor unit (37) and securing them in a respective position with a first edge (4) of one of the metal blanks (1, 2) and an adjacent second edge (5) of the other of the metal blanks (1, 2) having a smallest possible gap therebetween;
• and
• welding the adjacent first and second edges (4, 5) together using a welding laser (6) to form a butt joint, wherein
• a gap width (7) between the first edge (4) and second edge (5) is measured and controlled via measured values from the welding process,
• the gap width (7) is measured via a reflected-light method wherein light rays (13, 14, 15, 16) from one or more light sources (11, 12) are reflected between the first and second edges (4, 5) and at least one reflected light ray (13) is captured by a camera,
• a true gap width (9) equal to the minimum distance between the respective edges (4, 5) is measured simultaneously by a transmitted light method wherein light (17) from a light source (18) is transmitted through the gap from above or below and is captured by a camera (20) from below or above, respectively, and
• the gap width (7) measured via the reflected-light method and the true gap width (9) measured via the transmitted light method are used to estimate a missing area (8) or missing volume in the gap.