The invention relates to a process for cutting and/or welding preferably geometrically differently shaped metal sheets (10a, 10b), preferably sheet-metal panels, of the same or different gauges and straight and/or irregular weld seams, especially for motor vehicle coachwork, with jet tools, in which: a) the metal sheet(s) to be cut and/or at least two sheets to be butt-welded together are fitted and secured on a support (3) in the position to be cut and/or welded together; b) the sheets secured on the support are taken at irregular distances and/or discontinuously in front of the cutting or welding device (15) (machining device), on which c) for cutting and/or welding processes the machining device is moved at least transversely to the direction of transport of the sheets in accordance with the course of the irregular cutting line or weld seam, and in which d) the sheets (10a, 10b) secured to the support (3) are continuously and/or with an optimum spacing moved along beneath the machining device (15) at a speed depending on the cutting or welding rate and/or the course of the cutting line or weld seam, and an appropriately designed processing installation for implementing said process.