Abstract: Disposed on a central machine portion (10) are two clamping devices (32,34), each for a respective body blank (P.sub.l,P.sub.r), and a welding device (20) for welding together overlapping margins of the blanks (P.sub.l,P.sub.r). Disposed one at each side of the central machine portion (10) are feed tables (80,82) on each of which a blank (P.sub.l R.sub.r) can be fed through one of the clamping devices (32,24), transversely to the proposed weld seam, into an overlapping position. A supporting device (50) is disposed between the two clamping devices (32,34) to support the margin to be welded of the blank (P.sub.l) fed in on one of the two feed tables (80). This supporting device can be moved out of a supporting position in which it supports the margin to be welded of the blank (P.sub.l) in question, into a position of rest in which it allows this margin to come to lie on the margin of the other blank (P.sub.r).