Method for producing from a metal sheet a hollow profile which is longitudinally slotted and provided with several longitudinal segments having different cross sections

Method for producing from a flat metal sheet a hollow profile, which is longitudinally slotted, in particular as a pre-product of a longitudinal seam welded hollow profile, which consists of several longitudinal segments having different cross sections, at least one longitudinal segment of which becomes larger or smaller along its length, comprising the following features:

• One starts with one piece of cut metal sheet, which at each transition segment from a small cross section to a larger cross section of the later hollow profile has either concave and/or convex longitudinal profile edges in order to provide material to compensate for material shortage and/or material excess in each transition segment during later forming.
• The cut metal sheet is formed as a U-shape in its central segment extending in the longitudinal direction, while material is transferred to compensate for material shortage and/or material excess in each transition segment.
• The U-shaped formed metal sheet with its closed segment is inserted into a first half of the die corresponding to the hollow profile
• The sides of the U-shaped formed metal sheet are brought together with a second half using a guide blade for the longitudinal edges, material being transferred in each transition segment to compensate for material shortage and/or material excess.
• Release of the hollow profile from the die.