A New Method of Manufacturing Hollow Sections for Hydroformed Body Components 2000-01-2671
For auto-body structures, thin walled steel sheet sections are recommended as a replacement for mainly spot-welded box-shape components. Run-of-the-mill tube products receive their properties during traditional tube making processes, such as roll-forming, and widely used HF-welding. However, a new process has emerged using laser-beam energy as the welding source thus resulting in a very narrow weld seam. For this tube making method typical automotive steel sheet grades which includes all coated steel products can also be applied.
Some years ago, ThyssenKrupp Stahl AG started to produce a variety of prototypes for thin walled sections made from various steel grades in particular zinc coated, longitudinal laser beam welded up to 4000 mm in length. In the meantime we have developed a new section forming process, the “Thyssen Tube Curling Process”, which allows us to supply a broader spectrum of tubular blanks. Thyssen Tailored Tubes, variable cross and longitudinal sections, round-oval, conical or conical-oval shaped section are all possible (1).
A blank is pushed into a annular gap between outer die and inner core halves. After closing the V-butt joint by a postforming roller, the seam is welded at the same time.
The method has been directly designed for making various hollow sections in one production unit, while integrating tube forming and laser-beam welding. This forming method is suitable for cost and working space minimized production and in particular for mid-size series quantities.
This paper describes the method used for the tube making process by means of laser-beam welding and will concentrate on wall thicknesses below 2.5 mm.