Advanced welding line supplies tailored blanks with non-linear laser welds for automotive construction

Developed by Thyssen Krupp Stahl AG (TKS), Thyssen Engineered Blanks® - laser-welded tailored blanks with non-linear seams - are now firmly established on the market. Based on current orders alone, TKS subsidiary Thyssen Fügetechnik GmbH will produce some 1,100,000 Thyssen Engineered Blanks® (around 17,500 metric tons) for the automotive industry in 2002. Automakers use TEB®s from Thyssen Fügetechnik to make components such as floor panels, door inner panels and wheel arches.

Tailored blanks with linear laser welds were invented back in 1983 by TKS engineers and are now used in virtually all makes of car. Vehicle designers particularly appreciate the load-oriented design of the blanks, which comprise steel sheets of different thickness, quality and finish. Higher-strength grades can be used exactly where they are needed, allowing the rest of the part to be made from weight-saving thinner sheet.

The new engineered blanks provide even greater flexibility and weight-reduction potential. Whereas tailored blanks feature only straight-line welds, the seams on TEB®s can be virtually made to measure, allowing functional parts to be tailored even more accurately to the load and force conditions in the vehicle. For example, the housing for a suspension strut can be made from a blank incorporating a thick circular welded-in reinforcement. In the finished component this reinforcement is in exactly the position where the strut is inserted and where the highest loads occur during use.

Thyssen Fügetechnik has the technology required for the fully automatic volume production of these engineered blanks at its Duisburg-Hüttenheim facility. TEB®s are manufactured there on a state-of-the-art laser welding line which also features a second welding head to produce three-piece blanks with two weld seams. This is the world`s first twin-head welding line for non-linear tailored blanks, developed in a collaborative effort by Thyssen Fügetechnik, Thyssen Krupp Stahl AG and Nothelfer GmbH, a company from ThyssenKrupp`s Technologies segment. As the processes and technologies required for the continuous high-volume production of TEB®s are more complex than for conventional tailored blanks, in many respects the three companies were breaking new ground.

At the heart of the welding line are two solid-state lasers with a capacity of up to four kilowatts. The two laser heads are attached to a gantry; the pallets with the assembled TEB®s pass beneath this gantry. The independent laser heads move laterally to follow the course of the joints on the TEB®s. To ensure the accuracy and strength of the welds, the laser beams are not permitted to stray more than 0.05 millimeters from the joints. Only a few basic points of the seam geometry are programmed into the welding head control system; the real precision is provided by an optical seam tracking sensor on each welding head which guides the laser beam along the seam. The sensors are capable of recognizing virtually any joint variant and can swivel to follow even the tightest radius. A second sensor system behind the welding heads measures the geometry of the weld and documents its quality for the customer. The sensor data for each TEB® are recorded. Sensor-based guiding for the welding heads is a development made specifically for Thyssen Fügetechnik`s TEB® line and used successfully for the first time for non-linear TEB®s in the Duisburg-Hüttenheim facility.

The development team from Thyssen Krupp Stahl, Nothelfer and Thyssen Fügetechnik also introduced a new method of fixing the blank components on the transfer pallets. To avoid interference in the welding zone, the precision-stamped, form-fitting blank components are clamped not mechanically but magnetically. The magnets are switchable and are cooled to prevent them from heating up or losing their magnetic properties during welding. The pallets are conveyed through the line by two CNC axis drives. While one axis moves a pallet through the gantry twin-head at welding speed, the other shuttles back to the starting point to pick up the next pallet. This set-up allows impressive cycle times, with only seconds separating the welding processes.

And even greater efficiency is planned for a new facility in Wolfsburg: Thyssen Fügetechnik Nord GmbH - Thyssen Fügetechnik`s fourth German operation - was inaugurated in September 2000 close to the main Volkswagen plant there. Work is currently under way on an improved TEB® line, scheduled to go into operation in summer this year, featuring a gantry which can be moved in two planes.

For further reference: ThyssenKrupp AG, Trade Press, Bernd Overmaat
Tel: +49-211-824-36012, Fax: +49-211-824-36035
e-mail: overmaat@tk.thyssenkrupp.com