16 April 2007

Laser scanner welding used in the doors of the new Audi A4

Conventional welding with solid-state lasers is an established process in automotive car body manufacturing. The development of this process led to robot-controlled laser scanner welding in which the movement of the bending arm robot can be combined with the highly dynamic positioning movements of a laser scanner. Audi has introduced this highly efficient manufacturing technology for the first time in the doors of the successor to the Audi A4.

A significant challenge in this development was the availability of suitable laser sources with appropriate available beam quality. Lamp-pumped rod systems with a beam quality of 25 mm*mrad have already demonstrated their industrial suitability a thousand times in conventional laser welding applications. With values clearly exceeding 99 percent, these beam sources set new availability standards. However, a much higher beam quality is needed for laser scanner welding because the size of the processing space for a scanning optical system and possible the work area are dependent on beam quality. Since the potential of rod geometry has been exhausted as far as beam quality is concerned, only novel laser concepts can meet the requirements of improved beam quality. TRUMPF developed the disk laser for industrial use, and it has been successfully used worldwide for some time. Boasting a standard beam quality of 8 mm*mrad for the high power series, with a maximum power range of 8 kW, the disk laser is used in all laser applications, from cutting and conventional welding to laser scanner welding.

Another TRUMPF development is a scanner welding head for industrial use specifically for this power range. It has so far been the only robot-guided solution to pass the tough qualification tests of the German automotive industry, and it's already being used in series production. Recently, DaimlerChrysler began using this process in the manufacturing of its new car bodies. Since January 2007, Audi has been welding with the new laser technology, thereby putting to good use the experience it gained with previous laser welding applications.

The advantages over conventional processes are mostly in clearly improved productivity. The time that had been spent positioning the robot has been greatly reduced by the fast mirror movements of the scanner head, thus drastically reducing processing time. Compared to resistance spot welding in which an average of about 0.5 welds per second can be achieved, laser scanner welding typically can complete three to four welds per second. This results in a much better utilization of the laser beam source, which in turn results in significantly higher economic efficiency. In addition, the high efficiency of the disk laser ensures the low operating costs of the laser source. A wall plug efficiency of about 25 percent lowers energy costs compared to lamp-pumped systems and demands much less from the user's supply infrastructure (such as floor space and cooling requirements).

The development engineers at Audi and VW researched the advantages of the laser scanner process. Special challenges included fixturing and the preparation of parts, but Audi solved these tasks, and today the quality of the manufactured parts are excellent. The Audi experts developed a laser-aided pre-treatment for the individual parts that guarantees high welding quality in spite of existing zinc coating. The tools they used were the pulsed Nd:YAG-lasers made by TRUMPF.

Starting in 2005, following a pilot program in the current production of the Passat, the laser scanner welding process and its system components have been used in series production by the VW Group. A very high availability of the system components has been reached, and the process has shown improved profitability. Now Audi has started to implement the process consistently in its series production. Since early 2007, the doors of the Audi A4 successor have been welded with a scanner system and the 4 kW disk laser made by TRUMPF. Four manufacturing cells produce 1,800 doors per day using this technology. Every scanner system is supplied by TRUMPF's TruDisk 4002 from the latest disk laser generation. The tool's 4 kW output is generated by only two disks. Audi relies on the advantages of The Laser Network (TLN) that allows lasers to be interconnected with one another as needed, thus ensuring ease of back-up and maximum of laser utilization.

Contact: Gerry Jones

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