The trend toward more gas-efficient cars has led automakers to consider using lighter materials such as aluminum for exterior paneling. By 2000, several car manufacturers plan to introduce models incorporating more of this metal. Meanwhile, aluminum already has found use with heavy-truck manufacturers such as Freightliner Corp., which uses it for the exterior shells of its Argosy line of cabs. A new $1.6 million laser welding system installed in the company's Gastonia, N.C., operations may serve as the prototype for tomorrow's auto manufacturing methods.Freightliner Corp.'s truck manufacturing plant in Gastonia, N.C., is using three 4-kW Nd:YAG laser systems to weld aluminum decks. The system could be a prototype manufacturing method for tomorrow's aluminum automobiles. Courtesy of Freightliner Corp.Faster than rivetsThe laser system has not entirely displaced Freightliner's use of rivets to join aluminum parts. "If you see old trucks, you see rivets. That's still the main technology for truck manufacturers, but the laser technology is a big improvement," said Andreas Bachhofer, process development engineer for Daimler-Benz, which is Freightliner's parent company. He explained that the laser can weld decks at a rate equaling the collective speed of three or four riveting systems and that the reduction of rivets used also has reduced costs for the company. Bachhofer and Daimler-Benz joined other automakers in 1994 in a collaborative research project aimed at developing a system for laser-welding aluminum. After experimenting with both CO2 and Nd:YAG lasers, the researchers selected for the current system a 4-kW, tunable Nd:YAG laser (1.64 µm) from Trumpf GmbH in Ditzingen, Germany. "The YAG wavelengths provided better processing stability over a CO2 laser operating at 10.6 µm that was tested," said Bachhofer. "CO2 lasers, often used for steel welding, created a lower viscosity in the mold material when welding aluminum. This resulted in the material being blown out of the weld." Bachhofer also said that the Nd:YAG laser provided a larger ratio between the depth and width of the weld, compared with CO2 systems. "The weld is much deeper than it is wide." Based on the success of the project, Freightliner is considering plans to install a similar system in one of its other plants. Three lasers have been installed thus far at the Gastonia plant.