LASERS, a Bright Spot for AUTOMOTIVE WELDING

Manufacturing Engineering, Sep 2005 by Koelsch, James R

Technology emigrates from Europe

If you're a Tier One supplier in the auto industry, what do you do when one of your customers in Germany can't fit side-impact beams inside the doors of a new model? If you're Magna Cosma, the forming group of 14,000-employee Magna International Inc. (Aurora, ON), you invest in laser welding.

The manufacturing engineering team at the Cosma plant in Heuigenstadt, Germany specified laser welding because the automaker's designers had trimmed away so much material that other methods simply would not work. Because the pieces had too little mass to absorb much heat, MIG welding caused excessive distortion, and would not fit in the allotted space, according to Franz Divjak, engineering manager at Heuigenstadt. And the flanges were too small for spot welding.

Working with Trumpf GmbH (Stuttgart, Germany), the engineering team designed and installed a welding cell around a YAG (yttrium aluminum garnet) laser. As the operator loads two mating 1.3-mm and 1.0-mm stampings of high-strength steel into a fixture, a vision system verifies that the parts are in the fixture and oriented properly. When the table indexes, it presents the part to the laser-welding unit. After welding, the part goes to a third station, where a robot transfers the welded assembly to a measuring system that checks a number of features. Then it goes into a marking station where an engraving tool scribes a serial number into it for tracking the part and the process parameters used to make it.

Not only does the laser weld the 574-mm seam in about 12 sec, but it also does so without distorting the high-strength-steel assembly outside the specified tolerances. Moreover, only one person is needed to make the parts. "If we had done it with conventional welding, we would have needed two or three cells to do the same number of parts," says Divjak. The reduction in outlays for equipment and labor more than paid for the large capital expenditure required by lasers.

Because of this success, the Heiligenstadt plant now has three laser-welding cells putting together side-impact beams, each for different cars. Moreover, the company's North American operations, like many of its competitors in this market, are looking to import a technology that has been very successful in European automotive factories.

"We're trying to promote laser welding here," says Harish Mistry, engineering manager of joining processes in the Research & Development Group at the US headquarters in Troy, MI. To do so, he is commissioning a new remote laser-welding cell over the summer for R&D, and any prototyping work for programs where lasers might be the welding technique of choice.

For example, the manufacturing engineers at Heiligenstadt had to ensure that the edges being welded together were within 0.2 mm of each other, which is much closer than is customary in MIG and spot welding. "So we launched a two-pronged program of developing strong and accurate fixtures, and installing a restrike station in the die to produce parts to tighter tolerances in the stamping operation that precedes the welding cell," says Divjak.

Because of their ability to weld from only one side of the material, and to produce relatively clean welds without distorting the material, lasers are finding more work welding steel joints on Class A surfaces and other sheetmetal assemblies with surfaces. "More hollow sections made by hydroforming are being incorporated into the body-in-white systems now," notes Peter Busuttil, manager, process development, lasers, Comau Pico (Southfield, MI), a builder of automation for the automakers and their suppliers. Lasers have a big advantage in these applications because the inside surfaces are usually inaccessible to spot-welding guns.

The system Comau built for welding motorcycle gas tanks illustrates the suitability of lasers for Class A surfaces headed for the paint shop. "Laser welding still leaves a little scar, but it gives you the least amount of distortion on the panel," says Busuttil. "So very little subsequent work needs to be done in order to produce a paintable surface." The motorcycle gas tank, for example, needed only a little brushing and polishing.

Another application proving the ability of lasers on bodies in white is brazing of roofs to body sides, which has been one of the body shop's biggest headaches. "With this joint, the laser brazes it, and you're done," says Busuttil. "After a little bit of polishing and inspection, you send it to the paint shop." Although a fine line is still visible, there is no ditch to seal and cover with epoxy or plastic trim, as there is with resistance spot welding and laser welding. Consequently, laser-brazing these joints saves anywhere from $6 to $8 per vehicle.

For this reason, the technique has been catching on quickly, even though it's only about five years old and is still evolving. Having already taken root in Europe, laser welding has begun to migrate to North America. Comau Pico reports that it has its first order on this side of the Atlantic.