GM says it’s first to weld steel to aluminum
Warren — General Motors Co. believes it is the first automaker to weld steel to aluminum through resistance spot welding, a technique it spent some two years developing and expects will save weight and be less expensive.
The automaker said Wednesday that within a few months it will deploy welded steel to aluminum joinings on a seatback for the Cadillac CT6 luxury vehicle and shortly thereafter on a CT6 hood reinforcement (a steel pedestrian protection reinforcement will be welded to an aluminum hood inner panel). The CT6 structure includes 11 different materials and uses multiple joining processes. The car is built at GM’s Detroit-Hamtramck Assembly Plant.
The method allows GM to avoid riveting steel to aluminum, reducing the number of parts. GM plans to use the technique, which is cheaper than riveting steel and aluminum, for parts in other vehicles, Blair Carlson, GM’s lab group manager for lightweight material processing, said during a media event at its Warren Tech Center.
Automakers are looking to cut weight in vehicles in part to boost fuel economy and to meet increasing federal fuel economy mandates.
GM “rose to the challenge” and had to overcome issues such as steel and aluminum having different melting points, and oxides on aluminum that cause weld failures, Carlson said. The U.S. Energy Department in 2013 granted GM $1.3 million to develop a new welding technique of aluminum to advanced high-strength steel.
The process has weight-reduction possibilities. If the carmaker were to attach an aluminum roof to a steel body, “you’d have a significant mass savings there, maybe 50 percent,” said Warren Parsons, global chief architect of body structures for GM.
GM says it’s also is the first automaker to spot-weld aluminum to aluminum, a process it started using in 2008 on a vehicle liftgate. That process now is a mainstream solution it uses in nine assembly plants and on many more vehicles. The technology allows GM to avoid riveting aluminum, saves weight and has a cost savings of $5 to $100 per vehicle, depending on the number of rivets used.
The carmaker is exploring more use of magnesium in vehicles, which is lighter than steel and aluminum. It showed a magnesium door inner panel that weighs about 10 pounds vs. the same steel panel weighing about 20 pounds. Anil Sachdev, GM light metals systems lab group manager, said the company plans to put the magnesium door into production, but he wouldn’t elaborate on timing or vehicles.
Magnesium is more expensive than aluminum, so GM is evaluating the benefits on vehicle-by-vehicle basis, Sachdev said.
The company also is looking to put carbon-fiber wheels on a production vehicle, said Will Rodgers, a GM technical fellow. A set of four carbon-fiber wheels would be 35 pounds lighter than aluminum wheels, while also stiffer.
Separately, GM said it would expand its use of stop-start technology to 30 vehicle/powertrain combinations in North America by 2018. That’s up from 12 engine/model configurations this year. The fuel-saving system automatically turns off the engine when the vehicle is stopped and seamlessly turns it back on as a driver lets up on the brake.
GM said stop-start can improve city fuel economy by 14 percent. The technology is standard on vehicles such as the Chevrolet Impala, Malibu and the 2016 Cruze.