GM's learning curve on lightweighting

General Motors is just weeks away from beginning production validation of a new process for joining aluminum and steel parts that will help cut vehicle weight while simplifying manufacturing and lowering tooling costs in its factories, executives say.

The automaker developed the process in-house and says it solves the problem of joining the two disparate metals through spot welding, a hurdle due in large part to the widely different melting points of aluminum and steel.

GM announced earlier it would begin using the process this year in production of the Cadillac CT6 sedan, and officials at a backgrounder here on the company’s extensive efforts to take weight out of its cars and trucks say they are finally close to startup at the Hamtramck, MI, assembly plant, where the technology will be employed first for seatback construction, followed closely by hoods.

The aluminum-to-steel spot-welding system makes use of a uniquely designed welding tip patented by GM. However, the tip fits with conventional tooling, so there is no need for specialized welding equipment. GM is expected to make the process available to other automakers interested in licensing the technology.

The process is the next step in the manufacturing evolution that saw aluminum-to-aluminum welding capability, introduced around 2008, reach widespread application in today’s factories. GM is hoping it can exceed the pace of that 8-year ramp-up when it comes to proliferating the aluminum-to-steel welding technology.

The automaker says the welding process allows it to eliminate rivets used to join aluminum and steel body parts, cutting costs and mass. With aluminum-to-aluminum welding, cost savings in rivets alone are estimated at $5-$100 per vehicle, depending on the number used, with weight savings of 0.7-11 lbs. (0.3-5 kg) per vehicle. Manufacturing costs also are lower, the automaker says.

In the initial aluminum-to-steel program for seatbacks, GM will move cautiously, replacing a couple of the rivets currently used with the advanced spot welds to test the manufacturing process and prove part durability before moving on to more extensive applications.