As Ford spends big, GM joins aluminum with simple welds

DETROIT -- General Motors is adding more lightweight aluminum to its vehicles. But unlike Ford Motor Co., GM is not spending hundreds of millions of dollars to retool its assembly plants for the metal.

Instead of joining aluminum parts with rivets and industrial adhesive -- as Ford does to assemble the redesigned 2015 F-150 -- GM is rolling out a new welding system.

GM's system spot welds aluminum sheet, such as doors, hoods and tailgates, on existing production lines with the same robots and welding guns used for steel.

Ford, on the other hand, spent $359 million and lost 10 weeks of production this fall when it converted its Dearborn, Mich., F-150 plant from steel to aluminum for the 2015 model. Early next year, Ford plans to make the same expensive switch at its Kansas City, Mo., truck plant.

Richard Schultz, managing director of Ducker Worldwide, a consulting firm in suburban Detroit, says GM's aluminum welding system is a breakthrough in manufacturing technology.

"It is a great leap. And I think that is very important. I don't know of anyone else who has that," he said. "GM will not have to spend $359 million to retool a plant if they decide to do an aluminum Silverado."

GM has not committed to producing an aluminum-bodied vehicle. But reducing weight with more aluminum is a high priority, said Mark Reuss, GM's global product chief.

"We can no longer bring out new vehicles that weigh the same or more as the competition. We have to be the best in the world at how we do vehicle design," said Reuss.

The new alumi-num spot welding system, which GM internally calls multiring domed electrode, is used at GM's Grand River plant in Lansing, Mich., to weld the aluminum doors on the 2015 Cadillac CTS.

It also is used in Arlington, Texas, on the aluminum liftgates of the Chevrolet Tahoe and Suburban, GMC Yukon and Yukon XL, and Cadillac Escalade and Escalade ESV. GM also uses the system in Bowling Green, Ky., to weld the aluminum underbody of the Chevrolet Corvette.

GM can quickly and inexpensively roll out the welding system to its assembly plants, Reuss said.

Only minor changes are required to production equipment. Liquid cooling lines must be installed to keep special copper welding tips at the proper temperature.

A machine that resurfaces the copper welding tips also is required.

And the production line robots need an additional transformer to handle the higher voltage required to weld aluminum sheets.

"Our view is we want to be able to reuse our existing infrastructure. We don't want to have to retool," said Blair Carlson, GM's manufacturing systems research lab group manager.

During a demonstration this month at GM's Tech Center in Warren, Mich., officials showed a visitor a standard Fanuc production line robot that quickly and quietly zipped through 48 welds on a series of aluminum sheets. Each weld took about a second.

The robot's arm holds pincers with copper caps. The pincers gently squeeze the two aluminum sheets together, making a sound like the soft clicking of castanets.

Electricity is applied, and the weld is complete, usually with little or no smoke and no sparks.

Here's the problem with welding aluminum: Oxide on the surface of the metal makes it difficult to create a strong, durable weld. Among other things, oxide traps hydrogen gases in the melted metal causing porosity, which weakens the weld.

GM's system solves these problems with copper welding caps. Circles scribed on the ends of the caps help ensure strong welds by disrupting the oxide.

GM has been granted nearly 20 patents for its aluminum welding technology. The key components are the copper caps and the circles scribed into them by the resurfacing machine.

Each cap lasts for about 4,000 welds. They are resurfaced after every 50 welds until they wear out. GM spends less than $1 for each cap.

Aluminum helps automakers cut vehicle weight. The redesigned 2015 aluminum-bodied F-150 pickup now on its way to dealers cuts as much as 700 pounds from the steel-bodied 2014 model's curb weight. Ford is promising fuel economy gains for the new pickup as high as 20 percent from the 2014 model, as the company works to meet government fuel economy standards that call for automaker fleet averages to rise to 54.5 mpg by the 2025 model year.

Reuss says GM can meet its fuel economy obligations without switching to a full aluminum body. He says a combination of "mixed materials" can give GM the weight savings it needs.

For example, a welded aluminum Cadillac CTS door weighs 15 pounds, while the same door made of steel weighs 27 pounds.

Carlson spelled out another advantage to GM's welding system: It can weld steel to aluminum parts on the same line by changing only the voltage.

Land Rover, Ford, Audi and several other automakers assemble stamped aluminum body parts into complete bodies with industrial adhesive and rivets. That production method, used on such vehicles as the Range Rover SUV, 2015 Ford F-150 pickup and Audi A8 luxury sedan, produces strong, lightweight bodies.

But the method is more complex than simply welding metal parts together. And it is more expensive.

In September, Ford warned investors and analysts that its profit margin on the 2015 F-150 will shrink because of higher material and manufacturing costs. Bonded and riveted bodies use thousands of steel rivets of varying lengths, widths and styles, all of which have to be perfectly inserted in the proper section of the body.

"We explored many options to build the all-new F-150. We determined our current manufacturing approach is the best way to meet the needs of our customers," said spokesman Mike Levine.

Ford does weld one part of the aluminum truck's components: the cargo box floor and cross-members. They are joined using a combination of resistance spot welding -- in which the two aluminum parts are squeezed together under pressure and welded -- and high strength adhesive.

GM says its spot welding method of attaching stamped aluminum parts is far cheaper than riveting and bonding.

Each weld costs less than one-tenth of a cent, said Michael Karagoulis, a GM manufacturing systems welding engineer who helped develop the copper welding tips that GM uses.

Jay Baron, CEO of the Center for Automotive Research in Ann Arbor, Mich., said: "The technology that GM has allows them to use a more economic joining methodology. There are many places in a vehicle body where you don't need superstrength joints. GM has managed to keep a well-known and well-established technology and apply where it makes sense."

GM's welding system, Carlson said, can be used to produce a complete body out of aluminum, or a combination of steel and aluminum welded together.

He said: "From the product side, the philosophy on lightweighting is: the right material for the right application. Being able to provide flexibility to the body shop enables our product people to enable that lightweight strategy."