February 28, 2002
Advances in the use of aluminum for cars and trucks could pave the way for greater use of the metal in the future.
Exciting ideas, new applications, and experimental joining processes for welding automotive aluminum drove conversations and presentations at the 22nd annual Automotive Aluminum Design and Fabrication Seminar in October.
Sponsored by The Aluminum Association's Automotive & Light Truck Group (www.autoaluminum.org), the seminar took place in Livonia, Mich., just outside Detroit, and included speakers from the Ford Motor Co., the European Aluminum Association (www.eaa.net), the U.S. Army, and other organizations interested in how aluminum plays a role in automotive industry sectors.
Key to the possibilities of using aluminum in the automotive industry is how it can be manufactured.
Jo Ann Clarke, formerly applications engineer for Alcan Automotive Products, now with Raptor Technology, spoke about the different types of welding processes suitable for automotive aluminum, the newest of which combine traditional arc welding processes with lasers.
While arc welding and laser welding processes are not new, their combination is.
At first, laser-welding aluminum was a challenge because aluminum has high reflectivity.
"It's like shining a flashlight on a mirror—it's hard to absorb the energy," Clarke said.
Now, however, another concern is gap bridging. Lasers have a tiny beam with high density, causing the area of heat density to be small. This makes welding gaps difficult. For this reason, some automakers are experimenting with hybrid welding processes.
Two arc welding processes are being used with lasers. Gas metal arc welding (GMAW), for instance, uses a shielded electric arc to heat the base metal and adds filler metal for gap bridging. Plasma arc welding (PAW) can be controlled more than gas tungsten arc welding (GTAW), and also provides good gap bridging ability.
On their own, these arc welding processes are slow, but can bridge gaps.
Specific advantages to combining laser and GMAW include higher welding speed, lower heat input and less distortion, moderate weld width and heat-affected zone (HAZ), and better gap bridging than laser welding. However, it can be an expensive investment and has limited accessibility. It can be suitable for welding extrusions, castings, and thicker-gauge sheet.
In addition to arc welding processes, direct diode lasers—which have lower energy density and are not as fast as other lasers—also can be coupled with a Nd:YAG or CO2laser for speed. Experiments are being conducted with this type of hybrid process, which is a more expensive alternative to combining arc and laser welding.
The bottom line is the ability to bridge gaps, Clarke said.
"You need gap bridging, which adds production robustness, and that's what these guys are all about," she said. "The key thing is robustness way beyond what a laser can do on its own."
Coupling processes can be difficult, however.
"You have to think about your shielding gas, and you have a somewhat delicate laser process and MIG splattering metal everywhere. I would say integration is the biggest challenge," Clarke said.
Although not a speaker at the Automotive Aluminum Design and Fabrication Seminar, Fronius is a German developer and manufacturer of welding products and technology that has been researching the laser-GMAW process for the past three years. The company set up a mobile laser-GMAW test rig at the Essen Welding Fair last September in Essen, Germany.
Other speakers at the conference spoke about a range of topics, including using aluminum for postal and Army vehicles, and manufacturing applications.
Automotive Applications of Aluminum. According to Andrew Sherman, senior staff technical specialist with the research laboratory at Ford Motor Co., estimated that an average of 250 lbs. of aluminum is used in each vehicle produced today. Most aluminum components in vehicles are radiators and heat exchangers, and as trends go, Americans tend to go for larger vehicles, which use more aluminum.
Aluminum closure panels and body structures can be designed to meet all vehicle requirements, but cost in materials and manufacturing are higher than for steel. Lead times, risk, and investment also are higher when automakers consider using aluminum.
More than half of the increase in cost to make aluminum vehicles is in the material. When considering material, these considerations are important:
Yield, or how much is used versus how much ends up as scrap
Recognizing the value of scrap through sorting technologies, plant practices in handling scrap
Aluminum in the European Auto Industry. Karl-Heinz von Zegen, automotive market manager for the European Aluminum Association, noted several trends in aluminum use, including an increase in fabricated aluminum wheels for lower energy use and higher comfort, aluminum door concepts, and several fabricating processes, including:
Aluminum and the V-Rod. Michael Caughell, director of automotive sales and marketing for American Trim, took a different approach to why aluminum is valuable to the automotive industry. Harley Davidson V-rods are being made with aluminum for some of the same reasons other automotive fabricators choose it—lighter weight, recyclability, and corrosion-resistance. However, styling and appearance also are important considerations.
"Willie G. Davidson had a vision for a high-precision cruiser, a whole new type of project. It has the lightweight, stainless steel look by using the 6022 T-4 alloy for its stability for heat treating, strength, geometry, finish, and good paint bake response," Caughell said. "Aluminum has the ability to differentiate from the styles of different metals."
He noted that steel parts are painted, which can hide some of the blemishes. With anodized aluminum, however, it's harder to hide blemishes.
Aluminum and Postal Vehicles. Long-life vehicles are necessary to meet transportation needs for postal services, said Tom Dolan, engineering manager at Grumman Olson. For this reason, aluminum can be an advantage because it provides light weight and corrosion resistance.
U.S. postal vehicles are expected to last 24 years in all weather, all climates, all terrain. They also have to be easily repaired, Dolan said. Doors, door hinges, and locks have more wear and tear than those of other vehicles because they have to stop an average of 300 times a day. Each time, the vehicle has to be shut off and locked, and the sliding door opened and closed.
Postal vehicles also have their own set of manufacturing challenges. Appearance is important, for instance. Paint preparation and adhesion are the top priorities because, for example, UPS expects paint to adhere to a vehicle for 30 years.
Welding is all manual, mostly GMAW at his company. Gas tungsten arc welding (GTAW) is avoided because it's costly and requires expertise.Other manufacturing considerations include:
Minimum buys required for materials and lead times assigned
Special alloys used
Forming and stamping spring-back
U.S. Army. The U.S. Army's 21st-century initiative includes using vehicles that are more lightweight, more fuel-efficient, and more mobile, according to Paul Skalny, associate director of technology advancement for the National Automotive Center for the U.S. Army. It is the Army's goal to reduce the numbers of special-purpose equipment and mechanics, and decrease deployment closure times.