Recent refinements to a manufacturing method engineered for attaching varying thicknesses of aluminum together with fewer rivets, fasteners and other components is expected to ultimately deliver much higher amounts of aluminum content throughout the automotive supply chain.
“A technology has been found to actually make ‘tailored blanks’ for aluminum,” says General Motors engineering spokesman Klaus-Peter Martin. “You take a tailored blank and then you put it in your stamping process,” he explains, adding that the new production development “is at the required speed to make it interesting for the industry.”
In a partnership among GM, Alcoa, the TWB Co. and the U.S. Department of Energy’s Pacific Northwest National Laboratory (PNNL), researchers report that they have made significant progress in perfecting a tailored blank-oriented aluminum joining technique known as FSW, or friction stir welding.
Four automakers are actively evaluating the latest improvements in FSW-produced parts and two others are “looking for applications” that can be adapted to their specific needs, says PNNL program manager Yuri Hovanski.
“Every new process of technology that makes our process more cost-efficient, faster and also contributes to our vehicle lightweighting is something we are always interested in,” Martin said.
This ability to join aluminum sheets of varying thicknesses is critical for making lighter-weight auto parts that still retain the necessary strength requirements. It is also less costly and 10 times faster than current FSW manufacturing strategies, presenting production speeds that meet OEM high-volume assembly line demands.
By using fewer steel parts and more aluminum, a car door can be created that is 62 percent lighter and 25 percent cheaper – which also reduces aftermarket shipping and replacement costs along the way.
“We looked at the barriers preventing the use of more lightweight alloys in cars, picked what we felt was a top challenge, and then formulated a team that represented the entire supply chain to tackle it,” says Hovanski. “The result is a proven process that overcomes the speed, scale and quality limitations of FSW that previously were showstoppers for the auto industry.”
Currently “they’re putting in multiple parts and just riveting them together,” Hovanski tells Aftermarket Business World. “There aren’t pieces that wiggle and break in there” when FSW is utilized. “You put the material only where it’s needed.”
An aluminum-centric model such as the Ford F-150 could have fewer steel parts within the doors to lighten the curb weight with no drawbacks in performance or maintenance. “Installing a door aluminum-inner doesn’t change how you would repair the door,” he points out.
“You wouldn’t use the FSW process in the repair facility because it would be one piece with the FSW already in it,” explains TWB product development/sales director Mark Eisenmenger.
“It’s a more integrated stamping – it’s a single component,” he adds. “There are less part numbers involved, which will be a benefit to the repair business.”
Martin notes that vendors and installers will be brought fully up to speed as FSW comes into full production. “Whatever materials are used, our dealers and independent repair shops would be trained and have the abilities,” he says. “There are not materials in the car that can’t be repaired – that is something that no manufacturer could afford.”
Ford reports that 757 dealerships and 750 independent shops are currently trained in structural repairs on the aluminum F-150; additional shops have been conducting cosmetic work on aluminum panels since 1997.
Customized applications
The two-phase, six-year PNNL-led project is funded by the DOE’s Office of Energy Efficiency and Renewable Energy in conjunction with contributions from the participating companies.
To create door frames, hoods and other components, sheets of metal are welded together end-to-end into a “tailor-welded blank” that is subsequently cut into appropriate sizes before being stamped into the final shape.
Allowing a high degree of customization, a thicker gauge of metal, for example, can be used on one side of a car part where extra strength is needed and then joined via FSW to a thinner gauge on the side where sturdiness is less of an issue.
Conventional laser welding is highly effective for joining varying thicknesses of steel, but it can be problematic when applied to aluminum due to the reactivity of molten aluminum to air.
Instead, manufacturers currently create several components from single sheets that are riveted together after being stamped, resulting in additional production steps and more parts that drive up cost and weight.
“Reducing the weight of a vehicle by 10 percent can decrease fuel consumption by 6 percent to 8 percent, so the auto industry is very interested in a welding technique such as FSW that is aluminum-friendly,” Hovanski says.
A friction-stir welding machine looks and acts like a cross between a drill press and a sewing machine. Lowered onto two metal sheets sitting side-by-side, a drill bit-like pin tool spins against both edges. As it travels along the pin creates friction that heats, mixes and joins the alloys without melting them.
By auto industry production standards, however, the process was too slow – just one-half meter welded per minute – which is why the technique has been used only in niche applications, according to Hovanski.
Researchers initially compared several joining methods before selecting FSW, which was the only one to pass all of GM’s rigorous weld quality specifications. They then conducted a comprehensive series of lab-scale welding tests on aluminum sheets provided by Alcoa.
In all, dozens of unique tool designs with varying shapes, lengths and diameters of the pin were created. These were assessed against a variety of weld parameters, such as the depth, rotation speed and angle of the tool. Through statistical analysis, the team identified the optimal combination of tool specification and weld parameters that could consistently withstand high-speed production demands.
“What we discovered was a win-win,” Hovanski says. “The faster the weld, the better the quality and strength of the join, thus the significant increase in speed.”
Combining materials
PNNL provided the weld and tool specifications to both TWB and GM, and TWB welded, formed and analyzed more than 100 aluminum blanks in close coordination with GM, making it the first qualified supplier of aluminum tailor-welded blanks.
GM was then able to stamp an imperfection-free full-sized inner door panel out of aluminum sheets in varying thicknesses.
TWB has installed a dedicated FSW machine at its production facility in Monroe, Mich. that is capable of producing up to 250,000 parts per year. “TWB can now provide aluminum tailor welds not only to GM, but the entire automotive industry,” reports Blair Carlson, a GM manager who co-conceptualized the project.
“We can supply that service to other OEMs,” says TWB’s Eisenmenger. “We have multiple automakers in the development stage; we’re working on future products that will apply this technology.”
With more than two years of funding left, the PNNL-led team continues to collaborate with a focus on even faster weld speeds and the ability to maneuver around the contours and corners of complex aluminum parts for which laser welding is not commercially feasible.
The researchers are also modifying FSW to join different metals, such as automotive-grade aluminum alloys with light, ultra-high strength alloys currently reserved for aerospace applications.
“Going forward, we see this process, and future versions of it, enabling completely novel combinations of materials that will revolutionize material use in the auto industry,” Hovanski says.
By 2025, more than 75 percent of all new pickup trucks produced in North America will be aluminum-bodied, according to a survey of automakers conducted by consulting and research firm Ducker Worldwide and commissioned by the Aluminum Association’s Aluminum Transportation Group (ATG).
It forecasts that the number of vehicles with complete aluminum body structures will reach 18 percent of North American production, up from less than 1 percent today. Vehicle segments identified as emerging aluminum content leaders are pickups, SUVs and both mid-sized and full-size sedans.
For 2015, Tesla, Mercedes, BMW and Ford will all exceed the average aluminum content; more than 500,000 pickups and electric vehicles will roll off the assembly line with all-aluminum bodies.
However, says GM’s Martin, “aluminum is not the silver bullet. The ‘smart mix’ of materials, just to give an example, can range from steel, aluminum, magnesium, composites and carbon fiber.”
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