Hydroformed tubes are seeing slow but steady
growth in automotive applications, and aluminum is getting in
on some of that action as well.
The increased use of aluminum tubes likely
follows a more general trend toward lightweight structures,
said Robert Perkins, director of supply chain and technology
forecasts at CSM Worldwide, Northville, Mich.
Jay Baron, director of the manufacturing,
engineering and technology group at the Center for Automotive
Research in Ann Arbor, Mich., agrees that there has been slow
but steady growth in hydroformed tubular products, whether
they're steel or aluminum. But manufacturers have been slow to
adopt hydroformed tubes not so much because tubes cost more but
because they take longer to make than stamped parts. The slower
forming process and the integration of the tube into the
overall structure (e.g. joining) drives up their total
"You can stamp out a part in six seconds; to
hydroform a tube takes more like a minute. It's almost a factor
of 10," Baron said. Even in optimized processes, it still takes
30 seconds to hydroform a tube, five times slower than a
As a result, hydroformed tubes are most
common on high-end, low-volume vehicles like the Chevrolet
Corvette. And aluminum tubes are used only in more rarified
luxury vehicles such as the Audi A8 and certain Jaguar models,
which use far more aluminum than most cars.
"All-aluminum cars are not something that
you're going to see anytime soon, except in high-end niche
vehicles," Baron said. "You won't start seeing aluminum in the
body structure until you see major subassemblies or the entire
substructure in aluminum."
The use of aluminum tubes is further
complicated by joining problems associated with welding steel
and aluminum together, he said. As a result, aluminum tubes are
used in aluminum subassemblies and aren't directly integrated
into a vehicle's steel body. BMW AG, for example, made an
entire rear-axle subassembly from aluminum, including
hydroformed aluminum tubes and struts.
In general, aluminum use is confined to parts
such as hoods and doors that can be isolated from steel in the
rest of the vehicle, Baron said.
But hydroformed tubes-both steel and
aluminum-should continue to gain ground, particularly as a
result of higher European safety standards, which are beginning
to be adopted in North America as well. That's because
hydroformed tubes are good not only at reducing vehicle weight
but also at transferring impact forces away from passengers
during a crash.
"Hydroformed tubes are much more prevalent
than they used to be," Baron said. "You would expect the
percentage of tubular products to increase, but not at an
exponential rate." As this point, most of the technology has
been developed and it is simply a matter of optimizing the
production process, he said.
Many analysts don't follow tubular products
in the automotive sector because most of the companies that
make such products are either private or have been bought out
by other companies, Charles Bradford, analyst at Bradford
Research/Soleil Securities Inc., New York, said. "We tend to
focus on things where there is stock you can buy and sell."