Suppliers might be bullish on the prospects
for hydroformed tubes in car and truck bodies, but many
consumers are more cautious. Hydroformed tubes can help reduce
weight and boost safety, they acknowledge, but in most cases
they take longer to make and are more expensive than
traditional stamped parts.
In general, there aren't many hydroformed
tubular structures in Chrysler LLC vehicles, said David Reed,
the Auburn Hills, Mich.-based automaker's body-in-white core
lead. Part of the problem is that hydroformed tooling is
expensive-roughly double the cost of stamped construction.
"Your business case has to be really solid as far as piece-cost
savings to pay for the tooling," he said.
Tubes also are limited by the vehicle
manufacturing process, which typically involves resistance spot
welding, Reed said. That involves two electrodes coming
together and sending an electric current through two metal
panels in order to join them. However, because a tube is hollow
the current won't move between the two sides. Instead,
single-sided welding or laser welding is required-and those
technologies aren't as easy to integrate into the traditional
vehicle manufacturing processes.
Nonetheless, tubes are lighter, safer and
less expensive for some applications, he said, noting that the
Dodge Dakota and Dodge Ram pickups, as well as the Jeep
Wrangler, use hydroformed steel tubes for "body-on-frame"
applications such as the engine box. In addition, the Chrysler
Sebring sedan and the convertible version of the Dodge Avenger
use tubular structures to protect against side impact.
While no major increases in tubular content
are planned, the calculus could change as automakers drive for
safer, more fuel-efficient vehicles.
Ford Motor Co., Dearborn, Mich., for example,
has hydroformed tubes lined up for use in the D-pillar box
structure of a handful of its vehicles this year. The Ford
Super Duty pickup truck, the Expedition SUV and the F-150
pickup will each carry about 65 pounds in their front ends. The
F-150 also will use the tubes in the body side, weighing
between 24.2 pounds and 37.2 pounds per vehicle, while the
Sport Trac SUV will have 29.1 pounds in the box assembly.
Hydroformed tubes have gone through a lot of
growth and are more common now than they were a decade ago,
John K. Catterall, General Motors Corp.'s representative to the
American Iron and Steel Institute's Auto/Steel Partnership,
said. But the growth has likely leveled off. "All the places it
can be applied have been studied," he said.
GM uses hydroformed tubes in frames and
cradles and to a lesser extent in body structures. In cars,
cradles are bolted onto the body and carry the engine and
front- and rear-end suspensions. In contrast to "unibody" cars,
most trucks and sport utility vehicles employ a "body-on-frame"
design. Frames form the backbone of such vehicles, provide
strength and stiffness and carry most of the load. The body, or
exterior, simply sits on top of the frame.
Most body panels are stamped, and it's
tougher to integrate them with tubes because of welding issues,
Catterall said. Manufacturers use single-sided, or metal inert
gas, welding to make chassis, frames and cradles. That makes it
easier to integrate tubular components, which generally require
the same kind of welding. Spot welding is more commonly used to
join the stampings in body structures.
But the competition between stampings and
tubing continues, especially in the wake of new fuel-efficiency
standards in the United States, Catterall said. "There has been
a little bit of backwards and forwards on which one is best,
which pretty much tells you that you can make either one better
depending on how you go about it. There is no reason for it to
be a huge battle. It's whatever one works best at the
Tubes do in some cases allow for weight
savings because they eliminate the extra mass of flanges
inherent in stampings. They also allow for parts consolidation
and fewer welds in some instances, he said. "Is it going to be
a game changer? I wouldn't say so. But it's another tool in our
But steel stampings have one big advantage
they are more versatile. "You can shape them into pretty much
anything you want. There is a reason they've stuck around for
so long," he said.