2013 Ford Fusion B-pillar and A-pillar roof rail (shown in blue) laid bare on a display buck. The orange stampings are DP780 coated advanced high-strength steel formed using a transfer die process. The green component behind the vertical tubes are in HSLA, CR300/340LA. (Lindsay Brooke)
Ford’s 2013 Fusion uses hydroformed steel tubes for its B-pillars, an application that Ford body engineers claim is a production world’s first for hydroformed components. The car also features a hydroformed A-pillar roof rail.
Using hydroforming instead of hot-stamped welded sheet to create the car’s roof-pillar structure reduced mass, saved cost, reduced the bill of material, and helped improve the new Fusion’s crash performance, said Shawn Morgans, Ford’s Technical Leader and Global Core Manager, Body Structure, Closures, and Body CAE.
“The benefits we’re getting from using a closed continuous section, including giving us better structural continuity throughout the pillars, are driving big improvements to our body structures,” Morgans told AEI. He said in developing the Fusion pillars, his team uncovered no other similar production applications featuring hydroformed tubes.
Ford is driving increased use of hydroformed components across its global body structures going forward, Morgans said. The new C/D-segment Fusion sedan is built on Ford’s new CD4 architecture developed by Ford Europe. It replaces the seven-year-old Mazda G-derived CD3 platform used on the previous-generation Fusion. The CD4, which also underpins Lincoln’s new MKZ, is a predominantly steel structure featuring a high level of high- and ultrahigh-strength alloy content. It is claimed to be stiffer in torsion and bending and more mass-efficient than the former platform.
Proven on F-Series programs
Morgans said the genesis of the Fusion pillar designs came in 2003, during development of a new front end for the F-250 pickup.
“In that first go-around we took our front structure from 18 stampings down to 9 components, including the hydroforms,” he recalled. “We also had a big reduction in spot welds, and we found that we could reduce the mass significantly—the first design was about 42 kg and by the third generation, which ended up on the F-150, we were down to about 26 kg.
“Based on that work, we realized there are huge benefits in using hydroform, so we started to push the envelope,” he said. A hydroformed A-pillar roof rail for the P415 program (2009 F-150) followed, again bringing significant mass savings with lower variable cost.
At the time, Ford had separate Truck and Car engineering groups. Since the groups were combined under one vehicle-engineering organization, the hydroforming “book of knowledge” has been shared across the body-on-frame and unibody teams. Morgans’ boss, Chief Engineer Bruno Bartholemew, has been pushing the teams to advance the technology.
“Bruno’s a very thorough engineer who understands that closed sections and continuous structures are much better than what we were getting by welding a bunch of sheet-metal stampings together,” Morgans explained. The next major hydroform application—the 2011 Explorer front rail—enabled a 5-kg (11-lb) weight-save on that vehicle.
On the Fusion program, the initial direction was to take the F-Series design for the A-pillar roof rail and get it into a unibody. Compared with the truck application, the sedan’s design is slightly modified because the load requirements are different than what the truck sees due to its separate frame. Still, much effort went into it, and the team was able to pull 4 kg (8.8 lb) out per vehicle using hydroform, compared with a hot-stamped design.
“We replaced two hot stampings and some other high-strength stampings, with the two hydroformed tubes in DP1000. This enabled the mass reduction as well as a significant cost save,” Morgans said. The concept was brought forward by a colleague who developed it working nights at home. “He brought it in and sold us all on the benefits,” Morgans noted.
The hydroformed parts are supplied by Cosma International, an operating unit of Magna International, for North American production.
The hydroformed B-pillar enabled Ford to improve the Fusion’s side-impact performance significantly over the hot-stamped design that was originally intended for the vehicle, Morgans said. The tubes give much less deformation and overall better control over the deformation—which helped improve the car’s roof-strength numbers as well.
“If you meet the IIHS [Insurance Institute of Highway Safety] side-impact requirement, the 4X roof crush test is very, very close. It didn’t take a whole lot more to get up to the 4X,” Morgans said. In the test procedure, a metal plate is pushed against one side of the vehicle’s roof panel at a constant speed. The roof must withstand a force of four times the vehicle's weight before reaching 5 in (127 mm) of crush.
“Tubular structures definitely help here,” he asserted. “We maximized the sectional values within the package space we’re given. When you eliminate the weld flanges you get more usable structure out of the components, as well as greater continuity—without the weld joints between the A-pillar and the roof rail. Typically that’s four parts coming together so you get those joints staggered around. And depending on how the vehicle’s built, you don’t always get the ideal connection between those two.”
He explained that because the hydroform tube runs all the way through, there is no discontinuity in the structure. It’s a much better load path.
Laser welding = better joints
The ability to combine parts and moving away from the hot stamping process brought “significant cost benefits,” Morgans said. Hot stamping is time-consuming due to the time it takes to heat up the blanks as well as post-treatment of the parts including using a laser to trim edges. “We were able to get rid of that with the hydroforming,” he said.
Ford has moved to some single-side joining operations in its assembly plant body shops. For the hydroforms, the company is using some stamped brackets to make the transition from the stampings to the hydroform tube.
“Typically on the F-Series we would MIG-weld those on to the tube and then use that stamping as the interface to the other stampings in the structure that allow us to use spot-welds within the plant,” Morgans explained. “For the Fusion, we took a step forward—all the brackets have been laser-welded on, and the brackets we’re using are primarily for tube-to-tube connections. They’re all laser welded and they’re giving us better joints. That’s allowed us to eliminate a number of the holes that would have needed to be there.
“And the process allows more welds within a given cycle time than is typically possible with a spot welding or MIG-weld system.”