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Special Report: Automotive

Fabricating the F-150

By J. Neiland Pennington

It’s well known that Ford’s light-duty pickup trucks donned aluminum bodies, but how’d they do that?

May 2017 - Reams have been written about the business case for building aluminum bodies for Ford’s half-ton pickup trucks, starting with the 2015 model year. The critics indulged in much tongue-clucking about the supposedly conservative pickup truck market never accepting the radical change to a lighter weight material. Ford, they proclaimed, would lose its coveted position as the nation’s top-selling light passenger truck. The only acceptable aluminum product for pickup truck drivers was beer cans.

So much for the critics. Ford engineers produced an aluminum truck body weighing 660 pounds with closure panels, 700 pounds less than the previous all-steel version. Mileage improved by between 5 and 29 percent, depending on model and engine type. The F-150 SuperCrew and SuperCab versions are Top Safety Picks by the Insurance Institute for Highway Safety, and the entire line also has a five-star crash test rating from the National Highway Traffic Safety Administration. And that all-important sales record? It’s now forty years and counting.

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Robotic cells insert self-piercing rivets and apply structural adhesive. This process eliminates heat, sparks and smoke.

Press lines

Much less has been said about how Ford actually engineered this success. The automaker is no stranger to aluminum forming and fabricating. Serious  involvement began with an aluminum-intensive vehicle study on the 1993 Mercury Sable, and Ford built aluminum unit bodies for Jaguar and Land Rover when it owned those two brands. (For details, see the September 2013 issue of Modern Metals magazine.)

To tell the F-150 aluminum story, our guide is Peter Friedman, Ford’s global manager for structures and stamping in research and advanced engineering. The F-150 bodies are composed of aluminum sheet and extrusions, with stamping to produce the body panels and hydroforming for the extrusions. 

“To do the volume of stamping that we need for the trucks, we needed to update our presses,” he says. “We bought five new tandem press lines.”

Those presses are not exclusively for aluminum, he adds. “We launched the new presses while we were still stamping steel for the 2014 bodies, five to eight months before we switched over to aluminum. We made changes in the tooling design for aluminum, but the die sequences remain the same.”

Manufacturing output for aluminum vehicles is the same as for steel, both in stamping and final assembly. In addition to the new presses, Ford built a body shop in Dearborn, Michigan, designed to maintain comparable production rates. Five hundred new robots assemble the body panels and install the roof and doors. They also transfer the bodies to final assembly and scan the finished product for assembly quality. 

Ford has three light truck assembly plants, Dearborn, Kansas City and Louisville, but Dearborn Stamping (in the original River Rouge Plant) supplies all of the presswork. The refurbished facility also includes a new paint shop engineered for aluminum. The pretreatment is formulated for maximum adhesion on the metal, and emissions are below all required minimums.

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Ford assembly team member Levi Rouse is among the legion of workers who made possible Ford’s conversion to aluminum fabricating.

Joining technology

The primary assembly technology for one-sided joining is flow-drilled screws. It’s particularly advantageous in joining sheet to extrusions, which are closed sections where the opposite side is inaccessible. 

Peter Friedman explains the process: “A screw is spun at very high speeds and is loaded axially in a way that produces heat. The screw extrudes the metal forward so that it creates a longer length of thread engagement. There is no external heat source or applied heat; the screw generates the heat.” 

The screw extrudes a projection into the metal surface; think of it as a self-forming screw anchor. “Like a self-tapping screw, the fastener is drilling its own hole. But a self-tapping screw can cut threads only into the existing thickness of the metal,” he adds. “This process extrudes the metal further out, which creates a significantly longer length of engagement.”

There is a range of techniques for two-sided joining. Ford uses self-piercing rivets and resistance spot welding, and the entire floor of the cargo box is spot welded to the cross members. Clinching is the choice for lower-load requirements.

Loads are transferred between components through the joints, and Ford increases the joint area with adhesive bonding. “Adhesive bonding,” Friedman notes, “is continuous joining and a great way to capture stiffness by increasing the surface area of a joint. We have a very efficient structure because of adhesive bonding.”

When Ford advertises “high-strength, military grade aluminum alloys,” it is talking about 5000- and 6000-grade metal. And for extrusions, it’s 6082, hardened to T6. They are the same alloys and tempers used in the Bradley Fighting Vehicle.

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Final quality checks use computer-aided tests for assembly parameters.

Design eliminates castings

The form of aluminum not used in the F-150 is castings. “We have no problem with structural castings,” Friedman says. “We had a fair amount of experience with them when we owned Jaguar and Land Rover. But given the very high volume of the F-150 and the fact that it’s a body-on-frame vehicle, we didn’t need castings to develop a very efficient design.”

Although Friedman classifies the F-150 as essentially a stamped vehicle, there are a number of extrusions, primarily cross-car components like roof bows and headers. Ford purchases its extrusions, but does all of the fabricating in house. These components are typically CNC bent, pre-formed in a press, then hydroformed with high-pressure fluid in closed dies.

Two major extrusions are what Friedman calls the shotguns. These are the components that originate in the cowl, extend straight forward, and both secure the fenders and tie into the frame.

One of the largest extrusions is the A-pillar roof rail. It is purchased as a straight tube, over 9 ft. long. It originates at one side of the cowl, rises up the A-pillar, crosses the entire width of the roof and forms the opposite side of the A-pillar, connecting to the opposite side of the cowl.

“The A pillar extrusion starts at a CNC bender, goes to a pre-forming press, followed by hydroforming and hydro-piercing.” Friedman relates. “It is then heat-treated to a T6 temper and immersed in a conversion coating to remove the native aluminum oxide. That oxide is replaced with a coating that is more stable for long-term adhesive durability. The part is not painted, but it is both mechanically fastened and adhesive bonded.” All work is done in house, in the same plant.

The aluminum structures are what Friedman calls the “three major chunks” of the truck: the front end, the cab and the cargo box. But the steel chassis on which the truck rides also received close attention.

Steel also reduces weight

The weight of that frame is reduced with advanced high-strength low-alloy steel. These grades provide the same or greater strength with less material than mild carbon steels, and the manufacture of the structure was also revised.

“The model year 2014 and before were hydroformed,” Friedman reports. “The 2015 frame was changed to roll forming. It is a more modular approach. We make the F-150 in six different body styles, with three cabs and three boxes. The high-strength steel frame saves some 60 pounds over its predecessor.”

To prevent galvanic corrosion between steel and aluminum, the chassis and body-in-white are isolated with two separate e-coats. Frame brackets pre-coated with zinc—a third layer—are installed in areas of high contact such as the junctures between the frame and the cargo box.

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Cost control

It’s no secret that aluminum costs more than steel. Using aluminum in premium vehicles is no longer a story. Light alloys are much less common in mass-market cars and particularly in trucks.

Aluminum by itself doesn’t achieve cost neutrality, Friedman says. Ford spends a premium overall using both aluminum and high-strength low alloy (HSLA) steel.

“One of the ways we’re capturing a lot of aluminum’s value, which goes to both the cost structure of the vehicle and our environmental footprint, is in recycling,” he says. “We have close to two-thirds material usage and only one-third scrap.”

That one-third scrap is processed through a closed-loop recycling system. Four grades of aluminum sheet scrap go to four separate recycling buckets.

There are two 6000-alloy streams and two for 5000s. The 6000-series is an aluminum, silicon and magnesium formulation, with either low or high copper content. These scraps are divided into two streams according to the amount of copper. Alloys in the 5000 series are separated by lower and higher magnesium content. These are also divided into two individual streams.

“At every stamping trim die, there is a vacuum system with cyclones on the roof of the plant,” Friedman adds. “Each stream of scrap is dumped directly into waiting trucks. The trucks are the same ones that delivered the coils of metal from the mills. The specially built trucks are fully utilized; they are never driven empty. They deliver coils to Dearborn Stamping and return to the suppliers with scrap.”

Ford does not use third-party recyclers. One month’s scrap may return to Dearborn the following month as fresh coils to feed the stamping lines.

Ford’s downstream savings have kept the F-150 price competitive with all-steel vehicles. The manufacturer’s suggested retail price of the 2016 model F-150 was $700 less than the comparable Chevrolet Silverado. Moreover, Kelley Blue Book gave the F-150 the lowest projected cost of ownership in 2016. 

Repair shop

A criticism of light metal structures is their assumed greater difficulty of repair. Ford assists dealer collision centers with staff specialists and F-150 bodies-in-white to demonstrate repair techniques. Dealers also receive help when upgrading their body shops.

Aluminum has expanded to the F-250 and F-350 Super Duty trucks for the 2017 model year. These are the big honkers at over 8,500 pounds GVWR (gross vehicle weight rating). Ford also re-engineered the HSLA steel chassis, which weighs 350 pounds less overall than those made for previous models. FFJ

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