Nearly 70 years after Peterbilt began producing aluminum truck cabs, company engineers have been surprised to learn how revolutionary Ford’s 2015 F-150 pickup is.
“When we saw the articles about the F-150 and saw the media attention it was getting, we started laughing, thinking, ‘we’ve been doing this for years,’” says Landon Sproull, chief engineer for the Class 6 to Class 8 truck manufacturer. In January, when he and other Peterbilt engineers saw the Ford truck in person in Detroit, “We were looking at the different stampings and noticing how similar they are to the panels we’re using these days.”
As automakers increasingly opt for lightweight body panels, Peterbilt’s engineers offer some advice from a company that has been working with aluminum since 1945.
Heavy-truck producers and light-vehicle makers both use aluminum to cut weight. For the truck companies, it’s a need to limit cab weights so haulers can have more capacity for cargo, while automakers are slimming down to improve fuel economy. The motivations may be slightly different, but the manufacturing processes and challenges are remarkably similar.
Designing for aluminum
Peterbilt Senior Project Engineer Terry Manuel says car and light-truck designers need to rethink the shapes and curves they’ve typically used in vehicle designs because steel and aluminum react very differently to the part-forming process.
Sharp angles, for example, don’t work as well in aluminum as in steel. In the stamping process, steel deforms easily, accepting sharp angles and deep draws into machines without complaint. Aluminum can tear in deeper draws, Manuel states.
“We had to work with a lot of new alloys to get the draw of the stampings right so we could get a Class A surface,” Manuel says. “When you look at a car door and see those nice, sharp creases, they look really good. That gets tougher in aluminum.”
For example, the 2014 F-150 has a cosmetic crease about halfway up the steel side panel, running from the front of the truck to the rear. The 2015 model lacks that design cue on its aluminum side panels.
Because aluminum doesn’t hold its shape well, Manuel says perfecting stamping tools is a painstaking process.
“Springback was a big issue for us in the design phase. Once you stamp it in a press, all metals try to bounce back to their original shape some, but it’s much worse with aluminum,” Manuel says.
The European Aluminum Association says the elastic modulus of aluminum, the propensity the metal has to deform when pressure is applied to it, is one-third that of steel. Engineers can’t just take panel designs and create a simple corresponding tool, as they can in steel. Because aluminum resists forming, Manuel’s team studied the material properties of several different alloys and tried to predict how parts would respond in stamping presses.
“You can simulate it up to a point on the computer, but you’re not going to know exactly what’s going to happen to that panel until you cut the tool and run the part,” Manuel explains.
The stamping plants that supply Peterbilt’s Denton, Texas, plant had to test tools and send them back to toolmaking shops multiple times to get working parts. That’s fairly typical in any stamping operation, but Manuel says aluminum requires more back-and-forth steps, adding time and cost to getting a new vehicle launched.
Body assembly
Though the company has used aluminum construction for nearly six decades, Peterbilt only began using precision stampings and automation about two years ago in Denton. In order to increase production and improve structural stiffness, Sproull says the company updated processes in which workers joined aluminum extrusions to each other by hand. Instead, Peterbilt now uses a robotic assembly cell to connect the stamped panels.
The most common technique for joining aluminum body panels with each other and to the vehicle frame is adhesive bonding coupled with mechanical fastening, as opposed to welding processes used with steel. Manuel says Peterbilt uses Henrob self-piercing rivets to join panels on its trucks, the same mechanical fasteners Ford is using with the F-150.
“Our robotic assembly cell had to be programmed very carefully,” Manuel says. “The way the Henrobs are fastened, they use some pretty big clamps, so you have to be really careful with the programming so you don’t run a robot into the sheet metal.”
He adds that programming the robotic cell, because of metal-joining difficulties, was more complicated than engineers had assumed when Peterbilt switched to a more automated system. However, the size and toolpath issues may be less unexpected in high-volume, mass-market vehicle plants.
“That programming time, I think that’s standard for every OEM robotic assembly line, but it was new for us,” Manuel states.
For example, Sproull adds, when Peterbilt used its more labor-intensive, manual process, engineers often didn’t notice how often workers had to position parts for assembly. When they had to program robots to line up each metal panel, the scope of the programming difficulties became clear.
“We underestimated the number of times you’d have to go through a metal-match process when we began programming,” Sproull says. “We made very few mistakes. The challenges were well anticipated, and we were able to make the transition in three years, which is pretty good considering the size of the challenge.”
Opportunities to learn
Peterbilt has been building trucks out of aluminum for more years than Ford has been making the F-Series line – which debuted in 1948, three years after Peterbilt’s aluminum trucks. Because of that experience, Peterbilt’s engineers know that what Ford is starting isn’t easy, especially given the scope of the undertaking.
The F-150 has been the most popular vehicle in the United States for nearly 40 years. Last year, Ford sold more than 750,000 pickups, while Paccar, parent company of Peterbilt, Kenworth, and DAF, sold 140,000 trucks.
And the costs differences between the vehicles are massive. The cab is a relatively inexpensive part of a Class 8 truck, with most of the cost coming from the engine, transmission, and axles. Cab production expenses don’t affect vehicle costs much. With the F-150, analyists estimate aluminum body panels add $1,000 per truck in costs, a significant portion of its overall value.
Despite those differences, Sproull says there are lots of opportunities for the big and small vehicle makers to learn from each other. Peterbilt has decades of materials experience with aluminum that it can share with companies producing smaller vehicles. However, automation, robotics, and precision stamping are new to the company. The truck producer hopes to follow examples from the mass-market automakers such as Ford and General Motors to improve production volumes at its plants.
“Our industry is benefiting from the economy,” Sproull explains. “As people buy more products, you’ve got to move them, so we’re seeing truck volumes moving up. Our challenge now will be the productivity of the robotic cell.”
Peterbilt Motors Co.
www.peterbilt.com
About the author: Robert Schoenberger is the editor of TMV and can be reached at 330.523.5381 or rschoenberger@gie.net.