Mass producing Ford’s aluminum-bodied -F150
Ford has garnered a great deal of publicity for its 2015 F-150 pickup truck in which everything in the body except the firewall is aluminum.
Ford says this body plus other weight saving measures reduces the 150’s mass by some 317 kg.
Less mass enables the use of Ford’s smaller EcoBoost engines to provide the same or better performance, payload capacity and towing capability as the current pickup while yielding both fuel savings and lower emissions. It’s a bold trail-blazing move that will no doubt be followed by others.
Ford is confident that reducing mass will allow it to continue building its full size trucks even as stricter fuel economy legislation phases in between 2016 and 2025. The F-150 is a huge profit maker for Ford, so failure would be disastrous.
Ford began planning for its aluminum pickup in 2009, during the recession, and deserves kudos for its pioneering vision. And not only did it have to design an all-new aluminum truck, it had to ensure that aluminum suppliers Alcoa and Novelis could provide the necessary quantity, and that its manufacturing system would accommodate the new material.
Others manufacturers have, of course, built aluminum vehicles, but producing a relatively small number of upscale aluminum-bodied, unit construction Audi A8s or Jaguar XJRs, for example, is quite different than turning out a mainline body-on-frame vehicle at the rate of one a minute, up to 700,000 per year, some 25% of Ford’s vehicle sales.
Although the F-150’s body is military-aerospace grade aluminum, the ladder type, box section, eight-cross member frame is steel, more than 75% of it the high strength variety.
This allows the frame to be lightened some 60 kg, while increasing torsional rigidity. It also raises the challenge of joining steel and aluminum, whether by adhesive bonding or mechanical connections.
And there is the corrosion consideration from galvanic action when joining dissimilar metals. Ford dealt with this with by e-coating and/or painting the parts, or by inserting a barrier material between the metals.
The steel frame is assembled by traditional resistance spot welding in which the metal pieces are held securely together by a “C-shaped” clamp and the contact spot zapped with a short intense electrical current that melts the metals, causing them to fuse together.
Although significant progress has been made in spot welding aluminum, it can still be difficult because aluminum’s high conductivity keeps it cooler, requiring a much higher current to melt it. In addition to its traditional steel spot welding, Ford added special aluminum fastening procedures to body assemble.
Included in the variety of aluminum-to-aluminum and aluminum-to-steel fastening techniques are self-piercing rivets, flow drill screws, friction stir welding, friction bit joining, and adhesive bonding.
A self-piercing rivet does not require heating or a pre-formed hole. The split rivet is punched through the metal pieces, then flares its legs to mechanically bind the parts together.
The flow drill screw has the advantage of being applicable when the assembler has access to one side of the component only. The sharp pointed screw is spun and pressed through the metal. This heats the metal causing it to flow and form a deep, solid threaded bond around the screw.
Friction stir welding (see video above), invented by The Welding Institute in the U.K. in 1991, is a solid-state process in which a spinning tool runs along the metal’s edges that are abutted together. This heats them to a softened state below the melting point but hot enough to be mixed. When pressure is applied the two fuse together. It is versatile because it can be used for joining dissimilar metals like steel and aluminum
Another technology, friction bit joining, is used for attaching dissimilar metals. The friction bit is a consumable unit that is rotated and pressed through the metals, melting and fusing them together. It remains in place to form an integral part of the joint.
In addition to these mechanical fastening methods, increasing use is made of adhesive bonding. The new F-150 uses three times more adhesives than the previous model.
Ford’s aluminum-bodied pickup deserves credit for showing the way to move lightweight metal vehicle production into the automotive mainstream.
Bill Vance (firstname.lastname@example.org) is an author and founding member of the Canadian Automotive Journalists Association of Canada.