Audi's A2 refined the aluminum spaceframe concept of the larger, more expensive A8, and applied it to a relatively high volume (at least 60,000 units/year), low-cost (under $20,000) small car.
The relative simplicity of the Panoz Esperante's bonded and extruded chassis allows for inexpensive additions to the line. A longer wheelbase 2+2 is in the works. Ferrari's 360 Modena, meanwhile, uses the full menu of extrusions, castings, and sheets to produce an extremely rigid structure.
The Alcoa concept car's spaceframe placed maximum emphasis on flexibility. A number of variants could be pulled from this basic structure with minimal increases in either cost or tooling. It could support a front-drive or four-wheel drive layout powered by a flat-six, or a rear-drive or four-wheel drive V8 arrangement. It was penned by J Mays before he joined Ford.
If you were to start with a clean sheet of paper–throwing out all of the preconceived notions about how cars are built and the equipment necessary to do it–how would you design a vehicle...an aluminum-intensive vehicle (AIV)? Would it be a stamped and welded structure made from sheet? Would it utilize castings, extrusions, and sheet in a single structure? Or would it be enough to form a tub with extrusions over which you’d place an aluminum body that utilized semi-plastic forming insteadof stamping?
Rick Winter, president, Alcoa Automotive Engineering, replies: “It would depend on the volume you’d want from the vehicle because there’s no single answer to every situation with aluminum. So it becomes a matter of choosing the best combination of products you can create from it for use with each design.”
Winter knows what he’s talking about. He was working with Audi engineers at the automaker’s Ingolstadt, Germany, headquarters when Audi’s continuing fascination with aluminum began. First up was an all-aluminum Audi 100 body structure–“a straight material swap to see what the baseline was,” says Winter–that proved a stamped structure was both lighter and adaptable to current production practice. “But straight material swaps don’t get you anything,” he says, “because you haven’t optimized the design and the production methods for the material.”
This realization brought Audi and Alcoa both literally and figuratively back to the drawing board. A thorough rethink, driven by Audi’s intention to use aluminum construction in a new luxury sedan, caused the design team to look at a spaceframe structure utilizing extrusions, castings, and sheet aluminum.
“We learned a lot from the Audi A8 structure, and applied that to the higher volume [60,000 units/year versus 15,000 units/year], lower price [under $20,000 versus over $62,000] A2,” says Winter. In fact, the Audi A2 uses a smaller optimized version of the A8 spaceframe with greater parts consolidation. “The section from the A-pillar through to the leading edge of the C-pillar, for example, is made of a single extruded section,” says Winter. Also, the lower A-pillar and entire B-pillar are cast units of varying section width, with the lower A-pillar also forming the front strut tower and forward chassis rails. So this must be the way to engineer an AIV today, right?
Says Winter: “If you’re going for high volume, probably not. I think you would use much more sheet aluminum for the structure, and a few nodes and extrusions. That technology combination would be inline with production in the hundreds of thousands, cost targets the OEM has set, and closer to what the industry is familiar with. But if flexibility was your major concern, you might want to build something closer to our concept vehicle.”
The vehicle in question was penned by J Mays in the mid-1990s. It used an extruded aluminum spaceframe with a common structure from the A-pillar to the C-pillar and hang-on body panels. Different modules could be fitted to make the vehicle a van, SUV, pickup truck, etc. “The same basic structure could accommodate a front-drive or four-wheel drive drivetrain with a flat-six engine, or a rear-drive layout with a V8. The engine was located at least partially under the driver’s [flat-six] or passenger’s [V8] feet,” says Winter, “and–since Lotus did the packaging, drivetrain, and suspension work–it would have used a version of the very compact Lotus V8. It wasn’t the most conventional looking vehicle, but it proved the safety and flexibility of this type of structure.” A structure that was designed to allow the cost-effective production of 250,000 units per year. High volume indeed.
To keep costs in line, the extrusions used a one-dimensional, blunt-end cut instead of the expected machined face. This simplified the blank used allowed Alcoa to hold weld gaps to 0.5 mm. In addition, each extrusion was designed to do as many jobs as possible. The front quarter beam, for example, carried the glass, located the front strut tower, acted as an interior trim surface, and closed out both the cantrail and the top of the A-pillar. “That concept really pointed to where the market is going with the increased segmentation we’re seeing, and would be very competitive with steel,” says Winter.
Alcoa, however, has shifted away from promoting AIVs to the industry, so the concept is on the shelf until someone expresses interest in this type of flexible vehicle. “Europe is big in terms of looking at the aggressivity and passivity of vehicles in accidents,” says Winter. “Eventually that will come here, and it will open doors for aluminum-intensive vehicles.” In the interim, there are a number of projects in the pipeline at Alcoa designed to fit in with current production practice.
The first is a composite aluminum pickup tailgate. At 20 lb. it is just about half the weight of an all-steel counterpart, and would be an easy substitution on any current or plan-ned pickup. A one-piece molded polymer insert provides the structure for the design, which is covered in a skin made from a single aluminum sheet.
“It significantly reduces opening and closing effort,” says Rick Milner, president of Alcoa Automotive, “and the plastic insert features multiple reinforcements for strength. The beauty for automakers, however, is the fact that it reduces the number of pieces to two, improves component quality, and seriously reduces the amount of scrap.”
Next is a sliding minivan door that Alcoa says is 50% lighter than its steel counterpart, and half the thickness. “This one is a no-brainer as far as we’re concerned,” says Milner, “because the price of this solution is well below the cost OEMs have stated they’d pay for weight reduction. We think it won’t be a hell of a lot more than what they are paying now for a steel door.”
The door concept combines an aluminum skin and magnesium brackets around a polymer insert. Specially engineered depressions in the surface of the inner skin eliminate the need for a separate welded-on reinforcement to increase panel rigidity. As a result , the door is just 3-in. thick, approximately half the width of the steel unit it replaces.
“Just like that,” says Milner, “we are able to give the designers and engineers three inches of interior width with no loss of integrity or quality. Plus, our design is lighter and easier to open, and can take a larger window, if desired. We can even deliver complete units to the factory, should the OEM want that.”
The final project was created in cooperation with the U.S. Department of Energy (DOE). It is a one-piece cast- aluminum liftgate whose vertical cast- ing process can be adapted to the production of door frames, firewalls, engine subframes, vehicle pillars, shock towers, and floor frames. (Even bulkheads for aircraft.)
“This has significant part consolidation potential,” says Milner. “On a current production minivan liftgate we were able to reduce the number of parts from 11 to one, and reduce weight by 20%.” The casting process uses multi-port, low-pressure injection, and produces wall thickness from 2.5 to 3.5 mm. Alcoa says this process can easily pump out 100,000 liftgates per year. “Like the sliding door,” says Milner, “the mass reduction means you can use a smaller motor to open and close the liftgate, or none at all.”
This is all well and good, but can aluminum keep pace with automakers’ desires to cut component costs each year? “First,” says Milner, “we won’t win this long term in the purchasing department. It will take the designers, engineers, and product planners pulling us in because of what we can do, and how we can help them build and sell more vehicles. We do, however, have to meet the desire for a cost reduction over the life of the vehicle. The experience we’ve gained from the Audis, the Ferrari 360 Modena, Panoz Esperante, and our concept vehicle helps us to find new ways to make things lighter, stronger, and less expensive. And it doesn’t hurt that gaining this experience has been a whole lot of fun as well.”
As Old As the Industry
Aluminum has been in cars almost since the automobile was born. Here are a few notable examples:
- The first documented use of aluminum was the crankcase of the 1895 Haynes-Apperson automobile. Studebaker’s 1893 wagon contained 125 lb. of aluminum. This was equivalent to the entire U.S. production of the material a decade earlier.
- In 1904, the Pierce Great Arrow used a cast-aluminum body. It was followed in 1905 by Marmon. Parts of the Marmon body were 5/32-in. thick!
- The 1916 Premier offered an all-aluminum six-cylinder engine that produced 56 hp. It also had an aluminum body with no exterior hinges or handles.
- By 1924, Marmon had abandoned its cast-aluminum body, and produced a car with an aluminum six-cylinder engine producing 84 hp, and an aluminum body and radiator shell. It weighed 3,865 lb.
- The Duesenberg Model J used an aluminum Lycoming straight eight with four valves per cylinder. It produced 265 hp from its 420 in.3
- The 1923 Ford Model T Four Door Sedan featured a body with aluminum panels that weighed about 80 lb. less than a comparable steel body. However, by 1925, all Model Ts had steel body panels.
- In 1928, the auto industry used 120 million lb. of aluminum, or 40% of total aluminum output. Steel was used to the tune of 5.6 million tons, just 16% of total steel output.
- In 1946, the experimental Gregoire had a frame made of five aluminum castings that weighed a total of 100 lb. The castings were dovetailed and bolted together, and formed the basis for a four-passenger automobile that weighed just 948 lb. It never reached production.
This 1901 Haynes-Apperson used an aluminum crankcase. It was nothing new for the company as its 1895 model started this trend.