Assembly in Action: Adhesive Bonds Aluminum
Panoz Auto Development has produced the Panoz Roadster, a retro-looking, state-of-the-art automobile for several years. It has a Ford Special Vehicles Team modular V8 drivetrain and adhesive-bonded superformed aluminum and magnesium alloy skin. It was the world’s first aluminum-intensive vehicle. Panoz is now producing its new Esperant¿which features several new engineering ideas.
When visitors enter the Esperant¿ssembly building, the first thing they notice on the assembly line is the gleaming extruded aluminum chassis components. The second thing they notice is the absence of a welder. Panoz bonds the chassis together with a structural adhesive. With adhesive, stress is better distributed throughout the entire contact between the rails and corner nodes. This stiffens the chassis and minimizes flex.
John Leverett, chief engineer at Panoz, was instrumental in the chassis design. He was convinced that the frame could be fabricated with adhesive technology. However, he wanted to avoid difficult-to-mix ratios, the need for primers to gain metal adhesion, low tensile or shear strengths, or a low modulus that would result in more chassis flex than was permissible for this vehicle.
Panoz selected a methylmethacrylate-based product from Adhesive Engineering & Supply Inc. (Seabrook, NH). Working closely with Panoz, the company developed Extreme Adhesives 5375HS. This 1-to-1 ratio, methylmethacrylate, structural adhesive passed all of the design requirements. It has also passed impact, vibration and durability testing required for federal certification of the vehicle.
"Adhesive Engineering & Supply was able to meet the properties of an epoxy with a room temperature-curing methacrylate, which is a much more cost-effective solution," says Leverett.
Chassis assembly begins on a precision fixture. The aluminum components consist of extruded rails and corner nodes, which slide together. They are cleaned and assembled dry on the fixture. No other surface treatment is required with the adhesive. The adhesive is then injected into each joint through a series of small holes in the tubular rail extrusions.
To maintain alignment and eliminate component movement during curing, a bolt is placed through each chassis intersection and tightened. This results in full bond line coverage and eliminates problems with pot life or set time.
By using this assembly technique and adhesive, Panoz has been able to achieve a torsional stiffness of over 7,400 pounds per degree of twist. The adhesive-bonded chassis has survived Ford Motor Co.’s 150,000-mile torture test, with virtually no change in torsional stiffness or adhesive failures.
Collision crush boxes of 6063 aluminum, hidden inside the body’s rocker panels at final assembly, are bonded to the frame rails with the adhesive for strength and serviceability. The parts fixture themselves by snapping into place for alignment during curing.
Extreme Adhesive 5375HS achieves handling strength at room temperature within 90 minutes, minimizing work in process and allowing assembly to quickly continue.
After completing the basic chassis rail assembly, a separate firewall and floor pan assembly is riveted, welded and bonded within the chassis perimeter. This creates a rigid structure that every other chassis component depends on. The firewall assembly incorporates all mounting points for the windshield, dual air bags, heating and ventilation systems, dashboard, seats and remaining chassis modules. All bolted and riveted attachment points for the independent rear suspension and front pillar assembly are bedded with the adhesive as well. This eliminates movement between the mating parts. This also stiffens the chassis platform.
Lastly, the superformed panels, which comprise the body, are bonded in place with the adhesive, removing the need for cosmetic touchup caused by welding or riveting.
For more information on adhesives, call 800-888-4583 or visit www.stick-it.com.