A new innovative steering wheel with an injection-molded design featuring SABIC IP’s Lexan* EXL copolymer resin offers benefits of weight out, high performance, manufacturing ease, styling freedom, and parts integration.
Importantly, Lexan EXL resin avoids key environmental drawbacks of existing steering wheels, whose materials can be difficult to recycle and involve potentially hazardous waste products from casting and processing. The company’s investment in new technologies provides automotive industry customers with advanced materials solutions for the most demanding applications. Typical steering wheels are comprised of a die-cast magnesium or aluminum armature overmolded with flexible urethane foam. This creates a solid rim section with no package space for integration of electronic components. Additionally, the soft polyurethane makes structural attachment of components impractical. This approach also restricts styling possibilities such as advanced shapes and innovative aesthetics.
In addition to meeting these challenges, updated steering wheel design called for improved energy management for head and torso impacts; net weight-out even with the addition of integrated components; durability and long service life; avoidance of secondary operations; and overall system cost reductions.
Lexan EXL glass-filled polycarbonate-siloxane copolymer resin provides excellent stiffness and a high degree of impact over a very wide temperature range. SABIC Innovative Plastics has developed two designs; a two-part injection molded design with a leather wrap as a high-end solution and a one-piece injection-molded armature with a polyurethane overmolding. Both are attached to the steering column with a small metal hub. They have been shown to cut system costs by up to 20% and reduce mass by up to 40% compared to a magnesium or aluminum alloy steering wheel.
Both designs also provide other benefits:
• In the two-piece design, the space created by the hollow rim and spokes enables integration of damping and sensing technology, switch housings, wiring and other functionality inside the steering wheel.
• Injection molding Lexan EXL copolymer resin is a more environmentally responsible process than die-casting magnesium alloy as it reduces carbon dioxide (CO2) emissions dramatically. Compared to die casting 1.1 kg of magnesium alloy, which generates nearly 70 kg of carbon dioxide, manufacturing 1.0 kg of Lexan EXL copolymer resin only generates 7.6 kg, about one-tenth the emissions.
• Greater design flexibility to create new shapes and ergonomic configurations
• New styling options such as special colors and effects
• Part consolidation through integration of driver airbag attachment and reaction plate, horn mechanism, etc.
• Simpler manufacturing by reducing the number of secondary processes
Overall technical feasibility of the new steering wheel design has been tested. Prototype parts have been built and further OEM validation on vehicles is in progress.