Mercedes will break new ground with the sixth generation of its inimitable Mercedes SL roadster next year by making it the very first Mercedes in large-scale series production to use an almost exclusively aluminium lightweight construction.
At a preview event held close to last week’s Los Angeles motor show, Mercedes showed journalists a completed example of the new two-seater grand convertible’s ‘body-in-white’ superstructure.
Made from a mix of chill cast-, vacuum die cast-, stamped- and extruded aluminium, it allows the finished 2012 SL to be at once 140kg lighter than the outgoing steel car, and 20 per cent more torsionally rigid – to the enhancement of handling precision, rolling refinement, performance and fuel-efficiency.
Mercedes’ CAD-optimised design for the SL’s monocoque is even stiffer than other aluminium-constructed rivals – or so the firm claims. “Our engineers have measured a Jaguar XK’s body stiffness at around 16,000Nm per degree of torsional deflection,” said SL Product Manager Bernd Stegmann. “The new SL has just under 20,000Nm per degree.”
The various metal castings and tailored blanks of the SL’s body-in-white are connected via different methods, depending on how much load they transmit. While some parts of the underbody are MIG welded, hemmed, bonded and bolted, others are joined via state-of-the-art friction stir welding – a technique that allows for particularly stiff, precise joins.
With mainly aluminium body panels, the only significant parts of the new Mercedes that aren’t aluminium are its pedestrian-protection-oriented plastic ‘soft nose’ grille, its super-lightweight magnesium rear bulkhead, and its tubular steel A-pillars and header rail. Steel is chosen here for its extremely high strength in the event of a rollover.