The bodywork: A first: frameless, all-aluminium doors

Intelligent lightweight construction plays a decisive role in bridging the classic conflict of objectives between low weight and high strength in the new CLS. The CLS is thus the first vehicle from Mercedes-Benz to have frameless, all-aluminium doors. These are made from deep-drawn aluminium panels with extruded sections, and in comparison with conventional steel doors, are some 24 kilograms lighter. This is not only beneficial to the environment, operating convenience is increased too: the Coupé doors can be opened and closed more easily, particularly on an incline. The new construction has called for new joining techniques: instead of welding, a combination of gluing and riveting has been used.

In order to assure quality, in the production process the doors are positioned in the frames by extremely precise robots; and the side windows are fitted with the greatest precision using laser measurement technology. As a result, this door design meets the same seal requirements as for the door frames on a saloon, which has to be demonstrated in a Mercedes internal test (one of several) in which it is subjected to high-pressure testing with water pressure at 80 bar. To put this in context: this pressure is about five times higher than the pressure needed by an espresso machine to produce a good crema.

Apart from the doors, the bonnet, front wings, boot lid, parcel shelf, various support profiles and substantial parts of the suspension and engines are all made of aluminium. The front end is a hybrid construction made of aluminium panels and plastic strengthened with fibre-glass. The one-piece aluminium crash boxes in the front area are fitted in the side members and are screwed into the side with them.

The large front bumper with the integral grille with the centred star is made of polypropylene. The materials experts at Mercedes-Benz have worked together with the experts from the supplier of this part to develop the plastics formulation, which has a specific talcum content of 15 percent, in order to achieve an optimum compromise between weight and rigidity, as well as excellent thermal properties. As supporting structure for the bumper there is a front end which is a hybrid construction of aluminium sheet and plastic strengthened with fibre glass. For every CLS, special adjustable fixtures are used to ensure the front fits exactly and the gap dimensions are the same all round.

About 72 percent of all panels used for the bodyshell of the new Mercedes-Benz CLS-Class are made from rigid and ultra-rigid steel alloys. The ultra-rigid high-tech alloys, which have three to four times more tensile strength than conventional rigid types of steel, account for around eight percent of total weight. They are deployed in areas in which there could be extreme material stresses in the event of an accident - for example, in the event of a side-on collision, in the B-pillars and side frame of the roof; as well as in the rear, to create a stable crossmember.

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