The new Mercedes-AMG SL: the body shell

Oct 28, 2021

It began in 1952 with a filigree space frame, which in the first SL combined low weight with the highest possible torsional rigidity. This construction was conceived for its original use in motorsport and further developed to provide the backbone for the later production model in coupé and roadster form. The latest new edition of the roadster icon is based on a completely new vehicle architecture developed by Mercedes-AMG. The lightweight composite aluminium chassis offers the highest rigidity and the basis for precise driving dynamics, high comfort, optimal packaging and sporty body proportions.

The new roadster architecture consists of an aluminium space frame combined with a self-supporting structure. As with the first SL in 1952, it was literally created on a blank sheet of paper: Not a single component was adopted from the predecessor SL or any other model such as the AMG GT Roadster.

"Our development team in the body shell area was faced with an extremely appealing, but also challenging task: When we were tasked to do the overall development of the new SL, we were able to start from scratch, so to speak, without building on an existing structure. We can be justifiably proud of the result and it proves once again the high level of engineering expertise in Affalterbach. Because on the one hand, we have managed to meet the high package demands. On the other hand, we were able to achieve excellent rigidity values with a favourable weight in all areas, thus laying the foundation for agile driving dynamics, high comfort and maximum safety", says Jochen Hermann, Chief Technical Officer of Mercedes-AMG GmbH.

The demands on the body shell architecture of the new SL were high: the specifications demanded a much more comprehensive performance scope than for the predecessor model series. In particular, the basic layout with 2+2 seats and the alignment with a large variety of drives presented the developers with completely new challenges in terms of complexity. The aim was to represent the driving performance typical of the Mercedes-AMG brand as well as to meet the high standards on comfort and safety of a Mercedes-Benz.

Intelligent material composition with high aluminium content and new fibre composites

The intelligent material mix of aluminium, steel, magnesium and fibre composites enables the highest possible rigidity at a low weight. Optimised material cross-sections and sophisticated component designs create space for the required comfort and safety features, the sophisticated technology and the soft top. Other targeted measures include aluminium thrust panels on the underbody and function-integrated struts at the front and rear. The instrument carrier made of magnesium and the cover bridge made of a fibre composite material with a mixture of glass fibres and carbon also demonstrate the engineers' striving for the best possible mix of materials. This also applies to the windscreen frame made of high-strength, hot-formed tubular steel. This serves as roll-over protection in conjunction with a roll bar system behind the rear seats that can be extended at lightning speed when needed.

Cast components with tailor-made wall thicknesses

Cast aluminium components are used at the nodal points where forces come together or where functions are highly integrated, i.e. where large forces have to be transferred. Cast components have the advantage of enabling the specific discharge of forces, and make it possible to vary wall thicknesses locally according to the loads encountered. This makes it possible to realise higher rigidities that are required at certain points, for example at the chassis mounts. In addition, only the required wall thickness is implemented at each point of the component. This saves weight in less stressed areas.

Compared to the previous model series, the torsional stiffness of the body shell structure has increased by 18 percent. The transverse rigidity, for example, is 50 percent higher than the excellent value of the AMG GT Roadster, while the longitudinal rigidity is 40 percent higher. The likewise improved introduction rigidity for the chassis mounts guarantees very precise handling and high agility. The weight of the plain body shell without doors, bonnet and boot lid is around 270 kilograms.

The entire vehicle concept is designed to keep the centre of gravity as low as possible. This applies both to the low connection of the drivetrain and axles and to the arrangement of the rigidity-relevant components in the body shell structure. Examples of this are the connections between the front and rear sections and the passenger safety cell, with their high flexural strength and torque rigidity, systematically realised via force paths that are as low as possible.

Quality and processing at the highest level

Modern joining methods such as MIG welding, laser welding, punch riveting, blind riveting, MIG soldering, bonded seams or flow-drilling screws and, of course, high-precision toolmaking raise the body shell quality to top level. This applies equally to gap dimensions and to radii or joint runs. It goes without saying that the new Mercedes-AMG body shell architecture meets all internal crash requirements, which are significantly stricter than legal requirements in many areas.

Despite the high quality standard, the chassis development was implemented in the shortest possible time thanks to maximum efficiency: It took less than three years from the time a team of initially just six people was tasked with the job to the approval for series production. The high quality of the software used in the digital development made it possible to give the go-ahead for the production of the series-production tools without a real chassis prototype. And the so-called structural validation vehicle, which is of immense importance for passive accident safety, already met the demanding internal requirements during the first real crash test.

The new SL is manufactured at the Bremen site, where its predecessor already rolled off the production line.