With its wing doors, the Mercedes Benz SLS AMG is sure to be the dream of many car drivers. Mercedes-AMG GmbH describes their new super sports car with words such as "automotive fascination" and "high-tech at the highest level". But high-tech is not only required during the construction of the wing doors - the highest of standards also apply during production and quality control. For example, the steering coupling that is produced by DURA Automotive Systems Reiche GmbH is mounted manually and simultaneously subjected to strict quality controls. Modern measurement technology from HBM is used here.
With a peak performance of 420 kW, the 6.3 liter engine in the SLS AMG accelerates the 1,620-kg (3,564-pound) sports car from zero to 100 km/h (more than 62 mph) in just 3.8 seconds. At 317 km/h (about 197 mph), the electronics intervene and limit the top speed. The aluminum space-frame body with the wing doors, a seven-speed double coupling drive and the sports chassis with aluminum double wishbone axles all contribute to the corresponding driving dynamics. The SLS AMG is the first vehicle to be independently developed by Mercedes-AMG GmbH, and this super sports car is designated by them as their masterpiece in their 40 years of company history.
High standards are also set in production. With a sales price of 177,310 Euro (more than $250,000 U.S.), just 25 to 30 of these wing-door cars are produced per day. Craftsmanship is used here in the production of the aluminum space-frame, the engine production and in the final assembly. Magna Steyr Fahrzeugtechnik GmbH produces the chassis and body, the engines come from AMG Motorenmanufaktur and the assembly lines and production equipment in Sindelfingen were modernized for the final assembly of the SLS AMG.
Craftsmanship is also frequently found in the supplier companies due to the low quantities. The steering coupling—a central component of the new SLS AMG steering system—is for example produced and mounted by DURA Automotive Systems Reiche GmbH. This automotive supplier, which employs around 100 people at its German facility, is part of the internationally active DURA Automotive Systems Inc., which is headquartered in the United States. Steering components and crash absorbers are the main items manufactured in Germany. One of the main product groups here are so-called corrugated tubes, where the diameter periodically changes over a section of length. In a frontal collision, the corrugated tube absorbs part of the energy through defined deformation. This principle protects the driver, preventing the steering column from being pressed into the driver compartment during a crash and causing injuries. The corrugated tubes are produced using a special forming process. The corrugations are produced in a tool similar to a press with forming elements and interior high-pressure support. The forming processes can be implemented with comparably low pressures in these corrugating machines developed by Dura Automotive Systems Reiche GmbH.
The test bench also acquires the data of the other stations within production where quality is checked. After the joint is checked, the tubes are fitted with threaded inserts. These are press-fitted into bores that are positioned laterally at the ends of the tubes. Modern measurement technology from HBM is once again in use here. The press-fit procedure is monitored with a process controller, type MP85A (see box). This records the force and displacement during the press-fit process. "The proven window technology of the MP85A has impressed us in particular," Strothmann said enthusiastically about the process controller. The measured data are directly evaluated in the process controller. This checks whether the values lie within a specified window.
Assembly is also monitored in the next step—the screwed connection of the individual components. The tightening torque and the angle of rotation of the screws, which are screwed in with a hand-operated screwdriver from DSM Messtechnik, are measured and recorded. In the last step, the length of the completely assembled steering coupling and the torsion angle of the connection interfaces to each other are measured.
All values are recorded and monitored by the PC that controls the test bench. The simple option of integrating the process controller into a test bench environment was an important criterion for Strothmann. "The process controller sends both the status - i.e. 'OK' or 'not OK'—and the measured values via Ethernet to the central PC," he said.