Dream car with wing doors - Production of steering couplings for the new SLS AMG

Seamless monitoring of steering assembly

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 HBK 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.

Monitoring press-fit processes

The process controller MP85A from HBK is used, among other things, to monitor press-fit processes during production and assembly. The measured values are acquired here from the connected transducer and evaluated directly in the controller. This permits a direct statement to be made about the quality of the production step. The process controller can be seamlessly integrated into a superordinate system via fieldbus interfaces or Ethernet. In addition to the overall status—the produced part is deemed OK or not OK—complete curves of e.g. a press-fit process and up to nine evaluation windows can be transmitted. Data can be observed in real time via a web browser. This allows the press-fit process to be monitored live without the need for anyone to be present directly at the machine. If problems occur during production, immediate reaction is possible. The person responsible for production can be automatically notified by SMS or email if an error message is output. This rapid error evaluation allows product quality to be improved and, in contrast, costs related to recall actions are reduced.

The data can also be analyzed in detail in order to determine trends in the measured values, for instance. This permits early reaction to problems even before faulty parts are produced. In addition, all data can be stored long-term in a database so that seamless traceability of produced parts is guaranteed.

100% traceability

Every steering coupling that leaves the works of Dura Automotive Systems Reiche GmbH in Lage is given a unique number. "Based on this number, we can precisely determine at any time when assembly and the values measured during assembly took place," Strothmann said. This means that total traceability is assured for customers.

The assembly and test equipment for the SLS AMG steering coupling was mainly designed and built by Dura Reiche. Only the test bench for measuring the bending moment of the joint was completely delivered by Reorg GmbH, including the control PC and software. The construction of the test equipment on the other stations and subsequent integration was implemented at Dura Reiche. The automotive supplier places great value on an uncomplicated connection with the test system when selecting components. Strothmann explained the decision to use the MP85A: "We have already had good experiences in the past with compact process controllers from HBK."

Currently, the Lage operation produces approximately 25 steering couplings each day on average. These are then assembled into a complete steering system in the SLS AMG, together with the components produced in Hamburg, at the Sindelfingen works. The driver of this wing door car can, thanks to the modern HBK measurement technology, rely on the fact that safety-relevant components of their sports car are manufactured with the highest of quality and precision.

About AMG

AMG – these three letters stand worldwide for supreme automotive performance, exclusivity, efficiency and highly dynamic driving pleasure. Today, as a wholly owned subsidiary of Mercedes-Benz Group AG, the Affalterbach-based company represents the sporting spearhead of the Group.

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