Precision CMM Laser Scanner Speeds Up Tool Development

Analysts assume that, in the future, car makers will have to overhaul their range of models annually to integrate the latest hardware and software. This will require suppliers like Robert Bosch Automotive Steering GmbH to develop and manufacture innovations with even greater speed and efficiency. In order to reduce the iterative loops in tool development for the production of racks at the company’s facility in the city of Schwäbisch Gmünd, Germany. The site’s technology department started working with the latest laser scanner from ZEISS specially designed for measuring machines with multi-sensor capabilities.

In a report published by analysts PwC they anticipate the standard model cycle of five to eight years to be reduced to one. For Stefan Fröhlich, who heads the Process Development department at Robert Bosch Automotive Steering “Reacting more quickly is not a new issue. We‘ve been confronted with increasingly short development times for many years.“ In addition, the component vary enormously, which means that there is even less time available for the development of individual parts. “And all the while, tolerance specifications are becoming even stricter,“ says Fröhlich. Yet the Bosch manager does not let these trends worry him: “We see ourselves as innovators who are actively shaping
the future.“ As proof, he points out the wide array of solutions available from his company, including one that enables a car and trailer hitch to be steered from outside the vehicle.

Analysts assume that, in the future, car makers will have to overhaul their range of models annually to integrate the latest hardware and software. This will require suppliers like Bosch to develop and manufacture innovations with even greater speed and efficiency. In order to reduce the iterative loops in tool development for the production of racks at the company’s facility in the city of Schwäbisch Gmünd, the site’s technology department started working with the latest laser scanner from ZEISS specially designed for measuring machines with multi-sensor capabilities.  The 750 patents submitted by the steering control experts in Schwäbisch Gmünd within just 15 years are a testament to how often employees‘ seize the initiative. “This power to innovate is something anchored and cultivated at this development center for steering systems,“ says Fröhlich. The site‘s integration in the Bosch company landscape, with its numerous know-how centers, encourages such an optimistic outlook. “Our major strength was and is working on solutions together – and doing so across different functional areas.“ As this manager sees it, the corporate culture drives cutting-edge solutions within the extensive Bosch network for autonomous vehicles or for fending off cyber-attacks on electronics in cars or commercial vehicles.

The Steering Systems Challenge

Fröhlich explains that, even when it comes to basic issues like the design and manufacture of steering systems, everyone at the site strives to push the limits of what is possible in production: “We want to stay ahead of the rest.“ The engineer cannot help but be enthusiastic when discussing steering systems. There is no doubt that a lot of knowhow goes into this modular system, especially since steering systems can vary enormously. “Basically, every system we develop is one of a kind,“ says Fröhlich. Depending on the model and features, not only does the installation space vary, but OEMs must meet many additional requirements that affect the design and consequently steering system production.

As the name implies, a steering system transforms the rotational motion of the steering wheel into linear motion along the tie rod, which connects to the control arm on the spindle and ultimately moves the wheels. These days, the most common steering solution in passenger cars is the rack and pinion combination. Electric power steering has largely replaced hydraulic steering systems. When a driver turns the steering wheel, the pinion turns as well, engaging the teeth on the tie rod. As Fröhlich explains, the unique feature of the rack, which enables power transfer, is the spacing of the gears: this increases the further out you go, thereby changing the steering transfer based on how far the wheel is turned. Thanks to this design, the steering angle is reduced while still maintaining high-precision when turning the steering wheel. The benefit is that the steering wheel movements are reduced when turning, manoeuvring and when driving at greater speeds – making the driver feel more in control by combining comfort with safety. However, for this to work, the narrow tolerances stipulated by the design department must be achieved, including the helix and pressure angles for the individual gear teeth and the distance between them.

Outstanding Dimensional Accuracy

Sadet Hadzijakupovic, Head Automotive Steering Technical Center (left), and Daniel Hübscher, measurement technician discuss rack measurement strategy.

At the site in Schwäbisch Gmünd, a process called ‘wobbling’ is used, transforming a blank by creating the gear teeth and the special structure for the variable ratio. The term ‘wobbling’ refers to the process where a blank is pressed via a wobbling motion in the tool mold. With pressure of up to 1,000 tons, the steel is rolled out on the press to create a shape around 20 cm wide. There is no need to heat the steel, making it easier to maintain dimensional tolerances and stability. Wobbling ensures a high level of precision when processing complex parts. “The method is so well designed that, in spite of the significant pressure, individual characteristics on the rack deviate by no more than a few µm,“ says Daniel Hübscher, Technology Planer for Measuring Technology at Bosch. This scale is difficult to even imagine, given that a micrometer is 1/50 the size of a human hair. This high level of accuracy ensures that the pinion catches with the rack at exactly the right spots for safe and comfortable steering. To ensure outstanding precision, the pressing tool and the mold for wobbling the blank must meet even stricter tolerances specifications. “These days, we are pushing the limits of what is possible in production,“ says the Technology Planner, who works right alongside Mathias Mück, his colleague from Forming Technology, to produce these tools.

Up until now, multiple iterative loops were necessary to achieve the stipulated tolerances, and it generally took weeks to go from the design to fine-tuning the wobbling process for batch production. During this time, the tool had to be corrected based on the measuring results. Fröhlich explains that Bosch no longer wanted to invest so much time in this process. The decision was made to enhance the coordinate measuring machine (CMM) with an optical measuring solution. This would enable the company to combine the benefits of a CMM, like CNC operation and simple programming, with the quick capture of forms via point clouds. After defining various benchmarks, a rigorous selection process began. Ultimately, Sadet Hadzijakupovic, Head of the Automotive Steering Technology department in Schwäbisch Gmünd, decided to invest in the ZEISS ACCURA multi-sensor measuring machine. This system came equipped with an extremely precise laser scanner from ZEISS featuring a 25 mm measuring range. A mesh model of the rack can be created in just a few minutes. The tool makers use the 3D model for tool correction once it has been edited by Hübscher and his colleagues. In comparison to the CMM previously used, which required around 10 hours just to measure important individual characteristics, Hübscher reports that the switch “has significantly sped up the process. Now we just need 10 minutes for a scan.“

New Scanner For Greater Precision

“The latest ZEISS scanner calculates a precise image that reflects the actual condition of these highly reflective racks,“ says Hübscher. In turn, eliminating the need to manually optimize the point cloud acquired with a laser scanner has reduced outlay. With the completion of the pilot project, Hübscher reports that he and his colleagues at Bosch have reached a consensus: “We have further optimized tool development with the new laser scanner and will therefore continue to work with the ZEISS LineScan sensor in the technology department.“ Department head Fröhlich even goes one step further and plans to also use the high-precision sensor for monitoring production in the future. “This would enable us to identify potential manufacturing problems even more quickly,“ says Fröhlich. Just like the transformation of the European automotive industry outlined by PwC, he understands that “innovations and efficiency are indispensable if we want maintain our competitive edge.“

For more information: www.zeiss.com/metrology


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