The supreme discipline in metrology

Wolfsburg - In order to continuously improve quality, productivity and process efficiency, it must be ensured right from the development phase that every Volkswagen Group automobile is measurable. This applies to the complete range of brands and variants, from the roof to the floor assembly. With the RAX Horizontal Armfrom WENZEL , Volkswagen has implemented the appropriate solution. In the meantime, 5 duplex systems are in use.

Quality assurance at the pre-series centre in Wolfsburg practices the supreme discipline of metrology. New trends in metrology are set on test vehicles. The developers are first confronted with new measurement tasks here. The controllability of these measurement tasks may have an impact on the product development process.

"In product development, we have to define as early as possible which requirements and quality criteria have to be taken into account," explains Stefan Eckhardt, QA Pre-Production Centre Department, Analysis Centre. His supervisor Frank Eggeling adds: "We cover the complete range of Volkswagen. Therefore, a large measuring range was very important for us so that, for example, a VW bus can also be measured with high precision."

Recipe for success: Close cooperation

"Of course, before the introduction of our measuring solution, measurements were already being taken with relatively large coordinate measuring machines," describes Thomas Werner, Head of Technical Sales at WENZEL. "But the mechanics used were getting on in years and the control technology, software and probes were no longer technologically up-to-date." Volkswagen's considerations ranged from a comprehensive modernization to a new acquisition. It was important that the new solution was future-proof, i.e. that it would meet the requirements for at least 10 years.

After an intensive in-house selection process, Volkswagen opted for a completely new development from WENZEL. The decision in favor of the RAX horizontal arm measuring machines was a great sign of confidence in the innovative competence of WENZEL. The project was carried out in close coordination with Volkswagen from start to finish. "The requirements were very high. But working with measurement engineers who have years of experience was a great asset for us," explains Thomas Werner.

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The result is the RAX, the latest CNC horizontal arm measuring device from the proven R series of WENZEL. WENZEL is proud of the fact that the RAX has become more accurate than required and, despite the high Z-range, measures more accurately than comparable smaller measuring machines . The limit value of the length measurement deviation MPEE was specified as 40 + L/40 μm. The coordinate measuring machine is suitable for use with switching, scanning and optical measuring systems.

The measuring machines was equipped with Renishaw's PHS infinitely adjustable motorised rotary and swivel head. The PHS was developed to meet the high demands for measuring car bodies in the automotive industry. In particular, where fine angular positioning and a long probe length are required, it increases the functionality of the machine.

The RAX already offers a very large measuring range of 3,100 mm in the Z axis in the standard version. Depending on the touch probe, the measuring range in Z starts at 70 mm above the base plate.

This means that the measuring arm can be moved under the vehicle at road level. The mirror-image design of the duplex version makes optimum use of the measuring range in the X-axis. At Volkswagen, the X-axis is 6,000 mm because the foundation pits of the old systems were used. If necessary, much longer multi-column installations can also be realised.

Perfect accessibility for all measuring and maintenance tasks

The RAX is equipped with high-precision linear guides in all axes. These ensure optimum service life and rigidity. The X-axis guide is integrated in the base plate at floor level and covered so that it can be driven over. This design allows vehicles to be driven onto the RAX despite the limited space in the measuring room. The measuring device is perfectly accessible from all sides, both for measuring and maintenance tasks. All relevant components can be removed and reattached in a few simple steps. This shortens maintenance times and increases the availability of the coordinate measuring machines.

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The RAX systems are equipped with active temperature compensation. This ensures that accurate measurement results are determined despite possible deviating temperatures. The workpiece temperature sensors are installed wirelessly. The existing foundations could be re-used. These are equipped with damping devices so that the influence of vibrations on the measurement result is minimised.

The access monitoring of the measuring machine by light barriers enables the high machine speeds to be run completely. The mirror columns of the light barriers can be easily removed for driving in a vehicle and reinserted reproducibly without adjustment.

Wide range of applications

Everything in the automotive sector is measured with the RAX measuring systems at VW. Complete vehicles, car bodies and individual body parts. In addition, the RAX can be used in many other industries. For example, it is used to measure large-volume machine components, trucks, agricultural and construction machinery, but also workpieces from the aerospace and energy sectors.

"In the meantime, we have been working with the RAX measuring devices for two years and are very satisfied with them," explains Hans-Jürgen Bach, head of the QA pre-series center at Volkswagen AG in Wolfsburg. "It was also important for us that we get the complete service portfolio from a single source." Stefan Eckhardt adds, "With this solution, we are well positioned for the future. Thanks to the constant further development at WENZEL , it is possible for us to upgrade to the latest technology at any time."

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