From larger and smaller dimensions

Every two years, the Conference on Production Metrology is held at the Interstate University of Applied Sciences NTB in Buchs SG in September. On 5 September 2019, Institute Director Prof. Dr.-Ing. Michael Marxer, who also chaired the conference, and Thomas Jordi, President of the Swiss-mem Dimensional Metrology Group, which acted as co-organiser, once again welcomed over 150 visitors, who were able to find out about new developments for practical applications.

Calibration and measurement uncertainties
The first speaker of the day was Dr. Rudolf Thal-mann from the Swiss Federal Institute of Metrology METAS. He spoke on the subject of "Verification and calibration of optical microcoordinate measuring instruments". Since work is being carried out in ever smaller dimensions, measuring instruments must also be able to keep pace. The challenge is that smaller and smaller calibration spheres are required for their calibration. In addition, the ISO standard 10360 Part 2 does not provide any specific information for the calibration of optical microcoordinate measuring machines. METAS has therefore developed, among other things, in collaboration with NTB and Saphirwerk, a new test piece with optically cooperative microspheres for checking imaging sensors. METAS also provides evaluation software which is supplied with each calibration. Various test series have shown that this test method can be used to determine standard-compliant deviations and parameters for corrections.

What are the causes of deviations in measurements? These do not always have to be found in the workpiece to be measured. Measurement uncertainties originating from the measuring device can also be responsible. The presentation by Dr. Daniel Heisselmann from the Physikalisch-Technische Bundesanstalt in Braunschweig dealt with how geometric deviations of the measuring devices - caused mechanically or thermally - influence the measurement results and how these can be taken into account in measurement series. He presented the measuring method using the virtual coordinate measuring machine VCMM. This measuring device works on the principle of a digital twin: a completely virtual device with ideal parameters is placed opposite the real measuring device. The measurements are performed on the real device and simulated on the digital twin (Monte Carlo simulation method). The real and simulated measurements are compared and evaluated. Based on the derived value tables, users can then take into account any measurement uncertainties in their own measurement series. However, such a determination of measurement uncertainties is still very time-consuming. Accordingly, there are currently only five DAkkS-accredited laboratories.

Precision in production
Not only are workpieces becoming smaller and smaller, but their geometries are also becoming more and more complex. Dipl.-Ing. Tobias Seyler from the Fraunhofer Institute for Physical Measurement Techniques IPM spoke about "High-precision 3D measurement of precision components with digital holography". He showed how this method can be used to measure turned parts to be manufactured with high precision and installed in diesel engines. The measuring arrangement - a system consisting of a camera, laser illumination and lenses - can also be installed directly in machine tools. The advantage of this is that the measurements can be carried out directly during the production process. However, the vibration-free positioning of the measuring system is a challenge. In the future, however, it should also be possible to carry out measurements in motion or even gear measurements.

Hanspeter Schlup from Hänggi Stanztechnik went even more into practice in his presentation "Coordinate measuring technology with multi-sensor technology in everyday production using the example of complex stamped parts". In particular, the speaker mentioned the measurement of injection hole discs for gasoline injection systems in engines. Since openings are punched at an angle (at an inclination of 27 degrees) in sheet metal, conventional optical measuring systems "from above" reach their limits. Therefore, a hole center is determined by calculation and then the measured hole pattern is compared with the data from the CAD. An optical as well as tactile (by means of a fiber probe) measurement of valve bodies was also demonstrated in the presentation. In particular, the avoidance of vibrations was discussed.

foray into the nano range
As the conference chairman, Dr. Michael Marxer, pointed out, the next two presentations left the micro range and moved into much smaller dimensions. Dr. Kai Schmidt from LT Ultra-Precision Technology GmbH spoke about "Measurement technology in the field of ultra-precision machining". In this environment, roughnesses in the range of 1 to 10 nanometers are nothing unusual. Applications can be found in metal optics, infrared optics, astronomical mirrors and even contact lenses. Accordingly, the challenge in the production processes is to minimize the manufacturing uncertainties and to optimize the surface quality and the shape accuracies. High-resolution measuring systems are used to measure machines and their components, products and the measuring technology itself. As an example, the speaker showed an application in so-called flycutting (single tooth milling).

There, an interferometer is located directly in the machine. In fact, in-situ measurements are the method of choice because otherwise components would have to be removed from the machine. A RhySearch research project involving the PWO is working on further developments in this field.

Prof. Dr. Eberhard Manske from the Technical University of Ilmenau dealt with the nanometer range in his presentation. It was about nano-positioning and nano-measuring machines, the development of which is in full swing. By 2025, dimensional measurements down to the subnanometer range should be possible. However, the technological challenges are not entirely trivial, especially in the 3D range. Here, positioning in the Z-axis is proving to be a problem. Specifically, this involves minimizing the so-called Abbe error and keeping the angular deviations of the axes as close to zero as possible. Furthermore, high-precision lasers, e.g. He-Ne fiber lasers, are necessary. The measurement setups themselves are also complex: The heat generation must be compensated by cooling systems and all heat-generating parts must be located as far away as possible from the measuring table. Ideally, the measurement is carried out in a vacuum chamber so that the laser can work as free of refraction as possible. Last but not least, the processing of the measurement data - high-precision images of 160 × 109 pixels comprise around 5 terabytes - requires a great deal of computer power.

Software off the shelf or not?
Prof. Dr. Heiko Wenzel-Schinzer from the Wenzel Group GmbH & Co. KG in his lecture. He gave some recommendations on what to look out for when investing in measuring equipment and measuring software. Depending on how a company is set up, the arguments are different: Do you purchase measuring devices and software from the machine manufacturer or from third-party suppliers? The contrast of "best-of-breed" vs. "all-in-one" is at the center of the considerations. In the case of software, for example, the connection to various CAD systems, machines, probes and sensors speak in favor of purchasing from a third-party supplier, while the support provided by the manufacturer speaks more in favor of an "all-in-one" solution. However, the latter can also lead to a lock-in effect and thus to a restriction of entrepreneurial flexibility.

Measurement technology for full speed
The conference concluded with a presentation on "Measurement technology in the Swiss high-speed train 'Giruno'" by Dipl.-Ing. Thomas Legler of Stadler Bussnang AG. The new train compositions that will be used on the new Gotthard route through the base tunnel are to be the "flagships" of the SBB. Accordingly, attention was paid to contemporary design and the fulfilment of the highest standards in their construction. What the passenger does not see, however, is the extensive sensor technology that had to be installed to ensure the operational safety of the train and ride comfort. The speaker specifically mentioned the pressure protection system. This ensures that the pressure fluctuations - caused, for example, by train crossings at high speeds in tunnels - do not mean any loss of comfort for the passengers.

The conference and the accompanying exhibition, in which many well-known manufacturers presented their measurement technology solutions, once again proved to be an opportunity for lively professional exchange and knowledge transfer between research and industry.