Tracking down wear and tear

The damage caused by wear and tear in industrialized countries amounts to around seven percent of the gross national product every year. The following applies here: The earlier a critical condition is detected, the smaller the impact – both in terms of safety and economic efficiency. This is precisely what the scientists and students at the Chair of General Mechanical Engineering at the University of Leoben / Styria are researching. The focus of the research, which is often also carried out on behalf of international industrial cooperations, is on machines from the mobility and energy sectors and their mechanical components. In order to assess and calculate component wear in advance, the (prospective) engineers carry out damage analyses of components subjected to tribological stress on a model scale – for example, gears, valve train systems, crankshafts, connecting rods, cylinder tracks or piston pins. A second focus of the chair is the fatigue strength of components. For this purpose, their fatigue behavior is primarily investigated using small test objects. "To test the fatigue strength, for example, we carry out elaborate tests with vibration testing machines," explains Dr. mont. Michael Pusterhofer, senior scientist at the chair. "This involves designing a component, such as a connecting rod or crankshaft, for operation and putting it through its paces by pulling and pushing." The aim is to optimize the technical systems, whether in terms of load capacity, wear behavior, efficiency or manufacturing costs.

Testing the samples with the MarSurf VD 140

After the test series, the samples are examined in detail. An important tool is the MarSurf VD 140, which has been supporting the work in the laboratory for about a year. The roughness and contour measuring station with 140 mm scanning distance offers high speed and a lot of flexibility. This is particularly evident in the large measuring range, a workpiece weight of max. 80 kilos and a very simple clamping system that allows workpieces to be positioned safely, quickly and correctly. "The latter also supports the high repeatability and accuracy of the measurements, and with the fast CNC axes and MarWin software, the process can also be automated," explains Michael Parzer, Field Sales Engineer at Mahr Austria GmbH. The measurements with the MarSurf VD 140 are mainly taken by students from the fourth semester onwards, as well as dissertation students, according to Pusterhofer. The measuring range at the institute is 70 millimeters for contour and about half a millimeter for roughness. Because the measuring device can be automated, up to 100 samples can be measured in a single run and used to develop questions – for example, for later theses. Multiple measurements of 30 to 40 profiles in parallel are possible with the tactile all-rounder from Mahr, "the machine does this automatically, for example at intervals of 0.5 millimeters each time. The scatter with the device is extremely low," emphasizes the engineer. Software written in-house then creates a 3D surface from the measurements, allowing the wear plane to be identified.

Tactile vs. optical

The measurement results are finally transferred to real components using various methods and models. As Pusterhofer reports, optical 3D measurement is also used at the institute. "With a 3D device, the measurement tasks described above can also be solved, but such extensive measurements are often not necessary for all problems. With a confocal microscope, one would need about eight hours for this task – with the tactile VD 140, on the other hand, only five minutes at a peak resolution. There would be no better quality assurance for this case," summarizes the researcher. He is highly satisfied with the Mahr device because it is ideally suited for fast and recurring measurement tasks. In the meantime, this is also appreciated by colleagues from other departments who like to use the device, for example to check the thermal expansion of layered composites or to investigate the influence of different casting parameters on the surface morphology.

Direct service due to close location

The device has now been in operation at the institute for about a year and thus expands the large equipment pool at the Chair of General Mechanical Engineering. As Pusterhofer reports, the machinery was expanded in 2021, and he himself had strongly advocated for a tactile device. "We did an internal award process, which Mahr won. In addition to the very high accuracies, the price also convinced us. And what we also benefit from is the proximity to the Mahr site, which makes direct service possible," explains the engineer. Michael Parzer was always available and provided great support, he says. "The VD 140 works damn well, and I'm very, very happy with the purchase, as are my colleagues." Pusterhofer and a technician from the institute completed a two-day training course at Mahr Austria and have since taken over passing on the knowledge to colleagues and students at the institute. Equipped with this powerful 2D technology, the research team can now fully concentrate on its core competencies and specifically counter wear and material fatigue. And ultimately also drive forward the energy and mobility revolution.