For industrial grinding processes, the workpiece cooling by metalworking fluids, which strongly influences the workpiece surface layer quality, is not yet fully understood. This leads to high efforts for the empirical determination of suitable cooling parameters, increasing the part manufacturing costs. To close the knowledge gap, a measurement method for the metalworking fluid flow field near the grinding wheel is desired. However, the varying curved surfaces of the liquid phase result in unpredictable light deflections and reflections, which impede optical flow measurements. In order to investigate the yet unknown optical measurement capabilities achievable under these conditions, shadowgraphy in combination with a pattern correlation technique and particle image velocimetry (PIV) are applied in a grinding machine. The results show that particle image velocimetry enables flow field measurements inside the laminar metalworking fluid jet, whereby the shadowgraph imaging velocimetry complements these measurements since it is in particular suitable for regions with spray-like flow regimes. As a conclusion, optical flow field measurements of the metalworking fluid flow in a running grinding machine are shown to be feasible.

The thermal load that occurs during grinding can be reduced with the aid of an optimized metalworking fluid (MWF) supply. In previous work, mainly the free jet was considered for the determination of the conditions required for an optimized MWF supply. An investigation of the interaction area between the MWF and the grinding wheel has not yet been carried out due to the lack of suitable measurement techniques. In the presented work, both the free jet and the interaction area are analyzed with the aid of new metrological analysis and evaluation methods based on high-speed records (shadowgraphy and shadogram imaging velocimetry) in order to assess the free jet geometry and velocities, as well as the velocity distribution and the MWF amount in the interaction area. Using this approach, the following main results were derived: (1) The free jet velocity remains approximately constant in a defined free jet cross-section even at high distances from the nozzle outlet. (2) The velocity distribution in the interaction area is mainly influenced by the flow rate. (3) A new image parameter (black pixel fraction) was derived for the evaluation of the MWF supply to the contact zone.

Zusammenfassung Kühlschmierstoff (KSS)-strömungen werden in Schleifprozessen eingesetzt, um Schleifbrand am Werkstück zu verhindern. Bislang wurde die KSS-Zufuhr heuristisch optimiert.Um eine zielgerichtete KSS-Strömungsoptimierung zu ermöglichen, wird erstmals die optische schleifscheibennahe Messung von KSS-Strömungsfeldern mittels Particle Image Velocimetry (PIV) und durch Nachverfolgung von Mustern in Schattenwurfbildern untersucht. Als erster Schritt wird an der rotierenden Schleifscheibe, jedoch ohne die Bearbeitung eines Werkstücks, gemessen. Beide Messmethoden liefern vergleichbare Ergebnisse, wobei nahe der Schleifscheibenoberfläche mittels PIV Messwerte mit geringerer Messunsicherheit erzielt werden. Mit dem verwendeten Messaufbau lassen sich mittels PIV Geschwindigkeiten in einem Abstand zwischen 0 cm bis 2 cm und mittels Schattenwurf zwischen 0 cm bis 5 cm zur Schleifscheibenoberfläche messen. Im Ergebnis konnte erstmals der für die Kühlleistung relevante Parameter des Geschwindigkeitsverhältnisses zwischen KSS-Anströmung und Schleifscheibenoberflächengeschwindigkeit in situ gemessen werden. Es wurde festgestellt, dass eine aus der Literatur bekannte Verringerung der Kühleffizienz ab einem Geschwindigkeitsverhältnis von 0,8 mit einem Abprallen des KSS-Strahls beim Auftreffen auf die Schleifscheibe korreliert. In zukünftigen Untersuchungen ist zu klären, wie sich die hier gewonnenen Erkenntnisse zur Messfähigkeit und zum Strömungsverhalten auf den Schleifprozess mit Werkstück übertragen lassen.

Since the cooling mechanism of industrial grinding is not yet fully understood, a measurement of the coolant liquid flow field near the grinding wheel is desired. However, the curved surfaces of the liquid phase result in unpredictable light deflections and reflections, which impedes optical flow measurements. In order to obtain qualitative and quantitative information regarding the flow velocity field of the coolant liquid, shadowgraphy in combination with a pattern correlation technique as well as particle image velocimetry are applied in a grinding machine and studied with respect to their measurement capabilities. Particle image velocimetry enables flow measurements inside the laminar coolant jet, whereby the shadowgraph imaging velocimetry complements these measurements and is in particular suitable for spray-like flow regimes. As a result, optical flow field measurements of the coolant flow in a grinding machine are shown to be feasible, which is required to understand the flow mechanisms that affect the grinding cooling process.

Article Frontmatter was published on December 1, 2021 in the journal tm - Technisches Messen (volume 88, issue 12).