Metalworking operations rely on the successful application of metalworking fluids (MWFs) for effective and efficient operation. Processes such as grinding or drilling often require the use of MWFs for cooling, lubrication, and chip removal. Electrochemical machining processes require electrolyte flow to operate. However, in those machining operations, a fundamental understanding of the mode of action of MWF is lacking due to the unknown flow dynamics and its interaction with the material removal during the process. Important information on the behaviour of MWFs during machining can be obtained from specific experimental flow visualisation studies. In this paper, promising flow visualisation analysis techniques applied to exemplary machining processes (grinding, sawing, drilling, and electrochemical machining) are presented and discussed. Shadowgraph imaging and flow measurements, e.g., particle image velocimetry, allow the identification of typical flow and MWF operating regimes in the different machining processes. Based on the identification of these regimes, efficient machining parameters and MWF applications can be derived. In addition, detailed experimental analyses of MWFs provide essential data for the input and validation of model development and numerical simulations within the Priority Programme SPP 2231 FluSimPro.

Minimum quantity lubrication (MQL) technologies possess great potential for improving the sustainability of manufacturing processes, which can reduce the absolute quantity of metalworking fluid (MWF) and also enable near-dry chips that are easier to recycle. During drilling in particular, the MWF is transported to the contact zone through internal cooling channels of the drilling tool. The MWF supply and its associated flow behaviour in the transfer from the outlet of the cooling channels to the contact zone have not been sufficiently investigated yet. Great potential is seen in the proper delivery of the MQL into the contact zone. This work aims to visualize and quantify the cooling lubricant supply into the cutting zone using the MQL technique. The visualization of the MQL application is made possible by high-speed shadowgraphic imaging. Detailed image processing is used to evaluate the resulting images. The developed evaluation routine allows for the assessment of the impact of the main process parameters such as the varying pressure of the aerosol generator and the cooling channel diameter. It is found that the oil leaves the cooling channels at the tip of the drill bit in the form of ligaments. An increase in pressure and cooling channel diameter leads to an increase in the frequency of oil ligament separation. Three main flow regimes are identified with different separation frequencies. Low inlet pressures result in intermittently dispersed droplets. The most upper pressure levels lead to an almost continuous dispersion of the oil. At the same time, the air and oil mass flow rates also increase.

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.

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.

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