Tangential surface tension forces on a gas–liquid interface due to surface tension gradients have been implemented in the computational fluid dynamics (CFD) solver icoReactingMultiphaseInterFoam provided by the open-source software environment of OpenFOAM OpenCFD Ltd (ESI Group) OpenFOAM (online) https://www.openfoam.com/ (accessed 21 May 2021), so that the Marangoni effect can be taken into account, which is a main driver of heat transfer in additive manufacturing processes that comprise a melt pool. The solver surpasses the capabilities of similar open-source projects by considering a wide range of physical effects, e.g. multiple phases, melting, solidification, evaporation, and laser beam heat sources with an arbitrary intensity distribution and thus makes it an appealing framework, especially for the simulation of the laser powder bed fusion (LPBF) process. Herein, all relevant details and derivation considering the Marangoni effect are provided and validated by means of a benchmark problem by comparing the obtained results with the available analytical solution, with the results obtained from a commercial CFD tool and with the results of other authors. The modified solver is additionally validated by comparing the results from LPBF simulations with experimental data. Furthermore, the influence of the surface tension modeling on the mushy region is investigated. The optimized implementation shows improvements of the simulation results in both the dimensions and shape of the melt pool and the resulting surface with regard to the experimental data.

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.

The distribution of metalworking fluid (MWF) during a stationary variant of the vibration-assisted drilling using minimum quantity lubrication is analyzed. Two numerical approaches are employed to simulate the MWF transport: a droplet-based Eulerian-Lagrangian-Eulerian model for spray supply, and a volume-of-fluid method for jet-like MWF delivery. The simulations reveal distinct deposition patterns: spray supply results in a broad wetting of the bore ground from the drill center up to approximately three quarters of the radius, while jet supply leads to wetting of the outermost region. Drill rotation significantly affects jet-based wetting but has minor influence on spray supply. The findings highlight the complementary strengths of both supply strategies and point to an optimization goal for minimum quantity lubrication in vibration-assisted drilling: the tailored combination of spray and jet supply to target specific regions of the chisel edge and cutting edge for improved lubrication and tool performance.