Numerical and experimental analysis of turbulent flow and heat transfer of minimum quantity lubrication in a turning process using discrete phase model

Abstract

Utilizing coolant strategies is vital in the manufacturing industry to reduce the tool wear and heat dissipation through the workpiece and cutting insert consequently maintaining workpiece mechanical properties and enhancing tool life. This becomes more significant when machining difficult to cut materials, such as Austempered Ductile Iron (ADI), where the amount of heat generated significantly affects the insert life and the mechanical properties of the workpiece. To the best of the authors knowledge there is a gap in the open literature on machining of ADI. An environmental friendly coolant strategy known as minimum quantity lubrication (MQL) uses small amounts of oil such as rapeseed or castor. A computational fluid dynamics (CFD) model was developed in this investigation using ANSYS Fluent to model the temperature profile and the oil droplet behavior in the cutting zone. The tool temperatures employed in the CFD model were generated by a numerical frictional model. The CFD model compared multiple coolant strategies (MQL, Dry, Flood, Aerosol Water) at different flow rates and inlet pressures to predict the thermal effects on the tool and to select optimum process parameters. Experimental tests, conducted using a CNC Lathe on Grade 2 (ADI), validated the numerical model's results for both dry, flood coolant and MQL with a 1.25%, 1.33% and 6.56% relative error respectively. The experimental results indicated that the measured flank wear of the cutting insert was 1.260 mm, 0.341 mm and 0.302 mm for the dry, flood and MQL coolants respectively.