Surface properties in turning of aluminum alloys applying different cooling strategies

The generation of heat during chip removal can affect the residual-stress state and thus the performance of machined parts. For this reason, the aim of this study is to determine and modify the process temperatures in turning of the aluminum alloy EN AW-2017. Therefore, the influence of dry machining, cold-air cooling (CAC), flood lubrication (FL), and minimum quantity lubrication (MQL) is investigated by measuring the temperature with a tool–workpiece thermocouple. In regard to the correlation between the cutting power and the temperature, the cutting speed is varied in the range of 50 m/min to 550 m/min while the depth of cut and the feed are kept constant. The results show that the contact area between the tool and the workpiece has to be considered for the evaluation of the measured temperature as it represents an average value over the tool–workpiece interface area. Since there is only a slight decrease of the process forces with increasing cutting speed, the modification of the surface properties has to be mainly influenced by the change of temperatures. Thus, process cooling entails a reduction of tensile residual stresses as a consequence of a decrease of the cutting temperature. Furthermore, the surface roughness values (Ra, Rz) are smaller when applying cooling lubricant. In contrast for low cutting speeds, the intensified built-up edge (BUE) formation leads to compressive residual stresses but deteriorates the surface quality. Hence, the combination of an effective cooling strategy and the temperature measurement allows for the generation and monitoring of advantageous surface properties during machining.