OBRABOTKAMETALLOV TECHNOLOGY Vol. 26 No. 4 2024 A constant burnishing depth of 0.5 mm was maintained while varying the feed, cutting speed and the number of passes in the experiments without coolant and with nanofl uid as coolant under MQL conditions. Alumina nanoparticles (Al2O3) were combined with a vegetable-based sunfl ower oil base fl uid to create the nanofl uid. Surface roughness, microhardness and roundness error, three main characteristics that contribute to the impact of stability performance, were studied using the design of experiments (DOE) method. All responses were analyzed and empirical models were developed using the central composite design (CCD). The experiments were designed using the central composite rotatable design (CCRD) test matrix, which has an alpha value of 1.6817. Five levels were used to vary each numerical parameter: center point, plus and minus 1 (factorial points) and plus and minus alpha (axial points). In this work, twenty roller burnishing tests were conducted under NFMQL and dry conditions with diff erent process parameters to construct models of surface roughness, microhardness and roundness error. Table 2 lists the coded levels along with the corresponding actual cutting parameter values. Ta b l e 2 Coded levels and corresponding actual cutting parameters Parameters Levels for alpha value −1.6817 −1 0 +1 +1.6817 Cutting speed (V) (rpm) 100 200 300 400 500 Feed (f) (mm/rev) 0.1 0.15 0.2 0.25 0.3 Number of passes (N) 0.5 1 1.5 2 2.5 Taylor Hobson Talysurf, Surtronic Duo and an off -line surface roughness measuring device were used to determine the average values of surface roughness. The surface roughness was measured at three equally spaced points around the perimeter of the workpiece to obtain a statistically signifi cant value. The surface quality assessment was performed accurately and consistently using this approach. A bridge type CMM (Manufacturer: Zeiss, Model: Contura, Range: 1,200×800×800 mm) was used to test the roundness. Geometrical errors were determined by measuring the roundness in twelve parts of a calibrated area using a millesimal dial indicator having a measuring range of 12.5 mm, a scale division value of 0.001 mm and a maximum permissible error (MPE) of 4 μm. Additionally, a Vickers microhardness tester was used to evaluate the microhardness using a 136° diamond indenter at 100 grams and a 20-second dwell time. Using surface roughness, microhardness tests and roundness measures together allowed a thorough examination of the workpiece properties. Results and Discussion In this section, the impact of roller burnishing process parameters on the process responses under dry and NFMQL cutting conditions is discussed based on the established regression equations. The curves showing the diff erent responses are plotted by varying one of the input parameters while keeping the other parameters constant in order to understand the physics of the process and the interaction eff ects of the cutting parameters on the diff erent responses. It also gives the contribution of the cutting parameters to the diff erent responses. Finally, the optimization of the process responses in roller burnishing of Al6061-T6 alloy is considered using the desirability function method. The cutting speed, feed and number of passes (input parameters) were varied during the experiments. Table 3 shows the experimental matrix and the results of the largest roundness error (roundness error), microhardness and surface roughness in roller burnishing of Al6061-T6 alloy under dry and NFMQL cutting
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