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In any machining operations, quality is the important conflicting objective. In order to give assurance for high productivity, some extent of quality has to be compromised. Similarly productivity will be decreased while the efforts are channelized to enhance quality. In this study, the experiments were carried out on a CNC vertical machining center to perform 10mm slots on Al 6351-T6 alloy work piece by K10 carbide, four flute end milling cutter. Furthermore the cutting speed, the feed rate and depth of cut are regulated in this experiment. Each experiment was conducted three times and the surface roughness and chip thickness was measured by a surface analyser of Surf Test-211 series (Mitutoyo) and Digital Micrometer (Mitutoyo) with least count 0.001 mm respectively. The selection of orthogonal array is concerned with the total degree of freedom of process parameters. Total degree of freedom (DOF) associated with three parameters is equal to 6 (3X2).The degree of freedom for the orthogonal array should be greater than or at least equal to that of the process parameters. There by, a L9 orthogonal array having degree of freedom equal to (9-1= 8) 8 has been considered .But in present case each experiment is conducted three times, therefore total degree of freedom (9X3-1=26) 26 has been considered. Finally, confirmation test (ANOVA) was conducted to compare the predicted values with the experimental values confirm its effectiveness in the analysis of surface roughness and chip thickness. Surface Roughness (Ra) is greatly reduced from 0.145 µm to 0.1326 µm and the chip thickness (Ct) is slightly reduced from 0.1 mm to 0.085 mm, because of in the measurement collected the chips after machining of every experiment, from that randomly selected a few chips for measuring of their thickness using digital micrometer.
