Thin Wall Milling at a Maximized Axial Depth of Cut

The objective of the study was to determine the minimum thickness of a thin wall for milling at a maximized axial depth of cut, considering the effect of cutting speed on residual stress and post-machining distortion. Test samples were made of aluminum alloy 7050 T7451. The milling operation at a maximized axial depth of cut was performed during finishing. Response surface methodology was employed. Wall thickness and cutting speed were considered as two independent variables, while dependent variables were flatness deviation, wall thickness deviation, and residual stress. Flatness deviation and wall thickness deviation were used as the indicators of post-machining wall deformation and their measurements were made using a coordinate measuring machine. Residual stress was measured with an X-ray diffractometer. The obtained results showed that thin wall milling at a maximized axial depth of cut was feasible; nevertheless, for a wall thickness of t = 1 mm, the formation of considerable post-machining deformation was observed. Therefore, for milling with the employed axial depth of cut, the wall thickness should be t ≥ 1.5 mm. The highest strain and residual stress were observed at v_c ≈ 600 m/min; despite its subsequent decrease, the strain at v_c = 900 m/min was still higher than that at v_c = 300 m/min. The results also showed tensile stress to be dominant, while compressive stress only occurred at v_c = 300 m/min for wall thicknesses of t = 1.5 mm and t = 2 mm. The developed response surface quadratic models make it possible to predict the tested variables under similar conditions.