فهرست نشریات علمی دسترسی آزاد ایران

Precision drilling is essential for achieving dimensional and geometric tolerances in high-hardness materials, where conventional drilling (CD) encounters challenges due to elevated cutting forces and inadequate chip evacuation. This study investigates the effects of tool rotational speed (255–1500 rpm) and feed rate (0.08–0.15 mm/rev) on hole circularity and cylindricity in alloy steel 1.7225 (Mo40) with hardness levels ranging from 20 to 50 RC, comparing CD with Ultrasonic-Assisted Drilling (UAD). UAD superimposes high-frequency, low-amplitude longitudinal vibrations on the tool to enhance precision in hardened workpieces. A multilevel factorial design was conducted and analyzed in Minitab using ANOVA, yielding an R² of 99.98%, confirming robust statistical validity. UAD significantly improved circularity with increasing hardness—by 62.5% at 20 RC, 72.1% at 35 RC, and 80.1% at 50 RC. These improvements result from vibration-induced reductions in cutting forces, minimized tool wear, and optimized chip evacuation that mitigate deformation. Cylindricity improved as hardness increased from 20 to 50 RC; spindle speeds of 255–950 rpm initially degraded it due to thermal effects but recovered slightly at 1500 rpm, while higher feed rates (0.08–0.15 mm/rev) enhanced stability. Optimization identified the best performance at 1500 rpm, 50 RC, and 0.08 mm/rev, achieving a circularity of 0.000102 mm and a cylindricity of 0.0111967 mm. UAD reduced cylindricity deviations to 0.02–0.14 mm (compared with 0.12–0.22 mm in CD), confirming its superiority for precision applications involving high-hardness alloys.