Experimental investigation on longitudinal-bending composite ultrasonic vibration-assisted milling of C194 copper alloy

Copper is an important engineering material for precision micro-devices, due to its superior electrical/thermal conductivity and ductility. However, its high plasticity and toughness introduce significant challenges in traditional milling, including work hardening, tool adhesion, burr accumulation, and poor surface finish, which limit further improvement of machined surface quality. Ultrasonic vibration-assisted machining (UVAM) can improve surface integrity of difficult-to-machine materials by introducing high-frequency intermittent cutting, which reduces cutting force, heat accumulation, and tool wear. Compared with one-dimensional longitudinal or two-dimensional longitudinal-torsional vibration, the longitudinal-bending composite vibration enables independent adjustment of amplitude and phase via two separate ultrasonic signals, thus offering greater flexibility under varying machining conditions. Nevertheless, the research on longitudinal-bending UVAM of copper remains scarce. In this study, we experimentally investigated longitudinal-bending composite vibration-assisted milling (LBVAM) of copper. Burr morphology, surface roughness, and microstructure were systematically compared among conventional milling, longitudinal vibration-assisted milling, and LBVAM. The influences of vibration amplitude and spindle speed on surface quality were also examined. Experiments were conducted using a 1 mm diameter four-edge tungsten steel micro-milling cutter, with amplitudes ranging from 1 to 5 μm and spindle speeds of 1000–3000 r/min. Our results showed that longitudinal-bending composite vibration significantly suppresses burr formation and reduces surface roughness by 40.27% compared to conventional milling, and by 23.44% compared to single longitudinal vibration-assisted milling. Furthermore, surface roughness further decreases with increased amplitude, reaching a minimum of 129 nm at 5 μm, accompanied by a uniform “fish-scale” microstructure. The best surface quality was achieved at 2000 r/min, whereas speeds that were too high or too low caused disordered surface texture or secondary damage. This work confirms the feasibility and advantages of longitudinal-bending UVAM in enhancing machined surface quality of copper, thus providing valuable processing support for the microfabrication of high-precision copper components in precision electronic applications.