Dynamic model of ultrasonic assisted milling for aluminum alloy with Variable helix angle milling cutter and chatter suppression

With the growing emphasis on lightweighting in new energy vehicles, the demand for machining thin-walled aluminum components such as automotive frames has increased significantly. However, the combination of high-strength aluminum alloys and thin-walled geometries makes these components highly susceptible to chatter and deformation during milling. Although ultrasonic-assisted machining and variable helix angle tools have demonstrated certain effectiveness in suppressing chatter, issues such as localized stress concentration and instability in flexible regions of thin-walled parts still arise under extreme conditions. Currently, research on ultrasonic-assisted variable helix angle milling remains insufficient, and there is a lack of systematic stability analysis methods for predicting the critical depth of cut. To address this gap, a dynamic model for ultrasonic-assisted variable helix angle milling is established in this study. Firstly, an instantaneous milling force model is developed, taking into account the time-varying cutting thickness induced by ultrasonic tool motion and the variable time delays between adjacent cutting edges caused by non-uniform helix angles. Secondly, by treating the thin-walled workpiece and tool as flexible bodies and integrating the dynamic response of the machine tool system, a modal parameter-based milling dynamics model is constructed. The limiting depth of cut is determined using a closed-loop control strategy. Numerical simulations demonstrate that the proposed method achieves significantly higher stability than conventional milling and standard ultrasonic-assisted milling across different spindle speeds. Experimental validation under spindle speeds of 1500 rpm, 2000 rpm, and 2500 rpm with cutting depths of 0.2 mm and 0.3 mm confirms that the synergistic effect of stiffness enhancement from ultrasonic excitation and the unique geometric design of variable helix angle tools leads to superior chatter suppression in thin-walled workpiece machining, particularly under challenging conditions of 2500 rpm and 0.3 mm depth of cut.