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Recently, vibration assistance has been mainly applied to feed and cross-feed directions for milling processes. This paper investigates the effect of ultrasonic vibration assistance in tooling’s axial direction for improvement of machined surface with reduction of chatter marks. With the designed ultrasonic vibration assisted milling process with 39.7 kHz and a few micro-meter amplitudes, workpiece vibrates along tooling’s axial direction while various cutting speeds and feed rates are applied. In addition to a cutter rotation motion, the axial directional vibration assistance acts as additional cutting motion which further reduces the leftover surface error. Experimental results validate that surface roughness can be improved with the reduced chatter marks through the axial directional vibration assistance for the tested conditions. Finally, process simulation demonstrates that milling stability can be enhanced with the tooling’s ultrasonic vibration assistance, which explains the experimental phenomenon of the chatter marks reduction of the mesoscale milling processes.

In the conventional use of vibration assisted machining, vibratory motion is mostly applied to the continuous machining processes such as turning where the cutting speed is much lower than the vibration speed. Even the recent articles on vibration assisted milling processes are also quite limited to low spindle speed less than 3k RPM. This study investigates vibration assistance that is applied to the workpiece in a high speed micro/meso-scale intermittent milling system where the cutting speed is much higher than the vibration speed. In addition to this, the vibration effect is analyzed considering feed and cross-feed directional application separately, which gives an idea of a right vibration assistance direction for surface quality improvement. To validate this, a one-directional ultrasonic vibration assisted milling system with ultrasonic frequency at 40 kHz and with amplitudes of a few microns is designed and its effect on the machined surface quality is investigated at high spindle RPMs over 15k. As a result, cusp heights are found to be reduced with ultrasonic vibratory motion of cutting edge in high cutting speed. Furthermore, the machined surface quality clearly tells that feed directional vibration assistance is able to generate better surface quality with reduced wavy burrs than cross-feed directional vibration assistance.

Chatter has been a problem in CNC machining process especially during pocket milling process using an end mill with low stiffness. Since an iterative time-domain chatter solution consumes a computing time along tool paths, a fast chatter prediction algorithm for pocket milling process is required by machine shop-floor for detecting chatter prior to real machining process. This paper proposes the systematic solution based on integration of a stability law in frequency domain with geometric information of material removal for a given set of tool paths. The change of immersion angle and spindle speed determines the variation of the stable cutting depth along cornering cut path. This proposed solution transforms the milling stability theory toward the practical methodology for the stability prediction over the NC pocket milling.