Modification of oscillation modes in low frequency vibration assisted drilling

Low frequency vibration assisted drilling (LFVAD) is applied to generate small chip sizes in order to avoid chip accumulation in drilling processes. In contrast to ultrasonic assisted drilling the oscillations are characterized by relatively high amplitudes of up to 200 µm at significantly lower maximum frequencies of around 300 Hz. This enables an interrupted cut which leads to a chip breakage, almost independent of the mechanical properties of the workpiece material. However, significantly higher cutting forces are generated in comparison to conventional drilling processes (at the same material removal rate). In the present study the shape of the vibration oscillations (which is usually sinusoidal) was modified in order to affect the uncut chip shapes. The geometrical cutting conditions have been visualized using a kinematic cutting model. Due to the modification of the oscillation mode the maximum cutting forces could be decreased by at least 13 %. Furthermore, the cutting force progression during the generation of each pair of chips (two fluted cutter) could be improved regarding a smoother slope of the forces. As a consequence, “shock loads” to the tools are avoided and higher values of the axial feed are enabled, which contributes to a raise of productivity in LFVAD.