Vibration Assisted Drilling of Aerospace Materials

Insufficient chip extraction often leads to disruptions of automated drilling processes and will have a negative impact on the surface qualities. One opportunity to avoid chip accumulation is based on a kinematically enforced chip breakage caused by sinusoidal axial oscillations of the drilling tool. Recent investigations have shown that the quality of chip extraction is, amongst others, considerably depending on the chip shape and mass which are defined by the cutting parameters feed, amplitude and frequency. So far only mechanical systems in the form of tool holders have been available on the market, which are restricted to a fixed frequency (oscillation frequency is coupled to the spindle speed). In the present study a spindle with magnetic bearings was used which allows to adjust the oscillation frequency independent of the spindle speed and therefore enables all opportunities to affect the generated chip shapes. Based on a kinematic model of the uncut chip shape, cutting parameters have been selected specifically, in order to achieve appropriate chip extraction. It was shown, that the number of oscillations per revolution does have a major influence on the resulting chip shape and the corresponding quality of chip extraction as well as the resulting borehole quality.