A method to quantify the drilling machinability of machinable ceramics from the viewpoint of preventing chipping

A method to quantify the drilling machinability of machinable ceramics is proposed from the viewpoint of preventing chipping in the rear side of the specimen, and its feasibility has been tested by using a 100 μm-diameter drill and two types of BN-containing machinable ceramics sintered by hot pressing in a laboratory-scale instrument. Based on the optical microscopy observation of the drilled holes at the varying feed velocity V (mm/min) at given rates of the spindle rotation R (10k–40k rpm), there exists a critical boundary in V–R space, above which chipping transpires and below which no chipping occurs. For the investigated specimens, the critical boundary is roughly linear in the investigated range of R. The position and shape (linear or non-linear) of the boundary may be dependent on material type as well as on the geometry of the drill. The fitted equation of the critical boundary in the V–R space may serve to quantify the drilling machinability of machinable ceramic materials.