A mechanistic model for prediction of exit-chipping width in rotary ultrasonic drilling of sapphire

Exit-chipping of the drilled hole produced in rotary ultrasonic drilling (RUD) process significantly influences the assembly accuracy and technological performance of the sapphire components. To reduce or eliminate the exit-chipping of the RUD hole, an efficient prediction model should be established to facilitate the optimization of the drilling parameters. Based on the probability statistics on the abrasive number and the associated cutting depths, the present investigation intrinsically related the cutting force F average of the diamond tool to the maximum cutting depth δ_max^max of the maximum abrasive on the tool end-face. Also, the essential correlation between δ_max^max and the maximum depth SSD _max^max of the subsurface cracks on the machined surface was developed. Subsequently, a mechanistic method for the prediction of exit-chipping width b chipping was proposed with respect to the activation effects of the maximum equivalent moment M max on SSD _max^max at the margin of the machined surface. Ultimately, the theoretical prediction was validated by the experimental measurements of b chipping from the literature, revealing the acceptable consistency.