Comparative analysis of ultrasonic drilling process using static and rotary tools

Ultrasonic drilling (USD) is widely used for drilling of glass. A comparative study of USD for 2.0 mm diameter hole in 3.0 mm thick soda lime glass has been performed using static (USD-ST) and rotary tool (USD-RT) of mild steel. To make the process more cost effective and productive, statistical models of material removal rate (MRR), hole circularity at entry and exit (HCentry, HCexit) and hole taper (Ht) have been developed using Box–Behnken approach of response surface methodology. The effect of abrasive size, frequency, ultrasonic power and tool rotational speed have been investigated and it was observed that abrasive size is the most significant factor to control MRR during USD-ST. In USD-RT, MRR, HCentry, HCexit and Ht are significantly affected by frequency. The combination of low frequency and small grain size produces high MRR in USD-RT. Increase of frequency from 22 to 24 kHz increases HCentry by 4.3% in USD-ST, whereas for rotating tool the increase of frequency from 22 to 25 kHz decreases the value by 2%. HCentry increases with the rise of frequency at constant ultrasonic power, USD-ST provides 7.14% more circular hole at entry compared to USD-RT for a combination of frequency and grit size. In multi-objective optimization of USD-ST, a desirability value of 0.8589 was obtained at ultrasonic power of 90%, frequency 23.47 kHz and abrasive grit no 60, whereas for USD-RT the desirability value of 0.8499 were correspondingly obtained at 78.48%, 25.5 kHz, 770.20 rpm and 60.