Table 5.

Experimental factors for DOE.

Factors		Miniature Tube A *		Miniature Tube B **
		Low Level	High Level	Low Level	High Level
DOE Code		−1	+1	−1	+1
$X_1$	Pulse frequency, $f$ (Hz)	700	900	750	1000
$X_2$	Pulse width, $\tau$ (ms)	0.18	0.20	0.18	0.20
$X_3$	Peak power, $P_{\mathrm{peak}}$ (W)	160	180	160	180
$X_4$	Cutting speed, $v$ (mm/min)	250	1250	250	1250
$X_5$	Assist Gas $N_2$ Pressure, $P$ (Bar)	10.34	13.78	10.34	13.78

* Miniature Tube A: Annealed 1.8 mm OD and 110 µm wall thickness; ** Miniature Tube B: Hard Drawn 1.8 mm OD and 160 µm wall thickness.