Developments in Ceramic Materials Research

Recent Advances in Rotary Ultrasonic Machining of Ceramics 43
Surface roughness (μm)
0.6
0.5
0.4
0.3
0.2
20 40 60 80
Air pressure (psi)
Figure 10. Effect of air pressure (in the intermittent coolant delivery mode) on surface roughness (after
[Li et al., 2005]).
4. RUM OF SILICON CARBIDE
Silicon carbide has superior properties such as high strength at elevated temperatures,
resistance to chemical degradation, wear resistance, low density, high stiffness, low
coefficient of thermal expansion, and superior creep resistance. The combination of these
properties makes them attractive in many engineering applications but difficult to machine
into desired geometry and surface quality [Datta et al., 2004; Yin et al., 2004].
Up to 2001, no attempt has been reported to machine silicon carbide by RUM.
4.1. Effects of Process Parameters on Cutting Force
The spindle speed has a significant effect on the cutting force when RUM of silicon
carbide. The cutting force increases as the spindle speed decreases, as shown in Figure 11(a).
The feedrate also has a significant effect on the cutting force. The cutting force increases
as the feedrate increases, as shown in Figure 11(b).
The ultrasonic vibration power and grit size do not affect the cutting force significantly.
Figure 12 shows the interactions effects of process parameters on cutting force in RUM
of silicon carbide. The interaction effect between spindle speed and feedrate is significant. As
shown in Figure 12(a), at the high level of feedrate, the change of spindle speed causes a
larger change in cutting force than at the low level of feedrate.
The interaction effect between ultrasonic vibration power and feedrate is significant. As
shown in Figure 12(b), at the high level of feedrate, the cutting force increases with the
change of vibration power from low level to high level, whereas, at the low level of feedrate,
the cutting force decreases with the change of vibration power from low level to high level.
The interaction effect between ultrasonic vibration power and grit size are significant. As
shown in Figure 12(c), at low level of grit size, the cutting force increases with change of