Developments in Ceramic Materials Research

Recent Advances in Rotary Ultrasonic Machining of Ceramics 41
The cutting force with the water-based coolant is much lower than those with the synthetic
coolant and tap water. The difference of surface roughness between these three coolant types
is not statistically significant.
3.2. Effects of Coolant Pressure
Coolant pressure (in continuous coolant delivery mode) has a significant effect on hole
surface roughness as shown in Figure 6. As the coolant pressure increases, the hole surface
roughness decreases. The hole surface roughness is improved because the higher coolant
output pressure would wash away more micro swarfs, which had a negative effect on the
machined surface roughness [Hu et al., 2003].
Surface roughness (μm)
1.5
1.3
1.1
0.9
0.7
0.5
20 25 30 35 40
Coolant pressure (psi)
Figure 6. Effect of coolant pressure (in the continuous coolant delivery mode) on surface roughness
(after [Hu et al., 2003]).
3.3. Effects of Coolant Delivery Mode
In RUM, the coolant can be delivered to the cutting zone in at least two modes:
continuous and intermittent. The continuous mode, which delivers the coolant at a constant
pressure, as shown in Figure 7(a), can be realized with the regular centrifugal pump. In the
intermittent mode, the coolant pressure will alter between on and off status, as shown in
Figure 7(b).
The intermittent coolant delivery mode has been set up approximately using an airoperated
double diaphragm pump (AODDP) [Li et al., 2005]. Figure 8 shows the actual
coolant delivery mode when using AODDP. The coolant pressure in this mode is adjusted by
changing the air pressure.
At a similar coolant pressure level, compared to the continuous mode, the surface
roughness on the machined hole surface can be much improved using the intermittent mode,
as shown in Figure 9. When using the intermittent coolant delivery mode, the surface