Developments in Ceramic Materials Research

40
Z. C. Li, Z. J. Pei and C. Treadwell
2.3. Practical Ways to Reduce Edge Chipping
The cutting force is related to RUM process parameters (including spindle speed,
feedrate, and ultrasonic vibration power, etc.). It also has a correlation with the edge chipping
thickness. It is reported that larger edge chipping is almost always accompanied by a higher
cutting force as shown in Figure 5 [Jiao et al., 2005]. Therefore, any ways to reduce the
cutting force will also reduce the edge chipping. Since higher spindle speed and lower
feedrate result in smaller cutting force [Jiao et al., 2005], higher spindle speed and lower
feedrate should be used in order to reduce edge chipping thickness.
Chipping thickness (mm)
1.2
1
0.8
0.6
0.4
400 800
Cutting force (N )
Figure 5. Relationship between the cutting force and edge chipping thickness (after [Jiao et al., 2005).
Based upon finite element analysis and experimental verifications, it has been found that
the maximum values of the maximum normal stress and von Mises stress (in the edge
chipping initiation area) decrease significantly as the support length increases [Li et al.,
2005]. The smaller the maximum values, the deeper the tool can drill into the workpiece
without edge chipping. Therefore, another practical way to reduce edge chipping thickness is
to increase the support length when RUM of alumina [Li et al., 2005].
3. COOLANT
Coolant is an important factor in RUM. It is pumped through the core of the drill,
washing away the swarf, preventing jamming of the drill, and keeping the drill cool [Pei et al.,
1995 a ]. Without coolant, the debris will stick on the tool and workpiece surface, causing the
feed speed to slow down, and the tool may be burnt or even completely ruined by high
temperatures in the cutting zone [Hu et al., 2003].
3.1. Effects of Coolant Type
Coolant type (Coolant type A: Water-based coolant; Coolant type B: Synthetic coolant;
and Coolant type C: Tap water) has significant effects on the cutting force [Hu et al., 2003].