Developments in Ceramic Materials Research

38
Z. C. Li, Z. J. Pei and C. Treadwell
2. EDGE CHIPPING
2.1. Edge Chipping Phenomenon in RUM
Figure 2 illustrates the edge chipping phenomenon in the RUM process. RUM is a core
drilling process and produces two pieces as shown in Figure 2(a). One piece is the machined
part with the desired hole, the other is a rod (or slug) removed from the workpiece. Figure
2(b) shows the side view and top view of the machined rod. In RUM, when the cutting tool
nearly drills through the workpiece, the rod breaks off from the workpiece, causing the edge
chipping around the hole exit edge.
The edge chipping in a machined ceramic component not only compromises geometric
accuracy, but also causes possible failure of the component during service [Ng et al., 1996;
Yoshifumi et al., 1995]. Generally, edge chipping is not acceptable on finished products, and
has to be machined off by other processes after the RUM operation. The larger the edge
chipping, the higher the total machining cost.
Machined hole
Machined rod
Edge chipping thickness
Edge chipping size
(a) Two pieces after RUM (b) Side and top view of machined rod
with edge chipping
Figure 2. Illustration of edge chipping phenomenon in RUM (after [Jiao et al., 2005]).
2.2. Effects of Process Parameters on Edge Chipping
The spindle speed is the rotational speed of the core drill. It has a significant effect on
edge chipping thickness when RUM of alumina [Jiao et al., 2005]. The edge chipping
thickness decreases as spindle speed increases, as shown in Figure 3(a).
The feedrate is the rate at which the core drill drills into the workpiece. It affects the edge
chipping thickness significantly [Jiao et al., 2005]. The edge chipping thickness decreases as
feedrate decreases, as shown in Figure 3(b).