Biomedical Engineering Reference
In-Depth Information
The effect of margin engagement is incorporated into the equation by
adding a spring constant, making the model a function of the depth of
penetration into the hole:
..
.
M
C
K
F
ext
r
..
r
.
rM
m
c
m
M
,
m
m
c
2
k
(1
k
z
)
m
c
K
rm
2
c
k
(1
k
z
)
m
where: m, c, k - mass, damping, stiffness, ξ - η - tool fixed frame
It has been experimentally confirmed that the drill natural frequency
increases with the depth of the hole. By showing that this doesn't happen when
machining a tube, it has been proven that the margin effect is the sole reason
of this frequency increase. Both of Dilley's papers have been aimed at
obtaining and constructing predictive models for engineers with the aim of
drilling process optimization.
2.2. Bending Model
Apart from the axial and torsional vibrations, bending vibrations have
been found to be common in the drilling process as well. It has been suggested
that bending vibrations have a more detrimental effect on hole quality due to
the fact that the hole form changes drastically with the effect of bending
(Figure 6).
Figure 6. Striations in the bottom of the hole caused by vibration of the drill: (a)
bending chatter; (b) torsional chatter [18].
