Biomedical Engineering Reference
In-Depth Information
t
d
(43)
cos(
)
sin
b
And so,
2
d
(44)
r
s
.
cos
sin
.
b
Equation 44 predicts that a positive chip radius will occur at negative rake
angles. The approximations considered in this model are appropriate when one
considers that the model assumes that a secondary shear plane exists and that
multiple primary shear planes exist at discrete intervals of time.
4.
E
XPERIMENTAL
P
ROCEDURES
4.1. Micromachining Apparatus
The machining of bovine femur was performed using a modified
machining centre. The micromachining centre was constructed to incorporate a
high-speed air turbine spindle rated to operate at 460,000 rpm under no load
conditions. When operating at relatively deep depths of cut, the speed of the
spindle decreases to approximately 320,000 rpm. The table of the machine tool
was configured to move in x-y-z co-ordinates by attaching a cross-slide
powered by a d.c. motor, in all three principal axes. Each motor was controlled
by a Motionmaster
TM
controller with a resolution as low as 500 nm. The
cutting tools used were coated with diamond. The bio-machining centre is
shown in Figure 2. The bovine femur samples were machined at various
depths of cut at high speed and were machined in an aqueous saline solution.
The cutting tools were inspected at the end of all machining experiments using
an Environmental Scanning Electron Microscope. The measured spindle speed
was 320,000 rpm during the machining experiments. The depth of cut ranged
between 50 m and 100 m for all machining experiments. The machining
feed rate was conducted at 5 mm/s (0.3 m/min). The microscale cutting tool
used was 700 m in diameter (microscale) and was associated with a cutting
speed of 117 m/min and a machining feed rate of 0.3 m/min. The results of the
experimental procedures are shown in Table 1. The machined chips were
examined in an environmental scanning electron microscope where the
