advances in numerical modeling of manufacturing processes

TRANS. INDIAN INST. MET., VOL. 57, NO. 4, AUGUST 2004
contact with workpiece due to the applied water
coolant on the rake face.
b. Heat exchange with air condition is assigned to
the rest of the nodes on the tool surface. If a
specific node is in touch with the workpiece
during the cutting cycle, heat transfer calculation
will be automatically conducted by the program.
Otherwise, the heat exchange with air calculation
will be performed.
Variables
Depth of cut
Rake angle
Relief angle
Tip radius
Coating thickness
Cutting speed
Table 1
CUTTING CONDITIONS
Value
0.35 mm
5 o
6 o
0.005 mm
0.05 mm
12 m/min, 60 m/min, 120
m/min., 240 m/min., 600
m/min.
Table 2
TOOL MATERIAL PROPERTIES
Materials Tool substrate Coating
Elastic modulus 558 (GPa) 672 (GPa)
The experiments were conducted on a CNC Turning
Center at cutting speeds of 60, 120 and 240 m/min,
feeds of 0.127 and 0.35 mm/rev and depth of cut of
2.54 mm. The cutting forces were measured with a
Kistler dynamometer, Type 9121. Workpiece was a
Ti-6Al-4V annealed rod. The results of these
experiments and the model predictions are presented
in Fig. 11. The difference in force magnitudes
between those measured experimentally and predicted
is less than 5% for both the feeds.
Figure 12 compares of chip morphology measured
and predicted by the numerical model. The shape
and the pitch of the serrated chip segments in these
figures show good geometric resemblance as well as
reasonably close dimensional attributes. It should be
noted that the original chip collected from the turning
test was a curled chip. The collected chip was then
straightened and mounted. After etching and
polishing, the chip morphology shown in Fig. 12(a)
was obtained from the mounted chip. The
straightening process increases the distance between
chip serration and reduces the thickness of the segment
connecting the serration.
3.4 Benefits to Industry
The developed numerical model with phase
transformation implicitly included in the flow stress
and fracture is being used to address industrial
Poisson’s ratio 0.22 0.22
Thermal conductivity 80 36, 80, 130
(W/m/ o K) (W/m/ o K)
Heat capacity 2.7910 6 2.7910 6
J/m 3 / o K J/m 3 / o K
Thermal expansion
6.8´10 -6 (/K) 6.8´10 -6 (/K)
3.4 Validation of the Numerical Model
Several assumptions are made for the FEM model
including rigid-viscoplastic workpiece, rigid tool, and
the strain rate and temperature dependent flow stress.
The model was verified by comparing predictions of
cutting forces and chip morphology (metal flow) with
carefully conducted experiments in the machining
laboratory.
Fig. 11: A comparison of measured and predicted cutting
forces at different feed rates and cutting speeds
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