Prediction of Cutting Forces in Micro Milling of p-20 Steel by TiAln coated wc tool: An Analytical Approach



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Fig. 4. Coating window showing the application of coating on the tool
Table 1. Johnson cook parameters [14]
A (MPa)
B (MPa)
n
c
m
T
room
(°C)
T
melting
(°C)
908.54 321.39 0.278 0.028 1.18 20 1487
Table 2. Thermo Mechanical Properties [4, 14]

P-20 Steel
WC/Co
TiAlN
Thermal conductivity (N/S.C
-1
)
28.4 55 Tb Heat capacity (N/mm

2
.C
-1
)
4.396 T Tb Thermal expansion coefficient (C

-1
)
12.8×10
-6 4.7×10
-6 9.4×10
-6
Young’s modulus (MPa)
211000 5.6×10 5
6×10 The contact between tool and work piece has been chosen to be hybrid relationship in
Deform-3D software. Hybrid friction model has been chosen for assignment of the inter object relationship. The constant for shearing friction has been taken as 0.9 and coefficient of Columb friction has been taken as 0.4 for TiAlN coating and 0.7 for uncoated
WC/Co tool, respectively [4]. Friction factor between chip and work piece has been taken as 0.2. Simulation for orthogonal machining has been carried out at feed rate of


8 2, 4, 6 and 8 μm/tooth and a constant depth of cut and curting speed as 30 m and
523.59 mm/sec respectively. The specific cutting force values (RMS of force values/depth of cut) obtained by simulation for both coated and un-coated tool are shown in figure 5. The figure shows higher magnitude of cutting forces both in tangential and normal directions for un- coated tool compared to those of coated tool. Further, induced temperature by uncoated tool is higher than that by coated tool as shown in figure 6. The higher values of cutting force and temperature of the un-coated tool is due the difference in thermomechanical properties and higher friction coefficient as compared to the coated tool. Finally, the force coefficients have been calculated by linearly fitting the specific cutting forces obtained in both tangential and normal directions (Table 3). Cutting coefficients have been evaluated as function of undeformed chip thickness and rubbing coefficient as y- intercept by considering equation 4.
Fig. 5. Cutting coefficient calculation by linear fitting of simulated cutting forces
Fig. 6. Simulated temperature distribution using Deform D (a) TiAlN coated tool, b) Un-coated tool


9

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