advances in numerical modeling of manufacturing processes

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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 354
RAJIV SHIVPURI : NUMERICAL MODELING OF MANUFACTURING PROCESSES Fig. 12: A comparison of chip morphology between experiment (top) and predictions (bottom) at various cutting conditions 355
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