advances in numerical modeling of manufacturing processes

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TRANS. INDIAN INST. MET., VOL. 57, NO. 4, AUGUST 2004 Fig. 5 : Effect of microstructure modeling on (a) rolling load and (b) material spread predictions 350
RAJIV SHIVPURI : NUMERICAL MODELING OF MANUFACTURING PROCESSES 3. PHASE TRANSFORMATIONS, THERMAL SOFTENING AND FRACTURE 3.1 Machining of Titanium Alloys: Application in Aerospace Industry Titanium and its alloys are used extensively in aerospace industry because of their excellent combination of high strength-to-weight ratio, high elevated temperature strength, high fracture toughness, and exceptional resistance to corrosion. On the other hand, titanium and its alloys are classified as difficultto-machine materials due to their inherent properties such as 1) high chemical reactivity and therefore a tendency to weld to the cutting tool during machining, thus leading to chipping and premature tool failure; 2) low thermal conductivity that prevents heat transfer in the material, consequently increasing the temperature at the tool/workpiece interface affecting the tool life adversely; 3) high melting temperature and high strength maintained at elevated temperature and its low modulus of elasticity impairing its machinability. Increase in cutting speed usually results in rise of cutting temperature since heat generation per unit time increases. This increase in temperature is deleterious to the tool life, dimensional accuracy of the product or machining efficiency. Extensive tool wear, cyclic loads and segregated chips are often observed in the face milling of titanium slabs leading to fast tool wear, distortion of work piece surface and increased tooling cost. To achieve optimal cutting conditions for reduced machining times, the cutting conditions and the tool are changed with the cutting requirements, Fig. 6. Research was initiated in the Laboratory of Excellence for Machining Technology to study chip segmentation in titanium machining 27-30 , development of a diffusion based tool wear model 31 , study the effect of thermophysical properties 32 and to model discontinuous cutting in titanium milling 33 . 3.2 Effect of temperature on the titanium flow stress High temperature over the tool/workpiece interface is mainly contributed by the heat generated in the workpiece/chip during the cutting process. It is well Fig. 6 : Different machining parameters are used to machine a titanium part optimally 351
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