From the main effects plots (Fig. 3) it is evident that an increase in cutting
speed causes rapid increase in the tool wear. The amplitude of the tool/chip
interface temperature fluctuation increases with an increase in cutting speed (S.M
Bhatia et al., 1978). In coated insert, during initial stages a few layer of coating
was taken away from the tool due to abrasion between the tool and the work
piece. This was due to the high instability of temperature at cutting zone which is
due to intermittent cut. As the inserts come in contact with workpiece in
alternative cycle (i.e., for every revolution, the tool has an entry and exit for the
workpiece) high instability of temperature was observed which lead to major tool
failure. Uncoated tools have higher wear as compared to coated tools, the least
wear is observed in TiN coating as shown in Fig. 3. The tool wear rate is low at
higher cutting speeds, but a very smaller difference is observed at different feed
rates, as seen in Fig. 4. Similarly, feed rate establishes a linear effect on the wear.
With increase in feed rate, the tool wear also gets increased since feed rate
increases with increase in force on cutting edge of tool.