3.2. Chip Study The effect of the cutting speed on the chip compression ratio is presented in Figure 9. At 150m/min, CC620 had a higher value than CC650 (9 for CC620, 7 for CC650). This is due to the higherhardness of CC650, which affects the tribological behavior at the tool-chip interface. The increase in the hardness of frictional surfaces during dry friction, reduces the value of the resulted coefficient of friction [20]. Upon reaching a cutting speed of 250 m/min, a remarkable decrease of the chip compression ratio value produced by CC620 was observed (from 9 to 5), while the chip compression value for CC650 was 6.7. At 700 and 1000 m/min, the values of the chip compression ratio were the same for the used ceramic tools (4.7 at 700 m/min, 3.9 at 1000 m/min).