4.3.3. Chip Morphology

Figure 14 shows the chip morphology under different cutting conditions. Overall, the chips produced under various cutting conditions can be characterised by the spiral feature. It can be seen from Figure 14a,c,g that the chip size and curling degree decreases with the increase in the cutting speed [30]. The chip length and curling degree are smaller under the spray cooling condition than that of the dry condition. Figure 14d–f shows the chips morphology under different tool inlet pressures at a cutting speed of 100 m/min. The chip length decreases gradually with the increase in tool inlet spray pressure due to the increasing fluid dynamic pressure applied on the chips, which made the chips more likely to be broken. For the internal turning, the small chips are beneficial to be removed by high-speed airflow to avoid chip blockage during turning.

**Figure 14.** Chip morphology under different cutting conditions. (**a**) Vc = 60 m/min-Dry, (**b**) Vc = 60 m/min−0.3 MPa, (**c**) Vc = 100 m/min-Dry, (**d**) Vc = 100 m/min−0.1 MPa, (**e**) Vc = 100 m/min−0.3 MPa, (**f**) Vc = 100 m/min−0.6 MPa, (**g**) Vc = 140 m/min-Dry, (**h**) Vc = 140 m/min−0.3 MPa.
