*4.2. Analysis of Instantaneous Cutting Force*

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In LUAT and CT, 80 sampling points are, respectively extracted when the tool is turning 5 mm under the condition of *v<sup>w</sup>* = 100 mm/s. The instantaneous cutting force in the main turning direction is compared in Figure 10.

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**Figure 10.** Instantaneous cutting force in main turning direction. (**a**) LUAT; (**b**) CT.

During the CT process, the tool extrudes the workpiece to deform, the stress and strain continue to accumulate until the workpiece material fails—this is how the chips generate. Conversely, as shown in Figure 11, due to the periodic contact separation between tool and workpiece, the stress form of workpiece changes from extrusion to high-frequency impact, and the peak value of instantaneous cutting force is significantly larger than that of CT.

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(a) Principle of chip formation (b) Simulation results

**Figure 11.** Formation of BMG chips. (**a**) Principle of chip formation; (**b**) simulation results.

Furthermore, due to the contact-separation phenomenon, the periodic change of cutting force with chip breaking is more obvious. In CT, when the tool contacts the workpiece continuously, the BMG is still squeezed by the tool when the chip generates. In contrast, during the LUAT, the larger instantaneous cutting force and the impact of the tool under the contact separation state are more conducive to the failure of BMG, which promotes the generation of chips.
