The mechanisms of burr formation and breakout in orthogonal cutting are analyzed. A burr formation/breakout model for orthogonal cutting is proposed, based on the observation of SEM micro-machining tests. It is found that a negative deformation plane begins to form when the steady-state chip formation stops as the tool approaches the end of the cut. Plastic bending and shearing of the negative deformation plane contributes to the burr formation, while crack propagation along the plane causes the breakout. Simulated orthogonal cutting experiments using copper, Al 2024-T4, and Al 6061-T6 were performed with a modified impact machine to verify the model. The tests showed excellent agreement with the model predictions.

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