ANALYSIS OF FRACTURE IN BURR FORMATION AT THE EXIT STAGE OF METAL-CUTTING

Even in a fully automated factory, many deburring operations are carri ed out manually. To remove or minimize the burr effectively or automat ically, understanding of the burr formation or fracture which occur at the exit stage of machining is necessary for a desired edge geometry. A quantitative model of burr formation is proposed for orthogonal mac hining including fracture of the workpiece during burr formation. Alth ough the burr is fully formed without fracture in a ductile material s uch as copper, a burr cannot be developed in cast iron due to fracture in the initial stage. The fracture strain, dependent upon the ductili ty of the material, is used to explain fracture during burr formation. McClintock's ductile fracture criterion is used to determine the frac ture location. Fracture during the development of a burr is represente d by a fracture negative shear angle and a fracture tool distance. The fracture negative shear angle is obtained from the strain developed a long the tool path, whilst the fracture tool distance can be calculate d from the point of initiation of burr formation and the fracture nega tive shear angle. Orthogonal machining tests with ductile and less duc tile materials were carried out in a modified milling machine using a scanning electron microscope to observe the behavior of the material t o verify the predictions of the proposed model.