Analytical study on the relationship between chip geometry and equivalent strain distribution on the free surface of chips in metal cutting

Abstract Chip breakage is one of the most important indicators for process stability in metal cutting. It ensures efficient chip removal in automated systems and prevents mechanical damage to the machined workpiece surface. It is well known that chip breakage initially occurs after the plastic strain on the chip surface, which is not contacting the tool (chip free surface), exceeds a critical value. However, the theoretical understanding on how the plastic strain on the chip free surface is affected by the tool/process parameters remains limited. In a first step this problem can be approached by assessing the relationship between the plastic strain on the chip free surface and the chip geometry. Both are direct and interdependent outcomes of the complex interactions between the cutting conditions, tool geometry and thermo-mechanical material properties. However, the impact of the tool/process parameters on the chip geometry is much easier experimentally assessable than the plastic strain, which is hardly measurable at all. Thus, the scientific understanding of the relationship between chip strain and chip geometry lays the foundation for understanding the influence of the tool/process parameters on the strain in the chip free surface and chip breakage. This paper proposes an analytic model of the equivalent plastic strain fields on the free surface of chips in metal cutting. The local strain tensors are derived as a function of the feed, depth of cut, cutting edge angle, tool nose radius, chip up-curl radius, side-curl radius and side flow angle. It is shown how each of these parameters influences the equivalent strain fields. The validation of the model includes longitudinal turning experiments on steel AISI 1045 and validated FEM-machining simulations.