Influence of machining parameters on surfacial strain hardening

This work, dealing with strain hardening in turning, is a comparison of experimental and numerical (FEM) results. Orthogonal cutting was assumed as the reference working condition. Experimental data were recorded by machining thin disks of C20 steel (1CD20 UNI 5598) with radial feed; grooving tools with both standard chipbreaker and flat rake surface (rake angle 11°) were used; several values of both cutting speeds and feed were tested. After machining, work hardening was evaluated by micro Vickers test as a function of the distance from the machined surface. Regression techniques were used to identify work hardening patterns (depth of the affected zone, maximum hardness). FEM simulations of the experiments were performed using a commercial code for forming processes. A plane strain model of a rigid plastic workpiece was setup and particular care was devoted to define suitable material and interface properties, as well as an effective damage model for the workpiece. Differences between hardness profiles measured with different speeds and tool geometries proved to be interesting; moreover, the good agreement between experimental and numerical results showed a remarkable level of both accuracy and robustness reached by the FEM code employed.