Surface integrity in precision turning of steel

The functional properties of a technical component depend directly on the geometrical and material properties, in particular the surface and surface layer properties of a component. Since material loads are generated in the material during a machining process, which cause alterations in the surface and surface layer properties, so-called material modification, the knowledge of these relationships is of great interest for a material-oriented manufacturing. In order to elucidate this for precision machining, there are two main process-specific challenges: (1) Cutting edge radius and undeformed chip thickness are of the same order of magnitude, so the engagement ratios and cutting conditions vary from cutting to plowing depending on the undeformed chip thickness. This phenomenon is known as the so-called size effect, occurring as a nonlinear increase in the specific cutting force with decreasing undeformed chip thickness. Therefore, the consideration of deformation and chip formation mechanisms is necessary. (2) The layers influenced by a precision machining process are very thin and thus difficult to characterize. The experimental investigation shows that a surface layer zone with a plastic deformation of a few micrometer depth below the surface is generated by precision turning of steel (42CrMoS4, AISI 4140). In addition, there is another size effect with regard to the depth of the plastic deformation, showing a nonlinear increase with decreasing undeformed chip thickness. The plastic deformation is influenced by the process parameters as well as the process kinematics.