Towards a differentiated understanding of process damping and the introduction of process stiffening effects

Abstract

The effect of process damping is an effective means to favorably influence the stability of machining processes. Its occurrence depends on the dynamic contact between the flank face of the tool and the workpiece surface. To specifically investigate the fundamentals of process damping effects in the context of process stabilization, different configurations of modified cutting tools were prepared and applied for this contribution. These modifications consisted of tools with conventional and functionally structured flank face chamfers and were expected to cause distinctly different interaction characteristics. While the use of conventional flank face chamfers was expected to cause a rather significant share of elastic deformation of workpiece material, the application of surface structures was intended to provoke an increased degree of dissipative, i.e., process damping effects due to plastic deformation of workpiece material. By conducting orthogonal cutting experiments using a sensor-integrated analogy setup, milling tests as well as representative simulation approaches, the fundamental interrelations of the dynamic interaction between the workpiece surface and tools with both conventional and structured chamfers were characterized. It was observed that a conventional flank face chamfer in contact with the workpiece surface causes predominantly elastic deformations of the workpiece material due to a relatively large contact area, resulting in distributed, low local contact stresses below the yield stress. These elastic deformations led to a temporary stiffening effect on the dynamic system significantly affecting its dynamic behavior, e.g., in form of increased vibration frequencies. In contrast, surface structures led to an increased share of plastic deformation due to concentrated contact stresses at the structure tips and, thus, to dissipative, i.e., damping effects. Based on the experimental and simulation-based results presented as part of this contribution, which are consistent with observations made in previous studies, a differentiated consideration of process damping as one of five methods for process stabilization is discussed. In this context, the introduction of process stiffening in addition to process damping as a stabilizing process inherent contact phenomenon is proposed for future consideration.