Basic investigation of the reduction of the regenerative effect by a targeted simulation-based design of the cutting edge macro-shape for the local adaption of the process forces to the compliance of milling tools

• Applicant: Professor Dr.-Ing. Dirk Biermann
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 548387008

Dynamic effects, such as the occurrence of tool and workpiece vibrations, reduce the achievable quality of machined workpieces or limit the performance of the processes. In particular, self-excited or regenerative chatter oscillations, which occur due to the so-called regenerative effect, can lead to rejects of parts and increased tool wear or tool breakage. Milling processes are particularly affected by chatter vibrations due to the process kinematics, which is based on interrupted cuts carried out by the individual cutting edges. One way to avoid the regenerative effect is to reduce the excitation amplitudes, for example by a temporal distribution of the tool load, which can be realized by locally adjusting the helix angle of the tool. By designing the process with an optimised axial infeed, in which exactly one tooth is engaged at each point of time, an excitation of the system by the interrupted cut and cutting forces can be avoided. However, this does not adapt the process forces to the dynamic compliance of the milling tool, which varies along the tool axis. Furthermore, such a constant, optimised infeed cannot be set for all workpieces and machining steps. In the presented project initiative, therefore, an optimisation of the macroscopic tool geometry with a helix angle locally varied along the cutting edges is to be investigated. The tool modification aims at influencing the amplitude and effective direction of the process forces for process optimisation under dynamic aspects by means of a locally differentiated adaption of the helix angle. To increase process stability, the portion of the active force acting perpendicular to the tool axis is adjusted according to the variable compliance along the tool. Thus, if a cutting edge section at the tool tip is in engagement, where typically the highest dynamic compliance is located, a large local helix angle ensures a considerable temporal distribution of the load on the tool and, consequently, lower force amplitudes. For this purpose, the correlations between the force modulation resulting from the interrupted cut, the local compliance of the tool and the excitation and deflection of milling tools are to be investigated. Geometric-physically based models for process simulation are to be used for the investigation of the effectiveness of different tool designs and in order to optimise the locally varied helix angle. Through the tool modification and a correspondingly adapted process design, the aim is to achieve a nearly quasi-static deflection of the tool. This can be taken into account and compensated for in the NC path planning in order to improve the quality of the workpieces and productivity of the processes.

• DFG Programme: Research Grants