Influence of regenerative effect and mode coupling on the stability of milling operations

Quality of milling operations requires dynamic stability of the process, which depends on the tool geometry, structural rigidity and type of vibrations. The study aimed to identify the influence of internal dynamic disturbances on the milling process, in particular, the mechanisms of self-excited vibrations arising from vibrational interactions and residual irregularities of the machined surface. The methodology included a comparative analysis of milling stabilisation models with an assessment of their advantages, limitations and practical recommendations for implementation in real production processes. Mathematical models were presented that addressed the effects of time delay and the interaction between the directions of oscillation of the tool and the workpiece. The study determined that repeated contact of the tool with the irregularities of the pre-treated surface leads to a variable thickness of the material layer and forms an unstable operating mode. The interaction between different oscillatory modes, when machining flexible or thin-walled parts, leads to more complex self-oscillatory processes, including chaotic oscillations. The most promising for practical use are models with adaptive control, which can respond to changes in process parameters in real time. The study established that the dynamics of the milling process significantly depend on the geometry of the tool, the length of the protrusion, stiffness, mass-inertial characteristics, and wear of the cutting part. Process damping, caused by the side contact of the tool with the workpiece, reduces the amplitude of vibrations in the low-frequency range. The control structure based on the system’s state vector included position, speed, vibration amplitude, spindle speed and tool feed. None of the methods is universal, so it is advisable to apply an adaptive approach to choosing a stability model, considering constructive, dynamic and economic factors. The practical value of the results is that they can be used by engineers and technologists to implement adaptive milling control to reduce vibrations and improve machining accuracy