Abstract
The process damping is the theoretical explanation for the stability improvement at low spindle speed cutting. The two main sources of the process damping are velocity-dependent effect and ploughing-indentation effect. In most existing studies, only ploughing-indentation effect is considered to establish a process damping model for simplified calculation. The influence of velocity-dependent effect on stability is less studied. Therefore, this study aims to establish a unified process damping model in milling considering both velocity-dependent effect and ploughing-indentation effect to predict the stability. The velocity-dependent effects in up milling and down milling are investigated by the energy dissipation. Results show that this effect provides a negative process damping in up milling at low-speed and low radial immersion, but improves the stability in down milling. However, the ploughing-indentation effect always damps chatter and improves stability regardless of milling form. To further research the weight of two effects, the ratio of velocity-dependent to ploughing-indentation effects is proposed. When the ratio is larger than 1, the velocity-dependent effect plays a more significant role in stability improvement than the ploughing-indentation effect. The predicted stability lobe diagram based on the unified model is verified by previous experiments.