Milling stability prediction of a hybrid machine tool considering low-frequency dynamic characteristics

摘要

Stability lobe diagram (SLD) is an important tool to select the spindle speed and axial cutting depth to avoid chatter vibration. For a parallel or hybrid machine tool, the low-frequency dynamic characteristics have a great impact on the SLD and need to be taken into account. One of the major issues related to dynamics analysis is the effective dynamic model of parallel mechanisms, since the stiffness of passive joints varies at different orientations and the structures of components are complex. This paper presents a method to establish an accurate dynamic model and considers the low-frequency characteristics to predict SLD. In this paper, an approach is put forward to get the stiffness and mass matrices of components with variable cross-sections and a structural dynamic model of the parallel mechanism is developed, which innovatively considers the variable stiffness characteristics of the passive joint under different loads. Based on the structural dynamic model, the frequency response function (FRF) of the moving platform is obtained and the results are validated through comparison with those of the hammer test. Using receptance coupling substructure analysis (RCSA) method, the machine-spindle-holder-tool system is divided reasonably and the FRFs at the tool tip are obtained to predict the SLD. It is shown that the low-frequency dynamic characteristics of hybrid machine tools have a great influence on the stability boundary of machine tools, mainly at the low speed region.