Dynamics modeling and stability improvement in the machining of thin-walled workpiece with force-tunable pneumatic fixture

It is very prone to cause large-amplitude cutting vibrations, or even regenerative chatter, when milling thin-walled workpiece due to its low dynamic stiffness. The utilization of fixture support is one of the most effective measures to mitigate vibrations and improve stability limits, which has gained more and more attention. However, the dynamics model of the tool-workpiece-fixture system and the influence of fixture support force have not been fully developed. In this paper, a pneumatic fixture is designed and used to exert controllable support force on the thin-walled workpiece by precisely tunning the air pressure. The position-dependent modal parameters of the thin-walled workpiece under different fixture support forces are identified by combining experimental modal test and finite element analysis. The milling dynamics is then modeled into a delay differential equation with position-dependent coefficients. On this basis, the three-dimensional stability lobe diagrams (SLDs) are obtained in the parameter space of tool path, spindle speed, and axial depth of cut. Both stable and chatter cutting tests are performed to verify the predicted SLDs, and the cutting signals under different fixture support forces are compared in detail. Experimental results reveal that the proposed model can accurately predict the chatter stability of thin-walled workpiece with fixture support, and the stability limit can be successfully improved by tunning the support force. Some important conclusions on the influence of fixture support forces are also drawn based on detailed simulation and experimental analyses.