Vibration suppression of balls in different contact states during mirror milling of curved thin-walled parts based on magnetic follow-up support fixture

Abstract

Milling of curved thin-walled parts is a critical step in the manufacturing of aircraft skins or rocket storage tanks. During the process of milling thin-walled parts using magnetic follow-up support fixture, the complex situation that the fixture balls in different contact states with the surface of the thin-walled parts occurs, leading to changes in the dynamic characteristics of the thin-walled parts, thereby causing machining vibration and even chatter, ultimately affecting machining quality. To this end, this paper focuses on the vibration of thin-walled parts under balls in different contact states. Firstly, the structure and function of the magnetic follow-up support fixture are illustrated. Then, a dynamical model of a mirror milling system that accurately reflects balls in different contact states is established using finite element technology, in order to explore the changing law of dynamic characteristics at milling points of thin-walled parts under balls in different contact states. To further investigate chatter under balls in different contact states of thin-walled parts, after obtaining modal parameters of the thin-walled parts through impact tests, three-dimensional stability lobe diagrams (3D-SLDs) of thin-walled parts under balls in different contact states are plotted using the full-discretization method, and chatter-free parameters are selected. Finally, the rationality of finite element analysis and stability analysis, as well as the practicality of the fixture, are verified through milling experiments. The experimental results show that after the fixture is applied, the dominant frequency of curved thin-walled parts can be increased by up to 6 times, its amplitude can be reduced by over 60 %, and the surface roughness can be reduced by up to 57.98 %.