Dynamic Modeling&Stability Analysis Of High Speed Milling Tool-Spindle System With Internal Damping

High speed milling (HSM) possessed outstanding advantages of high efficiency and high precision as its working speed is5-10times larger than conventional cutting speed, and has become an important part of the advanced manufacturing technology. With the development of industrial production, national defense, science and technology and many other fields, the working conditions of high speed milling tend to those tough limits. In high speed milling conditions, the multi-coupled influence of instable machining caused by high rotational spindle speed, centrifugal force, gyroscopic effect and internal damping makes the dynamic modelling and instability analysis process of high speed milling tool-spindle system more complicated. Although the study of the high speed milling system modelling and stability analysis are very important to improve the cutting efficiency, security processing precision, there is not enough research on this problem. Taking the dynamic modelling and stability analysis of high speed milling as the objects, the theoretical method and experimental verification are carried out in this work.In this paper, the high speed milling tool-toolholder-spindle system with collet chuck is taken as the research object, in which the tool and toolholder are connected interference fit by the collet chuck. The theoretical analysis method of internal damping is adopted to study the internal damping developing mechanism of the interference fitted tool-toolholder system. The values of interference fit and the length of tool overhang between tool-toolholder are considered as influence factors, an equivalent tool-toolholder system model is firstly presented and then a set of operating conditions are analysized in order to get the effect rules about the influence factors on the internal damping of tool-toolholder system. Free-free hange internal damping modal tests are operated. With the assumption of rigid connection between the spindle and toolholder, interference-fitted flexible connetion between tool and toolholder via collet chuck. Utilizing the second kind of Lagrange function, Rayleigh dissipation function and finite element modeling method which suited to the characteristics of high speed milling system, the dynamic model of high speed milling tool-spindle system is set up with respect to the influence of internal and external damping, gyroscopic moment due to high spindle rotating speed, interference fit due to tool-toolholder connection form with different length of tool overhang on dynamic characteristics of system. The dynamic equation of high speed milling tool-spindle system are given in fixed coordinate system and rotational coordinate system respectively.Based on the dynamic equation of high speed milling tool-spindle system, the natural characteristics and dynamic characteristics of the system are analysized in the absence of internal damping and have internal damping respectively. Then by taking the stability analysis, the influences of internal damping and its associated variables on system stability are investigated. Conditions for stable operation are obtained through Routh-Hurwitz criterion. Finally, statical modal tests and runup&coastdown rotation experiment are operated on high speed milling tool-spindle system in order to verify the accuracy of relevant theoretical analysis.