Research On High-Speed Machining Stability And Dynamic Optimization

High-speed machining (HSM) possessed outstanding advantages of high efficiency and high precision is one of the most important advanced manufacturing technologies and has wide application prospects. The HSM system (including machines, tools, workpierce and machining process) is complex dynamic one. With the increase of machining speed, the influence of instable machining caused by vibration in machining process on efficiency, surface quality, production cost as well as use time of machines and tools is larger than conventional cutting speed. The stable machining process is one of the preconditions of realizing the advantages of HSM technology. However, the shortage of research on stability predication and optimization theory and method of HSM system limits the development and reasonable application of the HSM technology. Therefore, a new conception of stability optimization used in the whole life cycle of the design, manufacture, inspection and machining operation and maintenance of HSM system is proposed, and the stability predication, optimization theory and method suitable HSM is researched. It is a important application foundation subject for promote high-speed machining technical development and application and have very important theoretical and realistic meaning to bring high-speed machining into technological advantage and economic advantage further.Studying the dynamic model and modeling method suit to the characteristics of HSM system, based on Lagrange's equation, the dynamics model of HSM system with multi-degrees of freedom are set up with respect to the influence of centrifugal force and gyroscopic moment due to high rotating speed on dynamic characteristics of system. Take DMU-70V five-axis machining center (with HSK spindle/holder) and ACE-V500 vertical-type machining center (with BT spindle/holder) as examples, the influence of centrifugal force and gyroscopic moment on dynamic characteristics of different spindle/holder and cutters (end milling cutter, face milling cutter) are analyzed and compared with matching in different bearing rigidity under different rotate speed. The critical rotate speed and operation speed ranges in which the influence of centrifugal force and gyroscopic moment must be considered are determined. And the results analyzed show that the dynamic characteristics of HSK spindle/holder in high speed are better than ones of BT spindle/holder.Considering the influence of different cutting condition and vibration in high speed cutting process on cutting force, a dynamic cutting force model with respect to high speed machining is established. Take helix end milling as an example, the influence of different cutting condition to dynamic cutting force is analyzed and compared by analytical predication and cutting experiments.Based on the dynamic cutting force and dynamics model established, the stability criterion and predicting method of the regenerative self-excited chatter and the mix vibration excited by both self-excited chatter and outside loads in high speed machining process is studied. The mode orthogonality are used to analyse the frequency response of the multi-degrees of freedom system, the predicting method of stability criterion and limits with respect to high order eigen-frequenceis of multi-degrees of freedom in high speed machining is proposed. In this way, the stability limits (lobe) diagram method of multi-degrees of freedom high speed machining system is established and the effect of structure parameter and cutting process parameter to high speed machining stability is analysed. And the stability lobe diagram of DMU-70V and ACE-V500 machining centers are given, which can be referenced in real production.Apply structural dynamic modification technique to the dynamic optimization for stability of HSM system, which is a "converse problem" of dynamics, and extent and improve it. Transforming the "converse problem" which aimed at high material remove ratio and high surface quality under stable cutting to "positive problem" which is based on step modification and reanalysis, the dynamic modification-based optimization theory and method for stability of HSM system are investigated. The synthetical optimization method for both the stability limit and machine tool's power utilization efficiency are proposed. In each stage of design and machining process, the different design variables including structural parameters and machining parameters are determined and modified repeat up to the desired optimum objectives are achieved by means of the sensitiveness and the perturbation analysis. And results achieved show that the material remove rate and surface quality had improved evidently and economically by optimizing drawbar force of spindle, rotating speed, axial cutting depth, number of teeth and overhung length of tool, as well as clamp of workpiece etc.Experimentations of modal analysis, idling of spindle and high-speed milling are designed and carried out to investigate and validate the dynamics models, theory andmethod proposed and the dynamic characteristics, machining stability on both DMU-70V and ACE-V500 machining centers. And the experimental methods suitable for performance examination and evaluation of HSM system with respect to stability are researched and established.