Enhancement of dynamic stability and productivity for machining systems with low-stiffness components

Slender elements, either workpiece or cutting tool, are often encountered in the machining process, such as turning a long slender part on a lathe or boring using long overhang boring bars. Chatter develops easily when machining with these slender elements due to their low stiffness and damping. It influences the accuracy of the machined workpiece and the productivity, especially in flexible machining systems. The stiffness and damping of a dynamic system are of the same importance for an important criteria: {dollar}Kxi{dollar}. To improve cutting stability, either stiffness of the slender elements or the damping of the cutting system (workpiece, tool and machine tool), or both need to be increased. Increased stiffness of the slender elements is sometimes impossible due to specifications of the machining process.; This research developed methods of improving cutting stability of such a system by adding damping to the system. A model of dynamic cutting process with the "effective cutting stiffness" as a spring constant and the "effective cutting damping" as a damping constant is given and used in the analysis. Dynamic properties of rubberlike materials have been tested and used in the damping addition to the system.; A concept of improving cutting stability by an adjusted high damping/low stiffness tool when cutting a slender bar has been proven to be effective both analytically and experimentally. A combination structure with optimized parameters has been used together with a properly tuned damped vibration absorber. Analytical and experimental results show that the absorber tuning according to self-excitation and random excitation is more effective than the traditional absorber tuning. The analytical and experimental results also show the effectiveness of a boring bar equipped with a compliant torsional head. A combined effect of the damped vibration absorber and torsional compliant head on the cutting performance of a cantilever boring bar has been discussed and shows improvement over a wider range of cutting speed.; All suggested approaches have been effectively used to improve the system stability, and hence increase the machining accuracy and productivity.