Research On Mechanisms And The Stability Considerations Of Cutting Chatter Of Machine Tool

Chatter usually occurs between the cutting tool and workpiece during machining operations,and becomes a common limitation to productivity and quality.The single degree of freedom(SDF),two degree of freedom(TDF),and multiple degree of freedom(MDF)of the dynamic chatter models of the regenerative turning process that take into account both the thermal deformation of the cutting tool and machine nonlinear stiffness is proposed in this thesis,respectively.The stability and nonlinear dynamic characteristics of the models are studied,the results may have theoretical and practical significances.The main con tents and achievements of this thesis are as follows:(1)Analytical methods have been employed to explore the variation rule of the critical chip width with the system's changing of the cutting parameters based on the SDF dynamic model.The result suggest s that the critical chip width is increased along with the increased equivalent stiffness and damping rate,but the cutting stiffness coefficient will be decreased.The increase of the natural frequency does not affect the critical chip width but it affects the transition of the stability lobe diagram(SLD)to the higher cutting speed direction.(2)The influence factors of the critical chip width of the TDF dynamic coupling vibration model between the cutting tool and workpiece when scanning the chatter frequencies around the natural frequency are analyzed by numerical simulation.The critical chip width will be increased as the cutting tool equivalent stiffness,the cutting tool damping rate,and the workpiece damping rate are increased,however,the critic al chip width is insensitive to the variation of the workpiece equivalent stiffness.It provides a powerful guidance for selecting the cutting parameters and improving the stability of the machine tool.(3)Both the thermal deformation of the cutting tool and the machine nonlinear stiffness are introduced to the proposed SDF and TDF of the dynamic models of the regenerative turning process to exhaustively study the dynamic characteristics of the system,we found that the motion of the cutting tool is sensit ive to the time delay and transitions among periodic,almost periodic,and chaotic motions with the time delay changing of the TDF dynamic model,which agree with the dynamic characteristics of the SDF dynamic model.What's more,the motion of the workpiec e of the TDF system transitions between periodic and quasi-periodic motion,without chaotic movement.(4)Considering the effects of the relative axial vibration both the cutting tool and workpiece,one kind of MDF coupling dynamic model is proposed to inv estigate the amplitude response characteristics of the tool.Based on observing the timing diagram,phase diagram and Poincaré cross section of the tool in the system within primary resonance,the results suggest that the bigger cutting width and cutting t hickness lead to chaotic movement for the tool system and its amplitude are increased correspondingly,and the amplitudes of the radial and axial directions are almost same.