Investigation On Milling Stability Prediction And Application Of Time-Varying System For Machine Tools And Tool-Workpiece

Milling technology which has been widely applied in domains of aviation,aerospace,automobile,ship medical and military industry is one of the most important foundational technologies in advanced manufacturing technology.Milling stability is one of the key factors to achieve the aim of high accuracy and high efficiency.The milling stability prediction also has theoretical and practical values to prove the surface processing quality and processing efficiency of components.According to the requirements of machine design and actual milling process,the investigation on milling stability prediction and application of time-varying system for machine tools and tool-workpiece has been carried out by the methods of theoretical modeling and experimental verification.The main contents of this dissertation are listed as following:Firstly,according to the requirements of actual milling process,the generalized geometric model which can describes respectively cylinder flat end mill,ring end mill and ball end mill according to different geometry parameters is established.The static milling force model based on real instantaneous milling thickness is presented and applied to the static milling force simulations of above three type end mills.Under four different operating conditions,the errors of static milling forces obtained by two different instantaneous milling thicknesses are compared,and the results show that the static milling force obtained by real instantaneous milling thickness has a universal applicability.In addition,the model of dynamic milling force based on the effect of regenerative chatter is established,and the model provides a theoretical basis for subsequent milling stability study.Secondly,aiming at the core problem of current popular machine design-process integrated design method,milling stability evaluation criteria of machine tools and according to the technology characteristics of aggressive cutting condition,several specific position combinations of moving parts of machine tools are set to be the samples.The values of minimum critical axial cutting depths are obtained,and the response surface model which can describes the relationship between spatial position of machine tools and the value of minimum critical axial cutting depth is established.Then,the rapid prediction method of milling stability with position-dependent based on response surface model is presented.The method is applied to a precision horizontal machining center with box in box structure to achieve the milling stability prediction comprehensively and rapidly.The method also provides a theoretical basis for subsequent machine design and optimization.Thirdly,thin-walled components milling process is a representative of nonaggressive cutting.Aiming to the condition that the stiffness of tool is approach to that of workpiece and considering the material removal factor and the interaction between milling force and deflection,the time-varying model of coupling deflection and dynamic characteristic of tool-workpiece system is established.In addition,a multiple delays using an improved semi-discretization method is presented.The algorithm can not only ensure the computational accuracy,but also improve the computational efficiency.Finally,thin-walled milling process is regarded as study object,and the dynamic stability lobe diagrams of tool-workpiece system are plot by the time-varying model and new algorithm.The milling stability prediction method of tool-workpiece system with time variation provides a theoretical basis for high accuracy and high efficiency milling process of thin-walled components.Finally,the milling force coefficient identification test,the milling force model validation test,machine tool dynamic characteristics test,machine tool milling stability prediction method validation test and tool-workpiece time-varying system milling stability prediction method validation test are carried out.The theoretical models and the methods are verified correctly by comparing the results of theory and test.The research achievements enrich and develop the methods of milling force modeling,machine tool design and thin-walled components milling parameters optimization,and have important theoretical significances,practical and social values to the engineering applications.