Stability Prediction And Chatter Suppression For The Milling Cutter System With Large Overhang And Variable Cross-sections

Horizontal milling is widely used to machine the box or housing part in the aeronautical,aerospace,auto and construction machinery industries.This kind of milling cutter system is usually characteristized by the large length-diameter ratio and the variable cross-sections.Due to the low rigidity of the cutter system,the regenerative chatter frequently occurs during milling process,which leads to poor machined quality,low processing efficiency,even the damage of the tool and spindle.Therefore,it is imperative to investigate the chatter prediction and suppression of the milling cutter system with the large overhang and variable cross-sections to achieve the stable and efficient process,which can provide the guiding role for the engineering application.To solve the chatter problem of the milling cutter system with the large overhang and variable cross-sections,a series of research work is carried out by the combination of the theoretical investigation,the simulation analysis and the experimental testing.The thesis mainly builds the prediction model of frequency response function(FRF)of the tool tip,proposes the stability prediction method of the milling process,and develops a novel milling cutter with the metal-polyurethane composite structure.The main research content are as follows:Firstly,modelling of the FRF prediction of the milling cutter system with the large overhang and variable cross-sections.Based on the structural traits,the cutter system is divided into four substructures,including the spindle-holder base,the extended holder,tool head and the screw join.Then,the methods of Timoshenko beam model and the experimental testing are used to build the FRF models of these substructures respectively.And the dynamic parameters of the screw join are identified by the genetic algorithm.Finally,based on the receptance coupling substructure analysis(RCSA),the prediction model of the FRF of the tool tip is built,which can determine the dynamic parameters of the milling system efficiently.Secondly,improvement of the full-discretization method(IFDM)and development of the high efficient and high accurate numerical integration method(NIM)based on the Lagrange polynomials.Considering the regeneration effect,the dynamic milling process can be described by a set of the delayed linear differential equations.For the IFDM,the delayed term is estimated using the Lagrange polynomials of orders one to four to investigate the effect of the interpolation order on predicting the system stability.Comparison with the existing FDM can verify the calculated advantage of the IFDM.For the NIM,the tooth passing period is divided into the free and forced vibration stages,in which the forced vibration stage is equally discretized.Then,the 2nd Lagrange and Simpson integral formulas are used to construct the state transition matrix,and thus the milling stability can be predicted via the Floquet theory.The results show that the proposed 2nd Lagrange-Simpson NIM has the better prediction performance compared with the 3rd NIM and 3rd FDM.Thirdly,development of a damping milling cutter with the metal-polyurethane composite structure based on the passive suppression method.The relationship between the milling stability and the modal parameter of the machining system is investigated.Based on the above analysis,a damping cutter with the metal-damping composite structure is developed,and its dynamic characteristics are qualitatively analyzed by the extended strain energy.Then,the optimal design of the geometrical dimensions and related materials of the damping cutter is performed by the finite element method.Finally,the damping cutter with metal-polyurethane composite structure is manufactured and assembled.Finally,verification of chatter suppression of the damping milling cutter system with the metal-polyurethane composite structure.The dynamic parameters of the damping cutter system are determined by using the above built FRF prediction model of the tool tip.Then,the stability lobe diagram of the damping cutter system is predicted by the proposed NIM,which is verified by the milling experiments.Most importantly,the motor shell is machined by the damping milling cutter system.Compared with the conventional cutter,the experimental results show that the dynamic stiffness and material removing rate of the novel milling cutter are increased by 3.75 and 2.8 times,respectively.