Study On Dynamic Characteristics Of Thin Wall Cutting Process

Thin-walled parts with its high strength,light weight and other characteristics of a wide range of applications in aerospace,precision instruments,automobiles and other fields.Especially in the requirements of complex structure,curved surface structure,coordination requirements of the aerospace industry has been very good application.As the basis of modern high-tech industry and high-tech defense equipment,the development level of the thin-walled parts manufacturing industry is an important symbol to measure the development level of a country's heavy industry and a breakthrough point to improve the core technology competitiveness of the modern advanced manufacturing enterprises.At present,the processing of thin-walled parts mainly adopts CNC milling.The rigidity of the thin-walled parts is reduced with the decrease of the thickness.Vibrations are easily generated during the processing and chatter vibration occurs,which affects the precision of the parts.Traditional manufacturing uses conservative cutting to reduce vibration,but this limits the CNC machine tools,tool performance.Therefore,in this paper,the thin-walled parts as the research object,in-depth study of its dynamic characteristics of cutting process,the construction of its cutting force and stability prediction model to carry out stability analysis of factors affecting the work to improve the theory of thin-walled parts to promote efficient,High-precision machining development is of great significance.The main contents of this paper are as follows:(1)The integral model of cutting force in the milling process of helical cutter considering the characteristics of cutting force is established.The model expresses the cutting force in different stages of the cutting process by a unified expression,which makes the form of cutting force easier.The cutting force micro-element obtains the cutting force along the helical thread of the cutter blade.Compared with the traditional cutting model,both in theory and in practice,Are more accurate.At the same time,based on the model,the variation law of the upper and lower corners of the cutting process under different radial cutting depths is analyzed.The results show that the cutting characteristics of the teeth show "three stages";(2)Based on the integral model of cutting force,the influence of cutter geometry,cutting parameters and other factors on cutting force is analyzed.The calculation results show that the helix angle,the axial depth of cut,the radial depth of cut,the axial ratio(axial depth of cut / radial depth of cut)and the number of tool teeth have an important influence on the cutting force.Compared with the large radial depth of cut,the influence of the tool helix angle on the cutting force is more pronounced at small radial depth of cut.At the same time,the influence of the tool helix angle on the cutting force becomes more obvious as the ratio of the axial diameter increases.Therefore,it is necessary to consider the helix angle when constructing cutting force model with small radial depth of cut or large axial ratio;(3)Based on the above-mentioned cutting force model,the process dynamics equation of thin-walled part with helical milling cutter is constructed.The stability prediction and analysis algorithm of the system is obtained by introducing semi-discrete method.The MATLAB program was developed to simulate the stability process under different cutting conditions and tool geometries.The effects of tool helix angle,forward and reverse milling form,radial cutting depth and tool tooth number on milling stability were analyzed.The results show that the cutter helix angle has little influence on the milling stability under large radial depth of cut,and is obvious under the small radial cutting depth.With the increase of cutter teeth number,the limit cut depth decreases,the stability area becomes smaller and the stability When the milling speed is lower,the stability is better,while the reverse milling is more suitable for milling in the high speed area.When the cutting depth is larger,the influence of the helix angle on the stability of the milling cutter is better than the milling speed More obvious,in the small radial cut depth,whether it is down milling or milling cutter helix angle on the stability of the effect is obvious;(4)Two kinds of numerical algorithms for the process dynamics analysis of thin-walled parts for helical milling cutter are constructed,and the cutting force signals and vibration signals under different cutting conditions are rapidly obtained.a)Using MATLAB Simulink unit to build a spiral milling cutter thin-walled process dynamics analysis module,including the judge module,the signal module and the definite integral module and other sub-modules.The module enables fast simulation without cutting parameters and tool geometries.b)Based on the Eulerian iteration,the procedure for milling thin-walled process dynamics with helical milling cutter was developed.The program can consider the eccentricity of the tool,the dynamic of the workpiece,the contact and separation of the workpiece and the tool,the change of the cutter tooth and many other actual cutting process characteristics and nonlinear characteristics.Based on the above two methods,the stability simulation without cutting parameter process is carried out.The unstable form of the cutting process is determined by spectral analysis and Poincaré mapping.The results show that the unstable form of the cutting process is mainly manifested For divergence,quasi-periodic bifurcation and double-period bifurcation.Finally,the Euler iteration program is used to verify the accuracy of the stability leaflet obtained by the semi-discrete method from two aspects: stability island and universal applicability.