Research On The Modified Model Of Fracture Damage And The Control Of Chip Formation During Titanium Alloy Cutting

Titanium alloy is widely used in the manufacturing of key parts of aerospace because of its low thermal conductivity,high strength and low density.At present,most of the fracture damage models used in the finite element simulation of chip formation in high-speed cutting of titanium alloy are based on the assumption of material isotropy,without considering the anisotropic characteristics of materials due to pre stretching,rolling and other processes,therefore it is difficult to accurately reflect the chip formation process in the cutting process,which restricts the prediction and analysis of material fracture damage model and the development of high-speed cutting simulation accuracy.In this paper,the aircraft titanium alloy Ti-6Al-4V pre stretched plate is taken as the research object,and the samples are taken along the plate 0°(RD),30°,45°,60° and 90°(TD)in multiple angles to comprehensively characterize the influence of the anisotropic characteristics of material.Through the dynamic tensile test of the samples with different orientations,the influence rules of orientation and strain rate on the mechanical properties are analyzed,and the rules are further explained from the aspect of micro angle(metallographic structure,fracture).At the same time,the quasi-static tensile test and the dynamic tensile test are carried out to obtain the basic data of the fracture damage model.The direction angle function is introduced to establish the J-C fracture damage model considering the influence of orientation,and the accuracy of the model is verified by the dynamic tensile test.Based on the above model,with the aid of the finite element software Third Wave AdvantEdge,the finite element model of high-speed orthogonal cutting was established,the cutting process and chip formation process under different orientations and cutting speeds were simulated,the sawtooth degree and sawtooth frequency parameters were introduced to characterize the chip evolution process and formation form,and the effect of material orientation and cutting speed on chip formation process and chip form was studied.With the help of YCM-V116 B vertical machining center,the high-speed orthogonal cutting experiments with different orientations and cutting speeds were carried out.The observation results of different chip samples were analyzed by SEM and other micro means.The chip formation mechanism of Ti-6Al-4V with different orientations and cutting speeds was revealed,and the critical speed of chip transition from serration to fragmentation was obtained.The mapping relationship between the mechanical properties of materials with anisotropic characteristics and chip formation was built.Taking sawtooth degree and sawtooth frequency parameters of serration as the evaluation indexes,the accuracy of the finite element model of high-speed orthogonal cutting is verified by comparing the experimental results with the simulation results.By synthesizing the experimental and simulation results,the efects of orientation and cutting speed on chip formation and chip shape evolution are studied,the formation process of chip shape and fracture analysis are predicted,and the active control of chip shape is realized.