| Ti-5553,as a newly developed near?phase titanium alloy,has the characteristics of high specific strength,high yield strength,good corrosion resistance,strong fatigue crack growth resistance and good hardenability.It is widely used in the manufacture of key structural parts in aerospace.However,due to its high strength,high toughness,low modulus of elasticity,high chemical activity and poor thermal conductivity,the cutting performance is poor,which is mainly reflected in that the cutting tool bears a large cutting force and the chip is not easy to break,generating a large amount of cutting heat that can not be dissipated in time,resulting in high temperature in the tool-chip contact area,causing serious tool wear,poor quality of the machined surface of the workpiece and other engineering problems.Conventional cooling methods such as flood cooling,high pressure cooling and minimum quantity lubrication can not effectively reduce the cutting temperature,and the cutting fluid used for cooling will cause environmental pollution.Liquid nitrogen cryogenic cooling technology(-196?)can effectively reduce the temperature of cutting area,improve the friction between tool and chip,reduce the wear of tool and improve the surface quality of workpiece,and is non-toxic and harmless to the environment.In this paper,the problem of uncoated cemented carbided tool wear in Ti-5553 cutting under the liquid nitrogen cryogenic cooling condition is studied.The tool wear test of Ti-5553 turning with uncoated carbide tool was carried out by setting up a cryogenic cooling platform of liquid nitrogen and selecting a wide range of cutting parameters.optical microscope and scanning electron microscope were used to detect the tool wear morphology,and energy spectrum analysis was used to detect the elements on the tool surface.The tool wear morphology and wear mechanism were analyzed,and the mapping relationship among wear morphology,wear mechanism and cutting parameters is studied to provide basic data for constructing tool wear diagram and determining tool failure limit.The flank face wear is chosen as a measure of tool wear failure because it exists under all test parameters,and the tool wear rate R is introduced as the evaluation standard of tool wear severity.Based on the central composite surface design method and using Design-Expert software to design three factors and three levels of central composite test,according to the test data,the explicit mathematical expressions of tool wear VB and wear rate R about cutting parameters v_c,f,and a_p are constructed by using the second-order polynomial and least square fitting method,and the quantitative evaluation and prediction of tool wear about cutting parameters are realized.According to the wear morphology of cutting tools under various cutting parameters in the tool wear test,the failure mode of cutting tools is determined.In view of the deficiency that the traditional two-dimensional tool wear map only contains two kinds of cutting parameters(v_c and f),a two-dimensional qualitative analysis tool wear map including three kinds of cutting elements(v_c-f-a_p)is constructed and the tool failure limit is determined.Based on the tool failure limits determined in the wear map,the mapping relationship between tool wear trend of rake and flank face and cutting parameters is established,so as to realize the qualitative analysis of tool wear.According to the test results,this paper classifies and summarizes the tool wear patterns of the rake and flank face,analyzes the shortcomings of the traditional two-dimensional tool wear pattern,and constructs a new two-dimensional tool wear pattern including three cutting elements(v_c-f-a_p).The tool failure limits are determined in the wear map,and the mapping relationship between the tool wear trend of the rake and flank face and the cutting parameters is displayed,so as to realize the qualitative analysis of tool wear.At the same time,by using VB and R mathematical model of tool wear,a quantitative analysis of the flank face tool wear map under the condition of two cutting parameters(v_c-f,a_p is a fixed value)is constructed to realize the quantitative evaluation of tool wear in the two-dimensional wear map.In view of the defect that the two-dimensional tool wear map contains incomplete cutting parameters in the quantitative evaluation of tool wear,a three-dimensional tool wear map of tool flank wear VB and the wear rate R including the three elements of cutting parameters(v_c-f-a_p)is constructed by using the method of visualization of three-dimensional space Iso-surface and response surface.Based on the idea of multiple coupling limit intersection,the optimization of cutting parameters is realized,which provides guidance and reference for the selection of cutting parameters of Ti-5553 machining with uncoated cemented carbide tool under the liquid nitrogen cryogenic cooling condition. |
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