Study On The Microstructure Characteristics Of The Workpiece Material Surface Layer With High Speed Cutting

In the high speed machining,the shear slip deformation of surface caused by the tool vibration and the contact surface severe friction in the shear zone changes the surface microstructure.The changed surface microstructure leads to the delamination of the surface or the fatigue source of the microfissure.They all affect the rigidity,strength,wear resistance,corrosion resistance,fatigue life and other properties of the workpiece.Therefore,the study of surface microstructure characteristics has practical significance for popularizing high speed cutting technology.In this paper,turning test is taken as the main part,the measurement of machined surface roughness and tool vibration during machining are taken as the supplement.The microstructure and surface morphology of the surface layer are observed.The surface layer microcosmic characteristics of high speed cutting workpiece are studied.The main contents and conclusions are as follows:(1)The method of single factor design is used.The turning experiments of pure titanium TA2 bar and titanium alloy TC4 bar are carried out by changing cutting parameters.By making metallographic specimens and observing the microstructure of the surface layer,it is found that the surface grain is twisted along the cutting speed direction due to the extrusion and friction of the lathe tool.The effect of different cutting parameters on the microstructure of the surface layer is investigated.It is found that the larger the feed rate is,the greater the change of the microstructure of the surface layer for the same material.The influence of cutting speed and cutting depth on the surface layer is not obvious.(2)By observing the surface metallography,it is found that the microstructure of base metal of TA2 and TC4 is very different.This is the reason for the addition of aluminum and vanadium in TC4,which reduces the grain size and expands the grain boundary of TC4.The metallographic difference of base metal leads to different metallographic changes in the surface layer.(3)On the basis of turning test,the machined surface morphology and surface roughness are observed.It is found that the width of each groove of surface morphology and surface roughness both increased with the increase of feed rate,both in TA2 and TC4.The change of microstructure of surface layer is greater,the groove width of the surface morphology and surface roughness value both are bigger.Under the same cutting condition,the machined surface roughness of TC4 is smaller than that of TA2.(4)After measuring and collecting the tool vibration acceleration value in the process of turning,the frequency spectrum diagram of vibration is drawn and analyzed by MATLAB.From the angle of time domain and frequency domain,it is found that for the same material,the vibration increases first and then decreases with the increase of cutting speed.The vibration increases with the increase of feed or cutting depth.By observing the surface metallography,the increase of the tool vibration makes the surface grain deformation more serious.