Geometric Characterization And Root-cutting Experimental Study Of Titanium Alloy’s Sawtooth Chips

The sawtooth chip is a typical chip shape in high speed cutting.The high frequency fluctuation of cutting force during its formating process will affect the surface roughness of workpiece and tool life.However,the formation process and mechanism of sawtooth chips have not formed a unified point of view,the geometric characterization methods of sawtooth chips are not unified and the changing rules of geometric characterization are also different in the published paper.In this paper,all the geometric characterization and variation rules of sawtooth chip are systematically and deeply studied,according to multiple sets of sawtooth-shaped metallographic samples of Ti6Al4 V titanium alloy,and the formation process of sawtooth chip and the variation law of cutting force in the cutting process are studied by observing and analyzing the root samples and cutting force data of sawtooth chip.Firstly,the various geometric characterization theories of sawtooth chips are systematically summarized and sorted out.Based on the metallographic samples of sawtooth chips from two groups of orthogonal experiments,the various geometric characterizations are measured and calculated by the same method,and the influence of cutting parameters on the geometric characterization is studied.The results show that the common geometric characteristics of two groups of sawtooth chip samples,such as sawtooth degree,sawtooth frequency,adiabatic shear band spacing,sawtooth spacing and bottom angle,are basically same with the change of cutting parameters,but the change range is different,because the tool materials used to obtain two groups of sawtooth chip samples are not same.Secondly,the response surface test method is used to carry out the right-angle free-cutting experiment with the rapid tool-dropping device.Based on the sawtooth chip samples and cutting force data obtained from the root-cutting experiment,the geometric characterization and the change rule of cutting force with cutting parameters are studied.The results show that compared with that of the two groups of samples mentioned above,the variation law of adiabatic shear band spacing and sawtooth frequency with back feed and feed is consistent,and the variation law with cutting speed is inconsistent,because the cutting speed range is small and the chips are in the transition stage from banded chips to sawtooth chips;the variation of other geometric characteristics with cutting parameters is consistent compared with that of the above two groups of samples;the feed force and tangential force increase with the increase of back feed and feed;the feed force and tangential force increase first and then decrease with the increase of cutting speed,which is also due to the low cutting speed and that the chip is in the process of transition from band to zigzag.Finally,by observing and analyzing the root samples of sawtooth chips obtained in the root cutting test,the adjacent inter-sawtooth cracks of sawtooth chips and the evolution process of sawtooth chips are discussed.The result shows that the cracks between the adjacent sawtooth elements occur during the formation of the sawtooth segments.In other words,when the sawtooth segments are formed,the cracks begin to appear between the segment and the material of the subsequent cutting layer.The reason for this is that there is a high temperature gradient between the adiabatic shear band and the material of the subsequent cutting layer during the formation of the sawtooth segments,which will generate a large shear stress.At the same time,the field temperature of the adiabatic shear band from the top surface to the tool tip varies from low to high,which also increases the shear stress at this point,so the adjacent sawtooth cracks occur here.