| Cutting is the most widely used workpiece processing method in the manufacturing industry,and in the cutting process,the quality of the tool is one of the important factors to determine the final quality of the workpiece.With the emergence of superhard and difficult machining workpiece,higher and higher requirements are put forward for cutting tools,and traditional carbide tools can not meet the requirements of modern cutting.Ceramic material has the advantages of high wear resistance and high hardness,and is a new tool material with great potential.At present,the commercial ceramic cutting tools are mainly Al2O3,CBN and Si3N4 materials,but in some special processing the hardness of these materials still can not meet the hardness requirements of the tool,therefore,with ultra high hardness of non-oxide ceramics as tool materials to develop super hard ceramic cutting tools for the development of tool industry has important significance.In this thesis,a B4C-Ti B2 ceramic tool with ultra-high hardness is developed,and B4C-Ti B2 ceramic tool cutting AISI 4340 as the application background,around the main line of―tool material preparation—microstructure—mechanical properties—ceramic tool design—cutting process simulation—cutting experiment verification—wear mechanism‖,the B4C-Ti B2ceramic tool is studied by finite element analysis combined with experimental verification,it lays the theoretical foundation for the practical application of B4C-Ti B2 ceramic tool.Firstly,B4C-x wt.%TiB2composite ceramics（x=0,10,20 and 30）were prepared by hot pressing sintering process at 1950℃and 60 MPa,and their microstructure and mechanical properties were studied.The results show that the addition of Ti B2 can effectively improve the relative density of B4C ceramics and change the fracture mode of B4C ceramics（from pure transgranular fracture to a combination of intergranular and transgranular fractures）,thus,the mechanical properties of B4C ceramics are significantly improved.The densification of B4C-Ti B2 composite ceramics increases obviously with the increase of Ti B2 content at first,and then does not change significantly with the increase of Ti B2 content.When 10%Ti B2 addition phase is introduced,the relative density of the sample increases from 92.4%to 99.2%.The fracture toughness and flexural strength increased significantly with the increase of Ti B2content.When 20%Ti B2 is added,the fracture toughness increased from 2.52 MPa/m2 to4.86 MPa/m2,and the flexural strength increased from 317 MPa to 492 MPa.Although the fracture toughness and flexural strength are slightly reduced when the Ti B2 content is 30%,it still has good comprehensive mechanical properties.The Vickers hardness did not change much with the increase of Ti B2 content and remained at about 32 GPa.Then,the cutting simulation model was established in deform-3D software.Through single-factor design,the two factors of fixed cutting speed,cutting depth and feed rate remain unchanged,the value of the third element is changed.The main cutting force and tool temperature data of B4C-Ti B2 ceramic tool with different Ti B2 content were simulated in the process of cutting AISI 4340 with different cutting speed,depth of cut and feed parameters,so as to compare the cutting performance and select the ceramic tool component with the best cutting performance.T hrough the orthogonal design the main cutting force and tool temperature data of the ceramic tool with the best cutting performance were analyzed by the method,and the optimal cutting parameters for cutting AISI 4340 were obtained.The single-factor simulation results show that the main cutting force of the four groups of ceramic tools with different components shows a trend of first increasing and then decreasing with the increase of cutting speed,and increases with the increase of depth of cut and feed.Under the parameters,the main cutting force of B4C-30%Ti B2 ceramic tool is the smallest.The tool temperature of the four groups of ceramic tools with different components increases with the increase of cutting speed,depth of cut and feed.Under different cutting parameters,the tool temperature of B4C-30%Ti B2 ceramic tool is the lowest.The main cutting force of B4C-Ti B2 ceramic tool decreases with the increase of Ti B2 content in the material,and the tool temperature shows a downward trend.B4C-30%Ti B2 ceramic tool shows the best cutting performance in terms of main cutting force and tool temperature.The orthogonal simulation results show that the main cutting force has obvious response to the change of cutting parameters,so the optimal cutting parameters are determined according to the change of main cutting force.Among them,the influence of cutting parameters on the main cutting force is:depth of cut>feed>cutting speed.The optimal cutting parameters of the B4C-30%Ti B2 ceramic tool predicted by cutting simulation are:cutting speed 300m/min,depth of cut 0.3 mm,and feed 0.1 mm/r.Finally,the accuracy of the optimal cutting parameters,the correctness of the cutting simulation model and the applicability of the ceramic tool were verified by experiments,and the wear mechanism of the tool was studied.Verification of the accuracy of the optimal cutting parameters by calculating the value of metal removal under 17 sets of different cutting parameters.The results show that the metal removal amount obtained in the seventeenth cutting experiment is the highest,which is 31.8 cm3,and the corresponding cutting parameters are:cutting speed of 300 m/min,depth of cut of 0.3 mm,and feed rate of 0.1 mm/r,which are consistent with the optimal cutting parameters obtained by the cutting simulation.The accuracy of the cutting simulation model was verified by comparing the chips generated in the cutting simulation process with the chips obtained by the cutting experiment.Cutting experiments show that the experimental chips are band-shaped chips,which are highly consistent with the simulated chip morphology,which verifies the accuracy of the simulation model.Under the same cutting conditions,the applicability of B4C-Ti B2 ceramic tools was verified by comparing the cutting performance of B4C-30%Ti B2 ceramic tools and YD carbide tools.As the cutting progresses,the wear rate gradually decreases.The initial wear of the YD carbide tool is smaller than that of the ceramic tool,but when the cutting length exceeds about 43.9 m,the wear rate increases sharply,and exceeds the wear rate of the ceramic tool when the cutting length is about 76 m.Overall,the service life of B4C-30%Ti B2 ceramic tools is longer than that of YD carbide tools sold on the market.By observing the micro-morphology of the tool wear area and analyzing the types and contents of chemical elements,the wear mechanism of the tool was further studied.The main wear forms of the B4C-30%Ti B2 ceramic tool are craters,chipping,and flank wear,and the wear mechanism can be attributed mainly to abrasive wear,adhesive wear,oxidative wear,and diffusion wear. |
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