| Because of their high hardness,high wear resistance,good chemical stability and hightemperature mechanical properties,ceramic tools are recognized as one of the most competitive high-speed cutting tools for processing superalloys.The length-diameter ratio of solid ceramic end milling tools is large,and the milling belongs to intermittent processing.Therefore,the shortcomings of the ceramic material,such as high brittleness,poor vibration and impact load resistance,are magnified,resulting in the failure of the cutting edge during the milling process.To sum up,reducing the vibration during the cutting process is the key to improve the tool life of solid ceramic end milling tools.This study aims to reduce the cutting vibration of the solid ceramic end milling tools and improve the tool life.Through the optimization design of tool structure,studying the vibration reduction mechanism,system milling stability and tool dynamic balance,a new type of solid ceramic end milling tool with unequal tooth pitch was developed.The optimal cutting parameters were selected by the discrete element numerical simulation method.The experimental results show that the designed solid ceramic end milling tool has excellent cutting performance.The main research contents of this paper are as follows:The structural design criteria of solid ceramic end milling tools were studied.Based on this,the preliminary design of the solid ceramic end milling tool was completed.The main structural parameters of the tool were optimized by finite element simulation,and the cutting performance and wear mechanism of the tool before and after optimization were studied by comparative experiments.The results show that the optimal structural parameters of the tool obtained by finite element simulation are:the radial rake angle of the circumferential cutting edge is-8°,the radial clearance angle is 10°,and the helix angle is 40°.After the structure optimization,the tool life is increased by 42.9%,the flank wear is reduced by 39%,the cutting force is reduced by 5.4%,and the machined surface roughness of the workpiece is reduced by 5.5%.The cutting force model of solid ceramic end milling tools with unequal pitch was studied.The optimal distribution function of tool teeth was established.Three types of tool structures with unequal pitch were optimized.The milling stability and dynamic balance characteristics of unequal pitch ceramic end milling tool were studied.The results show that the angle distributions between teeth of three optimized unequal pitch milling tool structures are:93°91°-88°-88°(abbreviated as T1),95°-85°-85°-95°(abbreviated as T2),83°-83°-98°-96°(abbreviated as T3).The main and second spectrum values of the three unequal pitch milling tools are lower than those of the pitch milling tool,and the spectrum of cutting force is more dispersed.The minimum limit cutting depth apmin of the equal pitch ceramic end milling tool and the three unequal pitch ceramic end milling tools is sorted as follows:T2>T1>T3>E2,the stable area ratio γ(the ratio of the stable area to the total area)is 0.417,0.631,0.680 and 0.575,respectively.It is verified from the theoretical point of view that the unequal pitch structure can improve the milling stability.The three tool structures are verified to meet the dynamic balance accuracy grade requirements of G6.3.Based on the three-dimensional discrete element numerical simulation method,the number of cracks and the number of shedding particles were used as indicators to study the wear condition of ceramic tools in the cutting process and optimize the machining parameters of solid ceramic end milling tools.The results show that with the increase in cutting speed,axial cutting depth and radial cutting width,the number of tool cracks and the number of shedding particles continue to increase.Considering the tool wear and machining efficiency,the optimal cutting parameters are selected as follows:cutting speed 500m/min,axial cutting depth 3mm,radial cutting width 1mm.The cutting performance of the new type of solid ceramic end milling tool with unequal pitch was designed and compared with that of equal pitch ceramic end milling tool E2.The vibration reduction performance of the designed solid ceramic end milling tool with an unequal pitch structure was verified by experiments.The results show that the unequal pitch solid ceramic end milling tool T1 and T2 have excellent performance in cutting tests.Compared with the equal pitch end milling tool E2,the tool life of T1 and T2 are increased by 30%and 40%respectively,the cutting force is reduced by 13.6%and 9.4%respectively,and the surface roughness of the workpiece is reduced by 21%and 10.95%respectively.Moreover,the machined surface defects of the workpiece are less,and the machining quality is improved.The vibration acceleration during the cutting process is reduced by 31.1%and 10.95%respectively,which verifies the good vibration reduction effect of the unequal pitch structure.Combined with the cutting performance of the tool,the comprehensive performance of the tool T1 is the best.The unequal pitch solid ceramic end milling tool T3 performs poorly.The increase in vibration caused by insufficient strength of tool teeth and large mass eccentricity is the main reason for the decrease in T3 cutting performance. |
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