Research On Processing Technology Of Super-hard Shaft Parts

GCr15 bearing steel is a high carbon chromium bearing steel with less alloy content,because of its high hardenability,after heat treatment such as quenching and tempering,it can obtain high and even hardness,excellent wear resistance and high contact fatigue strength.It is widely used in making ball screw of machine tool,nozzle,plunger,valve and bush of nozzle of turbojet engine.It can also be used to make dies,measuring tools,etc.Because of its high hardness,wear resistance and heat resistance,the superhard tool material CBN is often used for hard cutting of hardened steel.In the process of hard cutting of hardened steel with CBN tool,there will be a lot of cutting force,and with a lot of cutting heat,the cutting temperature will be very high,which will lead to the increase of tool wear.Aim at the phenomenon of high cutting force and increased tool wear during the hard cutting of super-hard shaft parts,a machining method witn surface texture is used to reduce cutting force and tool wear.In this paper,CBN tool is used to cut GCr15 Bearing Steel in hard state.After quenching,the hardness of GCr15 bearing steel reaches 60 ± 2hrc.The cutting speed(85m / min,99 m / min,119 m / min,151 m / min),feed rate(0.05mm/rev,0.1mm/rev,0.15mm/rev,0.2mm/rev),cutting depth(0.1mm,0.2mm,0.3mm,0.4mm)are selected to design single factor and orthogonal experiment.The influence of cutting parameters on cutting force is studied by single factor experiment,and orthogonal cutting experiment is simulated by metal cutting simulation software,and compared with orthogonal cutting experiment.The optimal cutting parameters(cutting speed 85 m / min,feed rate 0.1m/rev,cutting depth 0.3mm)were determined by orthogonal cutting experiment.Under this cutting condition,the minimum cutting force was 71.48 N.Using ANSYS to simulate the temperature field of the preformed pit texture in EDM.Selecting peak current(10a),voltage(15V),discharge channel radius(0.2mm)and pulse width(3MS)as parameters,the analysis of temperature field chooses 0.5ms,0.1ms,0.15 ms,0.2ms,0.25 ms and 0.3ms as the research object.The shape of the weld pool is drawn and the change trend of the depth and diameter of the weld pool with the pulse width is analyzed,the pit texture diameter was 0.44 mm,and the depth was 0.135 mm.Using electric spark high speed piercer to put the pre-set pit texture into the bearing steel of GCr15.The simulation parameters of the temperature field of electric spark piercing are selected to carry out the pre-set pit texture experiment.The pit texture is evenly distributed on the surface of GCr15 hardened steel,with an axial spacing of 5mm and a circumferential angle of 30 °.The diameter and depth of the texture were measured by the ultra depth of field microscope,and the simulation results were compared with the experimental results.Finally,the pit texture diameter was 0.4mm,and the depth was 0.13 mm.Under the optimal cutting conditions determined by orthogonal experiment,CBN tool is selected to carry out hard cutting experiment on the GCr15 hardened steel with preset texture.The measured value of cutting force is 83.67 N,which is about 46.65% lower than the minimum cutting force obtained by texturless cutting.CBN cutters perform the same amount of hard cutting processing on non-textured Gcr15 hardened steel and preset textures under the same cutting conditions.The morphology of the rake face and the flank face of the tool is observed through a super depth of field microscope.The amount of tool wear during non-texture cutting is much higher than that under pre-fabric cutting conditions.It is found that the method of presetting surface texture can effectively reduce cutting force and tool wear by comparison.