Study On Scratch Mechanism Of Gear Grinding On 20CrMnTi Steel With Microcrystalline Ceramic Abrasive Wheel

The development of automobile industry needs higher machining precision and efficiency of gear.Gear grinding is one of the important procedures in the gear machining technology which determines the machining precision and surface quality of gear.In this thesis,the simplified methods of cylindrical gear grinding and spiral bevel gear grinding were discussed.The scratch mechanism of gear grinding on 20CrMnTi steel with microcrystalline ceramic abrasive wheel was investigated through the single grit scratch and successive grits scratch experiment.An existing surface roughness model in grinding process was modified by considering the result of successive grits scratch experiment.Simplified methods of cylindrical gear grinding with a worm grinding Wheel and spiral bevel gear grinding with generating method were discussed.The relative velocity at the meshing point of the grinding wheel and the gear,and the curvature radius of conjugate surfaces in the direction of velocity vector were calculated out.The cylindrical gear grinding with a worm grinding wheel can be simplified as surface grinding,and the spiral bevel gear grinding with generating method can be simplified as internal grinding.The scratch mechanism of single grit scratch with microcrystalline ceramic abrasives on carburizing hardened 20CrMnTi was investigated.The result shows that the scratch groove is generated by multiple micro-cutting edges on single abrasive grit surface.The scratch groove is characterized by plastic flow.The scratch force including normal and tangential direction was increased with an increase in the scratch depth.With an increase of scratch velocity,the normal force was firstly increased and then decreased,and the tangential force and unit grinding force was decreased gradually.Wear behaviors of microcrystalline ceramic abrasives were analyzed.The result shows that the wear types of microcrystalline ceramic abrasives are micro fracture,abrasion and adhesion.And the micro fracture is the main wear type for microcrystalline ceramic abrasives.However,the strain rate strengthening effect dominates the plastic deformation of material at a low scratch velocity,and the material is removed in the form of blocky chips.At a higher scratch velocity,the adiabatic shear effect occurs in the front of the abrasive grit and the material is removed in the form of serrated chips.The effect of scratch depth and scratch velocity on the plastic uplift height was researched.It is shown that the plastic uplift height was changed as a fluctuation in diauxie curve with an increase in the scratch depth at a scratch velocity of lOm/s.At the rest three scratch velocities,the plastic uplift height changing trend was similar and slight variable.The plastic uplift height was decreased with an increase in the scratch velocity at a constant scratch depth.The scratch mechanism of successive grits scratch with microcrystalline ceramic abrasives on carburizing hardened 20CrMnTi was investigated.During the successive grits scratch experiment for same grit trajectory,the plastic uplift was observed besides the second scratch groove.The plastic uplift height was increased with an increase in the scratch depth,and was decreased with an increase in the scratch velocity.The plastic uplift modes are jagged edges and large-area block burrs.The tangential force of up scratch is bigger than that of down scratch.The plastic uplift height is higher than that of single grit scratch.During the successive grits scratch experiment for different grit trajectory,the edge on first scratch groove can be removed by the subsequent abrasive grit during the second scratch,and the plastic uplift besides the second scratch groove flows towards the first scratch groove as a result of the subsequent abrasive grit.The scratch force of successive grits scratch for different grit trajectory is less than that in single grit scratch and successive grits scratch for same grit trajectory.During the successive grits scratch experiment for variable grit spacing,the normal force of second scratch was decreased with a decrease in the grit spacing,but the tangential force reached its minimum at the grit spacing of 20μm,which demonstrates that the subsequent abrasive grit in successive grits scratch for different grit trajectory is shaper and of higher material removal efficiency.The scratch mechanism of successive grit scratch was analyzed.The result shows that the scratch process of subsequent abrasive grit includes rubbing,ploughing and cutting.Under the high strain rate and adiabatic status,the adiabatic shear effect occurs in the front of the abrasive grit,and the material is mainly removed in the form of serrated chips.The linear regression equation of plastic uplift height in the second scratch of successive grits scratch experiment for same grit trajectory was built.An existing surface roughness model in grinding process was modified taking into account the effect of the material plastic flow and the plastic uplift and verified experimentally.