Study On Creep Feed Grinding Mechanism And Surface Quality Of Cemented Carbide Shank-type Tool

The cemented carbide shank-type tool is widely used in metal cutting because of its wide range of processed materials,excellent cutting performance and long service life.The cutting performance and stability of the tool mainly depend on the quality of the grinding,so the grinding operation of the cemented carbide shank-type tool is very important.The process of cemented carbide shank-type tools with the structure of helical groove should be processed with creep feed grinding.Large depth of cut,long arc of cut and very slow feed rate are the predominant features of this process.The grinding force,the grinding heat and the surface quality of the grinding are different from the reciprocating grinding.The helical groove of shank-type tool is a complex space surface,it is difficult to process,and the quality is not easy to guarantee.Therefore,it is necessary to carry on the intensive research to the grinding mechanism of the helical groove of the cemented carbide shank-type tool.The grinding process of helical groove of twist drill and end mill is taken as the research object in this dissertation.The grinding geometrical parameters of the spiral groove are analyzed.The grinding force,grinding temperature during grinding and surface quality of the helical groove were measured.And the relationship between them and the process parameters is analyzed.These studies provide a theoretical basis for grinding surface quality control and grinding process parameter optimization.The main research work includes:(1)Geometrical parameters of the grinding of helical groove of cemented carbide shank-type tool were studied.Based on the machining principle of helical groove,the grinding contact area in flute grinding was determined by the grinding wheel position.The calculations included the grinding of twist drill helical groove by shape wheel,the grinding of twist drill helical groove by 1A1 wheel and the grinding of end mill helical groove by 1A1 wheel.The three-dimensional model of the tool was established by the contact area parameter and verified with the actual workpiece.The geometrical wheel-workpiece contact length,cutting path on the contact,equivalent diameters and speeds of the wheel and workpiece,undeformed chip thickness,removal rate per unit width in flute grinding were analyzed in the contact area.(2)The grinding force of the creep feed grinding of helical groove was studied.Based on the wheel discretization method,the shape wheel was considered to consist of a series of different diameter and unit thickness discs.The grinding force of a single disc was analyzed.The relationship between the axial grinding force and the tangential grinding force during the grinding process of the helical groove was obtained.Based on the axial grinding force and torque of the workpiece,a grinding force ratio mathematical model was established to characterize the sharpness of the grinding wheel.A set of dynamometer system for directly measuring the axial grinding force and axial moment during the grinding process of the helical groove was developed.The variation of grinding force changes with time was obtained.The effects of wheel speed,axial feed rate and grinding wheel grit size on grinding force and grinding force ratio were analyzed by orthogonal test.The correctness of grinding force ratio model was verified.Through the analysis of the grinding force ratio,the grinding wheel grain size parameters in the grinding process were optimized.(3)The grinding temperature of helical groove grinding was studied.Based on the circular arc heat source model,the size of creep feed grinding and high efficiency deep grinding temperatures was compared and analyzed.The effects of Pekler number,grinding wedge angle and deflection angle of grinding contact on the dimensionless grinding temperature were analyzed.The effects of the circumferential velocity and the radius of rotation on the temperature field in the spiral motion were analyzed by solving the temperature field of the continued point heat source.Based on the assumption that the workpiece temperature,the grinding fluid temperature and the abrasive grain temperature were the same,the distribution of the critical burn heat flux in the helical groove grinding contact of the twist drill was calculated.The method of increasing the convective heat transfer coefficient to the grinding contact was analyzed.Using the thermocouple temperature measurement technology,the influence of the ordinary parallel grinding wheel and the grooved grinding wheel on the grinding temperature was analyzed on the five-axis linkage tool grinding machine.The research provided a scientific basis and practical method for reducing the grinding temperature of creep feed grinding of helical groove.(4)Grinding temperature simulation in grinding of helical groove using finite element method was researched.The single groove and double groove finite element models of helical groove were established,in order to analysis the influence of the helical groove structure on the grinding temperature field.The relationship between per unit area tangential grinding force and dimensionless undeformed chip thickness was established through the plane creep feed grinding test.Then the relationship between heat flux density and dimensionless undeformed chip thickness in grinding zone of spiral groove was obtained.The convection heat transfer coefficient of the workpiece was calculated by using the flow heat transfer theory.The heat flux density of grinding contact zone was discretized and applied by non-uniform loading method.The position of grinding burns was predicted by the established model,which provided the theoretical basis for the grinding burn detection of helical groove.(5)The grinding surface quality of helical groove was studied.The surface morphology of the helical groove of the twist drill was detected by a white light interferometer.The characteristics of the surface topography were obtained and analyzed.The effects of grinding parameters on the surface roughness and the microstructure of the surface were analyzed by orthogonal test.The grinding process parameters were optimized by taking the surface roughness as the response value.(6)The surface roughness model of the helical groove of the end mill was studied.Considering the effect of plastic upheaval deformation of cemented carbide and tilt angle between wheel speed and workpiece speed on surface roughness,the theoretical model of the roughness of helical was established.The effects of grinding wheel diameter,grinding wheel speed and workpiece feed rate on grinding surface roughness were analyzed.The correctness of the theoretical model was verified by experiments.(7)The surface quality of cemented carbide grinding by cup grinding wheel was investigated.The influence of grinding wheel speed and feed speed on residual stress of workpiece surface was studied by cup grinding experiment.The surface topography of workpiece under different grinding wheel speed was analyzed.The gradient residual stress along the thickness direction was obtained by chemical exfoliation method.The surface morphology of the workpiece under different etching time was analyzed.The research provided a reference for the optimization of process parameters.