Study On The Grinding Performance Of A Novel CBN High Speed Point Grinding Wheel

The grinding processing is widely used in manufacturing process technology and usually regard as a final machining process,which is the process of the grains in grinding wheel surface carving workpiece and chip removal.Therefore,the precision and strength reliability of workpiece surface after grinding are very important.Point grinding processes the cylindrical workpiece in the way of point contact and high-speed.Point grinding as an advanced grinding technology has the advantage of process concentration,the large production,high precision,good surface quality and high efficiency.The abrasive layer width of point grinding wheel is only 4-6mm,which makes it have more processing flexibility and easy realizes complex rotary surface CNC machining compared with the traditional grinding method.In this paper,a novel point grinding wheel with coarse grinding area angle ? is prepared.The research of grinding mechanism,grinding force,grinding vibration,grinding temperature,grinding surface quality and acoustic emission signal monitoring are conducted to explore the grinding performance of the novel point grinding wheel.This paper main research work manifests in the following several aspects:(1)The novel point grinding wheel with coarse grinding area angle ? is proposed in this paper,which has the advantages of high machining efficiency and small grinding force.On the basis of the existing point grinding theory,the geometry shape between the novel grinding wheel and workpiece contact area is studied and the theory model of novel grinding wheel grinding is established.The size of novel grinding wheel is designed and performance parameters are selected,meanwhile the trilinear coordinates measuring instrument is used to check the processing precision.(2)There is inclining angle a between the grinding wheel axis and workpiece axis,the point grinding force and theory model changed with the grains motion path in grinding processing.On the basis of traditional grinding force theory,the grinding force theory model of the novel point grinding wheel are built by using the model transformation and the experiments are conducted to verify the correctness of the theory model.Point grinding force model provides an analysis and validation method for actual processing.The effects of the coarse grinding area angle ?,inclining angle a,grinding depth ap and grinding wheel speed vs on the tangential grinding force and normal grinding force are obtained.By grinding vibration experiment,the different wheel speed corresponding to the different grinding vibration is studied and the effects of various parameters on the tangential amplitude and normal amplitude are obtained.(3)Grinding temperature plays an important role in surface quality.The finite element method is used to simulate the grinding contact area temperature change and estimate the workpiece hardened layer thickness affected by the temperature,which provides an auxiliary prediction method for experiments.The infrared temperature measurement method is convenient and quick,but the measurement value is lack of accuracy.The thermocouple temperature measurement method is difficult to place thermocouples due to external cylindrical grinding and involved wire winding,but the measurement value is relatively accurate.These two methods are applied respectively to measure the grinding area temperature,The effects of coarse grinding area angle ?,inclining angle a,grinding depth ap,axial feeding speed vf and grinding wheel speed vs on grinding temperature are obtained.(4)Grains motion path will be changed in the point grinding process due to the existence of variable angle a.The particle trajectory in the manufacturing process changes due to inclining angle a existed point grinding.In order to verify the difference between the point grinding and traditional grinding,the motion relationship and coordinate transformation between grinding wheel and workpiece are used to obtain the point grinding cutting path by the particle movement function equivalent to parabola.Based on grains distribution on the grinding wheel surface,the 3D geometry simulation topography of workpiece is obtained by extending the effective interference trails along the axial direction.Simulation results are verified by the point grinding experiments.The results indicated that the simulation microstructures are coincided well with the experimental measurements and the values of simulation roughness are 0.5 times of experiments.So,geometric simulation model provides an auxiliary and prediction method for the actual processing topography analysis.In addition,grinding wheels with different 9 are used to grind ladder shafts with a series of grinding parameters.The influence trend of various parameters on surface roughness is obtained.(5)The machined surface microstructure observation found that the metallographical structure transformation did not occur on grinding surface and subsurface.However,the hardened layer appeared on workpiece surface after grinding,which increases the workpiece surface hardness by measuring the Vickers hardness of the grinding surface.The hardness of hardened layer 275HV is 34%more than matrix hardness 205HV.It can be also found that the hardness of hardened layer decrease gradually with the depth increased,until the same as the matrix.The influence of coarse grinding area angle ?,inclining angle a,grinding depth ap and grinding wheel speed vs on the hardness of grinding surface and subsurface can be obtained.By measuring the grinding surface residual stress,it can be concluded that there is residual compressive stress on workpiece surface and the compressive stress decreases gradually on the subsurface along the depth direction,then the compressive stress gradually transformed into tensile stress.The influence of parameters on grinding surface and subsurface residual stress along the depth direction is obtained.(6)Grinding processing is complex and prone to be instable state such as burns,vibration and grinding wheel dull,at the same time,the contact state of the grinding wheel and workpiece should be aware.The different contact state of the workpiece and the grinding wheel and the grinding wheel wear before and after corresponding to different acoustic emission signals.So,it is a good way to conduct real-time monitoring the grinding process and the contact state between the grinding wheel and workpiece by using acoustic emission signal.In addition,the influence of different parameters on the acoustic emission signal RMS value and acoustic emission signal spectrum analysis are studied and it can be found that the surface roughness have some corresponding relation with the acoustic emission signal.At last,the obtained conclusions are summed up in this paper,and some suggestions are given aimed at the problems existing in the learning process in the whole study.