Experimental Study On The High And Ultra-high Speed Grinding Of The HVOF Sprayed WC-Co Coating

High velocity oxyfuel (HVOF) sprayed WC-Co coating is widely used in the fieldof surface engineering and repairing the size and precision of the key parts of machineryand equipments, because of its special properties, as well as low porosity, high bondstrength, microhardness and wear resistance. However, the physical properties of HVOFsprayed WC-Co coating including high hardness, wear resistance and poor thermalconductivity have become the bottleneck of the improvement of its processing efficiencyand quality. Researches show that, high and ultra-high speed grinding technology is thehigh effective and low damage way of processing hard and brittle materials. In order toanalyze its grinding performance, the surface quality and the removal mechanism of thecoating’s material in high and ultra-high speed grinding, experimental investigations ofgrinding HVOF sprayed WC-17Co coating are tacken place in this paper by using threegrinding wheels, and the main research contents are as follows:(1)The grinding forces in condition of different grinding parameters are gatheredand analysed, a signal conditioner is designed and manufactured according to theworking conditions of thermocouple and the grinding temperature are measured by theclip type of artificial thermocouple，and the surface residual stress of the coating aremeasured by using X ray diffraction, and the influence of different grinding parameterson grinding forces are studied, and the inner relationship between the grindingtemperature and residual stress is discussed.(2)Observing and analyzing the state and change regulation of the surfacemicro-topography, the surface roughness and the surface and subsurface damage withdifferent grinding parameters; discussing the removal mechanism of the material, andanalyzing the influence of grinding parameters on surface roughness, and revealing therelationship between the maximum undeformed chip thickness and the depth ofsubsurface damage layer.(3)Preliminary developing a method based on the thermogram detection andsegmentation technology to detect the grinding wheel loading; analysising the effect andapplicability of the three kinds of methods including threshold segmentation, edgedetection and region growth to segment the grinding wheel loading image; contrastingthe test results of loading characteristic between thermography and micrographic;discussing the error sources of the thermography way.The results show that: (1)With the increase of the grinding wheel velocity, the tangential grinding forcesfirst decrease sharply and then increase slowly, and the normal grinding forces decrease,and the grinding temperature rise, and the residual stress change from compressive stressto tensile stress; with the increase of table speed and grinding depth, the grinding forcesincrease gradually; but the change trend of normal grinding forces which use thegrinding wheel Ⅲ is opposite, the reason is that the high grinding temperature causes asharp drop in the grinding performance of it.(2)In the range of grinding parameters used in experiments, the removal mode ofthe coating materials is both plastic and brittle, and the mian removal mode is brittle;with the increase of the grinding wheel velocity, the ductile removal trend of the coatingmaterials becomes enhanced gradually, and the surface roughness decreases gradually,but with the increase of table speed and grinding depth, the surface morphology and thesurface roughness almost remain unchanged.(3)The main form of the coating surface and subsurface damage are scratch,fracture and crack, the surface and subsurface damage of the coating ground by wheel Ⅰis mainly represented as the fracture on surface material, and represented as crackground by wheel Ⅱ，and represented as crack in low speed and scratch and fracture inhigh and ultra-high speed ground by wheel Ⅲ; with the increase of the maximumundeformed chip thickness, the depth of surface and subsurface damage layer ground bygrinding wheelⅠ, Ⅱ increases gradually, but it decreases which ground by wheel Ⅲ.The reason is that the grinding force of wheel Ⅲ in high and ultra-high speed is unusual.(4)The method of thermography can realize quantitative detection of loadingcharacteristics of grinding wheel, but the detection precision is limit by the resolution ofthermal imager and the extraction method of loading characteristics, and the detectedaverage diameter of loading debris and the percentage of loading area is bigger than themicrographic method of. There is still a great room for improvement of the checkequipment precision and extraction method of loading characteristicss.Through a large number of experiments analyzed the impact of various processingparameters on the processing quality evaluation factors such as grinding force, grindingtemperature, residual stress, surface micro topography, surface roughness, surface andsubsurface damage，the test results have a certain significance.