Experimental Study On Grinding Process Of Superhard Coatings

Some key components of the nuclear main pump,which is the core of the nuclear power plant,have the requirements such as high hardness,high wear resistance and so on.Based on the requirements above,WC-12 Ni coating produced by HVOF is gradually applied in some key components of the nuclear main pump for its superior mechanical and physical properties.At presents,the study of WC-12 Ni coating processing is relatively few.The grinding of WC-12 Ni coating has an important theoretical significance and practical value to the early realization of the nuclear main pump manufacturing and WC-12 Ni coating`s subsequent engineering application.This paper uses precise horizontal spindle and rectangular table surface grinder to grind WC-12 Ni coating for experiment study.The experiment aims to explore the influence of grinding parameters,grinding wheel features on grinding force,grinding force component ratio,specific grinding energy,grinding roughness and grinding surface residual stresses,and analyze WC-12 Ni coating grinding material removal mechanism,combining with the grinding surface morphology and the sub-surface damage observation.The main work includes:(1)With the increasement of the grinding depth and workpiece feed speed and the increasement of grinding abrasive,the normal grinding force and tangential grinding force increase.With the increasement of the grinding depth,the grinding force component ratio increases and specific grinding energy decreases.With the increasement of the workpiece feed speed,the grinding force component ratio and specific grinding energy are characterized by decreasing gradually.The mathematical model of single diamond grit grinding force of WC-12 Ni coating is established by using the equivalent grinding thickness.(2)The grinding surface residual stress is characterized by residual compressive stress.As the grinding depth and workpiece feed speed rise and grinding abrasive falls,the residual compressive stress parallel to grinding direction and vertical to grinding direction increases.But it increases slowly and gradually.The residual compressive stress vertical to grinding direction is slightly higher than that parallel to grinding direction.A mathemathical model of WC-12 Ni coating grinding surface residual stress parallel and vertical to grinding direction is established.This model is reliable and practical whose average error is within 5%,comparing to calculated values.(3)With the increasement of the grinding depth and workpiece feed speed,the grinding surface roughness values are presented a trend of first increasing slightly,then decreasing and finally a small increasment again.But the grinding depth has few influences on surface roughness,and the best workpiece feed speed is 8 m/min.According to the surface morphology and sub-surface damage observation of WC-12 Ni coating after grinding,it found that the grinding surface feature is mainly characterized for the trench.Also the width and depth of the trench increase with the increasement of the grinding depth and workpiece feed speed.The comparsion between the measured single diamond grit normal grinding force and theoretical calculation of critical load of lateral or radial cracks combining with the surface morphology and sub-surface damage observation under different grinding depths and workpiece feed speeds showed that there is no lateral or radial cracks and WC-12 Ni coating grinding material removal mechanism is mainly characterized for plastic deformation mode,accompanied by a small amount of material powder broken.