Self-sharpening Characteristic Of PCBN Superabrasive Grain And Workpiece Scratch Profiles Evolution During Grinding

Polycrystalline cubic boron nitride(short for polycrystalline CBN),synthesised by microcrystalline CBN particles and Al N ceramic binders under high–temperature and high–pressure conditions,is a typical kind of super–hard material which has the high hardness and high wear resistance similar to the conventional CBN material.The single–layer brazed grinding wheel made of the polycrystalline CBN superabrasives has been thought as the ideal tool to mahine the workpiece made of nickel–based superalloys.The reason is mainly attributed to that,the microcrystalline CBN particles can be outcropped on the polycrystalline CBN grain surface to enhance the grain cutting performance by spalling the Al N ceramic binders during grinding due to the special CBN–Al N microstructures of the polycrystalline CBN.The polycrystalline CBN grain shows promising self–sharpening characteristics in the actual grinding process.However,most of the investigations performed on the self–sharpening characteristics are only qualitative analysis,and the grinding performance of the polycrystalline CBN grain is estimated by judging the grain wear/fracture morphologies.The self–sharpness of the polycrystalline CBN grain which differs with the conventional CBN grain has not been characterized quantitatively.Moreover,the factors which contribute to the better grinding performance of polycrystalline CBN grain still remain unclear.Therefore,the wide application of the polycrystalline CBN superabrasives in high effecuency and high quality grinding of the nickel–based superalloys has not been accepted in the actual grinding operation.For these abovementioned reasons,an investigation on the self–sharpening characteristics of the polycrystalline CBN grain and the workpiece scratch profiles in grinding is performed in this work.The factors that contribute to the self–sharpening characteristics of the polycrystalline CBN grain during grinding are analyzed from the viewport of the polycrystalline CBN grain wear/fracture mechanisms and the grinding performance of the conventional CBN grain and the polycrystalline CBN grain.In addition,the workpiece scratch profiles caused respectively by the conventional CBN grain and the polycrystalline CBN grain are investigated to understand the grain wear differences between the conventional CBN and the polycrystalline CBN.The main work and results are summarized as follows:(1)The grain wear/fracture characteristics of the polycrystalline CBN during grinding are investigated by numerical simulation analysis and experimental validation.The obtained research results indicates that the main fracture mode of the polycrystalline CBN grain during grinding is the intergranular fracture,the grain micro–fracture behavior mainly appears on the grain vertex region,while macro–fracture behavior tends to appear around the grain–filler region.In order to avoid the grain macro–fracture behavior,the underformed chip thickness per grain should be kept lower than1.0 ?m during grinding.(2)The comparative single grain grinding operations by respectively using the polycrystalline CBN grain and the conventional CBN grain are carried out.The grinding performance of the polycrystalline CBN grain that differs with the conventional CBN grain is presented from the viewport of the grain wear morphologies,the grain relative height,the grinding force and the grinding force ratio.In addition,a mechanical model of the abrasive grain in grinding is established to understand the factors that results in the self–sharpness ability of the polycrystalline CBN grain.(3)The GH4169 workpiece scratch profiles are observed in the single grain grinding operations.The influence of the grain wear characteristics differences between the conventional CBN and the polycrystalline CBN on the workpiece scratch profiles are investigated to better understand the self–sharpening characteristics of the polycrystalline CBN grain during grinding.This research could deeply understand the self–sharpening characteristics of the polycrystalline CBN grain and the corresponding single-layer brazed grinding wheel,and extend their wide application in grinding of the difficult–to–cut metallic materials in the aerospace and aviation industry.