Experimental Study On Cutting Ultrafine Crystalline Cemented Carbide With Single Abrasive Grain

Ultrafine grained cemented carbide has higher hardness and strength compared with conventional cemented carbide,and is widely used in cutting tools,military industry and other fields.It has a broad market space and application prospects.Cemented carbide is prone to crack in machining area,resulting in deterioration of machined surface and difficult to realize its ultra precision machining.Therefore,it belongs to typical difficult to machine material.Scholars at home and abroad have carried out a great deal of research work,but most of the research focuses on how to improve their physical and mechanical properties,keep the stability of their quality and evaluate the wear resistance of them,and have not studied the mechanism of material removal and the quality of the surface processing.The essence of grinding is micro edge cutting,so single abrasive grinding is a simplified model of grinding wheel grinding process.It is an effective method to study the mechanism of complex grinding.In this paper,a single abrasive cutting experiment is carried out on common cemented carbide and ultrafine grained cemented carbide.The influence of grain size,wheel speed,workpiece speed and cutting depth on cutting force is analyzed.The results show that the cutting force decreases with the increase of the linear speed of the grinding wheel,and increases with the increase of workpiece speed,and increases with the increase of cutting depth.Under the same grinding technology,the smaller the grain size is,the greater the cutting force of cemented carbide will be.The experiment also found that the influence degree of cutting force ranged from large to small in order of cutting depth,grinding wheel linear speed and workpiece speed.The influence of cutting depth and grinding wheel line speed on cutting force is very significant,and the speed of workpiece is generally related to cutting force.The scratch morphology is studied from macroscopic to microscopic by means of the ultra deep microscope system and scanning electron microscope.It is found that the ordinary cemented carbide and superfine crystalline cemented carbide are slightly erasing during the scratch phase,and the bonding phase Co forms a smooth area in the local coating.There is no micro cracks and pits on the scratch surface of the superfine crystal cemented carbide,and the surface of the scratch and concave pit can be seen on the scratch surface of the ordinary hard alloy.In the middle stage,the cutting force increases significantly with the increase of the cutting depth,and the adhesive phase is more easily extruded and plastic deformation migration.The cutting force acts on the hard phase on the scratched surface,making the error density in the hard phase increase.When the dislocation density accumulates to the critical value,the micro crack will be formed on the hard phase.Along with the increase of cutting depth,micro cracks will expand directly along the hard boundary,resulting in brittle fracture and visible chip formation.Ultrafine grained cemented carbide has smaller grain size and smaller hard phase defects,which is more difficult to break or fall off.In addition,based on the existing critical transition depth model,the three-dimensional surface contour method is used to study the cutting depth of the plastic brittle critical transition,and the applicability of the existing model is verified.In addition,it is found that the critical transition depth of the ordinary cemented carbide is greater than that of the superfine crystal cemented carbide,indicating that the superfine crystal cemented carbide is more difficult to be processed than the ordinary hard alloy.In order to realize high efficiency and low damage precision machining of superfine crystalline cemented carbide,it often needs larger grinding wheel speed,smaller workpiece feed speed and cutting depth compared with ordinary cemented carbide.