Research On Cutting Performance Of WC-Co Ultrafine Cemented Carbide Cutting Tools

With the development of high speed cutting, super high speed cutting, precision moldsand tools, nano-machining and micro-machining, the requirements considering cuttingperformances are higher and higher. Compared with traditional medium-and fine-grainedcemented carbide, ultrafine-grained WC-Co cemented carbide possesses higher hardness,wear resistance and transverse rupture strength. Therefore, it is the trend in the developmentof cemented carbide cutting tools. In this paper, two kinds of ultrafine WC-Co cementedcarbide cutting tools were prepared by low pressure sintering method: one has0.2μm WCbut with different cobalt amount; one has0.5μm WC and cobalt10wt.%with and withoutgrain growth inhibitor, powder heat treatment and direct sintering. In this paper, themicrostructure of ultrafine cemented carbide tools was analyzed by SEM, mechanical andphysical performance was tested. Through some tests, the cutting force, cutting temperatureand the surface roughness of machined surface were measured, and tool wear and breakagewere observed. The cutting performances and cutting mechanisms of ultrafine cementedcarbide cutting tools were analyzed and discussed. The cutting performances of ultrafinecemented carbide tools were evaluated with the method of fuzzy mathematics, whichprovides a theoretical and technical basis for the development and application of ultrafineWC-Co cemented carbide cutting tools. The main research works and results are as follows:(1) The microstructure of0.2μm and0.5μm ultrafine cemented carbide materials wasanalyzed, and the mechanical and physical properties were tested. The results show that theultra-fining of WC grain and powder heat treatment before sintering can improve themicrostructure and the mechanical properties of ultrafine cemented carbides to some extent.The microstructure is closely related to the cobalt content of ultrafine cemented carbide, toohigh or too low cobalt content can bring negative effects to the microstructure, and alsoreduce the physical and mechanical properties of ultrafine cemented carbide cutting tools.Additive grain growth inhibitor can improve the grain size uniformity, density and hardness,but it leads to the decrease of toughness(2) Superalloy GH2132were cut by0.2μm and0.5μm ultrafine cemented carbide tools,the cutting force, cutting temperature and surface roughness of machined surface weremeasured, the micro morphology of machined surface was observed. The test data wereanalyzed by the linear regression, the law and empirical formula of cutting force, cutting temperature and the machined surface roughness were obtained. The three factors of cuttingparameter have no obvious effects on the average friction coefficient between tool and chip,but it has an influence on cutting force, unit cutting force, cutting temperature and themachined surface roughness. With the increasing cutting speed, the surface roughnessdecreases. With the decreasing of grain size, unit cutting force decreases, the surfaceroughness increases, and the relationship between grain size and cutting temperature isnon-linear. The effects of cobalt content on the cutting force, tool-chip average frictioncoefficient, cutting temperature and surface roughness show a complex non-linearrelationship, the appropriate cobalt content can make the cutting force, tool-chip averagefriction coefficient and the cutting temperature maintain at a lower level. The unit cuttingforce and tool-chip average friction coefficient of0.5μm ultrafine cemented carbide toolsincrease after adding grain growth inhibitors, and the surface roughness decreases, theeffects on cutting temperature which is related to the cutting parameter and thermalconductivity coefficient. Powder heat treatment makes the unit cutting force, tool-chipaverage friction coefficient and the surface roughness decrease, improve the surface qualityof machined surface, and it can reduce the cutting temperature to a certain extent, but thedegree of reduction is related to grain growth inhibitor.(3) The cutting experiments of difficult-to-machine material were performed by ultrafinecemented carbide tools, the micro morphology of tool flank wear and chemical compositionwere observed and analyzed respectively. The results show that the main wear of ultrafinecemented carbide tool is adhesive wear when cutting super alloy. The finer the WC grainsize, the better the tool’s wear resistance. To lower cobalt content appropriately can improvethe resistance performances of abrasive wear, diffusion wear and oxidation wear; on theother hand, the increasing of cobalt content is helpful to improve the resistanceperformances of adhesive wear and breakage, but too high or too low cobalt content isharmful to the resistance performances of tool wear and breakage. Powder heat treatmentand grain growth inhibitor can improve the wear resistance and anti-breakage performanceof ultrafine WC-Co cemented carbide cutting tools to a certain extent.(4) According to the experimental data of microstructure, fuzzy clustering diagram ofWC-Co cemented carbide cutting tool was obtained by fuzzy cluster analysis method. Afuzzy evaluation model of cutting performances was established based on fuzzy theory, andthe comprehensive model includes various factors which influence the cutting performanceof tool materials. The cutting performance of ultrafine cemented carbides tool was evaluated comprehensively, the optimal value of grain size, ingredient and processingtechnology of ultrafine cemented carbide cutting tool were determined.(5) The microdrilling tests of0.5mm micro-drills were performed. Both0.5μm,0.6μmultrafine cemented carbide and fine-grained were chosen as the tool materials, the wear andworking life of micro-drills were measured, the drilling performance of0.5μm WC-Coultrafine cemented carbide micro-drills were studied. The results show the working life ofYG10U-Ar-GGI micro-drill is the longest. The wear on cutting edge and fracturemorphology of YG10U-Ar-GGI micro-drill were observed and analyzed, and a preliminarydiscussion on the mechanism of wear and fracture failure were progressed in this paper.