Study On Cutting Tool Matching For High Speed Machining Of Compacted Graphite Iron

Compacted graphite iron(CGI)is an ideal material for the cylinder block and cylinder head of diesel engine because of its excellent physical and mechanical properties.At present,the researches on CGI mainly focused on experimental study of machining CGI,and there are few studies on the cutting simulation of cast iron,especially the high-speed machining process of cast iron.In addition,the selection of cutting tools and processing parameters for the machining of CGI in factories is mostly based on the experience of machining gray cast iron or the recommendation of tool manufacturers,lacking of theoretical guidance.In this paper,the Power-law constitutive equation of GJV450 was established and applied to finite element simulation.A model of the matching of the properties between cutting tool and workpiece materials was established to provide a basis for the rational selection of tool materials.The effects of cutting tool materials and cutting parameters on the machined surface integrity during the process of high-speed milling CGI were studied,which is helpful for the selection of processing parameters of CGI.The power-law constitutive equation of GJV450 under the condition of high temperature and high strain rate was established and then applied in FEM simulation.By fitting the plastic stage of quasi-static tension curve,the parameters of strain hardening term of the Power-law constitutive equation were obtained.The sensitivity of cutting force to the parameters of temperature softening term and strain rate hardening term in the Power-law constitutive equation was studied.The results showed that the main cutting force decreased with an increase in strain rate hardening parameter m1,while the parameters of temperature softening term had little effect on the cutting force.The parameters of temperature softening term in the power-law constitutive equation of GJV450 were approximately obtained by polynomial fitting the temperature softening term in JC model of pearlite.The parameter of strain rate hardening term was obtained by orthogonal cutting experiment and the iteration of finite element simulation,and the power-law constitutive equation of GJV450 material was established.Compared with the JC constitutive equation of pearlite which was commonly used in the literature for CGI cutting simulation and the constitutive equation of CGI in the AdvantEdge software,the power-law constitutive equation established in this study had higher simulation accuracy.And the finite element simulation of the orthogonal milling of CGI showed the same results.A model of the matching of the properties between cutting tool and workpiece materials was established and used to select the proper cutting tool materials for high-speed milling of CGI,and its effectiveness was verified.By combining rule-based reasoning(RBR)method with comprehensive gray complex proportional assessment(COPRAS-G)method in multi-criteria decision-making method,the matching model under actual cutting conditions was established.Carbide,ceramics and PCBN materials were selected as alternatives by RBR method,and the most suitable cutting tool materials for milling CGI were obtained by COPRAS-G method,which were alumina ceramic with carbide as the additive or cemented carbide with alumina as the coating material.The high-speed milling experiments of CGI with alumina-coated cemented carbide tool and silicon nitride ceramic tool were carried out.The results showed that the wear mechanism of coated cemented carbide tools in milling CGI were adhesive wear,thermal crack,and slight oxidation wear,while the main wear mechanisms of ceramic tools were diffusion,which resulted in a rapid increase in flank wear and a reduction in tool life.Coated cemented carbide tool had a longer life and it was more suitable for milling CGI,which verified the effectiveness of the matching model.The influence of cutting tool materials and processing parameters on the milling force and machined surface integrity of CGI during high speed milling process was studied.The results showed that the milling force increased proportionally with an increase in feed rate,while,with an increase in cutting speed,the milling force increased firstly and then decreased,and the milling force of ceramic tool was greater than that of cemented carbide tool.Within the range of processing parameters in this paper,the surface roughness decreased and then increased slightly with an increase in cutting speed.At lower speed,the surface roughness increased with an increase in feed rate,while at higher speed,the feed rate had little effect on the surface roughness.The microhardness of the machined surface increased with an increase in feed rate.There was compressive residual stress on the machined surface,which is helpful to prevent crack propagation,and the compressive residual stress increased with an increase in cutting speed while decreased with an increase in feed.It can be concluded that the suitable range of cutting speed in milling process(800 m/min ? v ? 400 m/min)was helpful to obtain a smaller surface roughness.In order to reduce surface roughness and avoid tensile residual stress on the machined surface,it is suggested that CGI be machined at higher cutting speed(v? 400 m/min)and lower feed rate(f ?0.1mm/tooth).