Study On Fatigue Damage Characteristics Of Heavy Milling Cemented Carbide Tools

Water chamber head is an important part of steam generator in nuclear power plant,the material is of high strength steel 508Ⅲ steel,the blank part of the head of the water chamber is forged as a whole,and the size and weight of the blank are large,and the machining allowance is also large.Its manufacturing process is extreme manufacturing,depending on the large size of the parts,the allowance for processing and the difficulty of processing.The main processing method is heavy milling.There are forging defects on the surface,which make the cemented carbide tool bear random shock and vibration in the machining process.At the same time,the mechanical and thermal load of cycle causes the tool failure seriously,and the tool life is low.In particular,fatigue damage seriously affects processing efficiency.Therefore,the fatigue damage of cutting tools during heavy milling of water chamber head is studied,and the crack propagation damage evolution of cemented carbide cutting tools during machining is analyzed,which lays a solid foundation for improving cutting performance and machining efficiency of cemented carbide cutters.Firstly,the feasibility of damage mechanics is studied,and the initial state,crack propagation and failure process of cemented carbide cutting tools in heavy milling are analyzed by using damage mechanics.The damage evolution of the tool under cyclic mechanical-thermal load is described.The field test of heavy milling was carried out to determine the wear and fatigue failure of the tool.The microcosmic morphology of crack growth and the macroscopic behavior of damage were studied by observing the blade under different milling time.In the end,the micro crack propagation behavior of carbide tool is analyzed from two aspects of cyclic loading and temperature change,which provides a theoretical basis for the study of the crack propagation of tool materials.Secondly,the damage parameters are studied,and the damage variable D is defined to describe the internal damage quantity of the material,and the quantitative relationship between the damage parameter and the macroscopic parameter is established,damage dynamics of material internal plasticity and energy dissipation during milling.The stress intensity factor K is established to characterize the stress state at the crack tip,and the mechanical stress distribution and heat source distribution at the crack tip of the tool are analyzed.The theoretical parameters are provided for the simulation study.Finally,the fatigue crack propagation analysis principle,the establishment of Paris formula to describe the crack growth damage stable phase change,analysis and definition of the stress intensity factor of the crack tip plastic zone size,get the fatigue damage model of cemented carbide tool materials,provide theoretical research for fatigue damage characteristics of heavy milling hard alloy tool and evolution analysis.Thirdly,the high temperature mechanical property test of the cemented carbide tool material is carried out,and the change tendency of the strength and modulus of the hard alloy material in the high temperature state is analyzed,and the parameters are provided for later simulation.The fatigue crack propagation test of cemented carbide material is carried out,and the relationship between the number of cycles and the crack length is established.At the same time,the stress intensity factor amplitude and crack growth rate curve are obtained by fitting the data,the Paris formula is established,and the basic research is provided to study the fatigue crack propagation characteristics of the hard alloy cutter material.Finally,the fatigue crack propagation model of cemented carbide tools is studied,the internal force-displacement model of the crack tip is established,the relationship between the stress and the opening displacement of the crack surface is analyzed,meanwhile,the stress and displacement changes in the crack propagation process are analyzed,the evolution curve of the fatigue damage is established,the internal damage evolution of the hard alloy cutter material is explored,the fatigue life of the hard alloy material is researched,and the technical support for improving the anti-fatigue performance is provided.