Study On Damage Characteristics Of Carbide Tool Material Under Heavy Cutting Heat

Water chamber head is the key part of nuclear power plant equipment,which has the characteristics of large mass,large volume and complex profile.The material is high-strength steel 508?,and the material removal rate from rough machining to finished product can reach more than 70%.The processing method is typical extreme manufacturing,mainly heavy milling processing.In the heavy cutting process,the cutting parameters are large,the impact of the tool is large,and the cutting force and heat change violently.The tool is required to have high hardness and good impact toughness.However,under a large amount of cutting heat,the cemented carbide tool will have local plasticity and plastic deformation,which provides for the damage and microstructure expansion of the original micro cracks,micro holes and other defects of the tool material under the action of cyclic mechanical load,the damage evolves continuously,resulting in accelerated tool wear and fracture failure.Therefore,based on the damage mechanics to analyze the damage characteristics of cemented carbide tools under the thermal effect,the research results can provide the basis for revealing the nature of the damage of cemented carbide tool materials in heavy milling,solving the failure problem of heavy milling tools and improving the machining efficiency,which has important theoretical and practical significance.First of all,the head test of milling water chamber is carried out.Based on the test data,the orthogonal analysis method is used to establish the milling force and milling temperature model.Combined with the finite element simulation software,the size of milling temperature and milling force is determined.Finally,through the comparative study of the test and simulation data,the basis is provided for the study of crack growth and damage failure of tool materials.Secondly,in the process of cutting,the front face and the tip of the tool will be affected by mechanical stress and thermal stress.Based on the low cycle and high impact thermal mechanical load of the carbide tool material,the distributioncharacteristics of the thermal mechanical stress of the tool are discussed.The stress field,strain field and temperature field are analyzed through the thermal stress coupling simulation,so as to further study the damage of the tool material Features provide a reference.Thirdly,based on the fracture mechanics theory and the relationship between the number of cycles and the length of the cracks,the crack propagation model of the tool material is established;the mechanical properties of the cemented carbide tool material under the external load are discussed,and the hopkinson pressure bar experiment is carried out.The stress-strain relationship of the cemented carbide tool material is explored by controlling the impact load and temperature of the pressure bar,so as to further study the tool material the damage mechanism of the material provides the basis.Finally,the theory of fracture mechanics and damage mechanics is used to study the critical stress and fatigue cumulative damage of cemented carbide tool material.The tool is affected by cyclic thermal mechanical load and thermal mechanical impact load,which leads to the tool damage and failure.Through the establishment of the tool failure criteria,the basis is provided for the tool design and the improvement of tool life.