| The water chamber head is an important part of nuclear steam generator of nuclear power plant.508? steel is a kind of difficult-to-cut material which has high strength,high melting point,high toughness and high hardness Blank of the water chamber head is formatted by integral forged and the forging surface has forging defects.It results in random impact and vibration of the cutter during milling.The tool breakage is serious in the actual processing production.Cemented carbide cutting tools cutting tools belongs to brittle material.Its main damaged form is brittleness damage and fatigue damage,especially collapse edge,fatigue damage,the impact fracture and so on,which seriously affects the processing efficiency and shorten the tool life.Aiming at the above problems,the milling of high strength steel cemented carbide tool is studied.Firstly,the fracture process of cemented carbide is analyzed theoretically from the aspects of energy transformation,grain characteristics of cemented carbide fracture and carbide crack propagation.The transformation of the energy during the fracture of the tool,the influence of the micro grain boundaries on the flexural and tensile strength of the cemented carbides are all obtained.On the other hand,the model of critical condition of tool impact fracture is established to analyze the influence of cutting load on impact fracture load.All of these provided the theoretical support for determining the range of process parameters and judging the impact fracture of the tool.The theoretical model of fatigue life of the tool is established to provide theoretical basis and technical support for establishing the reliability of tool fatigue damage and predicting tool life.Secondly,the damage life of the tool is explored and the damage mechanism is studied by the milling experiment of cemented carbide tool.It provides experimental reference for optimizing the milling parameters,blade geometry,coating material and so on by analyzing the influence of different cutting parameters on the damage ofcarbide inserts and comparing the milling life of five kinds of inserts.In addition,carbide tool material parameters,which can be used as a reference to determine the limit of impact load and the theoretical model of tool breakage life are determined through high temperature tensile test and carbide bending test.Thirdly,the milling process of cemented carbide cutting tool is simulated and analyzed to obtain cutting force trend and cutting heat distribution during milling process.The simulation and experimental results of cutting force and cutting heat at different cutting speeds were compared by milling 508 ? steel experiment under laboratory conditions.The reliability and effectiveness of the milling model were validated.The finite element simulation analysis of stress and strain and fatigue life of carbide inserts were finished to obtain stress-strain field distribution law and fatigue safety factor distribution of cutting tool.Finally,the fatigue life reliability of cemented carbide inserts was verified by Monte-Carlo method.The fatigue life reliability model of carbide inserts can provide theoretical support for predicting the time of tool breakage,determining tool breakage life,and preventing damage to workpieces and personnel when tool breakage occurs.The optimum technological parameters of high strength steel milling with carbide cutting tools are optimized based on fatigue damage and the impact fracture of cemented carbides to provide technical support for the efficient milling of high-strength steel. |
PDF Full Text Request