Research On Tool Wear Of Prestressed Cutting Based On Discrete Element Method And Experiment

Nickel based superalloys such as GH4169are extensively used in the aerospaceand nuclear industry, especially in the high temperature flow area of engines, becauseof their excellent mechanical resistances to high temperature and corrosion. However,the combined effect of high shear strength, lower thermal conductivity, presence ofabrasive carbide particles and high tool-workpiece affinity make this class of materialvery difficult to machine, which result in the problems of high cutting force, highcutting temperature and serious tool wear. Morever, residual tensile stress is liable tooccur on the machined surface by traditional machining which will influence themachined surface quality, fatigue strength and corrosion resistance of workpiece. Andthe prestressed cutting technology can effectively improve surface residual stress. Inthis dissertation, a prestress-loading device for ring parts is designed and manufactured;by using discrete element method and experiments, a comprehensive study is carriedout on the tool wear of sialon ceramic tool in prestressed cutting of GH4169ring parts,which is instructive to the machining and application of nickel based superalloy.Themain work is as follows:1. The background and significance of this research is introduced first. Then, thestate of the art in the research of machining and tool war of nickel based superalloy,prestressed cutting and the application of discrete element method. Finally, the maincontents and frame structure of this dissertation are discussed.2. Relevant theories of metal cutting are reviewed first. Then, based on theprestressed cutting theory, a prestress-loading device for ring parts is designed andmanufactured; sialon ceramic tools are used in orthogonal prestressed turning of nickelbased superalloy GH4169ring parts. The effects of prestress and cutting parameters tocutting force and flank wear VB of tool are investigated in prestressed cuttingconditions. Additionally, the wear appearances and mechanisms of the ceramic tool atvarious cutting conditions are experimentally observed and analyzed.3. The discrete element method (DEM) and its calculation process are introduced.And then the estabishe of DEM model of sialon ceramic tool and nickel basedsuperalloy GH4169are investigated. In order to matching the mechanical behavior ofreal materials, the micro-parmeters of DEM model are constantly modified and theDEM mechanical models are continuously tested. For further study on the tool wear,considerating the the effects of cutting temperature to tool wear, the discrete element method (DEM) model which describes the friction and wear behavior of the interfacebetween sialon ceramic tool and chip were established based on the periodic boundarycondition.4. The evolution process of material wear, damage accumulation and localspalling of Sialon ceramic tool in machining, and the effects of prestress, cutting speedand feed rate on tool wear including micro-cracks, delamination, detached particles,wear rate, flank wear VB and rake wear NB are numerically simulated and investigatedin prestressed cutting conditions. It is further validated that discrete element method isfeasible to simulate the tool wear behaviour.5. The whole work in this dissertation is systematically summarized, and futurework is discussed.