Research On Tool Wear Of Prestressed Cutting Based On FEM-DEM Method And Experiment

Nickel based super alloys such as GH4169is extensively used in the aerospace andnuclear industry, National defense and military，because of their excellent mechanicalresistances to high temperature and corrosion. However, the combined effect of highshear strength, lower thermal conductivity and so on make this class of material verydifficult to machine, which result in the problems of high cutting force, high cuttingtemperature and serious tool wear. Moreover, residual tensile stress is liable to occuron the machined surface by traditional machining which will influence the machinedsurface quality, fatigue strength and corrosion resistance of work piece. And thepre-stressed cutting technology can effectively improve surface residual stress. In thisdissertation, a pre-stress-loading device for ring parts is designed and manufactured;by using DEM-FEM combined method and experiments, a comprehensive study iscarried out on the tool wear of sialon ceramic tool in pre-stressed cutting of GH4169ring parts, which is instructive to the machining and application of nickel based superalloy. The main 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 super alloy,pre-stressed 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 thepre-stressed cutting theory, a pre-stress loading device for ring parts is designed andmanufactured; sialon ceramic tools are used in orthogonal pre-stressed turning ofnickel based super alloy GH4169ring parts. The effects of pre-tress and cuttingparameters to cutting force and flank wear VB of tool are investigated in pre-stressedcutting conditions. Additionally, the wear appearances and mechanisms of the ceramictool at various cutting conditions are experimentally observed and analyzed.3. The discrete element method (DEM) and its calculation process are introduced.And then the established of DEM model of sialon ceramic tool and nickel based superalloy GH4169are investigated. In order to matching the mechanical behavior of realmaterials, the micro-parameters of DEM model are constantly modified and the DEMmechanical models are continuously tested. For further study on the tool wear,consider ting the effects of cutting temperature to tool wear, the discrete elementmethod (DEM) model which describes the friction and wear behavior of the interface between sialon ceramic tool and chip were established based on the periodic boundarycondition.4. The evolution process of material wear, damage accumulation and localspelling of sialon ceramic tool in machining, and the effects of pre-stress, cuttingspeed and feed rate on tool wear including micro-cracks, delaminating, detachedparticles, wear rate, flank wear VB and rake wear NB are numerically simulated andinvestigated in pre-stressed cutting conditions. It is further validated that discreteelement method is feasible to simulate the tool wear behavior.5. The whole work in this dissertation is systematically summarized, and futurework is discussed.