Study On Tool Wear Mechanism Of Ti-6Al-4V Micro Milling And The Influence Of Wear State On Machined Surface Quality

Micro milling can process workpieces with various materials and complex geometry.It is one of the most suitable processes for micro scale manufacturing.With the rapid development of high-precision device technology,the demand for miniaturized components is becoming higher and higher.Micro milling is not the traditional macro machining,which is simply reduced in proportion.The traditional basic theories and methods are no longer applicable.This process is considered to be expensive and difficult.Especially when machining Ti-6Al-4V and other difficult machining materials through micro milling,the rapid wear of tools leads to high production cost and poor machining surface quality,which seriously limits the machining and application of micro milling.Therefore,it is of great significance to systematically study the wear state and machined surface of micro milling tool for micro milling Ti-6Al-4V to improve the machined surface quality and reduce the production cost.This paper focuses on the influence of micro milling tool wear state on Ti-6Al-4V machined surface quality,puts forward a new standard for comprehensively judging micro milling tool wear failure,and studies the wear form and wear mechanism in the machining process.The machining surface quality is studied,the mapping law between the wear state of micro milling tool and the machining surface quality is revealed,and the machining surface prediction model of tools in different wear states is established.Firstly,the experimental scheme of milling Ti-6Al-4V with WC Cemented carbide micro milling tool is designed,and four micro milling tools with different wear states are obtained.The wear failure standard,wear form and wear mechanism of micro milling tool are comprehensively analyzed by obtaining data through confocal microscope,SEM and EDS.The results show that the wear forms of micro milling tool mainly include friction trace,material adhesion,chip accumulation tumor and micro chipping of progressive normal wear failure,and the cutting edge of abnormal wear failure is seriously plastic deformation,chipping and edge peeling.Due to the lack of relevant international standards for micro milling tool wear,it is considered that the formulation of micro milling tool wear standard needs comprehensive consideration,and the wear of end face 30μm,wear of flank 35μm and tool diameter reduction 55μm can be used as the failure criterion of the micro milling tool.The wear form and wear mechanism of micro milling tool are analyzed.Adhesive wear exists in the whole cutting process and plays a leading role,Abrasive wear,diffusion wear and oxidation wear occur only when the cutting temperature reaches the critical value,and oxidation wear aggravates the failure of binder and the peeling off of tool particles.Secondly,aiming at the problems of rapid tool wear,poor machining surface quality and high machining cost in the process of Ti-6Al-4V micro milling,this thesis studies the influence of micro milling tool in different wear states on the machining surface,and reveals the influence law and mapping relationship between micro milling tool wear and machining surface quality.The micro milling tools in different wear states are used to process respectively,and the corresponding machined surfaces of micro milling tools in different wear states are obtained.The relevant data are obtained by confocal microscope,SEM,EDS and nano mechanics test system.The results show that the wear of micro milling tool will cause different variation laws of various surface roughness evaluation parameters.It is insufficient to evaluate the impact of micro milling tool wear on the machined surface by relying on a single parameter,which needs to be comprehensively considered by multiple parameters.The wear of micro milling tool seriously affects the machined surface roughness and makes the surface quality deteriorate rapidly.The change of cutting force is affected by the alternation of chip buildup and cutting edge collapse.Vickers hardness and nano indentation hardness increase with the deepening of wear.Finally,in order to predict the surface morphology after micro milling,the machining surface prediction model of micro milling tool in different wear states is established.According to the tool wear data obtained from the micro milling experiment,according to the geometric conditions of different worn tools,the tool models with different wear states are established,and the influence law of tools with different wear states on the machined surface is revealed.It is found that due to the existence of size effect and minimum chip thickness,the influence of edge radius must be considered.The tool wear is accompanied by the increase of edge radius and contact area.The scheme of modeling tools in different wear states by changing edge radius and bottom contact area is feasible.With the continuous wear of the tool,the cutting force of the tool under the thermal mechanical coupling is gradually increased under the neglect of the influence of chip accretion,which is consistent with the law obtained in the experiment.In the initial wear stage,the chip size generated by cutting is small,it is not easy to adhere to the tool and workpiece surface,and the machining surface quality is good.The tool wear makes the chip size gradually larger,the machining surface roughness increases,and the machining surface quality gradually deteriorates.The geometric size of the tool is closely related to the generation of chips.