Study On Surface Generation Mechanism And Modification Approach In Nanocutting

Nano-cutting is one of the most efficient machining methods in generating components with nanometric surface roughness and sub-micrometric form accuracy or with micro/nanometric sized features.Ideally,with a reduction in the feed rate and an increase in the tool nose radius,the surface roughness would decrease without limit.But in practice,it does not work in this way when the surface roughness decreases to a certain value,due to the effects of the cutting tool,workpiece properties and the dynamic characteristics of machine tools.In order to obtain the surface roughness generation mechanism and surface modification method in nano-cutting,the influences of the anisotropy of workpiece materials,cutting tool edge shape,side flow,recovery,and hard particles on the material removal mechanism and surface generation will be investigated.In addition,the method about surface modification will be proposed to improve the surface roughness.The progresses are summarized as follows:(1)The effects of the anisotropy of workpiece materials on the plastic deformation are investigated.The results show the evolution of the twins,stacking faults,dislocations on different crystal plane under the action of the cutting tool edge.The relationship between the minimum uncut chip thickness and the material removal mechanism,including shearing,extrusion and rubbing mechanism,has been revealed.The influence of the material removal mechanism on the surface generation is clarified.(2)The effects of the cutting tool edge shape on the material removal,subsurface damage,and cutting forces are investigated.A new parameter which is different from the former used tool edge radius is proposed to characterize the tool edge.In this method,only part of the profile of the cutting tool edge,which ranges from the separate point to the flank face and relates to the machinability of the cutting tool,is taken into consideration when fits the tool ege radius.(3)The formation mechanism of the side flow and the recovery in nano-cutting process and their effects on surface generation is investigated.The influence of the anisotropy of workpiece materials,its relationship with the minimum uncut chip thickness,and the effects of the cutting tool geometries are studied.(4)The effects of hard particles on the surface generation in nano-cutting are investigated.When a hard particle is removed,only a small shallow pit is left on the machined surface.However,a larger and deeper pit is left on the generated surface and its size decreases with a further increase of the depth.After the tool edge cutting through the pressed-down hard particle,it recovers back making its top higher than the machined surface which would further deteriorate the machined surface quality.(5)A new method,force controlled rolling(FCR)integrated with nano-cutting technology based on an ultra-precision machine tool,is demonstrated to improve the surface quality of soft and sticky lead(Pb).After the soft and sticky workpiece is modified by FCR,the surface becomes hard enough to suppress the scratch of the chips,the formation of BUE,and the side flow of the workpiece material under the action of the cutting tool edges.Nano-cutting of Pb mirrors validates the effectiveness of the method.