Study On The Key Technology And Mechanisms In Dry Cutting Of Green Ceramics By Tools With Surface Textures

Aiming at the problems of severe tool's flank-face wear and poor surface processing quality in the processing of green ceramics,material removal mode,analysis of mechanical model,and the study of discrete element modeling in the processing of green ceramics are studied.The material removal mechanism of green is revealed,and cutting performance of tools with textured flank-face during the processing of green ceramics is systematically studied.A new tool with textured flank-face is developed to machine green ceramics by isostatic pressing,providing new ideas and theoretical basis for solving the problems of severe flank wear of tools and poor processing quality of the machined surface.The effects of isostatic pressing technology on the densification of green compacts and the yield strength criteria followed during the production of ceramic green compacts molding are analyzed.The microstructure of green ceramics,hardness,flexure strength and fracture toughness tests etc.are performed to obtain the relevant physical and mechanical properties of the Al2O3 green ceramics prepared by the cold isostatic pressing.The stress characteristics between the green ceramic particles are revealed.The Al2O3 green ceramics that can fully meet the machining requirements are prepared by isostatic cool pressing.Considering the elastic deformation of materials and the friction at the interface between flank-face of tools and the machined surface of workpieces,a mechanical model of dry cutting of Al2O3 green ceramics composed of cutting force for chip formation Fc and friction force between flank-face of tools and the machined surface of workpieces Ff is established.Results show that the ratio of friction to the total tangential force Ff/Fx decreases with the increase of depth of cut,and the ratio of Ff/Fx is always>50%.Furthermore,a new idea was proposed to predict the cutting peak force by the edge-indentation test,and the mechanical model of edge-indentation for the prediction of the cutting peak force is established.Dry cutting experiments of Al2O3 green ceramics are conducted.Results show that the proposed models can accurately predict the force of chip formation,tangential peak force,and friction force between flank-face of tools and the machined surface of workpieces during dry cutting of green ceramics.Based on the scratch test,the material removal mechanism of the green ceramics is studied.Results show that the material removal is mainly in the form of ploughing at a small depth of cut or a large cutting speed;material removal is mainly in the form of ductile cutting accompanied by partial brittle fracture at a larger depth of cut or a smaller cutting speed.There exists a transition between ductile and brittle forms for material removal.A dry cutting BPM model of green Al2O3 ceramics is established by discrete element PFC2D software.The mechanisms of chip formation and characteristics of cutting force under different processing parameters are studied.The formation of chips basically spreads along the arc through cracks.Processing parameters and tool parameters have an important influence on the chip morphology.Properly reducing the cutting depth,increasing the cutting speed and reducing the tool rear angle can effectively improve the quality of the machined surface and reduce surface residual cracks.When the rake angle of tools is negative,the phenomenon of edge peeling may occur.Compared with the positive rake angle of tools,the residual cracks on the machining surface will increase significantly.The accuracy of the mechanical model of dry cutting of green Al2O3 ceramics can be also verified by the discrete element model of dry cutting of green ceramics.Tools with textured flank-face are proposed to process the green ceramics prepared.The cutting performance of tools with textured flank-face,the mechanism of tool wear,the anti-friction mechanism and the quality of machined workpiece surface are studied.Compared with traditional tools(WT-0),the minimum flank wear is obtained by the tools with textures parallel to the main cutting edge on the flank face(AT-1 tools).All the tools with textured flank-face can improve the flank wear resistance,and the optimal texture parameters are obtained:texture width is 75?m,texture spacing is 100?m,distance of texture groove to main cutting edge is 75?m.The surface processing quality can be also improved by these tools with textured flank-face.There is nearly no obvious influence of texture shape on the surface processing quality,but the texture parameters have significant influence on the it.The mechanisms of the improvement of flank wear resistance and the processing quality of machined surfaces are as follows:(1)the textures function of the"derivative-cutting phenomenon" on the flank-face of tools,i.e.the cutting behavior of bottom edge of textures to the hard phases and rebounded materials on the machined surfaces.That can reduce the flank wear of tools and prevent flank wear expanding to the unworn flank-face;(2)the textures on the flank-face of tools also have the function of collecting,storing and accommodating abrasive debris.The flank wear of tools caused by plough effect of abrasive debris can be reduced;(3)the function of "derivative-cutting"on the flank face of tools can contribute to the additional cutting to the machined surface,making the machined surface smoother.Further,powder chips generated by the"derivative-cutting" are compressed and adhered to the machined surface,that leads to the further improvement of processing quality of the machined surface.