Prediction Of Mechanisms And Residual Stress For Curved Surface Turning Considering The Effect Of Tool Microgeometry

The macro posture and microgeometry both make difference to the material removal area in metal cutting,which will directly influence the process physical variables and surface integrity.Among all the machining methods,the current analytical models for turning always simplify the complex cutting condition and weaken the effects of edge microgeometry,making it different from the real turning.Further,the modeling of force and temperature rarely focuses on the local contact area,making the distribution of physic variables along engaged edge an open question.At last,the investigations on turning-induced residual stress didn’t cover the continuous turning condition considering edge microgeometry and the dynamic tool-workpiece contact,which is not able to realize low-stress machining for components with complex features.This work analytically modeled the cutting force,temperature,and residual stress for curved-surface turning considering the tool microgeometry,emplying AISI304 as the workpiece material.Further,the experimental study of the distribution of surface integrity along the fillet surface is investigated.The main contributions are listed below:The influence of tool edge on material flow was analysed.A two-dimensional cutting force prediction were established.For the primary deformation zone,parallel shear zone model and unequal division shear zone model were used to calculate the shear force.For cutting with honed edge tools,the slip-line models were employed to demonstrate the influence of honed edge on material flow and to calculate the edge force.For chamfered edge tools,a semi-analytical force prediction model was proposed concerning a modified function characterizing the weights of chamfer plane and rake face on cutting force.Finally,orthogonal cutting experiments were employed to validate the effectiveness of the proposed model.A three-dimensional cutting force prediction model was developed for turning based on the discretization on the rake face.We analysed the influence of tool nose on uncut chip area and proposed a new discretization method that using rake face as a reference to determine the local parameters.The global chip flow direction was calculated considering the equilibrium of interaction forces between chip increments.Then,the distributions of cutting force components,as well as the total cutting force were obtained with the consideration of edge effect and size effect.At last,turning experiments were performed to validate the correctness of the cutting force predictive model proposed in this section.A three-dimensional thermal model for turning considering distributed heat sources in space was proposed.Two discretization methods were presented to divide the heat sources on the primary shear plane and the tool-workpiece contact area,respectively.For an arbitrary increment of heat source,the heat intensity can be calculated based on the results given in the second part.A three-dimensional analytical model was proposed based on the semi-infinite boundary assumption and imaginary heat source theory to calculate the temperature rise in tool,workpiece,and chip caused by an arbitrary heat source in space.Then,the three-dimensional temperature field of longitudinal turning with round insert can be achieved.Finite element method and literature data were employed for validation.A dynamic residual stress prediction model for varying-contact turning was proposed using fillet surface as an example.The time-varying contact area caused by tool nose and posture was analysed.On the basis of the methodology of discretization,cutting force and temperature predictive modeling,the force-temperature information can be obtained for each increment.The residual stress in curved-surface turning was assumed as the production of direct contact edge.The histories of mechanical load and temperature in workpiece were determined considering the stress and heat sources in the primary shear band and flank face.Then,the loading procedure can be obtained based on rolling/sliding contact theory and Hybrid algorithm.Finally,the residual stress profile in-depth direction for an arbitrary position of curved surface can be determined after relaxation.Both CEL simulation and turning experiment were employed to prove the effectiveness of the proposed model.An experimental study was done for the distribution of surface quality along the stress concentration position,i.e.fillet surface.The evolutions of cutting parameters in curved surface turning were analyzed.The variation of geometric parameters of direct contact edge which might be the main factors of surface integrity was analyzed as well.The difference of chip morphology in longitudinal and end face turning was discussed.For the surface integrity,the surface roughness,microhardness,microstructure,and residual stress were measured using a three-dimensional scanning microscope,nanoindentation,SEM,EBSD,XRD,etc.Thus,the trend of surface integrity along fillet surface can be revealed.