Modeling And Experimental Research On Process Damping In Machining Based On Indentation Effect

Process damping effect widely exists in the cutting process.The primary source of process damping is considered to be the indentation of tool edge and flank face into wavy finish workpiece surface.It has a nonnegligible effect on cutting dynamics and chatter stability,especially at low cutting speeds,resulting in higher stability limit.Thus,the machining efficiency of some aerospace materials at low cutting speeds,such as aluminum,titanium,and nickel alloys,can be greatly promoted.Simultaneously,the component of ploughing force caused by process damping will affect the cutting force.The accuracy of the predicted cutting force can be improved when considering the effect of process damping.The modeling and identification for process damping have always been the difficulties in research on chatter stability of metal cutting.As there is almost no practical model for estimation of process damping,it has been mostly ignored in chatter analysis.As a result,the prediction of machining stability is not accurate.Process damping effect cannot be utilized to guide the high efficiency machining of aerospace materials effectively,which will seriously restrict the manufacturing efficiency of aero-engine parts.In order to evaluate the effect of process damping on cutting stability,this thesis models process damping in machining based on indentation effect and the model parameters of process damping are identified through experiments.At the same time,the prediction of cutting stability considering process damping is studied.Accordingly,the effect of process damping on chatter stability is comprehensively analyzed from the mechanism modeling,the experimental identification and the prediction of stability.The main original contributions of this thesis are as follows1.The primary source of process damping is due to the indentation of the tool flank face into the machined surface.The key fator of indentation effect is the extruded volume.With the analytical integration method and the numerical integration method,the improved calculation method of extruded volume considering the flank wear is established,which elevates the computational efficiency of extruded volume.Then three cutting states caused by the nonlinearity of process damping are analyzed and the stability prediction algorithms for three cutting states are established.The improved calculation method of extruded volume can promote the computational efficiency of cutting stability considering process damping.2.A semi-analytical method with high computational efficiency is presented to compute the extruded volume for honed tools in orthogonal cutting.Based on the energy dissipation principle,the relationship between the extruded volume and the equivlent process damping coefficient is revealed.Thus,the process damping model for the state of finite vibration amplitude is established.Based on this model,the finite amplitude stability for the state of finite vibration amplitude can be computed accurately and efficiently,which overcomes the insufficiency of analytical methods based on the assumption of small amplitude vibrations and the low computational efficiency of numerical method.3.The effect of the modified shearing forces considering the vibration velocity on process damping is evaluated for honed tools in milling operation.Based on the assumption of small amplitude vibrations,an analytical method with high computational efficiency is presented to compute the extruded volume.Accordingly,the equivalent process damping coefficient can be calculated analytically by the energy dissipation principle.And the process damping model considering both the velocity effect and the indentation effect is established.Then the equivalent process damping coefficient is integrated in the Full-Discretization Method to eatablish the stability lobes accurately,which improves the prediction result of stability under the assumption of small amplitude vibrations.4.The influence of regeneration effect on the parameters of process damping is evaluated.The special workpiece with spiral is designed to eliminate the regeneration effect for accurate identification of process damping parameters.Then the equivalent process damping coefficient is identified by the vibration signals during stable cutting tests with the method of operational modal analysis.The cutting stability experiment is conducted to verify the accuracy of the identified indentation coefficient.And the relation between the vibration amplitude under the finite amplitude vibration state and the surfave roughness is studied experimentally to offer a guide for improving the surface quality.