Developments Of New Two-dimension Elliptical Vibration-assisted Machining Methods And Their Apparatus

As one of the advanced manufacturing technologies(AMTs)with the most application prospects and development potential at present,elliptical vibration-assisted machining(EVAM)technologies have additionally introduced the micro-dimension and high-frequency vibrations on basis of traditional cutting processes,which not only can texture various microstructures and generate complex optical surfaces,but also have capacity of improving the machinability,especially suitable for the diamond processing various difficult-to-cut materials,for example,brittle materials like optical glass and monocrystal silicon,hard alloy like tungsten carbide(WC)and titanium carbide(Ti C),ferrous metal like stainless steel and die steel,and various fiber reinforced polymer/plastic(FRP).Based on the characteristics,the EVAM technology has drawn the widespread attentions of domestic and foreign scholars and engineers,which has been broadly integrated into various traditional machining methods,including the turning,milling,drilling,grinding,polishing and electrical discharge machining.The existing studies demonstrated that the EVAM have much more excellent advantages than traditional machining methods in term of weakening cutting force,increasing critical depth of the ductile-regime machining,extending tool life,improving finish quality and form accuracy,and reducing burr formation,but there are still some deficiencies that need to be solved and improved,including large coupling motions and errors in EVAM systems,uneven distribution of scallop-height on cutting surfaces,low forming accuracy of coining microstructures,etc.In order to overcome inadequacy and further improve performance benefits of the EVAM processes at present,this doctoral dissertation will concentrate on the developments of new two-dimension(2D)EVAM methods and their apparatus,whose main study content will include as follows:(1)In order to solve the problems of non-resonant EVAM devices,such as low motion accuracy and large coupling error,a new type of elliptical vibration machining apparatus and their close-loop control systems are developed.Taking the place of traditional flexure hinges with symmetric configurations,this thesis firstly design two kinds of non-symmetric flexure hinges with higher motion precision,a type of finite beam based matrix modeling(FBMM)method is introduced to build their compliant matrix model,and the performance comparisons and evaluations among different non-symmetric and symmetric flexure hinges are performed by adopting non-dimensional precision factors.Subsequently,the parallel-kinematic constraint map(PKCM)method is applied to the kinematics design of two-degree-of-freedom decoupledcompliant mechanism(CM)with parallel structure,and its embodiment design is finished based on the parallelogram flexure modules.The analytical compliant model of designed CM is constructed by the matrix-based compliance modeling(MCM)approach,the finite element analysis(FEA)then is employed for verifying the effectiveness of MCM model and analyzing the static and dynamic characteristics.Finally,a programmable multi-axis controller(PMAC)is adopted to build the fuzzy adaptive PID servo control system for EVM devices,and offline experimental tests are conducted for measuring its performance indexes,including coupling,maximum stroke,working bandwith and response speed.(2)To efficiently fabricate the microstructure functional surfaces,this thesis develop a new type of single-feature elliptical vibration coining/indentation(EVI)method.Firstly,based on the kinematical principle of precision NC lathe and EVM device,the tool-path generations and surface topography simulation of microstructrue surfaces are respectively performed.Meanwhile,the matching analysis between the up-feed velocity of workpiece and the coining velocity of indenter are conducted in the elliptical vibration coining processes,the influence of kinematic coupling on the forming accuracy of coining microstructures,the optimal process parameters are thus determined for minimizing the coupling motions and coining errors.In consideration that the traditional EVI toolpaths can only guarantee the relative static condition between the workpiece and indenter in the points where the indenter has maximum coining depth,therefore,a kind of perfect velocity curves are constructed to make relatively static in entire period of workpiece-indenter coining contact.The constructed ideal velocity curves are fitted and replaced based on the Fourier series expansion,then the fitted velocity curves can generate a kind of non-elliptical tool trajectory through mathematical integration,and a new type of non-elliptical vibration coining(NEVI)approaches are further proposed.Afterwards,the commercial FEA software is applied to investigate the influence of indentation pile-up and sinking-in behaviors as well as material rebound on the forming accuracy of microstructures.Finally,a series of coining experiments are conducted to demonstrate the effectiveness and feasibility of the developed elliptical/non-elliptical vibration coining approaches,also some kinds of common defects easy to occur in coining processes are respectively discussed for avoiding their repeated emergence in follow-up studies.(3)To expand the application flexibility and further strengthen processing performances of traditional elliptical vibration cutting,a new type of elliptical vibration cutting with varying multi-parameters(VMP-EVC)method are proposed for fabricating complex optical surfaces,which will real-timely adjust ellipse geometric parameters including amplitude,rotation angle and center position in term of geometric characteristics of the desired surfaces,the tool-path generation and surface morphology simulation of different VMP-EVC are also finished.Toevaluate the influences of changing ellipse parameters on the surface roughness and forming accuracy,the residual tool marks and forming error of simulated surfaces need to be separated off based on the wavelet transform,the optimal ellipse parameters of VMP-EVC processes are then determined.In addition,a new type of elliptical vibration cutting with different frequency(DF-EVC)to further extend the working life diamond tool of and reduce the scattering effect of machined surface,but there are existing problems of the unsatisfactory of its effective machining capacity.As an improvement to optimize DF-EVC,another novel type of elliptical vibration cutting with varying phase difference(VPD-EVC)method are developed through evolving and deducing the motion equations of DF-EVC.Then the new VPD-EVC approaches are innovatively employed for cutting two kinds of microgrooves to effectively overcome the size limitations of tool nose radius on the minimum machining size,corresponding tool-path generations and surface morphology simulations are also performed.In VPD-EVC processes with different amplitudes of phase difference,their suppressing ability of scattering effect and their effective cutting capacity are respectively investigated through introducing the power spectral density(PSD)and defining an effective cutting rate,thus the amplitude of phase difference can be optimally determined by synthetically considering these two key VPD-EVC evaluating indicators above.In the end,these newly developed EVC approaches are adopted to perform cutting experiments on copper cylinders that have poor machining performances,the observed results of machined surfaces commendably validate the viability and effectiveness of these developed EVC methods.(4)The elliptical vibration polishing for optical surfaces with residual tool marks.For post-processing the difform residual tool marks of optical surfaces machined by singe-point diamond turning(SPDT),a type of elliptical vibration polishing(EVP)method are developed on the basis of precision lathe.In the light of the spatial position relation of elliptical vibration toolpaths relative to the residual tool marks,the EVP trajectory can be divided into three main types: up-feed toolpath,cross-feed toolpath and parallel toolpath.Meanwhile,the toolpath generation algorithms for complicated optical surfaces are derived respectively.Afterwards,the Workbench module of commercial FEA software ANSYS 15.0 is adopted to analyze the three-dimensional polishing forces and maximum stress of the EVP process.At last,both the elliptical vibration cutting toolpath with different frequency and varying phase difference are applied to conduct EVP experiments on three types of certain materials,also considering the cases of clockwise(CW)and counterclockwise(CCW)elliptical toolpaths.Subsequently,a series of polishing experiments are performed on prepared black surfaces with spiral-shaped(normal turning)and fish-scale(induced by cutting chatter)residual tool marks,also the material removal rates for two different blank surfaces are comparatively analyzed underdifferent EVP toolpaths and polishing parameters,the observed results of machined surfaces can well validate the viability and effectiveness of the developed EVP method to post-process the turned optical surfaces with difform residual micro-structures.This dissertation has theoretically analyzed and experimentally researched elliptical vibration-assisted machining methods and their EVM systems,some main conclusions have been summarized as follows:(a)Two sorts of non-symmetric flexure hinges both have higher motion accuracy than the traditional symmetric hinges,the two-degree-of-freedom compliant mechanism that is constructed with the PKCM method not only maintains the high-bandwidth property of parallel configuration,but also can effectively reduce the parasitic coupling motion between different motion axes.(b)In the elliptical vibration coining,the material rebound of plastic deformations and the pile-up/sinking-in of indentation edges have direct influence on the contour precision of coining microstructures,but the surface scratches caused by coupling coining motions depend mainly on processing parameters and diamond indenter parameters,the developed non-elliptical vibration coining process can weaken the influence of coupling motions on the contour precision,and then microstructure surfaces can be efficiently obtained.(c)The microsize and high-frequency vibrations in VMP-EVC can generate complex surfaces,and the height distribution of residual tool marks rely on both ellipse parameters and surface geometry,but the surfaces with even scallop-height distribution can be obtained by appropriate ellipse parameters.VPD-EVC method can fabricate U-shaped and V-shaped micro-grooves,also reduce the diamond tool wear and surface scattering effect.(d)In the EVP processes,the polishing efficiency of cutting surface depends on the direction relation of residual tool marks and elliptical vibrations,the removal efficiency will be optimum when they are perpendicular to each other.The EVP polishing efficiency is superior to traditional polishing process without elliptical vibration,but the motion direction and trajectory shape of polisher have slight effect.