Elliptical Vibration-assisted Cutting Technology And Experimental Study For Difficult-to-cut Materials

The complex optical surface and micro-nano structural functional surface of difficult-to-cut materials have been increasing demanded in many fields,such as biomedicine,new energy,aerospace and scientific instruments.However,how to fabricate the complex optical surface and micro-nano structural functional surface on difficult-to-cut materials with high precision,high efficiency and low cost has become a major problem.Elliptical vibration-assisted cutting(EVC)technology is now considered as an effective method,among which the non-resonant EVC technology which has the characteristics of the ellipse trajectory parameters are easy to be active controlled and the simple structure,has been gradually applied to fabricate the complex optical surface and micro-nano structural functional surface in recent years,and it has made some valuable research results.On the basis of the EVC device design and testing,cutting force modeling and experimental verification,monocrystalline silicon scratching experiments,and so on,this paper carried out an indepth exploration on machining of difficult-to-cut materials and the key technologies.The main research contents are as follows:(1)A two-dimensional EVC device with decoupling design was developed based on flexure hinge structure,the kinematics,statics and dynamics of device were analyzed by using analytic method and finite element method(FEM),and the feasibility of the design was verified.The performance tests of the prototype were carried out to verify the rationality of the design.The universal and angle adjustable EVC device was proposed based on the two-dimensional EVC device with decoupling design,the key dimensions of the flexible mechanism were optimized by using central composite design method combined with genetic algorithm.The performance test results show that the proposed deisgn can achieve the design goal with fast response,large working stroke,high working bandwidth and low crosstalk under the service conditions.The angle-adjustable EVC device can realize the three-dimensional ellipse motion by using two-dimensional driving principle,the compact structure and angle adjustable make it flexible to different machine tools.(2)The time-varying characteristics of undeformed chip thickness,tool rake angle and tool relief angle were analyzed on the basis of EVC principle.The force geometry in oblique EVC was analyzed based on the thin shear plane theory,and the relevant angle predictive model is established to describe the geometrical relationship between chip deformation,velocity and force.The angle predictive modle was verified by using geometry angle parameters of one-dimensiaonl oblique vibration cutting and the shear angel of two-dimensional EVC.The cutting force predictive model was established by combining the shear stress in oblique EVC and the tool-chip friction angle,and the accuracy of the model was verified by the cutting force experimental results of two-dimensional EVC.The geometry angle and cutting force of the oblique EVC were predicted and analyzed,and the cutting characteristics of oblique EVC were revealed.(3)The critical undeformed chip thickness of brittle to ductile transition for single crystal(100)silicon was determined by the scratching experiment.According to the hertzian contact theory,predictive model of the critical undeformed chip thickness of brittle to ductile transition of monocrystalline silicon is established by the analogy of indentation and scratch theory.The ductile-regime machining scheme of EVC was proposed,and the influence of different technological parameters on critical undeformed chip thickness of brittle to ductile transition was explored.And the optimal selection scheme of technological parameters of monocrystalline silicon machining was proposed.(4)The EVC experiments for difficult-to-cut materials were carried out,taking the monocrystalline silicon microgroove fabrication as example,different areas of microgroove with different depth and microgroove fabricated by large amplitude and oblique EVC were dected and analyzed by using Raman spectra.The monocrystalline silicon phase transition mechanism of EVC was revealed.The monocrystalline silicon removal mechanism and the diamond tool wear mechanism were investigated combining the scanning electron microscopy and energy spectrum test.Based on the machining characteristics of oblique EVC,a new method for high efficiency fabrication of hard brittle materials is presented.The wettability of microtexture with different posture fabricated by angle adjustable EVC device was investigated to verify the feasibility of active control microtexture posture to regulate the wettability of surface.