| Optical freeform surfaces,microstructure functional surfaces,and brittle materials are widely used in precision engineering,optical instruments,semiconductors,aerospace,automotive,medical equipment,defense and military fields due to their excellent mechanical,optical,physical and chemical properties.Fast tool servo(FTS)diamond turning technology has become a promising technology for machining optical freeform surfaces,microstructure functional surfaces and brittle materials due to its high accuracy,high flexibility and high efficiency.This machining technology has attracted more and more attention and has been vigorously studied in the past few decades.Therefore,this paper has carried out in-depth theoretical research on FTS processing technology.First,a new type of FTS device was developed to improve the machining performance of the cutting system,thereby expanding the application fields of FTS cutting technology in the generation of optical free-form surfaces and microstructures on brittle materials.Then,combined with the FTS cutting device developed in this paper,the ductile processing mechanism of brittle materials was explored,and the single crystal silicon scribing processing experiment was carried out to verify the feasibility of the developed FTS device to process brittle materials.The main research contents of the article include:(1)A piezoelectric driven 2-DOF FTS device with high frequency and low coupling was developed.The main structure includes a flexible mechanism body,a piezoelectric actuator,a diamond cutter,a pre-tightened wedge block,and a pretightened screw.A high-rigidity four-bar mechanism is used to generate movement in the z-axis direction.In addition,a flexible bearing hinge is used,and a micro-rotation motion around the flexible bearing hinge is used to achieve translational movement in the x-axis direction.Considering the flexible characteristics of the mechanism connection unit,a flexible matrix modeling method was used to establish a complete flexibility model for the key components of the 2-DOF FTS device to analyze its static characteristics.In addition,the flexible matrix analysis method is briefly introduced,and the calculation method of the flexible matrix of the basic flexible unit and the flexible hinge connected in series and parallel is given.(2)The machining performance optimization and testing of the 2-DOF FTS device were carried out.The ABAQUS finite element method was used to perform static analysis and dynamic analysis on the mechanism,and the correctness of the compliance model of the system was verified.A prototype of the designed 2-DOF FTS mechanism was obtained using the wire cutting process.An offline experimental test system was constructed to study the machining performance of the designed device,which mainly includes performance tests such as natural frequency,working stroke,resolution,step response,crosstalk and hysteresis response.(3)Based on the principle of the FTS turning,the interaction relationship between the tool and the workpiece during the cutting process of the brittle material arc cutting edge was analyzed,and the different cutting modes in the cutting process were described.Based on the ultra-precision cutting model and crack propagation theory,a critical undeformed chip thickness model for ductile cutting of brittle materials is established.Considering the influence of relevant parameters such as tool radius,feed speed and cutting depth on cutting thickness during FTS cutting,a maximum undeformed chip thickness model was established.(4)FTS cutting experiments were performed on typical brittle material single crystal silicon.Firstly,the critical undeformed chip thickness of brittle-plastic transition of single crystal silicon was determined by using the deep-shear deep-drawing experiment,and the theoretical model of critical undeformed chip thickness of brittleplastic transition was established by analogy.In addition,scribing experiments were performed on single crystal silicon using different cutting speed.Finally,the white silicon interferometer was used to characterize the processed single crystal silicon surface to explore the influence of different cutting speed on the surface morphology and critical undeformed chip thickness of the single crystal silicon machining.This provided a theory guide for the ductile machining of brittle materials. |
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