Papers by Author: Ying Chun Liang

Abstract: In some special fields such as precision optics, the part surface has strict requirements on the frequency domain errors, besides the conventional spatial domain errors such as surface roughness error. In light of the available works lacking of the frequency domain error analysis in ultra-precision flycutting, this paper therefore presents its frequency domain error analysis. A case study of KDP crystal flycutting is carried out to show its detailed processes, where the processing parameters, tool geometry, motion dynamic error of the machine guideway and tool-work vibration induced dynamic error are considered. A surface profile generation method is put forward. Two cases with different tool-work vibration frequencies are carried out. The spatial frequency spectrum is obtained based on the FFT analysis of the generated profile in the specified direction. After the in-depth analysis, the inherent correlation of the generated spatial frequency components with feed spatial frequency and machine dynamic errors induced spatial frequency under certain machining conditions are found, which is very meaningful for the frequency domain error prediction in the real application. The proposed analysis method can also be applied into other types of surface machining.

Abstract: Monte Carlo (MC) method and molecular dynamics (MD) are combined to analyze the influence of ageing on mechanical properties of machined nanostructures. Single crystal copper workpiece is first cut in MD simulation, and then the machined workpiece is used in MC simulation of ageing process, finally the tensile mechanical properties of machined nanostructures before and after ageing are investigated by MD simulation. The results show that machining process and ageing have obvious influence of tensile mechanical properties. After machining, the yield strength, yield strain, fracture strain and elastic modulus reduce by 36.02%, 28.86%, 20.79% and 7.16% respectively. However, the yield strength, yield strain and elastic modulus increase by 4.84%, 1.41% and 1.02% respectively, fracture strain reduce by 24.53% after ageing process. To research the ageing processes of machined nanostructures by MC simulation is both practical and meaningful.

Abstract: A three-dimensional model of Monte Carlo (MC) simulation is proposed to study the effects of ageing on the surface quality of machined nanostructures. The model includes the utilization of the Morse potential function to simulate the interatomic force between the atoms in workpieces. The results show that the ageing processes have important influence on the surface morphology and internal structure of machined workpiece. Most of the disordered point defects and one large stacking fault structures in machined workpiece disappear after ageing, but still some defect structures remain. In addition, distribution of atomic potential and atomic stress in the workpiece become regular in the aging process, and the atoms of the defect structures have much higher potential energy and stress. Finally, surface roughness of machined workpiece definitely increases after ageing. To analyze the morphology of machined surface after ageing is very practical and meaningful.

Abstract: A novel design of high load capacity multiaxis positioning stages with accuracy in the range of nanometers is presented. For strokes of 2mm with no play and high stiffness a general design principle supporting five Cartesian degrees of freedom has been developed using a new parallel kinematic topology based on Parallelogram arrangements. The five uniform feed drives are improved dual mode mechanism with servomotor and ballscrew as macro-actuator and piezoelectric transducer (PZT) with resolution of 1.2nm as micro-actuator. The performance of the setup and its kinematic properties are described as well as resolution of the five motions and their crosstalk. The setup has been implemented with outstanding characteristics and excellent reliability for alignment of a multigrating mosaic compressor in a PW-class CPA-laser.

Abstract: To study the removal mechanism of materials during nano cutting, molecular dynamics method is adopted to simulate single crystal copper nanomachining processes, and subsurface defects evolvements and chip forming regulation are analyzed by revised centro-symmetry parameter method and the ratios of the tangential cutting force and the normal cutting force. The results show that there are different defects under different cutting depths. When cutting depths is shallower, there are dislocation loop nucleation in the subsurface of the workpiece beneath the tool; however, when the cutting depths is deeper, there are dislocations nucleation and slipping along {101} plane and (111) plane. In addition, both tangential cutting force and the normal cutting force decrease as the cutting depths decreasing. When the ratios of the normal cutting force and the tangential cutting force is below 0.9, the chip will be formed.

Abstract: Molecular dynamics simulations of the single crystal silicon nanoscale cutting with a diamond tool in ductile mode are carried out to investigate the adhesion phenomenon. After relaxation the silicon atoms on the surface reconstruct to make the potential decrease. The silicon atoms close to the diamond tool have the lowest potential (<-5.5 eV) and form a stable structure with surface atoms on the tool surface.

Abstract: In this paper, the effect of minimum chip thickness on cutting temperature in micro-end- milling of aluminum alloy Al2024-T6 using a tungsten-carbide cutter are investigated and analyzed. The three-dimensional coupled thermal-mechanical finite element model is adopted to determine the effects of varying depth of cut on cutting temperature considering size effects. The simulation results show that the cutting temperature in micro-end-milling is lower than those occurring in conventional milling processes. When the depth of cut is approximately 40% of the cutting edge radius, there is no chip formation. The maximum temperature occurs at the contact region between micro cutting edge and workpiece, which shows an obvious size effect. The experimental verification of the simulation model is carried out on a micro-end-milling process of aluminum alloy 2024-T6 with a high precision infrared camera. The influence of various cutting depths on cutting temperature has been verified in experiments. The experimental measurements results are in a good agreement with the simulation results.

Abstract: As the dimensions of parts become smaller, understanding the mechanical properties of these small components was becoming more important. Till present day, the methods and technology used to investigate the deformation behavior in nanoscale were still lacking. In this paper, the specimens were single crystal copper wires with diameter in 50 microns. Atomic force microscope integrated with an in- situ tensile system were used to determine the mechanical behavior of copper wires and observe the surface topography deformation in nanoscale simultaneously. The results were as follows: the modulus of elasticity, tensile strength and failure strain of the sample were 167Gpa, 0.564GPa and 0.011, respectively. By using AFM, the separation process between the copper wire and impurities on it, such as oxide film, was observed. The nanoscale deformation process of the copper wire was also obtained.

Abstract: A completely interconnected macroporous and microporous poly(l-lactic acid) (PLLA) scaffold was fabricated from a PLLA–dioxane–water ternary system by an advanced manufacturing technology called low-temperature deposition manufacturing. A proper fraction of water and PEG added into the polymer solution induces liquid-liquid phase separation and gelation. The liquid-liquid phase separation brings in a new micro morphology and gelation effect produces higher fabrication accuracy.

Abstract: In order to improve the drift accuracy of aerostatic bearings, the air supply pressure and manufacturing errors effect on vortex torque of aerostatic bearings were studied by using the finite element method. This paper analyzed the influence of air supply pressure on vortex torque, in view of elliptical error, incline error of throttle slit and radial eccentricity ratio exist. The quadratic regression orthogonal design was adopted to establish function expression of vortex torque among air supply pressure, elliptical error, incline error of throttle slit and radial eccentricity ratio. In research, the simulation vortex torque values of a certain aerostatic bearing are compared with the experimental values. The predicted characteristics are in good agreement with experimental results and then prove that the finite element model, the method used to solve the problem and the function expression obtained are correct. The research has great significance for predicting performance and choosing the air supply pressure of aerostatic bearings.