Yingchun Liang

Adsorption of tripeptide RGD on rutile TiO2 nanotopography surface in aqueous solution

Molecular dynamics simulations were carried out to investigate the adsorption mechanisms of tripeptide Arg-Gly-Asp (RGD) on the nanotopography and perfect rutile TiO(2) (110) surfaces in aqueous solution. It is shown that the amino groups (NH(2) and NH3+) and carboxyl group (COO(-)) of RGD are the main groups bonding to hydrophilic TiO(2) surface by electrostatic and van der Waals interactions. It is also demonstrated that RGD adsorbs much more rapidly and stably on the nanotopography surface than the perfect surface. On the hydrophilic TiO(2) surface, the water molecules occupy the adsorption sites to form hydration layers, which have a significant influence on RGD adsorption. On the perfect surface, since the fivefold titanium atom is surrounded by surface bridging oxygen atoms above it and has a water molecule bonding to it, the amino group NH(2) is the adsorption group. However, because the pit surface exposes more adsorption sites and has higher surface energy, RGD can adsorb rapidly on the surfaces by amino groups NH(2) and NH3+, and the carboxyl group COO(-) may edge out the adsorbed water molecules and bond to the surface titanium atom. Moreover, the surface with higher surface energy has more adsorption energy of RGD.

Dynamic design approach of an ultra-precision machine tool used for optical parts machining

The article presents a dynamic design approach of an ultra-precision machine tool based on the morphology requirements of the workpiece. Compared with common parts, optical parts not only have as many high requirements for surface finish and flatness, but also topographic properties, which leads to a big difference in design with traditional machine tools. This approach, from the topographic properties and functional requirements of the workpiece, demonstrates how to design and analyze the kinematic chain and configuration of the machine tool. Then, a finite element model and mathematical model are established to predict the topographic properties of the workpiece. The design and optimization of an ultra-precision flycutting machine tool is employed as a case study to elaborate the approach in detail. Preliminary machining trials have been carried out and provided evidence of the approach being helpful to design and optimize the ultra- precision machine tool used for optical parts machining.

Modeling and experimental analysis of microburr formation considering tool edge radius and tool-tip breakage in microend milling

The microburr formation in the microend milling of aluminum alloy Al2024-T6 using tungsten-carbide cutter is investigated in this article. The three-dimensional finite element model is developed to analyze microburr formation in microend-milling process. This model predicts the effects of various tool edge radiuses and tool-tip breakage on the burr formation. The microburr formation is dynamically simulated. The simulation results show that there are three basic types of burrs (entrance burr, top burr, and exit burr) along the feature edges. The burrs formed in microend milling are larger than those formed in conventional milling in certain range. The effect curve of tool edge radius on the top-burr height is obtained. Various tool edge radii are found to have significant influence on the top-burr formation. The salient size effect of microburr morphologies is observed in the experiment and simulation. Experimental verification of the simulation model is carried out in the process of microend milling of a...

An integrated method for waviness simulation on large-size surface

The surface waviness of the KH2PO4 crystal has important influence on its optical performance, but it is difficult to simulate by the current simulation models. This article presents an integrated machining performance forecasting method, which considers the interaction between manufacturing process and machine tool and integrates the cutting simulation, machine tool dynamic performance simulation and the control system. The profile and waviness prediction on the large area are achieved by this method with short time and high accuracy. The machining trials on a fly cutting machine tool are carried out to demonstrate the effectiveness of the proposed approach.

3D PLLA/nano-hydroxyapatite scaffolds with hierarchical porous structure fabricated by low-temperature deposition manufacturing

A new Precision Extrusion nozzle based ball screw transmission was developed. 3D hierarchical porous PLLA/nano-Hydroxyapatite(PLLA/nHA) scaffolds were fabricated by low-temperature deposition manufacturing. Scaffolds with macropores of 200–500 μm and micropores about 10 μm were fabricated through a thorough study and control of the processing parameters, in which the processing path and speed of material extrusion determine the macropores and there is a suitable temperature zone for fabricating qualified macropores. Micropore morphology can be controlled by adjusting supercooling of solvent crystallization or adding water into the solvent system. The compressive modulus of the scaffolds in air and phosphate buffer solution was measured, which increased with HA addition. In-vitro cell culture results showed a good biocompatibility of PLLA/HA scaffolds with the pre-osteoblastic MC3T3-E1 cells.

Investigation of the tool-tip vibration and its influence upon surface generation in flycutting

Flycutting is a major machining process for flat-surface machining, which is a typical intermittent-machining process. This paper is dedicated to study the influence of the intermittent-machining force on the workpiece surface generation. In the present study, some defects are identified on the machined surface and found to be corresponded to the tool-tip vibration by the dynamic analysis and the surface-generation simulation. A theoretical model is proposed to capture the dominant factor based on the characteristic. It reveals that the defects are attributed to the changing period of the intermittent-machining force and the dynamic performance of the machine tool. Hence, a surface-generation model is proposed to take account of the tool-tip vibration and the changing of the cutting locus. The simulation results have been found to agree well with the experimental results.

Hydrostatic spindle dynamic design system and its verification

A design system for hydrostatic spindle is presented in light of the dynamic synthesis, which is based on the laws of the fluid mechanics, engineering thermodynamics and rotor dynamics. The finite element theory and hydrostatic principle are integrated into the design process, which provides not only the analyses and determination of the stiffness and temperature rise of the hydrostatic bearing but also the dynamic performance optimization. The proposed design system was implemented through a hydrostatic spindle on ultra-precision machining tools with the flycutting process.

Investigation of the influence of constant pressure oil source fluctuations on ultra-precision machining

The waviness errors on the machined surfaces have significant impact on the performance of optical components. Mid-spatial frequency errors (amplitude near 10 nm, wavelength about 1 mm) are found on the machined surfaces along feeding direction, and the oil pressure fluctuations of the hydrostatic slide are confirmed to be the main source which produces such waviness errors. In this article, the influence of oil pressure fluctuations on the machined surface is studied quantitatively for the first time, and the corresponding experiments are carried out. Besides, the three-dimensional surface profile simulations of workpieces considering the oil pressure fluctuations are achieved. The simulation results have been verified by the experiments on an ultra-precision flycutting machine.

Analysis about diamond tool wear in nano-metric cutting of single crystal silicon using molecular dynamics method

Tool wear not only changes its geometry accuracy and integrity, but also decrease machining precision and surface integrity of workpiece that affect using performance and service life of workpiece in ultra-precision machining. Scholars made a lot of experimental researches and stimulant analyses, but there is a great difference on the wear mechanism, especially on the nano-scale wear mechanism. In this paper, the three-dimensional simulation model is built to simulate nano-metric cutting of a single crystal silicon with a non-rigid right-angle diamond tool with 0 rake angle and 0 clearance angle by the molecular dynamics (MD) simulation approach, which is used to investigate the diamond tool wear during the nano-metric cutting process. A Tersoff potential is employed for the interaction between carbon-carbon atoms, silicon-silicon atoms and carbon-silicon atoms. The tool gets the high alternating shear stress, the tool wear firstly presents at the cutting edge where intension is low. At the corner the tool is splitted along the {1 1 1} crystal plane, which forms the tipping. The wear at the flank face is the structure transformation of diamond that the diamond structure transforms into the sheet graphite structure. Owing to the tool wear the cutting force increases.

Multiscale simulation of nanometric cutting of single crystal copper—effect of different cutting speeds

A multiscale simulation has been performed to determine the effect of the cutting speed on the deformation mechanism and cutting forces in nanometric cutting of single crystal copper. The multiscale simulation model, which links the finite element method and the molecular dynamics method, captures the atomistic mechanisms during nanometric cutting from the free surface without the computational cost of full atomistic simulations. Simulation results show the material deformation mechanism of single crystal copper greatly changes when the cutting speed exceeds the material static propagation speed of plastic wave. At such a high cutting speed, the average magnitudes of tangential and normal forces increase rapidly. In addition, the variation of strain energy of work material atoms in different cutting speeds is investigated.