Ying Chun Liang

Research on Micro Machining Using AFM Diamond Tip

In this paper, micro machining is performed using AFM diamond tip, which is similar to a single abrasive particle, and a high precision stage. Using mechanical scratching, microstructures are machined on the surface of single crystal copper. Based on the system, some experiments are carried out: Parameters such as velocity of machining, applied force and amount of feed, which will influence process of micro machining, are analyzed. The diamond tip statex92s influence on micro machining is also studied. And using the optimum parameters and proper machining technique, the microstructures are machined. This approach is a novel unconventional micro machining technology. It can be applied in some micro machining fields such as: MEMS micro devicesx92 fabrication, mask fabrication of lithography, micro-partsx92 micro machining, and machining or dressing on the micro-parts fabricated by other ways. Introduction Since 1986, STM has been used as an important apparatus for surface observation. But with the development of Scanning Probe Microscope (SPM) research, SPM (including AFM and STM) has been applied in surface modification on a very localized region. Particularly, AFM is studied by many researchers because of its ability of controlling the force between the tip and the sample surface. Recently micro machining using AFM ordinary measuring tips has two main methods: oxidation and mechanical scratching. Won Bane Lee and H. Dai machined nano lines by oxidation [1-2]. Hideki, S. Tegen, and H. F. Chen machined two-dimensional figures using mechanical scratching [3-5]. Using diamond tip, most researchers investigated micro wear. Ti Miyamoto, G. J. Zhao and R. Kaneko investigated micro wear characteristics of different materials using this method [6-8]. Only simple figures such as square holes are machined in these experiments to find out the influence of material and scratching parameters on wear process. As a novel machining way, AFM diamond tip has been used as a cutting tool and it has been applied in the fields of nano cutting mechanism and microstructures fabrication. T. Sumomogi and his coworkers carried out the micro machining experiments using the diamond tip on surface of Ni, Au and Cu. They found out several factors influencing micro machining of metal materials on nano meter scale [9]. Jae-Mo Lee and his coworkers developed a system which is similar to AFM. Based on this system, they performed micro machining using diamond tip. And they thought that this way may be used as the procedure before etching or as a new method to machine moulds of micro parts [10]. Similar studies are also conducted by Q. L. Zhao of our team. The diamond tipx92s theoretical model was established. And experiment results showed that the surface alterative layer using this method was less than that of surface machined by conventional polish and grinding [11-12]. In this paper, micro machining is performed using an AFM diamond tip and precision stage. Some experiments are carried out: Parameters such as velocity of machining, applied force and amount of feed, which will influence process of micro machining, are analyzed. Two fabrication methods of two-dimensional microstructures are investigated. The diamond tip statex92s influence on micro machining is studied. Finally using the optimum parameters and proper machining technique, microstructures are machined. Experimental Setup Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 577-581 doi:10.4028/www.scientific.net/KEM.259-260.577

Hole/crack identification by static strains from multiple loading modes

A method using static strains measured from multiple loading modes for the identification of holes and cracks in linear anisotropic elastic materials is introduced. Because of the localized effects of holes/cracks, their existence may not be clearly reflected by a single set of remotely measured boundary strains. By the combining of the concept of multiple loading modes with the technique of nonlinear optimization, several examples of hole/crack identification have been done. During the iteration procedure, the values of the static strains corresponding to the assumed hole/crack geometry and location are obtained by using a recently developed boundary element, which is for linear anisotropic elastic materials and has also been extended to piezoelectric materials. The identified results show that our method for hole/crack identification is stable and accurate for the model problem considered and shows that the method has promise for more complex problems. In addition, the generality of hole profile, the tolerance of measurement error, the spacing and arrangement of sensors, and the flexibility of multiple loading modes are all discussed in detail.

Research on Influence of the Cutter Rake Angle to the Surface Quality during SPDT Machining of Crystal KDP

Influence of the cutter rake angle to the surface quality of crystal KDP is analyzed theoretically in this paper. Analysis result shows that the tension stress reaches minimum in the crystal KDP cutting region and optimal value of the surface quality is obtained as cutter rake angle is about -45°. Cutting experimental of different cutter rake angle is realized on the machine tool. Experimental results show that the surface roughness of the crystal KDP reach minimum (rms is 6.521nm, Ra is 5.151nm) as the cutter rake angle is about -45°, this experiment certifies the correctness of this theory analysis. Theory analysis and experimental results show that influence of the cutter rake angle to surface quality of the crystal KDP is very large, for ultra-precision machining of the crystal KDP, when large negative rake diamond cutter (-45°) is adopted, the super-smooth surface can be obtained.

Analysis of Mechanical Property of Crystal KDP and Simulation of Ultra-Precision Cutting Process in the Ductile Mode

In order to study mechanical property with different crystal-plane and different crystal orientation of the crystal KDP, nano-indentation experiments are first done. The mechanical properties of crystal KDP, such as elastic modulus, yielding stress, are obtained from the analysis of the experimental curve. To obtatin the stress-strain curves of crystal KDP, by using the spherical tip can get characteristic of continuous strain, the spherical indentation experiments is proposed firstly and carried out. According to obtained parameters, A finite element cutting model of crystal KDP is established. The cutting process of crystal KDP is simulated by the model, and the influence of rake angle and depth of cut on chip and surface quality is studied. The theory shows that when the cutter’s rake angle is in the range of -40° to -45°, an perfect super-smooth KDP crystal surface will be obtained. Finaly, the experiments is carried out on special ultra-precision machine tool for crystal KDP by ourself devoloping. Experiment results show that when the cutter’s rake angle is about -45°, an super-smooth surface (rms: 6.521nm and Ra: 5.151nm )is obtained on the plane (001), and this experiment certified correctness of theory analysis.

Research on Influence of Crystal KDP Anisotropy on Critical Condition of Brittle-Ductile Transition in Ultra-Precision Cutting

In order to machine high accuracy Potassium Dihydrogen Phosphate (KDP) crystal part, the indentation experiments are carried out with various loads and various orientation angles. The experimental results show that the critical condition of brittle-ductile transition of KDP has strong anisotropy. Therefore, the influence factors on the surface quality of crystal KDP was discussed, it is shown that influences of the tools geometry parameter, feed rate and Nominal depth of cut etc on the surface quality of KDP are main. Afterwards the cutting experimental study on crystal KDP material is carried out. The experimental results show that the super-smooth surface quality only can be obtained while KDP is ultra-precision machined in ductile mode.

Study on Nanometric Machining Process of Monocrystalline Si

A three-dimensional model of molecular dynamics (MD) was employed to study the nanometric machining process of Si. The model included the utilization of the Morse potential function and the Tersoff potential function to simulate the interatomic force between atoms. By analysis of snapshots and local radial distribution function (RDF) during the various stages of the cutting process, amorphous phase transformation of chip and machined surface are observed, but no phase transformation of bulk. Chip volume change is observed due to the amorphous phase transformation. Dislocations around the tool and elastic recovery of the machined surface do not appear. The effects of surface adsorption on machined surface state have been studied on the basis of surface energy and surfaces hardness. Surface energy decreases and hardness increases by adsorption. Oxygen atoms adsorbed are on the machined surface and subsurface region.

Mechanism of Material Removal and the Generation of Defects by MD Analysis in Three-Dimensional Simulation in Abrasive Processes

Molecular dynamics (MD) simulations of nanometric scratching with diamond tip are conducted on single crystal copper crystal plane (010), and MD simulations are carried out to investigate the mechanism of material removal and the generation of defects on the surface, subsurface and inner of material. During the process of diamond tip scratching the surface of single crystal copper on conditions of different scratching speeds, depths and widths. We achieved the forming details of the chip. While the generation and moving process of defects, such as dislocation, are recorded. The different times of atomic displacement and interaction force are also shown through MD simulation. The evolvement of the lattice pattern in the abrasive processes are analysed by radial distribution function (RDF) and computing the changes of workpiece’s atomic displaces and forces. At the same time, the lattice reconfiguration and the onset and the evolvement process of defects and are analysed by RDF and atomic perspective method, respectively. The simulation results show that scratching speed play role in the course of the form of removing chips, and that different scratching widths and depths of tool have effect on onset and evolvement of lattice defects of workpiece in abrasive processes. This study can give more fundamental understanding of nanosconstruction from atomistic motions and contribute to the design, manufacture and manipulation of nano-devices

Molecular Dynamic Simulation Study of AFM Single-Wall Carbon Nanotube Tip-Surface Interactions

Carbon nanotubes (CNTs) represent ideal Atomic Force Microscope (AFM) tip materials due to their remarkable mechanical properties. Dynamic interactions of a Single-wall Carbon nanotube (SWCNT) indenting towards a monocrystalline hydrogen-free Silicon surface (001) are investigated using molecular dynamic simulation. The critical strain and strain force along the axis of the tube from elastic to plastic regimes are calculated. The simulation shows the deform process in elastic regimes is similar to the process of two ends inward compressed. The atoms of nanotube tip adsorption to the Silicon surface has been observed in the plastic regimes. The mechanical microprocess of AFM’s single-wall Carbon nanotube tip and Silicon surface interactions from elastic to plastic regimes can be well comprehended from the view of nanoscale energetic evolution.

Crack Identification by Artificial Neural Network

Current development in smart materials has improved the conventional composite materials in the ability of self-monitor during service. The massless sensor of micro-electro-mechanical system makes the work successful to embed the sensor into the composite material without changing the original system. For an ideal on-line identification, the measured values of sensors are obtained during service not from experiment. Due to this important reason, the study of the crack identification by using the static deformation as the input is gradually an interested research which will be different from the conventional non-destructive techniques such as, ultrasonics, magnetic flux leakage, X-rays, penetrant, eddy current, etc. To achieve the on-line identification, the artificial neural network is considered instead of the usual nonlinear optimization technique. An artificial neural network is a parallel, distributed information processing structure consisting of processing elements interconnected with weights. In this paper, a most popular learning scheme called the back-propagation neural network (BPN) will be applied for implementing the crack identification. A typical architecture of BPN contains three basic layers input, output and hidden layers. According to Kolmogorovs mapping theorem, any continuous function could be mapped exactly by a three-layer feedforward neural networks. The input pattern is propagated forward, and the calculated responses are obtained. The errors between the desired outputs and the calculated outputs then propagate backward through the network, providing vital information for weight adaptation. It is known that the crack effects are localized which may not be clearly reflected

Atomics simulation of cutting velocity dependency in AFM-based nanomachining process

Three-dimensional molecular dynamics simulations are performed to investigate the AFM-based nanometric cutting process of single crystal copper. The effects of cutting velocities (180, 360, and720 m/s) on the cutting force, the ratio of the thrust force and cutting force and subsurface layers. The results show that the dislocations nucleate beneath the tool, and propagate along the [-11-1] direction in the (111) plane. The effects of the nanocutting action from the tool on the subsurface damaged layers decrease gradually as the distance from the tool tip increases. With the increasing cutting speed, the cutting forces increase accordingly. However, the ratio of the the ratio the thrust force and cutting force decrease as the cutting speeds increase. With the proceeding of the cutting process, that tends to the same on the whole.