Key Engineering Materials Vols. 315-316

Abstract: Since adhesion plays a significant role in microtribology, properties of adhesion work of several materials, such as Si, and mica are investigated by AFM. Experimental results indicate that, measured adhesion work varies with contacting velocity, surface roughness and so on, which is more than a constant. Meanwhile, under invariable loads, friction force of these materials is also measured over a wide range of velocity, which is found that adhesion work of the sample surface directly influences the velocity dependent property of micro friction force. This makes the observed micro frictional behaviour significantly differs from the traditional macro friction laws, in which friction force is proved be independent of sliding velocity. Additionally, with zero or negative load, friction forces are proved to be determined by adhesion work and adhesion contact area. Finally, a relationship between micro friction force and adhesion work is outlined.

Abstract: Knowledge of a vehicle’s inertial parameters is essential for safety research and accident reconstruction. A precision measure system is proposed to determine the weight and gravity center for heavy vehicles. Based on a static gravity measuring principle with three measuring points, a hydraulically driven 2-DOF motion platform is developed. The transfer function model is derived for the hydraulically driven system. By means of a degree-of-freedom control scheme, the platform can realize accurate positioning to construct two intersected planes and work out the three-dimensional coordinates of the vehicle gravity center. Experiments demonstrate that the system has less than 0.3% measurement error in weight, and is able to measure the gravity centre accurately with deviation ≤3mm in X and Y direction, and ≤5mm in Z direction.

Abstract: 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.

Abstract: The measuring system was developed based on a reconstructed atomic force microscope (AFM) combined with the precision rotating air-bearing and assistant transform shaft. By this system the experiment was carried out according to the principle of three orthogonal orientations towards a micro sphere about 0.46 mm in diameter, and nine one-dimensional traces around the sphere were obtained. Analyses on roundness and sphericity are carried out from the measured data.The results show that the maximal roundness is 0.3895 μm, and the sphericity error is 0.3880 μm.These evaluations are significant references to evaluate its fabrication accuracy or to reform its machining processes.

Abstract: With the development of science and technology, Atomic Force Microscope is widely applied to the field of machining process in nanometer scale. Due to the limitation of the inventive purpose of AFM, only height mode and deflection mode can be applied in AFM-tip micromachining. It can’t control the machining depth during the micromachining process at present. In this paper, a new micromachining system is set up, which composed of a high precision three-dimensional stage, an AFM, a diamond probe and a special control device. By utilizing variation parameters PID algorithm and controlling the machining depth directly, the micromachining system can resolve the problem mentioned above.

Abstract: This paper analyzes the changes of cutting force, cutting temperature, and cutting-tool wear in the process of precision cutting. All these factors are considered in the test on GCr12, Cr12 and 45 steels. This test uses the sub-dry cutting method with green-air cooling and a little additive. Furthermore, it discusses the feasibility of sub-dry cutting on the basis of a comparison with other cutting methods

Abstract: A new visual servo control system under microscope was introduced based on the research of image-based computer visual control system, including the installation and calibration of camera, deduction of the image Jacobian and the algorithm of controlling and so on. The experiments of motion controlling and positioning showed that one pixel about 2.97μm can be reached easily in single axes under 5× eyepiece and under the same condition a 400μm micro shaft was assembled into a micro-gear with 415μm inner bore. Knowing from the control algorithm, the accuracy of the system is independent on errors in the robot kinematics or the camera calibration. The research results indicate that this method is a full closed-loop visual servo control system with a high reliability and simple control algorithm and it can be used in microassembly system.

Abstract: This paper presents a sophisticated trajectory tracking algorithm based on the utilization of the compound control and fuzzy contour control for the ultra precision machine tools. The main idea is to use the compound control to broaden the bandwidth of the servo system and, therefore, improve the tracking accuracy of the single axis. Then, FUZZY cross coupled contour control is introduced to compensate for the contour error caused by imperfect dynamics of the tracking axis and the mismatch of the control parameters of the servo systems. Experiments carried out on the HCM-1 ultra precision machine tool with a T-type layout show that the integration of the compound control with the fuzzy cross coupled contour control can effectively improve the contour tracking accuracy of the ultra precision machine tool.

Abstract: Profiting from its high stiffness and ratio of push to weight, the stage directly driven by linear motor can reach extremely high acceleration. However, because the stage doesn’t have transmission parts, signals of the control system may excite high frequency vibrations in it directly, which limit the tuning range of controller’s parameters, prolong the stage’s settle time and influence its efficiency and positioning performance. This paper presents the stage’s dynamic characteristics by modeling simulation and experimental modal analysis (EMA). According to the dynamic characteristics, a time delay filter (TDF) is used in the controller, then the stage’s vibrations are restrained and its settle time is reduced distinctly.

Abstract: Coloring stainless steel is a kind of corrosion-resistant and ornamental industry material. Whereas, the oxide film on stainless steel is sensitive to heat. At about 200
, the oxide film would be oxidized or dehydrated. With lesser cutting force and no thermal influence on target material, AWJ may be a suited method in cutting coloring stainless steel. In this paper, an experimental study on cutting coloring stainless steel by abrasive waterjet was carried out. By analyzing macroscopic features of kerfs, a damage model was established and a principle to optimize process parameters was presented.