Papers by Author: Dong Ming Guo

Abstract: Although Single Point Diamond Turning (SPDT) can do pretty well in optical surfacing of large scale KDP crystal, both the surface accuracy and integrity are considerably high; meanwhile as the defects of micro-waveness and stress are inevitable, the laser-induced damage threshold of KDP optical elements after SPDT still cannot be satisfied. Because of the characters of deliquescent and water-soluble, the process of computer controlled Micro-nano deliquescence is attempted to remove the residual micro-waveness on KDP surface after SPDT. Based on the assumption of Preston and the characters of Micro-nano deliquescence, the model of material removal ratio is suggested, the dwell time for ascertained KDP surface is solved, the processing of computer controlled Micro-nano deliquescence is simulated and the processed surface condition on theory is obtained. Besides, the influences of different parameters on the surfacing efficiency and accuracy are analyzed. Finally, three polishing tracks are comparatively analyzed. The simulation results are quite important in guiding the experimental polishing of large scale KDP by computer controlled Micro-nano deliquescence

Abstract: Frequency-aimed optimal structural design of stiffened shell is concerned. It is a reverse design problem for the first several modal frequencies to converge to a set of target value. A design method combined modified bi-directional evolutionary structural optimization (BESO) and size optimization is presented. Optimization model consists of skin and regular grid frame structure. To solve irregular branches and holes that often exist in ordinary topology optimization results, instead of elements, the existence states of ribs in the frame are used as design variables and sensitivity of the rib is discussed. Detailed design is conducted by size optimization. Example shows that frequency requirements are achieved. And the optimum structure is regular and clear, the localized modes problem is avoid. This is very suitable for designing airplane wind tunnel flutter test models.

Abstract: Under the demands of aviating aerocrafts’ pressure, heat and hard circumstance, the design of radome’ electrical properties must reduce the influences of radome to antenna electromagnetic field.So it is essential to analysis the radome electrical system performance and simulate accurately .The most widely-used methods in the radome engineering application currently is the ray-tracing (RT) method and the plane wave spectrum - surface integration (PWS-SI) method. The measured data and computing data of RT and the PWS-SI methods show their respective advantages.

Abstract: This paper is concerned with crashworthiness design of a reinforced thin-walled column under oblique impact. To transform the failure mode of the column under oblique loads from low energy-absorption global bending to high energy-absorption progressive collapse, Magic Cube (MQ) approach, a systematic design approach, is employed to assist the design process: by applying time (process) decomposition, the original difficult nonlinear dynamic crashworthiness design problem is converted into a sequence of simplified linear design problems; by applying multi-domain topology optimization technique to the simplified linear design problems, the optimal configuration of the reinforcement is obtained. Numerical simulation results show that, compared with the original column with same weight, the optimal reinforced thin-walled column has higher energy absorption performance and lower initial crushing force under oblique impact.

Abstract: ECMP (Electro-Chemical Mechanical Polishing) presents high removal rate, low polishing pressure and good polished surface because the action of electrochemistry accelerates copper dissolution. It is considered to be a most promising novel Cu planarization process to replace traditional CMP (Chemical Mechanical Polishing). However, the micro asperity heights of coarse surface are often too small compared to the distance between anode and cathode, so the asperities are difficult to be selectively removed. In this paper, high dielectric constant abrasives were used in ECMP to solve this problem. High dielectric constant abrasives can improve the distribution of electric field, amplify the gradient of electric field and enhance the ability of selective removal. Based on the results of experiments, rutile TiO2, as one of high dielectric constant abrasives, is better than SiO2 and anatase TiO2 in ECMP process. The material removal rate of electrolyte containing rutile TiO2 is 0.078mg/min, and the surface roughness is Ra18.2nm.

Abstract: To reduce stair-step effect when layered forming samples using 2.5D slices, a geometric model with variable thickness slices was developed. Experiments were performed with varying of powder feed rate. Relationships between geometrical precision of samples formed by laser clad forming (LCF) and a variable of powder feed rate were investigated. While the variation of powder feed rate with a calculated step was approximately continuous, clad layers with height increasing approximately linearly along clad length were achieved. Clad height increased from 0.05 to 0.39 mm with powder feed rate varying from 0.5 to 2.5 g/min. Scanning paths were planned by simulating forming process of the ramp through Matlab program. Using the scanning path, a relatively smooth ramp thin wall of 316L stainless steel was formed with a slope angle 3.37° by the experimental validation.

Abstract: In this paper, a three-dimensional finite element model is developed to compute thermal phenomena of 0.5 mm thick Hastelloy C-276 alloy sheets during pulsed laser beam welding (PLBW). Temperature-dependent thermal properties of Hastelloy C-276 alloy, effect of latent heat of fusion, and the convective and radiative boundary conditions are taken into account in the model. The space-time temperature distributions in a butt-joint weld produced by the PLBW process are predicted from the beginning of welding to the final cooling. The heat input to the model is assumed to be a double ellipsoid heat source. The finite element calculations are performed by using ANSYS code with the parametric design capabilities. Experiments were carried out to determine the temperature evolution during welding and to measure the cross section profile of the weld bead. By comparing the simulation results with the corresponding experimental findings, it is found that they are in a good agreement. The validity and applicability of the numerical simulation model are confirmed.

Abstract: Grinding forces during grinding silicon wafer have great influences on the accuracy, surface quality and grinding yield of the wafer. It is necessary to develop an accurate and reliable grinding dynamometer for measuring and monitoring the grinding process of the large and thin wafer. In this work, a new 3D (three-dimensional) grinding dynamometer using piezoelectric sensors is designed and developed, which is used for a wafer grinder based on wafer rotating grinding method. The calibrating experiments of the 3D grinding dynamometer are carried out. The FEA and modal analysis are made and compared with the results of mode testing. Furthermore, the static performance parameters of the dynamometer are obtained from the loading experiment. The experiment results indicate that the 3D grinding dynamometer can measure axial, radial and tangential grinding force of grinding wheel with high sensitivity, good linearity, good repeatability and high natural frequency, and fully satisfied requirement for measuring and monitoring of the grinding force in wafer grinding process.

Abstract: Using the cross-section angle polishing microscopy, the subsurface damage of the silicon wafers (100) ground by the diamond wheels with different grain size were investigated, and subsurface damage distributions in different crystal orientations and radial locations of the silicon wafers (100) were analyzed. The experiment results showed that the grain size of diamond wheel has great influence on the subsurface damage depth of the ground wafer. On the ground wafer without spark-out process, the subsurface damage depth increased along the radical direction from the centre to the edge and the subsurface damage depth in <110> crystal orientation was larger than that in <100> crystal orientation; but on the ground wafer with spark-out process, the subsurface damage depth in different crystal orientations and radial locations become uniform.

Abstract: A new method for laser milling of Al2O3 ceramic based on deteriorative layer controlled is presented in which no assistant gas was used during the laser milling. The new milling technology is developed by means of laser scanning of ceramic surface and forming a deteriorative layer directly. Laser milling parameters are determined through crystal phase’s analysis of the deteriorative layer. The laser milling depth, surface quality, and milling mechanism with different milling parameters were studied systematically on an Nd: YAG CNC laser and multi-layer laser milling experiments were also conducted with optimized processes on the surface of Al2O3 ceramic workpiece. Therefore, the practical experimental results are that each depth of layer milling is between 0.35-0.5 mm and the surface roughness of laser milling reaches to Ra 2-3.2μm. The experimental study has thus provided deeper understanding on laser milling technology for Al2O3 ceramic both in theory and application.