Papers by Author: Duc Nam Nguyen

Abstract: Deformation behavior; Aspheric surface; Finite element method; Contact area Abstract. Elastic deformation machining is a novel processing method for aspheric surface. In the machining process, the workpiece will deform and be in contact with the molded surface once load is applied. In this paper, a finite element model was built with Abaqus/CAE package to predict the deformation behavior of glass plate and some significative conclusions were obtained. The numerical simulation results show that the contact area between the plate and the mold is increasing with different pressure. Once the required pressure value is determined exactly, the glass plate can be deform and completely contact with the mold. The deformed shape of glass plate will completely contact with the mold at pressure p=100kPa. These conclusions have the positive significance for the applying of elastic deformation machining.

Abstract: Elastic deformation machining is a new developing machining method for machining aspheric optical workpieces. Fracture property of glass plate under uniform pressure has important influence on the design of mould which is the key part of elastic deformation machining. In this study, to explore the fracture property of glass plate under uniform pressure, the deformation property of glass plate under uniform pressure is analyzed, a fracture experiment of glass plate using vacuum absorption is carried out on a self-developed “fracture testing system” and the values of critical vacuum degree is fit to Weibull distribution. Results show that fracture of glass plate under uniform pressure is comminuted, and for glass plate with depth of 1.95mm and diameter of 96mm, the relative safe value of maximum center offset of the mould’s profile is 0.5mm.

Abstract: Plane lapping method using the elasticity of materials has many advantages comparing with current machining method for aspherical surface machining. Due to the deformation of the workpiece, the material removal characteristics of this method are different from the traditional lapping process of flat surface. In this paper, based on the Preston equation and plate theory, the theoretical model of the material remove rate is built in the case of proving experiment. Then the proving experiment of elastic deformation method is carried out, the recorded values fit well with theoretical ones, which shows that the theoretical model of material removal property is valid and the variation of MRR is related to the deformed profile of workpiece.

Abstract: The mechanics of elasticity is a novel aspheric fabrication technology that could transform aspheric optical fabrication technology into sphere optical fabrication technology. The shape accuracy of the optical lens changes significantly with deformation conditions and various parameters of machining process. Considering Polymethyl-methacrylate (acrylic PMMA) characteristic and elastic deformation aspheric surface generated by the load is uniformly distributed over the inner portion of the plate, the investigation of elastic deformation machining method for aspheric surface generation is introduced in this paper. The subject of this study is to determine finished surface shape of acrylic after lapping process. The experiment results are compared with the finite element analysis (FEA) and theoretical results. The mentioned finite element models were established using the software Abaqus/CAE. The experiment result showed that the error of deformation curves between analytical and experimental result is smaller than FEA and experimental result. The theoretical of deformation curves obtained close to the experiment curves. The results indicate that the experimental investigation of elastic deformation machining method can be used to fabricate the aspheric surface with simple machining process and high efficiency.

Abstract: As the consumer market in the optics, electronics and aerospace industries grows, the demand of ultra-precision aspheric surface increases. The shape accuracy of the optical lens changes significantly with deformation conditions and optical properties of the lens varies with stress distribution within the lens. Therefore, determining the deflection and stress of glass lens is very important to improve the quality of the lens. In this paper, the deflection and stress theoretical results of BK7 glass plate have been presented in different cases of elastic deformation processing. The results are compared with the finite element analysis (FEA) to demonstrate the robustness and accuracy of algorithm in calculation of stress and deflection. The mentioned finite element models were established using the software Abaqus/CAE. The analytical and FEA results showed that if the edge of plate is simply supported, the maximum deflection is 4 times larger than in the fixed edge case. Otherwise if the edge and centre point of plate is simply supported, the maximum deflection is 2.5 times lower than in the fixed edge case and 11.3 times lower than in the simply supported at edge case.