Papers by Author: Tae Wan Ku

Abstract: Multi-stage deep drawing process for rectangular cups with extreme aspect ratio using finite element analysis is performed. The process is mainly consists of four forming stages including blanking, drawing, ironing and trimming. However, main deformation of the rectangular cup is completed during the drawing-ironing procedure. Tool design and blank modification for the multi-stage deep drawing process are presented. To consider the deep drawing and the ironing operations, the multi-stage deep drawing process is applied to obtain the rectangular cup by using each numerical simulation models from first to fifth drawing. Based on the design results of the initial blank, the multi-stage deep drawing process is performed, but it is shown that severe earing phenomenon is occurred at the upper flange part. To solve the severe deformation at the upper flange due to normal anisotropy of the used sheet material, initial blank modification is carried out. The simulation results for the rectangular cup are compared with the final configuration before and after the modification of the blank shape. The predicted result is confirmed that the modified blank shape not only improve the quality of a deep-drawn product but also reduce the cost of production.

Abstract: This study is dedicated to three-dimensional finite element analysis of seaming process, which consists
of bending, curling and caulking process, of a large tubular mechanical bonded structure. The seaming process is often used to improve a high bonding strength as avoiding any kind of defect. Finite element simulations of the seaming process were preformed for two different initial conditions with pre-analyzed results and without those from bending process. The mechanical bonding strength of the seamed area in the large tubular structure was estimated and compared through finite element analysis among several different analysis conditions of the bending and the caulking. Tensile test for the specimen extracted from the large tubular mechanical bonded structure was also executed and compared with the results of finite element analysis, in order to verify which initial condition in finite element analysis was suitable for this kind of multi stage seaming process. As a result, the effect on an accuracy of finite element analysis for the multi stage seaming process was evaluated in this study. Finally, it is noted that the pre-analyzed results from bending process should be considered in order to obtain the accurate results from finite element analysis.

Abstract: Mechanical damping systems have been widely used to various industrial structures and are mainly hydraulic and pneumatic devices nowadays. This article presents an experimental investigation of a nano colloidal damper. Particularly for colloidal damper, the hydraulic oil is replaced by a colloidal suspension, which is consisted from a nano-porous matrix with controlled architecture and a lyophobic fluid. Nano colloidal damper test rig and the measuring technique of the hysteresis were described in this study. Influence of the water volume and particle diameters upon the nano colloidal damper hysteresis was investigated. As a result, the proposed nano colloidal damper (NCD) is proved as an effective one, which can be replaced for the conventional hydraulic damper.

Abstract: The main goal of this study was to develop the technique of process design and manufacturing for a rectangular deep drawn cup with very narrow width by using finite element analysis scheme and a series of experiments. The manufacturing process of this rectangular cup required several intermediate steps to generate the final shape. The multi-stage deep drawing process was applied to finite element analysis, and a continuous progressive press was employed in a series of experiments. Final specifications of the rectangular deep drawn cup were length of 33.70mm, height of 48.30mm and width of 3.46mm, respectively. In this study, finite element analysis for this drawing process was carried out from the first to the seventh stage, and a series of practical experiment was performed. These simulated results of the rectangular cup were compared with the prototypes of the experiments in view of the deformed shape in each mid-part. The results of finite element analysis showed good agreement with those from the experiments.

Abstract: A numerical approach for forming simulation and manufacturing of micro part, based on the elastic and the rigid-plastic finite element methods by using grain element and grain boundary element, is proposed to simulate MEMS/micro-structural deformation behavior of material during micro forming. The idea is to present the polycrystalline material by an aggregate of so-called grain element that describes the plastic deformations of each individual grain in view of micro-structure. This grain element is connected by grain boundary element to account for shear deformation between grains. The main objective in this study is to develop the reliable finite element model and scheme for micro forming simulation with very thin sheet. The reliability for micro forming analysis is described from the comparisons of the micro-structural deformation behavior between the conventional rigid-plastic finite element analysis and the FE analysis of the developed program with very thin sheet material.