Heon-Young Kim

Cylindrical tube optimization using response surface method based on stochastic process

Abstract This paper presents the optimization result in the crashworthiness problem for maximizing absorbing energy of cylindrical tube. To simulate a complicated behavior of this kind of crash problem, a self-developed explicit finite element code is used. The response surface method based on stochastic process is used, that is especially good at modeling the non-linear, multi-modal functions that often bring about in engineering. The main characteristics of using response surface for global optimization lies in balancing the need to exploit the fitting surface for improving the approximation. It can be shown that how these approximating functions can be used to construct an efficient global optimization algorithm. Especially, with the comparison of result by classical optimization method, it can be shown that presented optimization method is independent of noise factor and existence of local minimum.

Prototype tryout and die design for automotive parts using welded blank hydroforming

Abstract Hydroforming is the technology that utilizes hydraulic pressure to form tube and sheet materials into desired shapes inside die cavities. It can be characterized as tube hydroforming and sheet hydroforming depending on the shape of used blank. Hydroforming offers several advantages as compared with conventional manufacturing via stamping and welding, such as part consolidation, weight reduction, improved structural strength and stiffness, lower tooling costs, fewer secondary operations, tight dimensional tolerances, low springback, and reduced scrap. In this paper, the welded blank hydroforming (WBH) technology is discussed in the aspects of formability, and the engine mount bracket and the subframe are analyzed and manufactured for the application of the technology, which have been manufactured by stamping and welding processes. Die geometry and process parameters are suggested by the computer simulation using the explicit finite element code, PAM-STAMP™. Various defects, especially wrinkling in the area of big difference of die depth and large height deviation of the die flange face, are investigated and analyzed. The numerical results are compared with prototype tryout results, and the wrinkling and the local thinning under different forming conditions are predicted.

Physical and numerical modeling of hot closed-die forging to reduce forging load and die wear

Abstract A hot closed-die forging process is analyzed by physical modeling and by isothermal and non-isothermal numerical modeling with the finite-element method. The aim of the study is to obtain quantitative information regarding hot closed-die forging, especially in respect of the material flow, the die pressure, and the temperature. For the study of the flow, layered plasticine was used in physical modeling with a half-scale die set. For the numerical simulation, a thermoviscoplastic finite-element program has been developed. Pressure and temperature distributions are obtained at each stage. Also, the temperature changes in the workpiece and the dies per process cycle are simulated. It is expected that the information can be used in the design of preforming operations to reduce the forging load and to enhance the die-life.

Hydroformability assessment of AA6063 tubes using the polar effective plastic strain diagram

Conventional forming limit diagram concept to determine the forming severity in tube hydroformed products might be restrictive because materials experience complex stress and strain path changes during the shaping process. In this study, a polar effective plastic strain diagram approach was adopted as a strain path–insensitive measurement to establish a criterion for evaluation of necking and, consequently, bursting failures in the tube hydroforming process. The polar effective plastic strain–based failure prediction uses information of the effective plastic strain and the direction defined by the arctangent of the current strain-rate ratio. These values were measured and calculated from free-expansion tests of straight AA6063 tubes for various combinations of axial feed and internal pressure using a stereo vision-based surface strain measurement system. The polar effective plastic strain diagram was constructed and applied to finite element analysis to predict the forming limit of AA6063 tubes. The effect of pretensions was also considered.

The Effect of Temperature Rise in a Fine Blanking Tool

This study was performed to investigate the influence of the tool temperature rise in a fine blanking process. It is known that most of the plastic deformation energy changes into heat and the heat raises tool temperature increasingly in the continual fine blanking process. Real‐time measurement of the temperature distribution on the tool surfaces was carried out using a thermal infrared camera. Finite element analysis for the fine blanking process considering the heat transfer and thermal expansion was also performed, and the result was compared with the experimental data. It is found that the tool temperature rises rapidly within one minute (20 to 30 strokes) from the beginning of the continual process and thereafter increases very slowly. It is thought that the increase of tool temperature affects the decrease tendency of fracture zone in blanked workpiece. The phenomena could be properly predicted using finite element method and it is expected that effective information for the design and manufacture ...

Formulation of Tearing Energy for Fatigue Life Evaluation of Rubber Material

Fatigue life of metal material can be predicted by the use of fracture theory and experimental database. Although prediction of fatigue life of rubber material uses the same way as metal, there are many reasons to make it almost impossible. One of the reasons is that there is not currently used fracture criteria for rubber material beacuse of non-standardization, various way of composition process of rubber and so on. Tearing energy is one of the fracture criteria which can be applied to a rubber. Even if tearing energy relaxes the restriction of rubber composition, it is also not currently used because of complication to apply in. Research material about failure process of rubber and tearing energy was reviewed to define the process of fatigue failure and the applicability of tearing energy in estimation of fatigue life for rubber. Also, 1file element formulation of tearing energy which can be used in FE analysis was developed.

A Parametric Study of the Hemming Process by Finite Element Analysis

Implicit finite element analysis of the flat surface-straight edge hemming process is performed by using a commercial code ABAQUS/Standard. Methods of finite element modeling for springback simulation and contact pair definition are discussed. An optimal mesh system is chosen through the error analysis that is based on the smoothing of discontinuity in the state variables. This study has focused on the investigation of the influence of process parameters in flanging, pre-hemming and main hemming on final hem quality, which can be defined by turn-down, warp and roll-in. The parameters adopted in this parametric study are flange length, flange angle, flanging die corner radius, face angle and insertion angle of pre-hemming punch, and over-stroke of pre-hemming and main hemming punches.

Design and Strength Evaluation of Structural Joint Made by Electro‐Magnetic Forming(EMF)

Recently, weight reduction of vehicles has been of great interest, and consequently, the use of low‐density materials in the automotive industry is increasing every year. Materials should not be substituted such a way that material of component parts is simply changed because there is a problem in achieving stiffness and strength. To achieve these requirements, the automobile should be redesigned totally. Aluminum spaceframe is rapidly being adopted as a body structure for accommodating lightness, stiffness and strength requirement. In aluminum spaceframe manufacturing, it is often required to join aluminum tube. But there are few suitable methods for joining aluminum tube, so that much interest has been focused on testing suitable joining methods. Joining by electromagnetic forming(EMF) can be useful method in joining aluminum tube, which offers some advantages compared with the conventional joining method. In this paper, joining by EMF was investigated as a pre‐study for applying an automotive spacefram...

Muscular Condition Monitoring System Using Fiber Bragg Grating Sensors

Fiber optic sensors (FOS) have advantages such as electromagnetic interference (EMI) immunity, corrosion resistance and multiplexing capability. For these reasons, they are widely used in various condition monitoring systems (CMS). This study investigated a muscular condition monitoring system using fiber optic sensors (FOS). Generally, sensors for monitoring the condition of the human body are based on electro-magnetic devices. However, such an electrical system has several weaknesses, including the potential for electro-magnetic interference and distortion. Fiber Bragg grating (FBG) sensors overcome these weaknesses, along with simplifying the devices and increasing user convenience. To measure the level of muscle contraction and relaxation, which indicates the musle condition, a belt-shaped FBG sensor module that makes it possible to monitor the movement of muscles in the radial and circumferential directions was fabricated in this study. In addition, a uniaxial tensile test was carried out in order to evaluate the applicability of this FBG sensor module. Based on the experimental results, a relationship was observed between the tensile stress and Bragg wavelength of the FBG sensors, which revealed the possibility of fabricating a muscular condition monitoring system based on FBG sensors.

Straightening Process of Micro Wires

This paper deals with the effect of the direct heating method(DHM) for straightening the micro wire. Straightened micro wires have been widely used in the fields of the medicine and the semi-conductor. We have developed a micro wire straightening system by using the direct wire heating method. To controling the tension of the micro wire during the heating and straightening process, a precision tension sensor was set up. In order to avoid the surface oxidation during the heating process, the argon inert gas was supplied to the vicinity of the wire. And, this paper shows the correlation between the tension and the current when arson gas supplied to the tungsten wire. Through several experiments, the optimal tension and current were found. Also, higher straightness and roundness