Hyun-Sung Jeong

Parametric investigation on the curling phenomenon in CONFORM process by three-dimensional finite element analysis

Abstract Owing to the circular material flow, a CONFORM continuous extrusion forming process exhibits more complicated process characteristics compared to conventional front- and side-extrusion processes. One remarkable thing is the curling phenomenon in the material flow after it passes through the die, and which is caused solely by the non-uniformity in material velocity profile at the die section. Since this process has been introduced, this phenomenon has not been intensively studied, and furthermore most of analytical and numerical studies for the process have been carried out with the simplified two-dimensional plane-state model. Through the three-dimensional finite element analysis of CONFORM process, we in this paper address the parametric investigation on the curling phenomenon together with the more realistic understanding of the flow characteristics in the die region. For the parametric experiments, we take the wheel velocity, the abutment height and the flash gap size as considering parameters.

A study of the application of upper bound method to the CONFORM process

Abstract This paper is concerned with the calculation of the powers required in the steady-state CONFORM process. For this goal, similarity is applied to the CONFORM process for an equivalent side extrusion process, to which the upper bound method is used to derive the equation for calculating the powers. Even though the global flow characteristics between the real and the simplified processes are not similar, the calculated results for both processes show good agreement. Furthermore, FEM simulation is carried out using the DEFORM commercial program in order to verify the theoretical results.

A study on optimal design for CONFORM process

Abstract In this paper, we investigated the effects of several significant process parameters on the process characteristics in the CONFORM process, such as material flow, defect occurrence, temperature and effective strain distributions, using DEFORM commercial FEM code. Since there are many parameters governing the process, it is not so easy to obtain an optimal combination of process parameters. Therefore, here, according to the parametric investigation of general forming methods, we carried out numerous numerical simulations and suggest a qualitative guide for the optimal CONFORM process.

Parametric investigation on the surface defect occurrence in CONFORM process by the finite element method

Abstract It is widely known that the CONFORM process can produce ultra-long seamless products of complicated section-shapes without the need for pre-heating, but it may lead to products with a defect due to surface separation unless the process parameters are appropriately combined. Even though theoretical and experimental studies on the process itself have been intensively carried out, the study on the surface defect phenomenon is still in need of further study. In this paper, the authors address a parametric investigation on the occurrence of the surface defect in this process. Because several parameters are associated with the process, one has to parametrically analyze such a phenomenon. Here, the wheel velocity, the extrusion ratio, the abutment height, the friction coefficient and the flash-gap size are taken as parameters, and numerous parametric numerical experiments are carried out in order to analyze their effects on the surface defect occurrence.

CONFORM process: surface separation, curling and process characteristics to the wheel diameter

Abstract Even though CONFORM process can extrude ultra-long seamless products of various section shapes with high extrusion ratio, without pre-heating and post-mechanical treatment, it suffers two inherent process defects, the surface separation and the curling phenomenon. These process defects are caused basically by the circular material flow driving by the rotating wheel. Therefore, the parametric investigation on the process defects with respect to the wheel diameter is of importance, although the material flow is also characterized by other several process parameters. In this paper, we numerically examine the effects of the wheel diameter on the surface separation and curling phenomenon as well as other significant process characteristics, through the two-dimensional finite element analysis of CONFORM process for solid section aluminum products.

The Al-powder forging process: its finite element analysis

Abstract This paper addresses the finite element formulation and simulation of the powder forging process for cup-shaped aluminum products. This study is the preliminary analysis for the powder forging process of Al 6061 engine pistons of automobiles. The mechanical behavior of the powder is assumed to obey the isotropic compressible viscoplasticity, while the thermal behavior of powders is effectively modeled by a non-linear transient heat-transfer problem. A generalized Crank–Nicolson–Galerkin scheme is employed for the temporal and spatial approximations, and non-linear numerical equations are solved by the Newton–Raphson method. Through the numerical simulation, the distributions of density, temperature, stress, and punch load are investigated.

Rapid fabrication of aluminum shoe mold using vacuum sealed casting process

Abstract Rapid prototyping and manufacturing (RP&M) is the most appropriate technology for the small-lot production system, because the production cycle is getting shorter owing to various needs of the consumer. Recently RP products, which are made of plastics, wax, and paper, were used to examine the design of samples. These samples, however, cannot be applied to the real mold because soft materials, such as plastics lack the necessary strength to be a mold. So the materials have been changed from RP products to a metal powder filled mold like an epoxy-metal powder composite mold or metal mold, which is called rapid tooling (RT) technology. In this paper, RT technology is applied to the casting process. The casting process has the ability to reflect complicated shapes in one process. But it has not been widely used to make a die and mold because of the poor surface quality caused by air bubbles on the surface of the casting product. In this study, the porous casting mold is fabricated from a mixture of ceramic powder and water-soluble binder. The porous casting mold can improve the characteristics of aluminum casting products with the help of the vacuum sealed casting process. The vacuum sealed casting process is an advanced technology that removes the air bubbles between the porous casting mold and the liquid metal, thus making the surface of the aluminum casting product finer. The purpose of this paper is to develop a high quality shoe mold using porous casting mold and to apply the RP&M technology to the shoe industry.

Optimum Tire Contour Design Using Systematic STOM and Neural Network

An efficient multi-objective optimization method is presented making use of neural network and a systematic satisficing trade-off method (STOM), in order to simultaneously improve both maneuverability and durability of tire. Objective functions are defined as follows: the sidewall-carcass tension distribution for the former performance while the belt-edge strain energy density for the latter. A back-propagation neural network model approximates the objective functions to reduce the total CPU time required for the sensitivity analysis using finite difference scheme. The satisficing trade-off process between the objective functions showing the remarkably conflicting trends each other is systematically carried out according to our aspiration-level adjustment procedure. The optimization procedure presented is illustrated through the optimum design simulation of a representative automobile tire. The assessment of its numerical merit as well as the optimization results is also presented.

Optimum Design of Tire Crown Contour Utilizing Neural Network

Contacting with ground in the post-card area size only, tire supports entire automobile weight. As well, it characterizes most of automobile running performance. Among the design parameters, the carcass contour becomes a key design factor. This paper deals with the time-effective optimal design of tire crown contour in order to improve the tire wear performance by employing a back-propagation neural network model.