J.R. Cho

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.

High strength FGM cutting tools: finite element analysis on thermoelastic characteristics

Abstract In general, a metal cutting tool is composed of tip and shank of different materials, thus it exhibits crucial stress concentration near the material interface under thermomechanical loading while at work. Such an inherent defect is caused solely by the material composition discontinuity across two different material components, but it could be minimized by enforcing the material composition distribution be continuous. This would be achieved by inserting a graded layer between shank and tip, according to the concept of functionally graded material (FGM), in which the material composition varies continuously such that no discontinuity exists over the entire tool region. This paper intends to explore the possibility of FGM for improving the thermal strength of metal cutting tools, according to the parametric analysis by two-dimensional thermoelastic finite element method.

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.

Improvement of thermal regeneration of spent granular activated carbon using air agent : Application of sintering and deoxygenation

Thermal regeneration of spent granular activated carbon (GAC) using sintering, air-activation, and deoxygenation was investigated to determine the potential of this method for overcoming the drawbacks of thermal regeneration. The conditions for each step were optimized. The physicochemical properties of four regenerated GACs were assessed using BET, SEM, and FT-IR analysis. The suitability of the regenerated GACs for liquid-phase applications was assessed by phenol adsorption, using adsorption isotherms, kinetics, and thermodynamics. Sintering increased the micropore area and volume of regenerated GAC by 19% and 16%, respectively, and controlled excessive burn-off, reducing it by 19%. Air-activation has economic advantages because the reaction time is 80% less than that for steamactivation. Deoxygenation improved the maximum adsorption capacity by 7%, although the number of micropores was reduced. Regenerated GAC by sintering, air-activation, and deoxygenation was best for liquid-phase applications; the results show that these steps help to overcome the drawbacks of thermal regeneration.