Jun-Seok Yoon

The upsetting behavior of semi-solid aluminum material fabricated by a mechanical stirring proces

Abstract The fabrication processing of semi-solid material (SSM) of casting alloy has been studied to demonstrate the possibilities of mass production with a controlled solid fraction, the SSM being fabricated for various solid fractions and pre-heating temperatures of the mould. The behavior of the semi-solid globular microstructure has been investigated for various heating and die temperatures for the solid fraction. The influence of the reheating time on the globularization of the SSM microstructure has been determined and the compression behavior of a SSM having a solid fraction of 0.5% has been observed. The relationship between the stress and the strain were also obtained from the compression testing of the semi-solid materials. The rheological behavior of the semi-solid with a globular microstructure was investigated as a function of the compression velocity, under isothermal holding conditions.

A finite-element analysis on the upsetting process of semi-solid aluminum material

Abstract The behavior of alloys in the semi-solid state depends strongly on the imposed stress state and on the morphology of the phase, which can vary from dendritic to globular. A finite-element model for semi-solid material in the upsetting process is presented. The semi-solid material is assumed to be described by compressible rigid visco-plastic model for the solid region and by Darcys law for the liquid flow saturated in the interstitial space. The variation of the distribution of the solid fraction and the material behavior under the upsetting process is investigated for the various values of friction and die speed, the computed results being compared with experimental data. The semi-solid materials of the experiments are fabricated by mixing and cooling of the molten metal. The application validity of the yield criteria for semi-solid material is investigated in the upsetting process analysis.

Feasibility Study on Flexibly Reconfigurable Roll Forming Process for Sheet Metal and Its Implementation

A multicurved sheet metal surface for a skin structure has usually been manufactured using a conventional die forming process involving the use of both a die and a press machine in accordance with the product shape. However, such processes are economically inefficient because additional production costs are incurred for the development and management of forming tools. To overcome this drawback, many alternative processes have been developed; however, these still suffer from problems due to defects such as dimples and wrinkles occurring in the sheet. In this study, a new sheet metal forming process called the flexibly reconfigurable roll forming (FRRF) process is proposed as an alternative to existing processes. Unlike existing processes, FRRF can reduce additional production costs resulting from material loss and significantly reduce forming errors. Furthermore, it involves the use of a smaller apparatus. The methodology and applicable procedure of the FRRF process are described. Numerical forming simulations of representative multicurved sheet surfaces are conducted using FEM. In addition, a simple apparatus is developed for verifying the feasibility of this process, and a doubly curved metal is formed to verify the applicability of the reconfigurable roller, a critical component in this forming process.