Browsing by Author "FUH-KUO CHEN"

In the present study, the wrinkling problem occurred in a stamping part used for a motorcycle oil tank was studied using the 3-D finite element analysis. The material flow due to the original die design was first examined and the possible reasons causing the wrinkling problem were then identified based on the finite element analysis. In order to eliminate the wrinkles, the effects of the process parameters such as blank-holder force, blank size and draw-bead locations on the formation of wrinkling were studied and possible solutions were tried. However, the wrinkle problem could not be improved by changing the process parameters only. A detailed investigation on the material flow during the wrinkle formation process revealed that the uneven stretch between the highest portion of the part and the draw-wall at the part edge caused the wrinkling problem. After releasing the corner angle and cutting off some portion of the sharp corner, a sound part without wrinkles was achieved and the optimum die shape was determined. The modified die design for eliminating wrinkles is validated by the defect-free production part. The good agreement between the simulation results and the measured data obtained from the defect-free production part confirms the accuracy of the finite element analysis. © 2007 Elsevier B.V. All rights reserved.

In this study, an experimental machine for conducting flat strip drawing tests at high temperature was developed to investigate the interfacial tribological properties and evaluate the coefficient of friction in hot stamping. The strength and rigidity required for the testing machine were examined by finite element analysis and confirmed by actual drawing tests. The consistent and reproducible data further validated the reliable performance of the developed friction test machine. The high temperature tribological characteristics at the interface between the sheet specimen and clamping dies were also investigated. The thermal contact condition between the die and the blank was found to be significantly affected by the geometry of the clamping die, and an optimal clamping die design was then proposed accordingly for generating a nearly uniform contact condition in the experiment. With the developed testing machine, high temperature friction tests were conducted on three kinds of boron steel to evaluate the coefficients of friction under various temperatures and contact pressures. The experimental results revealed that the coefficient of friction at elevated temperatures was more sensitive to temperature than to contact pressure. A lower coefficient of friction was also noted for coated boron steel than for the bare equivalent.

The square cup drawing of magnesium alloy AZ31 (aluminum 3%, zinc 1%) sheets was studied by both the experimental approach and the finite element analysis. The mechanical properties of AZ31 sheets at various forming temperatures were first obtained from the tensile tests and the forming limit tests. The test results indicate that AZ31 sheets exhibit poor formability at room temperature, but the formability could be improved significantly at elevated temperatures up to 200 °C. The test results were then employed in the finite element simulations to investigate the effects of process parameters, such as punch and die corner radii, and forming temperature, on the formability of square cup drawing with AZ31 sheets. In order to validate the finite element analysis, the deep drawing of square cups of AZ31 sheets at elevated temperatures was also performed. The experimental data show a good agreement with the simulation results, and the optimal forming temperature, punch radius and die corner radius were then determined for the square cup drawing of AZ31 sheets. © 2003 Elsevier Ltd. All rights reserved.