Joon-Hong Park

Fabrication of miniature helical gears by powder extrusion using gas atomized Zn−22%Al powder

Abstract Powder extrusion, which is based on the superplastic behavior of Zn–22%Al eutectoid alloy, was proposed to reduce the forming load and promises to provide fine microstructures in the manufacture of miniature helical gears. The specifications of the helical gears were as follows: module, 0.3; number of teeth, 12; and helix angle, 15°. Compacted powders were consolidated by sintering and solution heat treatment. The consolidated billets consisted of lamellar and fine-grained microstructures. Extrusion experiments were carried out under the following conditions: temperature, 250 °C; strain rates, 2.36×10 −3 s −1 and 1.18×10 −1 s −1 . The mechanical properties of the extruded helical gears were investigated by measurement of the Vickers hardness and extrusion load, and by scanning electron microscopy.

Development of a partition panel of an Al6061 sheet metal part for the improvement of formability and mechanical properties by hot forming quenching

In this study, the hot forming quenching process was investigated to improve the deficiencies that arise in materials subjected to conventional cold stamping, such as low formability and undesirable mechanical properties. The hot forming quenching process was mainly discussed in terms of formability and mechanical properties in this study and was first evaluated by preliminary tests. To examine formability, an evaluation was conducted using hot-tensile and hemispherical-dome stretching tests at temperatures of 350°C and 450°C, respectively. In addition, the mechanical properties of the formed part were predicted using quench factor analysis, which was based on the cooling temperature during the die quenching process. These preliminary test results were then used to predict the formability and hardness of the partition panel of an automotive part, where the analytical results indicated high performance of the hot forming quenching process, in contrast to conventional forming. Finally, the hot forming quenching experiment of the partition panel was carried out to validate the predicted results and the obtained formability and hardness values were compared with conventional forming at room temperature using T4 and T6 heat-treated sheets. The analytical and experimental results indicate that the hot forming quenching process is a very effective method for obtaining desirable formability and mechanical properties in the forming of aluminum sheets.

Prediction and control of front-end curvature in hot finish rolling process

The purpose of this study is to predict the front-end curvature in hot strip finishing mills and to prevent it by controlling the rolling conditions. A theoretical model based on the slab method is developed for predicting the front-end curvature by taking into account the entrance angle of the strip, the friction condition and the back tension. To validate the developed theoretical model, the theoretically obtained curvature value is compared with the results of finite element analysis. Consequently, it is shown that the calculation results of the theoretical model are in good agreement with the measured results of the finite element analysis. Furthermore, a curvature control model based on geometrical and mathematical approaches that can reduce the front-end curvature by the control of the roll speed ratio of the upper to lower rolls is proposed. The proposed curvature control model is verified by finite element analysis, and it is shown that the front-end curvature can be reduced considerably using the proposed model. Therefore, it is concluded that the proposed control model for reducing the front-end curvature in a hot strip finishing mill can be used to improve the quality of the rolled product.

Optimization of Manufacturing Conditions for Spline of Drum Clutch Hub Taguchi Method

A large variety of metal forming processes is required in manufacturing for automotive applications. Traditionally the design process for metal forming tools is based on trial-and-error and on the skill of experienced diemakers. This approach results in high development cost and long lead-times. Especially spline of drum clutch hub requires tight dimensional accuracy in its inside diameter and gear shape because it is used as the main component for the automatic transmission. In this paper, the most desirable or feasible manufacturing conditions for spline of drum clutch hub were found or determined by using Taguchi method and FE-simulation(FORGE-3D). Taguchis optimization approach was used to obtain the optimal parameters. The significant parameters were identified and their effects on Manufacturing of spline were studied. As a results, a confirmation experiment with the optimal levels of manufacturing parameters was carried out in order to demonstrate the effectiveness of the Taguch method.