Abstract
KEYWORDS – High-pressure gas injection, Rear cross member, Forming analysis, Weight reduction, High-strength
ABSTRACT – Nowadays, due to the high demand for more strict regulation for CO2 emission, one of the main issues in automotive industry is to reduce the weight of vehicle as well as to increase the strength. To solve it, high-pressure gas injection forming has been introduced. High-pressure gas injection forming is to inject high-pressure air to the inside of steel tube heated above 960˚C and to take advantage of the high temperature characteristic of material. The objective of this study is to develop the side member that needs high strength and weight reduction through high-pressure gas injection forming.
In general, side member which one of rear cross member parts can be divided by upper and lower panel and is manufactured by the arc welding for joining each other. But, this method has some faults such as limited increase strength and the high weight by 2-pieces structure. In this study, to improve the faults, high-pressure air applied at the end of the heated steel tube which has closed-section structure and the formed tube has been quickly quenched by water. During the procedure, air pressure value, inside corner radius of steel tube and contact point between upper and lower stamping are very important parameters to achieve desirable results. Hyper-Mesh, LS-Dyna and try-out will be used to determine parameters in this study. Forming analysis that realized condition of high-pressure gas injection forming procedure has been carried out by using Hyper-Mesh and LS-Dyna. Consequently, optimal air pressure and inside corner radius of steel tube depending on side member shape is achieved. Also to prevent wrinkle possibility of steel tube by high-pressured air, suitable contact point between upper and lower stamping have been studied. As results, those are applied to shape design of die-stamping and side member, and verify reliability is conducted by try-out. To confirm validity that strength and weight reduction of side member, vickers hardness measurement for formed specimens, fatigue endurance test about rear cross member and weight measurement have been carried out. As a result, it is found that tensile strength of 130K over and weight reduction of about 35% is achieved compared to that of conventional side member.