Abstract
The tubular bumper structures, which are a new manufacturing method based on the principle of hot-stamping, structural design, theory of inventive solving problems and test evaluation, represent a new paradigm in vehicle bumper frame construction. This study focused on improvement of stress resistance of steel pipes through advances in materials science and hot-stamping techniques, verification of the formation part and proposed structure by manufacture examination, performance to improve by computer analysis and new vehicle testing methods. As a result of the application, this paper quantifies increases in strength, optimization of structural design and possibility of production for vehicle body. The latest automotive safety regulations have tightened automotive safety standards and performance of RCAR is a major concern vis-à-vis vehicle maintenance and automotive insurance cost. In particular, vehicular weight reduction is a primary focus as it enables ready reduction in fuel consumption, which is of major concern given depletion of fossil fuels and environmental concerns. Therefore, there is a need for an innovative technology in automotive engineering, capable of satisfying new safety regulations, performance with weight reduction. During the last 20 years, technical development has focused upon material optimization and dimension into preloading engineering through computer aided analysis, while existing structure and production method does not changed. A bumper is an exterior component of a vehicle and functions to prevent body deformation through absorption of energy while slight impact by location in front of most front and rear body, and excessive impact. The bumper is composed of a bumper cover, a bumper frame and 2 crash boxes. A bumper frame is assembled into a crash box that is installed in front of a vehicle body and absorbs the majority of collision energy. In terms of function, bumpers may be classified into pedestrian protection bumpers and RCAR bumpers. In accordance with national regulations and test procedures, many automotive makers have an intensified engineering target to develop parts. The type of bumper frame is divided into metal and plastic composites by a material, and the character of metal bumper frame is cheap cost and heavy weight while plastic composites are expensive yet light weight. This study introduces a new bumper frame concept against old steel frame to meet performance of RCAR. After drawing a conclusion that package space will be enlarged between a bumper cover and body to prevent body deformation, this paper proposes tubular frame. After CAE, prototyping and test evaluation, the feasibility result confirmed that a degree of body deformation while collision and performance of pedestrian protection about lower-leg. This study provides reduction in weight and cost as compared to existing rear plastic composite frames, while providing the same performance. Also, we demonstrate increase strength through hot-stamping of an existing front steel roll-forming frame, while satisfying RCAR performance standards while enhancing pedestrian protection. Therefore, this study proposes an alternative bumper frame as a future automotive technology. The pipes that tensile strength's 1.8GPa are developed by increasing carbon content into hot stamping process. Material properties were enhanced in that tensile strength was improved by approximately 44% compared to an existing hot stamping pipe applied to a door impact bar. The various cross sections and curvatures of bumper frames were developed by indirect quenching process. Various cross sections are ellipse and rectangular against circular and added maximum forming depth is inspected. The suggested bumper frame satisfied the pedestrian protection about lower leg.
KEYWORDS – Bumper Frame, Hot Stamping, Strength, Structural Design, Collision