Many efforts are being actively carried out to replace steel parts with aluminum alloys in automobile industry to reduce the weight of automobiles. A representative example is the car frame made of extruded aluminum tubes. A novel method of producing such aluminum car frame is rubber pad bending since it is capable of producing various bending curvatures with a single production set-up. However, as is the case for general bending processes, the cross-section of an extruded aluminum tube deforms during bending and the level of deformation increases with bending curvatures. This diminishes bending rigidity of the aluminum tube, hence making it inappropriate for a structural use. Thus, it is important to have a meaningful quantitative measure of cross-sectional deformation that can be used to determine whether the bent geometry is suitable.
In the present study, it is proposed to use the ratio of the second moments of inertia of the initial and deformed cross sections of the tube as a measure. In a rectangular tube-bending example, it was found that the value of this ratio generally decreases with increasing bending curvatures, but suddenly drops at a certain point. This point was considered to be the forming limit for the given bending condition. The effects of process parameters such as the rubber material property and roller diameter on forming limit were examined through finite element (FE) analyses. The accuracy of FE simulations was verified through comparison of deformed shapes with experiments. It was found that the stiffness of the rubber pad has much influence on the sectional deformation. With such knowledge of forming limit depending on process parameters, appropriate parameter values to decrease the amount of cross-sectional deformation for an arbitrary rectangular tube bending case were determined under the present investigation condition.
