Keii Ueno

A study of springback in the stretch bending of channels

Abstract The main problems associated with the bending of channels are springback, undesirable deformation of the sectional shape and buckling of the flanges; it is said1that the stretch bending method is effective in overcoming these problems. Regarding the springback, it is important in an actual process to know not only the amount of springback but also the variation of springback with the mechanical properties of the material of the channel and with its dimension. Especially, when SUS304 stainless steel is used for the channel material, the variation of mechanical properties is unavoidable and will depend upon the environmental temperature, the forming speed, the chemical composition and the working history. In this paper, springback in the stretch bending of channels has been studied theoretically and experimentally, and the relationship between the mechanical properties and springback has been clarified. The calculated values of springback are in good agreement with the measured values. Springback decreases with increasing tension, and an additional tension is more effective than an initial tension. It is confirmed that the variation of springback due to the variation of the mechanical properties and dimensions of channels is reduced by using the “fixed initial elongation method”, in which the initial elongation caused by the initial tension is kept constant.

Optimum Forming Conditions for Incremental Tube Burring witha Bar Tool Using FE Simulation

Suitable tool path conditions for incremental tube burring with a bar tool are determined to obtain a uniform wall thickness distribution at the edge of a branched tube by an explicit finite element simulation. In the determination, an aluminum alloy tube, A5083-O, of 400 mm diameter and 6.0 mm wall thickness and a bar tool of 65 mm diameter are modeled. In this study, the second stage of incremental tube burring process is focused on, which is the crucial burring stage predominating the feasibility of burring process and product quality. As to the rocking condition of a bar tool at this stage, it is found that decreasing rocking angle by 5 degrees per cycle is suitable for preventing fracture and achieving high product accuracy. In addition, the simulation results show that an initial rocking angle of 45 degrees is effective in decreasing burring torque and wall thickness reduction ratio at the edge part of branched tube. This reveals that simulation is valid as a design tool for the process optimization of this multistage incremental forming.