Residual stresses and strains analysis in press-braking bending parts considering multi-step forming effect

Abstract

Press-braking bending is a multi-step bending process and widely applied in the aerospace industry. Residual stresses and strains generated during the forming process play an important role in determining its forming parameters and bending path. This work aims to analyze the residual stresses and strains in press-braking bending parts using both the theoretical method and numerical method. First, the analytical model of residual stress and strain is established based on the elastic–plastic bending theory. Second, a fully finite element model of press-braking bending has been developed, and a procedure to simulate the multi-step bending process is presented by using the elastic–plastic large deformation finite element method. The simulation results are then compared with three-point bending experiments in terms of forming force and final shapes of the bent specimens, and excellent agreement is achieved. Finally, the results calculated from the analytical model are compared with the numerical results. The distributions of residual stresses and strains on the finished plate along the length and thickness direction, and particularly the multi-step forming effect on residual stresses and strains, are discussed. It is found that the residual stresses and strains decrease at the initial loading position along the thickness direction during the forming process of subsequent loading positions. With the same punch displacement, the residual stresses and strains at the initial loading position are less than those at the subsequent bending position.

Residual stress analysis and its effect on springback for multi-step pressbrake bending

“…For single-pass bending process, the initial shape of the specimen is flat before loading. The analytical model of tangential stress (σθ) and residual stress ( σ θ res ) in the plastic deformation zone during one-step pressbrake forming are expressed as follows, which have been derived detailed in our former study 29 :…”

“…The FE algorithms and criterions to simulate the multi-step press-braking bending process along the specimen’s length direction has been summarized in our preliminary study. 29 The FE simulation process of multi-pass press bending at the same contact point between the indenter and specimen is shown in Figure 5. In order to reposition the indenter and supporter for the next-pass bending to prevent interference with the specimen, it is noted that coordinate transformations are adopted to obtain specifically values of translation distance or rotation angle.…”

The influence of multi-point roller-dies on the shape deviation differences of profile in flexible stretch-bending forming

“…The FSB is a forming method in which the whole die is discretized into several roller dies which can be adjusted independently at different positions, so as to form different target shapes. 16–22 This forming method can be used for multiple purposes with one machine, reducing production costs, and improving production efficiency. Figure 1 is the schematic diagram of the overall die stretch bending forming and multi-point die stretch bending forming.…”

The experimental investigation of springback and roughness parameters in the three-point forming process using terpolymer punch

“…Quadrini, Santo 25 have experimented with aluminum alloy material and reported that high hardness rubber gives the best surface finish. Some authors 26–31 studied stamping operation, tool wear, single-point incremental forming, hydro-forming process with rubber tool by varying process parameters like compression ratio and speed and hot stamping process, multi-step forming reported that springback is less than the conventional process. From the literature review of conventional methods, it could be inferred that control of springback was attempted by analyzing the effect of various metal forming parameters, residual stresses, temperature, and friction.…”