Abstract: The lightweight thin-walled three-dimensional (3D) curved structure parts are key components in the high-end equipment manufacturing industry, which are difficult to form and process. In order to satisfy the requirements of complex bending and low cost forming, a new type of multi-points 3D stretch-press bending technology for aluminum profile is proposed. The structure of multi-point linked flexible fundamental unit(FFU) for stretch-press bending process is designed. The clamp is used to drive the workpiece to close with the multi-points die (MPD) in the horizontal direction. Once the clamps reach the target position, the hydraulic piston rod of each FFU presses down to shape the workpiece in the vertical direction. According to the forming principle of this new process, a prototype of forming equipment is developed, which realizes the forming of the W-shpae part. Then a numerical simulation model is established to analysis the forming procedure and to predict springback. The forming experiments are conducted to verify the simulation model. It can be seen that the simulation results are in good agreement with the experimental results. The maximum prediction error is less than 15%. In addition, the effect of tensile force on springback deformation in this process is studied. When the pre-stretch force reaches the critical plastic stress Aσ_s from zero, the total springback decreases by 26.81%. The conclusion can been drawn that the pre-stretch force has more obvious effect on springback reduction than post-stretch force. In order to ensure that the forming parts do not have forming defects such as section distortion and fracture, the springback are 6.13 mm and 4.11 mm in the horizontal and vertical directions with the optimum process parameters pre-stretch force Aσ_s and the post-stretch force 0.3 Aσ_s in forming of a W-shape target part. The multi-points 3D stretch-press bending process is proposed to realize complex bending of multi-direction radius of curvature, such as the W-shape part. A new method is provided to achieve the pairwise forming of the mirror symmetrical structural parts which will be applied in high-end equipment manufacturing industry.

Key words: multi-point forming, 3D stretch-bending, springback prediction, pre-stretch force, post-stretch force