Research On The Multi-point Forming And Springback Control Of Cylinder Surface Based On The Force-Displacement Model

Multi-point forming is a flexible forming technology, which can form different shape without mould. It has been widely used in aircraft skin, hull plate, the repair of skull and other fields. Force-displacement separated control multi-point forming(FDSC MPF) changes the sheet deformation mode from local normal constraint and overall deformation to overall normal constraint and local orderly forming. The stress state of the forming sheet is effectively controlled and improved. FDSC MPF has many advantages such as small rebound, restrained wrinkles, dispense of blank holder, high forming quality, etc.In this paper, the springback law of cylindrical FDSC MPF is systematically studied with the combination of theoretical analysis, numerical simulation and process experiments. Firstly, the theory of neutral layer ingression is used to deduce the calculation formula of the springback bending moment of FDSC MPF, and veracity of the theory is demonstrated by conducting 1060 Aluminum alloy and Q295 FDSC MPF experiments. Results from theoretical derivation prove that the FDSC MPF has significant advantages in springback inhibition compared with conventional MPF.Combination of normal compressive stress, incidental tensile stress and repeated bending can reduce the board springback. Repeated bending has most obvious inhibition effect on springback, while springback moment caused by normal force is the smallest.Mainly based on experiment, combined with numerical simulation, effect of forming mode, forming force, thickness, coefficient, material and the radius of the hemisphere head on the springback of FDSC cylindrical Point-to-Point forming is systematically studied. The results show that: the FDSC MPF has significant advantages in springback inhibition compared with conventional MPF. For the two FDSC MPF Methods, springback of firstly formed part is smaller, while that of latter formed is larger. The springback decreases with the increase of forming force, coefficient of friction and the radius of the hemisphere head. The springback first increases and then decreases with the increase of blank thickness. For different materials, the larger value of σs/E, the larger of springback.The springback law of FDSC Cylindrical Dislocation-Point forming is studied. The results show that the arrangement mode of 9×9 is suitable for forming a variety of surfaces, with less forming defects than that of the 9×10 arrangement mode. The surface of blank has neither indentations nor wrinkles when using nylon baseplate for forming.When forming with polyurethane interpolator, pits come into being at the surface of the blank, and the pits become larger with the increase of forming force. The springback ofDislocation-Point forming is larger than Point-to-Point forming. The springback decreases with the increase of forming force and thickness.