Research On Plastic Deformation And Instablity Behavior Of Hydroforming Of Overlapping Blanks

Thin-walled components with complex surfaces are the solid support for advanced equipment and are widely applied in aerospace field.The processing capacity of the components represents the level of a country’s aerospace manufacturing.Hydroforming is an advanced technology which uses liquid as the forming medium or dies to deform the parts.This forming technology is appropriate for manufacturing of high-precision and high-reliability thin-walled components with complex surfaces.However,there is a high risk of a severe non-uniform deformation,cracking,buckling,and wrinkling during the hydroforming of thin-walled tubular components with local protrusions or non-axisymmetric complex surfaces.It is particularly urgent to develop new forming methods to overcome these challenges.A new method was proposed to enhance the expansion ratio and improve the thickness distribution using overlapping tubular blanks based on integral material flow rather than plastic deformation.Theoretical analysis,numerical simulation,and experiment methods were used to investigate the hydroforming deformation behavior and instability mechanism of cylinder,spherical,and square hollow components.Deformation and instability behavior was performed in the hydroforming of overlapping blanks(HOB)through theoretical analysis.A theoretical model was built to elaborate on the deformation behavior of the outer layer of the overlapping blank based on the characteristic of the circumferential material flow.The displacement function was derived and the distributions of circumferential,axial,and radial displacements were obtained.The instability mechanism was revealed in the hydroforming of overlapping blank.A method was proposed to avoid the wrinkling defects,which was achieved by normal supporting load at the wrinkling zone.The critical anti-wrinkling pressure was derived using the energy method.The critical expansion pressure was derived.The effects of the overlap angle,the radius and thickness of the overlapping blank on the critical expansion pressure were obtained.The experimental study was carried out on the hydroforming of cylinder parts with overlapping blank to study the deformation behavior of developable surface.The wrinkling behavior was revealed under different boundary conditions.Wrinkling defects were prevented effectively by applying the normal load,which was achieved by a sub-plate covered upon the overlap at the outer layer.The effects of the initial overlap angle on the overlap amount and the wall thickness distribution and the characteristic of shape variation at the edge of the overlapping blank were studied.The stress and strain states were analyzed and the occurrence and development of wrinkles were studied under different boundary conditions through numerical simulation.The experimental study was carried out on the hydroforming of spherical parts with overlapping blank to study the deformation behavior of non-developable surface.The deformation and wrinkling behavior of the straight-edge overlapping blank was studied and displacement and stress distributions were compared between the cylinder part and the spherical part.Curved-edge overlapping blanks were designed using the compensation method and the wrinkling behavior was revealed.Wrinkling defects were completely eliminated by using a patch plate as a normal constraint.The cracking behavior was revealed under different thicknesses ofsub-plate.A sound spherical part was obtained with the usage of sub-plate.It was demonstrated that the forming limit was enhanced and the thickness distribution was improved by the overlapping tubular blanks.The experimental study was carried out on the hydroforming of square parts with overlapping blank to study the corner filling behavior.Theoretical model was built to study the effects of initial amount of overlap and overlap position on deformation behavior in the hydroforming of square part.The overlap position also influenced the variation of corner radius.However,the relationship between the overlap position and the corner radius was non-monotonous.The effects of the overlap amount and the overlap location on the corner radius and the wall thickness distribution were reveled.In addition,the law of stress distribution was revealed through numerical simulation.