Research On Springback Law Of Cylindrical Surface Bending For 1060 Aluminum Alloy In Multi-point Flexible Die Forming

Multi-point flexible die forming is a novel reconfigurable tooling technology,combined with the advantages of multi-point forming and flexible die forming.The surface quality of the sheet metal is improved and the amount of springback is significantly reduced in this technology.The mold structure and operation process are simplified because of the use of the flexible lower die.In addition,the production cycle is shorten and the manufacturing cost is reduced.Therefore,the study on the deformation characteristics and deformation rule of the sheet metal during the forming process can provide a useful reference for the improvement of the forming accuracy and economy of multi-point forming technology.Furthermore,the research can establish a theoretical foundation for the development and application of reconfigurable tooling technology.The cylindrical surface was selected as the research object in this paper.Based on the results of numerical simulation and experimental study,the deformation process and characteristics of polyurethane and sheet metal in multi-point flexible die forming process were analyzed.Then,the bending deformation law of sheet metal was investigated according to the deformation characteristics so as to reveal the mechanism of springback reduction in multi-point flexible die forming.Moreover,the theoretical calculation method of springback and geometric profile of sheet metal were obtained and then verified through the experimental results of 1060 aluminum alloy sheet.The results showed that the magnitude of the reaction force of the squeeze head in edge priority forming process increased with the increase of the distance to the center of symmetry while the variation tendency was opposite in center priority forming process.The bending moment of sheet metal decreased with the increase of additional stress and alternating bending,which resulted in the obvious decrease of the amount of springback.Besides,the cross-sectional profile of the sheet metal after forming was a multi-segment tangent arc with different radius of curvature under the action of alternating bending and the amount of springback in the priority forming area was smaller.In the multi-point flexible die forming process,the stress and deformation characteristics of sheet metal were different when the forming mode or the forming sequence was different.A single variable method was used to systematically study the the influence of different factors on springback under different conditions.Besides,the springback displacement and springback curvatur were used for the characterization of the amount of springback.Based on theoretical analysis and numerical simulation results,the characteristic of sheet metal deformation was analyzed and the mechanism of springback inhibition by multi-point flexible die forming was revealed from theaspects of stress and strain distribution,bending moment distribution,the variation of reaction force and polyurethane flow velocity.The results indicated that the amount of springback of the sheet metal with preloading reduced by 53.25% compared with that without preloading.Furthermore,the influence of different forming parameters on the springback was similar in the forming process with preloading or without preloading.With the decrease of the ratio of material yield strength and elastic modulus,the radius of curvature as well as the hardness of the polyurethane,the amount of springback decreased.Moreover,with the increase of the amount of preloading,the thickness of the sheet metal and polyurethane,the forming accuracy was improved.The springback of sheet metal was smaller when the thick sheet metal and the polyurethane with good fluidity were used.In the forming process without preloading and the forming process with preloading,the total amount of springback pre-correction varied with the increase of the distance to the center of symmetry,which were along the parabola and the quartic polynomial curve,respectively.After two-time pre-correction,the average springback displacement of sheet metal decreased by 93.40% and 97.85% respectively,which verified the superiority of springback pre-correction in the aspect of the improvement of forming accuracy.