The Theory Of Springback Analysis For Profile Plane Stretch-bending And Verification

Stretch-bending technique is a common method of metal profile bending processing.In recent decades, the theory, technology and equipments of stretch-bending have beencontinuously improved. Nowadays, stretch-bending technique is widely applied inautomotive, aerospace and building industry because of its advantages of high productsprecision and good surface quality.The research on stretch-bending springback law and accurate prediction ofspringback are always the key issues to be solved. The actual production and academicresearch indicates that, stretch-bending springback relates to the cross-section shape,material properties and loading control, etc. In the past few decades, many domestic andforeign experts have done great deal of research on profile stretch-bending and got a lot ofvaluable data and research methods which are worthy of reference. However, the pastresearch mainly focused on the profile with some given cross-section or some kind ofloading method. The common problem on stretch-bending springback of the profile withany cross-section and the influence of different loading methods on stretch-bendingspringback were rarely involved. In order to produce the advantages of stretch-bendingflexible manufacturing, it is necessary to do more in-depth research on stretch-bendingspringback of profile with any section.Under the basic hypotheses of plastic bending engineering theory, the straindistributions after loading and springback were described when taking no account of theshape of cross-section of profile or loading method. The process of stretch-bendingspringback was taken as process of reverse compress-bending. The springback equation ofplane stretch-bending was established based on the classical elastic-plastic theory and thecharacteristic of strain superposition.When the loading methods are pretension-bending, prebending-tension andpretension-bending-tension, different distribution states of stress and strain oncross-section after stretch-bending deformation were described in detail. Thestretch-bending deformation states were classified into different states. The mathematical expressions of tress and strain in different deformation states weregiven based on bilinear kinematic hardening material model. The mathematicalrelationships among stress neutral layer, strain neutral layer, moment, tension and bendingradius were derived through integrating of stress based on the relationship of staticequilibrium. The method of discriminating different deformation states was given.The universal analytic method and procedures of porfile plane stretch-bendingspringback were obtained. In different loading methods, the quantitative analysis wereexplored in this analytic method aiming at the profiles with U-section and rectangularsection. The springback law describes the influences brought by the tension, bendingradius and loading methods to springback.Based on the operational principle of double-sting stretch-bender, a set of hydrauliccontrol experimental system for profile plane stretch-bending was designed. Theexperimental research on stretch-bending of profile with U-section and rectangular sectionwas carried out. Based on the physical experiment, the finite element simulation analysiswas carried out using finite element analysis software ABAQUS. The springback lawsobtained by experiments and finite element analysis are agreed well with the analyticalresults.Aiming at the problem on stretch-bending and springback of profile with any sectionin different loading methods, this paper carried out systematical research on building ofmechanical models and mathematical analysis of springback. The theory of springbackanalysis for profile plane stretch-bending was established. The experimental andnumerical research was carried out to verify this thoery. The research indicates that, thetheory of springback analysis for profile plane stretch-bending is applicable to any profileand any loading method; the stretch-bending springback of profile with any cross-sectioncan be accurately predicted when loading method, bending radius and tension are alldifferent. This research breaks through the imitation of the research on the stretch-bendingof profile with single cross-section in a single loading method, enriches the theoreticalsystem of profile stretch-bending springback and provides a theoretical basis forstretch-bending flexible manufacturing.