Research On Formability Of Tailor Rolled Blank

Energy saving and environmental protection are the two great challenges that the automotive industry has to face in the21st century. The vehicle lightweight technology is an important measure to cope with these challenges. The adoptions of new materials (such as aluminum alloy, magnesium alloy, plastics, ceramics etc.) and lightweight structural metal sheets based on new material processing technology (such as Tailor Welded Blank, Tailored Rolled Blanks etc.) are two effective ways to achieve automotive lightweight. However, because of the high performance-price ratio of steel, extensive application of new materials in place of steel is unrealistic, so the metal sheets based on new material processing technology have been paid more and more attention.So far, Tailor Welded Blank(TWB) has been widely applied in the automotive industry. Tailor Rolled Blank(TRB) is another kind of metal sheet for lightweight strcuture based on new material processing technology after TWB. Flexible rolling technology is the key technology for TRB manufacturing. It is similar to the traditional longitudinal rolling technology, but the roll gap can be adjusted through computer real-time control during rolling, and thus the blank is rolled with the preset variable section shape in the rolling direction. Designers may select the optimized longitudinal section profile of TRB according to the actual load cases in forming and serving processes, which can greatly improve the design flexiblility. Auto panels made of TRB, which have advantages of better rigidity and strength, can improve the load-carrying ability, the dent resistance and the energy absorption capacity, and significantly lighten the weight of autobody.In order to promote the application of TRB in the automotive body, the research on the formability of TRB is imperative. The formability of TRB is studied by a combination method of analytical analysis, numerical simulation and experimental verification.TRB is annealed by the two-slope annealing process. The hardness of unannealed and annealed TRBs is tested and compared. The basic mechanical properties of TRB are studied by the uniaxial tension test. The mechanical analytical model for uniaxial tension is set up, and the formulae of deformation at the thinner side and at the thicker side are derived. On the basis of uniaxial tension test data, the Lagrange polynomial interpolation is adopted to construct the stress and strain fields of unannealed and annealed TRBs, which can solve the problem of TRB material parameters for simulation. Finally comparison of results among experiment, analysis and simulation are carried out. and the experimental results are explained by the mierostructure. The agreement of experiment, analysis and simulation confirms the correctness of the analytical model and the deformation formulae. The results show that the necking happens at the thinner side for both unannealed and annealed TRB tension specimens, the annealed TRB has lower strength and higher plasticity, and thus acquires greater elongation.The forming principle, the stress distribution state and the deformation characteristics of TRB box are analyzed. The forming defects are presented, including wrinkle, crack, thickness transition zone(TTZ) movement etc. The mechanisms of theses defects are discussed, the spots of the defects are fixed, and the measures solving the defects are offered. The formula of TTZ displacement is built on the basis of uniaxial tension analytical model. At the end, simulation and experiment of stamping forming process of TRB square box are carried out. Effects of annealing process, binder force type, binder force value, blank thickness difference, TTZ length, TTZ position and blank size on thinning and TTZ movement are discussed, and the numerical data and the experimental data are in good agreement.The bending springback mechanism is described. The mechanic problems during the course of bending springback are analyzed, and the formula for computing the amount of springback is deduced. The key factors that affect the springback simulation accuracy are offered. On this basis, the springback characteristics of longitudinally bended (bending axis is parallel to the rolling direction) and transversely bended (bending axis is perpendicular to the rolling direction) TRB U-shaped parts are studied. The thickness distribution, the stress strain distribution state and the springback trend after forming are analyzed. Effects of die clearance, friction coefficient, material properties, blank size, blank thickness, TTZ length and TTZ position on the springback of TRB U-shaped part are discussed, and a separate discussion on effects of above factors on the TTZ movement of traversely bended TRB U-shaped parts is carried out. The results show that numerical and experimental results have good consistency. After forming, the thickness of the whole TRB varies little, and the springback at the thinner side is much larger than that at the thicker side for the unannealed TRB U-shaped parts. Annealing treatment can greatly reduce the springback of TRB especially the springback at the thinner side, and make the springback of the whole TRB uniform. In addition, for traversely bended U-shaped parts, the TTZ, movement of the annealed TRB is larger than that of the unannealed TRB.For the purpose of achieving the autobody lightweight. TRB is applied to the sti Honor of A-pillar in some car. Through the use of stiffening ribs and annealing process, the springback and the TTZ movement of the TRB part can be controlled in a permitted range. The introduction of TRB into the manufacturing of panels can achieve the goals of saving material and lowering weight on the premise of meeting strength and rigidity.