Study Of Drawing Formability And Weld Line Movement Of Stiffening Plate Of A Front-carling Made Of Tailor-Welded Blank

Considering the requirements of future automotive in environmental protection and safety, structure optimizing and weight reducing of body-in-white, besides to the improvement of engine capability and aerodynamics character, has become an important goal of automotive manufacturing industry nowadays.The technique of laser welding blank is to use laser to weld up the tailors with different thickness or strength or surface coating and then press the tailor-welded blank (TWB) to the form as designed. The technique could provide the best combination of formability and strength to the blanks used in complex body of cars. In the last 20 years and in American and European automotive industry such as Volkswagen and General Motors, TWB has been widely used and the related techniques such as laser welding and forming have also been researched and developed. However, the product application and technique research of TWB in China is not enough. Facing the violent competing environment of international automotive industry, It is very significant for us do in-depth research to the formability of localized TWB.The test method for both parent tailor and welding of TWB mainly include cupping test, tensile test and forming limit test. Cupping test is the main testing method for TWB suppliers and OEMs to control the quality of welding seam. Tensile test is the basic method to test mechanical property such as yield stress, tensile limit and yield ratio, etc. Through the tensile test to parent tailors and different welding positions, basic mechanical property of total TWB could be acquired. As to the complex body part that is hard to form, forming limit diagram (FLD) is often used to describe the part formability. FLD is the most simple and straight way to evaluate the formability of metal sheet, a quantitative description of sheet formability, an effective tool to solve the problems of pressing and a criterion of forming technics. With the development of FEA technique recently, FLD has been used more and more widely as the criterion for wrinkle and crack in simulation.In this thesis, we use both test and simulation method to study the formability of localized TWB and the formability of the Stiffened blank of the front longitudinal rail made from TWB.In test study, cupping test (for both parent tailor and welding), tensile test and forming limit test have been made to the TWB with parent tailor of ZStE220P and different thickness of 0.8mm and 1.5mm. The result of cupping test showed that the welding seam is qualified with the enterprise standard. It is indicated by the contrast test between TWBs with different thickness ratio that, difference of tailor thickness is a key parameter for TWB. The bigger difference there is, the smaller maximum cupping ratio of welding and parent tailor and the larger deformation of thinner parent tailor side, will be got, which indicated a worse fluidity in welding seam than in the parent tailor. Through the tensile test, the basic mechanical property of parent tailor and welding is got. FLD is a key criterion for wrinkle and crack in pressing process, and a good direction to production. Through the forming limit test, the FLDs of parent metal and TWB are got. Comparison between them shows that, the forming limit of TWB is less than that of parent metal. The wrinkle and crack all occur in the thinner parent tailor side during all 3 tests, which indicated that the strength of welding seam increases but the deformation resistance of that position decreases. In simulation study, we use DynaForm software to study the formability of the Stiffened blank of the front longitudinal rail part. DynaForm is a professional fast simulating software specialized in the formability of metal sheet, which is based on the static force implicit algorithm and widely used in simulation analysis of formability of sheet and TWB and hydraulic forming. We used the test result got in the 3rd chapter as the simulation input and then form a CAD model, ignoring the type of welding seam and taking only the position of welding. Blank holder pressure is a key parameter affecting the formability. We get the best simulation result through the optimization of blank holder pressure parameter. With proper drawing reinforcement, clamping ring and blank holder pressure, the TWB with parent metal of ZStE220P and different thickness of 0.8mm and 1.5mm meets all the formability requirements of the Stiffened blank of the front longitudinal rail part.It is indicated by the simulation that, although the thinner tailor side possesses the bigger area and thus the welding position does not move greatly, the possible crack position and the maximum thinning position all occur at the thinner tailor side. So it is very important to make formability analysis to the welding seam while analyzing the pressing technics of part made from TWB.We have established the weld movement curve and given the movement rule of the welding seam.