Study On Key Technology Of Drawing Formability For Automotive Body Inner Side Panel Made Of Tailor Welded Blank

The auto-body tailor welded blanks (TWBs) and its forming craft and technique is an advanced manufacturing technology in vehicle mass reduction which develops resent years. So the studies of stamping formability and its key technique of high strength steel TWBs have important theories and realistic meaning for manufacturing auto-body panel and the development of vehicles.The paper bases on"985 project"of Jilin University, of automobile engineering technology innovation"the vehicle mass reduction and advanced manufacturing technology", and the automobile industry develop item of Jilin province"Key technology study of automotive body homemade made of TWBs", and the item of building automobile parts product study flat of Jilin University and Rui'an of Zhejiang province. In the paper, we combined homemade study of the automotive body inner side panel, analyzed the stamping formability of homemade TWBs, explored the key factor of formability, established the basic mechanics model, and analyzed the metal flow of automotive body inner side panel and stress-strain regulation through FEA software. The main contents of the paper are as follows:1)The initial condition for insuring quality of TWBs is the base metal thickness proportion through the analysis of main influencing factor in the process. When the thickness proportion of the minimum weld-line and base metal is higher than 80%, the quality is stable and better. Analyzed the mechanical properties of weld-line, the result is that the hardness of weld-line obviously increases with the carbon content in base metal.2)The Stamping formability test were made using for types TWBs of the automotive body inner side panel. The basic mechanics capability was measured through the tensile test. The test result is that the yield strength and tensile strength of TWBs is higher than its base metal, but the extension rate lessens, the shape is lower than base metal. So Stamping formability degrades.3) Based on tensile test, the rule of mixtures method was put forward, namely, computing mechanics capability of weld-line using test date of base metal and TWBs. The calculation result shows: the stress of weld-line is in inverse proportion to the cross sectional areas for the TWBs made in the same base metal. Namely, the width of weld-line increases, the stress degrades. Then the result is opposite for the different base metal. The width of weld-line increases, the stress increases. Compared the calculation result with the tensile test result (the width of weld-line is 1mm), it shows that in the rule of mixtures method when the weld-line width is between 0.75mm and 1.25mm, the stress-strain relation fits in with the calculation result.4) The mulriple formability of TWBs was checked by Erichsen test. The affect of the direction of weld-line and crack form of each direction were analyzed. The reason of crack was elaborated. Experiment result show: the influence of the direction of weld-line is not great with the same base metal of TWBs two sides. Compared with base metal, the IE of material of weld-line degrades 28%; the IE degrades 35% with different thickness of base metal. The direction of weld-line has little influence in crack form. The crack position is lie at 45oof the thicker base metal where plumps strain direction Punch meridian. So minishing strain which is lie at 45o of TWBs can raise forming limit.5) From theory, the influence on weld-line and on microstructure and microhardness of heat affect zone was analyzed; Tests were made at weld-line and heat affect zone. The microstructure of weld-line is bainite and martenite. This form raises hardness, degrades impact toughness, and has disadvantageous influence in formability. The hardness of weld-line and heat affect zone is higher than base metal. The hardness of weld-line is 1.5～2.5 times harder than base metal, the hardness of HAZ is 1.5 times harder than base metal.6) The mechanics model of TWBs tensile drawing was established. Weld-line movement quantity formula was deduced in condition of the same blank holder force of welded blanks. The main factor that influence on weld-line movement was analyzed. When the hardness of one side base metal is much harder than the other, the strain value of harder side is much small, the weaker one is bigger; the strain value of two sides decreasing is along with proportion of the weaker side increasing. When the proportion is a certain value, the rate values of two sides strain tend to a fixed one.7) The stamping formability of automotive body inner side panel was studied though simulation. Metal flow and stress-strain distribution regulation in the process of stamping formability were analyzed adopting eta/DynaForm that is a professional fast simulating software specialized in the formability of metal sheet. Because this part is welded by four kinds of welded blanks which are made of five base metals, and it has big structure size, it is difficult to control weld-line movement of four directions. The paper adopts the control method that blank holder force integrated with dreadbead to control weld-line movement, and eliminates wrinkle, crack in formability. Put the craft parameter after simulation into production, and verify the correctness and practicality of result.The study provides test data and theories foundation for production structure design of large and complicated automatic body using homemade TWBs and for design of Stamping formability. This also has done preceding basic work for deep study in TWBs formability technique and extending its application.