Numerical Simulation And Test Research On Forming And Stiffness For Auto Door Made Of Tailor Welded Blanks

The energy shortage had become more and more severe, it is essential to reduce the weight of the auto body to save the energy.And at the same time the light weight of auto body will influence the stiffness, safety and NVH performances. So it is necessary to form a completely and effectively analysis methods on auto lightweight technology, and it has become a hot topic in the design of modern auto body. Tailor welded blanks (TWBs) which based on modern technology is applied in the production of auto body components, it can reduce the weight of auto body effectively, but the overall formability of the TWBs is different from single blank, moreover it also influences the overall stiffness of the entire component, so it is necessary to analyse the complete performance of TWBs. The research content of this paper is integrated with the subproject that is "Lightweight of Auto Body and Advanced Manufacturing Technology" (2005—2010) which belongs to the big project automotive technology innovation platform that is Jilin University "985 project", and the project "Aluminum Stamping and Cold-die Quenching Forming in Lightweight Design and Finite Element Analysis of Auto Body Structure"(51075178) which belongs to the National Natural Science Fund. Applying metal plastic flowing theory and large deformation of metal plastic FE method, numerical simulation is carried out for auto door made of tailor welded blanks, based on the calculation results the formability is analyzed, and the influence factors for formability is analysed. Numerical simulation results which adopting actual parameters is comparing with the components produced, validity of the numerical simulation is verified, then perfect simulation result is found by optimizing technical parameters, and this can make reasonable suggestions for production.For example, adopting partition stepped blank holder, through analyzing the influence of varied blank holder force on the formability, appropriate variable blank holder force was determined, thus improved the formability of the entire component. Numerical analysis and test research on modal and stiffness are carried out for auto door made of TWBs, the result demonstrated that the weight was reduced, and meanwhile the modal and stiffness are meeted the design requirements. The analysis methods for auto door made of TWBs has been developed based on numerical simulation technology,the method can simplify the design and development process and shorten the cycle of mold and product development as well. The method can apply to the similar production. The research contents of this paper are as follows: 1. The formability of TWBs which are used in auto door has been studied by the tests. Mechanical performance parameters of galvanized TWBs are gotten by tensile test; the basic formability is gotten by Erichsen test for base metal and weld-line. The Erichsen test result shows:the fracture is appeared at thin blank when the direction of maximum tension stress is perpendicular to the weld-line. It provides the experimental foundation for building weldline model in the simulation. The formability of weld-line is analyzed from microscopic view by microscopic tructure and microhardness test for weld-line.2. The numerical simulation and test research on forming for auto door inner side panel was studied.Sheet metal forming is a typical nonlinear process of geometry, material and boundary contact condition etc. In accordance with metal sheet forming characteristics, Hill48 yield rule and BT shell element is used to simulate metal sheet in the numerical simulation. Numerical simulation method is that dynamic explicit algorithm and penalty function method were chosen for calculation and contact simulation, respectively.Generally weld modeling use rigid way in weld-line, because of the adoption of which the grid can not automatically choose the encryption algorithm in process of calculating, however for the purpose of the detailed simulation of the blank grid the griddling of the stock must be partitioned very small, thus for large component such as automobile panel, this method calculation method make lower efficiency and even cann't finish the calculation. Results from the analysis of Erichsen test for TWBs shows that, the fracture will not appeared on the weld-line in forming process generally as long as the weld is qualified.And, in the phase of the component design, what we are concerning more about is the overall formability of the component, therefore a new simulation method for weld-line is bringed out:simplified handling of the common node, which is a total of weld material at both sides of the node. Using this calculation method, grid can be encrypted automatically in simulation, so that the initial blank does not need to partitioned very small, the calculation efficiency and stability are improved in simulation.Numerical simulation on forming for automo door inner side panel made of TWBs was studied by metal sheet forming CAE software. Comparing with the components produced, validity of the simulation model and reliability of the simulation result are verified, and,and also the accuracy of simple model that shares common nodes at weld-line is accepted, the calculation precision can meet the requirement of engineering technology. The optimization of draw-bead and friction parameters can eliminate defects in formability. The CAE analysis of the forming can indicate internal stress-strain distribution, thickness variation and thickness reduction rate in the forming process, it provids a comprehensive analysis of formability for component before the design of die, the formability of component is improved, and meanwhile the cost of production is reduced. 3. Adopting partition stepped blank holder and varied blank holder force, numerical simulation on forming for auto door inner side panel was conducted. Firstly, theoretically analyzed the reason of why adopting partition stepped blank holder can reduce the wrinkles of forming. According to the stress analysis of numerical simulation on forming, the blanks suffered complicate stress state when transforming, it suffers drawing stress, press stress and shearing stress. Therefore, it came to the conclusion that the wrinkle of sheet metal edges is the composite of several wrinkling means. Adopting stepped blank holder and make it pressed by uniform press stress from outside. Improve the stress state of the sheets in the plane, therefore, the wrinkles in the forming of thin side material are very significantly improved.Secondly, applying the finite element model established before, changing the technologic structure, adopting partition stepped blank holder and the different isoline blank holder force on thick and thin blanks in the numerical simulation. The numerical simulation results are analyzed for several projects, the results showed that adopting partition stepped blank holder and different blank holder force could improve wrinkling phenomenon for TWBs at its thin side in the forming process. As a result, it was recommended that adopting stepped blank holder for the TWBs, for which there was a large difference in thickness on both sides.At last, adopting partition stepped blank holder and varied blank holder force, numerical simulation on forming was conducted.The simulation shows that adopting varied blank holder force could improve the formability more for component.4. The numerical simulation and test research on modal and stiffness for auto door components was studied. Firstly, the finite element model for auto door components is established.The connection modes of auto door components consist of tailor welded, spot welding, tipping, and bolts and so on. The connection modes are analysed, and the finite element model of each connection mode is established systematically. Studies suggest that simple model that shares common nodes were used in weld-line, CWELD model in spot welding, rigid element model in tipping and bolts.Secondly, the numerical simulation and test research on modal for auto door components was studied. The result showed that the modal are meeted the design requirements, and meanwhile the weight of auto door is reduced after adopting TWBs. Validity of the finite element model are verified.At last, the numerical simulation and test research on stiffness for auto door components was studied. The result showed that the stiffness are meeted the design requirements. And the analysis methods provide demonstration for side-by-side design for new product. The CAE analysis method in this paper can be used for the design of new auto product, it changes the procedure of testing and fixing die in traditional design, and the analysis methods provide demonstration for complicated component of auto body which adopting new technics. It can indicate the modal and stiffness of the components availably. And meanwhile, the method can provide demonstration for new product. The method can accelerate the accumulate for technology of the light weight of auto body, and improve the independent design and research level of auto.