Theoretical Analysis of Formability in Forming Process of Metallic Bipolar Plates by Using Stamping Process

The main purpose of this paper is theoretical analysis of formability in forming process of metallic bipolar plates in PEM fuel cells by using stamping process. First, the algorithms of Newton-Raphson and Quasi-Newton methods were written with MATLAB software to solve the system of forces equations in order to determine the thickness of different points in SS۳۰۴L sheet. Then, the critical height of channel was calculated by using final thickness. We also compared the critical height of micro-stamping and macro-stamping to investigate the effect of process type on fracture. Finally, in order to validate the results, simulation was performed with ABAQUS software for the macro-stamping process. The results show that the Quasi-Newton method has better convergence than the Newton method and the micro-stamping process describe formability in micro-scale better than the macro-stamping due to the crystallographic properties of material. Also, the theoretical results are in extremely good agreement with the experimental results.Fuel cells are a type of electrochemical converter that consists of various components, of which bipolar plates comprise a higher percentage. therefore, the choice of material and production methods of these plates are important. Metal bipolar plates are used more than Graphite bipolar plates due to their mechanical properties and lower weight. Among metal plates, Stainless steels, Titanium and Aluminum are good choice because of their corrosion resistance. Stamping process is better than Hydroforming and Rubber layer process due to its ability to produce mass parts. The purpose of this paper is to theoretical analysis of formability in forming process of metallic plates by using stamping processDue to symmetrical geometry, only half of the stamped SS۳۰۴L sheet with thickness of ۰.۱mm is divided into ۵ different parts. First, in order to determine the final thickness of different points, the system of force equations was solved numerically. The computer code of Newton-Raphson and Quasi-Newton methods were written by MATLAB software. Numerical methods require an initial guess that the initial guess for thickness calculated by limit effective strain and effective strain. According to the relationship between different points (forces equations system), the initial guess of the thickness for other points was calculated (.....)Finally, by using thickness, the critical height of channel was determined as follows: by placing different values for height and critical thickness in equation of angle and comparing the limit effective strain and effective strain, the critical height was calculated Equation of angle: (....)Also, in order to investigate the effect of process on formability, we assume the size grain in the microstampingequation equal ۸ according to Peng article and compared the results with the macro-stampingprocess.Size effect:(......)In order to validate the results, macro-stamping process was simulated by ABAQUS software.According to the experimental results, we expected that crack and failure would occur in the critical points ofC and D due to stress concentration earlier than other points. Comparing the theoretical thicknesses fordifferent points, demonstrate that points C and D are known as critical points as shown in figure ۱ these pointshave least thickness in thickness distribution. And figure ۲ shows that crack and failure occur in these pointsearlier than elsewhere. The macro-stamping model does not describe formability well, because the thicknessof sheet is in micro-scale, but the micro-stamping model predicts crack earlier than macro-stamping due to thecrystallography properties of material. By comparing critical height for two model, as shown in figure ۳, thecritical height of micro-stamping is less than the macro-stamping which can be attributed to the grain sizefactor in the forces equations system of micro-stamping model. The theoretical results were in goodagreement with experimental results for two models. The Quasi-Newton method has better convergence thanNewton-Raphson method because it achieves the same answers as Newton-Raphson method with fewernumber of repetitions.Figure۱. Thickness distribution Figure۲. Simulated sheet Figure۳. Comparing critical height for two modelIn this study, our aim was theoretical analysis and simulation of formability in forming process of metallicbipolar plates in PEM fuel cell by using stamping process, so the final thickness and critical height of SS۳۰۴Lwere determined by Newton-Raphson and Quasi-Newton methods where written with MATLAB softwareand in order to validate the simulation was done by ABAQUS software. We found that:۱- The numerical method of Quasi-Newton has more convergence than Newton-Raphson method.۲- The micro-stamping process, due to the crystallographic properties, describes the formability andcrack better than macro-stamping process

کلیدواژه ها:

Stamping process ، Bipolar plates ، Formability ، Numerical methods