Investigation of lubricant effect on directional thickness distribution of U-shaped micro channels of bipolar plates

The present study is the stamping of the metallic bipolar plates (MBPPs) with a thickness of ۰.۱ mm made of SS۳۳۱۶ with a parallel serpentine flow field. Plastic deformation of curved micro channels during the process are investigated to present a reliable model. For this purpose, Experimental tests together with the finite element (FE) model are utilized to define the directional thickness distribution of the formed MBPPs. The validity of simulation results is examined by comparing the thickness distribution and force-displacement curves indicating ۴.۷۶% and ۳.۸۵% error rate, respectively. According to the results, considering the friction factor of ۰.۱ during the FE analysis is capable of providing accurate results in terms of thickness prediction under lubricated conditions. The largest thinning percentages in the modified conditions are found to be ۲۷.۰۲%, ۳۰.۴۰%, and ۲۶.۰۰% in the longitudinal, diagonal, and transverse directions, respectively, indicating that the diagonal direction is the most critical one.A fuel cell is an electrochemical device that converts chemical energy into electrical energy. Proton-exchange membrane fuel cells (PEMFCs) have attracted more attention in the categories of the fuel cells due to their lower operating temperature [۱]. Bipolar plates contain a high percentage of the weight and cost of PEMFCs and are one of the critical components in their structure [۲]. Among the materials used in the manufacturing of the bipolar plates, metallic bipolar plates (MBPPs) are more appropriate due to their desired mechanical properties and desired electrical properties [۳]. The bipolar plates produced by the stamping method have higher dimensional accuracy and excellent mechanical properties compared to other production methods [۴]. The effect of lubrication on the thickness distribution in different directions in the stamping of the metallic bipolar plates process has not been investigated in a literature review, which is considered in the present study.To specify the mechanical properties of the sheet, the uniaxial tension test is used. The strength coefficient, strain hardening exponent, and pre-strain which are the coefficients of the Swift law equation are obtained, ۱۵۷۶ Mpa, ۰.۵۱, and ۰.۰۳۱۵, respectively, using the true stress-strain data. The other mechanical properties of the sheet, such as Young’s modulus and Yield strength, are ۲۰۰۰۰۰ and ۲۷۱ Mpa, respectively. In this study, the stamping process is used to deform a stainless steel ۳۱۶ sheet metal with a thickness of ۰.۱mm. The stamping die for MBPPs consists of a punch and a matrix. The dimensions of rib width, channel width, inner and outer corner radius, and draft angle, which are the geometric parameters of the microchannels are ۱.۱mm, ۰.۵ mm, ۰.۳mm, ۰.۱mm, and ۱۰ degrees, respectively. ABAQUS software is used to simulate the stamping process. The punch, matrix, and sheet are modeled as a rigid and deformable shell body. The type of all contacts is considered surface-to-surface with a friction factor of ۰.۲.The friction coefficient is the effective parameter in defining the contact behavior between process components in finite element simulation. Hence, the friction coefficient is calibrated by comparing the experimentally measured and numerically predicted results of the thickness distribution in the longitudinal direction to present the validated model for predicting the process status in the presence of a lubricant. For this reason, the finite element simulation is examined by considering the friction coefficients of ۰.۲, ۰.۱۵, ۰.۱, and ۰.۰۵. The experimental and numerical results of the thickness distribution are presented in Fig.۱ According to the results, the friction factor of ۰.۱ leads to the most accurate results in determining the thickness distribution. Therefore, the friction factor of ۰.۱ will be applied to determine the thickness distribution in other directions using the finite element simulations Fig.۱. Determination of friction coefficient in the simulation of SS۳۱۶ bipolar plate forming process using lubricantThe thickness distribution in different directions of the fabricated MBPPs in the presence of lubricant is examined using the results of finite element analysis. The results of thickness distribution (thinning percentage and equivalent strain) in the elements located on longitudinal direction, diagonal direction, and transverse direction are presented in Fig.۲ According to the results, the maximum thinning percentage is created in the longitudinal direction. The maximum value of thinning percentage in the longitudinal direction is ۲۷.۰۲%, and the corresponding values in diagonal and transverse directions are equal to ۳۰.۴% and ۲۶%, respectively. According to the results, the diagonal direction is the critical area under lubricated conditions despite the conventional stamping process Fig.۲. Thickness distribution of MBPPs formed by modified process together with the critical forming limit, a) longitudinal direction, b) diagonal direction, c) transverse directionThe present study evaluated the forming of the metallic bipolar plate using the lubricated stamping process. An appropriate finite element model is proposed. The results can be summarized as:The friction factor of ۰.۱ leads to the most accurate results in determining the thickness distribution. The largest thinning percentages in the modified conditions are found to be ۲۷.۰۲%, ۳۰.۴۰%, and ۲۶.۰۰% in the longitudinal, diagonal, and transverse directions, respectively, indicating that the diagonal direction is the most critical one.