In the present study, rubber pad forming process of metallic bipolar plates of PEM fuel cells is investigated. A 3D finite element model of the process with damage initiation criterion is developed. Design of Experiment (factorial design method) is used to find the key parameters of the forming process and their optimal levels. The required input data of the factorial design method is provided by the output results of the finite element model. The finite element results show that the thickness distribution in the formed bipolar plate is not uniform. Also, the corners of the micro-channels are the regions in which the damage initiation criteria (the von Mises stress and the plastic strain) reach maximum values. The design of experiments shows that the outer corner radius, draft angle, and the friction coefficient are the most critical parameters in the forming process. The optimal values for the draft angle, the outer corner radius, and the friction coefficient are found as 40, 0.4 mm, and 0.05, respectively. Finally, some experimental tests are performed to validate the results of the finite element simulations and the design of experiments. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.