Electromagnetic Micro-forming Processes Of Metal Bipolar Plate

With rapid development of micro-electro-mechanical system(MEMS), parts with micro-channels such as micro heat exchanger, micro fuel cell bipolar and micro biochips, have been widely used in the field of energy, microelectronics, aerospace and biomedical instruments. Electromagnetic micro forming is one kind of high-energy-rate forming technology, in which the pressure induced by impulse magnetic field is used to form micro-parts. Electromagnetic force with high speed and energy can improve the ductility and forming limit of deformed parts and avoid strict requirements of assembly accuracy for micro-forming die. Thus electromagnetic micro forming has become an important flexible technology. By taking T2 coper and SS304 stainless steel bipolar plates in micro fuel cell as the research object, micro deformation behavior and influence laws of processing parameters on electromagnetic bulging were investigated by numerical and experimental method. Electromagnetic micro forming mechanism was revealed and micro fuel cell bipolar was formed with good quality.A finite element model of electromagnetic bulging is established by using coupling analysis module of multi-physics field in ANSYS finite element simulation software. Electromagnetic force distribution and deformation characteristics were analyzed during electromagnetic bulging in metal foil. The results show that magnetic force increases with increasing of discharge energy and decreases with increasing of discharge capacity, and the distribution is kept uniform in the deformation area of metal foil. During electromagnetic micro bulging, effective strain increases with the direction from the channel edge to middle section and the effective strain distribution is uniform along the channel direction. In addition, effective strain distribution of micro-array channels is also uniform during electromagnetic micro forming, which indicates that micro array channels can be fabricated with good consistency by electromagnetic micro forming process.Electromagnetic micro bulging equipment was prepared based on uniform pressure coil of metal foil. The experimental results show that the formability of micro-channels is improved with increasing of discharge energy, discharge number and discharge frequency. While the formability of micro-channel decreases with the increase of foil plate thickness and grain size. In addition, the formability of micro electromagnetic bulging in metal foil can be improved using the convex die or concave die with a larger round corner.Electromagnetic micro forming process of micro-array channels were studied based on the results of micro single channel. The influence of the discharge parameters, die structure and material properties on the bulging height and forming uniformity were analyzed. The results show that the bulging height and uniformity of micro-array channels are improved with increasing of discharge energy and discharge frequency. The best formability of micro-array channels can be obtained using the discharge energy of ~7.2 k J. Concave die is benefit to improving the formability and uniformity during micro-electromagnetic forming of micro-array channels. There is a significant effect of material properties on the micro electromagnetic bulging process. T2 copper foil has a better formability of array channel due to lower yield stress and resistivity; while the formability of micro-array channels with SS304 stainless steel foil is reduced due to this material is a rate relevant material with higher yield strength and resistivity.Electromagnetic micro punching of metal foil was studied and electromagnetic punching process was analyzed. The influence of processing parameter on micro punching quality was discussed and the fracture mechanism during micro-blanking was revealed. The results show that the height of burr and rollover in the cross-section are reduced with increasing of discharge energy and. The height of burr decreases and the height of rollover increases with increasing of foil thickness. The blanking fracture of SS304 stainless steel foil exhibits ductile fracture with dimples, while various fracture modes of T2 copper foil during electromagnetic micro-punching are presented, including slip separation, tensile fracture with dimples, toughness tensile fracture without dimples. Experimental results show that the electromagnetic micro-punching process can fabricate micro-holes with good cross-section quality, high roundness and profile accuracy, having productivity,low cost, and high quality on producting of micro hole.Electromagnetic micro forming process and influence laws of material properties were investigated, discharge parameters and die parameters on the forming quality were analyzed to determine the best processing parameters, and then the quality of metal bipolar by micro electromagnetic forming was evaluated. The results show that forming performances of bipolar plate can be improve with the increase of discharge energy, but the bulging height uniformity of the bipolar plate micro-channel is reduced with increasing of discharge frequency. The formability can be influenced by the depth of female die and the height of channel, increases firstly and then decreases with increasing of depth of female die. The formability of bipolar plate is best when the Spacing between the billet and the die is ~1.0 mm. The mould structure is also an important factor in micro electromagnetic forming of metal bipolar plate. When the ratio of the micro-die ridge to width(S/W) is larger than 1, convex die was the better choosen; when S/W ≤ 1, concave die to fabricate metal bipolar plate with good forming quality was the better choosen. Micro fuel cell bipolar plate of T2 copper with excellent quality can be obtained by using the S/W = 2.0 of convex die under the condition of discharge energy of 7.2 k J and frequency of 7.424 k Hz, respectively.