Patent Application
20180248203
The present disclosure generally relates to the manufacture of a stainless steel alloy bipolar plate for use in a fuel cell environment that exhibits a significant improvement in dimensional accuracy, and more particularly to a manufacturing method to produce a stamped austenitic stainless steel bipolar plate having improved dimensional accuracy via reduced spring back and warpage.
In many fuel cell systems, hydrogen or a hydrogen-rich gas is supplied through a flow path to the anode side of a fuel cell while oxygen (such as in the form of atmospheric oxygen) is supplied through a separate flow path to the cathode side of the fuel cell. An appropriate catalyst is typically disposed to form on these respective sides: an anode to facilitate hydrogen oxidation and a cathode to facilitate oxygen reduction. From this, electric current is produced with high temperature water vapor as a reaction by-product.
The interior cells of the stacked assembly comprise one side of each of two opposing bipolar plates. The facing bipolar plates enclose cell elements comprising a proton exchange membrane-electrode assembly, gaskets, gas diffusion media, and the like. Each bipolar plate is formed of two like-shaped plates, in face-to-face arrangement, that have gas flow passages on their external faces and internal coolant passages defined by their inverse and facing sides. As shown in the example bipolar plate of
A bipolar plate is typically stamped from a thin, generally rectangular sheet of metal and, preferably, each sheet is of generally the same shape. Because the bipolar plate operates in a high temperature and corrosive environment, it is preferable to manufacture the bipolar plates from stainless steel given their desirable corrosion-resistant properties. Moreover, in situations where cost of fuel cell manufacture is an important consideration, metal-based bipolar plates may be preferable to other high-temperature, electrically conductive materials, such as graphite, in addition to being relatively inexpensive, stainless steel plates can be formed from relatively thin sheet metal (for example, between less than 0.1 and 1.0 millimeters in thickness).
It is also understood when subjected to a one-step stamping approach, austenitic stainless steel may incur early necking and fracture particularly where the draw depth is comparatively large in the one-step approach. Moreover, using a one-step stamping approach, austenitic stainless steels are also particularly subject to demonstrating lateral springback in the region having flow channels and metal bead channels such that the bipolar plate may have a varying width along the length of the plate. Warpage may also occur in the bipolar plate due to the lateral spring back in the regions having channels.
To improve the formability of thin stainless steel sheet, it is known that a hydro-forming process could be used. Nevertheless, such a process is slow, and requires expensive special equipment that would make it hard to meet either the required production rate or production cost Likewise, electro-magnetic forming could be used, but is a process that is still under development and not suitable for low-cost mass production.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. Accordingly, there is a need for a manufacturing method which is cost-effective, time efficient and could produce bipolar plates having improved dimensional accuracy with reduced lateral spring-back.
The present disclosure provides a method for manufacturing a bipolar plate includes the steps of: (1) providing sheet metal within a stamping press system; (2) stamping the sheet metal with a first die to define an interim flat land, a first interim sidewall, a second interim sidewall, and a first interim channel depth for a plurality of flow channels; and (3) stamping the sheet metal with a second die to widen the interim flat land in each flow channel in the plurality of flow channels forming a final flat land and to reduce each (upper and/or lower) radii of each flow channel in the plurality of flow channels.
One embodiment of a stamping press system according to the present disclosure includes a first stamping press having a first die set and a second stamping press having a second die set wherein the second stamping press is applied to the sheet metal after it has been formed by the first stamping press
Another embodiment of a stamping press system may be provided which includes a first stamping press (or press station) and a second stamping press (or press station)for use after the first stamping press (or press station). The first stamping press (or press station) includes a first die set, the first die set being operatively configured to define a plurality of flow channels in a piece of sheet metal wherein an interim channel depth, an interim first sidewall, an interim second sidewall, an interim sidewall orientation, an interim flat land, and an interim radius are formed in each flow channel in the plurality of flow channels. The second stamping press (or press station) may be operatively configured to receive the sheet metal after it has been deformed in the first stamping press (or press station). The second stamping press (or press station) includes a second die set, where the second dies set may be operatively configured to plastically form a final sidewall orientation, a final flat and, and a final radius from the interim sidewall orientation, the interim flat land, and the interim radius in each flow channel in the plurality of flow channels.
The present disclosure and its particular features and advantages will become more apparent from the following detailed description considered with reference to the accompanying drawings.
These and other features and advantages of the present disclosure will be apparent from the following detailed description, best mode, claims, and accompanying drawings in which:
Like reference numerals refer to like parts throughout the description of several views of the drawings.
Reference will now be made in detail to presently preferred compositions, embodiments and methods of the present disclosure, which constitute the best modes of practicing the present disclosure presently known to the inventors, The figures are not necessarily to scale. However, it is to be understood that the disclosed embodiments are merely exemplary of the present disclosure that may be embodied in various and alternative forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for any aspect of the present disclosure and/or as a representative basis for teaching one skilled in the art to variously employ the present disclosure.
Except in the examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the present disclosure. Practice within the numerical limits stated is generally preferred. Also, unless expressly stated to the contrary: percent, “parts of,” and ratio values are by length; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the present disclosure implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; the first definition of an acronym or other abbreviation applies to all subsequent uses herein of the same abbreviation and applies mutatis mutandis to normal grammatical variations of the initially defined abbreviation; and, unless expressly stated to the contrary, measurement of a property is determined by the same technique as previously or later referenced for the same property.
It is also to be understood that this present disclosure is not limited to the specific embodiments and methods described below, as specific components and/or conditions may, of course, vary. Furthermore, the terminology used herein is used only for the purpose of describing particular embodiments of the present disclosure and is not intended to be limiting in any way.
It must also be noted that, as used in the specification and the appended claims, the singular form “a,” “an,” and “the” comprise plural referents unless the context clearly indicates otherwise. For example, reference to a component in the singular is intended to comprise a plurality of components.
The term “comprising” is synonymous with “including,” “having,” “containing,” or “characterized by.” These terms are inclusive and open-ended and do not exclude additional, un-recited elements or method steps.
The phrase “consisting of” excludes any element, step, or ingredient not specified in the claim. When this phrase appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.
The phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps, plus those that do not materially affect the basic and novel characteristic(s) of the claimed subject matter.
The terms “comprising”, “consisting of”, and “consisting essentially of” can be alternatively used. Where one of these three terms is used, the presently disclosed and claimed subject matter can include the use of either of the other two terms.
Throughout this application, where publications are referenced, the disclosures of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this present disclosure pertains.
The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses of the present disclosure. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.
In light of the detailed features (flow channels) which must be manufactured into a bipolar plate, current bipolar plate manufacturing accounts for a high portion of overall fuel cell stack cost. While using stamped stainless steel bipolar plates would be beneficial in addressing a significant portion of this cost, the low formability of stainless steel in general is a significant challenge in producing bipolar plates. This challenge occurs due to the fact that the manufacturing process involves stamping very thin (for example, 0.100 millimeters or thinner) sheets which must possess the required channel strength and depth to satisfy functional requirements.
With reference to
As shown in
Referring now to
Referring now to
Referring to
Accordingly, the first and second edge regions 52, 52′, 54, 54′ experience plastic deformation via a load from the second die thereby widening the interim flat land 46 into a wider final flat land 46′. Again, the wider final flat land 46′ has a width that may be 20-50% greater than the width of the interim flat land 46. However it is understood that the center region 50 of the interim flat land 46 remains intact such that the center region 50 of the interim flat land 46 experiences almost no plastic deformation. Accordingly, the width of the center region 50 of the interim flat land 46 remains substantially the same when compared to the width of the center region 50′ of the final flat land 46′. It is understood that, by maintaining the structure of the center region 50 of the interim flat land 46 when stamped by the second die, no additional stretching of coating 60 on the sheet metal 26, 28 is applied thereby providing optimum bipolar plate performance against corrosion. It is understood that coating 60 is disposed across both surfaces of sheet metal 26, 28. Coating 60 is identified in a particular example region relative to an example flat land 46, 46′ for purposes of the present disclosure.
Therefore, it is understood that the interim flat land 46 and the final flat land 46′ may each include a first edge regions and a second edge region, 52, 52′, 54, 54′ (as shown in
Also as shown in
As each interim radii 44 (shown in
Due to the plastic deformation occurring at targeted locations in each channel 36, 38, it is understood that the dimensional variation among the channels decreases relative to the second hit. For example, after the first die set is applied, the channel height 74 (shown in
With reference to
Therefore, plastic deformation may occur in all regions of the channels 36, 38 (sidewalls 58, radii 44, edge regions 52, 54) except for the flat land center regions 50, 50′ for both the interim channels 36 and the final channels 38, As described earlier, the second die set 42 of an example system accordingly to the present disclosure may be operatively configured to plastically deform an interim first edge region 52 and an interim second edge region 54 in each flow channel 36 in the plurality of interim channels 36 while simultaneously plastically deforming the first and second sidewalls in each flow channel. As described, the second die set 42 is configured to maintain the structural integrity of the interim flat land center region 50 of each interim flow channel in the plurality of channels 36 while the second die causes plastic deformation at the first and second edge regions 52, 54 in each flow channel in the plurality of channels 36.
Referring now to
The second die set 42 is operatively configured to plastically deform the first edge region 52 and the second edge region 54 in the interim flat land 46 of each interim channel 36 in the plurality of interim channels 36 while simultaneously plastically deforming the interim sidewalls 58 in each flow channel. Accordingly, the second die set 42 is configured to maintain the structural integrity of the interim flat land center region 50 of the interim flat land 46 of each channel 36, 38 in the plurality of channels while the second die set 42 causes plastic deformation at the first and second edge regions 52, 52′, 54, 54′ in each flow channel in the plurality of flow channels. Therefore, the interim flat land 46 defines a width 46″′ which is less than a final width 46″ of the final flat land 46′.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the disclosure as set forth in the appended claims and the legal equivalents thereof.
