DE102016011841A1 - Method for producing bipolar plates for fuel cells, and bipolar plate - Google Patents

Abstract

The invention relates to a method for producing bipolar plates for fuel cells, comprising the following steps: forming a sheet-like starting material into a basic shape (1) for a bipolar plate; Calibrating the basic shape (1) in a Kalibrierumformwerkzeug (3), wherein in at least one die (5, 7) of the Kalibrierumformwerkzeugs (3) an elastomeric body (11) is used as an abutment body for the basic shape (1) during calibration. Furthermore, the invention relates to a bipolar plate.

Description

The invention relates to a method for producing bipolar plates for fuel cells and a bipolar plate for a fuel cell.

From the German patent application DE 10 2011 116 993 A1 is a method for producing a metallic foil component known as a fuel cell component, wherein two films are arranged one above the other and at least partially fluid-tightly interconnected. In a gap formed between the films, a fluid is introduced at a predetermined pressure, and the interconnected films are in a forming tool, which has at least two mutually movable tool mold parts, reformed, wherein at a maximum allowable internal pressure in the space at least one valve is opened, so that the internal pressure is reduced. It is also known to produce bipolar plates for fuel cells from thin steel sheets by hydraulic external high pressure forming and subsequent manufacturing processing steps. In this case, however, internal stresses are introduced into the bipolar plates produced, which can warp the plates, so that dimensional, dimensional and positional tolerances are too large to ensure reliable assembly.

The invention has for its object to provide a method for producing bipolar plates and a bipolar plate, wherein said disadvantages do not occur.

The object is achieved by the objects of the independent claims are created. Advantageous embodiments emerge from the subclaims.

The object is achieved in particular by providing a method for producing bipolar plates for fuel cells, in particular for motor vehicles, with the following steps: A plate-shaped starting material is formed into a basic shape for a bipolar plate. This basic shape is calibrated in a calibration forming tool, wherein in at least one die of the Kalibrierumformwerkzeugs at least one elastomeric body is used as an abutment body for the basic shape during calibration. In this calibration process compressive stresses are introduced into the basic shape, whereby their inherent stresses arising during forming from the starting material and optionally subsequent process steps are compensated, so that the resulting component can not be warped and reliably mounted. The bipolar plate is preferably obtained from the basic shape by calibration in the sizing tool. However, it is also possible for further process steps for the production of the finished bipolar plate to be connected to the calibration. It has been found that the compensation of the inherent stresses present in the basic form can be effected particularly effectively by the use of an elastomer body as the abutment body in the calibration forming tool.

It is possible that the at least one die of the Kalibrierumformwerkzeugs has exactly one elastomeric body. But it is also possible that the die has a plurality of elastomeric bodies.

As the starting material, a steel sheet or a steel plate is preferably used.

Preferably, a metallic bipolar plate is produced, in particular made of thin-walled, austenitic steel sheet, preferably with a thickness of at least 0.06 mm to at most 0.7 mm.

The fact that the at least one elastomeric body is used as a contact body means, in particular, that the basic shape during pressing in the Kalibrierumformwerkzeug on the elastomeric body is applied directly. The elastomer body thus acts directly on calibration to the basic shape.

According to one embodiment of the invention it is provided that the starting material is formed by ironing and / or by hydroforming to the basic form. Particularly preferably, the starting material is reshaped by external high pressure forming to the basic shape. In particular, the method of hydraulic external high pressure forming is used.

According to one embodiment of the invention, it is provided that a Kalibrierumformwerkzeug is used for calibrating, which has an upper die and a lower die. The basic shape is thus calibrated in the sizing tool between two dies, namely the upper die and the lower die, which together enclose a sizing cavity. In this case, the upper die and the lower die are displaceable relative to each other, it being sufficient in principle that one of the dies is held displaceable, wherein the other may be held fixed in space.

As already mentioned, at least in one of the dies, namely the upper die or the lower die, an elastomeric body is arranged as an abutment body for the basic shape.

According to one embodiment of the invention, it is provided that the basic shape after the forming of the starting material and before the Calibration by cutting or welding, in particular by laser cutting or laser welding, or processed in any other suitable manner. In particular, in such processing steps in which heat is registered in the basic form, but also in other processing steps, internal stresses are entered in the basic form, or the residual stresses of the basic form are changed. In particular, it is possible that a heat input in the basic form partially dissolves residual stresses, but introduces new ones. If, therefore, the basic shape is calibrated in the calibration forming tool after forming and after machining, in particular by cutting or welding, particularly preferably by laser cutting or laser welding, this results in a particularly suitable manner for compensating the residual stresses in the basic form and thus ensures reliable assembly of the resulting dies bipolar plate.

According to one embodiment of the invention, it is provided that the forming of the starting material to the basic shape by external high pressure forming, in particular by means of hydraulic external high pressure forming, is carried out, which is brought in contact with the elastomer body during calibration during external high pressure forming a pressure medium remote from the base mold surface. In the case of external high-pressure forming, one surface of the basic mold is subjected to a particularly hydraulic pressure medium, while the other surface facing away from the pressure medium is pressed against the surface of a solid, in particular a die. This facing away from the pressure medium during the external high pressure forming surface is now brought during calibration in contact with the elastomeric body, whereby it is possible to press the previous print media side of the basic shape with high pressure to a new engraving and compensate for existing residual stresses in the basic form. In this case, the previous pressure medium side, that is to say the surface facing the pressure medium during external high pressure forming, is particularly preferably pressed during calibration against an inelastic surface of a die of the Kalibrierumformwerkzeug so that they can be pressed there to a new engraving.

According to one embodiment of the invention, it is provided that during Außenhochdruckumformen the starting material, a first engraving is introduced into the basic shape, wherein a second engraving is introduced during calibration in the outer surface of the high pressure forming the printing medium facing surface of the basic shape, in particular the previous print media side of the basic shape with high Pressure on a new engraving is pressed. The elastomer of the elastomer body acts as a working medium on the opposite side.

According to a development of the invention, it is provided that a pressing surface of the elastomeric body that comes into contact with the basic shape during calibration has a contouring. The pressing surface is thus not simply planar but has a contour deviating from the planar shape, preferably an engraving, so that specific individual regions of the basic shape can be specially processed, in particular calibrated, which allows a defined calibration of specific locations under defined pressure. In particular, the elastomeric body is preferably contoured with Vorhaltegeometrien so that individual areas of the component are designed specifically so that the subsequent springback can be collected dimensionally.

According to one embodiment of the invention, it is provided that an elastomeric body made of polyurethane is used. This material has been found to be particularly suitable for the method proposed here.

It turns out that the elastomer deformation proposed here can be used selectively in the context of calibration in contrast to external high pressure forming: it is possible to introduce compressive stresses on the gravure-side surface after the external high-pressure forming in a targeted manner, which leads to the compensation of residual stresses and thus to planar components. In addition, geometry geometries can be integrated that enable a flat component after spring-back. The required tool and pressing technology for the Kalibrierumformwerkzeug is simple and associated with low costs. The geometry of the elastomeric body serving as the active medium can be easily produced, in particular by casting, or by - in particular mechanical - editing. Elastomeric bodies are available in a variety of Shore hardnesses, which allows a broad and flexible application of the method. Furthermore, the procedure proposed here allows a greater freedom of design for bipolar plates, since now also the media side can be specifically formed during external high pressure forming.

The method is not limited to bipolar plates. Rather, it is also generally possible by the method to calibrate metallic thin sheet structures.

The object is also achieved by providing a bipolar plate for a fuel cell, in particular for a motor vehicle, which is obtainable by a method according to one of the previously described embodiments. In particular, the advantages which have already been explained in connection with the method are realized in connection with the bipolar plate.

The invention will be explained in more detail below with reference to the drawing.

Showing:

1 a schematic representation of a step of an embodiment of a method for producing bipolar plates;

2 a schematic representation of a further step of the embodiment of the method according to 1 , and

3 a schematic representation of a second embodiment of the method.

1 shows a schematic representation of a step of an embodiment of a method for producing bipolar plates for fuel cells. As part of the process, a sheet-like starting material is initially a basic form 1 reshaped. The forming is preferably carried out by ironing and / or hydroforming. Particularly preferably, the forming takes place by external high pressure forming, in particular by hydraulic external high pressure forming.

The basic form 1 then becomes a calibration tool 3 introduced, wherein the Kalibrierumformwerkzeug 3 here an upper part 5 and a lower part 7 having. As shown by an arrow P, the upper die 5 and the lower part 7 Relocatable relative to each other, with one between the upper die 5 and the lower part 7 enclosed cavity 9 can be opened and closed. Preferably, here is the upper die 5 kept displaceable, the lower die 7 is fixed in space. But this can also be the case the other way around. Alternatively, it is also possible that both the upper die 5 as well as the lower part 7 are held displaceable relative to each other. In any case, the basic form 1 into the opened cavity 9 be introduced.

In at least one die of the Kalibrierumformwerkzeugs 3 , here in the upper Gesenk 5 , is an elastomeric body 11 arranged as an abutment body for the basic shape 1 when calibrating with the calibration tool 3 is used. The elastomer body 11 preferably has polyurethane or consists of polyurethane.

One when calibrating with the calibration tool 3 in touching contact with the basic form 1 reaching pressing surface 13 of the elastomer body 11 is in the embodiment of the Kalibrierumformwerkzeugs shown here 3 and thus also in the embodiment of the method illustrated here without contouring, that is to say purely planar, in other words planar.

The basic form 1 is preferably so in the cavity 9 introduced, that a previously facing away from the external pressure in a high pressure forming surface 15 the basic form 1 with the elastomeric body 11 , in particular with the pressing surface 13 , is brought into touching contact. Thus, it is possible in the calibration tool 3 a surface facing the pressure medium during external high pressure forming 17 , which is also referred to as the print media side, to press at high pressure on a new engraving, in particular, by these facing the pressure medium during external high pressure forming surface 17 against the preferably inelastic material of the lower die 7 is pressed.

Preferably, in external high pressure forming, a first engraving will be in the basic form 1 introduced, wherein during calibration in the calibration tool 3 in the surface facing the pressure medium during external high pressure forming 17 the basic form 1 a second engraving is introduced.

The basic form is preferred 1 machined after forming the starting material and before calibration, in particular by cutting or welding, preferably by laser cutting or laser welding.

2 shows a further step of the embodiment of the method according to 1 , Identical and functionally identical elements are provided with the same reference numerals, so that reference is made to the preceding description. It is shown that the basic form 1 in the sizing tool 3 is calibrated. This is the cavity 9 closed, and the lower part 7 as well as the upper die 5 are pressed against each other, preferably by the upper die 5 on the lower part 7 is lowered. In this case, the elastomer body is used 11 as active medium or pressure medium on the lower die 7 opposite side of the Kalibrierumformwerkzeugs 3 ,

In particular, by the calibration is now from the basic form 1 a bipolar plate for a fuel cell, in particular for a fuel cell of a motor vehicle, produced.

3 shows a schematic representation of another embodiment of the method. Identical and functionally identical elements are provided with the same reference numerals, so that reference is made to the preceding description. It turns out that in this embodiment of the method, an elastomeric body 11 with a pressing surface 13 is used, which has a contouring. The elastomer body 11 is therefore no longer pure elastomer cushion, but rather an elastomeric tool, wherein it is contoured in particular with Vorhaltegeometrien so that individual areas of the basic form 1 During calibration, targeted pressure is applied to a defined pressure, whereby a later springback can be compensated dimensionally.

Overall, it is shown that with the method proposed here and the bipolar plate proposed here, a reliable assembly can be achieved, in particular, a warping of the bipolar plate is avoided.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102011116993 A1 [0002]

Claims (9)

Process for producing bipolar plates for fuel cells, comprising the following steps: - forming a sheet-like starting material into a basic shape ( 1 ) for a bipolar plate; - Calibrating the basic form ( 1 ) in a calibration forming tool ( 3 ), wherein - in at least one die ( 5 . 7 ) of the calibration forming tool ( 3 ) an elastomeric body ( 11 ) as an abutment body for the basic form ( 1 ) is used during calibration. A method according to claim 1, characterized in that the starting material by stretch drawing, by hydroforming, and / or by external high pressure forming, in particular by hydraulic external high pressure forming, to the basic form ( 1 ) is transformed. Method according to one of the preceding claims, characterized in that for calibrating a Kalibrierumformwerkzeug ( 3 ), which is an upper die ( 5 ) and a lower die ( 7 ) having. Method according to one of the preceding claims, characterized in that the basic form ( 1 ) after forming the starting material and prior to calibration by cutting or welding, in particular by laser cutting or laser welding, is processed. Method according to one of the preceding claims, characterized in that the forming of the starting material to the basic form ( 1 ) is carried out by means of external high-pressure forming, wherein during calibration a surface facing away from a pressure medium during external high-pressure forming (FIG. 15 ) of the basic form ( 1 ) with the elastomeric body ( 11 ) is brought into touching contact. Method according to one of the preceding claims, characterized in that the forming of the starting material to the basic form ( 1 ) is carried out by means of external high-pressure forming, wherein a first engraving is introduced into the basic shape during external high-pressure forming, wherein during calibration in the surface facing the pressure medium during external high-pressure forming ( 17 ) of the basic form ( 1 ) a second engraving is introduced. Method according to one of the preceding claims, characterized in that during calibration in contact with the basic form ( 1 ) pressing surface ( 13 ) of the elastomeric body ( 11 ) has a contouring. Method according to one of the preceding claims, characterized in that an elastomeric body ( 11 ) is used, which has polyurethane or consists of polyurethane. A bipolar plate obtainable by a method according to any one of claims 1 to 8.

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