Method for establishing material connection

Abstract

The invention relates to a method for producing a material connection, in particular a welded connection, between an upper joining part (52) and a lower joining part (54), in which the following method steps are carried out: first, the upper joining part (52) is connected to the lower joining part (54); an upper engagement part (52) having a substantially flat first contact surface (66) is arranged above a lower engagement part (54) having a projection or projection (56). The arrangement is then supported by a load-bearing or support structure (50). A punctiform, flat welding head (64) is then positioned above the contact area (70) between the upper joining part (52) and the lower joining part (54). Finally, a material connection, in particular a welded connection, is produced in the contact region (70).

Description

Technical Field

[0001] The invention relates to a method for producing a material connection, in particular a welded connection, between an upper joining part and a lower joining part. The invention also relates to the use of the method for producing a material connection, in particular a welded connection, at a welding location that is difficult to access. Background Art

[0002] The core component of a fuel cell is the fuel cell stack, in which a chemical reaction between oxygen and hydrogen takes place, thereby generating an electric current. A cell stack can consist of hundreds of individual cells, which in turn consist of stacked anode sheets, membrane electrode units and cathode sheets. The connection formed by the anode and cathode sheets forms a bipolar plate. The main task of the bipolar plate is to conduct and separate hydrogen, air and cooling media, such as a water / ethylene glycol mixture. In terms of the performance of the fuel cell, the goal should be to minimize the electrical resistance within the bipolar plate. The electrical contact is made in such a way that the anode and cathode sheets of the fuel cell are usually connected in the active area using short laser welds in order to achieve the lowest possible contact resistance between the anode and cathode sheets. The channel structure in the active area is usually produced by a forming process such as stamping. In theory, during laser welding, the top sheet is welded through in order to be welded to the sheet below or welded through at the same time to establish electrical contact. This brings with it the risk of possible leakage upwards or downwards due to the occurrence of defective sites. In order to seal outwardly and inwardly between the various media at the ports of the anode and cathode pieces, laser beam welding is usually used to achieve the seal. This requires complex clamping tools to ensure gap-free contact between the anode and cathode pieces, as otherwise leakage may occur. During resistance welding, electrical connections are achieved in the flow field and / or active area.

[0003] During resistance welding, a joint connection is created between the sheets without the melt reaching the top or bottom. This is because the ohmic resistance at the contact surface between the anode sheet and the cathode sheet is greater than the ohmic resistance in the component flowing through, so the largest proportion of the energy is converted into heat and melt at this location. Leakage sites can therefore be avoided by this method. In addition, the electrodes apply the joining force required to eliminate any possible gaps to the components. If there are gaps (which is extremely unlikely due to the low component rigidity of the thin sheets), no current will flow and thus no joint connection will be formed. However, if laser beam welding is used to establish an electrical connection in the flow field, this results in complex and critical clamping, accompanied by a high failure rate, because the penetration of the top sheet can cause leaks.

[0004] DE 10 2019 210 633 A1 relates to a method for producing a distributor structure, in particular a bipolar plate, of a fuel cell from a plurality of components arranged in a stack. Here, the components of the distributor structure, in particular the bipolar plate, namely the cathode structure, the separator and the anode structure can be connected to one another in a materially connected manner in one process step using resistance welding. In addition, a plurality of weld seams or weld points can be produced in parallel in order to achieve short cycle times, in particular in mass production.

[0005] DE 10 2010 007 705 A1 relates to a method for producing bipolar plates for fuel cells. In this case, the individual plates are connected to one another in a material-connected manner by brazing in order to avoid the disadvantages of other processes such as laser or resistance welding, such as long production times and production costs or local temperature loads which could lead to damage to the bipolar plates.

[0006] DE 10 2022 204 913.6 relates to a method for producing a bipolar plate. According to this solution, the anode and cathode sheets of a fuel cell are processed according to the following method steps: a first stamping step is carried out in the anode sheet and / or the cathode sheet to form a channel with the largest possible radius, thereby producing a first channel depth. In a subsequent re-stamping step, a reduced radius and the required channel depth and a flat area are produced in the anode sheet and / or the cathode sheet with the required channel depth. By suitable design of the stamping tool, when the first stamping step is performed, a protrusion is retained in the anode sheet and / or the cathode sheet with the first channel depth. A welding point is produced at the protrusion between the anode sheet and the cathode sheet by resistance welding. A joint seam is then formed to ensure the sealing between the anode sheet and the cathode sheet. The proposed method is used to produce a bipolar plate comprising at least one anode sheet and at least one cathode sheet. Summary of the invention

[0007] According to the invention, a method for producing a material connection, in particular a welded connection, is proposed, wherein a welded connection is produced between an upper joining part and a lower joining part and the following method steps are performed:

[0008] a) arranging an upper engaging part having a substantially flat contact side above a lower engaging part having a protrusion;

[0009] b) supporting the arrangement according to method step a) by means of a carrying and supporting structure;

[0010] c) positioning a spot-shaped, flat welding head over the contact area between the upper and lower joining parts; and

[0011] d) Producing a material connection in the contact area.

[0012] The solution proposed according to the invention allows material connections, in particular welded connections, to be realized at relatively inaccessible welding locations, since the point-shaped, flat welding head has relatively small dimensions and short travel distances can also be realized in the X / Y / Z coordinate system.

[0013] In an advantageous development of the method proposed according to the invention, the spot-shaped, flat welding head comprises a first gap electrode and a second gap electrode, which are moved by an actuator unit common to both gap electrodes.

[0014] In an advantageous development of the method according to the invention, the contact force is used to bring the flat, point-shaped welding head into contact with the upper joining part, thereby ensuring that no gaps remain in the contact area between the upper joining part and the lower joining part due to the constant contact force, thereby avoiding air pockets and enabling a high-quality material connection, in particular a welded connection, to be produced.

[0015] In an advantageous development of the method proposed according to the invention, the upper joining part and the lower joining part are brought into contact with one another in the contact region by means of a pressing force.

[0016] In the method proposed according to the invention, the gap between the point-shaped, flat gap electrodes of the welding head is minimized. The gap width is advantageously selected so that it is between 0.1 mm and 0.5 mm. The gap electrodes are adjusted relative to each other within this range.

[0017] In the method according to the invention, a contact pressure is applied to the gap electrode of the point-shaped, flat welding head and a continuous current is maintained during method step d), thereby making it possible to produce a material connection, in particular a welded connection, free of cavitation.

[0018] In the method proposed according to the invention, a point-shaped, flat welding head is moved by an actuator unit, so that single-point welding can be performed as well as continuous or discontinuous welding seams. The compactly designed welding head can be moved by the actuator unit in an X / Y / Z coordinate system, so that even welding positions that are difficult to access can be reached, because the dimensions of the point-shaped, flat welding head remain very compact.

[0019] In the method according to the invention, the lower joining part of the joining parts to be joined to one another in a materially connected manner has a material thickness in the region of the projection or protrusion that is smaller than the material thickness of the lower joining part in its undeformed region.

[0020] In the method according to the invention, the ratio of the first material thickness of the upper joining part to the second material thickness of the lower joining part is substantially in the range of 1: 2. The thickness ratio of the upper joining part and the lower joining part to be joined to each other is important because the upper joining part into which the welding current is introduced must be designed to be thinner than the lower joining part so that heat is generated intensively there and a sufficiently short time period is achieved within which the welded connection is formed.

[0021] The invention further relates to the use of the method for producing material connections, in particular welded connections at welding locations which are difficult to access.

[0022] Advantages of the present invention

[0023] The method proposed according to the invention makes it possible to produce a material connection, in particular a spot weld, by means of a projection and a flat contact surface of the joining parts to be joined together, for which purpose a substantially point-shaped, flat spot electrode is used. As a result, single spot welds or weld beads can be produced continuously or discontinuously for joining parts to be joined together which are difficult to access or have complex joining geometries, since a welding head with relatively compact dimensions can be used.

[0024] In addition, the method according to the present invention can avoid the use of flat electrodes with relatively large external dimensions. The method according to the present invention can greatly simplify the complexity of the welding device, because for the relatively flat electrodes used, the current concentration can be generated at the protrusion, that is, in the area of ​​the contact area of ​​the upper and lower joining parts. The point-shaped, flat welding head used requires a significantly smaller contact area. The space required for establishing a welding connection can be significantly reduced by the method according to the present invention. The two gap electrodes combined with each other in the point-shaped, flat welding head only contact the upper joining part. However, since it transmits the pressing force, a stable contact between the upper joining part and the lower joining part to be joined to each other is ensured in the contact area.

[0025] In addition, in the method according to the invention, the number of contact points is significantly reduced. The material connection can be maintained in an advantageous manner in the contact area at the top of the projection. The edge areas formed on both sides of the projection, preferably in the lower engagement part of the engagement part, remain intact.

[0026] In the method proposed according to the present invention, it is proposed that uniformly formed protrusions are preferably formed in the lower joining part of the joining parts to be joined to each other, so that the current can be increased and the heat can be concentrated in the top end of the protrusion in the lower joining part, that is, in the contact area, and a flat welding electrode can be used for the upper joining part.

[0027] In the method proposed according to the invention, preferably a point-shaped, flat welding head of the parallel-gap type is considered, in which two gap electrodes are arranged very close to each other and can be moved in the X / Y / Z working space by the same actuator unit. This makes it unnecessary to have a second actuator unit.

[0028] The solution proposed according to the invention also has other advantages. For example, it should be noted that the electrode can be approached from one side. In addition, the welding power can be introduced in a more concentrated manner, thereby avoiding unintentional thermal effects on the surrounding area. In particular, if copper joints are to be connected to each other, the proposed welding method can achieve a better welding quality and a more simplified, less failure-prone welding process. The solution proposed according to the invention can also save the space required for welding. Miniaturization of the welding equipment can be achieved. In addition, the welding power used is used in a more concentrated manner, thereby providing a more cost-effective joining method overall. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Embodiments of the present invention are explained in more detail with reference to the accompanying drawings and the following description.

[0030] in:

[0031] Figure 1 A schematic diagram of a resistance welding process is shown, wherein current is directed to the welding location of one or more protrusions in a joining member;

[0032] Figure 2 shows a schematic diagram of a welding head with a gap electrode which limits the gap;

[0033] Figure 3 Shown according to Figure 2 A schematic diagram of a welding head moved by an actuator unit; and

[0034] Figure 4 It is shown that the joining pieces are joined by welding, wherein one of the joining pieces has a flat surface and the other joining piece has a protrusion facing the flat surface. DETAILED DESCRIPTION

[0035] In the following description of embodiments of the invention, identical or similar elements are denoted by the same reference numerals, wherein a repeated description of these elements is omitted in individual cases. The figures merely schematically illustrate the subject matter of the invention.

[0036] Figure 1 The welding device 10 is shown, in which a first electrode 12 which is substantially flat and planar comprises a flat side 14. The first electrode 12 cooperates with a second electrode 16. Figure 1In the embodiment of the present invention, there is a first joint member 20 and a second joint member 26 between the two electrodes 12, 16 shown one above the other. The two joint members (joint pairs) 20 and 26 can be manufactured as plate parts or the like that need to be joined together, for example. When a plurality of projections 22 are designed in the first joint member 20, the second joint member 26 that needs to be connected to the first joint member 20 in a material connection extends substantially flat. A pressing force 32 acts on the two electrodes 12, 16 arranged opposite to each other, and the pressing force is evenly distributed on the corresponding lengths of the first electrode 12 and the second electrode 16 opposite to each other.

[0037] When the first joining member 20 is materially connected to the second joining member 26, a weld nugget 30 is formed in the contact area between the protrusion / protrusion 22 and the flat surface 28 of the second joining member 26, and the two joining members 20, 26 to be joined to each other are joined to each other in a materially connected manner at the weld nugget by resistance welding.

[0038] from Figure 2 and Figure 3 As can be seen from the figure, a gap 40 extending substantially in the vertical direction is formed between the first gap electrode 36 and the second gap electrode 38 of the welding head 34. Figure 2 As can be seen in the figure, the welding head 34 is located above the first joining part 20 with a flat profile. A second joining part 26 also extends flatly below the first joining part 20. Due to the current flowing through the two gap electrodes 36, 38 of the welding head 34, a material connection is created in the region of the weld nugget 30, preferably as a resistance weld between the first joining part 20 and the second joining part 26 arranged below the first joining part. Figure 3 A welding head 34 is schematically shown comprising a first gap electrode 36 and a second gap electrode 38 which are separated by a gap 40 extending substantially in a vertical direction towards an actuator unit 42 .

[0039] Figure 4 It is schematically shown that, according to the present invention, the upper joining piece 52 constructed in a substantially flat manner and the lower joining piece 54 arranged below the upper joining piece are connected by material connection in a contact area 70. Above the upper joining piece 52 extending substantially flat, the first gap electrode 36 and the second gap electrode 38 extend in a manner arranged parallel to each other. The two gap electrodes 36, 38 arranged parallel to each other are separated from each other by a gap 40 extending substantially in a vertical direction. The two gap electrodes 36, 38 are applied with a pressing force 72. An electric current 74 flows through the two gap electrodes 36, 38 separated by the gap 40, by which a material connection is produced in the contact area 70 between the upper joining piece 52 constructed substantially flat and the lower joining piece 54, in the region of the protrusion 56, by resistance welding.

[0040] Figure 4 The lower engagement element 54 is shown extending below the substantially flat upper engagement element 52. The lower engagement element has a projection 56 arranged in the middle here. The radius of the projection 56 is indicated by the reference numeral 58. Figure 4 The illustration shows that the material thickness 60 in the region of the projection 56 in the lower joining part 54 is smaller than the material thickness 60 present in the undeformed region 62 of the lower joining part 54 .

[0041] In such Figure 4 In the welding method according to the present invention shown, the upper joining member 52 and the lower joining member 54 are in contact with each other in the contact area 70. The current 74 generated in the gap electrodes 36, 38 flows through the upper joining member 52 into the contact area 70. Therefore, in the method according to the present invention, the gap electrodes 36, 38 can form a point-shaped, flat welding head 64 at their ends facing the upper joining member 52, and the flat welding head 64 can be moved in a compact installation space, for example in the X / Y plane, and can also be moved relative to the upper joining member 52 in the Z direction. Due to the compact configuration of the point-shaped, flat welding head 64, the movement of the gap electrodes 36, 38 arranged together on the actuator unit 42 enables the point-shaped, flat welding head 64 to be moved, even to welding positions that are not easily accessible in other cases. In the arrangement of the upper joining member 52 and the lower joining member 54 according to the present invention, the contact area 70 is directly located below the two gap electrodes 36, 38 that form the point-shaped, flat welding head 64. These gap electrodes themselves are spaced apart from each other by a gap 40 extending essentially in the vertical direction. During the welding process, i.e. when the current 74 is maintained through the gap electrodes 36, 38, the current flows through the upper joint part 52 into the contact area 70 which becomes the welding area and from this contact area back through one of the gap electrodes 36, 38. The second material thickness 78 of the lower joint part 54 exceeds the first material thickness 76 forming the upper joint part 52. The first material thickness 76 of the upper joint part 52 is selected to be smaller than the second material thickness 78 of the joint part 54 arranged below, so that the heat generated during the welding process (heat generation) is concentrated on the upper joint part 52, and thus when the welded connection proposed according to the invention is established, a significantly faster melting process and a significantly faster time cycle can be achieved.

[0042] pass Figure 4The method according to the invention schematically shown in FIG. 1 also allows access to welding positions that are difficult to access and to which a material connection is to be established by resistance welding, since the point-shaped, flat welding head 64 is designed very compactly. The solution according to the invention makes it possible to significantly reduce the complexity of the welding unit, since on the one hand the advantages of a flat electrode are utilized, on which current concentration can be achieved by means of projections, and on the other hand the point-shaped, flat welding head 64, which is designed very simply, requires a smaller contact area and thus allows single-point welding, and welding positions that are otherwise difficult to access and to which a material connection is to be established by welding, are also more accessible. Figure 4 The solution proposed according to the invention can significantly reduce the area in which the weld seam or weld spot or weld bead is to be produced. Figure 4 As can be seen from the illustration, more densely packed gap electrodes 36, 38 can be used, wherein only the upper joining part 52 is in contact. The stability of the welding process is achieved by the concentrated generation of heat in the contact area 70, wherein the contact area 70 requires a projection or protrusion 56 in the lower joining part 54. The number of contact points can be significantly reduced by the method proposed according to the invention. Only in the area of ​​the contact area 70 is there a contact between one side of the lower flat side of the upper joining part 52 and the middle of the projection or protrusion 56, which is constructed approximately centrally in the lower joining part 54. During the establishment of the material connection, which is preferably by resistance welding, the surrounding area of ​​the contact area 70 will not be contaminated, soiled or damaged in any other way.

[0043] By means of the method according to the invention, on the one hand, the current 74 can be increased by forming a projection or protrusion 56 in the lower joining part 54, and on the other hand, heat concentration can be achieved in the contact area 70 where the material connection is formed by welding. Thus, by means of the method according to the invention, a flat upper joining part 52 can be connected in a targeted material connection to a lower joining part 54 located below the upper joining part, which has, for example, a centrally formed projection or protrusion 56. The point-shaped, flat welding head 64 only requires a small contact area to produce a single-point weld. Figure 2 As shown, the point-shaped, flat welding head 64 is preferably formed by two gap electrodes placed close to each other, namely the first gap electrode 36 and the second gap electrode 38. The two gap electrodes 36, 38 forming the point-shaped, flat welding head 64 are moved in the X / Y plane and in the Z direction by the same actuator unit 42. As a result, a second actuator for one of the two gap electrodes 36, 38 forming the point-shaped, flat welding head 64 can be saved.

[0044] From the basis Figure 4As can be seen from the illustration of FIG, the upper joining part 52 and the lower joining part 54 are placed one above the other. For example, the lower joining part 54 is supported by the carrying and supporting structure 50. The substantially point-shaped, flat welding head 64 is positioned above the protrusion or protrusion 56 in the lower joining part 54. The two gap electrodes forming the point-shaped, flat welding head 64, namely the first gap electrode 36 and the second gap electrode 38, only contact the upper side of the upper joining part 52. During the process of establishing the material connection in the contact area 70, the pressing force 72 and the current 74 are continuously applied, thereby producing a weld connection in the contact area 70 by producing, for example, a weld nugget 30.

[0045] From the basis Figure 4 It can also be seen from the illustration that the gap 40 extending in the vertical direction between the first gap electrode 36 and the second gap electrode 38 extends substantially centrally relative to the protrusion or projection 56 in the lower engagement member 54. Figure 4 Highly precise individual welds can be made in the contact area 70 .

[0046] The invention is not limited to the embodiments described herein and the aspects highlighted therein. On the contrary, numerous modifications are possible within the scope of the claims, which are within the scope of professional practice.

Claims

1. A method for producing a material connection, in particular a welded connection between an upper joining part (52) and a lower joining part (54), the method comprising the following method steps: a) arranging the upper engaging element (52) having a substantially flat first contact side (66) one above the other above the lower engaging element (54) having a protrusion or projection (56); b) supporting the arrangement according to method step a) by means of a carrying and supporting structure (50); c) positioning a spot-shaped, flat welding head (64) over a contact area (70) between the upper joint part (52) and the lower joint part (54); and d) Producing a material connection in the contact area (70).

2. The method according to claim 1, characterized in that The spot-shaped, flat welding head (64) comprises a first gap electrode (36) and a second gap electrode (38), which are moved by an actuator unit (42) common to the two gap electrodes (36, 38).

3. The method according to claims 1 and 2, characterized in that The point-shaped, flat welding head (64) is pressed against the upper joining part (52) by means of a pressing force (72).

4. The method according to claims 1 to 3, characterized in that The upper joining part (52) and the lower joining part (54) are brought into contact with each other in the contact area (70) by the pressing force (72).

5. The method according to claims 1 to 4, characterized in that The gap (40) between the gap electrodes (36, 38) of the point-shaped, flat welding head (64) is minimized, and the gap width (40) between the gap electrodes (36, 38) is between 0.1 mm and 0.5 mm.

6. The method according to claims 1 to 5, characterized in that During method step d), a contact pressure (72) is applied to the gap electrodes (36, 38) of the point-shaped, flat welding head (64), and a continuous current (74) is maintained.

7. The method according to claims 1 to 6, characterized in that The actuator unit (42) controls the point-shaped, flat welding head (64) in such a way that a single-point welding is performed or in such a way that a weld seam is produced continuously or discontinuously.

8. The method according to claims 1 to 7, characterized in that The material thickness (60) of the lower engagement part (54) in the region of the projection / protrusion (56) is smaller than the material thickness of the lower engagement part (54) in the undeformed region (62).

9. The method according to claims 1 to 8, characterized in that A ratio of a first material thickness (76) of the upper engaging member (52) to a second material thickness (78) of the lower engaging member (54) is substantially in the order of 1:

2. 10 . Use of the method according to claim 1 for producing material connections, in particular welded connections at welding locations which are difficult to access.

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