Method for laser welding steel plates

Abstract

In particular, in the industrial production of bipolar plates for fuel cells in the vehicle industry or heat exchanger plates, a large number of bipolar plates are required. The key factors for the large-scale success of this technology are then high manufacturing precision and efficient production. Here, a device and a method are presented, which allow bipolar plates to be welded at high speeds in a vertical position in a circular transport device 1 and thereby to a high extent to meet the high demands on loading, fastening, welding and loading / unloading of the structural members. Overall, a high productivity is achieved.

Description

Technical Field

[0001] The present invention relates to a method for laser welding of flat steel sheets, particularly bipolar plates for fuel cells or heat exchanger plates in commercial vehicle structures. The present invention also relates to the use of a method for the manufacture of bipolar plates or heat exchanger plates.

Background Art

[0002] In the automotive industry, the trend is increasingly towards CO2 reduction and towards alternative drive systems as a result of finite oil reserves and as a result of climate change. For passenger cars and trucks, electric motors with batteries as storage media are increasingly being used. In the future, however, other technologies such as fuel cells will also be built, particularly for the truck sector. The bipolar plate (BPP) is a main component of a fuel cell and, accordingly, decisively defines the manufacturing costs and efficiency of the fuel cell system. Based on various advantages regarding manufacturability and material properties such as stability, low sheet thickness, and various coating possibilities, the metallic configuration of the bipolar plate has moved to the center of research and development and is currently regarded as a favorable variation for the future large-scale use of fuel cells. A fuel cell system typically consists of a number of individual cells each having one BPP between the cells for use in vehicles having 300 to 400 bipolar plates (BPP). Based on the large number of BPPs per individual system, it is assumed that in a conservative scenario, the required number will rapidly reach extremely high dimensions in the future. This challenge is also regarded as a very big opportunity for subcontractors of BPPs. The prerequisite for this, however, is an economic and high-performance production technology. In particular, welding both bipolar plate halves to a single BPP is a central challenge, and still remains a critical obstacle to cost-effective manufacturing, due to the numerous weld seams, the associated long welding times, and the high demands on these seams under extremely difficult process conditions based on thin material.

[0003] BPPs themselves are known from the prior art. These BPPs typically consist of two bipolar plate halves, which are then combined. These bipolar plate halves are usually formed as embossed films or deformed metal sheets. These bipolar plate halves are stacked on top of each other and are typically sealed with a laser at the edges and contact points. In this process, the laser creates a weld seam several meters long and, in some cases, additional weld points. Selectively, resistance welding methods are also known. For this purpose, welding equipment is used, and within these welding equipment, the bipolar plate halves often need to be re-tightened multiple times so that a sealed contour and all weld points can be realized. In order to enable welding of all sealed contours and points, the bipolar plate to be welded must be detached from the fastening device and reinserted so that all areas of the BPP to be welded are accessible to the welding laser. In particular, the surrounding sealing contour presents a problem. When such a surrounding sealing contour is manufactured by laser within a single welding process, it has been found that it is difficult to position additional fastening elements that secure the bipolar plate half inside the surrounding sealing contour within the sealing contour itself. During re-tightening (Umspannen), there is a risk that the positioning may no longer match and that the welding points may be placed in the wrong location. Additionally, the entire manufacturing process of bipolar plates can be significantly delayed by the re-tightening of semi-finished bipolar plates.

[0004] Patent Document 1 describes an apparatus and method for manufacturing bipolar plates, in which structural member deformation is relatively small. Welding energy is introduced to the BPP from above and below. The orientation (Lage) in the space in which this is performed is not described.

[0005] Patent Document 2 shows a fastening device having a tightening lever. From the figure and text, it can be inferred that the alignment of the BPP is horizontal, that is, the surface is positioned horizontally on the base surface.

[0006] Graebener Maschinentechnik demonstrates a complete production line for BPP on its website. Two welding machines are similarly shown in more detail under Non-Patent Document 1 (URL: https: / / www.graebener.com / en / cutting-and-welding). BPP is welded horizontally in a stationary position.

[0007] SITEC (Non-Patent Literature 2 (URL: HTTPS: / / WWW.SITEC-TECHNOLOGY.DE / )) manufactures automated laser welding equipment in which welding is performed both while stationary and in a horizontal plane.

[0008] Patent Document 3 describes a method for increasing cycle time and, consequently, reducing production costs in the industrial production of welded metal sheet members—particularly tailored blanks for the automotive industry. This method is based on a transport system having a cantilevered optical system and a horizontal orientation of the workpiece throughout the welding process, and does not require any time-consuming cooling of the hot weld seam, nor does it require any means of securing the workpiece on one side with great force on the transport belt. Consequently, the unfavorable effect of substrate spacing on the machine's cycle time can be significantly reduced. Overall, welding-related time can be reduced by this method. In such known systems having a vertical moving surface, the back path is not used for operation, except when access is made from the underside of the machine. Patent Document 4 describes a welding apparatus in which sheet metal is welded to one another in a vertical plane, and therefore the required space for the welding apparatus is as small as possible.

[0009] The drawbacks of these solutions mentioned above are the high technical effort required for process-reliable fastening of structural members and for the removal of welding smoke and splatter from the equipment, the large machine dimensions resulting in high investment costs, and the overall low productivity of the equipment. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] German Patent No. 102016200387 [Patent Document 2] International Publication No. 2018149959 [Patent Document 3] European Patent No. 3038789 [Patent Document 4] Strength 6,639,176 B1 Specification [Non-patent literature]

[0011] [Non-Patent Document 1] Graebener Machine Technology (GRAEBENER Maschinentechnik) URL: https: / / www.graebener.com / en / cutting-and-welding

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0012] Therefore, the problem underlying the present invention is to disclose a method that does not have the aforementioned drawbacks.

Means for Solving the Problems

[0013] This problem is solved according to the present invention by a method having the features presented in claim 1. Variants of advantageous embodiments are presented in the dependent claims.

Effects of the Invention

[0014] Here, the device described with respect to the method is based on a transport device, and this transport device transports the workpiece to be processed in a circulating manner in a horizontal plane, whereby the number of required equipment members can be limited by strength.

[0015] Since the circulating transport device moves in a horizontal plane, access is made possible from both sides. This means that, on the one hand, the steel plates (workpieces) are welded, and on the other hand, these steel plates are loaded and unloaded. In each case, between them, the steel plates are fixed by clamping plates or this fixing is dissociated again.

[0016] Along with this, the following advantages: namely, · Reduction of investment costs by a smaller number of welding devices, · Reduction of investment costs due to reduction of mechanical dimensions (footprint, structural member size, etc.), · In short, reduction of investment costs that induces lower production costs, is generated.

[0017] Another advantage of the present invention is that the welding process is performed in a vertical plane, i.e., in the perpendicular direction, and substantially perpendicular to the transport direction. Along with this, the welding spatter does not remain on the workpiece to be processed, and as a result, less contamination of the workpiece and the apparatus occurs.

[0018] In the proposed configuration, the workpiece is clamped only once and subsequently processed, thus omitting multiple clamping operations that have the well-known problem of precise adjustment throughout the processing of the workpiece, and generally achieving high accuracy during loading, processing, and unloading.

[0019] The object of the present invention is to significantly increase the number of members manufactured per unit of time in the simultaneous reduction of member costs.

[0020] The invention presented here thus generally enables efficient and high-quality production. The present invention will be further described below based on examples in relation to the figures.

Brief Description of the Drawings

[0021] [Figure 1] It is a plan view of a transport device in a schematic illustration. [Figure 2a] It is a first perspective view of a clamping device. [Figure 2b] It is a second perspective view of a clamping device. [Figure 2c] It is a third perspective view of a clamping device. [Figure 2d] It is a fourth perspective view of a clamping device. [Figure 3] It is a side view of the equipment according to the present invention in a schematic illustration. [Modes for carrying out the invention]

[0022] Figure 1 shows a circulating transport device 1 in a plan view. The drive unit 7 of this transport device moves the transport belt 2 clockwise within the transport plane XY, passing through translational movement regions 5a and 5b and rotational movement regions 6a and 6b. The transport plane XY is essentially a horizontal plane. The transport belt 2 consists of numerous chain links 3, each of which is equipped with a tightening device 8. Each chain link 3 is fitted with a base plate 11 and a rotatable folding lever 13. A workpiece 14 to be welded can be accommodated between the base plate 11 and the folding lever 13. Loading 24 of the workpiece, i.e., the steel plate, onto the circulating transport belt 2 takes place within a translational region 5a, when the folding lever 13 is deployed and positioned horizontally within the loading / unloading zone 15. Within the welding equipment loading zone 16 in the rotational movement region 6a, the workpiece 14 within the fastening device 8 is moved to a vertical position by the return tilt (upward tilt) of the folding lever 13, and is then fixed on the base plate 11 using fastening means (fastening plates B 10b and A 10a). In the next step, the folding lever 13 is moved back to the horizontal position. This is necessary so that in the subsequent step, the laser beam 23 of the welding laser 22 can be directed onto the workpiece 14. In the translational region 5b, the workpiece 14 is processed within the welding / cutting zone 17 using the laser beam 23 of the laser optical system 22. Here, both steel plates of the workpiece 14 are welded to each other. Cutting or marking by the laser beam 23 can also be considered. Within the welding equipment loading / unloading zone 18, in the first step, the folding lever 13 is tilted to a vertical position, and in the second step, the fastening device 8 having the processed workpiece 19 is tilted from a vertical position to a horizontal position. Within the loading / unloading zone 15, the processed workpieces 19 are removed from the circulating transport belt 2 by loading / unloading 25. The washing station 26 is used for cleaning the fastening device 8.

[0023] Figure 2a shows a first perspective view of the fastening device 8 in its pre-loading state, without the workpiece 14 to be processed. A clamping plate A 10a is mounted on a base plate 11 which is firmly connected to the chain link 3, and is advantageously fixed in place. A clamping plate B 10b, which may have multiple partial clamping plates 9, is fixed on a folding lever 13 in a detachable manner. The fastening plate B 10b on the folding lever 13 is fixed and released by magnetic force or similarly by mechanical means. The folding lever 13 is positioned horizontally in the XY plane and is coupled to the fastening device 8 so as to be rotatable about the pivot axis 12.

[0024] Figure 2b shows a second perspective view of the fastening device 8 in the "loading" state, in which the workpiece 14 to be processed is positioned and fixed relative to the fastening plate B 10b. The workpiece 14 is therefore placed on the fastening plate B 10b. The folding lever 13 is positioned horizontally in the XY plane.

[0025] Figure 2c shows a third perspective view of the clamping device 8 in the "welded" state. The workpiece 14 to be processed is fixed between both clamping plates A 10a and B 10b. On the folding lever 13, the clamping plate B 10b is no longer present. The folding lever 13 is positioned horizontally in the XY plane. The workpiece 14, i.e., both steel plates to be welded, is clamped between the two clamping plates A 10a and B 10b. This clamping can be advantageously performed by magnetic force. The clamping plates A 10a and B 10b are configured to sufficiently press against each other across the entire surface of the steel plates to be welded, with a cutout in the clamping plate B 10b in which the laser beam 23 irradiates the workpiece 14.

[0026] Figure 2d shows a fourth perspective view of the fastening device 8 in the "closed" state. The folding lever 13 is tilted from the XY plane to the XZ plane, where it rests on the base plate 11 and is in a vertical position. This state occurs when the workpiece 14 is placed on the clamping plate A 10a, and similarly when the workpiece 14 is removed from the clamping plate A 10a.

[0027] Figure 3 shows a side view of the welding / cutting zone 17 of the circulating transport device 1, where the chain links 3 of the circulating transport device move continuously in the transport direction TR within the XY plane. The fastening device 8 is in the "welded" state. The workpiece 14 to be processed is clamped and fastened within the fastening device 8 using fastening plates A 10a and B 10b. Within the welding plane XZ, the laser optical system covers the entire working area 20. The folding lever 13 is in either the "downward tilt" or "upward tilt" status. Throughout the welding process, the folding lever 13 is tilted downward.

[0028] A method according to the present invention for laser welding of workpiece 14 proceeds as follows:

[0029] Within the loading zone 15, the folding lever 13, tilted downwards from the fastening device 8, loads at least one workpiece 14 to be processed and secures this workpiece 14 to the fastening plate B 10b, for example, by magnetic force. The fastening plate B 10b is placed on top of the folding lever 13 at this time. Within the welding equipment loading zone 16, the folding lever 13 is rotated approximately 90° around the pivot axis 12, from a nearly horizontal position to a nearly vertical position, and the workpiece 14 to be processed and the clamping plate B 10b are fixed to the base plate 11 and the clamping plate A 10a fixed to the base plate 11.

[0030] Subsequently, the folding lever 13, which does not have the clamping plate B 10b and the workpiece 14, is swung back from the vertical position to the horizontal position by approximately 90°.

[0031] Within the welding / cutting zone 17, the workpiece 14, which is then clamped between clamping plate A 10a and clamping plate B 10b, is welded using a welding laser. Subsequently, within the welding equipment loading / unloading zone 18, the folding lever 13 is again rotated approximately 90° around the pivot axis 12, from a nearly horizontal position to a nearly vertical position, and then receives the processed workpiece 19 and the clamping plate B 10b. The folding lever 13 then rotates the processed workpiece 19 and the clamping plate B 10b back 90° from a nearly vertical position to a nearly horizontal position. The transfer and securing of the workpiece 14 and similarly the clamping plate B 10b can be performed by magnetic force.

[0032] Within the loading / unloading zone 15, the processed workpiece 19 is removed from the clamping plate B 10b and supplied to the subsequent step. The clamping plate B 10b remains in the apparatus at all times. While this application relates to the invention described in the claims, it may also encompass the following other embodiments. 1. Apparatus for laser welding of workpieces (14), particularly for the manufacture of bipolar plates or heat exchanger plates, having a transport device (1) that circulates within a transport plane (XY), The circulating transport device consists of a transport belt (2) similar to a chain having a plurality of chain links (3), each of which is equipped with one fastening device (8), and the fastening device has a base plate (11) and a folding lever (13). The workpiece (14) can be fixed to the base plate (11) using clamping plates (10a, 10b) for the welding process. In the apparatus having at least one laser optical system (22) for welding the workpiece (14), The transport plane (XY) is located in the horizontal plane, and The welding process is performed within a welding plane (XZ), and this welding plane is preferably located approximately perpendicular to the space, i.e., in the vertical direction. A device characterized by the following features. 2. The apparatus according to claim 1, characterized in that at least one of the laser optical systems (22) is configured as a welding optical system and as a marking optical system or as a cutting optical system. 3. At least one of the laser optical systems (22) is either a fixed optical system or a scanning optical system that is movable parallel to the welding plane (XZ), each having at least one mirror. The apparatus according to 1 or 2 above, characterized by being configured as such. 4. The device according to any one of claims 1 to 3 above, characterized in that the pivot axis (12) of the folding lever (13) is attached to the upper side, lower side, or side of the fastening device (8). 5. The apparatus according to any one of claims 1 to 3 above, characterized in that the folding lever (13) is similarly able to be opened in a manner that is essentially parallel to the welding plane (XZ). 6. A method for laser welding a workpiece (14) using the apparatus described in any one of items 1 to 3 above, This method involves the following steps: - Within the loading zone (15): Loading at least one workpiece (14) to be processed onto the fastening device (8), and fixing the workpiece (14) to be processed on the fastening plate B (10b), - Within the welding equipment loading zone (16): The folding lever (13) rotates approximately 90° around the pivot axis (12) from a nearly horizontal position to a nearly vertical position, and the workpiece (14) to be processed and the clamping plate B (10b) are fixed between the base plate (11) and the clamping plate A (10a). - Within the welding equipment loading zone (16): The folding lever (13) of the tightening device (8) is rotated back approximately 90° from the vertical position to a nearly horizontal position. - Within the welding / cutting zone (17): The welding of the workpiece (14) which is fixed between the clamping plate A (10a) and the clamping plate B (10b), - Within the welding equipment loading / unloading zone (18): The folding lever (13) rotates approximately 90° around the pivot axis (12) from the nearly horizontal position to the nearly vertical position, and the processed workpiece (19) is received by the clamping plate B (10b). - Within the welding equipment loading / unloading zone (18): From a nearly vertical position to a nearly horizontal position, by only about 90 degrees. The folding lever (13) having the processed workpiece (19) and the tightening plate B (10b) are rotated in the return direction. - Within the loading / unloading zone (15): Removal of the processed workpiece (19) from the clamping plate B (10b), A method characterized by comprising the steps of: 7. The circulating transport device (1) traces an oval-shaped trajectory within the transport plane (XY), that is, in a substantially horizontal orientation direction. The method according to 6, characterized in that the trajectory is divided into two linear movement regions (5a, 5b) and two rotational movement regions (6a, 6b). 8. The transport device (1) circulating within the transport plane (XY) moves linearly within the welding / cutting zone (17) and / or the loading / unloading zone (15), and The method according to 6 or 7, characterized in that the device rotates within the welding equipment loading / unloading zone (18) and the welding equipment loading zone (16). 9. The workpiece (14) to be processed is fixed perpendicular to the transport plane (XY) within the fastening device (8) on the circulating transport device (1), and The method according to any one of 6 to 8 above, characterized in that welding is performed within the welding / cutting zone (17). 10. The method according to any one of 6 to 9 above, characterized in that the laser beam (23) is configured to achieve coverage of the entire work area (20) by at least one laser optical system (22). 11. Loading and unloading of the workpieces (14) to be processed within the loading / unloading zone (15) shall be carried out as follows: The method according to any one of 6 to 10 above, characterized in that it is performed directly on the clamping plate A(10a). 12. Use of any one of the methods described in 6 to 11 above for the manufacture of bipolar plates for fuel cells or heat exchanger plates for thermal energy transfer. [Explanation of symbols]

[0033] 1 Transport device 2. Transport belt 3 chain links 5a Translational movement region 5b Translational movement region 6a Rotational movement region 6b Rotational movement region 7. Drive system 8. Fastening device 9-part clamping plate 10a Clamping plate A 10b Clamping plate B 11 Base Plate 12. Swivel axis 13. Folding lever 14 Workpieces to be processed 15 Loading / Unloading Zone 16. Welding equipment loading zone 17 Welding / Cutting Zones 18. Welding equipment loading / unloading zone 19 processed workpieces 20 work area 22 Laser Optics 23 Laser beam 24 Loading 25 Loading and unloading 26 Washing Station TR transport direction XY transport plane XZ welding plane

Claims

1. A method for laser welding a workpiece (14) using an apparatus having a transport device (1) that circulates within a transport plane (XY), The circulating transport device consists of a transport belt (2) similar to a chain having a plurality of chain links (3), each of which is equipped with one fastening device (8), and the fastening device has a base plate (11) and a folding lever (13). The workpiece (14) can be fixed to the base plate (11) using clamping plates (10a, 10b) for the welding process. The apparatus has at least one laser optical system (22) for welding the workpiece (14), The transport plane (XY) is located in the horizontal plane, and The welding process is performed within a welding plane (XZ), and this welding plane is preferably located approximately perpendicular to the space, i.e., in the vertical direction. In the above method, the method involves the following steps: namely, - Within the loading zone (15): Loading at least one workpiece (14) to be processed onto the fastening device (8), and fixing the workpiece (14) to be processed on the fastening plate B (10b), - Within the welding equipment loading zone (16): The folding lever (13) rotates approximately 90° around the pivot axis (12), from a nearly horizontal position to a nearly vertical position, and the workpiece (14) to be processed and the clamping plate B (10b) are fixed between the base plate (11) and the clamping plate A (10a). - Within the welding equipment loading zone (16): The folding lever (13) of the tightening device (8) is rotated back approximately 90 degrees from the vertical position to a nearly horizontal position. - Within the welding zone (17): The welding of the workpiece (14) which is fixed between the clamping plate A (10a) and the clamping plate B (10b), - Within the welding equipment loading / unloading zone (18): The folding lever (13) rotates approximately 90° around the pivot axis (12) from the nearly horizontal position to the nearly vertical position, and the processed workpiece (19) is received by the clamping plate B (10b). - Within the welding equipment loading / unloading zone (18): From a nearly vertical position to a nearly horizontal position, by only about 90 degrees. The folding lever (13) having the processed workpiece (19) and the tightening plate B (10b) are rotated in the return direction. - Within the loading / unloading zone (15): Removal of the processed workpiece (19) from the clamping plate B (10b), A method characterized by comprising the steps of:

2. The circulating transport device (1) traces an oval-shaped trajectory within the transport plane (XY), that is, in a substantially horizontal orientation direction. The method according to claim 1, characterized in that the trajectory is divided into two linear movement regions (5a, 5b) and two rotational movement regions (6a, 6b).

3. The transport device (1) circulating within the transport plane (XY) moves linearly within the welding zone (17) and / or the loading / unloading zone (15), and The method according to claim 1, characterized in that the welding equipment rotates within the welding equipment loading / unloading zone (18) and the welding equipment loading zone (16).

4. The workpiece (14) to be processed is fixed perpendicular to the transport plane (XY) within the fastening device (8) on the circulating transport device (1), and The method according to claim 1, characterized in that welding is performed within the welding zone (17).

5. The method according to claim 1, characterized in that the laser beam (23) is configured to achieve coverage of the entire work area (20) by at least one laser optical system (22).

6. The loading and unloading of the workpieces (14) to be processed within the aforementioned loading / unloading zone (15) is as follows: The method according to claim 1, characterized in that it is performed directly on the clamping plate A (10a).

7. Use of the method according to any one of claims 1 to 6 for the manufacture of a bipolar plate for a fuel cell, or a heat exchanger plate for thermal energy transfer.

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