Method for laser welding of steel sheets

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 plates, in particular bipolar plates or heat exchanger plates for fuel cells in commercial vehicle construction. The present invention also relates to the use of the method for the manufacture of bipolar plates or heat exchanger plates. [Background technology]

[0002] In the automotive industry, the trend is increasingly towards CO2 reduction and alternative drives as a result of finite oil reserves and as a result of climate change. For cars and trucks, electric motors with batteries as storage medium are increasingly used, but in the future, other technologies such as fuel cells will also be developed, especially for the truck sector. Bipolar plates (BPPs) are the main components of fuel cells and therefore decisively determine the manufacturing costs and efficiency of fuel cell systems. Based on various advantages in terms of manufacturability and material properties, such as stability, low sheet thickness, and versatile coating possibilities, the metallic construction of bipolar plates has moved to the center of research and development and is currently considered as the favored variant for future large-scale use of fuel cells. Fuel cell systems consist of a large number of individual cells, each with one BPP between the cells, for use in automobiles that typically have 300-400 bipolar plates (BPP). Based on the large number of BPPs per individual system, it is assumed that in the future, in a conservative scenario, the number required will rapidly reach very high dimensions. This challenge is likewise seen as a huge opportunity for BPP's subcontractors. A prerequisite for this, however, is economical and high-performance production technologies. In particular, the welding of both bipolar plate halves into one BPP is a central challenge and currently still a crucial obstacle for cost-efficient production due to the high number of weld seams and the associated long welding times and the high demands on these weld seams due to the thin material and at the same time extremely difficult process conditions.

[0003] BPPs are known per se from the prior art. They usually consist of two bipolar plate halves which are assembled together. The bipolar plate halves are usually formed as embossed films or deformed sheet metal. The bipolar plate halves are stacked and are typically hermetically welded in the edge regions and at the contact points using a laser, which creates weld seams of several meters and possibly additional welds. Alternatively, methods are also known which involve resistance welding, for which welding devices are used in which the bipolar plate halves often have to be refastened several times in order that the sealing contour and all the welds can be realised. In order to be able to weld all sealing contours and points, the bipolar plate to be welded must then be disengaged 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 circumferential sealing contour presents problems: if such a circumferential sealing contour is produced in one welding step by means of a laser, it therefore turns out to be difficult to arrange additional fastening elements inside the circumferential sealing contour, which fasten the bipolar plate halves inside the circumferential sealing contour. During refastening, there is a risk that the positioning is no longer consistent and that the weld points are placed in the wrong position. In addition, the entire manufacturing process of the bipolar plate can be severely delayed by the refastening of the semi-finished bipolar plate.

[0004] US Pat. No. 5,399,433 describes an apparatus and a method for the manufacture of bipolar plates, in which the distortion of the structural members is relatively small. The introduction of welding energy is carried out on the BPP from above and below. The position in space in which this is done is not described.

[0005] In the document DE 10 04 06 13 A1 a clamping device with a clamping lever is shown. From the figures and the text it can be deduced that the orientation of the BPP is horizontal, i.e. the surface lies horizontally on the base surface.

[0006] GRAEBENER Maschinentechnik shows on its homepage a complete production line for the BPP. Under non-patent document 1 (URL: https: / / www.graebener.com / en / cutting-and-welding) the two welding stations as well are shown more precisely. The BPP is welded in a horizontal position at rest.

[0007] SITEC (URL: https: / / WWW.SITEC-TECHNOLOGY.DE / ) manufactures automatable laser welding installations, whereby welding likewise takes place here at rest and in a horizontal plane.

[0008] US Pat. No. 5,399,433 describes a method for increasing cycle times and thus reducing production costs in the industrial production of welded sheet metal components, in particular tailored blanks for the automotive industry. The method is based on a transport system with a cantilevered optical system and a horizontal orientation of the workpieces throughout the welding, and does not require any time-consuming cooling of the hot weld seam, nor any means for holding the workpieces on one side with great force on the transport belt. Thereby, the adverse effect of the substrate spacing on the cycle time of the machine can be strongly reduced. In general, in this way the welding-subsequence time can be reduced. In such known systems with a vertical movement plane, no backtracking is used for the operation, except that access is made from the underside of the machine. DE 10 200 03 133 A1 describes a welding apparatus in which the metal sheets are welded to one another in a vertical plane, so that the space required for the welding apparatus is as small as possible.

[0009] The disadvantages of these solutions mentioned above are the high technical effort required for process-reliable fastening of the structural parts and for the evacuation of welding fumes and welding splashes from the system, the large machine dimensions with high investment costs, and generally low productivity of the entire system. [Prior art documents] [Patent documents]

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

[0011] [Non-Patent Document 1] GRAEBENER Maschinentechnik URL: https: / / www.graebener.com / en / cutting-and-welding [Non-Patent Document 2] SITEC URL: HTTPS: / / WWW.SITEC-TECHNOLOGY.DE / Summary of the Invention [Problem to be solved by the invention]

[0012] The problem underlying the present invention is therefore to disclose a method which does not have the aforementioned drawbacks. [Means for solving the problem]

[0013] This problem is solved according to the invention by a method having the features set out in claim 1. Advantageous embodiment variants are set out in the dependent claims. Effect of the Invention

[0014] The apparatus described herein with respect to the method is based on a transport device, which transports the workpieces to be processed in a circular manner in a horizontal plane, so that the number of required equipment parts can be strongly limited.

[0015] Since the circulating transport device moves in a horizontal plane, access is possible from both sides, which means that here, on one side, the steel plates (workpieces) are welded and on the other side, these are loaded and unloaded, respectively, between which the steel plates are fixed by clamping plates or this fixation is released again.

[0016] This brings the following advantages: Lower investment costs due to fewer welding equipment Reduced investment costs due to reduced machine dimensions (footprint, component size, etc.) In short, lower investment costs, which induces lower production costs. is generated.

[0017] A further advantage of the present invention is that the welding process is carried out in a vertical plane, i.e. in a perpendicular direction and approximately perpendicular to the transport direction, so that no welding splashes remain on the workpieces to be processed, which results in less contamination of the workpieces and the equipment.

[0018] In the proposed configuration, the workpiece is clamped only once and subsequently processed, thus eliminating multiple clampings with the known problems of precise adjustment during processing of the workpiece, and generally achieving high precision during loading, processing and unloading.

[0019] An object of the present invention is to significantly increase the number of parts produced per time unit while simultaneously reducing part costs.

[0020] The invention presented here thus allows, overall, efficient and qualitatively high-value production.The invention is further explained below on the basis of examples and in connection with the figures. [Brief description of the drawings]

[0021] [Figure 1] FIG. 2 is a plan view of a transport device in a schematic illustration. [Figure 2a] FIG. 2 is a first perspective view of the fastening device. [Figure 2b] FIG. 2 is a second perspective view of the fastening device. [Figure 2c] FIG. 13 is a third perspective view of the fastening device. [Figure 2d] FIG. 4 is a fourth perspective view of the fastening device. [Diagram 3] FIG. 1 is a side view of an installation according to the invention in a schematic illustration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] 1 shows in plan view a circular transport device 1, the drive 7 of which moves the transport belt 2 in a clockwise direction in a transport plane XY and in so doing passes through translational movement areas 5a, 5b and rotational movement areas 6a, 6b, the transport plane XY being then essentially horizontal. The transport belt 2 consists of a number of chain links 3, which are equipped with clamping devices 8. A base plate 11 and a pivotable folding lever 13 are attached to each chain link 3. Between the base plate 11 and the folding lever 13, a workpiece 14 to be welded can be accommodated. The loading 24 of the workpieces, i.e. the steel sheets, onto the rotating transport belt 2 takes place in the translational region 5a, when the folding lever 13 is unfolded and horizontally positioned in the loading / unloading zone 15. In the welding device loading zone 16 in the rotational movement area 6a, the workpiece 14 in the clamping device 8 is moved to a vertical position by tilting back (upward) the folding lever 13 and fixed on the base plate 11 using the clamping means (clamping plates B 10b and A 10a). In the next step, the folding lever 13 is moved again into the horizontal position, which is necessary so that in the following step the laser beam 23 of the welding laser 22 can be directed onto the workpiece 14. In the translational region 5b, the processing of the workpiece 14 takes place in the welding / cutting zone 17 with the aid of a laser beam 23 of the laser optics 22. Here, both steel sheets of the workpiece 14 are welded to one another. It is likewise conceivable that cutting or marking takes place with the aid of the laser beam 23. In the welding device unloading zone 18, in a first step the folding lever 13 is tilted into a vertical position and in a second step the fastening device 8 with the machined workpiece 19 is tilted from the vertical position into a horizontal position. In the loading / unloading zone 15 the processed workpieces 19 are removed from the circulating transport belt 2 by unloading 25. A cleaning station 26 is used for cleaning the clamping device 8.

[0023] FIG. 2a shows a first perspective view of the clamping device 8 in the pre-loading state, without a workpiece 14 to be processed. A clamping plate A 10a is mounted, preferably fixedly attached, on a base plate 11 which is rigidly connected to the chain link 3. A clamping plate B 10b, possibly having several partial clamping plates 9, is then releasably fastened on the folding lever 13. The fixing and releasing of the clamping plate B 10b on the folding lever 13 is effected by magnetic forces or equally mechanically. The folding lever 13 is located in a horizontal position in the XY plane and is here connected to the clamping device 8 so as to be rotatable about a pivot axis 12.

[0024] 2b shows a second perspective view of the clamping device 8 in the "loading" state, whereby the workpiece 14 to be processed is positioned and fixed relative to the clamping plate B 10b. The workpiece 14 is thus resting on the clamping plate B 10b. The folding lever 13 is located in a horizontal position 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 clamped between both clamping plates A 10a and B 10b. Above the folding lever 13, the clamping plate B 10b is no longer present. The folding lever 13 is located in a horizontal position in the XY plane. The workpiece 14, i.e. both steel sheets to be welded, is clamped between the clamping plates A 10a and B 10b. This clamping can advantageously be achieved by magnetic forces. The clamping plates A 10a and B 10b are configured in such a way that they press the steel sheets to be welded against each other sufficiently over their entire surface, the area in which the laser beam 23 irradiates the workpiece 14 is cut out in the clamping plate B 10b.

[0026] FIG. 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 during the placement of a workpiece 14 on the clamping plate A 10a and also during the removal of this workpiece 14 from this clamping plate A 10a.

[0027] 3 shows in a side view the welding / cutting zone 17 of a circular transport device 1, the chain links 3 of which move continuously in the XY plane in the transport direction TR. The fastening device 8 is in the "welding" state. The workpiece 14 to be processed is clamped in the clamping device 8 by means of clamping plate A 10a and clamping plate B 10b. In the welding plane XZ, the laser optics cover the entire working area 20. The folding lever 13 is in a "downward tilt" or "upward tilt" status. During welding, the folding lever 13 is tilted downward.

[0028] The method according to the invention for laser welding of workpieces 14 then proceeds as follows:

[0029] In the loading zone 15, the folding lever 13 tilted downwards of the clamping device 8 loads at least one workpiece 14 to be processed and fixes this workpiece 14 on a clamping plate B 10b, for example by magnetic force. The clamping plate B 10b rests on the folding lever 13. In the welding device loading zone 16, the folding lever 13 is now pivoted about the pivot axis 12 by approximately 90° from an approximately horizontal position to an approximately vertical position, and the workpiece 14 to be processed and the clamping plate B 10b are fixed at the base plate 11 and at the clamping plate A 10a fixed to the base plate 11.

[0030] Thereafter, the folding lever 13, which does not carry the clamping plate B 10b and the workpiece 14, is again pivoted by approximately 90° from the vertical position to a horizontal position.

[0031] In the welding / cutting zone 17, the workpiece 14, clamped between clamping plate A 10a and clamping plate B 10b, is then welded using a welding laser. Thereafter, in the welding equipment unloading zone 18, the folding lever 13 is again pivoted about the pivot axis 12 by approximately 90° from an approximately horizontal position to an approximately vertical position and then receives the machined workpiece 19 and the clamping plate B 10b. The folding lever 13 then pivots the machined workpiece 19 and the clamping plate B 10b back from the substantially vertical position by 90° to a substantially horizontal position. The transfer and fixation of the workpiece 14, and likewise of the clamping plate B 10b, can be performed by magnetic forces.

[0032] In the unloading zone 15, the processed workpieces 19 are then removed from the clamping plate B 10b and fed further to the subsequent steps. The clamping plate B 10b always remains in the device. In addition, the present application relates to the invention described in the claims, but may also include the following as other aspects. 1. An apparatus for the laser welding of workpieces (14), in particular for the production of bipolar plates or heat exchanger plates, comprising a transport device (1) circulating in a transport plane (XY), the circular transport device comprises a chain-like transport belt (2) having a number of chain links (3), each of which is provided with a tensioning device (8), the tensioning device having a base plate (11) and a folding lever (13); the workpiece (14) can be fixed to the base plate (11) by means of clamping plates (10a, 10b) for a welding process; The apparatus as described above, comprising at least one laser optical system (22) for welding the workpiece (14), the transport plane (XY) lies in a horizontal plane, and The welding process is carried out in a welding plane (XZ), which is advantageously located approximately vertically in space, i.e. in the vertical direction; An apparatus comprising: 2. The device 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 optics (22) can be a fixed optic or a scanning optic movable parallel to the welding plane (XZ) with at least one mirror in each case, 3. The device according to claim 1 or 2, characterized in that it is configured as follows. 4. The device according to any one of claims 1 to 3, characterized in that the pivot shaft (12) of the folding lever (13) is attached to the upper, lower or side of the fastening device (8). 5. Device according to any one of claims 1 to 3, characterized in that the folding lever (13) is also releasable essentially parallel to the welding plane (XZ). 6. A method for laser welding of a workpiece (14) by means of a device according to any one of claims 1 to 3, comprising: The method comprises the following steps: - In the loading zone (15): loading at least one workpiece (14) to be processed into said clamping device (8) and fixing said workpiece (14) to be processed on a clamping plate B (10b); - in the welding equipment loading zone (16): rotation of the folding lever (13) about the pivot (12) by approximately 90° from a substantially horizontal position to a substantially vertical position and fixation of the workpiece (14) to be machined and the clamping plate B (10b) on the base plate (11) and the clamping plate A (10a); - in the welding equipment loading zone (16): 2. Rotating the folding lever (13) of the fastening device (8) back from the vertical position to a substantially horizontal position by approximately 90°. - in the welding / cutting zone (17): welding the workpiece (14) secured between the clamping plate A (10a) and the clamping plate B (10b); - in the welding equipment unloading zone (18): rotation of the folding lever (13) about the pivot axis (12) by approximately 90° from the substantially horizontal position to a substantially vertical position and receipt of the machined workpiece (19) and the clamping plate B (10b); in said welding equipment unloading zone (18): From a nearly vertical position, to a nearly horizontal position by only about 90° Return rotation of the folding lever (13) carrying the machined workpiece (19) and the clamping plate B (10b); - in the loading and unloading zone (15): Removal of the machined workpiece (19) from the clamping plate B (10b); A method comprising the steps of: 7. The circulating transport device (1) describes an elliptical orbit in the transport plane (XY), i.e. in a substantially horizontal alignment direction; 7. The method according to claim 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), which circulates in the transport plane (XY), moves linearly in the welding / cutting zone (17) and / or in the loading / unloading zone (15), and 8. The method according to claim 6 or 7, characterized in that the welding equipment unloading zone (18) and the welding equipment loading zone (16) are moved rotationally. 9. The workpiece (14) to be processed is fixed perpendicular to the transport plane (XY) in the clamping device (8) on the rotating transport device (1); and 9. The method according to any one of claims 6 to 8, characterized in that welding is performed in the welding / cutting zone (17). 10. The method according to any one of claims 6 to 9, characterized in that the laser beam (23) is configured to achieve coverage of the entire working area (20) by means of at least one laser optics (22). 11. The loading and unloading of the workpieces (14) to be processed in the loading / unloading zone (15) is carried out by: 11. The method according to any one of claims 6 to 10, characterized in that the method is performed directly on the fastening plate A (10a). 12. Use of the method according to any one of claims 6 to 11 for the manufacture of a bipolar plate for a fuel cell or a heat exchanger plate for the transfer of thermal energy. [Explanation of symbols]

[0033] 1 Transport device 2 Transport belt 3. Chain Link 5a Translational movement region 5b Translational movement region 6a Rotational moving area 6b Rotational movement area 7 Drive unit 8 Fastening device 9 Partial fastening plate 10a Fastening plate A 10b Fastening plate B 11 Base plate 12 Swivel Axis 13 Folding lever 14 The workpiece to be machined 15 Loading / unloading zone 16 Welding equipment loading zone 17 Welding / Cutting Zone 18 Welding equipment loading and unloading zone 19 Machined workpiece 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 of workpieces (14) by means of an apparatus having a transport device (1) circulating in a transport plane (XY), comprising: the circulating transport device comprises a chain-like transport belt (2) having a number of chain links (3), each of which is provided with a tensioning device (8), the tensioning device having a base plate (11) and a folding lever (13), the workpiece (14) can be fixed to the base plate (11) by means of clamping plates (10a, 10b) for a welding process; the apparatus having at least one laser optics (22) for welding the workpiece (14); the transport plane (XY) lies in a horizontal plane, and The welding process is carried out in a welding plane (XZ), which is advantageously located approximately vertically in space, i.e. in the vertical direction. In the method, the method comprises the steps of: - in the loading zone (15): loading at least one workpiece (14) to be processed into said clamping device (8) and fixing said workpiece (14) to be processed on a clamping plate B (10b); in the welding equipment loading zone (16): rotation of the folding lever (13) about a pivot axis (12) by approximately 90° from a substantially horizontal position to a substantially vertical position, and fixation of the workpiece (14) to be processed and the clamping plate B (10b) on the base plate (11) and the clamping plate A (10a); in the welding equipment loading zone (16): - a return rotation of the folding lever (13) of the fastening device (8) from the vertical position to a substantially horizontal position by approximately 90°; in the welding / cutting zone (17): welding the workpiece (14) secured between the clamping plate A (10a) and the clamping plate B (10b); in the welding equipment unloading zone (18): rotation of the folding lever (13) about the pivot axis (12) by approximately 90° from the substantially horizontal position to a substantially vertical position and receipt of the machined workpiece (19) and the clamping plate B (10b); in said welding equipment unloading zone (18): From a nearly vertical position, to a nearly horizontal position by about 90° Return rotation of the folding lever (13) with the machined workpiece (19) and the clamping plate B (10b), - in the loading and unloading zone (15): Removal of the machined workpiece (19) from the clamping plate B (10b); A method comprising the steps of:

2. The circulating transport device (1) describes an oval-shaped track in the transport plane (XY), i.e. in a substantially horizontal alignment direction, 2. A 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), which circulates in the transport plane (XY), moves linearly in the welding / cutting zone (17) and / or in the loading / unloading zone (15), and 2. The method of claim 1, further comprising rotating movement within the welding equipment 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) in the clamping device (8) on the rotating transport device (1); and 2. The method according to claim 1, characterized in that welding is performed in the welding / cutting zone (17).

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

6. The loading and unloading of the workpieces (14) to be processed in the loading / unloading zone (15) is carried out by:

2. The method according to claim 1, characterized in that it is performed directly on the clamping plate A (10a).

7. 7. Use of the method according to any one of claims 1 to 6 for the manufacture of bipolar plates for fuel cells or heat exchanger plates for the transfer of thermal energy.