Method and apparatus for laser welding of plate-shaped workpieces - Patent Application 20070122997

Abstract

The invention relates to an apparatus 1 and a method for the production of welded, plate-shaped workpieces 14, 15, in particular for the production of bipolar or heat exchanger plates. The workpieces 14 stand vertically and are transported and welded in a horizontal plane XY by an endlessly circulating product transport system 2. The workpieces 14 are transported with constant speed through the processing area and are welded there by at least two simultaneously operating welding lasers 22a, 22b, the position of the workpieces 14 being calculated and the at least two welding lasers 22a, 22b being controlled accordingly.

Description

[Technical Field]

[0001] The present invention relates to an apparatus and a method for laser welding of metal structural components in endlessly circulating transport systems, in particular bipolar plates for fuel cells or heat exchanger plates, for example in commercial vehicle construction. The present invention also relates to the use of this method. [Background technology]

[0002] In the automotive industry, the trend is increasingly towards CO2 reduction and the use of alternative drives as a result of finite oil reserves and progressive climate warming. Instead of combustion engines, electric motors with powerful batteries as storage media are increasingly used in cars and trucks. In the future, however, other technologies such as fuel cells will also be developed, especially for the truck sector. Bipolar plates (BPPs) are the main component of fuel cells and therefore crucially determine the manufacturing costs and efficiency of fuel cell systems. Due to various advantages in terms of manufacturability and material properties, such as stability, low sheet thickness, and various coating possibilities, metallic constructions of bipolar plates have moved to the center of research and development and are currently considered as the favored variant for future large-scale use of fuel cells. A fuel cell system consists of a large number of individual cells, each with one bipolar plate (BPP) between them, and typically requires 300 to 400 BPPs per system for automotive applications. Based on the large number of BPPs per individual system, it is assumed that in the future, the number required will rapidly reach very high dimensions, even in conservative scenarios. This challenge is also seen as an opportunity for BPP's subcontractors. A prerequisite for this, however, is economical and high-performance production technology. In particular, the welding of both bipolar plate halves to 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 as such are known from the prior art. They usually consist of two bipolar plate halves that are combined together. The bipolar plate halves are usually made of stamped film or deformed sheet metal. The bipolar plate halves are stacked and are typically hermetically welded at the overlap abutment using a laser, which creates a weld seam of several meters and possibly additional welds. Alternatively, resistance welding methods are also known, for which welding devices are used, in which the bipolar plate halves often have to be refastened multiple times so that the sealing contour and all the welds can be formed. In order to be able to weld all sealing contours and points, the bipolar plate to be welded must then be released from the clamping device and re-clamped with another clamping mask plate or welding mask plate so that all areas of the BPP to be welded are accessible to the welding laser. During production, in particular the circumferentially extending sealing contour presents problems: if such a sealing contour is produced by laser in one welding step, it has therefore proved difficult to arrange additional fastening elements inside the circumferentially extending sealing contour, which fasten the bipolar plate halves inside the sealing contour. When these plates are refastened, the positioning is no longer consistent and the welding points are positioned in the wrong place; and There is a risk that the bipolar plate will be distorted due to the released internal stresses during this refastening. Additionally, the entire manufacturing process of the bipolar plate can be severely delayed by the refastening of the semi-finished bipolar plate.

[0004] The patent document 1 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 into the BPP is carried out from above and below. The position in space in which this is done is not described.

[0005] In the patent application WO 02 / 04999 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] DE 10 2004 014 142 A1 describes an apparatus for welding bipolar plates with an electromagnetic clamping device, in which the plates are positioned horizontally and welded by means of a welding laser.

[0007] US Pat. No. 5,629,999 describes an installation for laser welding, in which vertically standing workpieces are fixed on a rotating platform and are welded using a laser.

[0008] Patent document 5 describes a nozzle changer for assembling and disassembling nozzles in a laser processing machine. US Pat. No. 5,649,499 describes a welding device in which metal sheets are welded together in a vertical plane, so that the space required for the welding device is as small as possible. DE 10 200 043 133 A1 describes a method for the separation of flat workpieces by the TLS (Thermisches Laserstrahl Separieren) method.

[0009] GRAEBENER Maschinentechnik shows on its homepage the complete production line for BPP. Two welding installations are also shown more precisely under non-patent document 1 (URL: https: / / www.graebener.com / en / cutting-and-welding). The BPP is welded in a horizontal position at rest.

[0010] SITEC (Non-Patent Document 2 (URL: HTTPS: / / WWW.SITEC-TECHNOLOGY.DE / )) manufactures automatable laser welding equipment, whereby welding is likewise carried out here in a stationary state and in a horizontal plane.

[0011] US Pat. No. 5,629,499 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. This method is based on a transport system with a cantilevered optical system and a horizontal orientation of the workpieces throughout the welding process, and does not require any time-consuming cooling of the hot weld seam, nor does it require 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 machine cycle time can be strongly reduced. Overall, in this way, the welding side time can be reduced.

[0012] In such known systems with a vertical travel surface, the reverse leg of the transport system is not used for operation, except that access is provided from the underside of the machine. Since the described method is intended only for static laser beams, they cannot be moved transversely to the transport direction for laser processing. In addition, the entire laser optics must be moved, which, as a result of the large mass, entails disadvantageous consequences in terms of dynamics, precision, and power demands. In addition, the ratio of the chain link length to the chain turning radius is often very large, so that when a chain is driven using a chain wheel, the known polygon effect induces significant position errors in the chain. It is a common practice to compensate for this undesirable effect at least in one chain span (in forward travel) by, for example, an electronic cam disc in the chain drive, but this only achieves a conditioned accuracy based on the given non-continuous kinematic situation and mass. In a chain with two turning sections, however, the inter-car section of the opposing chain (in the reverse run) may, in some circumstances, be overcompensated (accelerating in both directions throughout the move), and synchronizing the function with this inter-car section of the chain is highly unrealistic. The polygon effect, however, not only has an influence on the dynamics, but also on the chain length itself. This chain length change therefore needs to be compensated for by at least one dynamic chain tensioning mechanism or compensation-redirection curve, so that an approximately constant chain tension can be maintained. An unpretensioned chain can produce chaotic vibrations and the attendant additional inaccuracies.

[0013] The drawbacks of these solutions mentioned above are the high technical effort required for process-reliable fastening of the structural components, the large machine dimensions with high investment costs, and the generally low productivity of the entire installation. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] German Patent Invention No. 102016200387 [Patent Document 2] International Publication No. 2018149959 [Patent Document 3] Chinese Patent Application Publication No. 108637476 A [Patent Document 4] Chinese Patent Application Publication No. 107350623 A [Patent Document 5] European Patent Application Publication No. 3112074 A1 [Patent Document 6] U.S. Patent No. 6,639,176 B1 [Patent Document 7] German Patent Application Publication No. 10 2017 202 426 A [Patent Document 8] European Patent No. 3038789 [Non-patent literature]

[0015] [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]

[0016] The problem underlying the present invention is therefore to disclose an apparatus and a method that do not have the above-mentioned drawbacks. [Means for solving the problem]

[0017] This problem is solved according to the invention by a device having the features according to claim 1. Advantageous embodiment variants are presented in the dependent claims. The method according to the invention has the features of claim 8. [Effects of the Invention]

[0018] In the apparatus according to the invention, the workpieces, which usually consist of two metal plates stacked on top of each other, are transported and welded in a circular manner in a horizontal plane. The plate-shaped workpieces are then essentially vertical, i.e., standing upright. In contrast, in conventional installations, the workpieces are welded in a horizontal position. The advantage of the present invention is that the welding process is carried out in a vertical plane, i.e. perpendicularly 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.

[0019] According to the invention, workpieces are transported at a constant speed within a processing area where they are to be welded, and are welded there by at least two welding lasers operating simultaneously. In addition, a position measuring device is provided for calculating the position of the workpieces. The position measuring device is used to control the at least two welding lasers.

[0020] In order for the workpiece to be transported through the processing area at a constant speed, the polygon effect needs to be compensated for, which can be done, for example, by means of a helix. All chain links currently located in the machining area are then in engagement with the threads located in this area throughout the machining phase, which results in a more precise alignment of the chain links relative to one another and therefore an increase in quality. The movement of the inter-chain segments without superimposed acceleration means that the loading and unloading of workpieces onto and from the chain links can be carried out without time-consuming position adjustments, thereby enabling optimal utilization of the required space. Furthermore, the use of multiple welding lasers allows for increased production. These laser beams can then simultaneously process one workpiece, and immediately thereafter the next workpiece can move forward. The welding lasers arranged as closely as possible next to each other also reduce the cycle time and provide additional construction space. This use of special laser optics also allows the processing of large processing areas without the laser optics moving relative to the product transport system.

[0021] In the proposed configuration, the workpiece is clamped only once and subsequently processed, thus eliminating multiple clampings with the well-known problem of precise adjustment during processing of the workpiece, and overall achieving high precision during loading, processing and unloading.

[0022] The object of the present invention is to significantly increase the part production capacity per unit time while simultaneously reducing part costs. The use of a laser optics allows for a large processing area without the laser optics having to be moved relative to the product transport direction, which results in an improvement in quality. The overlapping of the laser beam and the simultaneous processing at several pitch positions allows for optimal utilization of the laser, a compact design and very long weld seams in a very short time and thus reduces processing costs.

[0023] The invention presented here thus allows for efficient and high-quality production as a whole. The invention will be further explained below on the basis of examples and in connection with the figures. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a plan view of a first laser processing and product transport system in a schematic view. [Figure 2] FIG. 10 is a plan view of an optional second laser processing and product transport system in a schematic view. [Figure 3] FIG. 10 is a plan view of an optional third laser processing and product transport system in a schematic view. [Figure 4] FIG. 2 is a side view of a first laser processing and product transport system, also in a schematic view. DETAILED DESCRIPTION OF THE INVENTION

[0025] FIG. 1 shows in plan view a first laser processing and product transport system 1 having an endlessly circulating product transport system 2 and at least one product transport system guide 8 . The product transport system 2 is moved in a clockwise direction in the transport plane (horizontal plane) XY by means of a screw drive 12 with a rotary encoder 13a, and in so doing passes through straight sections 5a, 5b and curved sections 6a, 6b in a compensation-direction curve 11. The product transport system 2, e.g. a chain-driven system, consists of a plurality of transport elements 3, e.g. chain links, each with a pivotable folding lever 20 and each with at least one cam roller 10, which engages in the helix 7. Loading 17 of the workpieces 14 into the welding device of the circulating product transport system 2 takes place in the linear region 5a when the folding lever 20 is unfolded and positioned horizontally in the loading / unloading zone 16. In the curved region 6a, the workpieces 14 are moved into a vertical position by tilting the folding lever 20 upward and are fixed in the welding device, for example by magnetic force. In the next step, the folding lever 20 is released again and moved to an approximately horizontal position, the workpiece then remaining in a vertical position. In linear region 5b, welding of workpiece 14 is performed using stationary welding lasers 22a, 22b in laser processing zone 21. Workpiece 14 is moved past welding lasers 22a, 22b in laser processing zone 21 by product transport system 2. In the loading / unloading zone 16, the processed (welded) workpieces 15 are removed from the circulating product transport system 2 by unloading 18 the welding equipment.

[0026] Figure 2 shows in plan view an optional second laser processing and product transport system 1 having an endlessly circulating product transport system 2, which is provided with a drive means and moves in a uniform rotational movement in a clockwise direction on a circular orbit 29 in the transport plane (horizontal plane) XY. The product transport system 2 consists of a plurality of transport elements 3, each equipped with a pivotable folding lever 20. Loading 17 of the workpieces 14 to be processed into the welding device of the circulating product transport system 2 takes place in the loading / unloading zone 16 when the folding levers 20 are unfolded and positioned horizontally. By tilting back the folding levers 20, the workpieces 14 are moved into a vertical position and fixed in the welding device. In the next step, the folding lever 20 is released again and moved again to an approximately horizontal position. In the laser processing zone 21, continuous position measurement 9 and welding of the workpiece 14 by means of the laser beams 26 of at least two welding lasers 22 take place, which are arranged as closely as possible next to one another. Here, five welding lasers 22 are shown, however, other numbers of welding lasers 22 are possible as well. The workpiece 14 is moved past the welding lasers 20, 22a, 22b by the product transport system 2 in the welding plane. In the loading / unloading zone 16, the processed workpieces 15 are removed from the circulating product transport system 2 by unloading 18 welding devices.

[0027] FIG. 3 shows, in plan view, a third optional laser processing and product transport system 1 having a product transport system 2 and at least one product transport system guide 8 . The transport elements 3 are equipped with drive means, e.g., motor-driven carriages, and move in a transport direction TR in the transport plane XY on a fixed path 27 with a fixed pitch and on a free path 28 with a free pitch. The drive means can, for example, be linear motors. The loading 17 of the workpieces 14 to be processed onto the welding device of the circulating transport elements 3 takes place in a loading / unloading zone 16 on the fixed path 27. Continuous linear position measurement 9 and welding of the workpiece 14 by at least two laser beams 26a, 26b of at least two welding lasers 22a, 22b take place in the laser processing zone 21, which is also located on a fixed path 27. The workpiece 14 is moved past the welding lasers 20, 22a, 22b by the product transport system 2 in the welding plane. In the loading / unloading zone 16, the processed workpieces 15 are removed from the circulating product transport system 2 by unloading 18 welding devices.

[0028] Figure 4 shows in a side view the laser processing zone 21 of a laser processing and product transport system 1 having a circulating product transport system 2, the transport elements 3 of which move continuously in a transport plane (horizontal plane) XY in a transport direction TR. The workpiece 14 to be processed is fixed on the transport element 3 and is processed in the welding plane XZ. At least two welding lasers cover the processing areas 23a, 23b above the current pitch position 3a, resulting in an overlap 24 of these processing areas 23a, 23b. The folding levers 20 are pivotable about pivot axes 19 and are used for positioning and fixing the workpieces 14 to be processed and the processed workpieces 15 on the transport element 3. The folding levers 20 are shown in the "half-open 20c" position in a "tilted down" or "tilted up" status. 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 production of welded, plate-shaped workpieces (14, 15), in particular for the production of bipolar plates or heat exchanger plates, comprising: The device has a product transport system (2) that circulates endlessly in a horizontal plane (XY), the product transport system comprises a plurality of transport elements (3) for fixing the plate-shaped workpieces (14) so ​​that the plate-shaped workpieces are transported essentially vertically standing through the processing areas (23a, 23b), In this processing area, the plate-shaped workpiece (14) is welded by a welding laser (22, 22a, 22b), The device is provided with drive means (12) for the transport of the transport element (3) through the processing zones (23a, 23b), The transport element (3) can be transported through the processing zone (23a, 23b) at a constant speed, and the workpiece (14) can be welded by at least two welding lasers (22, 22a, 22b) operating simultaneously in the processing area (23a, 23b), and a position measuring device (9) for calculating the position of the workpiece (14) is provided for controlling the at least two welding lasers (22, 22a, 22b); An apparatus characterized by: 2. At least both of said welding lasers (22, 22a, 22b) are each equipped with an optical system by which the laser beam (26, 26a, 26b) can be redirected in horizontal and vertical directions; 11. The apparatus according to claim 1, wherein every point on the surface of the workpiece (14) is therefore reachable. 3. The device according to claim 1 or 2, characterized in that the drive means (12) is configured as a screw drive (12) with a helix (7) or as a linear motor. 4. An apparatus according to any one of claims 1 to 3, characterized in that it is provided with more than two welding lasers (22, 22a, 22b), for example three, four, five, six, seven or eight. 5. Device according to any one of claims 1 to 4, characterized in that the transport element (3) is configured as a chain link or as a vehicle. 6. At least two of the welding lasers (22, 22a, 22b) are arranged in a fixed state, and the laser beams (26, 26a, 26b) are repositionable by a mirror system; 6. The apparatus according to any one of claims 1 to 5, characterized in that this allows the laser beam (26, 26a, 26b) to be repositioned from one workpiece (14) to the next workpiece (14) in the subsequent transport element (3). 7. An apparatus according to any one of claims 1 to 6, characterized in that the workpiece (14) is fixed on the transport element (3) by means of folding levers (20a, 20c) perpendicular to the transport plane (XY). 8. A method for the production of welded, plate-shaped workpieces (14, 15), in particular for the production of bipolar plates or heat exchanger plates, comprising: The method, in which the workpieces (14) are essentially vertically standing and transported in a horizontal plane (XY) by an endlessly circulating product transport system (2) on transport elements (3), and the plate-shaped workpieces (14) are welded in processing areas (23a, 23b), the transport element (3) is moved through the processing area (23a, 23b) at a constant speed, the workpiece (14) is welded by at least two welding lasers (22, 22a, 22b) operating simultaneously within the processing area (23a, 23b); A method comprising: calculating a position of the workpiece (14) and controlling at least two of the welding lasers (22, 22a, 22b) therewith. 9. The method according to claim 8, characterized in that the workpiece (14) is guided in a horizontal, straight line within the processing area (23a, 23b). 10. The method according to claim 8, characterized in that the workpiece (14) is guided on a circular track (29) within the machining area (23a, 23b). 11. A method according to any one of claims 8 to 10, characterized in that the overlap (24) of the welded areas is achieved by the arrangement of at least two welding lasers (22, 22a, 22b). 12. Use of the method according to any one of claims 8 to 11 for the manufacture of bipolar plates for fuel cells or heat exchanger plates for the transfer of thermal energy. [Explanation of symbols]

[0029] 1. Laser processing and product transport system 2 Product Transportation System 3. Transportation Elements 3a Current pitch position 5a Linear Region 5b Linear Region 6a Curve area 6b Curve area 7 spiral 8 Product Transport System Guide 9 Position measurement 10 Cam Roller 11 Compensation - Turning Curve 12 Screw drive unit 13a rotary encoder 14 Plate-shaped workpiece 15 Machined workpiece 16 Loading / Unloading Zone 17 Loading 18 Loading and unloading 19 Swivel axis 20 Folding lever 20a Folding lever in open position 20b Folding lever in closed position 20c Folding lever in half-open position 21 Laser Processing Zone 22 Welding Laser 22a welding laser 22b welding laser 23a Processing area 23b Processing area 24 Overlap 26 Laser Beam 26a Laser beam 26b Laser beam 27 Fixed Routes 28 Free Route 29 Circular Orbit TR transport direction XY transport plane (horizontal plane) XZ welding plane

Claims

1. 1. An apparatus for the production of welded, plate-shaped workpieces (14, 15), in particular for the production of bipolar plates or heat exchanger plates, comprising: In the above apparatus, the plate-shaped workpiece (14) stands vertically and is welded in a processing area (23a, 23b) by a welding laser (22, 22a, 22b), The device has a product transport system (2) that circulates endlessly in a horizontal plane (XY), the product transport system comprises a plurality of transport elements (3) for fixing the plate-shaped workpieces (14) so ​​that the plate-shaped workpieces are transported essentially vertically standing through the processing areas (23a, 23b), drive means (12) for the transport of the transport element (3) through the processing zones (23a, 23b) are provided, The transport element (3) is driven by the drive means (12) The material can be transported through the processing zones (23a, 23b) at a constant speed; the apparatus has at least two welding lasers (22, 22a, 22b); Thus, the workpiece (14) can be welded in the processing area (23a, 23b) by the two welding lasers (22, 22a, 22b) operating simultaneously; For the control of the at least two welding lasers (22, 22a, 22b), the device has a position measuring device (9) for determining the position of the workpiece (14). An apparatus characterized in that

2. at least both of the welding lasers (22, 22a, 22b) each have an optical system that allows the laser beam (26, 26a, 26b) to be redirected in horizontal and vertical directions; 2. Apparatus according to claim 1, characterized in that this therefore makes every point on the surface of the workpiece (14) reachable.

3. 3. The device according to claim 1 or 2, characterized in that the drive means (12) is configured as a screw drive (12) with a helix (7) or as a linear motor.

4. 3. Apparatus according to claim 1 or 2, characterized in that more than two, for example three, four, five, six, seven or eight welding lasers (22, 22a, 22b) are provided.

5. 3. The device according to claim 1 or 2, characterized in that the transport element (3) is configured as a chain link or as a vehicle.

6. at least two of the welding lasers (22, 22a, 22b) are fixedly arranged, and the laser beams (26, 26a, 26b) are repositionable by a mirror system; 3. The apparatus according to claim 2, wherein the laser beam (26, 26a, 26b) can thus be repositioned from one workpiece (14) to the next workpiece (14) on the subsequent transport element (3).

7. 3. The device according to claim 1 or 2, characterized in that the workpiece (14) is fixed on the transport element (3) by means of folding levers (20a, 20c) perpendicular to the transport plane (XY).

8. 1. A method for the production of welded, plate-shaped workpieces (14, 15), in particular for the production of bipolar plates or heat exchanger plates, comprising: The method, wherein the plate-shaped workpiece (14) is welded in a processing area (23a, 23b), the workpieces (14) are transported in a horizontal plane (XY) by an endlessly circulating product transport system (2) on essentially vertically standing transport elements (3), the transport elements (3) moving through the processing zones (23a, 23b) at a constant speed, the workpiece (14) is welded in the processing area (23a, 23b) by at least two welding lasers (22, 22a, 22b) operating simultaneously; A method according to claim 1, characterized in that the position of the workpiece (14) is calculated and at least two of the welding lasers (22, 22a, 22b) are controlled thereby.

9. 9. A method according to claim 8, characterized in that the workpiece (14) is guided in the processing area (23a, 23b) on a horizontal, straight line.

10. 9. A method according to claim 8, characterized in that the workpiece (14) is guided on a circular track (29) within the machining area (23a, 23b).

11. 11. The method according to any one of claims 8 to 10, characterized in that an overlap (24) of the welded areas is achieved by the arrangement of at least two welding lasers (22, 22a, 22b).

12. 11. Use of the method according to any one of claims 8 to 10 for the manufacture of bipolar plates for fuel cells or heat exchanger plates for the transfer of thermal energy.

Images