Patent Application
20240375215
The disclosed embodiments relate to a method for laser welding of flat steel plates, particular bipolar plates for fuel cells, in commercial vehicle manufacturing, or heat exchanger plates. They further relate to an application of the method for the production of bipolar plates or heat exchanger plates.
In the automotive industry, the trend is increasingly moving in the direction of reducing CO2 and using alternative drive systems as a result of finite oil reserves and the climate change. Cars and trucks are increasingly using electric motors with batteries as storage medium. However, other technologies such as fuel cells will also become established in the future, particularly in the truck sector. Bipolar plates (BPP) are main components of a fuel cell and therefore have a decisive influence on the manufacturing costs and efficiency of a fuel cell system. Due to several advantages in terms of manufacturability and material properties such as stability, low sheet thickness and a wide range of coating options, the metallic versions of bipolar plates are becoming the focus of research and development and are currently considered the preferred variant for future large-scale applications of fuel cells. A fuel cell system consists of a large number of individual cells, each with a BPP between the cells, for automotive applications typically with 300-400 bipolar plates. Due to the high number of BPPs per individual system, it can be assumed that the quantities required will quickly reach very large dimensions in the future, even under moderate scenarios. This challenge can also be seen as an enormous opportunity for BPP suppliers. However, this requires economical and high-performance production technology. In particular, the welding of the two bipolar plate halves to form a BPP is a key problem due to the large number of weld seams, the associated long welding times and the high demands on the weld seams combined with very difficult process conditions due to the thin materials. At present, this is still a significant obstacle to cost-efficient production.
BPPs as such are known from the state of the art. They usually consist of two bipolar plate halves that are joined together. These are usually embossed foils or formed sheets. The bipolar plate halves lie on top of each other and are usually laser-welded tightly around the edges and at the contact points. The laser produces several metres of weld seam and possibly additional spot welds. Resistance welding methods are also a known alternative. Here, welding devices are used, which often require the bipolar plate halves to be clamped several times in order to produce a seal contour and all the welding points. In order to be able to weld all sealing contours and points, the bipolar plate to be welded must be removed from the clamping device and re-inserted so that all areas of the BPP to be welded are accessible to the welding laser. In particular, circumferential sealing contours cause problems. If such surrounding sealing contours are produced with the laser in a single welding process, It may prove difficult to place additional clamping elements within the sealing contour to fix the bipolar plate halves within the surrounding welding contour. When re-clamping, there is a risk that the positioning will no longer match and welding points will be set in the wrong places. In addition, the entire bipolar plate production process can be significantly delayed by re-clamping the half-finished bipolar plate.
The patent specification DE102016200387 describes a device and a method for producing a bipolar plate in which the distortion of the component is comparatively low. Welding energy is applied to the BPP from above and below. The position in the room where this is done is not described.
WO2018149959 shows a clamping device with clamping levers. From the image and text it can be concluded that the orientation of the BPP is horizontal, i.e. the surface lies horizontally on a base.
GRÄBENER Maschinentechnik shows a complete production line for BPP on its homepage. Two welding systems are also shown in detail at https://www.graebener.com/en/cutting-and-welding. BPP are welded horizontally at standstill.
The company SITEC (HTTPS://WWW.SITEC-TECHNOLOGY.DE/) manufactures automated laser welding plants, whereby welding is also carried out during standstill and in a horizontal plane.
European patent specification EP3038789 describes a method for increasing cycle times and thus reducing production costs in the industrial production of welded sheet metal parts—in particular, tailored blanks for the automotive industry. The method is based on a transport system with flying optics and horizontal alignment of the workpiece during welding, and does not require any complex cooling of the hot weld seam or any means of holding the workpieces with high force on one side of the conveyor belt. This can greatly reduce the negative impact of the gap between blanks on the machine's cycle time. Overall, the method can reduce non-productive welding time.
However, in such a system with vertical movement, the return path cannot be used for manipulation unless access is gained from the underside of the machine.
US 6,639, 176 B1 describes a welding device in which metal sheets are welded together vertically to minimize the space required for the welding device.
The disadvantages of the aforementioned solutions are the high technical effort required to reliably clamp the components, for the removal of welding fumes and spatter from the system, large machine dimensions with high investment costs, and the overall low productivity of the entire system.
The inventive embodiments are thus based on the task of describing a method by which the above-mentioned disadvantages are eliminated.
The device for the method described here is based on a transport device that transports the workpieces to be welded in the horizontal plane, which greatly reduces the number of system parts required.
As the circulating conveyor belt moves in a horizontal plane, access is possible from both sides. This means that the steel plates (workpieces) are welded on one side and the steel plates are loaded and unloaded on the other side.
Respectively in between, the steel plates are fixed in place with clamping plates or the fixing is released again.
This generates the following advantages:
Another advantage is that the welding process takes place vertically, i.e. in perpendicular direction and approximately vertically to the transport direction. This means that welding spatter does not remain on the workpiece being processed, resulting in less contamination of the workpieces and the device.
In the disclosed preferred configuration, the workpiece is clamped only once and then welded, eliminating repeated clamping with the known problems of precise adjustment during welding of the workpiece and achieving a high level of overall accuracy during loading, welding, and unloading.
The embodiments significantly increase the number of produced parts per time unit while simultaneously reducing part costs.
Hence, the disclosure enables efficient and high-quality production overall.
The present invention is further explained in the following on the basis of example embodiments and referring to drawings. In the drawings,
The disclosed method for laser welding of workpieces 14 can proceed as follows:
In the loading zone 15, the folded-down folding lever 13 of the clamping device 8 is loaded with at least one workpiece 14 to be machined and the workpiece is fixed on the clamping plate B 10b, for example with the aid of magnetic forces. Thereby, the clamping plate B 10b rests on the folding lever 13. In the loading zone 16 of the welding device, the folding lever 13 is now turned about the swivelling axis 12 by approximately 90 degrees from the approximately horizontal to an approximately vertical position and the workpiece 14 to be welded and the clamping plate B 10b are fixed to the base plate 11 and to a clamping plate A (10a) which is attached to the base plate 11.
After this, the folding lever (13) without the clamping plate B 10b and the workpiece 14 is turned back by approximately 90 degrees from the vertical to an approximately horizontal position.
In the welding/cutting zone 17, the workpiece 14, which is clamped between the clamping plate A 10a and the clamping plate B 10b, is then welded by a welding laser. Then, in the unloading zone 18 of the welding device, the folding lever 13 is turned again about the swivelling axis 12 by approximately 90 degrees from the approximately horizontal to an approximately vertical position and then takes on the welded workpiece 19 and the clamping plate B 10b. The folding lever 13 with the welded workpiece 19 and the clamping plate B 10b is turned back from an approximately vertical position by 90 degrees to an approximately horizontal position.
The workpiece 14 and the clamping plate B 10b can be transferred and fixed in place using magnetic forces.
In the unloading zone 15, the welded workpiece 19 is then removed from the clamping plate B 10b and moved on to subsequent steps. The clamping plate B 10b always remains in the device.
| Number | Date | Country | Kind |
|---|---|---|---|
| A 50761/2021 | Sep 2021 | AT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/071320 | 7/29/2022 | WO |
