Method of manufacturing stamping tool having structure

Abstract

The invention relates to a method for producing a stamping tool having a structure, in particular a stamping tool for producing bipolar plates for fuel cells. The method comprises the steps of: defining a target geometry and an intermediate geometry for the structure; the workpiece is installed in a machine tool; machining the workpiece by a first type of machining based on the intermediate geometry to obtain an intermediate part; measuring the geometry of the machined intermediate part by a measuring device to obtain geometry data thereof; determining, by the processing unit, geometry deviation data representing a difference between the machined intermediate component geometry and the target geometry based on the geometry data and the target geometry; calculating, by the processing unit, a machining path based on the geometry deviation data; and selectively machining the structure of the intermediate component by a second type of machining according to the calculated machining path to eliminate the difference by removing material on the intermediate component to obtain a final component having the structure with the target geometry.

Description

Technical Field

[0001] The invention relates to a method for producing a punching tool having a structure. In addition, the invention relates to a system for producing a punching tool having a structure. Background Art

[0002] Currently, new energy sources are becoming increasingly important as they contribute to improving climate change. One of these new energy sources is based on proton exchange membrane (PEM) fuel cells. This technology is considered a promising technology for generating electricity for transportation systems such as electric transportation because it prevents environmental pollution and provides high energy density.

[0003] The bipolar plate is considered to be a key component of such fuel cells. It serves as a carrier plate for the two poles required for the fuel cell, namely the negatively charged anode plate carrying H2 and the positively charged cathode plate carrying O2. Different materials can be used for bipolar plates, such as graphite, composites and metals. Compared with the other two materials, metals have the advantages of being characterized by good electrical conductivity, high mechanical strength and low production cost. So far, many methods have been developed to manufacture metal bipolar plates. The known methods are: roll forming, hydroforming, rubber pad forming and stamping.

[0004] WO 2008 / 034818 discloses a device for producing bipolar plates for fuel cells. The device comprises a reactor, wherein a workpiece forms a first electrode and a tool forms a second electrode. The workpiece and the tool are connected in an electrically conductive manner via an electrolyte, and a potential difference is at least temporarily formed between the workpiece and the tool. The poles of the workpiece and the tool are reversible with respect to their mode of action as cathode or anode, for performing removal processes on the workpiece, generating structures on the surface of the workpiece, and for coating processes for applying a coating to the workpiece directly and continuously in the reactor.

[0005] However, developing a method suitable for large-scale production remains a challenge. Among these methods, the stamping process is a favorable process for many manufacturers due to its processing efficiency. For large-scale production, it is meaningful to find an effective method to produce bipolar plates with high quality. For the stamping process, it is crucial to have a stamping tool with very high precision and good surface finish.

[0006] Typically, punching tools are machined by machine tools. In particular, milling is used. This process has the advantages of high surface quality and high machining speed. However, the machining precision has limits. In particular, punching tools include a number of tiny structures. The precision of the tiny structures must be very high. Such precision is difficult to achieve by milling. Summary of the invention

[0007] The object of the present invention is to provide a method for producing a punching tool having a structure with high surface quality and high precision. In particular, the object is to provide a method for producing a punching tool having a structure with improved processing adequacy.

[0008] According to the invention, these objects are achieved by the features of the independent claims.Further advantageous embodiments can be derived from the dependent claims and the description.

[0009] The present invention is directed to a method for manufacturing a stamping tool having a structure, in particular a stamping tool for producing a bipolar plate for a fuel cell. The method comprises the following steps: defining a target geometry and an intermediate geometry for the structure, wherein the intermediate geometry defines the geometry of an intermediate component, the geometry of the intermediate component requiring further processing to reach the target geometry; installing a workpiece in a machine tool; processing the workpiece by a first type of processing based on the defined intermediate geometry to obtain the intermediate component; measuring the geometry of the processed intermediate component by a measuring device to obtain geometry data of the intermediate component; determining by a processing unit geometry deviation data representing the difference between the processed intermediate component geometry and the target geometry based on the measured geometry data and the defined target geometry data; calculating by the processing unit a processing path based on the determined geometry deviation data; and selectively processing the structure of the intermediate component by a second type of processing different from the first type of processing according to the calculated processing path to eliminate the difference between the processed intermediate component geometry and the target geometry by removing material on the intermediate component to obtain a final component having a structure with the target geometry.

[0010] Preferably, the first type of machining is milling and the second type of machining is laser ablation machining.

[0011] Alternatively, the first type of machining is electrical discharge machining, electrical discharge chemical etching or electrochemical etching.

[0012] The accuracy of the stamping tool, in particular the accuracy of the structures formed on the stamping tool, has a direct impact on the accuracy of the parts produced by stamping. Therefore, it is crucial to manufacture structures with high precision. However, if high precision is required, the processing time may increase. Combining different types of processing techniques can benefit from the advantages of both processing techniques to optimize the processing of such stamping tools. The milling process has the advantages of high surface quality and high processing speed, while the laser processing process is a very precise processing process. In addition, laser processing has certain limitations in terms of the geometry to be achieved, for example, it is difficult to process seams, grooves or cavities with straight side walls by a laser beam. The present invention provides a method for selectively processing different parts on a workpiece by different processing techniques to obtain a final component with a target geometry.

[0013] The intermediate component is not a final component, but a component that requires further processing. Therefore, the intermediate geometry is defined to be applied to the first type of processing. The purpose of the first type of processing is to achieve this intermediate geometry. In particular, the intermediate geometry is designed in such a way that sufficient material on the intermediate component is available for removal by the second type of processing.

[0014] In one variant, the milling process and the laser machining process are performed by the same machine tool. In particular, the measuring device is also integrated in the machine tool.

[0015] In another variant, the first type of machining (e.g., milling process) is performed by a first machine tool, and the second type of machining (e.g., laser machining) is performed by a second machine tool. In particular, a five-axis laser machining tool can be applied. EP 2301706 and EP 3047932 disclose such laser machining processes using a five-axis laser machine tool.

[0016] In an advantageous variant, only a part of the structure is machined by the second machine tool for laser machining in order to save machining time. Sometimes, not the complete structure, but only a specific part of the structure requires very high precision. Therefore, only this specific part is machined again by the second machine tool in order to achieve high precision. Therefore, a second machining tool is applied to selectively machine the structure. Selectively machining the structure by the second machine tool can further improve the quality of the produced component and at the same time save machining time.

[0017] In particular, the method further comprises inputting the measured geometric shape data into a processing unit, and calculating the machining path by the processing unit based on the measured geometric shape data and the target geometry of the structure. In addition, the measuring device can also measure the surface roughness to determine the surface quality.

[0018] The measuring device is configured to be able to measure the entire component of the machined intermediate component, in particular, the measuring device measures all positions of the entire component.

[0019] The processing unit is configured to determine a difference between a machined geometry and a target geometry of the machined intermediate component. The determined difference allows calculation of a machining path for machining of the second type.

[0020] The processing unit may be an external computer, or may be a control unit of the first machine tool or the second machine tool.

[0021] In some embodiments, the structure includes a plurality of recessed portions, each of which has two side walls and a bottom surface. In particular, the recessed portion may have a high aspect ratio or a low aspect ratio. Therefore, the recessed portion is one or more of the following: a hole, a groove, a pit. In addition, the groove is one or more of the following: a rectangular groove, a semicircular groove, a T-slot. The groove may have a straight path or a curved path. In some embodiments, the stamping tool is applied to manufacture a bipolar plate for a fuel cell. The structure of the stamping tool includes a plurality of grooves. The grooves may be divided into different groups according to their geometric shapes. The grooves in each group have the same geometry, and the grooves in different groups have different geometries, for example, different cross-sections or different sizes. Each groove has two side walls and a bottom surface. The cross-section of the groove may have various shapes, such as a rectangle, a semicircle, and a trapezoid.

[0022] In some variants, the cross section of the groove may vary along the longitudinal direction of the groove. In some variants, the depth of the groove may vary within a groove. In particular, the depth of the groove may vary along the longitudinal direction. Since the measuring device is configured to measure all positions of the intermediate component, the difference between the target geometry and the geometry of the intermediate component at all positions of the component can be accurately determined.

[0023] The method comprises the following steps: defining at least one target depth and at least one intermediate depth for each groove, wherein the intermediate depth is less than the target depth; machining a workpiece by a milling process performed by a first machine tool to obtain an intermediate component having a plurality of grooves with intermediate depths; measuring the machined intermediate component by a measuring device to obtain measured geometric shape data of the intermediate component; determining, by a processing unit, depth deviation data representing a difference between the machined intermediate component depth and the target depth based on the measured geometric shape data and the defined target geometry; and machining a bottom surface of the groove of the intermediate component by a laser machining process based on the determined depth deviation data to eliminate the difference between the machined intermediate component depth and the target depth by removing material on the bottom surface of the groove to obtain a final component having a structure with the target depth.

[0024] Bipolar plates made of metal for fuel cells have the advantage of very good electrical conductivity. However, the depth of the grooves on the stamping tool must be processed with high accuracy and high precision, because deviations in the depth of the grooves can lead to corrosion on the bipolar plates. The depth of the grooves should be accurately processed, because the cross-sections of all grooves should not vary too much, and in particular all grooves should have the same depth. In addition, the depth of each groove should be accurately processed to reach a defined depth. The milling process has a limit to the required accuracy, which is, for example, + / -1 μm. This disadvantage can be compensated by a laser machining process, which is known as a high-precision and high-precision machining process. However, in order to maintain the adequacy of the machining, only the grooves are machined by a laser machine tool for correction. Preferably, only the bottom surface of the groove is machined by a laser machining process to correct the depth of the groove of the machined intermediate component to reach the target depth. In this way, the machining time can be further optimized.

[0025] The measured depth data can be compared with the target depth and the deviation can be determined. The deviation defines the thickness of the material to be removed from the bottom surface. For laser ablation, the remaining material can be divided into several layers and the ablation can be performed layer by layer. If the bottom surface is too large to be processed at one position of the laser head, the bottom surface is divided into several so-called slices. To ablate an area defined in one slice, the laser head stays at the same position and the optical scanner moves the laser beam to ablate all positions within one slice. To process the next slice, the laser head is moved to another position.

[0026] If necessary, the laser head can be rotated during the processing of a slice in order to be able to ablate locations on the workpiece that would be difficult to reach if the laser head was not rotating.

[0027] In addition, the intermediate depth is smaller than the target depth so that there is certainly enough remaining material on the bottom surface of the groove for laser machining.The inventive stamping tool manufacturing method allows the production of cost-effective and corrosion-resistant bipolar plate stamping tools due to milling roughing and laser finishing.

[0028] After milling, the measurement is performed mechanically or optically. In particular, the measurement is performed by means of a coordinate measuring machine, a touch probe, a laser distance sensor, a laser time-of-flight sensor, a confocal sensor, an interferometer or optical coherence tomography in order to determine the geometrical data of the machined intermediate component. In particular, the groove depths of all grooves of the intermediate component are measured and stored.

[0029] The geometrical shape data of the intermediate component are obtained by measuring the intermediate component at all positions.

[0030] The difference between the geometry of the machined intermediate component and the target geometry is calculated based on the measured geometry data. The difference is corrected by applying a second type of machining to further remove material. An effective machining path can be calculated by a processing unit (e.g., a computer) and applied to control the machine tool to selectively remove material from the machined intermediate component.

[0031] In one variant, the measurement is performed during a machining pause by the first machine tool. If the measured depth reaches a defined intermediate depth, the machining process can be stopped. If the measured depth is less than the defined intermediate depth, the milling process can be continued. When the measurement is performed during a machining pause, it is preferred that the measuring device is integrated in the first machine tool, or that a tool changer can remove the cutting tool and install the machining device in the first machine tool for the measurement.

[0032] In another variant, the measurement is performed at the end of the milling process.

[0033] It is of considerable importance whether the measuring device is arranged outside the machine tool or integrated in the first machine tool or in the second machine tool.

[0034] In one variant, a plurality of measuring devices are provided and integrated in the first machine tool and in the second machine tool. For example, the first measuring device is integrated in the first machine tool and the second measuring device is integrated in the second machine tool. This provides greater flexibility for measuring and optimizing the machining process.

[0035] Typically, the workpiece is clamped by a clamping system on the machine table. The clamping system consists of a pallet and a chuck. The chuck is mounted on the machine table and the workpiece is mounted on the pallet. For ease of handling, the pallet with the intermediate component is automatically transferred from the first machine to the measuring device or the second machine after processing by the first machine. This saves time for removing and mounting the workpiece and ensures accurate positioning of the workpiece on the machine table.

[0036] One disadvantage of laser processing is that the laser beam has a certain width, so when the laser beam hits the bottom surface of the groove, the laser beam cannot reach all positions on the bottom surface, especially at the connecting edge of the side wall and the bottom surface. In order to avoid this disadvantage and ensure that the laser beam can reach the entire bottom surface of the groove, the machine table of the laser machine tool can be slightly tilted or rotated during processing. Usually, the laser beam scanning is performed by an optical scanner integrated in the processing head, so the machine table does not move during the laser scanning. However, by tilting and / or rotating the machine table during processing, the laser beam can reach more positions. Therefore, the second machine tool includes a machine table for mounting the intermediate component thereon, and during processing, the machine table is tilted or rotated. In a preferred variant, if the component is too large or too heavy, the laser head is tilted and rotated instead of the component.

[0037] Furthermore, the invention is directed to a system for machining a punching tool having a structure, the system comprising the following stages: a first machine tool configured to machine a workpiece by a milling process to obtain an intermediate component having a structure with a defined intermediate geometry; a measuring device configured to measure the intermediate component to obtain geometric data of the intermediate component; and a second machine tool configured to machine the structure of the intermediate component by a laser machining process based on the measured data to obtain a final component having a structure with a defined target geometry. In particular, the laser machining is a laser ablation process.

[0038] In one variant, the system includes a tool changer configured to replace a machining tool for milling installed in the first machine tool by the measuring device.

[0039] The present invention provides a system for manufacturing a punching tool for producing a plate, which allows for better precision in the production of groove geometry, thus highly improving the corrosion resistance of the metal plate produced by applying such a punching tool. In addition, the system allows both the feasibility of fuel cell engines and the cost-effective production of bipolar plates.

[0040] In one variant, a femtosecond laser is used for laser ablation. Due to the short pulse duration of this type of laser, the thermal effects caused by the laser beam can be reduced. Thus, the surface quality achieved by ablation can be optimized.

[0041] The application of laser ablation allows high precision of the target geometry, in particular high precision of the target depth. Compared with other machining processes that require machining tools, laser ablation processes are inherently less sensitive to inaccuracies in the machine axis. For example, in the milling process, inaccuracies in the axis are immediately reflected in the tool end points. Therefore, such inaccuracies in the tool end points lead to geometric inaccuracies in the machined component, in particular depth inaccuracies in the machined structure on the component. The laser ablation process does not require a machining tool. The laser beam is controlled by the optical axis to reach a defined position on the component. If the laser beam reaches the surface of the component within the so-called focus tolerance (i.e., for example, a range of + / -0.1 mm), the ablation is performed accurately as defined, without geometric inaccuracies caused by inaccuracies in the mechanical axis. This means that inaccuracies in the laser machine axis do not affect the overall accuracy of the ablation process. Compared with other machining processes such as milling, the target geometry can be achieved more accurately using the laser ablation process. Therefore, the laser beam correctly ablates the part that needs to be ablated with reference to the geometric measurement results.

[0042] Therefore, in a preferred variant, a milling process is applied as rough machining and laser ablation is applied as finishing machining to obtain the target geometry. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In the following, a more specific description of the present invention is further described. Embodiments are described and explained in detail with reference to the accompanying drawings, in which: Figure 1 illustrates a three-dimensional view of a stamping tool including a plurality of slots; Figure 2 Graphics Figure 1 The enlarged portion D shown in FIG. Figure 3 The diagram shows the cross-sections of several grooves; Figure 4 The figure shows a top view of several grooves; Figure 5 A cross section of the intermediate member is partially illustrated; Figure 6 partially illustrating a cross section of the final component; and Figure 7 A diagram illustrating the steps of the method. DETAILED DESCRIPTION

[0044] Figure 1 A three-dimensional view of a stamping tool 1 for manufacturing a bipolar plate for a fuel cell is shown. The stamping tool is a metal plate having dimensions of, for example, a length of 450 mm, a width of 150 mm and a height of 30 mm. It comprises a plurality of grooves 10 formed thereon. There are several groups of grooves having different shapes and sizes. In the subsequent description, only one group of grooves is explained to illustrate the application of the method of the present invention. However, the method can be applied to other groups of grooves, even if they have different shapes and sizes.

[0045] The set of grooves extend in parallel in the horizontal direction and have equal distances, such as Figure 2 As shown in Figure 2 yes Figure 1 An enlarged view of the portion D indicated in FIG.

[0046] Figure 3 is a cross-sectional view of a number of grooves of the group, and Figure 4 1 is a top view of several grooves of the group. The groove has a rectangular cross section with two side walls 12 and a bottom surface 11. Figure 3 As shown in FIG. 1 , the groove has a defined groove width W1, for example 1.25 mm. The surface between two grooves is called rib 20, and the distance between two grooves is called rib width. Figure 4 The groove also has a defined groove depth d, which is the distance between the top surface of the rib and the bottom surface of the groove. Figure 3A simplified example is shown. However, the grooves may have different depths. The depth within a groove may also vary. The ribs may have a curved surface. The bottom surface of the groove may also have a curved surface.

[0047] The examples shown here should not be understood as limiting the application of the method. The method can also be applied to the manufacture of other metal parts with structures that require high accuracy and precision. Such metal parts can be produced by combining milling with laser ablation.

[0048] Figure 5 and Figure 6 Depicts a cross section of a groove during different machining stages. The workpiece is arranged and mounted in a first machine tool for a milling process. It is also possible to first perform surface machining and / or grinding of the workpiece before the workpiece is milled. The first machine tool may be any machine tool capable of a milling process. The groove and the rib are milled to a defined intermediate depth d1. Alternatively, the first machine tool is a machine tool for grinding and milling.

[0049] Milling offers productivity for producing intermediate geometries, as well as very good surface quality on the surface, so the ribs will not be processed by laser machining. In particular, it can process straight walls and very good surfaces on the top rounded edges, which is very important for the stamping process. Therefore, the ribs, the upper corners of the grooves and the side walls are only processed by milling and not by laser machining.

[0050] Figure 5 The machined intermediate part is shown. The groove has two upper corners 13 and two lower corners 14 and a bottom surface 11. The depth of the groove of the machined intermediate part is not milled to reach the target depth, but only to reach an intermediate groove depth of d1. The intermediate groove depth is defined before machining and is less than the depth of the final part, which is defined as the target groove depth. Milling is performed in such a way that the final surface roughness of the ribs, the upper corners of the groove is achieved.

[0051] A measuring device is used to measure all positions of the intermediate component to calculate the difference between the intermediate depth d1 and the target depth df. The intermediate depth is calculated by comparing the position of the rib with the position of the bottom surface.

[0052] Figure 6 is an illustration of the final component. Compared to the intermediate component, the groove of the final component is machined by a second machine tool, namely a laser machine tool. A five-axis laser machine tool can be used. During this stage, the bottom surface of the groove is ablated by the laser beam to remove further material in order to reach the defined target depth of the groove. Figure 6 As shown in , the final part has a greater depth than the intermediate part, and the lower corner has a different shape caused by laser machining. However, the shape of the lower corner is not relevant for this application.

[0053] Figure 7 A flow chart of the method of the invention is shown. In a first step S1, a workpiece is milled by a first machine tool to obtain an intermediate component with a groove having an intermediate depth. In a second step S2, the intermediate component is measured by a measuring device. The measuring device can be arranged outside the machine tool or integrated in one of the first machine tool and the second machine tool. It is also quite important to integrate two measuring devices in both machine tools in order to be able to measure during machining. In a third step S3, the remaining depth is calculated by comparing the measured intermediate depth and the final depth. In a fourth step S4, the intermediate component is processed again by a laser machining machine tool to obtain a groove having a final depth. Reference numerals list 1. Punching tool 2 Workpiece 10 slots 11 Groove bottom surface 12 Slot side wall 13 Groove bottom corner 14 Groove upper corner 20 grooved ribs.

Claims

1. A method for producing a stamping tool (1) having a structure (10), in particular a stamping tool for producing a bipolar plate for a fuel cell, the method comprising the following steps: a. defining a target geometry and an intermediate geometry for the structure, wherein the intermediate geometry defines the geometry of an intermediate component, the geometry of the intermediate component requiring further processing to achieve the target geometry; b. Install the workpiece in the machine tool; c. machining the workpiece by a first type of machining based on the defined intermediate geometry to obtain the intermediate component; d. measuring the geometry of the processed intermediate component by a measuring device to obtain the geometry data of the processed intermediate component; e. determining, by a processing unit, geometry deviation data representing a difference between a machined intermediate component geometry and said target geometry based on said measured geometry data and said defined target geometry; f. calculating a machining path based on the determined geometric deviation data by the processing unit; and g. selectively machining the structure of the intermediate component by a second type of machining different from the first type of machining according to the calculated machining path, so as to eliminate the difference between the machined intermediate component geometry and the target geometry by removing material on the intermediate component, so as to obtain a final component having the structure with the target geometry.

2. The method according to claim 1, wherein: The first type of machining is milling and the second type of machining is laser ablation machining.

3. The method according to claim 1 or 2, wherein: The first type of machining is performed by a first machine tool and the second type of machining is performed by a second machine tool.

4. The method according to any one of claims 1 to 3, wherein: Machining the structure includes machining a plurality of recessed portions (10), each of the plurality of recessed portions (10) having two side walls and a bottom surface.

5. The method according to claim 4, wherein: Only the bottom surface of the recessed portion is processed by the second type of processing.

6. The method according to claim 4 or 5, wherein: Machining the structure includes machining a plurality of grooves (10).

7. The method according to claim 6, further comprising the steps of: a. defining at least one target depth (df) and at least one intermediate depth (d1) for each groove, wherein the intermediate depth is less than the target depth; b. machining the workpiece by a milling process performed by a first machine tool to obtain the intermediate component having the plurality of grooves having the intermediate depth; c. measuring the intermediate member by the measuring device to obtain the measured geometric data of the intermediate member; d. determining, by the processing unit, depth deviation data representing a difference between a machined intermediate component depth and the target depth based on the measured geometry data and the defined target geometry; and e. Based on the determined depth deviation data, processing the bottom surface of the groove of the intermediate component by laser processing to eliminate the difference between the processed intermediate component depth and the target depth by removing material on the bottom surface of the groove, thereby obtaining a final component having the structure with the target depth.

8. The method according to any one of claims 1 to 7, wherein: The measurement is performed mechanically or optically, in particular by a coordinate measuring machine.

9. The method according to any one of claims 1 to 8, wherein: The measurements are performed in a machining pause during machining of the first type or at the end of machining of the first type.

10. The method according to any one of claims 2 to 9, wherein: The measuring device is arranged outside the machine tool or integrated in the first machine tool or in the second machine tool. In particular, a plurality of measuring devices are integrated in the first machine tool and in the second machine tool.

11. The method according to any one of claims 2 to 10, wherein: The workpiece is clamped on a pallet and, after the milling process, the pallet with the intermediate component is automatically transferred from the first machine tool to the measuring device or to the second machine tool.

12. The method according to any one of claims 2 to 11, wherein: The second machine tool comprises a machine table for mounting the intermediate component thereon, and during machining, the machine table is tilted or rotated.

13. The method according to any one of claims 3 to 12, wherein: The second machine tool includes a machining head including a galvanometer for emitting a laser beam, and during machining, the machining head rotates.

14. A system for manufacturing a stamping tool having a structure, comprising: a. a first machine tool, said first machine tool being configured to machine a workpiece by a milling process to obtain an intermediate component having a structure with a defined intermediate geometry; b. a measuring device configured to measure the intermediate member to obtain geometric data of the intermediate member; and c. A second machine tool configured to machine the structure of the intermediate component by a laser machining process based on the measurement data to obtain a final component having the structure with a defined target geometry, in particular the laser machining is a laser ablation process.

15. The system of claim 14, wherein: The measuring device is removably integrated in the first machine tool or in the second machine tool.

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