Method for producing a combination of expanded metal meshes, stack of expanded metal meshes, and portal machine

Abstract

The invention relates to a method for metallurgically bonding multiple metallic layers (10, 10', 10'', ...) over a large surface, in which method a capacitor discharge welding process is used in which several capacitors are used that are discharged one after the other, at least two pulses (V, H, N) being used, the at least two pulses (V, H, N) differing by at least 10% at least in terms of energy density in J / mm².

Description

[0001] Method for producing a composite of expanded metal mesh, stack of expanded metal mesh and gantry machine

[0002] The invention relates to a method for producing a composite of expanded metal grids, which are used in particular in electrolysis, a stack of expanded metal grids and a gantry machine.

[0003] For a PEM electrolysis cell, fine-pored and graduated structures are required for surface contact of the electrodes.

[0004] This is done using sintered structures that are complex to produce and therefore very expensive (see also EP 3 625 379 A1).

[0005] Recent developments rely on alternative graded structures such as interconnected expanded metal layers. Such expanded metal layers are known, among others, from EA 010551 B1, EP 0 204 126 A1, or EP 3 625 379 A1.

[0006] The connection is made using a so-called capacitor discharge welding process under inert gas. Such a process and system are known from EP 1 852 207 A2.

[0007] This process uses a capacitor discharge welding process, which is created by discharging a capacitor. This generates a welding pulse.

[0008] If you want to weld with more energy, the loading level of this pulse must be increased significantly.

[0009] However, the problem is the formation of so-called welding spatter due to the sudden heating of the atmosphere around the welding point and the resulting discharge of liquid metal, especially when processing stainless steel.

[0010] In addition, the standard use of a so-called C-arm machine limits the size of the welding stamp (welding electrodes), which makes many welds in the x and y directions necessary over large areas and promotes the formation of spatter due to the introduction of a one-sided magnetic field.

[0011] Furthermore, the flatness of the expanded metal mesh is relevant to the quality of the PEM electrolysis cell.

[0012] It is therefore an object of the invention to solve the above-mentioned problems.

[0013] The object is achieved by a method according to claim 1, a stack according to claim 17 and a gantry machine according to claim 18.

[0014] The subclaims list further advantageous measures which can be combined as desired to achieve further advantages.

[0015] It shows

[0016] Figure 1 shows a schematic plan view of an arrangement during welding,

[0017] Figure 2 shows an arrangement of expanded metal mesh,

[0018] Figure 3 shows an exemplary time course of pulses used,

[0019] Figure 4 is a detailed view of an expanded metal mesh.

[0020] The figures and the description represent only exemplary embodiments of the invention.

[0021] A new type of welding machine, a portal welding machine, which also contains several parallel-connected capacities / capacitors, which can be controlled one after the other in a time-controlled manner, significantly improves the KE welding process.

[0022] This ce welding process can be used to join both stainless steel and titanium structures. If a longer welding pulse is required, the energy of a capacitor does not necessarily need to be significantly increased, resulting in a more even heat input into the weld zone and reducing unwanted weld influence zones.

[0023] The welding die size has been significantly increased, which means that significantly fewer welds are required per joint.

[0024] It also enables a flow-through process that can therefore take place continuously.

[0025] Figure 1 schematically shows an arrangement 1 with a plan view of a stack 7 (or composite) of at least two or more expanded metal grids 10, 10', 10'', ... (Fig. 2) and electrodes 4.

[0026] The expanded metal mesh 10; 10', 10'', ... preferably has a rectangular shape and an aspect ratio of at least 1.2, in particular at least greater than 2.0.

[0027] Such a stack 7 of expanded metal mesh 10; 10', 10'', ... is introduced into the gantry welding machine and welded together there by means of stamps which represent the electrodes 4.

[0028] The electrodes 4 preferably also have a rectangular cross-section which is at least as long as the stack 7 or the expanded metal grids 10; 10', 10'', ... are wide, and preferably projects beyond them.

[0029] As a result, the stack 7 can be welded together in sections only along its longitudinal direction by the electrode 4.

[0030] The stack 7 and the electrodes 4 are only displaced relative to each other to connect the entire length of the stack 7, since the entire width of the stack 7 is covered by its stamping surface (or electrode surface). This temporal progression is indicated by the dashed line 4 ' (1st weld) to 4 '' (2nd weld).

[0031] Thus, improvements can be achieved with regard to the flatness of individual expanded metal grids 10, 10', 10'', ... and of the entire stack 7.

[0032] In addition, the welding pulse can be controlled by the presence of several capacities in such a way that spatter formation is almost avoided.

[0033] The arrangement of the control technology of the gantry machine generates two opposing magnetic fields, which means that no force is exerted on ferromagnetic particles and thus the formation of spatter can be massively reduced.

[0034] Such a capacitor discharge welding system has several capacitors that are used for discharging during welding.

[0035] The capacitors can be charged to different levels. This is made possible by controlling the portal machine.

[0036] The portal machine can also have several capacitors with different charging capacities.

[0037] The portal machine also has a control system that can charge and discharge the capacitors in different ways.

[0038] The following processing windows were identified as favorable:

[0039] - Multiple pulses with up to five pulses;

[0040] - Waiting time between pulses of up to 50ms.

[0041] In this case, a distinction must be made between at least one pre-pulse V and at least one main pulse H, as well as optionally subsequent post-pulses N. The pre-pulse V serves to activate the surfaces of the expanded metal 10, 10', 10'', ... to be joined and thus to reduce the spatter.

[0042] The at least one optional post-pulse N improves the joining zone with regard to the connection, thus making it possible to achieve good connections with reduced peak currents and thus very low spatter formation.

[0043] Prepulse

[0044] The purpose of the pre-pulse is to activate the surface to reduce weld spatter.

[0045] By selecting capacitors with a capacitance of preferably 25% ... 50% of the main pulse H or correspondingly different capacitor capacitances, extremely short current rise times can be achieved.

[0046] The energy per stamp area is 0.3...1.75J / mm 2 , especially 0.3...0.75 J / mm 2 for steel, especially for stainless steel, and 1.0 ... l.75J / mm 2 , especially 1.0 ... 1.3 J / mm 2 , for titanium (Ti) or for titanium alloys.

[0047] The ignition interval, i.e. the pulse pause, between pre-pulse V and main pulse H is selected so that they are electrically and thermally coupled.

[0048] The ignition intervals are preferably between 2ms ... 10ms.

[0049] Main pulse

[0050] The main pulse H is the first joining pulse.

[0051] The main pulse energy has an energy per area of ​​0.75 ... 3.25 J / mm 2 in particular 0.75 ... l.3J / mm 2 for steel, especially VA steel, and 2.0 ... 3.25J / mm 2 , especially 2.5 ... 3.25J / mm 2 , for titanium (Ti) or for titanium alloys.

[0052] The ignition interval between the main pulse H and the optional post-pulse N is chosen so that they are electrically and thermally coupled.

[0053] The ignition intervals are preferably between 10ms ... 30ms.

[0054] Afterpulse

[0055] By changing the resistances across the joining surface of the expanded metal mesh 10, 10', 10'', ... in conjunction with the sinking after the main pulse H, the post-pulse N is tuned and serves as a second joining pulse.

[0056] The necessity of applying the after-pulse N is to be selected depending on the materials of the expanded metal 10, 10', 10''.

[0057] By selecting capacitors with a capacity of 120% ... 190% for the main pulse H, the necessary welding energy is provided.

[0058] The post-pulse energy per stamp area is 1.1 ... 4.0 J / mm 2 , especially 1.1 ... 2.0 J / mm 2 , especially 1.1 ... 1.3 J / mm 2 , for steel, especially VA steel, and 2.2 ... 4.0J / mm 2 , especially 2.6 ... 4.0 J / mm 2 , for titanium (Ti) or titanium alloys.

[0059] Figure 3 shows an example of a waveform of 3 pulses V, H, N.

[0060] The energy content E or the used capacitance of the capacitor(s) is plotted on the y-axis against the time course t of the discharge on the x-axis.

[0061] The area under the curve is a measure of the energy input during welding. In this case, for example, this is a pre-pulse V, a main pulse H, and a post-pulse N.

[0062] It is clearly evident from the lower height of the maximum of the pre-pulse V compared to the main pulse H or the post-pulse N that the energy used in the pre-pulse V or the capacitance of the capacitor used is significantly lower.

[0063] The curves of the pulse patterns resemble a Weibull function with a steep rise to the maximum.

[0064] The distances between the maxima of the different and successive pulses V, H, N are also a measure of the distances between the firing of the different capacitors for the different pulses.

[0065] Relatively shortly after the pre-pulse V, the main pulse H is ignited, which has a significantly higher energy than the pre-pulse V and leads to the first welding of the metallic expanded metals 10, 10', 10'', ... to be joined.

[0066] The use of the afterpulse(s) N is not mandatory.

[0067] Not absolutely necessary, but carried out and recognizable here, is a larger distance between the afterpulse N and the main pulse H, whereby a measurably higher energy is used for the afterpulse N compared to the main pulse H.

[0068] The following configurations for the pulses V - H - N are possible: 1- 1- 0 1- 1- 1 1- 1-2 1-2- 1 1-2-2 . The following welding parameters are advantageous:

[0069] - Force 20kN ... 130kN,

[0070] - Total energy 28kJ ... 128kJ for steel (VA) and up to 350kJ for titanium or titanium alloys,

[0071] - Peak current 300kA ... 550kA.

[0072] The following welding parameters in relation to the electrode area are advantageous:

[0073] NN

[0074] - Force 0.5 - -..3.5 - -, mm 2 mm 2

[0075] NN in particular 0.5 - -...0.8 -, and / or mm 2 mm

[0076] - Total energy 0.7 .8, 75 mm 2 mm 2 in particular 3.4 — ...8.75 and / or mm 2 mm 2

[0077] - Peak current 7.5 .

[0078] Or in absolute values:

[0079] Press force of the punches (4) 20kN ... 130kN and / or

[0080] Total energy 28kJ ... 350kJ depending on material and / or

[0081] Peak current 300kA ... 550kA depending on material.

[0082] The electrodes 4 preferably have the following sizes of 50x500 ... 250x500mm, preferably 50x400 ... 100x400mm.

[0083] Figure 2 shows a cross-section through an arrangement 1 according to Figure 1.

[0084] The individual expanded metal mesh panels 10', 10'', 10'' can be seen. A mechanical prestress F is used during welding.

[0085] To create a stack 1, several expanded metal mesh panels 10, 10', 10'', etc. can be welded together at once, or added individually, in pairs, or multiple times to create thicker stacks. The main advantages are:

[0086] • Faster and more cost-efficient production possible through inline process.

[0087] • Avoidance of welding spatter through multiple pulse technology.

[0088] • Improvement of flatness through larger welding electrodes .

[0089] Figure 4 shows an exemplary top view of an expanded metal mesh 10.

[0090] The expanded metal 10 has a longitudinal direction 16.

[0091] The expanded metal mesh 10 has a plurality of through openings 13, which are preferably evenly distributed over the surface of the expanded metal mesh 10.

[0092] The openings 13 are preferably not round and have an aspect ratio of significantly greater than 1, i.e. at least 1.1, ie they are elongated and preferably extend in the direction of the longitudinal direction 16 of the expanded metal 10.

[0093] The openings 13 can be oval or elliptical.

[0094] Further cross-sections are conceivable.

[0095] The expanded metal grids 10' ... 10'' (Fig. 2) are preferably arranged one above the other in such a way that the longitudinal directions 19 of the respective openings 13 of the respective layers 10', 10'', ... of the expanded metal grids each run in the same direction.

Claims

Patent claims 1. A method for the large-area metallurgical joining of at least two metallic layers (10, 10', 10'', ...), in particular of several metallic layers (10, 10', 10", ...), very particularly of expanded metal mesh (10, 10', 10'', ...), in which a capacitor discharge welding method is used, in which several capacitors are used which are discharged one after the other, wherein at least two pulses (V, H, N) are used, in particular wherein at least one pre-pulse, at least one main pulse and optionally at least one post-pulse are used, wherein the at least two pulses (V, H, N) differ at least in energy density in J / mm 2 by at least 10%, in particular by at least 20%.

2. Method according to claim 1, in which the capacitors are discharged one after the other in the millisecond range, i.e. in the range from 1ms to 800ms, in particular from 1ms to 50ms.

3. Method according to one or both of claims 1 or 2, in which a total of at least three to five pulses (V, H, N) are used, in particular three pulses (V, H, N) are used, and the time intervals between the pulses (V, H, N) differ by at least 10%, in particular by at least 20%. Method according to one or more of claims 1, 2 or 3, wherein the waiting time between the pulses (V, H, N) is between 1 ms and 50 ms, in particular between 2 ms and 30 ms. Method according to one or more of claims 1, 2, 3 or 4, wherein no welding takes place during the at least one pre-pulse (V), wherein the at least one pre-pulse (V) has an energy per stamping surface of 0.3 ... 1.75 J / mm 2 where for steel, especially for VA steel, 0.3 ... 0.75J / mm 2 be used, where for titanium (Ti) or titanium alloys, 1.0 ... 1.75J / mm 2 , in particular 1.0 ... l.3J / mm 2, can be used. Method according to one or more of claims 1, 2, 3, 4 or 5, in which a first welding takes place during at least one main pulse (H), in which the at least one main pulse (H) has an energy per stamp area of ​​0.75 ... 3.25J / mm 2 where for steel, especially for VA steel, 0.75 ... l.3J / mm 2 be used, where for titanium (Ti) or titanium alloys, 2.0 ... 3.25J / mm 2 , especially 2.5 ... 3.25J / mm 2 , be used. Method according to one or more of claims 1, 2, 3, 4, 5 or 6, wherein the at least one pre-pulse (V) is characterized by the selection and discharge of capacitors with a capacity of 25% ... 50% of the main pulse (H) in order to realize an extremely short current rise time. Method according to one or more of claims 1, 2, 3, 4, 5, 6 or 7, wherein the post-pulse (N) is tuned based on the change in the resistances across the joining surface in conjunction with the sinking after the main pulse (H) and serves as a second joining pulse, wherein the at least one post-pulse (N) has an energy per stamping surface of 1.1 ... 4.0 J / mm 2 , whereby for steel, especially for VA steel, 1.1 ... 2 , 0 J / mm 2 in particular 1.1 ... 1.3 J / mm 2 , where for titanium (Ti) or titanium alloys, 2.2 ... 4 , 0 J / mm 2 , especially 2.6 ... 4.0 J / mm 2, can be used. Method according to one or more of the preceding claims, in which the necessary welding energy is made available for the at least one post-pulse (N) by selecting capacitors with a capacity of 120% ... 190% of the main pulse (H). . Method according to one or more of the preceding claims, in which the ignition interval between the pre-pulse (V) and the main pulse (H) is chosen so that they are electrically and thermally coupled. . Method according to one or more of the preceding claims, in which the ignition interval between the pre-pulse (V) and the main pulse (H) is 2 ms to 10 ms. . Method according to one or more of the preceding claims, in which the ignition interval between the main pulse (H) and the post-pulse (N) is 10 ms to 30 ms. . Method according to one or more of the preceding claims, in which the following welding parameters are used: Press force of the punches (4): 20 kN ... 130 kN and / or total energy 28 kJ ... 350 kJ depending on the material and / or peak current 300 kA ... 550 kA depending on the material. . Method according to one or more of the preceding claims, in which the welding electrodes (4) have a cross-section of (50-250)mm x (400-500)mm, preferably (50-250)mm x 500mm or (50-100)mm x 400mm. Method according to one or more of the preceding claims, in which the following welding parameters are used with respect to the electrode area: Power of the electrodes: 0.5 -3.5 -0 mm z mm z NN especially 0.5 — 7...0.8 — 7 mm z mm z and / or Total energy 0.7 -^...8.75 mm z mm z especially 3.4 and / or Peak current 7.5 — ^-...13.75 — mm z mm z 16. A method for carrying out a method according to one or more of the preceding claims, in which electrodes (4) are used which are at least as long as the width of the metallic layers to be welded, in particular the expanded metal mesh (10, 10 ', 10'', ...).

17. Stack (7) of expanded metal grids (10', 10", ...) welded together, preferably produced by a method according to one or more of the preceding claims, wherein each expanded metal grid (10' ... 10'' ') has through-openings (13), wherein each opening (13) has a longitudinal direction (19) which has an aspect ratio greater than 1.1, wherein the longitudinal directions (19) of the openings (13) of each expanded metal grid (10' ... 10'' ') run in the longitudinal directions (16) of the expanded metal grids (10, 10', 10'', ...).

18. Gantry machine for capacitor discharge welding processes, in particular for carrying out a process according to one or more of claims 1 to 16, which has a plurality of capacitors which can be used for discharging for welding.

19. A gantry machine according to claim 18, comprising a plurality of capacitors, wherein the capacitors have different charging capacities.

20. A gantry machine according to claim 18 or 19, which has a controller that can charge the capacitors differently.

Images