Method for producing composite of expanded metal grids, expanded metal grid stack and gantry machine

Abstract

The invention relates to a method for metallurgically connecting a plurality of metal layers (10, 10 ', 10' ',...) over a large area, in which a capacitor discharge welding process is used, in which a plurality of successively discharged capacitors are used, in which at least two pulses (V, H, N) are used, in which the at least two pulses (V, H, N) differ by at least 10% at least in the energy density (in J / mm2).

Description

Technical Field

[0001] The invention relates to a method for producing a composite body of expanded metal grids, in particular for use in electrolysis, an expanded metal grid stack and a gantry machine. Background Art

[0002] For PEM electrolyzers, fine pores and hierarchical structures are required to achieve surface contact of electrodes.

[0003] This is achieved using sintered structures which are complex to produce and are therefore very expensive (see also EP 3625 379 A1).

[0004] More recent developments are based on alternative hierarchical structures, for example interconnected expanded metal grid layers, which are known in particular from EA 010551 B1, EP 0 204 126 A1 or EP 3 625 379 A1.

[0005] The connection is made under protective gas using the so-called KE (capacitor discharge) welding process. Such a method and such an apparatus are known from EP 1 852 207 A2.

[0006] This is a so-called capacitor discharge welding process, which is produced by discharging a capacitor. This generates a welding pulse. If welding is to be performed with more energy, the load level of this pulse must be significantly increased.

[0007] However, a particular problem when machining stainless steel is the formation of so-called weld spatter due to the sudden increase in temperature of the atmosphere around the weld point and the resulting expulsion of liquid metal.

[0008] Furthermore, since so-called C-arc machines are usually used, the size of the welding punch (welding electrode) is limited, which necessitates multiple welding over a large area in the x and y directions, and the introduction of a one-sided magnetic field promotes the formation of spatter.

[0009] In addition, the flatness of the expanded metal grid composite is closely related to the quality of the PEM electrolytic cell. Summary of the invention

[0010] Therefore, the object of the present invention is to solve the above-mentioned problems.

[0011] This object is achieved by a method according to claim 1 , a stacking according to claim 17 and a gantry machine according to claim 18 .

[0012] Further advantageous measures are listed in the dependent claims, which can be combined with one another as desired to achieve further advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a schematic plan view of the apparatus in welding;

[0014] Figure 2 An apparatus for expanding metal grating is shown;

[0015] Figure 3 An exemplary time course of the pulses used is shown;

[0016] Figure 4 is a detailed view of expanded metal grille. DETAILED DESCRIPTION

[0017] The drawings and description merely represent embodiments of the invention.

[0018] A new type of welding machine, a gantry welding machine, significantly improves the KE welding process. The gantry welding machine also includes multiple capacitors / capacitors connected in parallel, which can be controlled sequentially in a time-controlled manner.

[0019] Through this KE welding process, both stainless steel structures and titanium structures can be connected.

[0020] If longer welding pulses are required, the energy of the capacitor does not necessarily have to be increased significantly, which results in a more uniform heat input in the weld area and a reduction in undesirable weld affected zones.

[0021] The welding punch size is significantly increased, thereby significantly reducing the number of welds required per composite body.

[0022] Furthermore, a continuous process can be achieved, ie it can be carried out continuously.

[0023] Figure 1 The device 1 is schematically shown, which has a plan view of at least two or more expanded metal grids 10, 10', 10", ... ( Figure 2 ) and the electrode 4 constitute a stack 7 (or a complex).

[0024] The expanded metal grid 10 , 10 ′, 10 ″, . . . has a preferably rectangular shape and an aspect ratio of at least 1.2, in particular at least greater than 2.0.

[0025] Such a stack 7 of expanded metal grids 10 , 10 ′, 10 ″, . . . is introduced into a gantry welding machine and welded together there by means of a punch representing the electrode 4 .

[0026] The electrode 4 also preferably has a rectangular cross section which is at least as long as the width of the stack 7 or the expanded metal grid 10 , 10 ′, 10 ″, . . . and preferably exceeds this width.

[0027] As a result, the stack 7 can only be welded together in places in its longitudinal direction by the electrodes 4 .

[0028] The stack 7 and the electrode 4 are only moved relative to one another in order to connect the entire length of the stack 7 to one another, since the entire width of the stack 7 is covered by its punch surface (or electrode surface).

[0029] This time course is indicated by the process 4' (first welding) to 4" (second welding) shown by the dotted line.

[0030] As a result, it is possible to achieve an improved flatness of the individual expanded metal grids 10 , 10 ′, 10 ″, . . . and of the entire stack 7 .

[0031] Furthermore, due to the presence of a plurality of capacitors, the welding pulse can be controlled in such a way that the formation of spatter is virtually avoided.

[0032] The gantry machine's control technology generates two opposing magnetic fields, which do not exert forces on the ferromagnetic particles and thus significantly reduce the formation of spatter.

[0033] Such a device for capacitor discharge welding process has a plurality of capacitors which are discharged for welding.

[0034] The capacitors can be charged to different degrees. This is achieved by controlling the gantry machine. But the gantry machine can also have several capacitors with different charge capacities.

[0035] The gantry machine also has a controller that can charge and discharge these capacitors to varying degrees.

[0036] The following processing windows were identified as favorable:

[0037] - Multiple pulses, up to five pulses;

[0038] - The waiting time between pulses is at most 50ms.

[0039] Here, it is necessary to distinguish at least one pre-pulse V and at least one main pulse H and optionally a subsequent post-pulse N.

[0040] The front pulse V is used to activate the surface of the expanded metal grid 10, 10', 10", ... to be connected, thereby reducing splashing.

[0041] At least one optional post-pulse N improves the joint area of ​​the connection so that a good connection can be achieved while reducing the peak current and thus forming little spatter.

[0042] Prepulse

[0043] The task of the front pulse is to activate the surface in order to reduce weld spatter.

[0044] By selecting a capacitor with a capacitance which is preferably 25% ... 50% of the main pulse H or a correspondingly different capacitor capacitance, extremely short current rise times can be achieved.

[0045] For steel, especially VA steel, the energy per unit punch area is 0.3…1.75 J / mm 2 , especially 0.3…0.75J / mm 2 ; For titanium (Ti) or titanium alloy, the energy per unit punch area is 1.0…1.75 J / mm 2 , especially 1.0…1.3J / mm 2 .

[0046] The triggering interval between the pre-pulse V and the main pulse H, ie the pulse pause, is selected such that they are electrically and thermally coupled.

[0047] The trigger interval is preferably between 2ms...10ms.

[0048] Main pulse

[0049] The main pulse H is the first engaging pulse.

[0050] The energy per unit area of ​​the main pulse energy is 0.75…3.25 J / mm for steel, especially VA steel. 2 , especially 0.75…1.3J / mm 2 , for titanium (Ti) or titanium alloys: 2.0…3.25 J / mm 2 , especially 2.5…3.25J / mm 2 .

[0051] The triggering interval between the main pulse H and the optional afterpulse N is selected such that they are electrically and thermally coupled.

[0052] The trigger interval is preferably between 10ms...30ms.

[0053] After Pulse

[0054] The post pulse N is adjusted by changing the resistance on the joint surface of the expanded metal grid 10, 10', 10", ..., combined with the sink after the main pulse H, and is used as the second joint pulse.

[0055] Whether or not to use the post-pulse N is determined based on the material of the expanded metal grid 10, 10', 10".

[0056] By selecting a capacitor whose capacitance is 120% ... 190% of the main pulse H, the necessary welding energy is provided.

[0057] For steel, especially VA steel, the back pulse energy per unit punch area is 1.1…4.0 J / mm 2 , especially 1.1…2.0J / mm 2 , more particularly 1.1…1.3 J / mm 2 For titanium (Ti) or titanium alloy, the back pulse energy per unit punch area is 2.2…4.0 J / mm 2 , especially 2.6…4.0J / mm 2 .

[0058] Figure 3 An exemplary progression of 3 pulses V, H, N is shown.

[0059] The energy content E of the capacitor or the used capacitance is plotted on the y-axis, while the time course t of the discharge is plotted on the x-axis.

[0060] The area under the curve is a measure of the energy introduced during welding.

[0061] These are, for example, a front pulse V, a main pulse H and a rear pulse N.

[0062] From the lower height of the maximum value of the front pulse V compared to the main pulse H or the rear pulse N it can be clearly seen that the energy used in the front pulse V or the capacitor capacitance used is significantly lower.

[0063] The curve of the pulse process is similar to the Weibull function, with a sharp rise in the process to a maximum value.

[0064] The intervals between the maxima of different successive pulses V, H, N are also a measure of the intervals between the triggering of different capacitors of different pulses.

[0065] Shortly after the front pulse V, the main pulse H is triggered, which has a significantly higher energy than the front pulse V and leads to a first weld of the expanded metal grids 10, 10', 10", ... of the metals to be joined.

[0066] The use of one or more post-pulses N is not strictly necessary.

[0067] Although not absolutely necessary, it is achieved here and can be seen that the distance between the post-pulse N and the main pulse H is greater, with significantly higher energy being used for the post-pulse N than for the main pulse H.

[0068] The following arrangement of pulses V–H–N can be envisaged:

[0069] 1-1-0;

[0070] 1-1-1;

[0071] 1-1-2;

[0072] 1-2-1;

[0073] 1-2-2.

[0074] The following welding parameters are favorable:

[0075] -Force 20 kN…130 kN;

[0076] - Total energy for steel (VA) 28 kJ…128 kJ, up to 350 kJ for titanium or titanium alloys;

[0077] -Peak current is 300kA…550kA.

[0078] The following welding parameters related to the electrode area are favorable:

[0079] -Force 0.5N / mm 2 …3.5N / mm 2 , especially 0.5N / mm 2 …0.8N / mm 2 ; and / or

[0080] -Total energy is 0.7J / mm 2 …8.75J / mm 2 , especially 3.4J / mm 2 …8.75J / mm 2 ; and / or

[0081] - Peak current is 7.5A / mm 2 …13.75A / mm 2 .

[0082] Or in absolute value:

[0083] The pressure of the punch (4) is 20 kN ... 130 kN; and / or

[0084] Total energy 28 kJ…350 kJ, depending on the material; and / or

[0085] Depending on the material, the peak current is 300kA…550kA.

[0086] The electrode 4 preferably has the following dimensions: 50x500 . . . 250x500 mm, preferably 50x400 . . . 100x400 mm.

[0087] Figure 2 Shown according to Figure 1 A cross section of the device 1.

[0088] It can be seen that the individual expanded metal grids 10 , 10 ′, 10 ″ are subjected to a mechanical prestressing force F during welding.

[0089] To produce the stack 1 , a plurality of expanded metal grids 10 , 10 ′, 10 ″, . . . can be welded together at once or added individually, in pairs or multiple times to produce thicker stacks.

[0090] The main advantages are:

[0091] Faster and more cost-effective production is possible through in-line processes;

[0092] Avoid welding spatter through multi-pulse technology;

[0093] Improved flatness through larger welding electrodes.

[0094] Figure 4 is an exemplary plan view of the expanded metal grid 10 .

[0095] The expanded metal grid 10 has a longitudinal direction 16 .

[0096] The expanded metal grid 10 has a plurality of through openings 13 , which are preferably evenly distributed over the surface of the expanded metal grid 10 .

[0097] The opening 13 is preferably not circular and has an aspect ratio significantly greater than 1, ie at least 1.1, ie is longitudinally elongated and preferably extends in the longitudinal direction 16 of the expanded metal grid 10 .

[0098] The opening 13 may be elliptical or oval in shape.

[0099] Other cross sections are conceivable.

[0100] Expanded Metal Grating 10'...10" ( Figure 2 ) are preferably arranged one above the other so that the longitudinal directions 19 of the respective openings 13 of the respective layers 10 ′, 10 ″, . . . of the expanded metal grid extend in the same direction.

Claims

1. A method for metallurgically connecting at least two metal layers (10, 10', 10", ...), in particular a plurality of metal layers (10, 10', 10", ...), more particularly expanded metal grids (10, 10', 10", ...) over a large area, wherein: A capacitor discharge welding process is used, wherein a plurality of successively discharged capacitors are used, wherein at least two pulses (V, H, N) are used, in particular wherein at least one front pulse, at least one main pulse and optionally at least one rear pulse are used, wherein the at least two pulses (V, H, N) have at least a certain energy density (in J / mm 2 ) differ by at least 10%, in particular by at least 20%.

2. The method according to claim 1, wherein: The capacitors are discharged successively in the millisecond range, ie in the range from 1 ms to 800 ms, in particular from 1 ms to 50 ms.

3. The method according to one or both of claims 1 or 2, wherein: In total, at least three to five pulses (V, H, N) are used, in particular three pulses (V, H, N), and the time intervals between the pulses (V, H, N) differ by at least 10%, in particular by at least 20%.

4. The 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.

5. The method according to one or more of claims 1, 2, 3 or 4, wherein: No welding occurs during at least one pre-pulse (V), wherein the energy per unit area of ​​the punch of the at least one pre-pulse (V) is 0.3 ... 1.75 J / mm 2 , where for steel, especially VA steel, 0.3…0.75 J / mm 2 , where for titanium (Ti) or titanium alloy, 1.0…1.75 J / mm 2 , especially 1.0…1.3J / mm 2 .

6. The method according to one or more of claims 1, 2, 3, 4 or 5, wherein: A first welding occurs during at least one main pulse (H), wherein the energy per unit area of ​​the punch of the at least one main pulse (H) is 0.75 ... 3.25 J / mm 2 , where for steel, especially VA steel, 0.75…1.3 J / mm 2 , where for titanium (Ti) or titanium alloy, 2.0…3.25 J / mm 2 , especially 2.5…3.25J / mm 2 .

7. The 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 in that a capacitor having a capacitance of 25% ... 50% of the main pulse (H) is selected and discharged in order to achieve a very short current rise time.

8. The method according to one or more of claims 1, 2, 3, 4, 5, 6 or 7, wherein: Based on the resistance change on the bonding surface, combined with the sinking after the main pulse (H), the post pulse (N) is adjusted and used as a second bonding pulse, wherein the energy per unit punch area of ​​at least one post pulse (N) is 1.1 ... 4.0 J / mm 2 , where for steel, especially VA steel, 1.1…2.0 J / mm 2 , especially 1.1…1.3J / mm 2 , where for titanium (Ti) or titanium alloy, 2.2…4.0 J / mm 2 , especially 2.6…4.0J / mm 2 .

9. The method according to one or more of the preceding claims, wherein: By selecting a capacitor with a capacitance of 120% ... 190% of the capacitance of the main pulse (H), the necessary welding energy is provided for at least one of the post-pulses (N).

10. The method according to one or more of the preceding claims, wherein: The trigger interval between the pre-pulse (V) and the main pulse (H) is selected so that they are electrically and thermally coupled.

11. The method according to one or more of the preceding claims, wherein: The trigger interval between the pre-pulse (V) and the main pulse (H) is 2ms to 10ms.

12. The method according to one or more of the preceding claims, wherein: The trigger interval between the main pulse (H) and the after pulse (N) is 10ms to 30ms.

13. The method according to one or more of the preceding claims, wherein: The following welding parameters were used: The pressure of the punch (4) is 20 kN ... 130 kN; and / or Total energy 28kJ…350kJ, depending on the material; and / or Depending on the material, the peak current is 300kA…550kA.

14. The method according to one or more of the preceding claims, wherein: The cross-sectional area of ​​the welding electrode (4) is (50-250) mm x (400-500) mm, preferably (50-250) mm x 500 mm or (50-100) mm x 400 mm.

15. The method according to one or more of the preceding claims, wherein: The following welding parameters were used relative to the electrode area: Electrode force is 0.5N / mm 2 …3.5N / mm 2 , especially 0.5N / mm 2 …0.8N / mm 2 and / or, Total energy is 0.7J / mm 2 …8.75J / mm 2 , especially 3.4J / mm 2 …8.75J / mm 2 and / or, Peak current is 7.5A / mm 2 …13.75A / mm 2 .

16. Method for carrying out the method according to one or more of the preceding claims, wherein: Electrodes (4) are used, the length of which is at least as long as the width of the metal layers to be welded, in particular the expanded metal grid (10, 10', 10", . . .).

17. A stack (7) of expanded metal gratings (10', 10", ...) welded to one another, preferably produced by the method according to one or more of the preceding claims, wherein: Each expanded metal grille (10'...10'") has a through opening (13), wherein each opening (13) has a longitudinal direction (19), the opening having an aspect ratio greater than 1.1, wherein the longitudinal direction (19) of the opening (13) of each expanded metal grille (10'...10'") extends along the longitudinal direction (16) of the expanded metal grille (10, 10', 10", ...).

18. A gantry machine for a capacitor discharge welding process, in particular for carrying out the method according to one or more of claims 1 to 16, the gantry machine having a plurality of capacitors which can be used for discharging for welding.

19. The 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, having a controller capable of charging the capacitor to different degrees.

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