METHOD FOR WELDING WITH A MOBILE VACUUM CHAMBER

Description

[0001] The invention relates to a method for welding two joining partners along a joining gap arranged between them, wherein for welding an energy beam illuminates the joining gap through a mobile vacuum chamber, in particular over the entire depth of the joining gap, which is moved along the joining gap on the joining partners, in particular covering the joining gap in some areas, and in which a local vacuum is generated.

[0002] An energy beam is understood to be a beam of electromagnetic radiation or a beam of particles, e.g. electrons, which is suitable for depositing energy onto the joining partners at the point of impact in order to cause the joining partners to weld there. Such an energy beam is preferably a laser beam or an electron beam. For such a process, a mobile vacuum chamber can be used which comprises a chamber housing with a vacuum connection, which has an opening towards the surface of the joining partners to be welded, the edge of which opening can be placed in a sealed manner on the surface of the joining partner to be welded and which has a generation area or coupling area for an energy beam, e.g. a laser beam, opposite the opening. This coupling area for a laser beam or other electromagnetic beam can preferably have a window, e.g.Made of glass or another material permeable to the beam but impermeable to gas. If the energy beam is a particle beam, it can also be provided to generate the energy-carrying particles in a generation area within the vacuum chamber, in particular to accelerate them from there toward the aforementioned opening.

[0003] The vacuum connection is connected to a pump via a line to pump air and / or protective gas out of the vacuum chamber.

[0004] Methods and vacuum chambers of this type are known in the prior art, e.g., from publication DE 10 2019 107 887 A1 by the same applicant. Furthermore, a method according to the preamble of claim 1 is known from GB 2 568 696.

[0005] They are used to weld joining partners under vacuum conditions. A vacuum is created in the vacuum chamber relative to the surrounding area not covered by the vacuum chamber, allowing the welding to be performed under vacuum conditions.

[0006] With this method, even very large components that do not fit completely into a vacuum chamber can be welded under the effect of the negative pressure at the welding location, since the local area of ​​negative pressure generation surrounds the welding location and is moved along the joining gap as the welding progresses.

[0007] The problem with welding joining partners with a large thickness using a vacuum welding process with a mobile vacuum chamber, especially with joining partners with a thickness of more than 10 mm, is that the opposing end faces of the joining partners, between which the joining gap is formed, must be ground very precisely in one possible design so that the joining partners lie against each other with a so-called technical zero gap as the joining gap, because this is the only way to sufficiently prevent ambient air from being sucked through the joining gap into the areas below the vacuum chamber.

[0008] A technical zero gap is still required if no welding consumables can be introduced into the vacuum chamber. However, such a zero gap is complex to achieve when joining components with a large thickness, especially those exceeding 10 mm.

[0009] A technical zero gap is defined as a joint gap between the joining partners of less than 25 micrometers. Obviously, maintaining such a requirement is difficult, especially with large joining partner thicknesses, due in particular to the tolerances that occur under manufacturing conditions.

[0010] The aforementioned publication also fundamentally enables welding without a zero gap using welding consumables that are fed into the vacuum chamber through a preferably gas-tight feedthrough, which is illuminated by an energy beam, preferably a laser beam. The invention is preferably also carried out with a mobile vacuum chamber into which such welding consumables can be fed, but can also be used without welding consumables.

[0011] Without a zero gap, the problem arises that large air leaks occur through the joint gap. According to the aforementioned publication, these leaks are prevented by temporarily sealing the joint gap gas-tight in all surface areas prior to welding, except for a starting area, onto which the mobile vacuum chamber is placed and through which the joint gap is evacuated in its internal volume. These preparatory measures also prove to be very complex, especially with regard to the overall time required for welding.

[0012] It is therefore an object of the invention to provide a method for welding, preferably for laser welding, joining partners with a mobile vacuum chamber, which overcomes the aforementioned disadvantages, in particular with which even comparatively thick joining partners can be welded without complex preparatory measures on the joining partners.

[0013] According to the invention, this object is achieved in that the vacuum chamber illuminated by the energy beam, preferably a laser beam, forms a first vacuum chamber in which a vacuum with a first pressure level is generated during welding and in a second vacuum chamber adjacent to the first vacuum chamber, which partially covers the joining gap during welding, a vacuum with a second pressure level is generated, wherein the pressure levels in both vacuum chambers are equalized to one another using a pressure control system or the first pressure level is raised above the second pressure level.

[0014] Preferably, it can be provided that the second vacuum chamber directly adjoins the chamber wall of the first vacuum chamber, in particular both vacuum chambers have a common chamber wall.

[0015] For example, the second vacuum chamber can be arranged in advance of the first vacuum chamber in the welding direction, in particular covering the part of the joint gap that lies in front of the first vacuum chamber in the welding direction. The two vacuum chambers are arranged linearly one behind the other.

[0016] In a preferably possible embodiment, the second vacuum chamber can surround the first vacuum chamber at least in regions, preferably completely, in particular viewed in a plane in or parallel to the joining partner surface.

[0017] For example, the second vacuum chamber can be divided into several, in particular at least two, chamber regions in the circumferential direction around the first vacuum chamber, wherein the chamber regions are interconnected. All chamber regions thus collectively form the second vacuum chamber. The connections between the chamber regions, preferably between adjacent chamber regions, can be made by lines, preferably having a cross-section that is smaller than the cross-section of the connected chamber regions, particularly when viewed in a section transverse to the circumferential direction.

[0018] In this case, for example, an embodiment is possible in which the second vacuum chamber has a first and a second chamber region, between which the first vacuum chamber is arranged. The first and second chamber regions of the second vacuum chamber are fluidically connected by at least one line and have at least substantially the same pressure level. The first and second chamber regions are preferably located one behind the other with the first vacuum chamber on a line, in particular on a line which covers the joining gap. The first and second chamber regions of the second vacuum chamber and the first vacuum chamber are preferably located on this line with regard to their respective centers on the joining partner surface. The two chamber regions can therefore preferably surround the first vacuum chamber on diametrically opposite sides.

[0019] It can be provided that the first and the second chamber area of ​​the second vacuum chamber are the only chamber areas or that further chamber areas of this second vacuum chamber are arranged between the first and second chamber area of ​​the second vacuum chamber.

[0020] It can also be provided that the second vacuum chamber completely surrounds the first vacuum chamber, preferably with an at least substantially constant cross-section, in particular viewed in the plane of the wing partner surface.In this embodiment, the second vacuum chamber is preferably annular, wherein the annular inner wall of the second vacuum chamber can simultaneously form the annular outer wall of the first vacuum chamber.

[0021] The method according to the invention ensures, regardless of the specific chamber design, that the control either ensures that the negative pressure in both negative pressure chambers is the same or that the pressure in the second negative pressure chamber is lower than in the first negative pressure chamber.

[0022] Without a pressure difference between the chambers, there is no gas flow between the vacuum chambers across the joint gap. This creates a particularly calm melt pool.

[0023] If, however, a pressure difference exists, this is regulated according to the invention such that the pressure in the first, particularly inner, vacuum chamber, in which the welding process takes place, is greater than in the second vacuum chamber. Due to the supply of shielding gas through at least one shielding gas connection into the first vacuum chamber, at most the shielding gas flowing into the first vacuum chamber can flow from the first vacuum chamber into the second vacuum chamber through the joint gap. However, a flow of oxygen-containing ambient air from the second vacuum chamber into the first vacuum chamber is not possible due to the pressure conditions.

[0024] The invention therefore ensures that the melt bath created in the first vacuum chamber is always present in a protective gas atmosphere under negative pressure conditions.

[0025] The method according to the invention therefore eliminates the need to prepare the joining partners for the formation of a technical zero gap.

[0026] In particular, it is even advantageous to have a sufficiently large joint gap between the joining partners so that, at least when the pressure in the second vacuum chamber is lower than in the first, the resulting pressure equalization can generate a protective gas flow through the joint gap in the direction of the second vacuum chamber.

[0027] Preferably, the joint gap can be designed to be larger than a technical zero gap. A required or desired joint gap can be set before welding begins, and the joining partners can be secured, e.g., by welding them together.

[0028] It is therefore preferred that, according to the invention, the joining gap between the joining partners is formed by placing the joining partners against one another, with the distance between the opposing joining partners being outside the tolerances of a technical zero gap, in particular, the joining partners are arranged in an I-joint with unground edges. Thus, according to the invention, the preparatory measures for creating a technical zero gap can be eliminated.

[0029] In particular, the joining partners can be placed together to form a joining gap with the roughness of their surfaces defining the joining gap, which is provided by a conventional process for separating / cutting material, such as water jet cutting, laser beam cutting, plasma cutting, sawing, burning, etc.

[0030] Particularly preferably, joining partners with a thickness greater than 10 mm, preferably greater than 20 mm, more preferably greater than 30 mm, more preferably greater than 40 mm, more preferably greater than 50 mm, more preferably greater than 60 mm, even more preferably greater than 70 mm, even more preferably greater than 80 mm, preferably greater than 90 mm, and more preferably greater than 100 mm or even more can be welded together with significantly reduced effort compared to the prior art. More preferably, this can be done in a single welding pass.

[0031] However, particularly when the pressure in the two vacuum chambers is equal, welding can also be carried out when the joining partners are positioned with a technical zero gap to each other.

[0032] Preferably, the invention can provide that the difference between the pressure levels of both vacuum chambers is kept within a predetermined control range, in particular within 1 to 30 mbar, preferably 10 to 20 mbar.

[0033] This has the advantage that the pressure difference causes a shielding gas flow, particularly through the not yet welded joint gap area, which leads the laser beam in the welding direction, from the first vacuum chamber into the second vacuum chamber, but the volume flow is so low that the molten pool at the welding location is not negatively affected.

[0034] The invention can provide that the control system is configured such that, taking into account a system-specific control inaccuracy, the pressure level in the second vacuum chamber is always lower than that in the first vacuum chamber, or at most equal to it. This can be achieved, for example, by selecting a setpoint value for the pressure difference that is greater than the maximum possible control range.

[0035] The invention can preferably provide that, in order to adjust the relative position of the pressure levels to one another, the first pressure level is changed by technical control measures within the scope of the control, in particular depending on the actual negative pressure measured in both vacuum chambers. To record pressure measurements, both vacuum chambers can each comprise at least one pressure sensor, the measured value of which is made available to the control system.

[0036] The control can be achieved, for example, by changing the volume flow of the protective gas supplied to the first vacuum chamber and / or by changing the volume flow of the gas pumped out of the first vacuum chamber, in particular the protective gas. Respective changes can be made, for example, by controlling at least one valve, i.e., in particular, a valve in the at least one protective gas supply line that opens into the first vacuum chamber, and / or by controlling a valve in the pumping line, via which the first vacuum chamber is connected to a pump that pumps out the gas, in particular the protective gas.

[0037] Particularly advantageously, it can be provided that control can be achieved without changing the pump train used to evacuate the second vacuum chamber. The vacuum in the second vacuum chamber can therefore, for example, be uncontrolled, especially even if it varies, e.g., due to a variation in the joint gap width along the welding path.

[0038] However, it is also possible to regulate the negative pressure in the second negative pressure chamber to a specific target value and then to change the pump train for this purpose, e.g. by changing at least one valve cross-section in the pump train and / or the pump output.

[0039] It can generally be provided that the setpoint for regulating the pressure in the first vacuum chamber is determined directly by the actual vacuum in the second vacuum chamber, or the setpoint is determined depending on the actual vacuum in the second vacuum chamber, e.g., by adding the desired differential pressure value that should exist between the chambers. As mentioned above, this actual vacuum value in the second vacuum chamber can itself be subject to regulation or be unregulated.

[0040] Furthermore, it can preferably be provided that the welding parameters of the energy beam, preferably the laser beam or an electron beam, in particular the beam power, are changed depending on the first and / or second pressure level, i.e., the pressure in the first and / or second vacuum chamber. A variation in the joining gap along the welding path, which affects the respective pressure level, can thus be compensated.

[0041] The welding parameters preferably also include the welding speed and / or the beam power and / or the oscillation amplitude and / or frequency and / or the point of impact of a preferably supplied welding wire relative to the beam. This point is preferably selected such that approximately half of the wire is immersed in the molten pool, while the other half of the wire is fed directly into the energy beam, preferably a laser beam.

[0042] Although the desired pressure difference is maintained by the control system, the absolute pressure level of both vacuum chambers can vary along the welding path.

[0043] In an advantageous development, the invention can provide that, before the welding of the joining partners begins, the joining gap on the root-side surface of the joining partners is sealed. This prevents ambient air from entering the first vacuum chamber through the joining gap in the thickness direction of the joining partners.

[0044] Even more preferably, before the start of welding the joining partners, the joining gap can be closed in all surface areas of the joining partners in which the joining gap is open to the environment, with the exception of the surface areas on the side to be welded.

[0045] In the case of butted joining partners, where the joining gap is also open at the beginning and end of the joining gap, the invention can also provide for closing the joining gap at these end surfaces. For this purpose, for example, inlet and / or outlet plates can be used, which are sealed and attached to the end faces of the joining partners, e.g., by welding.

[0046] According to the invention, it can preferably be provided that the sealing of the joint gap with respect to the environment on the root side is locally destroyed again during the welding process, in particular replaced by the created weld seam. Therefore, any measures and sealing means can be used to effect the preferably gas-tight sealing, since the sealing means used for sealing can also evaporate under the action of the energy beam, preferably the laser on the root side. Preferably, the sealing means for sealing the joint gap is selected so that it can also become part of the weld seam.

[0047] A particularly preferred procedure provides for the at least one sealing means to be formed by a weld seam that is arranged to bridge the gap on the surfaces of the joining partners, in particular at least on the root side. Such a weld seam can be implemented, for example, by means of arc welding.

[0048] If the joining partners are arranged with a technical zero gap, arc welding can be performed without filler metal, for example, meaning that surface fusion, which closes the zero gap, is created solely by the action of the arc. In an arrangement without a technical zero gap, which is precisely the advantage of the process, arc welding can also be performed with the addition of a filler metal. The filler metal is preferably a metal alloy that can remain in the subsequent weld seam created under the vacuum chamber. In particular, it can be the same filler metal that is also used if the filler metal is added under the first vacuum chamber.

[0049] Alternatively, the invention can provide for a metal sheet strip or a metal foil to be arranged on the joining partner surfaces in a gap-bridging manner, in particular to be glued, soldered or welded to the surfaces, in order to close the joining gap on the root side, if necessary also on the front side at the inlet and / or outlet.

[0050] Alternatively, an adhesive tape can be applied, specifically glued, to bridge the gap between the surfaces of the joining partners. The only requirement for the adhesive tape is its sufficient gas-tightness. This can be achieved, for example, by a gas-tight lamination of the adhesive tape, such as a metal or plastic film lamination.

[0051] As mentioned at the beginning, the invention also allows welding of the joining partners under zero-gap conditions. However, it is an advantage of the invention that such a condition is not a prerequisite for the invention.

[0052] It can be provided that the joining partners lie against each other during welding with a joint gap that does not meet the requirements for a technical zero gap, in particular, the joint gap is at least locally, preferably everywhere along the joint gap, wider than 25 micrometers. In practice, even such a joint gap, when implementing the invention with a differential pressure between the chambers, allows for a better flow of the shielding gas from the first to the second vacuum chamber.

[0053] The invention can provide for setting the joining gap at least locally, preferably everywhere along the joining gap, to be greater than 25 micrometers, more preferably greater than 100 micrometers, more preferably greater than 1000 micrometers, more preferably greater than 2500 micrometers, even more preferably greater than 5000 micrometers.

[0054] In all possible embodiments, in particular in the case of a joining gap larger than a technical zero gap, the invention can provide that the energy beam, preferably a laser, is guided in a tumbling / oscillating or circling manner over the joining gap during welding, in particular thus repeatedly crossing the joining gap.

[0055] The invention can preferably provide for welding without filler material for joint gap widths of less than or equal to 500 micrometers / 0.5 mm. For joint gaps larger than 500 micrometers or 0.5 mm, welding is preferably carried out with filler material, which can be supplied by a welding wire.

[0056] Irrespective of the aforementioned limiting criterion, the invention can, in a preferred embodiment, provide for a welding wire to be fed into the molten zone of the energy beam / laser beam and / or into the energy beam / laser beam through a vacuum-tight passage in the wall of the first vacuum chamber. Thus, the invention also allows the use of a welding filler material of the welding wire in the molten zone.

[0057] The invention can provide for a vacuum-tight passage for a welding wire to be arranged in the chamber wall of the first vacuum chamber. Such a passage can, for example, have a guide sleeve with which a welding wire can be guided along a line that intersects the axis of the energy beam, in particular the optical axis of the laser beam, preferably in or below the opening plane / surface of the joining partner.

[0058] The invention can also provide, preferably in the case of electromagnetic energy beams, in particular laser beams, for the energy beam to be guided at least partially into a protective chamber, in particular a protective chamber arranged within the first vacuum chamber, which surrounds the energy beam and through which the protective gas flows. The electromagnetic energy beam can be coupled into the protective chamber, for example through an optical coupling element, for example a window or a transparent lens permeable to the energy beam, and can preferably leave the protective chamber through an opening to the first vacuum chamber opposite the coupling element in the beam direction. The opening thus also serves to allow the energy beam to pass from the protective chamber into the first vacuum chamber, in particular after which the energy beam passes through the first vacuum chamber in the direction of the joining partners.

[0059] It can be provided that the shielding gas introduced into the protective chamber forms a shielding gas flow that passes at least partially, if necessary completely, through the opening into the first vacuum chamber. In particular, a shielding gas inlet is arranged closer to the coupling element than to the opening of the protective clamp facing the first vacuum chamber.

[0060] Preferably, at least the shielding gas flow passing through the opening runs at least partially parallel to and in the direction of the energy beam. It can also be provided that a shielding gas flow is generated in the protective chamber which crosses the energy beam. For this purpose, for example, an outlet nozzle for shielding gas can be arranged such that it generates a shielding gas jet that crosses the energy beam. Opposite the outlet nozzle, an extraction opening can preferably be provided in order to extract at least part of the shielding gas directly from the protective chamber, whereas another part of the shielding gas is extracted from the first vacuum chamber after passing through the opening thereto. In particular, this portion of shielding gas passing through the opening effects the pressure regulation in the first vacuum chamber.

[0061] The protective gas flow in the protective chamber can protect the coupling element from particles flying from the first vacuum chamber, in particular from the location of the melt bath in its direction.

[0062] Embodiments of the invention are described below with reference to Figures 1 and 1a explained.

[0063] The figures show the application of the process for welding two flat sheet metal strips as joining partners 1 and 2. A joining gap 3 is arranged between these strips, which is larger than the conditions for a technical zero gap. The figures represent a sectional view in the vertical plane in which the joining gap 3 lies, i.e., looking into the joining gap. The welding direction is indicated by the arrow SR.

[0064] The joint gap can preferably be closed to the environment at least at the root W.

[0065] This is achieved, for example, with a sealant 5 that is applied to the underside / root-side surfaces of the joining partners 1 and 2, e.g., a weld seam or a gas-tight adhesive tape, to bridge the gap. A seal on the inlet-side and / or outlet-side end faces 1a, 2a and 1b, 2b can also be provided, but is not shown in this section.

[0066] The welding device has a first vacuum chamber 6, which is essentially formed by a pot-shaped or bell-shaped chamber wall 6a. This is placed in a sealed manner on the upper surface of the joining partners 1, 2, so that the first vacuum chamber 6 partially covers the joining gap 3, which is completely open on the side to be welded. The ring-shaped or frame-shaped chamber edge facing the surface of the joining partners 1, 2 has a seal 7, so that gas can only flow into or out of the first vacuum chamber 6 through the joining gap 3. The first vacuum chamber 6 is evacuated by a schematically visualized pump 9 through the vacuum connection 10 via the line 11 and the valve 12, so that a first pressure level prevails in the first vacuum chamber 6.

[0067] The welding device has a further second vacuum chamber 13, which, at least in the welding direction SR, leads directly to the chamber wall 6a of the first vacuum chamber 6, in particular here surrounding the first vacuum chamber 6 in a ring shape. The second vacuum chamber 13 shares a common, in particular here annular, chamber wall 6a with the first vacuum chamber 6. The second vacuum chamber 13 rests with its annular chamber walls on the surface of the joining partners 1, 2 via the seals 7 and 8. ^

[0068] In general, preferably in all possible designs, including those not shown here, the end faces of the chamber walls of the first and second vacuum chambers facing the surfaces of the joining partners are tightly seated on the joining partner surfaces via sealing elements.

[0069] By pumping the air out of the second vacuum chamber 13 through the vacuum connection 14 via the line 15 with the pump 16, a second pressure level is achieved in the second vacuum chamber 13. According to the invention, this second pressure level is lower than or exactly equal to the first pressure level in the first vacuum chamber 6.

[0070] This is achieved by regulating the pressure level in the first vacuum chamber 6, namely by varying the pumping cross-section in the line 11 by adjusting the valve 12 and / or by varying the volume flow of shielding gas with a valve 17 or pressure reducer 17 from a gas reservoir 18, which flows into the first vacuum chamber 6 via the shielding gas connection 16. A controller 23 can control the valves 12, 17, e.g., depending on the measured pressure in the second vacuum chamber 13.

[0071] The second pressure level can be unregulated or regulated.

[0072] For the control of the first pressure level, the actual pressure in the second vacuum chamber 13 can be detected with a pressure sensor 19 and from this the setpoint for the control of the first pressure level can be formed.

[0073] The invention ensures that, in a first possible embodiment, when the pressure in both vacuum chambers 6, 13 is regulated, there is no gas flow in the joint gap 3, even though an air flow 22 from the environment enters the second vacuum chamber 13.

[0074] In a second embodiment, with a regulated differential pressure between the vacuum chambers 6, 13, due to the higher pressure level in the first vacuum chamber 6, it can be achieved that protective gas from the first vacuum chamber 6 flows over the joining gap 3 via a protective gas flow 23 in the not yet welded area into the second vacuum chamber 13, whereby ambient air only reaches the second vacuum chamber 13 via the air flow 22.

[0075] In both cases, this prevents ambient air from entering the welding zone within the first vacuum chamber 6, which is generated by a laser beam 20 that enters the first vacuum chamber 6 through an entrance window 21 and illuminates the joining partners 1, 2 in the joining gap area on the side to be welded.

[0076] The figures also show a design in which the laser beam 20 is surrounded in the beam direction by a tube forming a protective chamber. On the beam inlet side, the tube is provided with the aforementioned entrance window 21, through which the laser beam 20 passes. On the beam outlet side, the tube opens into the first vacuum chamber 6 via an opening, is thus fluidically connected to it and thus also forms part of the first vacuum chamber 6.

[0077] The shielding gas inlet into the tube / protective chamber is positioned closer to the entrance window 21 than to the opening, resulting in a directed shielding gas flow through the tube in the direction of the laser beam 20 and parallel to it. Particles flying from the melt pool toward the exit window cannot contaminate it, as they are prevented from reaching the entrance window by the shielding gas flow.

[0078] The Figure 1adiffers from the Figure 1 only by showing the situation with an existing welding progress in which, with respect to the welding direction, the area of ​​the joining gap 3 lying behind the laser beam 20 has already been closed by welding.

[0079] Thus, gas can only flow between the two vacuum chambers 6 and 13 in an area of ​​the joining gap 3 located in front of the laser beam 20. For this reason, it is also possible to arrange a second vacuum chamber only in front of the first vacuum chamber in the welding direction, at least if the welding process is started on an inlet plate, so that the beginning of the joining gap lies below the first vacuum chamber and in front of the laser beam 20 in the welding direction SR.

Claims

1. Method for welding two parts to be joined (1, 2) along a joining gap (3) located between them, wherein, for the welding, an energy beam (20) illuminates the joining gap (3), in particular over the entire depth of the joining gap (3), through a mobile negative-pressure chamber (6) which is moved on the side to be welded on the parts to be joined (1, 2) along the joining gap (3) and in which a negative pressure is generated, wherein a. the negative-pressure chamber (6) illuminated by the energy beam (20) forms a first negative-pressure chamber (6) in which during welding a negative pressure with a first pressure level is generated, and b. in a second negative-pressure chamber (13) which adjoins the first negative-pressure chamber (6), in particular directly adjoins the chamber wall (6a) thereof, preferably so as to at least regionally, further preferably completely, surround the first negative-pressure chamber (6), and which during welding regionally covers the joining gap (3), a negative pressure with a second pressure level is generated, and characterized in that c. a pressure regulating system (23) is used to align the pressure levels in the two negative-pressure chambers (6, 13) with one another or to raise the first pressure level above the second pressure level.

2. Method according to Claim 1, characterized in that the difference between the pressure levels is kept within a predetermined regulating range, in particular within from 1 to 30 mbar, preferably 10 to 20 mbar.

3. Method according to either of the preceding claims, characterized in that, for setting the position of the pressure levels relative to one another, the first pressure level is changed by technical regulating measures, preferably by changing the volume flow of the protective gas fed into the first negative-pressure chamber (6) and / or by changing the volume flow of the gas pumped out of the first negative-pressure chamber (6), preferably by means of at least one adjustable valve (12, 17), in particular without changing the pump line (15, 16) with which the second negative-pressure chamber (13) is evacuated.

4. Method according to one of the preceding claims, characterized in that, in dependence on the first and / or second pressure level, the welding parameters of the energy beam (20), in particular the beam power, are changed.

5. Method according to one of the preceding claims, characterized in that, before the start of welding of the parts to be joined (1, 2), the joining gap (3) is closed on the root-side surface (W) of the parts to be joined (1, 2).

6. Method according to one of the preceding claims, characterized in that, before the start of welding of the parts to be joined, in all surface regions of the parts to be joined (1, 2) in which the joining gap (3) is open to the environment, with the exception of the surface regions on the side to be welded, the joining gap (3) is closed.

7. Method according to Claim 5 or 6, characterized in that, for closing the joining gap (3), at least one sealing means (5) which bridges the joining gap (3) is applied to the root-side surface (W) of the parts to be joined (1, 2), in particular if present also to the inlet-side and / or outlet-side surface (1a, 2a, 1b, 2b) of the parts to be joined (1, 2), the root-side surface (W) preferably being closed first.

8. Method according to Claim 7, characterized in that, as the at least one sealing means (5), a. at least one weld seam (5) is arranged on the surfaces of the parts to be joined so as to bridge the gap, in particular by means of arc welding, preferably with feeding of a welding filler, and / or b. a metal sheet strip (5) or a metal foil (5) is arranged on the surfaces of the parts to be joined so as to bridge the gap, in particular is adhesively bonded, soldered or welded to the surfaces, and / or c. an adhesive tape (5) is arranged, in particular glued, on the surfaces of the parts to be joined so as to bridge the gap.

9. Method according to one of the preceding claims, characterized in that the joining gap (3) between the parts to be joined (1, 2) is formed by placing the parts to be joined (1, 2) against one another, wherein the distance between the opposite parts to be joined (1, 2) lies outside the tolerances of a technical zero gap, in particular the parts to be joined (1, 2) are arranged relative to one another in a square butt joint with edges / end faces which are not polished and which preferably have cutting roughness.

10. Method according to one of the preceding claims, characterized in that parts to be joined (1, 2) having a thickness greater than 10 mm, preferably greater than 20 mm, further preferably greater than 30 mm, further preferably greater than 40 mm, further preferably greater than 50 mm, are welded to one another, in particular in a single welding pass.