Apparatus and method for welding under vacuum, with a constriction for generating a venturi effect

Description

[0001] The invention relates to a device and a method for welding under vacuum, see claims 1 and 14.

[0002] Metal welding can be performed in a variety of ways. Common methods include applying the energy required to melt the base materials via an arc, an electron beam, or a laser. This creates a molten weld pool, which, after solidification, joins the base materials together through the weld. Depending on the width of the welding gap, a filler material in the form of wire or powder may be added to ensure sufficient material for the joint.

[0003] It is also known to perform welding under a shielding gas to prevent oxidation or scaling of the material forming the weld. Welding under a shielding gas is particularly suitable when welding easily oxidized metals, such as light metals and especially aluminum.

[0004] In addition, vacuum welding is also known to prevent oxidation. Electron beam vacuum welding has been known for a very long time, namely since 1949. After lasers were developed in the 1960s and their performance was continuously improved, laser welding under vacuum also became possible.

[0005] From DE 10 2014 103635 it is known to protect the lens of a laser optic in a vacuum laser welding arrangement.

[0006] DE 10 2014 210838 A1 also discloses protection for the laser optics in a process in which welding takes place in a vacuum chamber.

[0007] Gas flows for protecting laser optics are known from EP 3 412 401 A1.

[0008] US 5,756,962 discloses a gas nozzle for protecting the optics during a laser welding process.

[0009] Electron beam welding is known from US 3,609,287, whereby a local vacuum is to be applied.

[0010] A vacuum head is known from 3,719,791 A.

[0011] DE 11 2013 004 531 T5 discloses a vacuum head for a welding process that is said to have a seal with varying degrees of elasticity. This is said to make it possible to achieve the necessary seal even with a comparably uneven weld bead by using a more elastic sealing section in the area of ​​the weld bead that can adapt better. To improve adaptation, the softer sealing section should be able to move into a recess while the remaining part of the seal is pressed against the workpiece. The disadvantage of this, however, is that such a seal is damaged too quickly by the hot weld bead, and the seal as a whole severely impedes the forward movement of the vacuum head.

[0012] From EP 2 130 636 A1 (disclosing the preamble of claim 1) a welding process with electron beam is known in which a local vacuum is to be applied.

[0013] The object of the invention is to provide a device with which welding can be carried out reliably and with less maintenance.

[0014] The problem is solved with the features of claim 1.

[0015] Advantageous further training is specified in the dependent claims.

[0016] Another task is to create a laser welding process with which aluminum and especially aluminum blocks can be reliably welded under vacuum.

[0017] The problem is solved with the features of claim 14.

[0018] Advantageous further training is specified in the dependent claims.

[0019] According to the invention, a welding device is provided with a welding head comprising a welding cover. The welding cover is bell-shaped or hood-shaped with a lower opening and a surrounding cover edge.

[0020] In the area of ​​the edge, where a weld would be, a recess is provided so that the cover does not sit on the weld.

[0021] To create a seal, the cover extends outward in the recess in a tunnel-like manner. At least one brush pack is present in the tunnel; multiple brush packs can also be used consecutively. In addition to or as an alternative to the brush packs, sealing lips, preferably made of thin metal or heat-resistant plastic, e.g., PTFE, can be provided. The sealing lips can also be arranged in slatted fashion. Brush packs and sealing lips or sealing slat packs can also be arranged alternately.

[0022] According to the invention, in order to keep the device compact, the negative pressure beneath the welding cover is generated by at least one Venturi nozzle being created in the wall of the hood in such a way that a gas flow is guided through a bore in the wall and is guided over a constriction at least at one point. In this area, a second bore is arranged transversely to the first bore, which extends from the interior of the cover to the Venturi nozzle, so that gas is sucked out of the hollow area beneath the cover using the Venturi effect. The wall of the hood can have several such arrangements distributed around the circumference. Furthermore, a bore can have several Venturi stages.

[0023] In an advantageous development, at least one bore extends into or even beyond the tunnel area, with at least one Venturi stage being present in the tunnel area in such a way that gas from the tunnel area, and in particular inflowing gas, is also extracted. For this purpose, at least one transverse bore extends from the interior of the tunnel to a Venturi stage. There may also be several bores and, accordingly, several Venturi stages. The transverse bores are arranged, for example, such that they always extend into a chamber-like cavity between two brushes or brush packs or sealing lips or lamella packs.

[0024] It has been found that the vacuum required is lower than initially assumed, so that extreme sealing as in the state of the art is not necessary; rather, a lower negative pressure is sufficient, but it is sufficient to maintain it evenly.

[0025] The device according to the invention and the method according to the invention are used in particular to weld thick-walled blocks of aluminum and in particular thick-walled chambers which are composed of several wall parts.

[0026] According to the invention, the chamber is assembled from the wall, floor, and ceiling sections, and the desired parts are then welded together. After the parts have been aligned, the chamber is placed under negative pressure. This has two advantages: firstly, the parts are secured together; secondly, the welding joint prevents gas from the interior from being sucked into the weld seam or the weld cover. This improves the weld quality and, secondly, ensures that the negative pressure under the cover can be better maintained.

[0027] The cover rests on the workpiece with the edge that defines the lower opening, whereby the edge can have a sliding coating or a corresponding attachment, e.g. made of PTFE or polyamide (nylon).

[0028] The invention thus relates to a device for welding under vacuum, comprising a bell- or hood-like welding cover with a circumferential side wall and a cavity delimited by the latter, wherein a circumferential free edge is provided with which the welding cover can be placed on a flat surface, so that the cavity (8) is closed off by the flat surface and the circumferential wall and optionally a ceiling wall, wherein in the circumferential side wall there is at least one arrangement with a bore with a connection area for a fluid supply and a fluid outlet, wherein in the bore there is a constriction for generating a Venturi effect and there is also a transverse bore from the cavity into the bore in order to suck gas out of the cavity through the transverse bore via the Venturi effect in order to generate a negative pressure.

[0029] A further development provides that a plurality of arrangements with the bore are provided in the circumferential side wall.

[0030] A further development provides that the plurality of arrangements are fed with fluid via an annular channel and the annular channel has one or more fluid supply areas.

[0031] A further development provides that the fluid outlets of the at least one arrangement open into a second annular channel in which the fluid is collected and discharged via one or more outlets.

[0032] A further development provides that in the area of ​​a planned weld seam, the circumferential side wall is extended outwards with a projection, wherein a passage tunnel for a weld seam is provided in the area of ​​a weld joint.

[0033] A further development provides that the passage tunnel has a width that is wide enough for a weld seam usually produced with a laser to pass through it.

[0034] A further development provides that a bore extends above the passage tunnel, wherein the bore extends above the passage tunnel parallel to the passage tunnel to the outside, so that the passage tunnel can be cooled with the fluid flowing through the bore.

[0035] A further development provides that one or more brush packs, in particular metallic brush packs, are provided within the passage tunnel, which extend the circumferential side wall and preferably terminate with the circumferential edge, so that they rest on a weld seam and are deflected by it and are guided along the weld seam when the welding cover moves.

[0036] A further development provides that, in addition to or instead of brush packs, lamellae or sealing lips made of a heat-resistant material, in particular a metal foil or a thin metal sheet or a heat-resistant plastic, such as PTFE, are present, wherein brush packs and lamellae or sealing lips are arranged alternately or successively.

[0037] A further development provides that in the area of ​​a tunnel ceiling of the passage tunnel, one or more transverse bores are provided opening into the bore, each with a cooperating Venturi constriction in order to extract gases flowing through the passage tunnel from the outside towards the cavity and at the same time to cool this area intensively.

[0038] A further development provides that for welding in the immediate vicinity of edges of workpieces to be welded, an automated covering device is provided, which is arranged on one or both sides of the welding cover, wherein the covering device has an automatically actuated extension block and which, when the welding cover reaches the edge, is pivoted towards the corresponding edge and held there while the welding cover slides over this extension block, wherein the extension block is automatically pivoted downwards by means of a guide structure or a guide slot the moment there is no longer a workpiece underneath it, wherein, for example, two control cams control the movement and an actuating element, for example a pneumatic or hydraulic cylinder, actuates the extension block, wherein the control cams,the actuating element and the extension block are arranged on a support structure, which in turn is arranged on the device.

[0039] A further development provides that in the area of ​​the circumferential side wall, slots are arranged downwards from the circumferential edge, which slots extend from the circumferential edge into the circumferential wall, wherein the slots or the slot, for example, describe a semicircular arc, so that the front half of the circumferential edge in the direction of movement is provided with a slot, wherein an adhesive cushion or seal, which can be extended in particular by inflation, is mounted in the slot, which cushion or seal lies against the side wall of the workpieces and adheres there, while the welding cover is moved with the circumferential side wall or the circumferential edge over the edge.

[0040] A further development provides that the welding cover is box-shaped or is arranged within a box-like arrangement, wherein the box-like arrangement has a passage opening for the laser beam on the underside, which opening is delimited by the circumferential edge, wherein the box-like arrangement has a flat bottom wall, wherein a displaceable plate is arranged in the flat bottom wall in a leading direction in the direction of movement and is flush with the bottom wall, which, when the opening delimited by the circumferential edge comes into the area of ​​the edge, can be moved with the corresponding edge flush over the opening, so that it is ensured that no vacuum leak occurs, wherein on the opposite side of the opening a passage groove is provided which is located in the bottom wall, so that a corresponding weld seam can be guided therein.A plate-like element is also guided in the passage groove, which is capable of protruding into the opening defined by the peripheral edge to ensure a vacuum seal in the area of ​​the edge when the welding process begins. The movable plate and the plate-like element are only moved in the area of ​​the edge and are otherwise located outside the peripheral edge to protect them from the welding heat.

[0041] In a further aspect, the invention relates to a method for welding under vacuum by means of a laser, wherein a device according to one of the preceding claims is guided along a welding joint between a first workpiece and a second workpiece and a laser beam melts the workpieces in the region of the welding joint and thus joins them together.

[0042] A further development provides for the holes of the device to be flowed through with a gas or a liquid.

[0043] A further development provides that the supplied liquid is absorbed and in particular discharged at the fluid outlet.

[0044] A further development provides that for welding hollow bodies, in particular made of aluminum, the hollow body is evacuated during the welding process to a desired negative pressure, so that the welding joint in the area of ​​the welding cover supports the negative pressure or no gas from the interior of the hollow body is drawn into the welding cover by the negative pressure in the welding cover.

[0045] A further development provides for a movable vacuum chamber to be carried below the welding cover on the other side of the welding joint in order to prevent gas from being introduced into the cavity by the welding joint and to ensure improved weld seam quality.

[0046] A further development provides that a block element is arranged in a form-fitting manner and flush with the edge on a common edge of the workpieces which must be passed over by the device for welding in order to secure the vacuum, so that the welding cover rests positively on all sides with the surrounding edge beyond the edge, so that the vacuum can be maintained.

[0047] A further development provides that the block element is arranged on the edge with appropriate clamping elements and / or laterally from the weld joint, for example

[0048] Dovetail guides are milled or arranged in another way and the block element is formed with corresponding dovetails so that the block element is arranged firmly, positively and finally on the edge.

[0049] A further development provides that after the weld seam is completed, the vacuum is also released by turning off the flow and the welding cover is removed and then the block element is moved by taking it out of the dovetail guides and inserting it into corresponding dovetail guides on the other side of the edge and then the welding process is started by putting the welding cover back on accordingly, pulling the vacuum and if necessary the welding cover also starts moving at a short distance from the edge and thus the laser starts welding.

[0050] A further development provides that the distances of the dovetail guides are arranged equally, so that the block element preferably has dovetails on one side which correspond to the one distance of the dovetail guides on one side of the edge, wherein the other side of the edge has dovetails at a different distance, so that the dovetail guides of the edges are not at the same height.

[0051] A further development provides that the dovetail guides have the same distance but are offset by a certain amount on the respective sides of the edge, whereby the block element is then selected to be large enough that even with such an offset, the welding cover is reliably covered from below with the block element.

[0052] A further development provides for the dovetail guides in the workpieces to be closed with fitting pieces after welding has been completed.

[0053] The invention is explained by way of example with reference to a drawing. It shows: Figure 1: highly schematic representation of an embodiment of the device; Figure 2: the device according to Figure 1 highly schematic in a corner area of ​​a workpiece; Figure 3: a possible embodiment of a pivotable attachment for corner welding on the device according to the invention; Figure 4: an embodiment for corner welding with a movable inflatable seal; Figure 5: highly schematic of the device in a perspective view from below with movable panels; Figure 6: schematic of the device in a cross-section, showing a passage tunnel for a weld seam; Figure 7: the device according to Figure 6in a longitudinal section seen from the side; Figure 8: the device according to Figure 6 and Figure 7 in a view of the tunnel for the weld seam; Figure 9: highly schematic of the device with another vacuum chamber on the other side of the weld seam or weld joint.

[0054] State-of-the-art vacuum solutions for beam welding, such as electron beam welding or laser beam welding, primarily concern relatively large devices used to weld "endless" seams, such as pipes longitudinally or transversely. Especially with relatively thick-walled aluminum structures, it is necessary to achieve a very high penetration depth. Furthermore, these areas may have relatively complex shapes, necessitating adaptability of the welding device, particularly at corners. For example, when two square or rectangular blocks are welded together with a circumferential weld, the vacuum cannot usually be maintained in the area of ​​the edges.

[0055] Fundamentally, creating a vacuum requires that more gas, particularly air, be evacuated from a confined space than can flow in from the outside. In fixtures of the aforementioned type, the fixture rests on two usually flat surfaces belonging to the blocks that are to be welded together. Any ingress or inflow of air from the outside can generally occur below the seating edge of the fixture (although here it is very small) in the area of ​​the weld joint, but especially in the area of ​​the finished weld seam, as this usually protrudes beyond the blocks and is also uneven. A high evacuation rate is therefore essential. This is usually achieved by using a vacuum pump with a large capacity and keeping the evacuation rate as high as possible.The extraction rate can be increased, for example, by making the extraction line cross-section very large, which in turn makes the device larger and more cumbersome. However, particularly with large and complex components that need to be welded, this in turn means that the evacuation is not as good as it should be and therefore the achieved vacuum cannot be as great as the extraction performance would promise. In particular, if the extraction lines are relatively long due to complex components and the complex routing of such a device, the extraction performance is reduced relatively significantly. The effective air extraction performance of a pump can decrease by a factor of 10 due to a 2 m long extraction line with a relatively small diameter.

[0056] According to the invention, this is circumvented by generating the vacuum in the immediate vicinity of the bell- or hood-like covering device, or even within it. Accordingly, the device for generating the vacuum, i.e., a vacuum pump or a correspondingly designed device, is guided together with the shielding device over the workpieces along the planned weld seam.

[0057] Although there are numerous suitable vacuum pump types, the invention preferably utilizes the Venturi principle, in which the Venturi effect is realized within a gas flow line in the wall of the shielding device. A plurality of flow lines can also be implemented using the Venturi principle.

[0058] The inventive principle of utilizing the Venturi effect in the walls has a number of advantages. On the one hand, the structure is relatively simple, and on the other hand, such a Venturi nozzle arrangement is also very robust when used in the dirt-prone environment of a weld. A further decisive advantage, however, is that the provision of at least one, but preferably several, corresponding lines in the wall of the covering or shielding device, i.e., the bell- or hood-like element under which the vacuum is created, ensures that this device is cooled. Relatively large gas flows can be realized in this way, thus creating a good cooling effect and, moreover, very effectively evacuating air, including incoming air, from the area beneath the cover.

[0059] In Figure 1The device 1 according to the invention is shown in a highly schematic manner, wherein the device 1 has the shielding device 2, wherein the shielding device 2 is designed in a hood-like or bell-shaped manner, with a circumferential side wall 3 and a top wall 4, wherein the circumferential side wall 3 has a free circumferential edge opposite the top wall 4, with which the device 2 stands on a first workpiece 6 and a second workpiece 7. The circumferential side wall 3 and the top wall 4 of the welding cover 2 as well as the first workpiece 6 and the second workpiece 7 thus delimit a cavity 8 of the welding cover 2 during operation.

[0060] In the ceiling wall 4 there is an opening 9, which is optionally covered on the outside with a laser glass 10 to allow a laser beam 11 to pass through, the laser beam 11 being optionally generated by a laser generator which is arranged on the welding cover 2 (not shown).

[0061] A bore 12 is arranged in the circumferential side wall 3, extending from the top wall 4 toward the circumferential edge 5. The bore 12 runs parallel to the longitudinal extent of the circumferential side wall 3. The bore 12 has at least one constriction 13 as a Venturi stage, but can also have a plurality of constrictions 13 along its length. In the area of ​​the constriction 13, a transverse bore 14 is provided from the cavity 8, which opens into the bore 12 in the area of ​​the constriction. On the upper side, in the area of ​​the top wall 4, the bore 12 has a fluid connection area 15 for receiving a fluid supply hose 16.

[0062] A fluid can be guided through the bore 12 through the fluid supply hose 16 in the direction indicated by the arrows 17, with a Venturi effect being induced in a known manner by the constriction 13. This Venturi effect draws gas or air out of the cavity 8 of the welding cover 2 through the transverse bore 14.

[0063] The bore 12 has a fluid outlet 18 which is directed outwards slightly away from the circumferential edge 5.

[0064] During operation, the welding cover 2 of the device 1 is guided so that the laser beam is directed onto the welding joint 19 between the first workpiece 6 and the second workpiece 7.

[0065] In a further development (not shown), a plurality of bores 12 are provided, wherein, for example, the bores 12 are supplied with fluid via an annular channel (not shown) in the top wall 4, wherein a corresponding fluid connection region 15 of the annular channel is correspondingly provided for receiving a fluid supply hose 16. With a plurality of bores 12, it is of course advantageous that gas can be extracted at several points on the circumference of the circumferential side wall 3 via the correspondingly multiple transverse bores 14. In addition, the cooling effect is improved by the fluid which is guided through the bores 12, so that the entire welding cover 2 can be cooled more effectively.

[0066] In the Figures 6, 7 and 8schematic cross sections through a device according to the invention, in particular the welding cover, are shown, whereby some details, such as the opening in the ceiling wall, have been omitted for reasons of clarity.

[0067] Figure 6 shows a cross-section above the workpieces 6, 7, wherein it can be seen that in the area of ​​a planned weld seam, i.e. the weld joint, which in this figure corresponds to the section line CC, trailing a laser beam or the direction of movement of the welding cover 2, which also corresponds to the arrows B, the circumferential side wall 3 is formed with a projection 20 extended outwards. In the area of ​​a weld joint 19 ( Figure 8), a passage tunnel 21 for a weld seam (not shown) is provided below a gas outlet 18. The passage tunnel 21 has a width that is slightly less than the width of the projection 20, but is wide enough for a weld seam, usually produced with a laser, to pass through it.

[0068] Within the passage tunnel 21, a plurality of brush packs, in particular metallic brush packs (not shown), are preferably provided, which extend the circumferential side wall 3 and preferably terminate with the circumferential edge 5, so that they rest snugly on a weld seam and are deflected by it, guiding them along it during movement. Instead of brush packs, lamellae or sealing lips made of a heat-resistant material, in particular a metal foil or a thin metal sheet, or a heat-resistant plastic, such as PTFE, may also be provided.

[0069] An alternating arrangement of brush pack(s) and sealing lip(s) is also conceivable within the scope of the invention. The one or more Venturi stages in the form of the constriction 13 and the transverse bore 14 are Figures 6, 7 and 8 not shown, but are of course present. Additionally, in the area of ​​the tunnel ceiling 22 of the passage tunnel 21, one or more transverse bores can be provided in the bore 12 with corresponding Venturi constrictions to extract gases flowing from the outside through the passage tunnel 21 to cavity 8 and simultaneously intensively cool this area.

[0070] In the embodiment according to the invention, in which at least one fluid-carrying bore 12 is present in the circumferential side wall 3, preferably a plurality of bores 12, it is advantageous that a negative pressure can be built up and maintained in the cavity 8 in a simple but reliable manner and, moreover, good cooling of the entire device is possible. The bores 12 can be supplied with a gas as the fluid. In cases in which the welding cover 2 is particularly small and therefore heats up considerably, it is also conceivable to flow a coolant as the fluid through the bores, which likewise brings about the Venturi effect and a water flow vacuum pump effect because the cooling may be even more intensive. In this case, the escaping coolant is collected and recirculated.

[0071] A particular problem when welding square or rectangular blocks, in particular, is that the weld coverage near corners will always be larger than the diameter of the laser beam. Therefore, beyond a certain distance from the edge, the cavity 8 would protrude beyond the workpieces to be welded, making it impossible to maintain the vacuum. Known devices from the prior art are not suitable for this problem, as they only deal with "endless" weld seams.

[0072] However, maintaining the vacuum even beyond an edge is essential for good weld quality.

[0073] The method according to the invention provides for a block element 24 to be arranged on an edge in a form-fitting manner and flush with the edge, so that the welding cover 2 rests positively on all sides with the circumferential edge 5 beyond the edge, so that the vacuum can be maintained. Such a block element 24 can be arranged on the edge with appropriate clamping elements. Furthermore, it is possible to mill dovetail guides, for example, laterally from the weld joint and to form the block element 24 with appropriate dovetails, so that the block element is arranged firmly in a form-fitting manner and flush with the edge. Another advantage here is that the dovetail arrangement ensures that the blocks to be welded are particularly well fixed to one another.After the weld seam is completed, where necessary to avoid welding the block element to the workpieces, a small distance from the edge is maintained, the welding process is stopped, the vacuum is also released by turning off the flow and the welding cover 2 is removed. The block element 24 is then moved by removing it from the dovetail guides and inserting it into corresponding dovetail guides on the other edge. The welding process is then started by replacing the welding cover accordingly, pulling the vacuum and, if necessary, also moving the welding cover at a small distance from the edge and thus the laser begins welding.The short distance from the edge at which the welding is started or stopped is unproblematic, as the welding of such blocks involves very deep welds, ensuring sufficient overlap. If necessary, these very small areas, which are not particularly deep due to the 90° offset of the welds, can be rewelded by hand.

[0074] The distances between the dovetail guides are preferably always the same, so that the block element 24 preferably has dovetails on one side which correspond to one distance of one edge, the other edge having dovetails at a different distance, so that the dovetail guides of the edges are not at the same height.

[0075] The dovetail guides can also have the same distance but be offset by a certain amount, in which case the block element 24 is selected to be so large that even with such an offset the welding cover 2 is reliably covered from below with the block element 24.

[0076] In a further embodiment of the device or a further embodiment of the method, an automated device is used which is arranged on one or both sides of the welding cover 2.

[0077] This covering device 25 has an automatically actuated extension block. When the welding cover 2 reaches the corner, it is pivoted towards the corresponding edge and held there while the welding cover 2 slides over this extension block 26. The extension block 26 is automatically pivoted downwards by means of a guide structure or a guide slot at the moment when there is no longer any workpiece 6, 7 underneath it. Two slots, for example, control the movement and an actuating element, for example a pneumatic or hydraulic cylinder 27, actuates the extension block 26. Control cams 27 of the actuating element 28 and the extension block 26 are preferably arranged on a support structure 29, which in turn is arranged on the device 1. In a further advantageous embodiment ( Figure 4) slots 30 are arranged in the area of ​​the circumferential side wall 3 at the bottom, wherein the slots or the slot, for example, describes the semicircular arc, so that the front half of the circumferential edge is provided with a slot.

[0078] In the slot rests an extendable and adhesive cushion 31, which is particularly extendable by inflation and which lies against the side wall of the workpieces 6, 7 and adheres there, while the welding cover 2 with the circumferential side wall 3 or the circumferential edge 5 is moved beyond the edge.

[0079] The cushion 31 is designed in particular as an inflatable seal which is so elastic that it can adhere to the workpieces accordingly.

[0080] It is advantageous that the expansion of the cushion 31 or the inflatable seal 31 only occurs when the corresponding section of the peripheral edge 5 moves over the edge. The seal preferably moves inwards automatically ( Figure 4 Center), as this is the lowest energy state. Increased stiffness at the tip of the seal increases the tendency to move inward.

[0081] In a further advantageous embodiment ( Figure 5 ), the welding cover is designed to be somewhat larger, so that the welding cover as a whole is box-shaped or is arranged within a box-like arrangement 32.

[0082] The box-like arrangement has a passage opening for the laser beam on the underside, which is defined by the circumferential edge 5. Furthermore, the box-like arrangement has a flat bottom wall 33, wherein a movable plate is arranged in the flat bottom wall 33, advancing in the direction of movement, and is flush with the bottom wall 33. When the opening defined by the circumferential edge 5 comes into the region of the edge, the plate is moved over the opening with the corresponding edge, thus ensuring that no vacuum leak occurs. On the opposite side of the opening, a passage groove 35 is provided, which is located in the bottom wall 33, so that a corresponding weld seam can be guided therein.A plate-like element is also guided in the passage groove 35, which is capable of projecting into the opening defined by the peripheral edge 5 to ensure vacuum tightness in the area of ​​the edge when the welding process begins. The movable plate 34 and the plate-like element 36 are only displaced in the area of ​​the edge and are otherwise located outside the peripheral edge 5 to be protected from the welding heat.

[0083] In a further advantageous embodiment of the method, a movable vacuum chamber 38 is carried below the welding cover 2 on the other side of the welding joint in order to prevent gas from being introduced into the cavity 8 by the welding joint and to ensure improved weld seam quality.

[0084] The vacuum chamber 38 can be designed essentially like the welding cover 2 or slightly larger, wherein the vacuum is preferably generated according to the same principle.

[0085] In yet another advantageous embodiment, when blocks are welded which are later to be assembled to form a larger cavity, the cavity can already be assembled from the non-welded blocks, fixed to one another and then the entire cavity can be placed under vacuum, so that when welding from the outside, gas is sucked in through the possibly not entirely tight weld joints and in the area of ​​the weld cover the cavity 8 can be more easily subjected to vacuum and in addition the weld seam quality can be improved in this area by the gas being evacuated from the weld joint immediately before welding.

Claims

1. Device for welding under vacuum, having a bell- or hood-like welding cover (2) having a circumferential side wall (3) and a cavity (8) delimited by the latter, wherein a circumferential free edge (5) is provided, with which the welding cover (2) can be placed on a flat surface, so that the cavity (8) is surrounded by the flat surface and the circumferential wall (3) and, optionally, a ceiling wall (4), characterized in that in the circumferential side wall there is at least one arrangement having a bore (12) having a connection area (15) for a fluid supply and a fluid outlet (18), wherein in the bore (12) there is a constriction (13) for producing a Venturi effect and there is also a transverse bore (14) from the cavity (8) into the bore (12) in order to suck in gas from the cavity (8) through the transverse bore (14) via the Venturi effect to produce a vacuum.

2. Device according to claim 1, characterized in that a plurality of arrangements with the bore (12) are provided in the circumferential side wall.

3. Device according to claim 1 or 2, characterized in that the plurality of arrangements is fed with fluid via an annular channel and the annular channel has one or more fluid supply areas (15).

4. Device according to any of the preceding claims, characterized in that the fluid outlets (18) of the at least one arrangement open into a second annular channel, in which the fluid is collected and discharged via one or more outlets.

5. Device according to any of the preceding claims, characterized in that in the area of a planned weld seam, the circumferential side wall (3) is designed to be extended outwards having a projection (20), wherein in the area of a weld joint (19) a passage tunnel (21) for a weld seam is provided.

6. Device according to claim 5, characterized in that the passage tunnel (21) has a width which is wide enough for a weld seam usually produced with the laser to pass through.

7. Device according to claim 5 or 6, characterized in that a bore (12) runs above the passage tunnel (21), wherein the bore (12) above the passage tunnel (21) runs outwards parallel to the passage tunnel (21), so that the passage tunnel (21) can be cooled with the fluid flowing through the bore.

8. Device according to one of claim 5 to 7, characterized in that one or more brush packs, in particular metallic brush packs, are provided within the passage tunnel (21), which, extending the circumferential side wall (3), preferably terminate with the circumferential edge (5), so that they rest on a weld seam and are deflected by it and are guided along the weld seam when the welding cover (2) moves.

9. Device according to any of claims 5 to 8, characterized in that in addition to or instead of brush packs, lamellae or sealing lips made of a heat-resistant material, in particular a metal foil or a thin metal sheet or a heat-resistant plastic, such as PTFE, are present, wherein brush packs and lamellae or sealing lips are arranged alternately or successively.

10. Device according to any of claims 5 to 9, characterized in that in the region of a tunnel ceiling (22) of the passage tunnel (21) one or more transverse bores (14) are provided opening into the bore (12), each having a cooperating Venturi constriction (13) in order to suck off gases flowing through the passage tunnel (21) from the outside to the cavity (8) and at the same time to cool this region intensively.

11. Device according to any of the preceding claims, characterized in that for welding in the immediate vicinity of edges of workpieces (6,7) to be welded, an automated covering apparatus (25) is provided, which is arranged on one or both sides of the welding cover (2), wherein the covering apparatus (25) features an automatically actuatable extension block (26) and which, when the welding cover (2) reaches the edge, is pivoted towards the corresponding edge and held there while the welding cover (2) slides over this extension block (26), wherein the extension block (26) is automatically pivoted downwards by means of a guide structure or a guide slot at the moment when there is no longer any workpiece (6, 7) underneath it, wherein, for example, two control cams (27) control the movement and an actuating element, for example a pneumatic or hydraulic cylinder (28), actuates the extension block (26), wherein the control cams (27), the actuating element (28) and the extension block (26) are arranged on a support structure (29), which in turn is arranged on the device 1.

12. Device according to any of the preceding claims, characterized in that in the region of the circumferential side wall (3) from the circumferential edge (5) downwards slots (30) are arranged which extend from the circumferential edge (5) into the circumferential wall (3), wherein the slots or the slot (30) describes, for example, a semicircular arc, so that the front half of the circumferential edge (5) in the direction of movement is provided having a slot (30), wherein an adhesive cushion (31) or a seal (31), which can be extended in particular by inflation, rests in the slot and lies against the side wall of the workpieces (6, 7) and adheres there, while the welding cover (2) with the circumferential side wall (3) or the circumferential edge (5) is moved beyond the edge.

13. Device according to any of claims 1 to 11, characterized in that the welding cover is box-shaped or is arranged within a box-like arrangement (32), wherein the box-like arrangement (32) has a passage opening (37) for the laser beam (11) on the underside, which passage opening is delimited by the circumferential edge (5), wherein the box-like arrangement (32) has a flat bottom wall (33), wherein in the flat bottom wall (33) leading in the direction of movement there is arranged a moveable plate (34) which is in contact with the bottom wall (33), which, when the opening (37) which is delimited by the circumferential edge (5) comes into the region of the edge, can be moved with the corresponding edge in contact over the opening (37), so that it is ensured that no vacuum leak occurs, wherein on the opposite side of the opening there is provided a passage groove (35) which is located in the bottom wall (33), so that a corresponding weld seam can be guided here, A plate-like element (36) is also guided in the passage groove (35), which is able to protrude into the opening (37) delimited by the circumferential edge (5) in order to ensure vacuum tightness in the area of the edge when the welding method is started, The movable plate (34) and the plate-like element (36) are only moved in the region of the edge and are otherwise located outside the circumferential edge (5) in order to be protected from the welding heat.

14. Method for welding under vacuum by means of a laser, wherein a device according to any of the preceding claims is guided along a weld joint (19) between a first workpiece (6) and a second workpiece (7) and in the region of the weld joint (19) a laser beam (11) melts the workpieces (6, 7) and thus joins them together.

15. Method according to claim 14, characterized in that a gas or a liquid flows through the bores (12)n of the device (1).

16. Method according to claim 14 or 15, characterized in that the supplied liquid is received and in particular discharged at the fluid outlet (18).

17. Method according to any of claims 14 to 16, characterized in that for welding hollow bodies, in particular made of aluminum, the hollow body is evacuated during the welding process to a desired vacuum, so that the weld joint (19) in the region of the welding cover supports the vacuum or no gas from the interior of the hollow body is drawn into the welding cover (2) by the vacuum therein.

18. Method according to any of claims 14 to 16, characterized in that a movable vacuum chamber (38) is carried below the welding cover (2) on the other side of the weld joint (19) in order to prevent gas from being led into the cavity (8) through the weld joint and to ensure improved weld seam quality.

19. Method according to any of claims 14 to 16, characterized in that on a common edge of the workpieces (6, 7) which has to be passed over by the device (1) for welding, a block element (24) is arranged in a form-fitting manner and in a manner that terminates with the edge in order to secure the vacuum, so that the welding cover (2) rests in a form-fitting manner on all sides with the circumferential edge (5) beyond the edge, so that the vacuum can be maintained.

20. Method according to claim 19, characterized in that the block element (24) is arranged on the edge with corresponding clamping elements and / or laterally from the weld joint (19), for example, dovetail guides are milled or arranged in another way and the block element (24) is formed having corresponding dovetails, so that the block element (24) is arranged firmly, in a form-fitting manner and terminally on the edge.

21. Method according to claim 19 or 20, characterized in that after the weld seam has been completed, the vacuum is also released by switching off the flow and the welding cover (2) is removed and then the block element (24) is moved by taking it out of the dovetail guides and inserting it into corresponding dovetail guides on the other side of the edge and then the welding process is started by putting the welding cover (2) back on accordingly, drawing the vacuum and, optionally, the welding cover (2) also starts moving at a short distance from the edge and the laser thus starts welding.

22. Method according to any of claims 19 to 21, characterized in that the distances of the dovetail guides are arranged equally, so that the block element (24) preferably has dovetails on one side which correspond to the one distance of the dovetail guides on one side of the edge, wherein the other side of the edge has dovetails at a different distance, so that the dovetail guides of the edges are not at the same height.

23. Method according to any of claims 19 to 21, characterized in that the dovetail guides have an equal distance but are arranged offset by a certain amount on the respective sides of the edge, wherein the block element (24) is then selected to be so large that, even with such an offset, the welding cover (2) is reliably covered from below by the block element (24).

24. Method according to any of claims 19 to 23, characterized in that the dovetail guides in the workpieces (6, 7) are closed having fitting pieces after welding has been completed.