Electron beam welding device

Abstract

Title: Electron Beam Welding Device The invention relates to an electron beam welding device (1) comprising: a cathode (2) having an emitting surface (9) emitting electrons, an anode (3) with an anode hole (4), to which a positive voltage is applied relative to the cathode so as to create an electron beam (5) from the cathode to the anode, a beam-forming electrode (6) having a flared surface, arranged to focus the emitted electron beam between the cathode and the anode, characterized in that a portion (8) of the flared surface of the beam-forming electrode (6) extends behind the emitting surface (9) of the cathode in the direction of emission of the electron beam. Figure for the abstract: Fig. 1

Description

Title of the invention: Electron beam welding device

[0001] The present invention relates to an electron beam welding device, in particular for operation in space.

[0002] Welding is a process for joining elements. In space, under vacuum conditions, structures are most often assembled by mechanical docking interfaces such as latches.

[0003] However, welding may be considered for the future construction of structures in space. Most welding methods used for terrestrial construction are arc welding. However, under vacuum conditions, it is difficult to generate and maintain an arc discharge stably. Arc welding also involves providing a consumable such as ionized gas, which is a major drawback for use in space.

[0004] An alternative to arc welding is laser welding. However, this method has a relatively low energy efficiency. Some of the energy is dissipated as heat. Furthermore, some materials reflect some of the laser, reducing energy efficiency and creating potential risks for a spacecraft.

[0005] Electron beam welding is known as a method used on Earth in artificial vacuum conditions, given the presence of the atmosphere. Electron beam welding also has higher joining quality and mechanical properties than arc or laser welding.

[0006] Emitting an electron beam requires heating a cathode above its working temperature, and creating a high voltage between an anode and this cathode. The free electrons generated by heating the cathode are then accelerated by the electrical potential difference, the electron beam is shaped by a beam-forming electrode and then focused by a focusing coil, in order to converge the electron beam at an area to be welded.

[0007] The surface power produced by the welding device, allowing the material to be melted, is therefore in particular dependent on the voltage between the anode and the cathode, the distance between these elements, the heating temperature of the cathode as well as the focusing of the electron beam.

[0008] The use of high voltage is a source of constraints. It requires the use of heavy and bulky voltage sources and / or converters. Furthermore, high voltage requires spacing or isolating the components of the electron beam to avoid the creation of electric arcs.

[0009] In addition, high accelerating voltage generates X-rays during welding which can potentially damage the nearby spacecraft.

[0010] In the case of use in orbit, the weight and size of the welding system are decisive criteria for the viability of this method.

[0011] The invention therefore relates to a welding device improving the power of the electron beam, thus making it possible to reduce the voltage used, and therefore the weight and size of the welding device.

[0012] The invention relates to an electron beam welding device comprising: - a cathode comprising an emitting surface emitting electrons, - an anode with an anode hole, to which a positive voltage is applied relative to the cathode so as to create an electron beam from the cathode to the anode, - a beam-forming electrode, called a Wehnelt electrode, comprising a flared surface and arranged to shape and in particular focus the electron beam emitted between the cathode and the anode, characterized in that a portion of the flared surface of the beam-forming electrode extends behind the emitting surface of the cathode in the direction of emission of the electron beam.

[0013] The invention comprises at least one of the following features, taken independently or in combination:

[0014] The electron beam welding device is arranged for use in space under vacuum conditions.

[0015] The electron beam welding device is particularly arranged for the assembly of structures in space.

[0016] The emitting surface of the cathode defines a principal axis of emission, this axis being normal to the emitting surface at the center of the emitting surface, and crossing the emitting surface at its center.

[0017] A direction of emission of the electron beam is also defined.

[0018] The anode is placed after the emission surface in the direction of emission of the electron beam, and has an anode hole for the passage of the beam.

[0019] In the case where the emitting surface of the cathode is flat, it defines an emission plane.

[0020] In the case where the emitting surface is curved, in particular conical or curved, a set of emission planes is defined comprising all of the planes normal to the main emission axis intersecting the emitting surface.

[0021] The cathode, the anode and the beam-forming electrode are parts of revolution having as their axis the main emission axis of the electron beam.

[0022] A starting position of the flared surface is defined on the main emission axis, and an end position of the flared surface.

[0023] The flared surface therefore extends between a start plane of the flared surface and an end plane of the flared surface, these planes being parallel to each other and normal to the main emission axis.

[0024] In the case of a planar emission surface, the term: "a portion of the flared surface of the beam-forming electrode extends behind the emitting surface of the cathode in the direction of emission of the electron beam" means that the emission plane is placed between the start plane of the flared surface and an end plane of the flared surface.

[0025] In the case of a curved emitting surface, the term: "a portion of the flared surface of the beam-forming electrode extends behind the emitting surface of the cathode in the direction of emission of the electron beam" means that at least one emission plane is placed between the start plane of the flared surface and an end plane of the flared surface.

[0026] In particular, in the case of a curved emission surface, all of the emission planes of the emitting surface are placed between the start plane of the flared surface and an end plane of the flared surface.

[0027] The beam forming electrode comprises a cavity in which the cathode is placed.

[0028] The flared surface of the beam forming electrode is conical.

[0029] Alternatively, the flared surface of the beam forming electrode is concave, or domed.

[0030] In particular, the flared surface of the beam-forming electrode is a cone of half-angle α, in other words forms an angle α with the main emission axis, with α between 20° and 80°, in particular between 32.5° and 67.5°, in particular between 40° and 60°.

[0031] The voltage difference between the anode and the cathode is a voltage U1 called “low high voltage”, that is to say a voltage U1 lower than 35kV, in particular lower than 30kV, in particular between 10kV and 20kV.

[0032] The anode is placed at the floating ground of the welding device, at a potential of 0V.

[0033] The part to be welded is placed at the floating ground of the welding device at a potential of 0V.

[0034] The cathode is placed at a negative potential.

[0035] Thus, a voltage U1 between the anode and the cathode is obtained by placing the anode at a potential of 0V, and the cathode at a fixed potential of - Ul.

[0036] The welding device comprises a focusing coil arranged to produce a magnetic field for focusing the electron beam at a working distance corresponding to the welding area.

[0037] The focusing coil is placed after the anode in the direction of emission of the electron beam, and has a hole for the passage of the beam.

[0038] The welding device comprises a housing arranged to contain the cathode, the beam forming electrode, the anode, and optionally a focusing coil.

[0039] The envelope is cylindrical in shape.

[0040] Alternatively, the envelope may be, for example, of oval or rectangular section.

[0041] The envelope is made of metallic material.

[0042] Alternatively, the envelope is made of electrically and thermally insulating material, in particular ceramic, or a composite, electrically conductive or not.

[0043] The welding device comprises a set of insulating pieces placed between the beam forming electrode, the cathode and the casing of the welding device, and arranged to electrically insulate the beam forming electrode, the cathode and the casing.

[0044] The insulating parts are made of electrically insulating material, for example ceramic.

[0045] The welding device is arranged to be placed opposite a part to be welded, so that the electron beam strikes the part to be welded at a welding zone.

[0046] For example, the electron beam strikes the part to be welded perpendicular to its surface at a welding zone.

[0047] The welding device comprises a power supply unit comprising: - a power source, in particular a direct voltage source, - at least one high voltage converter, powered by the power source and arranged to provide a high voltage power supply, - at least one current converter, powered by the power source and arranged to provide a high current power supply, in particular to provide a current of intensity I greater than IA, in particular equal to 3A, - a power circuit, electrically connected to the high voltage converters and the current converter.

[0048] The power source is a battery.

[0049] The welding device comprises two high voltage converters arranged to place the beam forming electrode and the cathode at two separate potentials.

[0050] The welding device comprises two current converters arranged to supply the focusing coil and the cathode with currents of different intensity.

[0051] The power circuit is electrically connected to the anode, and fixes the potential of the anode to the floating ground of the welding device.

[0052] The power circuit is electrically connected to the enclosure of the welding device, and fixes the potential of the enclosure to the floating ground of the welding device.

[0053] The power circuit is electrically connected to the workpiece, and fixes the potential of the workpiece to the floating ground of the welding device.

[0054] The power circuit is electrically connected to the cathode, and supplies the cathode with current from the current converter so as to heat the cathode.

[0055] The electrical connection of the power circuit to the cathode also fixes the cathode to a fixed potential of -Ul.

[0056] Alternatively, the anode and cathode may be placed at any other determining potentials between the cathode and the anode a high voltage as determined above.

[0057] The power circuit is electrically connected to the focusing coil, and is arranged to power the focusing coil.

[0058] The power circuit is electrically connected to the beam forming electrode, and controls the potential of the beam forming electrode.

[0059] The welding device comprises a beam adjustment mechanism, making it possible to control the current emitted by the cathode and passing through the welding system.

[0060] The beam adjustment mechanism is the power circuit.

[0061] The power circuit is arranged to adjust the potential difference between the beam forming electrode and the cathode.

[0062] For example, the beam-forming electrode is placed at a variable potential lower than the potential of the cathode, in particular so as to determine between the cathode and the beam-forming electrode a voltage U2 of between OkV and 3kV.

[0063] Adjusting the potential difference between the beam-forming electrode and the cathode allows the electron beam to be shaped, and the current emitted by the cathode and passing through the welding system to be controlled.

[0064] Advantageously, the use of electronic control of the potential difference between the cathode and the beam forming electrode makes it possible to control the current emitted by the cathode and passing through the welding device almost instantaneously, without consuming additional energy, and without requiring the movement of mechanical parts.

[0065] Alternatively, the beam adjustment mechanism is the current converter.

[0066] The current converter is arranged to allow the heating current to be adjusted passing through the cathode and therefore the temperature of the emitting surface during use.

[0067] Adjusting the temperature of the emitting surface makes it possible to control the quantity of free electrons emitted, and therefore to control the current emitted by the cathode and passing through the welding system.

[0068] Alternatively, the beam adjustment mechanism comprises at least one moving part arranged to be moved linearly along the main emission axis.

[0069] The anode, cathode, and / or beam-forming electrode are placed on a movable part, and the movable parts are arranged to control the relative positions of the beam-forming electrode, cathode, and anode during use of the welding device.

[0070] Adjusting the relative positions of the beam forming electrode, the cathode and the anode during use of the welding device allows the shaping of the electron beam to be controlled, and thus the current emitted by the cathode and passing through the welding system to be controlled.

[0071] The use of a flared surface extending behind the emitting surface of the cathode allows for better extraction of electrons and shaping of the electron beam for a given acceleration voltage of the electron beam.

[0072] Thus, the use of a flared surface extending behind the emitting surface of the cathode allows the performance of the welding system to be improved, even for acceleration voltages significantly lower than the state of the art, in particular for acceleration voltages lower than 35kV.

[0073] In addition, the insulation distance for preventing discharge inside the electron gun housing can be reduced, so that the size of the welding device can be reduced.

[0074] The emissive surface of the cathode is made of a material with a low work function and resistance to high temperatures. For example, the cathode is made of tungsten.

[0075] Alternatively, the cathode is made of Lanthanum Hexaboride (LaB6).

[0076] The beam forming electrode is made of a non-ferromagnetic metal alloy.

[0077] For example, the beam forming electrode is made of stainless steel, or aluminum.

[0078] The anode is made of a non-ferromagnetic metal alloy.

[0079] For example, the anode is made of stainless steel, or aluminum.

[0080] The cathode and the anode are separated by a first isolation distance DI along the main emission axis of the electron beam, this isolation distance DI being between 3mm and 15mm.

[0081] The minimum distance D2 is defined along the main emission axis between the start plane of the flared surface and the emission plane of the emission surface closest to the start plane of the flared surface.

[0082] This distance D2 is between 0.001mm and 0.5mm, in particular is equal to 0.5mm.

[0083] The distance along the main emission axis between the start plane of the flared surface and the emission plane of the emission surface closest to the start plane of the flared surface can be mechanically adjusted by linear translation of the cathode or beam-forming electrode along the main emission axis.

[0084] Other characteristics, details and advantages of the invention will emerge more clearly on reading the description which follows on the one hand, and several exemplary embodiments given for informational and non-limiting purposes with reference to the appended schematic drawings on the other hand, in which:

[0085] [Fig-1] [Fig.l] is a schematic cross-sectional representation of the device of electron beam welding according to a first embodiment of the invention.

[0086] [Fig.2] [Fig.2] is a close-up, cross-sectional view of the cathode / electrode assembly beam forming of the electron beam welding device according to a first embodiment of the invention.

[0087] [Fig.3] [Fig.3] is a close-up, cross-sectional view of the cathode / electrode assembly beam forming of the electron beam welding device according to a second embodiment of the invention.

[0088] [Fig.4] [Fig.4] is a close-up, cross-sectional view of the cathode / electrode assembly beam forming of the electron beam welding device according to a third embodiment of the invention.

[0089] [Fig.5] [Fig.5] is a close-up, cross-sectional view of the cathode / electrode assembly beam forming of the electron beam welding device according to a fourth embodiment of the invention.

[0090] The features, variants and the different embodiments of the invention may be combined with each other, in various combinations, provided that they are not incompatible or mutually exclusive. In particular, variants of the invention may be imagined comprising only a selection of features described below in isolation from the other features described, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0091] Figures 1 and 2 show an electron beam welding device 1 according to the invention. [Fig.2] is a close-up view showing only the cathode 2 and beam forming electrode 6 of the welding device, for readability reasons.

[0092] The welding device 1 comprises a cathode 2, an anode 3, a beam forming electrode 6, and a focusing coil 20 placed in a cylindrical casing 22.

[0093] The cathode 2 comprises an emitting surface 9 emitting electrons, and this emitting surface of the cathode defines a main emission axis 15 of the electron beam 5, this axis being normal to the emitting surface at the center of the emitting surface, and passing through the emitting surface at its center. A direction of emission of the electron beam is also defined.

[0094] The cathode 2, the anode 3 and the beam forming electrode 6 are parts of revolution having as their axis the main emission axis 15 of the electron beam 5.

[0095] The cathode 2 is for example made of tungsten, or alternatively of Lanthanum Hexaboride (LaB6).

[0096] The emitting surface 9 is flat, and defines an emission plane 14.

[0097] The cathode 2 is placed in a cavity 10 of the beam forming electrode 6.

[0098] The anode 3 is placed after the emission surface 9 in the direction of emission of the electron beam 5, and comprises an anode hole 4 for the passage of the beam.

[0099] The anode 3 is made of a non-ferromagnetic metal alloy, for example stainless steel or aluminum.

[0100] The focusing coil 20 is placed after the anode 3 in the direction of emission of the electron beam 5, and has a hole for the passage of the beam.

[0101] The cathode 2 and the anode 3 are separated by a first isolation distance DI of 3 mm along the main emission axis 15 of the electron beam 5.

[0102] The beam-forming electrode 6 comprises a flared surface 7 arranged to shape the electron beam 5 emitted between the cathode 2 and the anode 3.

[0103] This flared surface 7 therefore extends between a start plane of the flared surface 18 and an end plane of the flared surface 19. These planes are parallel to each other, normal to the main emission axis 15, and placed respectively at a start position of the flared surface 16 and at an end position of the flared surface 17 on the main emission axis.

[0104] A portion of the flared surface 8 extends behind the emitting surface 9 of the cathode 2 in the direction of emission of the electron beam 5, and the emission plane 14 is therefore placed between the start plane of the flared surface 18 and the end plane of the flared surface 19.

[0105] The starting plane of the flared surface 18 and the emission plane 14 are separated by a distance D2 of 0.5 mm along the main emission axis 15.

[0106] This distance D2 can be mechanically adjusted by linear translation of the cathode 2 or beam forming electrode 6 along the main emission axis 15.

[0107] The flared surface 7 of the beam-forming electrode 9 is a cone forming with the main emission axis 15 an angle α equal to 50°.

[0108] The beam forming electrode 6 is made of a non-ferromagnetic metal alloy, for example stainless steel or aluminum.

[0109] The beam forming electrode 6, the cathode 2 and the cylindrical envelope 22 are electrically insulated by a set of insulating parts 23, made of ceramic and placed between the beam forming electrode 6, the cathode 2 and the cylindrical envelope 22.

[0110] The use of a flared surface 7 extending behind the emitting surface 9 of the cathode 2 allows better extraction of the electrons and better shaping of the electron beam 5 for a given acceleration voltage of the electron beam.

[0111] This thus makes it possible to improve the performance of the welding device 1 for acceleration voltages significantly lower than the state of the art, in particular for acceleration voltages lower than 35kV.

[0112] In addition, the insulation distance for preventing discharge inside the electron gun housing can be reduced, so that the size of the welding device 1 can be reduced.

[0113] The welding device 1 is arranged to be placed opposite a part to be welded 30, so that the electron beam 5 strikes the part to be welded at a welding zone 21.

[0114] For example, the electron beam strikes the part to be welded perpendicular to its surface at a welding zone perpendicular to its surface.

[0115] The welding device 1 comprises a power supply unit 24, comprising: - a battery 25, - a high voltage converter 26 powered by the battery and providing a high voltage power supply, - a current converter 27 powered by the battery and providing a high current supply of 3A, - a power circuit 28, electrically connected to the high voltage converter and to the current converter.

[0116] According to an embodiment not shown, the welding device 1 comprises two high voltage converters making it possible to place the beam forming electrode and the cathode at two distinct potentials.

[0117] The power circuit 28 is electrically connected to the anode 3, to the casing 22 of the welding device 1 and to the workpiece 30, and fixes and fixes their potential to the floating mass of the welding device.

[0118] The power circuit 28 is electrically connected to the cathode 2, and supplies it with the current from the current converter 27. This high current makes it possible to heat the cathode.

[0119] The electrical connection of the power circuit 28 to the cathode 2 fixes it for example at a potential of -12kV.

[0120] The potential difference between anode 3 and cathode 2 is therefore 12kV. This voltage could be obtained by placing anode 3 and cathode 2 at other fixed potentials.

[0121] The power circuit 28 supplies the focusing coil 20, which produces a magnetic field making it possible to focus the electron beam 15 on the welding zone 21.

[0122] In this embodiment, the power circuit 28 is an adjustment mechanism for controlling the current emitted by the cathode and passing through the welding system 1.

[0123] The power circuit 28 is electrically connected to the beam forming electrode 6, and controls the potential of the beam forming electrode 6 to adjust the potential difference between the beam forming electrode 6 and the cathode 2.

[0124] For example, the power circuit 28 places the beam-forming electrode 6 at a potential lower than the potential of the cathode, determining between the cathode and the beam-forming electrode a voltage U2 of between OkV and 3kV.

[0125] The use of electronic control of the potential difference between the cathode 2 and the beam forming electrode 6 makes it possible to control the current emitted by the cathode and passing through the welding device 1 in a quasi-instantaneous manner, without consuming additional energy, and without requiring the movement of mechanical parts.

[0126] In an embodiment not shown, the beam adjustment mechanism is the high current converter 27, which is then arranged to allow adjustment of the heating current passing through the cathode 2 and therefore the temperature of the emission surface 9 and thus control the quantity of free electrons emitted and the current of the electron beam 5.

[0127] In another embodiment not shown, the anode 3, the beam forming electrode 6 and / or the cathode 2 are placed on moving parts arranged to be moved linearly along the main emission axis 15 so as to control the relative positions of the beam forming electrode 6, the anode 3 and the cathode 2 during use of the welding device 1.

[0128] Adjust the relative positions of the beam forming electrode 6, the anode 3 and the cathode 2 during use of the welding device makes it possible to control the shaping of the electron beam 5, and thus to control the current emitted by the cathode and passing through the welding system 1.

[0129] [Fig. 3] is a close-up view, in section, of the cathode 2 / beam-forming electrode 6 assembly of the electron beam welding device 1 according to a second embodiment of the invention in which the emission surface 9 of the cathode is curved.

[0130] A set of emission planes 14a, 14b, 14c is then defined comprising all the planes normal to the main emission axis intersecting the emitting surface, and at least one emission plane of this set is placed between the start plane of the flared surface 18 and the end plane of the flared surface 19.

[0131] In particular, in this embodiment, all of the emission planes of the emitting surface 14a, 14b, 14c are placed between the start plane of the flared surface 18 and the end plane of the flared surface 19.

[0132] Figures 4 and 5 are close-up views, in section, of the cathode 2 / beam forming electrode 6 assembly of the electron beam welding device 1 according to a third and a fourth embodiment of the invention respectively, in which the flared surface 9 of the beam forming electrode is respectively concave or curved.

Claims

Claims

1. Electron beam welding device (1) comprising: - a cathode (2) having an emitting surface (9) emitting electrons, - an anode (3) with an anode hole (4), to which a positive voltage is applied relative to the cathode so as to create an electron beam (5) from the cathode to the anode - a beam-forming electrode (6) having a flared surface, arranged to shape the electron beam emitted between the cathode and the anode, characterized in that a portion (8) of the flared surface of the beam-forming electrode (6) extends behind the emitting surface (9) of the cathode in the direction of emission of the electron beam.

2. Welding device (1) according to claim 1, wherein the cathode (2), the anode (3) and the beam forming electrode (6) are parts of revolution having as their axis the main emission axis of the electron beam (15).

3. Welding device (1) according to one of the preceding claims, wherein the beam forming electrode (6) comprises a cavity (10) in which the cathode (3) is placed.

4. Welding device (1) according to one of the preceding claims, in which the flared surface (7) of the beam-forming electrode (6) is a cone of half-angle α, in other words forms with the main emission axis (15) an angle α, with α between 20° and 80°, in particular between 32.5° and 67.5°, in particular between 40° and 60°.

5. Welding device (1) according to one of claims 1 to 3, the flared surface (7) of the beam forming electrode is concave, or domed.

6. Welding device (1) according to one of the preceding claims, in which the voltage difference between the anode and the cathode is a voltage U1 known as “low high voltage”, that is to say a voltage U1 less than 35kV, in particular less than 30kV, in particular between 10kV and 20kV.

7. Welding device (1) according to one of the preceding claims, comprising a focusing coil (20) arranged to produce a magnetic field for focusing the electron beam (15) at a working distance corresponding to the welding zone (21)

8. Welding device (1) according to one of the preceding claims, comprising a casing (22) arranged to contain the cathode (2), the beam forming electrode (6), the anode (3), and optionally a focusing coil (20).

9. Welding device (1) according to one of the preceding claims, comprising a power supply unit (24) comprising: - a power source (25), in particular a direct voltage source, - at least one high voltage converter (26), powered by the power source and arranged to provide a high voltage power supply, - at least one current converter (27), powered by the power source and arranged to provide a high current power supply, in particular to provide a current of intensity I greater than IA, in particular equal to 3A, - a power circuit (28), electrically connected to the high voltage converters and to the current converter.

10. A welding device (1) according to claim 9, wherein the power circuit (28) is arranged to adjust the potential difference between the beam forming electrode (6) and the cathode (2).

11. Welding device (1) according to one of the preceding claims, in which the cathode (2) and the anode (3) are separated by a first isolation distance DI along the main emission axis (15) of the electron beam (5), this isolation distance DI being between 3 mm and 15 mm.

12. Welding device (1) according to one of the preceding claims, in which the minimum distance D2 along the main emission axis (15) between the start plane of the flared surface (18) and the emission plane (14, 14a) of the emission surface (9) closest to the start plane of the flared surface is between 0.001mm and 0.5mm.

13. Welding device (1) according to one of the preceding claims, in which the minimum distance D2 along the main emission axis (15) between the start plane of the flared surface (18) and the plane emission (14, 14a) of the emission surface (9) closest to the start plane of the flared surface can be mechanically adjusted by linear translation of the cathode or beam-forming electrode along the main emission axis.

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