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 latching interfaces such as latches.

[0003] However, welding can 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 a stable arc discharge. Arc welding also requires 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 under artificial vacuum conditions, taking into account the presence of the atmosphere. Electron beam welding also offers higher joint quality and mechanical properties than arc or laser welding.

[0006] The emission of an electron beam requires heating a cathode above its operating temperature and creating a high-voltage electrical potential 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 the area to be welded.

[0007] The surface power produced by the welding device, enabling the material to be fused, is therefore dependent in particular 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 necessitates spacing or isolating the components of the electron beam to prevent the formation of electric arcs.

[0009] In addition, a high accelerating voltage generates X-rays during welding which could potentially damage the nearby space vehicle.

[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 that emits electrons, - an anode with an anode hole, to which a positive voltage is applied relative to the cathode in such a way as to create a beam of electrons from the cathode to the anode, - a beam forming electrode, called a Wehnelt electrode, having a flared surface 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 to be used in space, under vacuum conditions.

[0015] The electron beam welding device is in particular 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 passing through 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 includes 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 convex, a set of emission planes is defined comprising all the planes normal to the principal 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 starting plane of the flared surface and an ending 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, it is understood by: "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" that the emission plane is placed between the starting plane of the flared surface and an ending plane of the flared surface.

[0025] In the case of a curved emitting surface, the following is meant by: "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" that at least one emission plane is placed between the starting plane of the flared surface and an ending plane of the flared surface.

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

[0027] The beamforming electrode includes 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 convex.

[0030] In particular, the flared surface of the beam forming electrode is a cone of half-angle a, in other words forms with the main emission axis an angle a, with a 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 less than 35kV, in particular less 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 on 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 includes a focusing coil arranged to produce a magnetic field enabling the electron beam to be focused to 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 includes 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, oval or rectangular in section.

[0041] The casing is made of metallic material.

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

[0043] The welding device includes a set of insulating parts placed between the beam forming electrode, the cathode and the housing of the welding device, and arranged to electrically isolate the beam forming electrode, the cathode and the housing.

[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 the level of a weld zone.

[0046] For example, the electron beam strikes the part to be welded perpendicularly to its surface at the level of a weld zone.

[0047] The welding device includes a power supply unit comprising: - a power supply, in particular a DC voltage source, - at least one high-voltage converter, powered by the power supply and arranged to provide a high-voltage supply, - at least one current converter, powered by the power supply and arranged to provide a high current 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 includes two high-voltage converters arranged to place the beam-forming electrode and the cathode at two distinct potentials.

[0050] The welding device includes 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 housing of the welding device, and fixes the potential of the housing to the floating ground of the welding device.

[0053] The power circuit is electrically connected to the part to be welded, and fixes the potential of the part to be welded 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 at a fixed potential of -Ul.

[0056] Alternatively, the anode and cathode can 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 supply power to 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 includes a beam adjustment mechanism, allowing control of 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 beamforming electrode and the cathode.

[0062] For example, the beamforming 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 beamforming electrode a voltage U2 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 in a quasi-instantaneous manner, 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 adjustment of the heating current passing through the cathode and therefore the temperature of the emitting surface during use.

[0067] Adjusting the temperature of the emission 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 includes at least one movable part arranged to be moved linearly along the principal emission axis.

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

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

[0071] The use of a flared surface extending behind the emitting surface of the cathode allows better extraction of electrons and shaping of the electron beam for a given accelerating 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 below 35kV.

[0073] In addition, the isolation distance to prevent 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 low work function and high temperature resistance. 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 non-ferromagnetic metal alloy.

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

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

[0079] For example, the anode is made of stainless steel, or of 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 principal emission axis between the starting plane of the flared surface and the emission plane of the emission surface closest to the starting 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 starting plane of the flared surface and the emission plane of the emission surface closest to the starting plane of the flared surface can be adjusted mechanically by linear translation of the cathode or beamforming electrode along the main emission axis.

[0084] Other features, details and advantages of the invention will become clearer upon reading the following description on the one hand, and several illustrative and non-limiting examples of embodiments given with reference to the accompanying schematic drawings on the other hand, in which:

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

[0090] The features, variants, and different embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of features, described hereafter in isolation from the other described features, 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. Figure 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 principal 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 beamforming electrode 6.

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

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

[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 3mm along the main emission axis 15 of the electron beam 5.

[0102] The beam forming electrode 6 has 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 starting plane of the flared surface 18 and an ending 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 starting position of the flared surface 16 and at an ending 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 starting plane of the flared surface 18 and the ending 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 0.5mm along the main emission axis 15.

[0106] This distance D2 can be mechanically adjusted by linear translation of the cathode 2 or beamforming 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 a equal to 50°.

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

[0109] The beam forming electrode 6, the cathode 2 and the cylindrical envelope 22 are electrically isolated by a set of insulating pieces 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 electrons and better shaping of the electron beam 5 for a given accelerating voltage of the electron beam.

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

[0112] In addition, the isolation distance to prevent 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 the level of a weld zone 21.

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

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

[0116] According to an embodiment not shown, the welding device 1 includes two high-voltage converters allowing the beam forming electrode and the cathode to be placed at two distinct potentials.

[0117] The power circuit 28 is electrically connected to the anode 3, to the housing 22 of the welding device 1 and to the workpiece 30, 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 allows the cathode to be heated.

[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 enabling the electron beam 15 to be focused onto the weld area 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 beamforming electrode 6, and controls the potential of the beamforming electrode 6 to adjust the potential difference between the beamforming electrode 6 and the cathode 2.

[0124] For example, the power circuit 28 places the beamforming electrode 6 at a potential lower than the potential of the cathode, determining between the cathode and the beamforming electrode a voltage U2 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 through the cathode 2 and therefore the temperature of the emission surface 9 and thus control of 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 movable 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 the use of the welding device 1.

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

[0129] Fig. 3 is a close-up, cross-sectional view 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 starting plane of the flared surface 18 and the ending plane of the flared surface 19.

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

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

Claims

Demands

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 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.

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 axis of emission of the electron beam (15).

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

5. Welding device (1) according to any 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 any one of the preceding claims, wherein the voltage difference between the anode and the cathode is a voltage U1 referred to as "low high voltage", i.e. a voltage U1 less than 35kV, in particular less than 30kV, in particular between 10kV and 20kV.

7. Welding device (1) according to any one of the preceding claims, including a focusing coil (20) arranged to produce a magnetic field enabling the electron beam (15) to be focused to a working distance corresponding to the weld zone (21)

8. Welding device (1) according to any one of the preceding claims, comprising a housing (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 any one of the preceding claims, comprising a power supply unit (24) including: - a power supply (25), in particular a DC voltage supply, - at least one high voltage converter (26), powered by the power supply and arranged to provide a high voltage supply, - at least one current converter (27), powered by the power supply and arranged to provide a high current 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 the current converter.

10. 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 any one of the preceding claims, wherein the cathode (2) and the anode (3) are separated by a first isolation distance DI along the principal emission axis (15) of the electron beam (5), this isolation distance DI being between 3mm and 15mm.

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

13. Welding device (1) according to any one of the preceding claims, wherein the minimum distance D2 along the principal emission axis (15) between the starting 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 beamforming electrode along the main emission axis.

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