Welding or additive manufacturing process by laser melting followed by cooling with powder inerting

Abstract

A process for shaping metallic materials by laser melting followed by cooling comprises applying laser radiation (110) to the material to be treated and progressively moving (D) said radiation along a processing path of the material. The material to be treated is coated with an inert gas powder (120), the inert gas powder being removed downstream of the radiation application after cooling of the melt pool (115). Abbreviated figure: 2A

Description

Title of the invention: Welding process or additive manufacturing by laser fusion then cooling with inerting by powder Technical context

[0001] The invention falls within the field of shaping metal parts for industry. The industries concerned are diverse: aeronautics and space, the military field, building and public works sites, the naval industry, and the nuclear industry, in particular. The shaping of the metal parts envisaged may be a welding of two metal parts of the same composition or of different compositions, with or without the addition of material, or additive manufacturing using an addition of metal to an already present metal base. These processes for shaping metallic material may in particular be used for the initial shaping of a single part or parts manufactured in small numbers, or for the repair of parts that are very expensive and complex to produce, for example on areas of wear on a part of the part or for repairs of cracks that appeared during the life of the part.Various welding and additive manufacturing techniques are known, including focused welding techniques using laser radiation, in which laser radiation is moved (relative to the parts) to the interface of the two parts to be welded, creating a weld pool slightly upstream of the point of impact and downstream of the impact, which solidifies to form the weld, in which the materials of the two parts have coalesced.

[0002] Technical requirements impose very high welding qualities, particularly in the nuclear field. Imperfections or defects are largely eliminated by rigorous cleaning of the parts before welding. But it is also very important to provide gas protection by inerting with a neutral gas which is generally argon or nitrogen, and which protects the molten pool from oxidation by contact with air, the latter containing oxygen and humidity from which the molten pool must be protected. The neutral gas is sprayed by a nozzle surrounding the laser towards the molten pool in order to locally reduce the humidity and the oxygen level. The main disadvantage of the gas is that it dilutes quickly in the ambient air, a phenomenon amplified by the strong temperature gradients generated by the laser heat source.

[0003] The high power densities and high speeds used for laser welding processes thus reduce the effectiveness of the gas shielding of the weld pool. Boxes or chambers or more broadly inerting systems, rigid or flexible, make it possible to confine the shielding gas to increase its effectiveness. They thus ensure good protection of the weld pool but must be adapted to the geometry of each part to be welded, which makes them very, or even too, restrictive to implement in many configurations due to the complexity of the geometries of the welds to be made. Inerting chamber systems are complex and must be created on a case-by-case basis. In particular, it is necessary to interface the inerting box with the laser welding head and the two parts to be welded, which is complex to implement.

[0004] Laser welding and laser-wire additive manufacturing for large parts in an ambient environment ultimately remain little practiced industrially, and there are few well-known methods although there is a growing demand to obtain higher welding speeds.Thus, the state of the art offers few solutions for the following difficulties: ensuring protection of the weld pool on complex mechanical assemblies where inerting chambers or boxes cannot be installed, simplifying laser beam welding and laser-wire additive manufacturing procedures, reducing costs related to laser welding and laser-wire additive manufacturing in configurations specific to parts in the nuclear industry, reducing preparation and intervention times on welding areas in ambient environments such as open-air construction sites or factories, enabling laser welding and laser-wire additive manufacturing on large parts at high speeds without inerting chambers or boxes, increasing laser welding performance and weld pool quality by 10 to 20%, and enabling inerting on 5- or 6-axis robotic systems in inerting chambers or boxes.

[0005] A difficulty with laser processes (with or without material input) in an ambient environment is, as has been said, the gaseous protection of the weld pool, because it determines the final quality of the welded assemblies. Such welding operations in an ambient environment, i.e. without an inerting box or chamber, are particularly envisaged for the naval industry or construction sites, and they can be carried out in an inerting box or chamber as an additional precaution for even more demanding industries such as nuclear, aeronautics and aerospace.

[0006] Electric arc welding processes, including TIG / MIG (Tungsten Inert Gas and Metal Inert Gas) and coated electrode processes, are widely used in industry. Currently, complex or difficult-to-access welds are carried out by welding processes other than laser welding. Electric arc welding uses a tungsten electrode - TIG welding - or a consumable electrode wire. When the electrode is not consumable, which is the case with TIG welding, a filler wire or filler rod can be used to add metal to the workpieces. If the electrode is consumable, which may be the case with MIG welding, it can be advanced gradually to provide such a supply of metallic material. knows, within the framework of these arc welding processes, the possibility of working with the submerged arc, namely the electric arc under a flow of inerting powder. This is a very specific process, limited to the creation of an electric arc between an electrode wire to which a potential opposite to another potential applied to the parts to be welded is applied, to which the end of the electrode wire is approached until contact is made under the flow of powder.

[0007] But TIG, MIG and coated electrode welding processes remain slow, and replacing them with laser welding (with or without material addition) not requiring inerting boxes would make it possible in certain areas to reduce welding times, including the currently laborious installation of the equipment necessary for inerting, and costs. Definition of invention

[0008] The invention consists of implementing a method for shaping metallic material by melting and then cooling, comprising an application of laser radiation to the material to be treated, and a progressive displacement (relative to the material to be treated) of said radiation on a treatment path of the material to be treated.

[0009] This method is particular because upstream or directly above the point of impact of the radiation, the material to be treated is covered with an inerting powder, the inerting powder being removed downstream of the application of the radiation after cooling of the molten bath, the laser beam being projected through the powder and focused on the material to be treated, on its surface or possibly slightly below.

[0010] Thanks to these principles, which consist of passing the unfocused laser beam through a thickness of inerting powder, having carried out the focusing at the bottom of the layer of powder, and waiting for the molten pool to cool before removing the powder, existing welding techniques are greatly improved and productivity is gained compared to processes not using a laser, or to processes requiring the production of specific inerting chambers.

[0011] Optionally and advantageously, - the laser radiation can be applied and moved together with a wire whose end is placed under the laser radiation so as to constitute a supply of material at the level of the impact of the laser on the metallic base of the material to be treated, the base being able to be single or composed of two parts to be welded, on which it is applied - the material input can be sized for additive manufacturing implemented on such a metal base receiving laser radiation - the laser radiation can be applied and moved to the junction between two metal parts to be welded, included in or constituting the material to be treated, previously placed surface to be welded against surface to be welded

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[0017] - the two metal parts can be of the same composition, or of different compositions (same alloy, or different alloys) - the metal parts and more generally the material to be treated can be made of steel or include steel - the process can be implemented with or without an inerting box comprising an inerting gas (argon, nitrogen, helium for example) to protect the molten pool, in addition to the inerting powder - the powder can be composed of 35% of a mixture of SiO2 + A12O3 and 65% CaF2 + CaO + MgO for laser beam welding of two X10CrMoVNb9.1 stainless steel plates, but this is one example among others, the powder being otherwise adapted to the nature of the metal or alloy - the laser beam can be delivered by an Nd-YAG source, but other sources exist and can be used - the powder can be deposited as a smooth flow. The advantage of this invention is, in terms of welding, of two kinds for identical technical and mechanical results: For a given welding thickness, the invention makes it possible to reduce the necessary laser power, and to reduce welding fumes, which are harmful to the environment, and for a given laser power, the invention makes it possible to considerably increase the thicknesses of parts that can be welded. For wire laser additive manufacturing, the invention makes it possible to reduce the laser power in order to lower the temperature of the part and thus standardize the temperature gradients across the entire part. List of figures [Fig.l] is a general cross-sectional representation of a laser welding operation in an inerting box. Figures 2A and 2B are longitudinal and cross-sectional representations of a welding operation according to the invention. [Fig.3] is a longitudinal sectional representation of a laser-wire additive manufacturing operation according to the invention. Detailed description [Fig.l] In [Fig.l], two metal parts 10 and 20 are shown, according to known principles, in section, placed side by side, with side faces to be welded being placed against each other. An inerting box 30 is placed above the junction between the two metal parts 10 and 20, and a gas insufflation system is connected to it, so as to create a regulated atmosphere. The laser source 40 is interfaced with the inerting box 30 so that it overhangs the junction between the two metal parts 10 and 20. The gas 50 is blown into the internal volume of the inerting box and the laser beam 60 is directed onto the junction, which melts and forms a weld 70. The transient molten pool is protected from oxidation and humidity by the gas 50, typically argon or nitrogen. The laser beam is moved transversely to the plane of the figure, along the junction interface between the parts 10 and 20. The displacement of the laser is relative to the parts: it may be the parts that are moved relative to the laser rather than the other way around, of course.

[0018] [Fig.2A] In [Fig.2A], an embodiment of the invention is shown. The figure is, on the left, a section with, this time, the direction of movement D of the laser parallel to the section plane. Again, the movement of the laser is relative to the parts: it may be the parts that are moved relative to the laser rather than the other way around, naturally.

[0019] [Fig.2B] In [Fig.2B], a cross-section of the same process, with the same position of the elements, is presented, so as to visualize both the laser beam and the two parts to be welded.

[0020] A single metal part 90 is visible in [Fig.2A], because the section is made in the joining plane of the two parts, these being brought into contact with each other by two flat faces, typically abutting edges. The second part, referenced 95, is visible in [Fig.2B].

[0021] It is possible to butt the parts to be welded by non-planar surfaces, which are nevertheless complementary to each other. The upper part of the butt surfaces is the progression path of the laser beam for the purposes of welding, i.e. the treatment of the material to be shaped. This path is often rectilinear, but it can be curvilinear if the butt surfaces are not planar.

[0022] Above the parts, in the joining plane, the laser source is placed, the nozzle 100 of which is visible, and through the nozzle 100 the laser beam 110 appears, which is focused on the surface of the metal parts (or slightly below) and causes the formation of a molten pool 115 in the metal, at the junction of the two parts. But before reaching the metal parts, it is projected through a powder of granules, over a path of, for example, 5 to 8 mm in the powder layer, along which it is not focused.

[0023] According to the invention, a powder 120 has in fact been placed dynamically upstream of the impact of the laser on the junction of metal parts to be welded by a deposition pipe C1, constituting an inlet E of powder projected onto the metal parts, which accumulates to form a layer which can be 5 to 8 mm thick depending on the nature of the materials used. The deposition of powder, carried out by the deposition pipe C1 is smoothed by it, on the surface, which is essentially flat in the area of ​​application of the laser and has been arranged horizontally, of the parts 90 and 95, which allows the formation of a uniform layer of powder. The powder, as soon as it is present on the metal, is ready to ensure its protection against atmospheric gases, in particular water and oxygen. Its thickness is adapted to the speed of movement D: if the movement is slow, more powder thickness is required, until the bottom of the nozzle 100 is eventually submerged in the powder 120.

[0024] Thus, the focusing of the laser 110 occurs at the bottom of the layer of powder deposited a few moments earlier and which covers the junction of the two metal parts at the location where the laser gradually moves. The powder, impacted by the laser in its unfocused portion, also melts, and the metal melts under a thickness of molten powder. Above the metal molten pool 115, the molten or even sublimated powder 116 is thus present.

[0025] As the movement continues, the materials cool downstream of the current impact of the laser, the molten powder solidifies into a slag 125, and the molten metal into the weld or weld bead 130.

[0026] A suction line C2, downstream of the impact of the laser, removes, by the effect of a depression D, the powder and at least part of the slag.

[0027] In one embodiment, the powder is composed of 35% of a mixture of SiO2 + A12O3 and 65% CaF2 + CaO + MgO for laser beam welding of two plates of X10CrMoVNb9.1 stainless steel (a steel that is difficult to weld, of application to the nuclear industry) each 11 mm thick with a laser beam of continuous power of 8 kW delivered by an Nd-YAG source.

[0028] The powder is applied in the form of a smoothed flow and may comprise an acidic or basic mixture according to the basicity indices commonly used.

[0029] Two types of inerting were compared: by argon spraying and by powder flow. For an identical penetration of the molten pool into the depth of the parts to be welded, it is possible to reduce the power of the laser beam from 8 kW to 6.3 kW at the same travel speed. This reduction in the firing power of the laser beam of more than 20% is considerable. The metallographic analyses carried out on these welds show a high quality and purity of the molten pool after solidification. There are no defects in the weld.

[0030] [Fig.3] In [Fig.3], an implementation of the process for welding with filler or laser-wire additive manufacturing is shown. The figure is like [Fig.2A] a section with the direction of movement D of the laser parallel to the cutting plane.

[0031] A single metal part 190 may be present this time, and the cut is then made in a plane in which an addition of material will be made - the plane of the laser path, knowing that this path may be curved, in which case the plane is chosen locally - on the surface of the metal part 190. But the representation of [Fig.3] is also compatible with the presence of two metal parts as in Figures 2A and 2B, and the formation of a weld with added material.

[0032] Also within the scope of this disclosure is the possibility of simultaneously combining welding and additive manufacturing.

[0033] A filler wire 250 is placed at the location targeted by the laser source. Above the part, in the deposition plane (the plane of the figure), the laser source is placed which causes the formation of the molten pool 115 in the filler metal and on the surface of the metal part 190 (and of the second metal part if applicable), on the path of the addition of material to be produced.

[0034] According to the invention, a powder flow 120 has also been put in place by the deposition pipe C1, dynamically deposited upstream of the impact of the laser on the path of the material to be deposited. The deposition, carried out by the deposition pipe C1, is smoothed by it (the surface on which the powder is deposited is flat in the area on which the laser is applied, which allows the smoothed powder layer to be formed). The powder, as soon as it is present on the metal, ensures its protection against atmospheric gases, in particular water and oxygen.

[0035] The powder, impacted by the laser beam before the latter is focused, melts, and the metal of the wire melts under the effect of the laser beam which touches it at its focal point or very close to it, under a thickness of molten or sublimated powder. The metal of the surface, at least of the metal part 190 (and of the second metal part if applicable) also melts, since it is touched by the laser at its focal point on the surface of the metal or slightly below.

[0036] As the movement continues, the powder partially solidifies into a slag 125, and the molten metal into the welded and / or additively added material, forming a weld bead 260 and / or an added relief 260 above the surface of the metal part 190. As in [Fig.2A], a suction pipe C2, downstream of the impact of the laser, removes the powder and at least part of the slag.

[0037] Once the parts have been confirmed to have been completed by the above-mentioned processes and their temperature has returned to room temperature, their surfaces can be electrochemically cleaned.

[0038] The quality of the assemblies and formed parts is highly satisfactory, with processes having increased performance.

[0039] The method is applicable to all metals and metal alloys, including for example zirconium or reduced activation ferritic / martensitic steels (RAFM).

[0040] Instead of a reel C1 upstream of the laser source, the powder can be deposited by a nozzle surrounding the laser source and constituting a powder reel, at right angles to, or directly above, the impact of the laser on the metallic material to be treated.

[0041] Ultimately, the invention consists, within the framework of the application of a laser to drown the bath fusion under a flow of inerting powder whose composition is adapted to the metals or alloys to be welded in the context of a weld or to be handled in the context of additive manufacturing. This solution is suitable for laser welding with or without material input and for laser additive manufacturing.

[0042] It can optionally be implemented in an inerting chamber, under an inerting gas, to further guarantee the quality of the welding or additive manufacturing carried out, for example for industries with the greatest demands in this area, such as the nuclear sector.

[0043] It saves time compared to known techniques, and / or improves the quality obtained.

Claims

Claims

1. Method for shaping metallic material by melting and then cooling, comprising an application of laser radiation (110) to a material to be treated, and a progressive displacement (D) of said laser radiation (110) on a treatment path of the material to be treated, characterized in that the material to be treated is covered with an inerting powder (120), the inerting powder (120) being removed downstream of the application of the radiation after cooling of a molten bath (115) produced by said application of the radiation, the laser beam being projected through the powder and focused on the material to be treated.

2. Method for shaping metallic material according to claim 1, characterized in that the laser radiation (110) is applied and moved together with a metallic filler wire (250) whose end is placed under the laser radiation (110) so as to constitute a filler for the material to be treated.

3. Method for shaping metallic material according to claim 2, characterized in that the supply of material is sized for laser-wire additive manufacturing.

4. Method for shaping metallic material according to one of claims 1 to 3, characterized in that the laser radiation (110) is applied and moved to the junction between two metal parts to be welded (90, 95) included in the material to be treated, previously placed surface to be welded against surface to be welded.

5. Method of shaping metallic material according to claim 4, characterized in that the two metallic parts (90, 95) are of the same composition, or of different compositions.

6. Method for shaping metallic material according to one of claims 1 to 5, characterized in that the material to be treated comprises a steel.

7. Method for shaping metallic material according to one of claims 1 to 6, characterized in that it is carried out with or without an inerting box comprising an inerting gas to protect the molten bath.

8. Method for shaping metallic material according to one of claims 1 to 7, characterized in that the laser beam is delivered by an Nd-YAG source.

9. Method of shaping metallic material according to one of the claims- indications 1 to 8, characterized in that the powder is deposited in the form of a smoothed flow.