METHOD FOR MANUFACTURING A STRUCTURE COMPRISING CAVITIES

Abstract

A method for manufacturing a structure comprising cavities, the method comprising the following steps: a) forming hollow areas (110) in a first face (101) of a substrate (100) made of a first material, b) depositing a plate (200) made of a second material onto the first face (101) of the substrate (100), so as to cover the hollow areas (110) of the substrate (100), c) performing resistance welding, electron beam welding, or laser beam welding, preferably under vacuum, around the hollow areas, thereby welding the plate (200) onto the substrate (100) and forming cavities, d) performing a hot isostatic compression diffusion welding step on the assembly obtained. Figure for the abstract: 5A

Description

Title of the invention: METHOD FOR MANUFACTURING A STRUCTURE COMPRISING CAVITIES technical field

[0001] The present invention relates to the field of heat exchangers, and more generally to structures comprising cavities, for example fluid circulation channels.

[0002] The invention relates to a method for manufacturing a structure comprising cavities.

[0003] The invention also relates to a structure comprising cavities.

[0004] The invention has applications in many industrial fields and, in particular, for the manufacture of heat exchangers.

[0005] The invention is particularly interesting since it makes it possible to obtain elements comprising cavities, the cavities being able to be of simple or complex shapes. PREVIOUS STATE OF THE ART

[0006] Currently, to create a structure comprising hollow parts, several methods are possible.

[0007] One solution is to manufacture the component by additive manufacturing (or 3D printing). Parts with complex geometric shapes and good mechanical properties can be obtained. However, dimensional and geometric tolerances are often not met.

[0008] A second solution consists of forming channels by removing material from a solid elementary part. However, such a machining technique does not allow for obtaining all the desired channel geometries, cross-sections, and lengths.

[0009] A third solution consists of assembling elementary parts together using various techniques, such as fusion welding, brazing, or diffusion welding.

[0010] Diffusion welding is currently one of the most promising methods, and more specifically Hot Isostatic Compression Welding (HIC). The compression force is obtained by applying a pressurized gas to all the surfaces of the components to be assembled. Three methods exist for manufacturing a component with hollow sections using this technique.

[0011] The first method, shown in [Fig. 1], consists of using tubes 1 which are sandwiched between two grooved plates 2, 3. The shape of the grooves is identical to the tubes. The tubes can be pre-formed to obtain different sections (example: square, rectangular) or to have different curvatures along the length.

[0012] However, with this first method, only hollowed-out parts of simple geometric shapes can be obtained.

[0013] The second method, shown in [Fig. 2], consists of creating an assembly using two diffusion welding cycles. Such a method is described in document WO 2011 / 026925 A1a. Several plates 4, 5, including at least one grooved plate, are superimposed. A weld bead is placed between the two plates. A processing step is carried out to achieve diffusion welding of the material bead onto the plates 4, 5. The first cycle is performed at low pressure. The hollowed-out parts are closed at the ends. Since the gas cannot penetrate the interface, diffusion welding occurs. The joint is leak-proof. However, large pores remain, and the assembly exhibits low mechanical strength. Therefore, the process then includes a step of consolidating the assembly by hot isostatic compression to achieve diffusion welding of its elements.This cycle is initiated at high pressure; the hollowed-out sections are opened to close the pores and eliminate the junction.

[0014] The main drawback of this second method is that it is virtually impossible to manufacture hollow parts without deforming them. Indeed, since no pressure is present inside the channels, they can deform during the first cycle.

[0015] To prevent channel deformation / sagging, a material that can subsequently be removed or eliminated, for example, chemically or mechanically, can be introduced into the channels. Such a solution is described, for example, in document JP 2006 / 263746 A. However, it can be difficult not only to find the right filling material, but also to successfully remove it completely.

[0016] A third method consists of performing laser welding of thin plates 6 onto channels formed in a substrate 7, and then welding a cover 8 onto the resulting assembly. This method is shown, for example, in [Fig. 3]. Such a method is also described in document WO 2006 / 067349 AL. More specifically, this method comprises the following steps:

[0017] - provide a substrate 7 in which grooves have been made in order to constitute the bottom of the hollowed-out section ([Fig.4A]),

[0018] - place 6 thin blades at the top of the grooves in order to close the hollowed-out part ([Fig.4B]),

[0019] - weld the blades 6 to the substrate 7 by edge-to-edge laser welding in order to guarantee a sealing ([Fig.4C]),

[0020] - place a lid 8 over the assembly formed by the substrate 7 and by the blades 6 ([Fig.4D]),

[0021] - weld the substrate 7 and the cover 8 by isostatic compression diffusion at hot ([Fig.4E]).

[0022] However, this latter method has many disadvantages. In particular, fitting thin blades into grooves requires strict width tolerances (0.1 mm), which not only increases machining costs but also complicates the process because it remains difficult to fit and weld thin blades into the grooves without deformation, displacement and / or offset, especially when dealing with hollow parts of complex shapes. Description of the invention

[0023] An object of the present invention is to propose a method remedying the disadvantages of the prior art, and in particular, a method for forming a structure comprising cavities, the cavities being able to be of simple or complex shape, while avoiding the phenomena of deformation, displacement and / or shifting.

[0024] To this end, the present invention proposes a method for manufacturing a structure comprising cavities, the method comprising the following steps:

[0025] a) form hollowed-out areas in a first face of a substrate made of a first material,

[0026] b) depositing a plate made of a second material onto the first face of the substrate, so as to cover the hollow areas of the substrate,

[0027] c) perform resistance welding, electron beam welding or laser transparency welding, preferably under vacuum, around the hollowed areas, thereby welding the plate onto the substrate and forming cavities,

[0028] d) perform a hot isostatic compression diffusion welding step on the assembly obtained.

[0029] The invention is fundamentally distinguished from the prior art by the deposition of a plate onto the substrate and the implementation of a transparent welding step, preferably under vacuum, of the plate onto the substrate around the entire perimeter of the hollowed-out areas of the substrate to form sealed cavities. The welding can be resistance welding, electron beam welding, or laser welding. This step ensures sealing at the substrate / plate junction. Thus, not only is the perimeter of the cavities sealed, but this step also limits or even prevents contamination / oxidation of the enclosed surfaces.

[0030] The use of a vacuum environment allows, at the same beam power Under inert gas, a thinner and more penetrating weld bead can be obtained. Welding takes place at the plate / substrate interface through the plate.

[0031] The hot isostatic compression diffusion welding step allows the assembly to be finalized.

[0032] Advantageously, during step c), a laser welding by transparency is also carried out on the contour of the plate.

[0033] As the weld bead is thinner under vacuum and the atmosphere is homogeneous (it is not necessary to have gas protection next to the fusion as in welding under neutral gas), it is possible to weld cavities of small widths and / or at the bottom of a narrow and deep well.

[0034] Advantageously, after step c) a degassing step is carried out at the plate / substrate interface.

[0035] According to this advantageous variant, the process comprises, between step c) and step d), the following successive steps:

[0036] - place a cover on the plate,

[0037] - weld the cover onto the plate,

[0038] Advantageously, after welding the hood onto the plate, the process includes a step in which a degassing step is carried out at the plate / hood interface.

[0039] Advantageously, the hood is welded to the plate by laser welding, through transparency, preferably under vacuum.

[0040] Advantageously, the first material and the second material are independently selected from copper and its alloys, titanium and its alloys, aluminum and its alloys, steels, and vanadium. The first material and the second material may be identical or different.

[0041] The process has many advantages:

[0042] - obtain a uniform weld (in terms of chemical composition and micro structure) almost free of residual constraints.

[0043] - to assemble identical materials together (such as steels, alloys aluminum, titanium alloys, copper alloys) or assembling materials with very different chemical compositions (for example, steel / copper assemblies, steel / vanadium...),

[0044] - present a lower implementation cost compared to state-of-the-art processes previous, and in particular a lower machining cost,

[0045] - the ability to manufacture structures having cavities of complex shapes,

[0046] - avoid deformation phenomena,

[0047] - do not implement a nesting step.

[0048] The invention also relates to a structure obtained by such a process. The structure comprises:

[0049] - a substrate in a first material comprising hollowed-out areas in a first side of the substrate,

[0050] - a plate made of a second material covering the hollowed-out areas of the substrate, the The plate is welded to the substrate around the hollowed areas by a weld obtained by transparency, preferably under vacuum, by resistance welding, by laser welding or by electron beam welding and by hot isostatic compression diffusion, the hollowed areas delimited by the substrate and the plate forming cavities,

[0051] - possibly, a cover welded onto the plate.

[0052] Advantageously, the first material and the second material are independently selected from copper and its alloys, titanium and its alloys, aluminum and its alloys, steels, and vanadium. The first material may be identical to or different from the second material.

[0053] Advantageously, the structure is a heat exchanger comprising cavities arranged to circulate a fluid, the cavities forming channels for the circulation of a fluid: gas or liquid (example: N2, water, mixture of molten metals).

[0054] Other features and advantages of the invention will become apparent from the following supplementary description.

[0055] It goes without saying that this additional description is given only as an illustration of the object of the invention and should in no case be interpreted as a limitation of this object. Brief description of the drawings

[0056] The present invention will be better understood upon reading the description of exemplary embodiments given by way of illustration only and in no way limiting, with reference to the accompanying drawings in which:

[0057] [Fig.1]

[0058] [Fig.2]

[0059] [Fig.3] previously described, represent different embodiments according to the prior art.

[0060] [Fig.4A]

[0061] [Fig.4B]

[0062] [Fig.4C]

[0063] [Fig.4D]

[0064] [Fig.4E] previously described, represent different stages of a process according to the prior art.

[0065] [Fig.5A]

[0066] [Fig.5B]

[0067] [Fig.5C]

[0068] [Fig.5D] represent different stages of a process according to a particular embodiment of the invention.

[0069] [Fig.6A]

[0070] [Fig.6B]

[0071] [Fig.6C]

[0072] [Fig.6D]

[0073] [Fig.6E] represent different stages of a process according to another particular embodiment of the invention.

[0074] [Fig.7A]

[0075] [Fig.7B] are schematic three-dimensional representations of different substrates used to implement the process according to different particular embodiments of the invention,

[0076] [Fig.8] is a photographic image of different substrates used to implement the process according to another particular embodiment of the invention.

[0077] [Fig.9] is a photographic image of different structures obtained after laser welding under vacuum by transparency of a plate on the different substrates of [Fig.8], according to another particular embodiment of the invention.

[0078] [Fig. 10] is a metallographic section of the weld of one of the structures shown in [Fig.9].

[0079] The different parts represented in the figures are not necessarily shown on a uniform scale, in order to make the figures more legible.

[0080] The different possibilities (variants and embodiments) should be understood as not being mutually exclusive and can be combined with each other.

[0081] Furthermore, in the description below, orientation-dependent terms such as "above", "below", etc. of a structure apply assuming that the structure is oriented in the manner illustrated in the figures.

[0082] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0083] Although this is not limiting in any way, the invention is particularly useful for manufacturing a structure comprising fluid circulation channels intended especially, but not exclusively, for the exchange of heat between two fluids.

[0084] We will now describe in more detail a method for manufacturing a structure comprising cavities, with reference to the attached Figures 5A to 5F. The method comprises the following steps:

[0085] a) form hollowed areas 110 in a first face 101 of a substrate 100 in a first material ([Fig.5A]),

[0086] b) deposit a plate 200 of a second material on the first face 101 of the substrate 100, so as to cover the hollow areas of the substrate 100 ([Fig.5B]),

[0087] c) perform resistance welding, electron beam welding or a laser welding by transparency, preferably under vacuum, around the hollowed areas, whereby the plate 200 is welded onto the substrate 100 and sealed cavities are formed ([Fig.5C]),

[0088] d) perform a hot isostatic compression diffusion welding step on the assembly obtained ([Fig.5D]).

[0089] According to one embodiment, the method further comprises, between step c) and step d), the steps of placing a cover 300 onto the plate 200 and welding the cover 300 to the plate 200. Thus, according to this embodiment, shown for example in the attached Figures 6A to 6E, the method comprises the following steps:

[0090] a) form hollowed areas 110 in a first face 101 of a substrate 100 in a first material ([Fig.6A]),

[0091] b) depositing a plate 200 of a second material on the first face 101 of the substrate 100, so as to cover the hollow areas 110 of the substrate 100 ([Fig.6B]),

[0092] c) carrying out a transparent welding such as resistance welding, laser welding or electron beam welding, preferably under vacuum around the hollow areas 110, thereby welding the plate 200 onto the substrate 100 and forming sealed cavities ([Fig.6C]),

[0093] - place a cover 300 onto the plate 200,

[0094] - weld the cover 300 onto the plate 200 ([Fig.6D]),

[0095] d) perform a hot isostatic compression diffusion welding step on the assembly obtained ([Fig.6E]).

[0096] The substrate 100 comprises a first face 101 and a second face 102. The first face 101 may be parallel to the second face 102. It may also not be parallel to the second face 102. For example, the first face 101 may be flat ([Fig.7A]) or have reliefs ([Fig.7B]).

[0097] In step a), the substrate 100 is machined to form hollow areas. The hollow areas 110 can be of simple shapes (for example, longitudinal shapes). The hollow areas are, for example, grooves (i.e., longitudinal notches that may be narrow). The hollow areas can also be of complex shapes (for example, they may have curves or zigzags).

[0098] The hollowed-out areas 110 can have very varied cross-sections and paths. In particular, they can have rectangular, polygonal, or semi-circular cross-sections. They can also have a cross-section that varies according to their length. Their path can be straight or curved. It can include back-and-forth movements and / or sharp turns.

[0099] The hollowed-out areas can be in 2D (i.e. in the same plane (x, y)) or in 3D (i.e. their position can vary in a plane (x, y, z)).

[0100] Advantageously, each hollowed-out area 110 opens at least into one of its ex hoppers. Preferably, the hollowed-out areas have two ends and both ends are open.

[0101] In a particular embodiment, it is possible to form hollow areas 110 in the first face 101 and in the second face 102 of the substrate 100. It is then possible to place another plate on the second face 102 of the substrate 100, the substrate being sandwiched between the two plates. This embodiment makes it possible to form a compact structure.

[0102] All surfaces to be joined are advantageously cleaned and / or pre-treated (for example by chemical pickling or light machining) in order to obtain a clean surface and to improve the characteristics of the joint (for example mechanical or electrical characteristics).

[0103] The plate 200 used in step b) is chosen so that it can be welded to the substrate through its transparency. The plate 200 is placed and aligned on the substrate 100. This adjustment is simple to perform because the plate 200 is a solid plate. The surface of the plate 200 covers at least all of the recessed areas 110. Preferably, it covers the entire first face 101 of the substrate 100.

[0104] Advantageously, before assembly, the plate 200 and the substrate 100 are cleaned and / or machined to remove any surface oxide that may be present on the surface of these parts and / or to ensure a good roughness. This guarantees the cleanliness of the joints to be assembled. This step leads to an improvement in the mechanical properties at the joint.

[0105] According to a first embodiment, the plate 200 can act as a lid. This reduces the number of steps and components required to implement the process, thereby lowering costs. The thickness of the plate 200 will be chosen to be sufficiently small to achieve a watertight seal with the substrate 100.

[0106] According to another embodiment, a hood 300 is subsequently welded onto the plate 200. The hood 300 acts as a cover. The surface area of ​​the hood 300 is at least equal to the surface area of ​​the plate 200. The hood 300 is the counter-form that allows material to be added where necessary.

[0107] According to this embodiment, the plate 200 may also have recessed areas. The recessed areas of the plate may be closed by the cover 300. The cover 300 may be without recessed areas or with recessed areas.

[0108] According to this embodiment, the thickness of the plate 200 can be thinner than in the embodiment where the plate also plays the role of a lid.

[0109] The first material of the substrate 100 and the second material of the plate 200 can be identical (i.e. it is a homogeneous assembly).

[0110] Otherwise, the first material and the second material may be different (i.e. it is a heterogeneous assembly).

[0111] The first material and the second material can be chosen independently of each other from: copper and its alloys, titanium and its alloys, aluminum and its alloys, steels and vanadium. In step c), the face of the plate 200 arranged opposite the first face 101 of the substrate 100 and the first face 101 of the substrate 100 form the interface to be welded by diffusion.

[0112] The plate 200 is welded to the substrate 100. The weld is made around the entire perimeter of the recessed areas 110. The resulting weld 210 follows the contour of the recessed areas 110 ([Fig. 5C], 6C). The periphery of the interface is welded in a leak-proof and degassed manner.

[0113] Thanks to welding, the use of brazing is eliminated. The maximum temperature at which the resulting element can be used is therefore increased.

[0114] Transparency welding can be performed by laser, electron beam, or resistance welding. Advantageously, for resistance welding, the thicknesses of the parts to be welded will typically be less than 3 mm. Resistance welding can be performed in air, under a controlled atmosphere, or under vacuum.

[0115] This step is preferably carried out by laser welding, and even more preferably by laser welding through vacuum.

[0116] It is possible to form two weld beads for each hollow area 110. However, if the hollow areas are very close to each other, a single weld bead may be sufficient.

[0117] The welding conditions are chosen so as to obtain a seal at the substrate / plate junction.

[0118] Thus, the pressurized gas which will be applied during the Hot Isostatic Compression (HIC) cycle and which will enter the hollowed parts will not be present at the substrate 100 / plate 200 interface between two laser weld beads.

[0119] Advantageously, a metallographic section can be carried out on test samples in order to verify the full penetration of the bead and the absence of disqualifying defects in the weld beads as defined in the standard NF EN ISO 13919 but this control is destructive.

[0120] Advantageously, a helium leak test with a leak detection limit of 1.10 10 mbar.ls 1 according to standard NF EN ISO 20485 can be carried out to ensure the proper sealing of the vacuum weld by transparency of each channel of the substrate 100. This test is non-destructive.

[0121] Advantageously, radiography or X-ray tomography can be performed to check for the absence of critical defects in weld beads as defined in standard NF EN ISO 13919. This check is non-destructive.

[0122] Advantageously, in step c), the contour of the substrate 100 / plate 200 interfaces is also welded. The weld 220 makes the assembly watertight ([Fig. 5D]). If necessary, the contour of the hood 300 / plate 200 interfaces is also welded. The weld 310 makes the assembly watertight ([Fig. 6D]). The contour welding is preferably carried out by vacuum welding.

[0123] At the end of step c), the cavities formed are sealed.

[0124] To implement step d), the cavities are opened at least at one end so that the gas can circulate inside the hollowed-out sections. Thus, during step d), the pressure inside the cavities can increase, and there is no deformation of the channels during the implementation of this step. This opening can be incorporated during the machining step of the substrate 100, prior to the CIC cycle.

[0125] Advantageously, before step d), the substrate 100 / plate 200 and / or hood 300 / plate 200 interfaces are degassed under secondary vacuum.

[0126] In step d), CIC diffusion welding is carried out. Sealing the hollow areas 110 by means of the plate 200 welded in step c) makes CIC diffusion welding possible without significant deformation of the channels formed.

[0127] This diffusion welding is carried out in the solid phase. A temperature of approximately 0.5 to 0.9 Tf, the melting temperature of the material, and high pressure are applied to the components to be assembled.

[0128] For steels and nickel alloys, the welding temperature is typically chosen between 900°C and 1250°C. The pressure is typically between 700 bar and 1500 bar (i.e., between 8 x 10⁷ Pa and 1.5 x 10⁸ Pa). The welding time is, for example, between 1h and 100, preferably between 2h and 5h.

[0129] Initially, contact is made at the rough peaks of the material. Then, various diffusion mechanisms, as well as migration of the grain boundaries, close the pores. Thus, the interface between the two parts to be assembled disappears.

[0130] If the vacuum from the laser welding in step c) is not satisfactory, it is possible to perform, prior to the CIC diffusion welding step, a step in which holes are formed, for example by drilling, and spigots (i.e., tubes that allow the substrate / plate and / or plate / cover interfaces to be drawn under vacuum). The greater the vacuum at the interfaces to be welded, the better the mechanical characteristics of the joint.

[0131] Diffusion welding produces no deformation of the channels.

[0132] In a particular embodiment, after the diffusion welding step, it is possible to reduce the thickness of the different elements of the structure in order to obtain the desired dimensions of the part to be produced.

[0133] Illustrative and non-limiting examples of an embodiment

[0134] In this example, a substrate 100 with zig-zag hollowed areas 110, and more particularly M-shaped hollowed areas, was manufactured ([Fig.8]). The substrate 100 is made of steel.

[0135] A 200 mm steel plate was placed on the substrate. Then, the following steps were carried out:

[0136] - a vacuum laser transparency welding step is performed to weld the plate 200 is welded to substrate 100 using a weld 210, thus forming watertight cavities; the contour of substrate 100 and plate 200 was also welded by laser welding through transparency.

[0137] - a hot isostatic compression diffusion welding step of the resulting set.

[0138] Fig. 9 represents the part obtained after the vacuum transparency laser welding step.

[0139] A helium test was performed to verify the leak-tightness of the laser weld. The test is that described in paragraph A.3 of ISO 20485:2018 (“Non-destructive testing — Leak testing — Tracer gas method”). The part exhibits good leak-tightness.

[0140] A metallographic section confirms that the weld 210 penetrates the substrate 100 ([Fig. 10]).

Claims

Demands

1. A method for manufacturing a structure comprising cavities, the method comprising the following steps: a) forming hollow areas (110) in a first face (101) of a substrate (100) of a first material, b) depositing a plate (200) of a second material on the first face (101) of the substrate (100), so as to cover the hollow areas (110) of the substrate (100), c) performing resistance welding or vacuum laser transparency welding around the hollow areas, thereby welding the plate (200) onto the substrate (100) and forming cavities, d) performing a hot isostatic compression diffusion welding step on the assembly obtained.

2. Method according to claim 1, characterized in that, during step c), a laser welding by transparency is further carried out on the contour of the plate (200).

3. A method according to any one of the preceding claims, characterized in that, after step c) a degassing step is carried out at the plate (200) / substrate (100) interface.

4. A method according to any one of the preceding claims, characterized in that the method comprises, between step c) and step d), the following successive steps: - placing a hood (300) on the plate (200), - welding the hood (300) onto the plate (200).

5. Method according to the preceding claim, characterized in that, after welding the hood (300) onto the plate (200), the method includes a step in which a degassing step is carried out at the plate (200) / hood (300) interface.

6. A method according to any one of claims 4 and 5, characterized in that the hood (300) is welded to the plate (200) by laser welding, preferably under vacuum.

7. A method according to any one of the preceding claims, characterized in that the first material and the second material are independently chosen from copper and its alloys, titanium and its alloys, aluminum and its alloys, steels and vanadium, the first material and the second material being able to be identical or different.

8. Structure comprising: - a substrate (100) of a first material having hollowed areas (110) in a first face (101) of the substrate (100), - a plate (200) of a second material covering the hollowed areas (110) of the substrate (100), the plate (200) being welded to the substrate (100) around the hollowed areas (110) by a weld (210) obtained by vacuum transparency, by resistance welding or by laser welding and by hot isostatic compression diffusion, the hollowed areas (110) delimited by the substrate (100) and the plate (200) forming cavities, - optionally, a cover (300) welded to the plate (200).

9. Structure according to claim 8, characterized in that the first material and the second material are independently chosen from copper and its alloys, titanium and its alloys, aluminum and its alloys, steels and vanadium, the first material being able to be identical or different from the second material.

10. Structure according to any one of claims 8 and 9, characterized in that the structure is a heat exchanger comprising cavities arranged to circulate a fluid, the cavities forming channels for the circulation of a fluid, such as a gas or a liquid.

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