Fabrication process for waveguide devices by additive manufacturing and polishing

Abstract

Lighter weight waveguide devices. The invention relates to a method for manufacturing a waveguide device (1), comprising the step of manufacturing, by additive manufacturing, a semi-finished metal core (2) comprising a sidewall (20) having an outer surface (21) and an inner surface (22), the inner surface (22) defining an internal waveguide opening (5). The manufacturing process further comprises the step of chemically polishing the metal core (2) to reduce the thickness of the sidewall (20) by an ablation thickness equal to at least twice the roughness (Ra) of the metal core (2) before polishing, to obtain a waveguide device. The invention also comprises a waveguide device (1) obtained according to said process.

Description

[Technical field]

[0001] The present invention relates to a process for manufacturing waveguide devices by additive manufacturing and polishing, and to waveguides manufactured according to this process. [Background technology]

[0002] Radio frequency (RF) signals can propagate in space or through waveguide devices that are used to direct RF signals in specific directions or to manipulate RF signals in the spatial or frequency domains.

[0003] The present invention particularly relates to passive RF devices that allow the propagation and manipulation of high frequency signals without the use of active electronic components. Passive waveguide devices can be divided into three different categories. ·Devices based on guiding waves in hollow metallic channels, commonly known as waveguides. Devices based on waveguides inside a dielectric substrate. ·Devices based on waveguides with surface waves on metallic substrates such as PCBs, microstrips etc.

[0004] The present invention is particularly directed to the fabrication of waveguide devices according to the first category above (hereinafter collectively referred to as waveguide devices). Examples of such devices include waveguides, filters, antennas, polarizers, mode converters, etc., which can be used for signal routing, frequency filtering, signal separation or recombination, transmission or reception of signals in or from free space, etc.

[0005] A conventional waveguide is a hollow device whose shape and proportions determine the propagation characteristics of an electromagnetic signal of a given wavelength. Conventional waveguides used for high frequency signals have an internal opening with a rectangular or circular cross section. Such a waveguide can propagate electromagnetic modes that correspond to different electromagnetic field distributions along its cross section.

[0006] The production of waveguides with complex cross sections is difficult and expensive. To remedy this, US Pat. No. 6,299,336 proposes the production of waveguides by 3D printing. For this purpose, a non-conductive plastic core is printed by additive printing and then metal plated by immersion. In order for the waveguide to work, its inner surface must be conductive. The use of a non-conductive core not only allows the device to be lighter and less expensive, but also allows the use of 3D printing methods suitable for polymers or ceramics, which allow the production of high-precision parts with low wall roughness. The parts described here have complex shapes and on the one hand comprise channels for wave propagation and on the other hand holes for the attachment of the legs of the waveguide, which are intended for fixing to other elements.

[0007] There are various 3D printing techniques, including selective laser melting (SLM) 3D printing, which is a selective powder bed melting process that uses a laser to fuse microscopic metal particles together. The metal particles are melted according to a computer-determined pattern until they fuse together. A powder distribution system then applies a new layer of powder. The laser then paints on the next layer. These steps follow one another until the object is completely printed.

[0008] SLM printing can print layer thicknesses ranging from 0.02mm to 0.10mm in the Z axis, while the resolution in the X and Y axes depends on the diameter of the machine's laser beam. Standard SLM machines use lasers with diameters of 0.080mm and 0.1mm. For aluminum, the melt pool around the laser beam has a diameter of about 0.250mm. Ideally, a minimum of two vectors are needed to create the waveguide walls, and therefore a minimum thickness of 0.5mm is required.

[0009] Depending on the desired geometry, metal parts obtained by this process can have layer thicknesses that far exceed the Z-resolution of the machine imposed by the constraints mentioned above, which has a direct impact on the weight of the produced part.

[0010] 3D printing by selective laser sintering (SLS) is also well known, especially for plastic printing, but suffers from the same problems of resolution, especially related to the diameter of the laser beam.

[0011] Non-Patent Document 1 discloses the use of a chemical polishing process in waveguide devices obtained by additive manufacturing, but in particular notes that this process has many drawbacks, such as the enlargement of the iris and its non-uniform effect, the fact that it can only be used for narrow-band filters, its slowness as well as the frequency center shift or the difficulty of predicting its effect.

[0012] Non-Patent Document 2 discloses a chemical polishing process, but does not address the issues of wall thickness or the weight of the polishing equipment.

[0013] Non-Patent Document 3 also discloses a chemical polishing process for parts manufactured by laser powder bed fusion, but the wall thickness of the parts envisaged is relatively large (and heavy) and does not correspond to the standards of modern RF parts obtained by additive manufacturing.

[0014] Patent Document 2 discloses an aluminum oxide-based chemical polishing liquid and its manufacturing method. There is no mention of using this liquid for polishing RF components. Furthermore, the liquid appears to be intended to improve the aesthetics of polished components.

[0015] US Patent No. 5,399,633 discloses a process for chemical polishing of titanium surfaces obtained by additive manufacturing, but does not disclose its use in RF devices. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] US Patent Application Publication No. 2012 / 084968 [Patent Document 2] Chinese Patent No. 106757039

Patent Document 3

Non-Patent Document

[0017]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0018] Therefore, one object of the present invention is to provide an SLM-type additive manufacturing process for the production of lighter weight waveguide devices.

[0019] In particular, one object of the present invention is to enable the manufacture of metal or plastic waveguide devices having a thickness over any part of the device of less than 0.5 mm, preferably less than 0.3 mm or even less than 0.2 mm. [Means for solving the problem]

[0020] According to the invention, these objects are achieved in particular by a manufacturing process for a waveguide device, comprising the step of manufacturing a semi-finished, metal or plastic core by additive manufacturing, the semi-finished core having a sidewall with an outer surface and an inner surface, the inner surface defining a waveguide channel, the manufacturing process further comprising the step of chemically polishing the metal core in order to reduce, preferably uniformly, the thickness of said sidewall by an ablation thickness equal to at least twice the roughness of the metal core (2) before polishing, to obtain a waveguide device.

[0021] In one embodiment, the ablation thickness is at least 0.02 mm, preferably at least 0.05 mm.

[0022] In one embodiment, the ablation thickness is greater than the thickness of the additive printed layer.

[0023] In one embodiment, the metal core is manufactured by laser melting on a powder bed of additive manufacturing (SLM) to obtain a semi-finished metal core, and the ablation thickness is at least 1.5 times the powder grain size of said powder bed.

[0024] In one embodiment, the metal core is manufactured by additive manufacturing using laser melting on a powder bed (SLM) to obtain a semi-finished metal core, the thickness of the laser spot used for melting has a diameter between 0.03 mm and 0.1 mm and the ablation thickness is between 0.02 mm and 0.06 mm.

[0025] In one embodiment, the metal core is produced by additive manufacturing using laser melting on a powder bed to obtain a semi-finished metal core with a sidewall thickness of less than 0.5 mm.

[0026] In one embodiment, the internal waveguide opening of the semi-finished metal core has an oval, hexagonal, pentagonal, oval or circular cross-section.

[0027] In one embodiment, the thickness of the sidewall is less than 0.3 mm, or even less than 0.2 mm, after the chemical polishing step.

[0028] In one embodiment, the manufacturing process further comprises generating a digital model of the metal core, the digital model being calculated for optimizing the shape of the semi-finished metal core as a function of the thickness removed by chemical polishing.

[0029] In one embodiment, the chemical polishing step consists of immersing the semi-finished metal core in an acid bath. The acid bath may comprise a mixture of two acids. For example, the acid bath may comprise orthophosphoric acid and sulfuric acid to obtain a polishing effect.

[0030] In one embodiment, the chemical polishing step comprises immersing the semi-finished metal core in a basic bath, for example to produce a matte finish. The basic bath may comprise a caustic solution and have a pH greater than 11.5.

[0031] In one embodiment, the method includes immersing the metal core in an acidic deoxidizing bath after immersion in the basic bath to remove oxidation residues from the surface of the component.

[0032] In one embodiment, the process may comprise immersing the metal core in an acid bath, for example a bath containing nitric acid and ammonium bifluoride, the pH preferably being below 2.

[0033] In one embodiment, the process may comprise immersing the metal core in a heated acid bath while applying ultrasound to clean the metal core.

[0034] In one embodiment, the density of the bath is 1.5 g / cm 3 and 2g / cm 3 and preferably in the range of about 1.7 g / cm 3 It is.

[0035] In one embodiment, the acid bath treatment temperature is between 70°C and 120°C.

[0036] In one embodiment, the acid bath additionally comprises dissolved aluminum in a concentration between 20 and 50 g / l, preferably between 25 and 45 g / l.

[0037] Another aspect of the invention relates to a waveguide device comprising a metal core having a sidewall with an outer surface and an inner surface, the inner surface defining a waveguide channel, the sidewall having a thickness less than 0.3 mm, or even less than 0.2 mm.

[0038] Embodiments of the invention are illustrated in the accompanying drawings and description. [Brief description of the drawings]

[0039] [Figure 1] FIG. 1 is a perspective view of a waveguide device with internal openings or channels obtained by an SLM process according to one embodiment. [Diagram 2] FIG. 2 shows a view similar to FIG. 1 after a polishing step according to one embodiment. [Diagram 3] FIG. 3 is a schematic diagram showing a portion of a waveguide device immersed in a polishing bath to smooth out the aluminum's microscopic surface roughness. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] The waveguide device 1 shown in Figures 1 and 2 has a metallic core 2 made, for example, of aluminium, titanium, steel, Invar or alloys thereof.

[0041] The core 2 is manufactured by additive manufacturing, preferably by stereolithography, selective laser melting, selective laser sintering (SLS), binder jetting or direct energy deposition (DED). The wall thickness of the core is, for example, at least 0.5 mm.

[0042] The shape of the core may be determined by a computer file stored on a computer data medium.

[0043] The core 2 defines an internal opening 5 forming a channel for guiding the wave. The core 2 therefore has an inner surface 22 and an outer surface 21 which define the internal opening 5, which is, for example, rectangular in cross section.

[0044] The chemical polishing bath 25 works by leveling out the fine surface roughness of the material used to form the core, e.g., aluminum 30. Polishing is a process that reduces the roughness Ra of the material, allowing it to better reflect light (specularity). This is accomplished by leveling out the peaks and valleys (or depressions) of the material surface, as shown in Figure 3. Polishing is done by immersing the part in the bath and constantly agitating it.

[0045] The roughness Ra or roughness average or arithmetic mean roughness of a material refers to the average distance between the peaks and valleys of a material on the scale of the particles (or grains) used in additive manufacturing.

[0046] It is known to reduce the roughness of a material using chemical or electrochemical polishing processes. Surprisingly, the polishing process of the present invention, in addition to improving the specularity of the material, is also aimed at reducing the wall thickness of the waveguide device. Such a reduction in wall thickness is primarily desirable since it allows a significant reduction in the weight of the device.

[0047] In order to significantly reduce the weight of the waveguide device, the thickness of the sidewalls of the device must be reduced by polishing to an ablation thickness equal to at least twice the roughness of the material before the polishing process. The Ra roughness before polishing depends on the material used for additive manufacturing of the metal core, but is generally between 0.05 μm and 20 μm for materials considered for the manufacture of the device, such as aluminum, titanium or steel or Invar.

[0048] In certain embodiments, the ablation thickness is at least equal to 0.02 mm. Preferably, the ablation thickness is at least 0.05 mm.

[0049] The sidewall thickness of the metal core can be thicker, but to reduce the weight of the device, the thickness after grinding is typically less than 0.5 mm, so the ablation thickness is a significant percentage of the wall thickness before grinding.

[0050] In one embodiment, the ablation thickness is greater than the thickness of the additive printed layer, which may vary depending on the printing technique used and the type of part being manufactured, but is typically between 0.03 mm and 0.06 mm.

[0051] In the embodiment where printing is performed by laser melting on a powder bed (SLM), the ablation thickness is greater than 1.5 times the grain size of the powder used. These grains have a diameter between 0.01 mm and 0.065 mm. The ablation thickness is therefore between 0.015 mm and 0.098 mm.

[0052] More precisely, the particle size distribution is usually between 0.01 mm and 0.065 mm, with a D10 factor, i.e. maximum 10% of the grains in the powder batch being smaller than 0.01 mm. In general, the ablation thickness is at least equal to the D10 factor of the powder batch used for production.

[0053] In the case of printing by powder bed fusion, the thickness of the laser spot used to fuse the powder can be between 0.03 mm and 0.1 mm, resulting in an ablation thickness between 0.02 mm and 0.06 mm.

[0054] The bath may consist of a mixture of two acids. The additives ensure a uniform surface polish in terms of roughness and thickness. To completely smooth the aluminum surface, the chemical attack must be faster at the peaks than in the valleys. When aluminum is immersed in a bath of the two acids, the sulfuric acid reacts with the aluminum to form a thin film of aluminum oxide 40, which is simultaneously dissolved by the orthophosphoric acid. These reactions occur more rapidly at the peaks than in the valleys because the bath is highly viscous and there is less fluid movement and agitation in the valleys than in the peaks.

[0055] The main variables of the polishing bath are: A bath consisting of two acids (e.g. orthophosphoric acid and sulfuric acid), The bath density is approximately 1.7 g / cm 3 , Processing temperature is 80℃ to 110℃. The bath density is approximately 1.7 g / cm 3 , Immersion time is 15 seconds to 10 minutes. Alu concentration dissolved in the bath (for better start-up and good chemical reactivity) = 25 to 45 g / l.

[0056] In a further embodiment, polishing can be performed using a basic mix, for example for a satin finish. This process involves immersing the semi-finished waveguide in a solution in the presence of salts of organic and inorganic acids, alkali and polyfunctional organic hydroxyl compounds. The solution may comprise, for example: - Caustic solution (70-90g / l), - satin finish active ingredient (5 to 10 g / l), - Dissolved aluminum (10g / l). The pH of the solution is preferably greater than 11.5.

[0057] In the case of aluminum or aluminum alloy waveguides, the parts thus textured with the previous bath may be immersed in a deoxidizing bath to remove any oxidation residues on the surface of the parts after textured finishing and to remove the aluminum oxide layer on the surface of the parts, which may be, for example, an acid bath containing nitric acid (pH preferably less than 2).

[0058] Parts thus satin finished may be bleached by immersion in an acid bath (preferably having a pH below 2, e.g. containing nitric acid and ammonium bifluoride), which is particularly applicable to aluminum or aluminum alloy waveguides.

[0059] The parts thus textured may be immersed in an acid bath with a pH below 3, for example 10% concentrated, with the application of ultrasound for cleaning. In one mode of operation, the parts may be immersed in a solution at a temperature of 60°C to 65°C, ultrasound may be applied for 2 to 30 minutes, and then the immersion may be repeated for 30 minutes to 1 hour without ultrasound, while the temperature remains at 60°C. To obtain good cleaning results, this sequence must be repeated five times. After each ultrasound sequence, the acid solution is removed and replaced with a new solution to allow effective chemical and ultrasonic action.

[0060] This bath therefore enables the reduction of the thickness of the wall 20 of the core 2, such that this thickness between the outer surface 21 of the core 2 and the inner surface of the core 2 defining the internal opening (channel) 5 is reduced to less than 0.3 mm, or 0.2 mm, after the chemical polishing step.

[0061] This has the advantage of reducing the weight of the waveguide device.

[0062] The invention also relates to a waveguide device obtained according to one of the above embodiments, comprising a metal core 2 comprising a side wall 20 with an outer surface 21 and an inner surface 22, the inner surface 22 defining an internal opening 5 of the waveguide, said side wall 20 having a thickness of less than 0.3 mm, or even less than 0.2 mm.

Claims

1. A process for manufacturing a waveguide device (1) comprising a manufacturing step by additive manufacturing, A process for manufacturing a waveguide device (1) comprising a semi-finished metal core (2) having a sidewall (20) with an outer surface (21) and an inner surface (22), the inner surface (22) defining an internal waveguide opening (5), comprising:

1. A process for manufacturing a waveguide device (1), characterized in that it further comprises a step of chemically polishing the metal core (2) to reduce the thickness of the sidewalls (20) by an ablation thickness equal to at least twice the roughness (Ra) of the metal core (2) before polishing, to obtain a waveguide device.

2. 2. The manufacturing process according to claim 1, characterized in that said ablation thickness is at least equal to 0.02 mm.

3. 3. A manufacturing process according to claim 1 or 2, characterized in that the ablation thickness is at least equal to 0.05 mm.

4. 4. The manufacturing process according to claim 1, wherein the ablation thickness is greater than the thickness of the additional printing layer.

5. 5. The manufacturing process according to claim 1, characterized in that the metal core (2) is manufactured by additive manufacturing using laser melting on a powder bed (SLM) to obtain the semi-finished metal core (2), and the ablation thickness is at least equal to 1.5 times the powder grain size of the powder bed.

6. 6. A manufacturing process according to any one of claims 1 to 5, characterized in that the metal core (2) is manufactured by additive manufacturing using laser melting on a powder bed (SLM) to obtain a semi-finished metal core (2) and a laser spot with a diameter between 0.03 mm and 0.1 mm and an ablation thickness between 0.02 mm and 0.06 mm.

7. 7. A manufacturing process according to any one of claims 1 to 6, characterized in that the metal core (2) is manufactured by additive manufacturing using laser melting on a powder bed (SLM) to obtain a semi-finished metal core (2) with a thickness of the side wall (20) of less than or equal to 0.5 mm.

8. 8. The manufacturing process according to any one of claims 1 to 7, characterized in that the internal waveguide opening (5) of the semi-finished metal core (2) has an oval, pentagonal, hexagonal, oval or circular cross section.

9. 9. A manufacturing process according to any one of the preceding claims, characterized in that the thickness of the side wall (20) is less than 0.3 mm, or even less than 0.2 mm, after the chemical polishing step.

10. 10. The manufacturing process according to any one of claims 1 to 9, characterized in that it further comprises a step of generating a digital model of the metal core (2), the digital model being calculated to optimize the shape of the semi-finished metal core as a function of the thickness removed by chemical polishing.

11. 11. A manufacturing process according to any one of the preceding claims, characterized in that the chemical polishing step comprises immersing the semi-finished metal core (2) in an acid bath.

12. 12. The manufacturing process of claim 11, wherein the acid bath comprises a mixture of two acids.

13. 13. The manufacturing process of claim 12, wherein the acid bath comprises orthophosphoric acid and sulfuric acid.

14. The density of the bath is 1.5 g / cm ３ and 2 g / cm ３ between about 1.7 g / cm ３ 14. The manufacturing process according to claim 13, characterized in that

15. 15. The manufacturing process according to any one of claims 11 to 14, characterized in that the treatment temperature of the acid bath is between 70°C and 120°C.

16. 16. A manufacturing process according to any one of claims 11 to 15, characterized in that the acid bath additionally comprises dissolved aluminium in a concentration between 20 and 50 g / l, preferably between 25 and 45 g / l.

17. 11. A manufacturing process according to any one of the preceding claims, characterized in that the chemically polishing step comprises immersing the semi-finished metal core (2) in a basic bath.

18. 20. The manufacturing process of claim 17, wherein the basic bath comprises a caustic solution and has a pH greater than 11.

5.

19. 19. A manufacturing process according to claim 17 or 18, comprising the step of immersing the metal core in an acidic deoxidizing bath after immersion in the basic bath in order to remove oxidation residues from the surface of the part.

20. 20. A process according to any one of claims 17 to 19, comprising the step of immersing the metal core in an acid bath, preferably having a pH of 2 or less, for example a bath containing nitric acid and ammonium bifluoride.

21. 21. A manufacturing process according to any one of claims 11 to 20, comprising the step of immersing the metal core in a heated acid bath with ultrasound to clean the metal core.

22. A waveguide device obtained according to any one of claims 1 to 21, comprising a metal core (2) including a sidewall (20) having an outer surface (21) and an inner surface (22), said inner surface (22) defining an internal waveguide opening (5), The waveguide device, characterized in that the thickness of the sidewall (20) is less than 0.3 mm, or even less than 0.2 mm.

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