Cleaning an optical element of an additive manufacturing device

Abstract

The present invention relates to an additive manufacturing machine (1), comprising: - an enclosure (2); - a source of energy beams (20) configured to selectively scan a powder bed (3a) and consolidate it; - an optical element (4) fixed in the enclosure (2) and made of a material transparent to electromagnetic waves, the optical element (4) having a surface (5) on which a deposit (7) resulting from vaporization of the powder bed (3a) is likely to form; and - a cleaning system (8) of the surface (5) of the optical element (4) comprising a plasma generator (11), the plasma generator (11) comprising a power electrode (9), placed opposite an opposite surface (6) of the optical element, (4) and a ground electrode (10) configured to generate a plasma (11) by capacitive coupling near the first surface (5). Figure for abstract: Fig. 2a

Description

Title of the invention: Cleaning an optical element of an additive manufacturing device FIELD OF THE INVENTION

[0001] The invention generally relates to the field of cleaning an optical element in an aggressive environment leading to the deposition of a thin layer on the surface, in particular a metallic one. The proposed method applies in particular to metallic additive manufacturing by electron beam or selective melting by low-pressure laser. STATE OF THE ART

[0002] Several thin-film deposition processes currently exist. These include, but are not limited to, selective additive manufacturing, thermal or electron beam vacuum evaporation, sputtering, or even metal additive manufacturing.

[0003] High-energy additive manufacturing consists of producing three-dimensional objects by consolidating selected areas on successive layers of powdered material (metal powder, ceramic powder). The consolidated areas correspond to successive sections of the three-dimensional object. Consolidation is carried out, layer by layer, by total or partial selective melting carried out with a consolidation source. This source is typically a radiation source (for example a high-power laser beam) or a particle beam source (for example an electron beam - technology known as EBM or "Electron Beam Melting" according to the English terminology generally used in the field).

[0004] In metal additive manufacturing processes, the vapor, in the atomic state or in the form of clusters of atoms up to powder (also called "clusters" or aggregates in French), is produced by the vaporization of the surface under the effect of the energy provided by the intense primary beam (electrons or laser). This vapor is essentially neutral, because the evaporation process generally takes place at thermodynamic equilibrium.

[0005] The vapor resulting from the heated solid thus formed has a strong capacity to deposit (condensation) on any solid material with which this vapor comes into contact, and in particular on all metals but also on dielectric materials (ceramics, glass, plastic, etc.) or semi-conductors (silicon, germanium, gallium arsenide, etc.).

[0006] The resulting deposits are particularly harmful. They lead to the formation, on optical elements inside manufacturing enclosures (lenses, camera optics, etc.) of thin layers which can make it opaque for wavelengths ranging from ultraviolet to infrared when the thickness of the deposit exceeds 30 nm. The formation of a deposit is all the more important at low pressure because the mean free path of the species is then very large, or comparable with the dimensions of the machine enclosure.

[0007] In order to clean these deposits, when the surface to be cleaned is ceramic, it is known to implement mechanical sandblasting or shot blasting methods. However, these mechanical methods cannot be used on glasses transparent to radiation since they generate pitting and end up frosting the glass.

[0008] It has also been proposed to use a chemical solution applied to the surface to be cleaned, such as an acid solution of the aqua regia type. This chemical method is very effective for dissolving metals without attacking the glass. However, it is incompatible with in situ treatment in a low pressure environment or vacuum, and more generally with dry processes. Statement of the invention

[0009] One aim of the invention is to remedy the aforementioned drawbacks.

[0010] Another aim of the invention is to propose a method for cleaning an optical element, which can be implemented at low pressure, independently of the material constituting the surface, which is effective and does not damage the surface to be cleaned.

[0011] For this purpose, according to a first aspect of the invention, an additive manufacturing machine is proposed, comprising: - an enclosure; - a mobile tray placed in the enclosure and on which a bed of powder is placed; - one or more energy beam sources configured to selectively scan the powder bed and consolidate it; - an optical element fixed in the enclosure and made of a material transparent to electromagnetic waves, the optical element having a first surface on which a deposit resulting from vaporization of the powder bed is likely to form and a second surface, opposite the first surface; and - a system for cleaning the first surface of the optical element comprising a plasma generator, the plasma generator comprising a power electrode, placed opposite the second surface of the optical element, and a ground electrode configured to generate a plasma by capacitive coupling near the first surface.

[0012] Certain preferred but non-limiting features of the manufacturing machine additive according to the first aspect are the following, taken individually or in combination: - the power electrode is mounted to be movable relative to the enclosure between a cleaning configuration, in which the power electrode is positioned opposite the second surface and a retracted configuration, in which the power electrode is offset relative to the deposit; - the first surface of the optical element is at least twice as large as an active surface of the power electrode, the optical element being movable relative to the power electrode; - the power electrode is fixed relative to the enclosure; - the first surface of the optical element is at least four times larger than the active surface of the power electrode, which optical element is rotatable about an axis relative to the power electrode, the power electrode being offset relative to the axis; - the additive manufacturing machine further comprises a plasma confinement enclosure positioned on the side of the first surface of the optical element and fixedly mounted relative to the power electrode so as to confine the plasma at an area of ​​the first surface facing the power electrode; - the additive manufacturing machine further comprises a magnetic trap mounted, fixed or movable, relative to the optical element and positioned near the first surface. - the additive manufacturing machine further comprises an impedance adapter configured to monitor an impedance of the plasma generator and, optionally, to control the plasma generator based on the measured impedance; - the plasma generator comprises a radiofrequency generator and a useful surface area of ​​the power electrode is less than a useful surface area of ​​the ground electrode in order to generate a self-polarization voltage at the power electrode; and / or - the enclosure is connected to ground and serves as a ground electrode.

[0013] According to a second aspect, the invention proposes a system for cleaning an additive manufacturing machine according to the first aspect, comprising a plasma generator, the plasma generator comprising a power electrode, configured to be placed opposite the second surface of the optical element, and a ground electrode configured to generate a plasma by capacitive coupling near the first surface.

[0014] Some preferred but non-limiting features of the cleaning system according to the second aspect are the following, taken individually or in combination: the cleaning system further comprises a fixedly mounted magnetic trap or movable relative to the optical element and positioned near the first surface; - the cleaning system further comprises an impedance adapter configured to monitor an impedance of the plasma generator and, optionally, to control the plasma generator based on the measured impedance; and / or - the plasma generator comprises a radiofrequency generator and a useful surface area of ​​the power electrode is less than a useful surface area of ​​the ground electrode in order to generate a self-polarization voltage at the power electrode.

[0015] According to a third aspect, the invention proposes a method for cleaning an optical element of an additive manufacturing machine according to the first aspect comprising the following steps: SI: placement of a power electrode opposite the second surface of the optical element; and S2: power supply of the power electrode so as to generate a plasma by capacitive coupling near the first surface so as to erode the deposit formed on the first surface of the optical element.

[0016] Some preferred but non-limiting features of the cleaning method according to the third aspect are the following, taken individually or in combination: - the method further comprises the following steps: S3: monitoring an impedance of the plasma; and S4: when a variation in the impedance exceeds a predetermined threshold, interrupting the power supply to the power electrode and / or moving one of the deposition electrode and the optical element; - during step SI, the power electrode is moved relative to the optical element so as to position it at the level of the deposit; - during step SI, the optical element is moved relative to the power electrode so as to position the deposit at the power electrode; - the optical element is moved by rotation around an axis; and / or - the optical element has a surface area approximately at least twice as large as an active surface area of ​​the power electrode and the optical element makes a fraction of a turn with each movement, for example the surface area of ​​the optical element is four times as large and the optical element makes a quarter of a turn with each movement. DESCRIPTION OF FIGURES

[0017] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0018] [Fig.1a] [Fig.1a] schematically illustrates an exemplary embodiment of an additive manufacturing device according to a first embodiment of the invention, the cleaning system being in a retracted configuration during additive manufacturing;

[0019] [Fig.lb] [Fig.lb] schematically illustrates the embodiment of [Fig.la], the cleaning system being in the cleaning configuration;

[0020] [Fig.2a] [Fig.2a] is a schematic side view of a first example of a sheave development of an additive manufacturing device according to a second embodiment of the invention;

[0021] [Fig.2b] [Fig.2b] is a schematic top view of a second example of production of an additive manufacturing device in accordance with the second embodiment of the invention.

[0022] [Fig.3] [Fig.3] is a flowchart showing steps in an example of a rea use of a cleaning process according to the invention.

[0023] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION

[0024] An additive manufacturing machine comprises a vacuum chamber, under primary vacuum, or at lower pressures. Typically, the pressure in the chamber can range from about 103 to 10 mbar.

[0025] Conventionally, an additive manufacturing machine 1 comprises: • an enclosure 2; • a mobile tray 30 placed in the enclosure 2 and on which a bed of powder 3a is placed; • one or more sources of energy beams 20 controlled to selectively scan the powder bed 3a and consolidate it; • a powder feed tank; • a tool, such as a squeegee or roller, that moves in translation over the powder bed to spread the powder; and • an optical element 4, placed in the enclosure 2 or in an opening provided in a wall of the enclosure 2, between the energy beam source(s) 20 and the powder bed 3a on the plate 30.

[0026] The optical element 4 is made of a material transparent to electromagnetic waves and has a first surface 5 placed opposite the powder bed 3a and a second surface 6 opposite the first surface 5. During the vaporization of the powder bed 3a during the consolidation phase, particles 3b are likely to form a deposit 7 on the first surface 5 (or “surface to be cleaned 5”) of the optical element 4. However, in the long term, this undesirable deposit 7 can make the optical element 4 opaque and block the manufacturing by preventing the beam 20 from passing to the plate 30 where the powder bed 3a is located. Generally, the second surface 6 (or “clean surface 6”) is located on the side of the energy beam source(s) 20.

[0027] Usually, in an additive manufacturing machine 1, the optical element 4 is made of glass and is therefore transparent to electromagnetic waves whose wavelength corresponds to those of visible light, infrared rays and ultraviolet rays. For example, when it is crossed by a laser beam, the optical element 4 must offer a transparency of at least 99.99% at the wavelength of this beam. This is not, however, limiting, the optical element 4 being able to be transparent for electromagnetic waves having any other wavelength, such as for example radio waves or radar.By way of non-limiting example, the optical element 4 may comprise glass (SiO2) (which is transparent to visible radiation), fused silica, quartz, potassium bromides (which are transparent to ultraviolet radiation), silicon, germanium, silicon carbide (which are transparent to infrared radiation), dielectric ceramics (A12O3, BN, ZrN, etc., which are transparent to radio / radar waves).

[0028] The optical element 4 may in particular be dielectric, and possibly metallized.

[0029] In order to clean the optical element 4, the additive manufacturing machine 1 further comprises a cleaning system 8 for the surface 5 of the optical element 4 to be cleaned, comprising a plasma generator 11. For this purpose, the plasma generator 11 comprises a power electrode 9 placed opposite the clean surface 6 of the optical element 4 and a ground electrode 10 which are configured to generate a plasma 11 by capacitive coupling near the surface 5 to be cleaned.

[0030] In this way, a plasma 11 - that is to say a medium consisting of a mixture of molecules of atoms and ions most often in excited states, as well as electrons, the whole being electrically neutral and the particles having in the majority of cases a high kinetic energy - develops near the surface to be cleaned 5 of the optical element 4 and erodes the deposit 7 present on this surface. This is therefore a mechanical cleaning carried out at the scale of the atoms, ions and electrons and other species activated by the plasma.

[0031] The cleaning system 8 thus makes it possible to clean the deposit 7 formed on the surface to be cleaned 5 of the optical element 4, whatever its composition. In particular, the deposits 7 capable of being eroded by the plasma 11 may comprise at least one of the following materials: metal, a metallic compound (such as metal oxides and nitrides, selenides, sulfides, etc.), a carbon-based material (graphite, carbon black, hydrogenated amorphous carbon, adamantine carbon, etc.), a silicon-based material or even an IILV compound (such as ammonium nitride, boron nitride or even gallium arsenide).

[0032] In addition, since a plasma 11 can be created over a wide range of pressures below atmospheric pressure, the cleaning system 8 is compatible with both secondary and primary vacuums and can be implemented at pressures between approximately 103 mbar and 10 mbar.

[0033] It is furthermore not necessary to cool the cleaning system 8.

[0034] In a first embodiment, and during the implementation of the cleaning ([Fig.lb]), the power electrode 9 is placed, for example using a translation or rotation system 17, against the clean surface 6 of the optical element 4, that is to say in contact with it. In this way, the plasma 11 develops at the level of the surface to be cleaned 5.

[0035] Alternatively, the power electrode 9 may be placed at a short distance from the clean surface 6 of the optical element 4. The distance between the power electrode 9 and the clean surface 6 is then chosen so as to guarantee that the plasma 11 is generated at the surface to be cleaned 5, and not at the clean surface 6. For example, a maximum distance between the power electrode 9 and the optical element 4 is at most equal to 1 mm.

[0036] The power electrode 9 may have any shape suitable for cleaning the optical element 4. For this purpose, the power electrode 9 may be circular, parallelepipedal (for example rectangular), etc. and may be flat or curved so as to best match the size and shape of the optical element 4. Preferably, when the surface to be cleaned 5 is flat, the power electrode 9 is also flat.

[0037] The power electrode 9 is made of an electrically conductive material, such as metal, and is insulated from ground.

[0038] If necessary, the power electrode 9 may be placed in a guard electrode 12, such as a metal sheath, which may be floating or connected to ground and is configured to accelerate the ions and allow bombardment of the deposit 7. The guard electrode 12 is dimensioned so that a distance between the guard electrode 12 and the power electrode 9 is as small as possible, so that the plasma 11 develops only at the surface to be cleaned 5 of the optical element 4.

[0039] The plasma generator 11 further comprises a control unit configured to control an electrical power source 13.

[0040] The power source is configured to supply the power electrode 9 in order to form the plasma 11 with a voltage greater than several kV. If necessary, the voltage may be bipolar.

[0041] In one embodiment, the electrical power source 13 comprises at least one of a radiofrequency generator, a high-frequency generator, and an alternating pulse generator. In this way, even when the deposit 7 that forms on the surface 5 of the optical element 4 to be cleaned comprises a metallic material, the current generated between the power electrode 9 and the ground electrode 10 manages to cross the deposit 7 during the transient phases of the excitations to form the plasma 11 at the level of the surface to be cleaned 5.

[0042] The plasma generator 11 also comprises a gas source 14, configured to inject a gas into the enclosure 2 and thus enable the generation of the plasma 11. In one embodiment, the gas comprises a rare gas (i.e. an inert or at least very slightly reactive gas), typically comprising at least one of the following elements: argon, neon, helium, krypton or xenon, so that the cleaning of the deposit 7 is carried out independently of the chemical nature of the material. The plasma 11 is therefore capable of cleaning any type of deposit 7 on the surface to be cleaned 5. In this embodiment, the erosion of the deposit 7 is therefore purely mechanical. Alternatively, the gas may comprise a molecular gas, for example comprising at least one of the following elements: oxygen, nitrogen, chlorine, fluorine, etc.In this case, it is possible, depending on the composition of the deposit 7, that the plasma 11 reacts chemically with the deposit 7, which can accelerate the erosion of the deposit 7 or possibly slow it down, without however preventing it.

[0043] It will be noted that, when the enclosure 2 already comprises a gas, for example for carrying out the additive manufacturing process, the gas used for manufacturing can also be used for generating the plasma 11. In this case, the gas source of the additive manufacturing machine 1 can be used as the gas source 14 of the plasma generator 11. Alternatively, a separate gas source 14 can be added, for example to inject a rare gas. In this case, the gas source 14 takes for example the form of a gas inlet positioned in the enclosure 2 near the area of ​​the optical element 4 to be cleaned. Optionally, the additive manufacturing machine 1 then also comprises a gas outlet, positioned near the surface 5 to be cleaned and connected to a pump, in order to suck in the gas injected by the gas source 14 of the gas generator once the deposit 7 has been eroded by the plasma 11.

[0044] When the enclosure 2 is under total or partial vacuum, a gas source 14 is then added to the additive manufacturing machine 1 in order to inject the gas close to the surface to be cleaned 5 to allow the formation of the plasma 11 and to suck it up once the cleaning is carried out.

[0045] In all cases, the flow rate of the injected gas is chosen as a function of the initial pressure in the enclosure 2 so as to minimize the time to reach the optimal condition for the creation of the plasma (the faster the flow rate, the more the gas possibly present in the enclosure 2 is diluted).

[0046] The enclosure 2 of the additive manufacturing machine 1 may be metallic and plays the role of the ground electrode 10 in the formation of the plasma 11. The cleaning system 8 then does not necessarily comprise a ground electrode 10, in addition to the metal enclosure 2. Alternatively, when the enclosure 2 of the additive manufacturing machine 1 can be made of a dielectric material, for example plastic: a ground electrode 10 is then placed in the enclosure 2, close to the surface to be cleaned 5 of the machine 1.

[0047] In one embodiment, the useful surface area of ​​the power electrode 9 is less than the useful surface area of ​​the ground electrode 10. By useful surface area of ​​an electrode, we will understand here the surface area of ​​the electrode which is not protected by the counter-electrode, and by which the applied electrical power can make its way to the ground. In this case, the total current measured being a function of the useful surface area of ​​the electrode and of the current density, a negative voltage called self-bias and continuous is self-generated at the level of the power electrode 9 when a discharge plasma is created. This negative voltage then attracts the positive ions of the plasma, thus inducing a weak ion bombardment.Now, the power electrode 9 being placed opposite the optical element 4, and preferably against or at a very short distance from it, the negative voltage makes it possible to accelerate the ions of the plasma 11 and to increase the erosion speed of the deposit 7.

[0048] Typically, when the enclosure 2 is used as the ground electrode 10, the surface area of ​​the power electrode 9 is small in comparison with the surface area of ​​the ground electrode 10, so that a self-polarization voltage is created which improves the efficiency of the physicochemical cleaning by the plasma 11.

[0049] Optionally, the cleaning system 8 may further comprise a magnetic trap 15 in order to increase the efficiency of erosion of the deposit 7 by the plasma 11. For this purpose, the cleaning system 8 may for example comprise permanent magnets and / or electromagnets placed close to the surface to be cleaned 5. Since the magnetic field thus generated is not homogeneous, the magnetic trap 15 may possibly be moved relative to the surface to be cleaned 5, for example rotated, so as to obtain homogeneous erosion of the deposit 7. This variant embodiment may in particular be advantageous when the speed of formation of the deposit 7 is greater than the speed of erosion by the plasma 11.

[0050] When the deposit 7 comprises an electrically conductive material, the cleaning system 8 further comprises an impedance adapter 16 of the circuit configured to provide a resistive load for the electrical power source 13, thus reducing power losses (reflected power). Indeed, the complete erosion of the deposit 7 on the surface to be cleaned 5 is accompanied by a change in the impedance of the assembly formed by the power electrode 9, the optical element 4, the deposit 7 and the plasma 11. Consequently, the monitoring of the impedance makes it possible to detect a change in the impedance of this assembly and therefore the complete erosion of the deposit 7, which makes it possible to stop the cleaning process and to preserve the window from the action of the ions that could damage it if the plasma 11 operated continuously, even in the absence of deposit 7.

[0051] Optionally, the impedance adapter 16 is configured to automatically determine a variation in the impedance which exceeds a predetermined threshold and allows the control unit to send a stop instruction to the electrical power source 13 of the power electrode 9 in order to stop the generation of the plasma 11.

[0052] When the electrical power source 13 comprises a radiofrequency generator, the plasma generator 11 also necessarily comprises a control unit with feedback loop on the radiofrequency generator. Advantageously, this control unit can then serve as an impedance adapter 16 in order to detect impedance variations and, if necessary, allow the control unit to block the power supply to the power electrode 9.

[0053] The power electrode 9 can be mounted to move relative to the optical element 4 between a cleaning configuration, in which the power electrode 9 is positioned opposite the second surface 6 ([Fig.lb]), at the level of the deposit 7 to be cleaned, and a retracted configuration, in which the power electrode 9 is offset relative to the deposit 7 ([Fig.la]) in order to allow the additive manufacturing to proceed correctly (by freeing the passage for the energy beam(s) 20 of the machine 1). In one embodiment, the movement of the power electrode 9 is carried out by an actuator which is controlled by the control unit.

[0054] In this embodiment, the useful surface area of ​​the power electrode 9 can be substantially equal to the surface area 5 of the optical element 4 to be cleaned. In this way, it is not necessary to move the power electrode 9 during the cleaning phase of the surface area 5 to be cleaned.

[0055] The power electrode 9 can be offset relative to the deposit 7 by translation in a direction parallel to the clean surface 6 of the optical element 4 ([Fig.lb], following the arrows 17) or by withdrawal, by spacing the power electrode 9 so as to place it at a distance from the optical element 4. The retraction movement is in particular chosen as a function of the space available and the possible size for the machine 1.

[0056] Alternatively, the optical element 4 may be movable relative to the power electrode 9, which remains fixed relative to the enclosure 2.

[0057] In order to allow continuous cleaning, in parallel with the deposition 7 of the layer by additive manufacturing in the enclosure 2 of the machine 1, the clean surface 6 of the optical element 4 is at least twice as large as the active surface of the power electrode 9. In this way, a part of the optical element 4 can be cleaned while the other part of the optical element 4 is crossed by the beam(s) 20. energy (see for example Figs. 2a and 2b).

[0058] For example, the optical element 4 can be mounted to rotate about an axis X which is substantially normal to the clean surface 6 of the optical element 4. When the surface to be cleaned 5 is clean, an actuator can then rotate the optical element 4 about its axis X in order to place the portion of the optical element 4, which has just been cleaned, facing the energy beam(s) 20, while the portion which was previously crossed by this / these beam(s) and whose first surface 5 is at least partially covered with a deposit 7 is brought facing the power electrode 9.

[0059] Optionally, when a gas must be injected into the enclosure 2 to generate the plasma 11, for example when the enclosure 2 is under total or partial vacuum or when the gas used during the additive manufacturing deposition process is different from the gas used to generate the plasma 11, the cleaning system 8 may further comprise a confinement enclosure 18, housed in the enclosure 2 so as to be positioned on the side of the surface to be cleaned 5 of the optical element 4 and configured to confine the plasma 11 during the cleaning step. The confinement enclosure 18 may in particular be mounted fixed relative to the power electrode 9 so as to isolate the plasma 11 at the level of the zone of the optical element 4 facing the power electrode 9.

[0060] Furthermore, a separation wall 19 can be placed on the clean surface 6 so as to separate the portion of the optical element 4 which is crossed by the energy beam(s) 20 from the portion of the optical element 4 which is cleaned by the power electrode 9. The wall 19 is then fixed relative to the enclosure 2, and in particular does not rotate with the optical element 4.

[0061] An exemplary embodiment is illustrated in [Fig.2b]. In this exemplary embodiment, the useful surface area of ​​the power electrode 9 is substantially equal to a quarter of the surface area of ​​the optical element 4. Here, the optical element 4 comprises a flat disk. The useful surface area of ​​the power electrode 9 may therefore be substantially flat and have, for example, a disk shape whose diameter is substantially equal to the radius of the disk or a disk sector whose surface area is equal to a quarter of the surface area of ​​the optical element 4. In the example illustrated in [Fig.2b], the electrode is circular.

[0062] During the additive manufacturing deposition process, the entire first surface 5 of the optical element 4, which is located on the side of the material source, is likely to be covered by a deposit 7. This first surface 5 is cleaned continuously, by quarter of the surface. In particular, at any time: a first quarter of the surface 21 of the optical element 4 is placed facing the energy beam(s) 20, thus receiving the deposit 7 due to the evaporation produced by additive manufacturing; a second quarter of the surface 22 of the optical element 4, which is immediately adjacent to the first quarter of the surface 21, comprises a deposit 7 on the surface to be cleaned 5; a third quarter of surface 23 of the optical element 4, which is immediately adjacent to the second quarter surface 22, is opposite the power electrode 9 and, where appropriate, the confinement enclosure 18, so that a plasma 11 erodes a deposit 7 formed on its surface to be cleaned 5; and a fourth quarter surface 24 of the optical element 4, which extends between the third 23 and the first quarter surface 21, has just been cleaned by the plasma 11. The second quarter surface 22 is therefore in a cleaning waiting area while the fourth quarter surface 24 is in a use waiting area, before receiving the energy beam(s) 20. The first 21, second 22, third 23 and fourth 24 surface quarters are moved by quarter turns at a frequency which may be regular and which is determined according to the speed of formation of the deposit 7 on the surface to be cleaned 5.

[0063] A separation wall 19 (here, a bent wall) is further placed around the portion which is crossed by the energy beam(s) 20 in order to prevent a deposit 7 from forming in the cleaning and use waiting areas. In [Fig.2a], the separation wall 19 is located at the level of the first quarter of the surface 21.

[0064] Cleaning and deposition 7 can then be carried out as follows.

[0065] During a first step, the first quarter of surface 21 is used to allow the energy beam(s) 20 to pass through in order to carry out a selective fusion on the powder bed 3 placed on the movable plate 30. During this fusion, a deposit 7 is formed on the face 5 of the window 4. The third quarter of surface 23 is facing the power electrode 9. A plasma 11 is then generated by the plasma generator 11, and possibly confined in the confinement enclosure 18, in order to erode the deposit 7 previously formed on the surface to be cleaned (when the third quarter of surface 23 was in position of the current surface 21 and allowed the energy beam(s) 20 to pass through for consolidation of a layer of powder in additive manufacturing).

[0066] During a second step, when the deposit 7 is completely eroded in the third quarter of the surface (for example when a change in impedance greater than the threshold is detected) and is therefore eliminated, the control unit controls the actuator so as to rotate the optical element 4 by a quarter of a turn. The second quarter of the surface 22 then comes face to face with the power electrode 9 for cleaning by the plasma 11 while the first quarter of the surface 21, the surface 5 to be cleaned of which is covered with a deposit 7, takes the place of the second quarter of the surface 22, between the electrode and the useful zone receiving the energy beam(s) 20. It will be noted that at this stage, the third quarter of surface 23 is clean (free of deposit 7) and comes into the waiting configuration before use, in place of the fourth quarter of surface 24 which comes under the beam(s), within the zone delimited by the wall 19.The first and second steps are then repeated several times until the additive manufacturing process is completed.

[0067] It will be understood that the generation of the plasma 11 and the erosion can be carried out continuously, since the optical element 4 is set in rotation as soon as the deposit 7 is removed from its surface to be cleaned 5. Furthermore, if the speed of erosion by the plasma 11 of the deposit 7 is equal to the speed of formation of the deposit 7, the additive manufacturing process can also be carried out continuously.

[0068] Where appropriate, if the erosion speed of the deposit 7 is lower than the formation speed of the deposit 7, the additive manufacturing machine 1 may further comprise a magnetic trap 15, placed in the confinement enclosure 18, in order to accelerate the erosion of the deposit 7.

[0069] Alternatively, when the deposit 7 is completely eroded, if the erosion speed of the deposit 7 is greater than the formation speed of the deposit 7 on the surface to be cleaned 5, the control unit can stop the power supply to the electrical power source 13 until the optical element 4 is turned a quarter turn. Once the optical element 4 has been turned, the control unit can control the power supply to the power electrode 9 in order to generate a new plasma 11 and clean the surface to be cleaned 5 located in the second quarter surface 22 of the optical element 4.

[0070] Preferably, the rotation of the optical element 4 is sequential, so that the deposit 7 has a substantially uniform thickness.

[0071] Of course, the example described is not limiting. It will be understood, for example, that the useful surface area of ​​the power electrode 9 may be equal to a fraction of the surface area of ​​the optical element 4 which is different from a quarter. Typically, the cleaning system 8 may also operate if the useful surface area of ​​the electrode is substantially equal to a third of the surface area of ​​the optical element 4 and if the rotation is done in thirds of a turn (and not in quarters of a turn). Similarly, the surfaces 21, 22, 23, 24 may be arranged so as to form a faceted truncated cone and thus present an angle between them. Thus, by way of example, the axis of rotation X may be placed at the top of the truncated cone and form an angle of 45° with the cleaning system 8, which is itself placed perpendicular to the direction of the energy beams 20.

[0072] According to yet another variant, both the optical element 4 and the power electrode 9 are mounted to move relative to the enclosure 2.

[0073] The control unit may in particular comprise a computer of the processor, microprocessor, microcontroller, etc. type, configured to execute instructions and control the electrical power source 13 and, where appropriate, the means for moving the power electrode 9 relative to the enclosure 2 and / or the means for moving the optical element 4 (typically, by rotation) relative to the power electrode 9.

[0074] The cleaning of an optical element 4 of an additive manufacturing machine 1 can then be carried out in accordance with the following steps:

[0075] SI: placement of the power electrode 9 opposite the second surface 6 of the optical element 4; and S2: power supply of the power electrode 9 so as to generate a plasma 11 by capacitive coupling near the first surface 5 so as to erode the deposit 7.

[0076] As indicated above, step S1 can be carried out either by moving the power electrode 9 relative to the optical element 4, which is fixed, so as to position it facing the deposit 7 to be eroded, or by moving the optical element 4 (for example by rotation) relative to the deposition electrode 7. In a variant, both the deposition electrode 7 and the optical element 4 are movable in the enclosure 2.

[0077] Furthermore, to protect the optical element 4, the method further comprises steps of monitoring an impedance of the plasma 11 (step S3) and of interrupting the power supply to the power electrode 9 when a variation in the impedance exceeds a predetermined threshold (step S4) and / or of moving one of the power electrode 9 relative to the optical element 4.

Claims

Claims

1. Additive manufacturing machine (1), comprising: - an enclosure (2); - a movable plate (30) placed in the enclosure (2) and on which a powder bed (3a) is placed; - one or more energy beam sources (20) configured to selectively scan the powder bed (3a) and consolidate it; - an optical element (4) fixed in the enclosure (2) and made of a material transparent to electromagnetic waves, the optical element (4) having a first surface (5) on which a deposit (7) resulting from vaporization of the powder bed (3a) is likely to form and a second surface (6), opposite the first surface (5);and - a cleaning system (8) of the first surface (5) of the optical element (4) comprising a plasma generator (11) comprising a radiofrequency generator, the plasma generator (11) comprising a power electrode (9), placed opposite the second surface (6) of the optical element, (4) and a ground electrode (10) configured to generate a plasma (11) by capacitive coupling near the first surface (5), a useful surface of the power electrode (9) being less than a useful surface of the ground electrode in order to generate a self-polarization voltage at the power electrode (9).;

2. Additive manufacturing machine (1) according to claim 1, in which the power electrode (9) is mounted to move relative to the enclosure (2) between a cleaning configuration, in which the power electrode (9) is positioned opposite the second surface (6) and a retracted configuration, in which the power electrode (9) is offset relative to the deposit (7).

3. Additive manufacturing machine (1) according to one of claims 1 or 2, wherein the first surface (5) of the optical element (4) is at least twice as large as an active surface of the power electrode (9), the optical element (4) being movable relative to the power electrode (9).

4. Additive manufacturing machine (1) according to claim 3, in which the power electrode (9) is fixed relative to the enclosure (2).

5. Additive manufacturing machine (1) according to one of claims 3 or 4, in which the first surface (5) of the optical element (4) is at least four times larger than the active surface of the electrode of power (9), wherein the optical element (4) is rotatable about an axis (X) relative to the power electrode (9), the power electrode (9) being offset relative to the axis (X).

6. Additive manufacturing machine (1) according to one of claims 3 to 5, further comprising a confinement enclosure (18) for the plasma (11) positioned on the side of the first surface (5) of the optical element (4) and fixedly mounted relative to the power electrode (9) so as to confine the plasma (11) at the level of an area of the first surface (5) facing the power electrode (9).

7. Additive manufacturing machine (1) according to one of claims 1 to 6, further comprising a magnetic trap (15) mounted, fixed or movable, relative to the optical element (4) and positioned close to the first surface (5).

8. Additive manufacturing machine (1) according to one of claims 1 to 7, further comprising an impedance adapter (16) configured to monitor an impedance of the plasma generator (11) and, optionally, to control the plasma generator (11) as a function of the measured impedance.

9. Additive manufacturing machine (1) according to one of claims 1 to 8, in which the enclosure (2) is connected to ground and serves as a ground electrode (10).

10. Cleaning system (8) of an additive manufacturing machine (1) according to one of claims 1 to 9, comprising a plasma generator (11) comprising a radiofrequency generator, the plasma generator (11) comprising a power electrode (9), configured to be placed opposite the second surface (6) of the optical element (4), and a ground electrode (10) configured to generate a plasma (11) by capacitive coupling near the first surface (5), a useful surface of the power electrode (9) being less than a useful surface of the ground electrode in order to generate a self-polarization voltage at the power electrode (9).

11. A cleaning system (8) according to claim 10, further comprising a magnetic trap (15) mounted fixedly or movably relative to the optical element (4) and positioned proximate the first surface (5).

12. A cleaning system (8) according to one of claims 10 or 11, further comprising an impedance adapter (16) configured to monitor an impedance of the plasma generator (11) and, optionally- ally, to control the plasma generator (11) according to the measured impedance.

13. Method for cleaning an optical element (4) of an additive manufacturing machine (1) according to one of claims 1 to 9, characterized in that it comprises the following steps: S1: placing the power electrode (9) of the plasma generator (11) of the cleaning system (8) opposite the second surface (6) of the optical element (4); and S2: powering the power electrode (9) so as to generate a plasma (11) by capacitive coupling near the first surface (5) so as to erode the deposit (7) formed on the first surface (5) of the optical element (4) and to generate a self-polarization voltage at the power electrode (9).

14. The method of claim 13, further comprising the following steps: S3: monitoring an impedance of the plasma (11); and S4: when a variation in the impedance exceeds a predetermined threshold, interrupting the power supply to the power electrode (9) and / or moving one of the deposition electrode and the optical element (4).

15. Method according to one of claims 13 or 14, in which, during step S1, the power electrode (9) is moved relative to the optical element (4) so as to position it at the level of the deposit (7).

16. Method according to one of claims 13 to 15 in which, during step S1, the optical element (4) is moved relative to the power electrode (9) so as to position the deposit at the level of the power electrode (9).

17. A method according to claim 16, wherein the optical element (4) is moved by rotation about an axis (X).

18. A method according to claim 17, wherein the optical element (4) has a surface area approximately at least twice as large as an active surface area of the power electrode (9) and the optical element (4) makes a fraction of a turn with each movement, for example the surface area of the optical element (4) is four times as large and the optical element (4) makes a quarter of a turn with each movement.

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