FR3079774A1 - LOCALIZED HEATING DEVICE FOR ADDITIVE MANUFACTURING APPARATUS - Google Patents

Abstract

The invention relates to a device for localized heating of a powder bed in an additive manufacturing apparatus, comprising - a localized plasma generation device (20) adapted to be placed and moved above a powder bed of so as to generate a localized plasma thereon, - a source for the electric power supply (22) of said plasma generating device (20), - a control unit (9) for controlling the power supply and the movement of the device for generating plasma (20), the plasma generating device (20) comprising several control modules (S1, S2, etc.) capable of controlling the localized projection of a plasma onto the powder bed, the power supply and the ignition of the control modules (S1, S2, …) being controlled individually by the control unit (9), during the movement of the plasma generation device (20). Figure of the aggregate: Fig. 4

Description

LOCALIZED HEATING DEVICE FOR ADDITIVE MANUFACTURING APPARATUS

GENERAL TECHNICAL AREA AND PRIOR ART

The present invention relates to the general field of selective additive manufacturing.

More particularly, it relates to the heating treatments, in particular preheating or post-heating, which are implemented on the powder beds before or after the selective melting.

Selective additive manufacturing consists of making three-dimensional objects by consolidating selected areas on successive layers of powdery material (metallic powder, ceramic powder, etc.). The consolidated areas correspond to successive sections of the three-dimensional object. Consolidation is done, for example, layer by layer, by a total or partial selective fusion carried out with a power source (high power laser beam, electron beam, etc.).

Conventionally, in order to avoid projections due to the electrostatic repulsion of adjacent powder particles which are charged under the effect of the beam of the power source, the powder bed is previously consolidated by preheating. This preheating ensures a rise in temperature of the powder bed at temperatures which can be quite substantial (around 750 ° C. for titanium alloys for example).

However, it has a high energy cost.

It also represents a significant loss of cycle time.

In addition, when the geometry of the part does not require it, it is not necessary to heat the entire powder bed at each selective melting step.

The total preheating of a layer of powder results in particular in cohesion of the powders which hinders the cleaning of the part when the manufacturing process is finished, in particular when the part has internal cavities with complex geometry.

It is also known to post-heat the part after selective melting, in particular in order to control its cooling rate and its crystallization.

This type of treatment requires an efficient and precise method of heating and temperature control.

OVERVIEW OF THE INVENTION

A general object of the invention is to overcome the drawbacks of the configurations proposed so far.

In particular, an object of the invention is to provide a solution which allows heating without loading and lifting of powder.

Yet another object is to propose a solution which makes it possible to reduce the costs and the heating times in the manufacturing cycles.

Another object of the invention is to propose a simple construction solution.

Another aim is also to provide an efficient heating solution over a wide range of pressures.

Another object is to limit the heating of the powder bed to only the zones which will be melted during the following melting phase, for the stratum during manufacture.

Another aim is to reduce the energy consumption of a heating cycle.

Another object is to allow uniform or differential heating (different local temperature) of the powder bed.

According to a first aspect, the invention provides a device for localized heating of a powder bed in an additive manufacturing device, characterized in that it comprises:

a device for localized generation of plasma, said device being adapted to be placed and moved over a bed of powder, at a distance from the bed of powder allowing the localized generation of the plasma thereon,

a source for the electrical supply of said plasma generation device,

a control unit for controlling the supply and movement of the plasma generation device, and in that the plasma generation device comprises several control modules, the supply and ignition of which are controlled by the control, each of the control modules being able to control the localized projection of a plasma above the powder bed, the control unit individually controlling said control modules during movement of the plasma generation device, according to sequences depending on the zone (s) of the powder bed to be heated and the desired heating for these.

This type of device makes it possible to heat the powder bed while avoiding the need to heat an enclosure containing the powder bed, considerably reducing the energy requirements and the time of the heating phase.

It also enables selective heating of the zones of the powder bed, in particular by heating only the zones which will then be consolidated.

Such a device is advantageously supplemented by the following characteristics, taken alone or in combination:

- The plasma generation device is adapted to be moved with a main component of displacement perpendicular to the direction in which it extends;

- The control modules are arranged relative to each other so as to allow at least one zone and / or the entire powder bed to be heated during movement of the plasma generation device;

- The heating device includes a mechanism for adjusting the distance of the plasma generation device from the powder bed;

the source for the electrical supply of said plasma generation device comprises an alternative source, radiofrequency and / or a pulse source;

- the source is configured to supply each control module independently;

- The control unit is adapted to supply each of the control modules according to several durations as a function of the surface to be heated, during the movement of the plasma generation device;

- The control unit is adapted to move the plasma generation device according to several movement speeds;

- at least one control module includes at least one control electrode;

the plasma generation device comprises a plurality of control electrodes aligned on either side of the opening, each control electrode comprising two electrode segments, a first odd segment disposed on one side of the opening and a second even segment disposed opposite the first segment and on the other side of the opening;

- The primary electrode has a spherical geometry and has a circular opening located opposite the powder bed, the control electrode having an annular geometry and being located opposite the opening.

According to a second aspect, the invention relates to an apparatus for manufacturing a three-dimensional object by selective additive manufacturing comprising in an enclosure:

- a support for depositing successive layers of additive manufacturing powder,

a distribution arrangement suitable for applying a layer of powder on said tray or on a previously consolidated layer,

- At least one power source suitable for the selective consolidation of a layer of powder applied by the distribution arrangement, characterized in that it comprises a localized heating device according to the invention, said device being adapted to be arranged and moved above the powder bed, at a distance from the powder bed allowing the generation of a plasma located thereon.

Such an apparatus is advantageously supplemented by the following characteristics:

the distribution arrangement comprises a squeegee or a layering roller, the plasma generation device extending close to said squeegee or roller and being movable therewith, or mounted on an independent mobile device, by example a robot arm.

According to a third aspect, the invention relates to a method of manufacturing a three-dimensional object by selective additive manufacturing, said method comprising the steps:

o Deposit of a layer of powder on a support, o Preheating of at least one localized zone of the powder bed by means of a heating device according to the invention, o Consolidation of the preheated zone, consolidation being carried out by means of a power source.

Advantageously, during the preheating step, the plasma generation device has two operating modes:

- a displacement mode, during which the displacement speed of the plasma generation device is maximized;

- A heating mode, during which at least one electrode is supplied for a determined period, the plasma generation device moving at a determined speed, thus carrying out the localized heating of at least one zone of the powder bed; in this way, the time of a heating cycle is reduced.

PRESENTATION OF THE FIGURES

Other characteristics and advantages of the invention will emerge from the description which follows, which is purely illustrative and not limiting, and should be read with reference to the appended figures in which:

- Figure 1 is a schematic representation of an additive manufacturing apparatus comprising a heating device according to a possible embodiment of the invention;

- Figure 2 shows a schematic sectional view of a device for generating a localized plasma according to the invention;

- Figure 3 shows a schematic perspective view of a device for generating a localized plasma according to the invention;

- Figure 4 illustrates the operating principle for localized heating according to the invention;

- Figure 5 illustrates a powder bed and highlights the heated areas before the selective melting phase of the powder.

DESCRIPTION OF ONE OR MORE MODES OF IMPLEMENTATION AND IMPLEMENTATION

Overview

The apparatus 1 for selective additive manufacturing of FIG. 1 comprises:

- A support such as a horizontal plate 3 on which are successively deposited the different layers of additive manufacturing powder (metal powder, ceramic powder, etc.) making it possible to manufacture a three-dimensional object (object 2 in the shape of a fir tree in the figure )

- a powder reservoir 7 located above the plate 3,

- An arrangement 4 for the distribution of said metal powder on the tray 3, this arrangement 4 comprising for example a squeegee 5 or a layering roller for spreading the different successive layers of powder (displacement according to the double arrow A) and forming thus a bed of powder,

- a set 8 of energy sources for the fusion (total or partial) of the spread thin layers,

a control unit 9 which controls the various components of the device 1 as a function of pre-stored information (memory M),

- A mechanism 10 to allow the support of the plate 3 to descend as the layers are deposited (displacement according to the double arrow B).

In the example described with reference to FIG. 1, the assembly 8 comprises a source 12 of the laser type.

As a variant, the assembly 8 may comprise any other type of localized energy source making it possible to merge powder grains under primary vacuum (10 ^-3 bar to 1 bar) such as for example a source of particles.

Still alternatively, the assembly 8 can also include several sources of the same type, such as for example several laser sources, or means making it possible to obtain several beams from the same source. In the example described with reference to FIG. 1, at least one galvanometric mirror 14 makes it possible to orient and move the laser beam coming from the source 12 relative to the object 2 as a function of the information sent by the control 9. Optionally, several galvanometric mirrors can be used, for example two.

Any other deviation system can of course be envisaged.

In another example not illustrated, the assembly 8 comprises several sources 12 of the laser type and the displacement of the different laser beams is obtained by moving the different sources 12 of the laser type above the layer of powder to be fused.

A heat shield T can be interposed between the source or sources of the assembly 8.

The components of the device 1 are arranged inside a sealed enclosure 17, if necessary connected to a vacuum pump 18.

The apparatus further comprises a heating device 19 disposed above the powder bed and able to move linearly with respect thereto.

This heating device 19 can be placed behind and / or in front of the squeegee 5 or the layering roller, or on the same sliding carriage. It can also be mounted on an independent trolley or on a robotic articulated arm.

In the case of a heater 19 located in front of the coating roller 5 (in the direction of movement of the coating roller 5), when moving the coating roller 5 to spread a layer of powder , the heating device 19 performs the heating of the powder layer which has just been fused or sintered selectively.

The heated layer is then covered by the next layer, thus limiting the losses of energy by convection between the heated layer and the medium of the enclosure 17, and heating by conduction the next layer.

In a variant, one can imagine two or more heating devices in succession, placed before and / or after the layering device 5, the layering device 5 being able to move in two opposite directions.

It is preferable to obtain a certain heating power to use several devices of lower power making it possible to obtain the desired heating power by adding their respective powers.

For example, the heat losses by the Joule effect being proportional to the square of the intensity of the supply current of the device 19, the use of two devices of identical power P / 2 makes it possible to individually reduce their energy losses by four compared to a single device with a power of P. The overall losses of the device are therefore reduced by half.

The movement of said device 19, its localized supply and its residence time in front of the different zones which it is desired to heat on the surface of the powder bed are also controlled by unit 9.

Control electrode device, or Triode

With reference to FIG. 2, the heating device 19 comprises a plasma generation device 20 which is moved above the bed of metallic powder (solid or granular surface 21, made up of micro or nanopowder).

In an embodiment illustrated in FIG. 2, the plasma generation device 20 comprises a primary electrode 24 which extends in a guard electrode 25 along a longitudinal axis X (represented in FIG. 3), a distance non-zero separating the guard electrode 25 from the primary electrode 24.

The primary electrode 24 and the guard electrode 25 have, in the embodiment shown, a semi-cylindrical geometry, their section forming an arc of a circle. It is understood that the term semi-cylindrical does not limit the angular opening of the section of the primary 24 and guard 25 electrodes, which can form an arc extending between 20 ° and 350 ° angle.

The primary electrode 24 can be constructed of a material which can be insulating, semiconductor or conductive.

In one embodiment, the primary electrode 24 is constructed from a metal which has a high melting temperature (typically, greater than the powder melting temperature) and which is a good electrical conductor (conductivity greater than 5 × 10 ⁶ S / m).

The surface 21 of the powder bed is for example connected to ground.

The primary electrode 24 and the guard electrode 25 each extend along a longitudinal axis, and are preferably, but not limited to, coaxial.

Alternatively, the longitudinal axis of the primary electrode 24 and the longitudinal axis of the guard electrode 25 may be parallel.

The primary electrode 24 and the guard electrode 25 each have an opening 26, 27 which directly faces the surface 21 to be heated.

Depending on the geometry of the electrodes, the two openings 26, 27 may have substantially similar dimensions.

In the embodiment illustrated in Figure 3, the openings 26, 27 extend longitudinally parallel to the longitudinal axis X, the respective dimensions of the openings 26, 27 in the transverse direction being different due to the arc angle of the cross section of the electrodes.

The guard electrode 25 may include sealing means 30 so as to delimit the plasma formation zone. The closure means may comprise plates fixed to the primary electrode 24 and the guard electrode 25 and extending longitudinally along the longitudinal axes of the primary electrode 24 and the guard electrode 25.

The sealing means 30 define a slot 31 extending parallel to the axis X of the electrodes and being located opposite the surface 21 of the powder bed and the openings 26, 27 of the electrodes.

The ignition of the discharge to the powder bed is favored by the guard electrode 25 - floating or connected to ground - and placed at a very short distance from the primary electrode 24 so as to prevent the discharge from developing over the entire surface of the primary electrode 24 and thus favor discharges inside the primary electrode 24.

Such a configuration allows the plasma to develop inside the primary electrode 24 and to project through the opening 26, and possibly through the slot 31, onto a controlled area on the surface of the powder bed 21 .

The area of the projection area on the surface 21 is close to the surface formed by the width of the slot 31 and the length of the control electrode 32.

Throughout the description, length is understood to mean the dimension along the longitudinal axis X of the plasma generation device.

20.

Preferably, the area of the projection area on the surface 21 is less than the developed internal surface of the primary electrode 24.

The plasma generation device 20 also includes at least one control module 32, which extends along the opening 26 on either side of the latter.

When the plasma generation device 20 comprises closure means 30, the control module (s) 32 can be fixed on the closure means 30.

Each control electrode 32 comprises two bodies 321 and 322 positioned on either side of the opening 26, and on either side of the slot 31 when the plasma generation device 20 comprises closure means 30 .

Depending on the supply voltage of a control electrode 32, the electric field formed between the primary electrode 24 and the control electrode 32 can prevent or allow the projection of charged particles, and therefore of plasma, through the opening 26, and through the slot 31.

Centering of the primary electrode 24 in the guard electrode 25 is achieved by means of a centering element 33, the centering element 33 possibly optionally being dielectric. For example, the centering element 33 can comprise two ceramic capillaries located between the primary electrode 24 and the guard electrode 25.

Optionally, the primary electrode 24 and the guard electrode 25 can be connected, physically but not electrically, to each other on either side of their opening 26, 27 by means of a sealing element 28, so to create a hermetic closed space 29 between the primary electrode 24 and the guard electrode 25.

In one embodiment, the sealing element 28 comprises two linear joints extending respectively on either side of the opening 26, each of the joints joining on the one hand the primary electrode 24 and on the other apart the guard electrode 25.

Optionally, a fluid can be circulated through this closed space 29 so as to cool the primary electrode 24 and the guard electrode 25.

Optionally, the primary electrode 24 is equipped at its ends with magnetic plugs (not shown) preventing the plasma from being evacuated through these openings. In one embodiment, these magnetic plugs can comprise a metal mesh causing the formation of a Faraday cage and limiting the leakage of the plasma through the ends of the primary electrode 24.

In embodiments not shown, actuators control the movement of several mobile elements making it possible to locally close or release the opening 26 according to their position, thus causing the localized or non-localized release of the plasma.

With reference to FIG. 3, the plasma generation device 20 comprises a plurality (four in the example illustrated) of control electrodes 32 aligned on either side of the opening 26.

Each control electrode 32 comprises two electrode segments, a first odd segment E1, E3, E5, E7 arranged on one side of the opening 26 and a second even segment, respectively E2, E4, E6, E8, arranged in opposite the first segment and on the other side of the opening

26.

During the polarization of the two segments of the same control electrode 32, such as for example the segments El and E2, the free charges of the plasma generated by the primary electrode 24 are collected by the pair El and E2 and in fact, the flow of charged particles to the powder bed below is severely limited, or even eliminated.

On the other hand, for other values of the electrical polarization of the pair E1 and E2, the charges can be efficiently extracted from the plasma generated by the primary electrode 24 and projected towards the powder bed leading to the localized heating of the latter.

If only the segments E5 and E6, for example, are polarized so as to extract the charges from the plasma, the charged particles can pass through the opening 26 over the length corresponding to the length of the segments E5 and E6, the plasma being of this fact projected onto the surface 21 of the powder bed opposite the length of the opening 26 located between the segments E5 and E6.

Each of the control electrodes 32 is independently supplied by the excitation source 22, associated with a distributor 23.

Each pair of electrode segments located face to face, for example the segments E7 and E8, can therefore be assimilated to a control module S4 configured to allow the localized projection of a plasma previously generated by the primary electrode 24 and l guard electrode 25.

For the sake of clarity in FIG. 3, only the control module S4, comprising the electrode segments E7 and E8 is shown.

It is obvious that the pairs of segments E1 and E2, E3 and E4, E5 and E6 also form control modules S, which could be called SI, S2 and S3 respectively.

In an embodiment not shown, the primary electrode 24 can have a substantially spherical geometry and define a substantially spherical internal cavity.

The guard electrode 25 also has a substantially spherical and hollow geometry, the primary electrode 24 being housed inside the guard electrode 25.

In this embodiment, the primary electrode 24 may have a circular opening 26, and the guard electrode 25 may have a substantially circular opening 27 opposite the opening 26 of the primary electrode 24.

The control electrode 32 can have an annular geometry and thus comprise an opening that can be positioned opposite the opening 27 of the guard electrode 25.

This embodiment is very compact and can be of particular interest if it is assembled at the end of an articulated arm.

The distance between on the one hand the assembly constituted by the primary electrode 24 and the guard electrode 25 and on the other hand the surface 21 of the powder bed is adjustable. The distance to the surface 21 is notably adjusted as a function, for example, of the pressure conditions in the enclosure 17.

The generation of electric discharges depends on the pressure-distance product (Paschen's law) and on the nature of the gas present in the enclosure. Thus, depending on the working pressure in the enclosure and the nature of the gas, it is possible to adjust this distance in order to obtain an optimum heating.

Principle of operation

With reference to FIG. 4, the plasma generation device 20 comprises a plurality of independent control modules (in this case twelve referenced from SI to S12) distributed over the length of said device 20.

These different control modules SI to S12 are supplied independently of each other by an excitation source 22, which is associated with a distributor 23.

In other embodiments, several excitation sources 22 can be used.

The length of these control modules SI to S12 is adapted to the desired precision on the location of the heating. This length is at least one millimeter.

The control modules SI to S12 can be excited by the source 22 to control the projection of a plasma of limited size, which provides localized heating of the surface 21.

By placing a control control module S in front of the powder surface 21, and after suitable polarization of the control electrode 32, it is possible to maintain a homogeneous and localized plasma between the module S and the powder bed, fed by the main plasma source which is located in the cavity of the main electrode 24.

Energy is thus efficiently transferred to the powder, which enables it to be heated.

The electrical polarization of the control modules SI to S12 allows localized control of the projection of the plasma produced inside the main electrode 24, either by keeping it inside the cavity, or by forcing the plasma to come out cavity to locally heat the surface

21.

The voltage applied to each of the control modules SI to S12 using the distributor 23 makes it possible to regulate the flow of plasma to the surface and to obtain, if necessary, a different temperature below each module.

The plasma generation device 20 is moved parallel to the surface 21, perpendicular to the direction in which it extends.

Such a configuration allows uniform heating over a limited length (the length of a control module S) of the surface of the powder bed opposite each control module SI to S12.

The heated surface depends on the distance of movement of a control module S with the plasma activated.

Such a heater is effective over a wide range of pressures, from 1 to a few hundred millibar.

The distance between the control module (s) SI to S12 and the surface 21 must be as small as possible, so that the localized electrical discharges develop between the main plasma (produced inside the electrode 24) and surface 21 only.

In this way, a localized plasma is projected if the control electrodes 32 are suitably polarized, otherwise the plasma remains confined inside the cavity 24.

A mechanism (not shown) allows the adjustment of this distance in addition to the mechanism 10.

In the aforementioned pressure ranges, the control module or modules SI to S12 are spaced from the surface 21 to be heated by a space of a few millimeters.

Implementation of localized heating

The sequence of the excitation durations of each electrode / generator is controlled by the distributor 23, as a function of the speed of advance of the plasma generation device 20 so as to locally heat only certain predefined areas of the surface 21 (four in the 'example illustrated in Figure 5) and depending on the desired heating for them.

Each localized heated zone is of a length substantially equal to that of a control module S, ie the length of a control electrode 32, and of a width corresponding to the distance vxt, where v represents the scanning speed. of the plasma generation device 20 (or that of the layering system, if the two are integral) and t denotes the activation time of a control module S.

By activation of a control module S, it is understood that this allows the plasma to be ejected through the slot 31. This effect is obtained when the electrodes E of the control module S are adequately supplied, either with direct voltage, or in radio frequency, either in pulse mode.

The combination of the different zones thus heated locally is adapted (by the distributor 23 controlled by the unit 9) as a function of the zone which it is desired to subject to selective melting on the surface 21.

This is illustrated in FIG. 5, in which several heated zones are represented over the entire surface of the powder bed 21, the zones being heated by a plasma generation device 20 moving in the direction indicated by the arrow in the figure.

These zones correspond to an activation, during the movement of the plasma generation device 20 at a speed V, of the only control modules SI, S2, S3, S7 and S10.

The control module S10 is triggered at a first instant for a duration t10, the control modules SI and S7 being activated at the same second instant for respective durations tl and t7.

The control modules SI, S2 and S3 are then activated at the same third instant, then the control module S2 is deactivated at a fourth instant, activated at a fifth instant, deactivated at a sixth instant and activated at a seventh instant.

The control module S10 is activated for a duration t10, the control module S7 for a duration t7 and the control module SI for a duration tl and therefore heat three local surface areas vxt10, vxt7 and vxtl.

The control modules SI, S2 and S3 are then activated for a duration t, then the control module S2 is deactivated for a duration t 'during which the control modules SI and S3 are kept activated.

The control module S2 is then reactivated for a period t, the control modules SI and S3 being always activated.

The control module S2 is then deactivated for a period t ′ during which the control modules SI and S3 are kept activated.

The control module S2 is finally activated for a duration t, simultaneously with the control modules SI and S3.

Having a plasma generation device 20 generating a continuous plasma inside the primary electrode 24 and different independent control electrodes 32 makes it possible to generate large and localized fluxes towards the surface 21, when the modules SI to S12 are suitably polarized, to heat the surfaces concerned by the fusion, thus making it possible to minimize the amount of energy necessary for the heating phase.

The limited switching time thanks to this type of control module improves the precision of the heated area.

Optionally, by modifying the speed of movement when the plasma generation device 20 passes over an area of the powder bed which will not be heated, the time of the heating phase can also be drastically reduced.

The productivity and the efficiency of the heating phase are therefore improved.

Advantageously, the distributor 23 can ensure different voltages on the control modules SI to S12 leading to different local plasma flows impacting the surface 21. Thus the temperature of each heated zone can be controlled independently, but it can also be the same for all heated areas.

During the generation of a localized plasma by electrical discharges, energy is transmitted to the powder by several means coexisting simultaneously in a plasma.

These are charged species, electrons and ions, but also energetic neutral species, in particular excited non-radiative (metastable) states, and photons. As the surface (powder) receives the two charged species, the charge effects (Coulomb repulsion) are reduced or even eliminated.

In addition, all visible and infrared (IR) photons heat the material when absorbed, while ultra-violet (UV) photons can also modify the surface superficially (pickling the surface for example) if their energy is greater than the binding energy of the species adsorbed on the surface.

The denser the plasma, the greater the energy transmitted to the surface. It is possible to create a plasma from a few 10 W and up to 5 kW and more. The amount of energy brought by the plasma to the surface to be heated can be easily adjusted by the power injected individually into each control module SI to S12 by electrical pulses of up to 10 kV, or more if necessary.

Depending on the excitation mode, it is possible to accelerate the ions (in particular nitrogen, argon or another inert gas) to very high energies.

For example, the excitation of the primary electrode 24 by the source 22 can be achieved by radio frequency (RF), while the mass is connected to the powder bed (and to the frame of the enclosure 17).

The operation of the radio frequency excitation (RF) discharge has the advantage of generating a plasma inside the primary electrode 24 independently of the surface state of this electrode (metallic, oxidized, etc.).

The operation of the radio frequency (RF) excitation discharge has the advantage of positive-negative alternations of the applied RF voltage which ensures the neutrality of the charge on the surface of the powder bed, thus avoiding the electrostatic rise of the powders.

The source 22 allows the application of a high voltage (> 0.5 kV) between the primary electrode 24 and the surface 21 of the powder bed.

The supply thus produced by the source 22 can be either sinusoidal or any other type of alternating signal, such as a square or triangle signal.

Other types of excitations are possible: high voltage pulses (IHT), mono polar or bipolar excitations.

Like RF power, positive-negative pulse alternation ensures the neutrality of the charge on the surface of the powder bed.

Bi-polar impulse power has the advantage, unlike RF power, of not requiring an impedance matching system (essential for RF polarization), while ensuring the neutrality of the treated powder .

Also, the pulse excitation of the S control modules allows supplies at much higher voltages (> 10 kV) than in RF (~ 1 kV).

Claims (15)

1. Device for localized heating of a powder bed in an additive manufacturing device, characterized in that it comprises: a device for localized generation of plasma (20), said device being adapted to be placed and moved over a bed of powder, at a distance from the bed of powder allowing the localized generation of the plasma thereon, a source for the electrical supply (22) of said plasma generation device (20), - a control unit (9) for controlling the supply and movement of the plasma generation device (20), and in that the plasma generation device (20) comprises several control modules (SI, S2,. ..) whose supply and ignition are controlled by the control unit (9), each of the control modules (SI, S2, ...) being able to control the localized projection of a plasma at- above the powder bed, the control unit individually controlling said control modules (SI, S2, etc.) during movement of the plasma generation device (20), in sequences according to the zone or zones of the powder bed to be heated and the desired heating for these. 2. Device according to claim 1, wherein the plasma generation device (20) is adapted to be moved with a main component of displacement perpendicular to the direction in which it extends. 3. Device according to claim 2, wherein the control modules (SI to S12) are arranged relative to each other so as to allow to heat at least one area and / or the entire powder bed during a displacement of the plasma generation device (20). 4. Device according to one of the preceding claims, comprising a mechanism for adjusting the distance of the plasma generation device (20) relative to the powder bed. 5. Device according to one of the preceding claims, in which the source (22) for the electrical supply of said plasma generation device (20) comprises an alternative source, radiofrequency and / or a pulse source. 6. Device according to one of the preceding claims, in which the source (22) is configured to independently supply each control module (SI to S12). 7. Device according to one of the preceding claims, in which the control unit (9) is adapted to supply each of the control modules (SI to S12) according to several durations as a function of the surface to be heated, during the movement of the plasma generation device (20). 8. Device according to one of the preceding claims, in which the control unit (9) is adapted to move the plasma generation device (20) according to several movement speeds. 9. Device according to one of the preceding claims, in which at least one control module (SI to S12) comprises at least one control electrode (32). 10. Device according to claim 9, in which the plasma generation device (20) comprises a plurality of control electrodes (32) aligned on either side of the opening (26), each control electrode ( 32) comprising two electrode segments, a first odd segment (E1, E3, E5, E7) disposed on one side of the opening (26) and a second even segment (E2, E4, E6, E8) disposed in opposite the first segment and on the other side of the opening (26). 11. Device according to claim 9, in which the primary electrode (24) has a spherical geometry and comprises a circular opening (26) situated opposite the powder bed, the control electrode (32) having an annular geometry and being located opposite the opening (26). 12. Apparatus for manufacturing a three-dimensional object by selective additive manufacturing comprising in an enclosure: - a support (3) for depositing successive layers of additive manufacturing powder, - a distribution arrangement (4) adapted to apply a layer of powder on said tray (3) or on a previously consolidated layer, - at least one power source (8) suitable for the selective consolidation of a layer of powder applied by the distribution arrangement (4), characterized in that it comprises a localized heating device (19) according to the one of claims 1 to 11, said device being adapted to be placed and moved above the powder bed, at a distance from the powder bed allowing the generation of a plasma located thereon. 13. Apparatus according to claim 12, wherein the dispensing arrangement (4) comprises a squeegee or a layering roller (5), the plasma generation device (20) extending near said squeegee or roller (5) and being movable therewith, or mounted on an independent mobile device, for example a robot arm. 14. Method for manufacturing a three-dimensional object by selective additive manufacturing, said method comprising the steps: - Deposition of a layer of powder on a support (3) or a previously solidified layer, - Preheating of at least one localized area of the powder layer by means of a heating device (19) according to one of claims 1 to 11, - Consolidation of the preheated zone, consolidation being carried out by means of a power source (8). 15. Method according to claim 14, in which during the preheating step, the plasma generation device (20) has two operating modes: - a displacement mode, during which the displacement speed of the plasma generation device (20) is maximized; - a heating mode, during which at least one control module (SI to S12) is supplied for a determined duration, the plasma generation device (20) moving at a determined speed, thus realizing the localized heating of at least one area of the powder bed.