WO2019193298A1

WO2019193298A1 - Heating device for additive manufacturing apparatus

Info

Publication number: WO2019193298A1
Application number: PCT/FR2019/050808
Authority: WO
Inventors: Gilles WALRAND; Tiberiu Minea; Gérard BAUVILLE; Stéphane PASQUIERS
Original assignee: Addup; Centre National De La Recherche Scientifique (Cnrs); Universite Paris-Sud
Priority date: 2018-04-06
Filing date: 2019-04-05
Publication date: 2019-10-10
Also published as: FR3079773B1; FR3079773A1

Abstract

The invention relates to a device for heating a bed of powder in an additive manufacturing apparatus, characterized in that it comprises: - a plasma generating device (28), said device being capable of being placed and moved above the powder bed, at a distance from the powder bed that enables the generation of the plasma thereon, a unit (22) for electrically powering said heating device, - a control unit (9) for controlling the power supply and the movement of the heating device.

Description

HEATING DEVICE

FOR ADDITIVE MANUFACTURING APPARATUS

GENERAL TECHNICAL FIELD AND PRIOR ART

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

More particularly, it relates to the heating treatments that are implemented on the powder beds before the selective melting.

Selective additive manufacturing consists in producing three-dimensional objects by consolidating selected areas on successive layers of powder material (metal powder, ceramic powder, etc.). The consolidated areas correspond to successive sections of the three-dimensional object. The consolidation is done for example layer by layer, by a total or partial selective melting performed with a power source (high power laser beam, electron beam, etc.).

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

However, it has a high energy cost.

It also represents a loss in important 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.

In addition, the total preheating of a layer of powder causes a 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. GENERAL PRESENTATION OF THE INVENTION

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

In particular, an object of the invention is to provide a solution that allows preheating and / or post-treatment by heating without loading and lifting of powder.

Yet another object is to provide a solution that can reduce costs and times of preheating and / or post-treatment by heating in 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 the only zones that will be melted during the subsequent melting phase, for the layer being manufactured.

Thus, according to a first aspect, the invention proposes a device for heating a bed of powder in an additive manufacturing apparatus,

characterized in that it comprises:

a plasma generating device, said device being adapted to be arranged and moved above the powder bed, at a distance from the powder bed enabling the plasma to be generated thereon,

a unit for supplying power to said plasma generating device,

a control unit for controlling the supply and the displacement of the plasma generating device.

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

the plasma generating device comprises an elongate electrode adapted to be displaced with a main component displacement perpendicular to the direction in which said electrode extends;

the heating device comprises at least one elongate electrode surrounded by a metal sheath, said sheath being, in its zone above the powder bed, provided with a slot;

- The unit for the power supply of said plasma generating device comprises an alternating source operating in RF and / or an alternating pulse source;

the heating device comprises a mechanism for adjusting the distance of the plasma generating device relative to the bed of powder;

the electrode comprises a straight section in an arc of a circle;

the developed internal surface of the electrode is greater than the area of the projection zone of the plasma on the powder bed;

the sheath comprises closure means, the slot being delimited by said sealing means;

the plasma generation device comprises several independent localized plasma generators, each of these generators being capable of generating a plasma located above the powder bed, the control unit controlling said generators, during the displacement of the plasma generation device, according to sequences depending on the zone (s) of the powder bed to be preheated and the desired heating thereof; the localized plasma generators comprise a plurality of electrodes juxtaposed linearly; the electrodes are distributed along one or more parallel planes, the electrodes of the same plane being distant from each other, the electrodes of a first plane being arranged in staggered relation to the electrodes of a second plane, so that an electrode of a plane is disposed facing the space between two electrodes of another plane;

- The power supply device is configured to independently power each localized device for generating plasma in a bipolar manner;

the control unit is adapted to move the plasma generating device according to several speeds of displacement;

the plasma is produced inside a cavity electrode and projected through a diaphragm.

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

a support for the deposition of the successive layers of additive manufacturing powder,

a distribution arrangement adapted to apply 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 heating device, including the plasma generating device, said device being adapted to be arranged and moved over the bed of powder, at a distance from the bed of powder allowing the generation of plasma on this one. Notably, in one embodiment, the dispensing arrangement includes a squeegee or a layering roll, the heater extending proximate to or independently of said squeegee or roll. this.

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

- Depositing a layer of powder on a support or on a previously solidified layer,

- Heating the powder layer by means of a preheating device as defined above,

- Consolidation of the previously preheated zone, the consolidation being carried out by means of a power source.

In particular, in one embodiment of the method of manufacture, during the heating step, the heating device comprises several electrode segments and has two modes of operation:

a mode of displacement, during which the speed of movement of the heating device is maximized;

a heating mode, during which at least one electrode segment is fed for a determined duration, the heating device moving at a predetermined speed, thereby heating at least one zone of the powder bed. PRESENTATION OF FIGURES

Other characteristics and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, 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;

FIG. 2 illustrates a possible embodiment for such a heating device;

FIG. 3a is a diagrammatic sectional view of a heating device comprising a cylinder-cylinder type electrode;

FIG. 3b is a schematic sectional view of a heating device comprising a wire-plane type electrode,

FIG. 3c is a diagrammatic sectional view of a heating device comprising a knife type electrode;

FIG. 3d is a diagrammatic sectional view of a heating device comprising a semi-cylindrical type electrode;

FIG. 4 schematically illustrates a bed of powder of which only certain zones have been heated in a localized manner, in accordance with the invention;

- Figure 5 schematically illustrates a localized heating device according to the invention; more specifically, Figure 5a shows a variant in which the generators are arranged in two parallel planes, Figure 5b illustrating an embodiment in which the generators are arranged on the same plane;

FIG. 6 schematically illustrates a bed of powder of which only certain zones have been heated in a localized manner, according to the invention;

FIG. 7 is a perspective diagram of an embodiment of a localized heating device according to the invention. DESCRIPTION OF ONE OR MORE MODES OF IMPLEMENTATION AND REALIZATION

Overview

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

a support such as a horizontal plate 3 on which are deposited successively the various 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 FIG. )

a powder reservoir 7 situated above the plateau 3,

an arrangement 4 for the distribution of said metal powder on the plate, this arrangement 4 comprising for example a squeegee 5 or a layering roll for spreading the different successive layers of powder (displacement along the double arrow A),

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

a control unit 9 which controls the various components of the apparatus 1 according to pre-stored information (memory M),

a mechanism 10 for enabling the support of the plate 3 to be lowered as the layers are deposited (displacement along 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 fuse a powder under primary vacuum (10 ³ to 1 bar), for example a source of particles.

Still alternatively, the assembly 8 may also include several sources of the same type, such as several laser sources, or means for obtaining multiple 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 of the source 12 with respect to the object 2 according to the information sent by the control unit 9.

Any other deflection system can of course be considered.

In another non-illustrated example, 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 apparatus 1 are arranged inside a sealed enclosure 17, possibly connected to a vacuum pump 18.

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

This heater 19 may be arranged behind and / or in front of the squeegee 5 or the layering roller on the same sliding carriage. It can also be mounted on an independent trolley or on a robot arm.

In the case of a heating device 19 located in front of the lay-up roll 5 (in the direction of displacement of the lay-up roll 5), during the displacement of the lay-up roll 5 to deposit a layer of powder the heating device 19 heats the powder layer which has been deposited during the deposition of the previous layer.

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

In a variant, it is possible to imagine two or more heating devices in succession, placed before and / or after the layering device 5.

It is preferable to obtain a certain heating power to use several appliances of lower power making it possible to totalize once together the desired heating power. For example, the heat losses by 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 allows to reduce individually their energy losses by four compared to a single device with a power P. The overall losses of the device are reduced by half.

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

Various examples of such heating solutions are described below.

Linear discharge heating

In the example illustrated in FIG. 2, the heating device 19 comprises a plasma generating device 28 that is moved above the metal powder bed (solid or granular surface 21, made up of micro- or nanoparticles). powder).

This plasma generating device 28 comprises an elongate electrode 20 supplied by an electric excitation source 22 and itself controlled by the control unit 9.

This electrode 20 generates, under the effect of said source 22, electrical discharges between said electrode 20 and the surface 21 and creates a plasma by the supply of energy particles of positive and negative charge, the plasma providing the heating of the surface 21.

The electrode 20 extends substantially parallel to the surface

21. It is moved parallel to said surface 21, perpendicular to the direction in which the electrode extends.

Such a configuration allows a homogeneous heating on a surface of the powder bed corresponding to the length of the electrode 21 and its displacement distance.

This solution to generate an electric discharge by an elongated electrode is effective over a wide range of pressures ranging from 1 to a few hundred millibar. The distance between the electrode and the surface of the powder bed should be as small as possible, so that the electric discharge (plasma) develops between the electrode and the surface of the powder bed 21 only.

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

In the aforementioned pressure ranges, the electrode 20 is spaced from the surface 21 to be heated by a space (gas) of a few millimeters.

The elongate electrode 20 is preferably constructed of a metal having a high melting temperature (By high temperature, it is understood that the melting temperature of the constituent material of the electrode is at least equal to or greater than the temperature. melting powders).

The electrode 20 may be made of dielectric material, or semiconductor material or ceramic.

Preferably, the electrode 20 is made of a material that is a good electrical conductor (conductivity greater than 5 x 10 ⁶ S / m).

The heat resistance depends on the possible cooling of the electrode.

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

The source 22 allows the application of a high voltage (typically> 0.5 kV, for a heating power of some 100 W) between the electrode 20 and the surface 21 of the powder bed.

The supply thus produced by the source 22 can be alternated, either low-frequency sinusoidal, or any other signal profile, (square, triangular, etc.) either radio frequency (RF) or pulse.

The operation of the discharge in radio frequency excitation (RF) ensures the perfect neutrality of the surface of the powders and thus avoids mutual repulsion of the powders.

The electrode 20 may furthermore - as illustrated in FIG. 3a in the particular case of an electrode with a substantially annular section - be protected by a metal sheath 26 ("guard electrode"), floating or connected to the ground. provided with a slot 27 on the surface 21. The electrode 20 may also be provided with a slot. The electrode 20 may also, alternatively, have a section of a different geometry, such as circular, elliptical, parabolic or hyperbolic.

Several other configurations are possible for the elongate electrode (knife geometry electrode, plane wire electrode, plane cylinder, etc ...). A preferred, but not limiting, configuration is that of a cylinder-cylinder electrode as described hereinafter.

Cylinder-cylinder electrode (Fig. 3a)

In the embodiment illustrated in FIG. 3a, the electrode 20 comprises a metal cylinder 25 which extends in a cylindrical metal sheath 26. The cylinder 25 and the sheath 26 can, however, be made of non-metallic materials.

Said cylinder 25 is centered on the axis of the sheath 26.

Said sheath 26 also has a linear slot 27 which extends parallel to the cylinder 25, along the generating line of said sheath 26 which is closest to the surface 21 to be preheated, and which thus directly faces said surface 21.

The cylinder 25 has a linear groove 251 facing the slot 27 formed on the sheath 26, so that the groove 251 faces the surface 21 to be heated.

The ignition of the discharge to the powder bed is favored by the sheath 26 - floating or grounded - and placed at a very short distance from the cylinder 25 so as to prevent the discharge from developing over the entire surface of the cylinder 25 and thus promote discharges inside the cylinder 25.

In order to maintain the sheath 26 at a small distance from the electrode 25, the centering of the cylinder 25 in the sheath 26 is achieved by means of a centering element 252, which may be made of dielectric material.

Such centering means 252 can be used regardless of the type of electrode used (wire, cylinder, knife, ...). In the illustrated embodiment, the centering element 252 may comprise, for example, two capillaries or two fine ceramic cylinders located between the cylinder 25 and the sheath 26.

Optionally, the cylinder 25 and the sheath 26 can be connected physically but not electrically to each other at the groove 251 and the slot 27 by means of a sealing element 253 of dielectric material, so as to create a closed space hermetically 254 between the cylinder 25 and the sheath 26. In one embodiment, the sealing member 253 comprises two linear plugs extending respectively on either side of the slot 27 and the groove 251, each of plugs joining on the one hand the cylinder 25 and on the other hand the sheath 26.

Optionally, a fluid can be circulated through this closed space 254 so as to cool the cylinder 25 and the sheath 26.

Such a configuration allows the plasma to develop inside the cylinder 25 and to project through the groove 251 and the slot 27 on a controlled area on the surface of the powder bed 21.

Preferably, the area of the projection zone on the surface 21 is smaller than the developed inner surface of the cylinder 25.

In this way, in fact, it is avoided that the electrode 20 and the sheath 26 absorb the bulk of the power, whereas the plasma has a sufficient volume to develop in order to efficiently heat the powder bed 21.

Optionally, the cylinder 25 is equipped at its ends with stoppers (not shown) preventing the plasma from escaping through these openings. In one embodiment, these plugs may comprise a metallic mesh resulting in the formation of a Faraday cage and limiting the leakage of the plasma by the ends of the cylinder 25.

The excitation of the cylinder 25 can be performed in radio frequency (RF), while the mass is connected to the powder bed (and to the frame of the enclosure 17). The positive-negative alternation of the applied RF voltage ensures the neutrality of the charge on the surface of the powder bed, thus avoiding the loading and ultimately the electrostatic rise of the powders. Other types of excitations are conceivable: high voltage pulses (IHT), mono polar or bipolar excitations.

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

The bi-polar power supply has the advantage, unlike in the case of an RF power supply, that it does not require an impedance matching system (essential for RF polarization), while ensuring the neutrality of the treated powder.

Also, it allows power supplies at much higher voltages (> 10 kV) than in RF (~ 1 kV).

Furthermore, the distance between on the one hand the assembly constituted by the cylinder 25 and the sheath 26 and on the other hand the surface 21 of the powder bed is adjustable. The distance to the surface 21 is in particular adjusted according to, for example, pressure conditions in the enclosure 17.

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

variants

In a variant, the electrode 20 comprises a wire 29 which extends inside the sheath 26.

This embodiment, called a wire-plane, is represented in FIG. 3b.

When the wire 29 is excited, the plasma is formed between the wire 29 and the powder bed 21, the slot 27 of the sheath 26 defining the projection area of the plasma on the powder bed 21.

Preferably, the wire 29 is coaxial with the sheath 26. When the wire is excited and the plasma heats the powder bed, the temperature of the wire increases and the wire expands, thus reducing its rigidity.

To prevent the wire from becoming loose and away from the axis of the sheath 26, it is possible to bond at the ends of the wire 29 a mechanical tensioning device, configured to maintain a constant tension in the wire 29 and therefore maintain the wire 29 along the axis of the sheath 26 regardless of the temperature and elongation of the wire 29.

In a second variant, the electrode 20 has a knife-like geometry, as shown in FIG. 3c.

The electrode 20 is a solid electrode, which ends, at its region for the generation of plasma, by a linear sharp edge 20a.

The edge 20a extends opposite the bed of powder to be heated.

The ignition of the discharge to the powder bed is favored by the sheath 26 - floating or grounded - and placed at a very small distance from the electrode 20 so as to prevent the plasma from settling on the sides side of the electrode 20.

In another embodiment, the sheath 26 and the cylinder 25 may not have an annular section but have an arcuate section (or ellipse), as shown in Figure 3d. The sheath 26 then comprises closure means 30 delimiting the slot 27 so as to delimit the plasma formation zone. The sealing means may comprise plates, preferably made of dielectric material, fixed on the sheath 26 and extending longitudinally with respect to the axis of the sheath 26.

It is understood that the length of the arc of the section of the electrode 20 is not limited to the illustrated representation, and may extend over an angular range of between 10 ° and 359 °.

This geometry makes it possible in particular to reduce the wear and the heating of the cylinder 25 and the sheath 26, in particular at the slot 27 and the groove 251, caused by the ejection of the plasma through the slot 27 and the groove 251. Implementation of a full field heating

By placing an elongated electrode 20 (cylinder assembly 25 / sheath 26 for example) in front of the powder surface 21, it is possible to maintain a homogeneous plasma confined between said electrode 20 and the powder bed.

By moving this electrode 20 it is possible to scan the surface 21. Keeping the plasma lit and performing a complete scan of the surface 21, this surface is heated superficially.

Optionally, depending on the ignition time of the plasma (time t _1, t ₁ or t ₃ ) and the position of the system 20 above the surface 21, only certain zones can be heated over the entire width of the surface. 21, as illustrated in Figure 4.

By limiting the ignition time of the plasma, it is possible to optimize the energy consumption while achieving the desired heating.

Energy is thus efficiently transferred to the powder, which makes it possible to heat it.

The energy is transmitted to the powder by several biases simultaneously coexisting in a plasma.

These are charged species, electrons and ions, but also energy neutral species, including non-radiative excited states (metastable), 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 infra-red (IR) photons heat the material when absorbed, while ultraviolet (UV) photons can also superficially modify the surface (eg etch the surface) 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 or more. The amount of energy delivered by the plasma to the surface can be easily adjusted by the RF or pulse power injected. Localized heating device

In an optimized embodiment, the plasma generating device 28 comprises a plurality of independent plasma generators (in this case twelve referenced from S1 to S12) distributed in the length of said device 28 illustrated in FIG. 5a.

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

The plasma generator 28 comprises for example an electrode 20 divided into a plurality of independent electrodes.

In the illustrated embodiment, the electrodes E1 to E12 are separated from each other and fed independently of each other.

Each of the generators S1 to S12 comprises at least one electrode.

The length of these electrodes El to E12 is adapted to the desired accuracy on the location of the heating. This length is at least one millimeter.

Optionally, the separation distance between electrodes can be of the order of one millimeter.

In the illustrated embodiment, the plasma generating device 28 comprises two rows of six electrodes powered by an electrical excitation source 22 and itself controlled by the control unit 9.

The two rows are located in two parallel planes A-A '(odd electrodes) and B-B' (even electrodes).

In the illustrated embodiment, the electrodes El to E12 are staggered so that an even electrode is located opposite the space between two odd electrodes, and vice versa.

The distance between the two planes depends on the size of the electrodes, depending on the type of electrode chosen. It is not dictated by plasma.

It is understood that this arrangement may vary, the electrodes may be more or less numerous and arranged on the same plane or on a larger number of planes, as in an embodiment illustrated in FIG. 5b, in which the electrodes E1-E12 are formed from the same elongated electrode.

Optionally, the electrodes El to E12 may be separated by a dielectric or have different shapes from each other.

Optionally, these electrodes El to E12 can be placed on one or more articulated arms.

The electrodes El to E12 are excited to generate, under the effect of said source 22, electrical discharges localized between said electrodes and the surface 21 and thus create a plasma of limited size, which ensures the localized heating of the surface 21.

The distance between the electrodes E1 to E12 and the surface 21 should be as small as possible, so that the localized electric discharges develop between the electrodes and the surface only, so as to generate a localized plasma.

The electrodes E1 to E12 are for example elongate electrodes (knife, wire, cylinder, etc.) which extend substantially parallel to the surface 21. A metal sheath may also be provided. The assembly is moved parallel to said surface 21, perpendicular to the direction in which it extends.

Such a configuration allows homogeneous heating over a limited length (segment) of surface of the powder bed corresponding to the length of each electrode and the heated surface depends on the displacement distance with the plasma of each activated segment (discharge).

This solution generating electric discharges by one, two or more electrodes is effective over a wide range of pressures, ranging from 1 to a few hundred millibar.

A mechanism (not shown) allows the adjustment of the distance between the electrode or electrodes in addition to the mechanism 10.

Implementation of localized heating

The sequence of the excitation times of each electrode is controlled by the splitter 23, depending on the speed of advancement of the assembly. the plasma generation device 28 to locally heat only certain predefined areas of the surface 21, such as in the example illustrated in Figure 5a or 5b, and depending on the desired heating therefor.

Each heated localized area is of a width substantially equal to the length of an electrode and a length corresponding to the distance vxt, where v represents the scanning speed of the plasma generating device 28 (or that of the delivery system). in layer, if both are integral) and f is the ignition time of the discharge (which corresponds substantially to the excitation time).

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

This is illustrated in FIG. 6, in which several heated zones are represented on the entire surface of the powder bed 21, by a plasma generating device 28 moving in the direction indicated by the arrow on the Fig.

These zones correspond to an excitation of only the electrodes El, E2, E3, E7 and E10 triggered at a first instant for the electrode E10, at the same second instant for the electrodes E1 and E7.

The electrodes El, E2 and E3 are excited at the same third instant, then the electrode E2 is extinguished at a fourth instant, excited at a fifth instant, extinguished at a sixth instant and excited at a seventh instant.

The electrode E10 is ignited for a duration fl0, the electrode E7 for a duration i7 and the electrode E1 for a duration f1 and thus heat three local surface areas vxfl0, vxt7 and vxfl.

The electrodes E1, E2 and E3 are then lit for a period t, then the electrode E2 is extinguished for a time t 'during which the electrodes E1 and E3 are kept on.

The electrode E2 is then re-lit for a period t ", the electrodes E1 and E3 being always powered. The electrode E2 is then extinguished for a time t '"during which the electrodes E1 and E3 are kept in excitation.

The electrode E2 is finally fed for a period t "" simultaneously with the electrodes E1 and E3.

Subdividing the plasma generating device 20 into different independent plasma generators makes it possible to excite only the generators S1 to S12 which heat the surfaces concerned by the fusion, thus making it possible to minimize the quantity of energy required for the phase heating, and to avoid possible cohesion of the powders in the non-melted areas facilitating their subsequent reuse.

In addition, by changing the moving speed when the plasma generating device 28 passes over an area of the powder bed that will not be heated, the time of the heating phase can also be drastically reduced.

This time can be, in some cases also reduced by installing independent plasma sources on articulated arms (not shown) allowing different trajectories of the example of a rectilinear trajectory of the sources described above.

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

An exemplary embodiment of a segmented plasma generation device 28 is shown in FIG.

In the embodiment shown, the plasma generating device comprises four staggered plasma generators S1, S2, S3 and S4, the odd generators S1 and S3 lying in a first plane AA 'and the even generators S2 and S4. lying in a second plane BB '.

The separation of the planes AA 'and BB' depends on the type of electrode chosen, here of the cylindrical type.

By choosing another type of electrode, for example of the knife type, the gap between the planes AA 'and BB' could be reduced. It would also be possible alternatively to place all the electrodes El E4 on the same plane, as shown in Figure 5b.

Each of the plasma generators S1 to S4 comprises an electrode E1 to E4.

Each of the electrodes E1-E4 is independently powered by an excitation source 22, which is associated with a distributor 23 itself controlled by the control unit 9.

Alternatively, for very short electrode segments (of the order of one centimeter), it is conceivable to have for each independent source an ejection diaphragm (instead of the slot) of the plasma created inside. of a cavity electrode and to obtain a reduced heated region (spot type). By cavity, it is understood that the electrode 20 forms a cavity in which the plasma is formed, similarly to the embodiments illustrated in FIG. 3a or 3d. This source variant (not shown) is particularly well suited to be installed on an articulated arm. By diaphragm, is meant an electrode provided with an orifice whose shape and position are adjusted to allow the plasma formed in the cavity to exit through said orifice.

Claims

1. Device for heating a bed of powder in an additive manufacturing apparatus,

characterized in that it comprises:

a plasma generating device (28), said device being adapted to be arranged and moved above the powder bed, at a distance from the powder bed for generating the plasma thereon,

a unit for the power supply (22) of said plasma generating device,

a control unit (9) for controlling the supply and the displacement of the plasma generating device.

The heating device according to claim 1, wherein the plasma generating device (28) comprises an elongate electrode (20, 25) adapted to be displaced with a main displacement component perpendicular to the direction in which said electrode (20) , 25) extends.

3. Heating device according to claim 2, comprising at least one elongate electrode (20, 25) surrounded by a metal sheath (26), said sheath (26) being, in its zone above the powder bed, provided with a slot (27).

Heating device according to one of the preceding claims, wherein the unit (22) for the power supply of said plasma generating device (28) comprises an alternating source operating in RF and / or an alternating pulse source.

5. Heating device according to one of the preceding claims, comprising a mechanism for adjusting the distance of the plasma generating device (28) relative to the bed of powder.

6. Heating device according to one of claims 2 to 5, wherein the electrode (20, 25) has a cross section in a circular arc.

The heating device of claim 6, wherein the developed inner surface of the electrode (20, 25) is greater than the area of the plasma spraying area on the powder bed.

8. Heating device according to one of claims 3 to 7, wherein the sheath (26) comprises closure means (30), the slot (27) being delimited by said closure means (30).

9. Heating device according to one of claims 3 to 7, wherein the plasma is produced inside a cavity electrode and projected through a diaphragm.

10. Heating device according to one of claims 1 to 9, wherein the plasma generating device (28) comprises several localized plasma generators (SI, S2, ...) independent, each of these generators being adapted to generating a plasma located above the powder bed, the control unit controlling said generators, during the displacement of the plasma generating device (28), according to sequences depending on the zone (s) of the powder bed to preheat and the desired heating therefor.

11. Heating device according to claim 10, wherein the localized plasma generators (SI, S2, ...) comprise a plurality of electrodes (E1, E2, ...) juxtaposed linearly.

12. Heating device according to claim 11, wherein the electrodes (E1, E2, ...) are distributed along one or more parallel planes (A-A ', B-B', ...), the electrodes of the same plane being spaced from each other, the electrodes of a first plane (A-A ') being arranged in staggered relation to the electrodes of a second plane (B-B'), so that a electrode of a plane is arranged opposite the space separating two electrodes of another plane.

13. Heating device according to one of claims 11 or 12, wherein the power supply device (22) is configured to independently power each localized device for generating plasma (SI to S12) in a bipolar manner.

14. Heating device according to one of the preceding claims, wherein the control unit (9) is adapted to move the plasma generating device (28) at several speeds of displacement.

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 dispensing arrangement (4) adapted to apply a layer of powder on said support (3) or on a previously consolidated layer,

at least one power source (8) adapted for the selective consolidation of a layer of powder applied by the distribution arrangement (4),

characterized in that it comprises a heating device (19) according to one of the preceding claims, said heating device (19) being adapted to be arranged and moved over the bed of powder, at a distance from the powder bed for generating plasma thereon.

An apparatus according to claim 15, wherein the dispensing arrangement (4) comprises a squeegee (5) or a layering roll, the heating device (19) extending in proximity to said squeegee (5). or roll and being movable with or independently thereof.

17. A method of manufacturing a three-dimensional object by selective additive manufacturing comprising the steps of:

- Depositing a layer of powder on a support (3) or on a previously solidified layer,

- Heating at least one zone of the powder layer by means of a heating device (19) according to one of claims 1 to 13,

- Consolidation of the previously preheated zone, the consolidation being performed by means of a power source (8).

The method of claim 17, wherein during the heating step, the heater (19) comprises a plurality of electrode segments (E1 to E12) and has two modes of operation:

a mode of displacement, during which the speed of displacement of the heating device (19) is maximized;

a heating mode, during which at least one electrode segment (E1-E12) is supplied for a predetermined period of time, the heating device (19) moving at a predetermined speed, thus achieving heating from least one area of the powder bed.