EP3852958A1

EP3852958A1 - Additive manufacturing device having a stabilised molten area

Info

Publication number: EP3852958A1
Application number: EP19813629.3A
Authority: EP
Inventors: Jean-Paul Garandet; Jean-Daniel PENOT
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2018-10-29
Filing date: 2019-10-24
Publication date: 2021-07-28
Also published as: FR3087682B1; WO2020089548A1; FR3087682A1

Abstract

Device for additively manufacturing at least one part (P), comprising: - a manufacturing plate comprising an area for manufacturing the part (P), - means for supplying (104) the material for manufacturing the part, - an energy source (106) which generates an energy beam to melt the material and form a molten area (ZF) at a given location in the manufacturing area of the manufacturing plate (102), - means for generating a time-independent magnetic field (108) in the molten area, the intensity of which is such that the Hartmann number, based on the maximum value of the magnetic field at the surface of the molten area and the maximum depth of the molten area, is greater than 5, the means for generating a time-independent magnetic field being arranged on one side relative to the part (P).

Description

ADDITIVE MANUFACTURING DEVICE HAVING A STABILIZED MOLTEN ZONE

DESCRIPTION

TECHNICAL AREA AND PRIOR ART

The present invention relates to an additive manufacturing device and to an additive manufacturing method having a stabilized molten zone.

The additive manufacturing processes include for example the powder bed fusion or PBF (Powder Bed Fusion in English terminology) and the deposition of material under concentrated energy or DED (Directed Energy Deposition in English terminology) processes

PBF processes consist in melting, for example by means of a laser beam, certain regions of a powder bed.

The DED methods consist in depositing a molten material, for example by means of a laser beam, the material being brought in solid form for example in the form of a wire or powder.

The step of passage through the liquid channel, generally in the form of a molten bath, takes place at very high temperatures, of the order of several thousand Kelvin, which has the effect of reducing the viscosity and the surface tension. materials. In addition, the temperature gradients are very intense and, as a result, the liquid phases can be the site of instability phenomena which can go as far as breaking the bath and ejecting droplets.

STATEMENT OF THE INVENTION

It is therefore an object of the present invention to provide an additive manufacturing device and an additive manufacturing method in which the problems of hydrodynamic instabilities, and in particular those leading to undulations of the free surface of the bath and to its fragmentation and the ejection of droplets are reduced or even eliminated. The object of the present invention is achieved by an additive manufacturing device for at least one part during manufacture, means for supplying the material on a support, at least one energy source for melting the material and means for generate a magnetic field independent of time at least at the melting zone of the material, the intensity of the magnetic field being such that the Hartmann number based on the maximum value of the magnetic field on the surface of the bath and the maximum depth of said fusion bath is greater than 5. The time independent magnetic field can be obtained by a permanent magnet or an electromagnet powered by a permanent current.

The generation of such a magnetic field in the bath of molten material has the effect of stabilizing the convective movements in the molten bath and thus avoiding the establishment of hydrodynamic instabilities which can go as far as the projection of droplets.

Advantageously, the means for generating a magnetic field are such that the magnetic field has a symmetry of revolution with respect to an axis normal to the surface of the bath of molten material and which passes through the center of the supply zone. heat. In a particular case of implementation, these means for generating a magnetic field are also such that the magnetic field is uniform at the level of the bath and is normal to the surface of the bath.

Preferably, the means for generating a magnetic field are located on one side of the area where the part is formed, for example above directly facing the bath of molten material in order to allow the generation of a field. magnetic of sufficient intensity with limited power.

As a variant, they can be located at the right below the part under construction, the part under construction being interposed between the magnetic field generation means and the molten zone.

Thanks to the invention, it acts locally to stabilize the bath of molten material by limiting the energy consumption and the cost and size of the device. The means for generating a magnetic field comprise for example at least one permanent magnet and / or one or more electromagnets.

The present invention therefore relates to an additive manufacturing device for at least one part comprising:

- a manufacturing area where the part is intended to be manufactured,

means of supplying the material for manufacturing the part,

- at least one energy source intended to generate at least one energy beam to melt the material and form at least one molten zone at at least one local location in the manufacturing zone,

means for generating a magnetic field independent of time at least in the molten zone, the intensity of which is such that the Hartmann number based on the maximum value of the magnetic field at the surface of the molten zone and the maximum depth of the molten zone is greater than 5, said means for generating a magnetic field independent of time being arranged on one side relative to the manufacturing zone where the part is intended to be manufactured.

Preferably, the means for generating a magnetic field independent of time at least in the molten zone generate a magnetic field whose intensity is such that the Hartmann number is greater than 10, and advantageously greater than 20.

The means for generating a time-independent magnetic field advantageously generate a magnetic field having, in the molten zone, a symmetry of revolution with respect to an axis normal to a free surface of the molten zone.

According to an additional characteristic, the means for generating a magnetic field independent of time can generate a uniform magnetic field, at least in the molten zone, and advantageously throughout the manufacturing zone, oriented in a direction normal to a free surface of the melted area.

The means for generating a magnetic field independent of time can be arranged at least in line with the local location of the manufacturing area. In an exemplary embodiment, the means for generating a magnetic field independent of time are arranged above the local location.

According to an additional characteristic, the means for generating a magnetic field independent of time can be mobile and their movements are controlled by the movement of the energy source. For example, the supply means, the energy source and the means for generating a time-independent magnetic field are configured to move together.

In another exemplary embodiment, the additive manufacturing device comprises a manufacturing plate on which the part is intended to be manufactured. The means for generating a time-independent magnetic field can be arranged under the manufacturing plate.

In another exemplary embodiment, the additive manufacturing device comprises a manufacturing plate on which the part is intended to be manufactured. The means for generating a time-independent magnetic field may extend over part or under the entire surface of the construction plate capable of being a manufacturing area.

In one example, the means for generating a magnetic field independent of time comprise at least one electromagnet. The device then advantageously comprises a control unit configured to control the supply of the electromagnet so as to maintain constant the intensity of the magnetic field in the molten zone.

In another example, the means for generating a permanent magnetic field comprise one or more electromagnets and the control unit is configured to control the supply of the electromagnet (s) situated only at the level of at least one local location in the zone where a molten zone is intended to be formed.

The material supply means may include a nozzle for supplying powdered material or a wire feed system and the supply means, the power source and the means for generating a magnetic field permanent are coaxial. As a variant, the supply means deliver powdered material in the form of a powder bed.

The present invention also relates to an additive manufacturing process for at least one part comprising:

- the supply of at least one electrically conductive material to at least one local location in a manufacturing area,

- the application of energy to the local location to melt said material and form a molten zone,

- The generation of a magnetic field independent of time at least in the molten zone whose intensity in the molten zone is such that the Hartmann number based on the maximum value of the magnetic field on the surface of the bath and the maximum depth of said the melt is greater than 5, said time independent magnetic field being generated on one side of the manufacturing area.

According to an additional characteristic, the magnetic field generated independent of time can be such that the electric potential in the molten zone is substantially uniform, at least in line with the energy source.

Advantageously, the means for generating a magnetic field independent of time are arranged with respect to the molten zone so as to generate a magnetic field having, in the molten zone, a symmetry of revolution around a direction normal to the free surface of the melted area.

The means for generating a time-independent magnetic field can be such that they generate a uniform field oriented in a direction normal to the free surface of the molten zone throughout the manufacturing zone.

Preferably, the time independent magnetic field is generated at the level of the molten zone at the local location of the manufacturing zone for substantially the entire duration of the production of the part.

The manufacturing process can be a powder bed fusion process or a material deposition process. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood on the basis of the description which follows and of the appended drawings in which:

- Figure 1 is a general schematic representation of an additive manufacturing device showing the means of supplying the material for the part under construction, the means for supplying energy and the means for generating the magnetic field located above room,

FIG. 2A is a schematic representation of an example of an additive manufacturing device by adding material in powder form,

FIG. 2B is a detailed view of FIG. 2A including the magnetic field lines,

FIG. 3A is a schematic representation of an example of an additive manufacturing device by adding material in the form of a wire,

FIG. 3B is a schematic representation of a variant of FIG. 3 A,

FIG. 4 is a schematic representation of an example of an additive manufacturing device by fusion on a powder bed with devices for generating the magnetic field located below the two parts under construction,

- Figure 5 is a schematic representation of another example of additive manufacturing device by melting on a powder bed, showing a plurality of magnets under the construction plate

FIG. 6 is a schematic representation of an example of an additive manufacturing device by melting on a powder bed in which the magnetic field generation means are located above the powder bed,

FIG. 7 is a schematic representation of another example of an additive manufacturing device by melting on a powder bed in which the magnetic field generated is substantially uniform, DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

In the following description, the expressions “melted bath” and “melted zone” are synonymous.

B denotes the magnetic field and I denotes the current flowing in the electromagnet when the field is created by an electromagnet.

The manufacturing device and the additive manufacturing method according to the invention use conductive materials, for example metallic, or even semiconductor materials. For example, the materials that can be used are, for example, iron, nickel, titanium, aluminum, chromium and cobalt, their mixtures and their alloys.

In Figure 1, we can see a schematic representation of the principle of a device for manufacturing parts by additive manufacturing according to the invention.

In the PBF configuration, the part is manufactured on a construction plate, which is generally removed at the end of manufacture, and in the DED configuration, the part is manufactured on a substrate which is sometimes part of the final part. This is particularly the case for repair processes or adding functionality to existing parts.

In the description of the device in FIG. 1, the principle of the invention is described schematically, the plate in PBF configuration and the substrate in DED configuration will be designated “support”.

The manufacturing device comprises means for supplying the material 4 and an energy source 6 configured to melt the material. A support 2 is provided on which the part is intended to be manufactured.

The energy source 6 is for example a laser whose beam is oriented towards the area where it is desired to manufacture the part P. The power of the laser can for example vary between 100 W and 5 kW. Alternatively, the heat source is an electron beam.

The means for generating a magnetic field 8 are advantageously arranged on one side of the molten bath. In the example shown in the Figure 1, they are arranged directly opposite the bath or the ZF molten area. They generate a local magnetic field. The means for generating a magnetic field 8 are arranged on one side of the molten bath by considering a vertical direction, ie The means for generating a magnetic field 8 are arranged above or below the molten bath.

This arrangement of the means for generating a magnetic field on one side of the molten bath makes it possible to achieve the desired magnetic field intensity while limiting the power of the means for generating a magnetic field.

The drop zone varies over time, both in plan and in height. Indeed in general the parts are formed in several passes. In an exemplary embodiment, the part P during manufacture is movable relative to the frame of the device in the three directions of space. In PBF configuration, the support 2 forming a production plate is placed on a support plate (not shown) generally mobile only in the vertical direction. The movements of the part and / or of the construction plate are controlled for example by a computer or a digital control.

The Z direction corresponds to the direction of the layers during the manufacturing process. The X and Y directions define the plane of each layer.

In another example, the means of supplying the material and the beam of the energy source are movable in the three directions of space with respect to the support and the part being manufactured.

In another example, the support is mobile in all or part of the directions of space and the means for supplying the material and the beam of the energy source are mobile in all or part of the directions of space. For example, the support is movable in the Z direction and the material supply means and the beam of the energy source are movable in the X and Y directions.

The energy source, for example a laser source, can be mobile or it is the energy beam, for example the laser beam, which is oriented for example by means of one or more mirrors. For example, the support and / or the means for supplying the material and the energy source are moved by actuators controlled by a control unit connected to a computer.

For example, the scanning speed can vary between 50 mm / s and several m / s and the molten area can be relatively large, typically between 100 x 100 pm ² and 5 x 5 mm ² .

The inventors have determined that by applying a magnetic field of sufficient intensity to the level of the bath of molten material, it can be stabilized.

The manufacturing device then also comprises means 8 for generating a magnetic field independent of time at least at the level of the fusion bath.

The term "means for generating a magnetic field independent of time" means capable of maintaining a magnetic field at least of a given value over time. It can be one or more permanent magnets or one or more electromagnets.

The means 8 are configured to generate, in at least part of the bath, a magnetic field whose intensity is chosen so that the Hartmann number is greater than 5, preferably greater than 10 and even more preferably greater than 20. A these values of the Hartmann number, the critical speed of destabilization leading to the formation of instabilities is greater than the speed of convection in the molten zone, and the molten zone is therefore stabilized.

Hartmann's number is defined by:

Ha = BH (s / h) ^1/2 .

With B the maximum field strength (in Tesla) on the surface of the bath,

H the maximum depth of the bath (in meters) of the bath, s the electrical conductivity of the material of the melt (in Siemens per meter)

h the dynamic viscosity (in Pascal. second) of the bath. For liquid metals near their melting point typical values can be taken at s = 2 10 ⁶ S / m and h = 1.5 10 ³ Pa.s.

By way of example, for a concentrated energy deposition (DED) configuration, with a thickness of weld pool of 2 mm, the condition on the number of Ha defined above results in a magnetic field of intensity greater than 0.07 T, preferably greater than 0.14 T, even more preferably 0.28 T. For a powder bed fusion (PBF) configuration, with a bath thickness of 200 μm, the conditions on the field to be applied become an intensity greater than 0.7 T, preferably 1.4 T, even more preferably 2.8 T. In general, the thickness of the molten zone is significantly less in the PBF configuration than in the DED configuration .

By increasing the intensity of the magnetic field independent of the time applied to the molten zone, the molten zone is further stabilized.

The application of such a magnetic field during deposition makes it possible to reduce the hydrodynamic speed within the bath, and therefore the instabilities in the bath and the ejection of droplets. The Lorentz force and consequently the reduction of the hydrodynamic speed are theoretically expected to be proportional at least to the Hartmann number.

The means for generating a time-independent magnetic field include, for example, one or more permanent magnets and / or one or more electromagnets.

The electromagnets are connected to a source of electric current, which is advantageously controlled so as to power the electromagnet (s) only during a manufacturing phase.

The use of permanent magnets simplifies the device, since no electrical connection is required, which is particularly advantageous in the case where the means for generating the magnetic field are mobile. However due to the very high temperatures at the molten area, the permanent magnets are to be protected so that they are not subjected to a temperature higher than the Curie temperature. For example, the Curie temperatures of Fe, Ni and Co are 1043 K, 627 K and 1388 K respectively.

The use of electromagnets offers greater freedom in terms of the intensity of the magnetic field independent of the time generated, they can for example allow the field produced to be modified as a function of their position relative to the molten zone.

In the following description, mention will be made of the generation means, and the following examples will be specified if they are permanent magnets made of ferromagnetic materials or electromagnets.

Very advantageously, the magnetic field has a particular orientation and / or distribution with respect to the free surface of the molten zone, making it possible to amplify the reduction in hydrodynamic speed and therefore the instabilities.

By combining a magnetic field of high intensity and orientation chosen for its efficiency, it is possible to very effectively stabilize the molten area.

The magnetic field according to the invention is advantageously oriented so that the maximum angle of the field lines with the normal to the molten bath over the entire surface of said molten bath is less than 45 °, preferably 30 °, or even more preferably the field lines are substantially normal to the surface of said molten bath.

As a variant, may provide for generating a field whose orientation makes it possible to very effectively stabilize the molten zone and to reduce the intensity of the field to reduce the energy consumed in the case of an electromagnet, which makes it possible to offer a additive manufacturing device with reduced electrical consumption while providing a stable molten area.

First, we assume that the molten zone has a hemispherical shape. It has an axis of symmetry Xc normal to the free surface of the molten zone and passing through the center of the latter.

The inventors have determined that by applying a magnetic field whose field lines have a symmetry of revolution with respect to the axis Xc, the electrical potential in the molten zone was uniform, resulting in a very effective Lorentz force to stabilize the flow. In a particular mode where magnetic field generation means large enough and powerful enough to generate a uniform magnetic field in the molten area can be implemented, and by orienting the means so that the field is normal to the free surface of the molten zone, ie parallel to the axis Xc, a uniform electric potential is obtained in the molten zone and a very effective Lorentz force to stabilize the flow.

When a uniform electric potential in the molten zone can be obtained, the Lorentz force can be proportional to the square of the Hartmann number, and consequently the reduction of the hydrodynamic speed in the molten zone can be proportional to the square of the number by Hartmann.

In the cases usually encountered in practice, the molten zone does not have an axis of symmetry, in particular it elongates in the direction opposite to the movement of the hot source to allow the evacuation of the heat. It is however possible to apply the above reasoning considering that the area of application of heat by the energy source has a symmetrical shape, ie a substantially circular free surface, of axis Xc normal to the surface of the passing bath through the center of said heat application area. Under these conditions, even if the electric potential is not uniform far from the Xc axis, the application of a magnetic field of revolution around the Xc axis makes it possible to effectively limit the convection movements at the most critical locations. of the bath, namely those where the temperature is the highest.

We will now describe various nonlimiting examples of embodiment of the additive manufacturing device.

In the PBF configuration, the depth of the bath varies for example between 50 μm and 500 μm. In DED configuration, this depth varies for example between 500 pm and 5 mm. In FIG. 2A, one can see an embodiment of a particularly advantageous additive manufacturing device representative of a DED configuration.

In this example, the supply means 4 comprise a nozzle 4.1 and the material to be melted is supplied in the form of powder. The powder may consist of a single material or a mixture of materials.

In addition, the means for generating a magnetic field 8 are arranged opposite the molten zone ZF. This arrangement of the means for generating a magnetic field makes it possible to achieve the desired magnetic field intensity while limiting the power of means for generating a magnetic field.

The supply means 4, the energy source 6 and the means for generating a magnetic field 8 are coaxial along the axis Xc defined above and form an integral unit in movement. Thus, the different means keep fixed relative positions. The axis of the assembly B is advantageously orthogonal to the free surface of the fused zone ZF.

The generation means 8 have a size sufficient to generate a magnetic field of controlled orientation and of sufficient intensity throughout the molten zone ZF. The coaxial arrangements of the generation means 8, of the energy source 6 and of the supply means 4 make it possible to generate a magnetic field having a symmetry of revolution around the axis Xc. As explained above, this orientation of the magnetic field makes it possible to obtain a magnetic field of symmetry of revolution about the axis Xc in the molten zone, and a very effective Lorentz force for reducing the hydrodynamic speed in the molten zone. In this example, the generation means comprise an electromagnet arranged so that the magnetic field lines have the symmetry of revolution around the axis Xc. The turn closest to the molten bath is located at a distance varying for example between 2 mm and 5 cm, preferably 5 mm to 2 cm from the surface of said bath. The current flowing in the electromagnet is preferably greater than 100 A, or even greater than 1000 A if it is desired to reach fields exceeding the Tesla. In FIG. 2B, one can see a detail view of the fused zone ZF and of the magnetic field lines B generated in the device of FIG. 2A.

In FIG. 3A, we can see another example of embodiment in DED mode in which the material is brought in the form of a wire F, the free end of the wire F being opposite the desired deposition zone. In this example, the supply means 104 and the generation means 108 are coaxial, but not the energy source 106. The supply means 104 and the energy source 106 are oriented so that the free end of the wire F either melted by the energy supplied by the energy source 106 in line with the desired deposition zone. The generation means 108 are arranged substantially along the axis Xc above with respect to the molten zone so as to generate the magnetic field in the molten zone ZF without interfering with the energy source 106.

Advantageously, the supply means and the energy source are integral in displacement.

According to a variant shown in FIG. 3B, the energy source extends along a first axis A and the supply means 104 extend along a second axis B, the axes A and B being intersecting and arranged d 'one side and the other of a plane containing the axis Xc of the desired fused area. The generation means 108 are arranged substantially at the point of intersection of the axes above with respect to the molten zone so as to generate the magnetic field in the molten zone ZF without interfering with the energy source 106 and the wire F of material.

The magnetic field thus generated advantageously also has a symmetry of revolution around the axis Xc. Thus, the electrical potential in the molten zone is uniform, the Lorenz force is then very effective. The melted area is then stabilized significantly. As in the previous example, the turn closest to the molten bath can be located at a distance varying between 2 mm and 5 cm, preferably 5 mm to 2 cm from the surface of said bath. The current flowing in the electromagnet is preferably greater than 100 A, or even greater than 1000 A if it is desired to reach fields exceeding the Tesla. Advantageously, the generation means and the energy source are integral in movement, thus the generation means follow the movement of the molten zone.

In Figure 4, we can see another embodiment of an additive manufacturing device implementing a powder bed melting process.

We can see an LP powder bed in which the PI and P2 parts are located during manufacture. The pieces PI and P2 are arranged on a manufacturing plate 202.

In the example shown, the production plate 202 is arranged on a support plate 210 able to move vertically along the axis Z. For example, the device comprises a jack 212, of which is fixed the support plate 210 along of the Z axis.

The supply means deliver powder in the form of layers of thickness varying between 40 μm and 200 μm over the entire extent of the LP powder bed. These means (roller, scraper ...) are well known to those skilled in the art and will not be described in detail.

The energy source is for example a laser, the beam of which is configured to move on the upper surface of the powder bed in the XY plane so as to melt the powder in certain areas only of the powder bed.

In this example, the generation means 208 comprise two elements capable of generating a magnetic field in two distinct zones of the powder bed LP, allowing the manufacture of two parts simultaneously. In this example, the elements 208.1 and 208.2 can be permanent magnets. They can advantageously be made in alloys of Samarium-Cobalt or Iron-Neodymium-Boron. These materials allow residual inductions to be reached on their surface exceeding the Tesla, with a Curie temperature between 700 ° C and 800 ° C for SmCo and a Curie temperature of the order of 310 ° C for FeNdB.

If the permanent magnets are in the form of a solid of revolution, their field lines have a symmetry of revolution. The two elements 208.1 and 208.2 are arranged under the support plate in line with the part manufacturing area and at a distance therefrom.

For example, the elements 208.1 and 208.2 are fixed to the jack without direct mechanical or thermal contact with the support plate. The elements 208.1 and 208.2 can advantageously be electromagnets.

This arrangement of the generation means under the support plate opposite the energy source makes it possible to limit the overheating of the generation means. In addition, the space between the generation means and the plate forms a thermal screen.

Advantageously, an insulating material acting as a heat shield can be added between the generation means and the support plate.

Element 208.2 is even further from the heat source. In addition, it is not in contact with the support plate, the risks of heating by conduction are therefore reduced.

In another embodiment, if the thermal stresses are acceptable for the elements 208.1 and 208.2, and the barrier offered by the support plate is sufficient, the two elements 208.1 and 208.2 can be directly in contact with the support plate.

It will be understood that a device with a single element for generating a magnetic field or more than two elements does not depart from the scope of the present invention. In addition, all the elements can be arranged at the same distance from the support plate or not, or some can be in contact with the support plate and others not.

All the elements 208.1, 208.2 can generate a magnetic field of the same intensity or all or part of them can produce a magnetic field of different intensity.

In this exemplary embodiment, the generation means move away from the molten zone each time a new layer of powder is deposited. Very advantageously, the generation means comprise one or more electromagnets whose supply intensity is adapted to the distance between the electromagnet (s) and the molten zone, so as to maintain the application of a magnetic field independent of the time of constant intensity in the zone or zones molten throughout the manufacturing.

For example, a control unit controls the supply of the electromagnet (s) as a function of the number of layers deposited.

In Figure 5, we can see another example of additive manufacturing device by melting on a powder bed which differs from the device of Figure 4, in that the generation means 308 comprise a plurality of permanent magnets made of ferromagnetic material arranged under the support plate 310 and covering the entire surface facing the production plate 302. Thus whatever the location and / or the shape of the manufactured part, it is located in the region of a field where a field is generated magnetic. In this example, several magnets are used to generate a magnetic field in a single piece.

Alternatively, the magnets are replaced by electromagnets. Advantageously, only the electromagnets in line with the part production zone or zones are supplied, or even only the electromagnets in line with the molten zone or zones subjected to the laser beam during the manufacture of the current layer, which makes it possible to reduce the power consumption of the device. The greater the number of electromagnets, the easier it will be to generate a magnetic field only at the level of the part being manufactured. For example, the power supply of the electromagnets is controlled by the scanning path of the energy source.

As a variant, the means for generating a permanent magnetic field arranged under the support plate are mobile and their movement is controlled by the movement of the beam of the energy source.

In FIG. 5, the construction plate comprises a workpiece support 314 to allow the manufacture of parts of complex shape, in the example shown the workpiece P2 is of ellipsoidal shape.

It will be noted that the support plate, the construction plate and the possible part supports are chosen from a material which is transparent to the magnetic field or which interacts little with it. In FIG. 6, we can see another example of an additive manufacturing device by fusion on a powder bed, in which the magnetic field generation means comprise an electromagnet 48 situated above the powder bed. In this example, the electromagnet is a coil and, advantageously, the energy beam crosses the coil to reach the surface of the powder bed. Thus, the generated field can have a symmetry of revolution with respect to the axis Xc of the molten zone. In addition, the electromagnet can be placed very close to the powder bed.

The energy source 406 is fixed and it is the energy beam emitted by the energy source 406 which is oriented towards the surface of the powder bed by a mirror 416. It scans the surface of the powder bed.

The electromagnet 408 moves in coordination with the path of the energy beam. For example the electromagnet 408 is mounted on a mobile system in the XY plane controlled by the movement of the energy beam.

For example, the energy beam moves at a speed of between 100 mm / s and 10 m / s, preferably 200 mm / s and 2 m / s.

In Figure 7, we can see another embodiment of an additive manufacturing device by melting on a powder bed in which the generation means are such that they generate a magnetic field throughout the powder bed.

In this example, the magnetic field generation means 508 are arranged under the support plate 410 and the powder bed around the jack 412. The generation means are stationary. In addition, they are far from the energy source and are therefore relatively protected from the heat emitted at the molten zone.

As a variant, the generation means are located above the powder bed.

The implementation of means for generating a magnetic field throughout the powder bed has the advantage of not having to control the movement of the means of generating a magnetic field according to the movement of the beam from the source of energy.

In the example shown, the generation means comprise an electromagnet whose axis is aligned with an axis of the powder bed. In this example the electromagnet is a coil and the powder bed has a shape of revolution so that the magnetic field generated crosses the entire cross section of the powder bed and is uniform throughout the powder bed. The winding is such that it covers the entire scanning surface

As a variant, the powder bed can be chosen to have a smaller section than the winding section.

In this example, three pieces PI, P2 and P3 are being manufactured, a uniform field is applied to each molten area. In addition, the magnetic field is normal to the surfaces of the molten areas, the electrical potential is therefore uniform. The Lorentz force is therefore particularly effective in reducing the hydrodynamic speed in the various molten zones.

The generation means of the device of FIG. 7 have a certain bulk and imply a high power to generate a field independent of time throughout the powder bed.

Means for generating a uniform magnetic field also apply to additive manufacturing devices by deposition of material, such as those of FIGS. 2A, 2B, 3A and 3B.

The generation means are arranged at a distance from the melting zone so that the temperature to which the generation means are subjected is lower in the case of a permanent magnet, at its Curie temperature, and in the case of an electromagnet at its operating temperature. It can nevertheless be envisaged in particular configurations to implement additional cooling means, for example with water or air, to control the temperature of the generation means.

In fact, in the case of a permanent magnet, its temperature is kept below its Curie temperature.

In the case of an electromagnet, its temperature is kept below its operating temperature

In the examples of FIGS. 2A, 2B, 3A, 3B and 4, the electromagnets could be replaced by one or more magnets. The present invention applies to any additive manufacturing device using one or more materials which are sufficiently electrically conductive.

Claims

1. Device for additive manufacturing of at least one part (P, PI, P2, P3) of a given electrically conductive material comprising:

- a manufacturing area where the part is intended to be manufactured,

- supply means (4, 104) of the given electrically conductive material for manufacturing the part,

- at least one energy source (6, 106, 406) intended to generate at least one energy beam to melt the given electrical conductive material and form at least one molten zone (ZF) at at least one local location of the manufacturing area,

- means for generating a magnetic field independent of time (8, 108, 208, 308, 408, 508) at least in the molten zone, said means for generating a magnetic field independent of time being arranged with a only side with respect to the manufacturing area where the part is intended to be manufactured.

a control unit configured to control the means for generating a magnetic field so that it generates a magnetic field whose intensity is such that the Hartmann number based on the maximum value of the magnetic field on the surface of the melted zone (ZF) and the maximum depth of the melted zone (ZF) is greater than 5.

2. Additive manufacturing device according to claim 1, in which the means for generating a magnetic field independent of time (8, 108, 208, 308, 408) at least in the molten zone generate a magnetic field whose intensity is such that the Hartmann number is greater than 10, and advantageously greater than 20.

3. Additive manufacturing device according to claim 1 or 2, in which the means for generating a time-independent magnetic field (8, 108, 408) generate a magnetic field having, in the molten zone, a symmetry of revolution with respect to an axis (Xc) normal to a free surface of the molten zone (ZF).

4. Additive manufacturing device according to claim 1, 2 or 3, wherein the means for generating a time independent magnetic field (508) generate a uniform magnetic field, at least in the molten zone, and advantageously in any the manufacturing area, oriented in a direction normal to a free surface of the melted area (Z).

5. Additive manufacturing device according to one of claims 1 to 4, in which the magnetic field is oriented so that the maximum angle of the field lines with the normal of the molten bath over the entire surface of said molten bath is less than 45 °.

6. Additive manufacturing device according to one of claims 1 to 5, wherein the means for generating a magnetic field independent of time (8, 108, 208, 308, 408) are arranged at least in line with the local location of the manufacturing area.

7. Additive manufacturing device according to claim 6, in which the means for generating a time-independent magnetic field (8, 108, 408) are arranged above the local location.

8. Additive manufacturing device according to claim 6 or 7, wherein the means for generating a time independent magnetic field (8, 108, 408) are mobile and their movements are controlled by the movement of the energy source.

9. Additive manufacturing device according to claim 8, in which the supply means (4), the energy source (6) and the generation means. of a time independent magnetic field (8) are configured to move together.

10. Additive manufacturing device according to claim 6, comprising a manufacturing plate on which is intended to be manufactured the part and in which the means for generating a magnetic field independent of time (208, 308) are arranged under the plate Manufacturing.

11. Additive manufacturing device according to claim 6, comprising a manufacturing plate on which is intended to be manufactured the part, and in which the means for generating a magnetic field independent of time (308) extend over a part or under the entire surface of the construction platform likely to be a manufacturing area.

12. Additive manufacturing device according to one of the preceding claims, in which the means for generating a time-independent magnetic field comprise at least one electromagnet.

13. Additive manufacturing device according to claim 12, comprising a control unit configured to control the supply of the electromagnet so as to maintain constant the intensity of the magnetic field in the molten zone.

14. Additive manufacturing device according to claim 12 or 13 in combination with claim 11, in which the means for generating a permanent magnetic field comprise one or more electromagnets, and in which the control unit is configured to control the supply of the electromagnet (s) situated only in line with the at least one local location in the manufacturing zone where a molten zone is intended to be formed.

15. Additive manufacturing device according to one of claims 1 to 9, in which the material supply means (4) comprise a nozzle intended to supplying powdered material or a wire feeding system and in which the supply means (4), the energy source (6) and the means for generating a permanent magnetic field (8) are coaxial.

16. Additive manufacturing device according to claim 1, in which the supply means deliver powdered material in the form of a powder bed.

17. Additive manufacturing process for at least one part comprising:

- the supply of at least one given electrical conductive material to at least one local location of a manufacturing area,

- the application of energy to the local location to melt said given electrically conductive material and form a molten zone,

the generation of a magnetic field independent of time at least in the molten zone, the intensity of which in the molten zone is such that the Hartmann number based on the maximum value of the magnetic field on the surface of the bath and the maximum depth of said melt is greater than 5, said time independent magnetic field being generated on one side of the manufacturing area, the Hartmann number being defined by

Ha = BH (s / h) ^1/2 .

With B the maximum field strength (in Tesla) on the surface of the bath,

H the maximum depth of the bath (in meters) of the bath, s the electrical conductivity of the given electrical conductive material of the melt (in Siemens per meter)

h the dynamic viscosity (in Pascal. second) of the bath.

18. The additive manufacturing method according to claim 17, in which the magnetic field generated independent of time is such that the electric potential in the molten zone is substantially uniform, at least in line with the energy source.

19. The additive manufacturing method according to claim 17 or 18, wherein the means for generating a time-independent magnetic field are arranged relative to the molten zone so as to generate a magnetic field having, in the molten zone, a symmetry of revolution around a direction normal to the free surface of the melted area.

20. Additive manufacturing method according to claim 17, 18 or

19, in which the means for generating a time-independent magnetic field generate a uniform field oriented in a direction normal to the free surface of the molten zone throughout the manufacturing zone.

21. Additive manufacturing method according to one of claims 17 to

20, in which the time-independent magnetic field is generated at the level of the molten zone at the local location of the manufacturing zone for substantially the entire duration of the production of the part.

22. Additive manufacturing method according to one of claims 17 to

21, wherein the method is a powder bed fusion method.

23. Additive manufacturing method according to one of claims 17 to

21, wherein the method is a material deposition method.