WO2020144442A1

WO2020144442A1 - Method and device for treating powders for additive manufacturing

Info

Publication number: WO2020144442A1
Application number: PCT/FR2020/050035
Authority: WO
Inventors: Tiberiu Minea; Gilles WALRAND; Albin EFFERNELLI
Original assignee: Addup; Centre National De La Recherche Scientifique (Cnrs); Universite Paris-Sud
Priority date: 2019-01-10
Filing date: 2020-01-10
Publication date: 2020-07-16
Also published as: FR3091662B1; FR3091662A1

Abstract

The invention concerns an assembly (7) for the surface treatment of powders, operating in situ, for additive manufacturing, the assembly (7) comprising a tank of etching agent (18) connected to a spray element (19) for spraying etching agent, the spray element (19) being arranged opposite a surface (26) of a layer of powder and being configured to spray the etching agent onto the grains of powder so as to carry out a method for the surface treatment of the powders in order to improve the energy absorption rate of the grains of powder, a corresponding surface treatment method, an additive manufacturing device and method implementing such a surface treatment of powders.

Description

PROCESS AND DEVICE FOR THE TREATMENT OF POWDERS FOR APPITIVE MANUFACTURING

GENERAL TECHNICAL AREA AND PRIOR ART

The invention relates to the field of manufacturing by adding material, or additive manufacturing, and in particular the manufacturing by adding metal powders.

Conventionally, a method of manufacturing a part by adding metal powders is carried out by depositing successive layers of powders on a flat support surface, thus forming a powder bed.

After the deposition of a powder layer, a power source selectively heats certain areas of the powder bed, so as to cause the powders to melt in the heated areas and thus form a coherent layer of room after cooling.

The layers of powders are thus successively deposited and selectively solidified so as to form a part by successive layers.

Conventionally, the power sources used to carry out the selective fusion of the powders may comprise one or more laser sources, or one or more sources with an electron or particle beam, or else a combination of sources using a laser, a beam of electrons or particles.

When producing metallic parts, the thermal and electrical conductivity and the reflection coefficient of the powders used limit the energy absorption rate of the powders.

The energy efficiency of the selective fusion operation is therefore greatly reduced.

In certain special cases, for example when using copper or aluminum powders during additive manufacturing, most of the laser light is reflected (up to 99%), thus leading to the selection of sources. of power using an electron or hybrid beam (laser / electron beam). These types of power source have the disadvantage of leading to the sintering of powders in areas not directly exposed to the electron beam, which do not form part of the strata constituting the part, in particular by the heating effect (Joule ) induced between the grains of powder during the flow of the electric charge towards the mass. This greatly limits the amount of material that can be recycled.

It is known to increase the absorption of energy, by increasing the surface exposed of a part to a coherent beam, for example a laser, by producing reliefs on said surface as illustrated in FIG. 1 , thereby increasing the roughness of the workpiece surface.

The reliefs induce multiple reflections thus increasing the probability of absorption of the photons even on very reflecting surfaces. According to the geometry of the relief, the beam performs multiple reflections against the surfaces of the reliefs as illustrated in FIG. 1a and 1b, each reflection causing a transfer of energy from the beam to the part. It can also be trapped for a relief as shown in Figure le.

Thus, instead of carrying out a reflection against a smooth surface, the multiple reflections of the beam on a surface having a large roughness make it possible to increase the rate of energy absorption of the part.

It is also known that the energy absorption factor depends on the wavelength of the beam to which the part is exposed. The more energetic the photons, the greater the absorption. Also, increasing the temperature of this surface improves energy absorption [L. K. Ang et al, Appl. Phys. Lett. 70 (6), 1997, p. 696].

It is also known to produce a nanostructure on the surface of a part, so as to produce resonant phenomena of absorption of laser radiation. If the surface roughness is produced on a nanometric scale (for example between 2 and 5 nm, for copper, while these dimensions are more important for other metals, for example Au, Ag, etc.), then a Resonant phenomenon of photon absorption can occur, known as the surface resonant phonon. However, the methods conventionally used to produce and control such significant nanostructures or roughness present application difficulties for powder grains used during additive manufacturing processes.

In the case of the immersion of all the grains in a liquid bath (acid or basic) prior to the arrangement of the powders in layers and the selective melting of the powders, it would be necessary to use significant amounts of harmful solution , causing in particular difficulties in the recovery of powders. It would also be necessary to introduce an additional step for drying the powders before depositing a layer of powders. In addition, it is necessary to carry out a step making it possible to stop the chemical attack, which can continue after the extraction of the powders from the liquid bath, until the total consumption of the active agents or else the use of several baths, for example.

OVERVIEW OF THE INVENTION

A first object of the invention is to optimize the energy absorption rate of metallic powders used during an additive manufacturing process.

Another aim is to optimize the energy efficiency of a selective melting operation during an additive manufacturing process.

Another object is to treat during the additive manufacturing process the surface of a metal powder so as to increase the roughness of said surface.

Another aim is to overcome the drawbacks of the prior art surface treatment methods.

To this end, the invention proposes a manufacturing process by adding material comprising the steps of:

- Deposit of a layer of powder,

- Selective fusion of at least one area of the powder layer, in which the method comprises, at the end of the deposition and prior to the selective melting, a step of surface treatment of the grains of powder carried out on site and comprising a step of surface attack during which an etching agent is sprayed onto the surface grains of powder, the etchant reacting chemically with the grains of powder and altering the surface of the grains of powder so that the surface of the grains of powder has a micrometric roughness.

Such a process can advantageously be supplemented by the following characteristics taken alone or in combination:

- the etching agent alters the surface of the powder grains to produce a nanostructure on the surface thereof;

the selective melting step is carried out by means of a power source comprising a laser source, the wavelength of said source and the roughness of the grains after surface treatment being adapted to the generation of radiation absorption phenomena laser by said grains;

the method further comprises a step of heating the powders carried out during and / or after surface treatment and prior to the step of selective melting of the powders;

the surface treatment step of the powder grains is carried out by means of a surface treatment treatment of the powders comprising a plasma spraying device configured to spray the etching agent onto the powder grains, and in which the step the powders are heated by means of the plasma spraying device simultaneously with the surface treatment step.

According to another aspect, the invention provides an apparatus for additive manufacturing comprising:

a support such as a horizontal plate on which various layers of powder are successively deposited,

- powder supply, a distribution arrangement configured to distribute the powder on the support, this distribution arrangement comprising for example a squeegee or a layering roller for spreading the various successive layers of powder,

a power source configured to perform the selective melting of at least part of the layer of powder deposited on the support,

a mechanism for allowing the support to be displaced as the layers are deposited, the support being able to be displaced in a vertical direction,

- a control unit which controls the various components of the device as a function of information pre-stored in a memory,

characterized in that the apparatus further comprises an assembly for surface treatment of the powders comprising an etching agent reservoir connected to an etching agent spraying element, the spraying element being arranged opposite a surface of a powder layer and being configured to spray the etching agent on the powder grains so as to carry out a manufacturing process by adding material according to the invention.

Such an apparatus can advantageously be supplemented by the following characteristics, taken alone or in combination:

the etching agent is a liquid, and in which the spraying device comprises a nozzle configured to project droplets of etching agent onto the powder grains;

- the nozzle is a micro-nozzle or an electro-nozzle configured to control the size of the drops of etching agent;

- the etching agent is a gas, and in which the spraying device comprises a plasma spraying device configured to spray the etching agent onto the powder grains;

- The plasma projection device is configured to project a plasma jet and includes an excitation source configured to operate in pulse mode and / or in continuous mode; the plasma projection device comprises an electrode extending in a longitudinal direction inside a sheath extending longitudinally and into which the etching agent is injected, the sheath comprising a slot extending longitudinally opposite from the surface of the powder layer, the electrode being excited so as to generate a linear plasma projected through the slit onto the powder, the ejection of the plasma causing the etching agent to be projected onto the powder.

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 la is a diagram representing a relief model of conical shape used to express the roughness of a surface, on which is represented the path traveled by several rays which undergo multiple reflections in said relief;

- Figure lb is a diagram showing a relief model of cylindrical shape used to express the roughness of a surface, on which is represented the path traveled by a ray "trapped" in said relief;

- Figure le is a diagram representing a relief model having a drop shape used to express the roughness of a surface, on which is represented the path traveled by a ray "trapped" in said relief;

- Figure 2 is a schematic representation of an additive manufacturing device according to the invention;

- Figure 3 is a schematic representation of a surface treatment device for powders according to one embodiment of the invention;

- Figure 4 is a representation of a surface treatment device for powders according to another embodiment of the invention; - Figure 5 is a representation of a surface treatment device for powders according to a third embodiment of the invention.

DESCRIPTION OF ONE OR MORE MODES OF IMPLEMENTATION AND

OF REALIZATION

The invention applies to a manufacturing process by adding material comprising the steps of:

- Deposit of a layer of powder,

- Selective fusion of at least one zone of the powder layer, in which the method comprises, at the end of the deposition and before the selective fusion a surface treatment step of the powder grains carried out on site and comprising a step d surface attack during which an etching agent is sprayed onto the surface of the powder grains, the etching agent chemically reacting with the powder grains and altering the surface of the powder grains so that the surface of the powder grains has a micrometric roughness.

During such a process, only the external surface of the powder bed is subjected to chemical treatment and not all of the powder.

This process is in particular carried out by means of an apparatus for additive manufacturing 1 as illustrated in FIG. 2, comprising:

a support 2 such as a horizontal plate on which successive layers of powder are deposited,

- a powder inlet 3 located above the support 2,

a distribution arrangement 4 configured to distribute the powder on the support 2, this distribution arrangement 4 comprising for example a squeegee 5 or a layering roller for spreading the different successive layers of powder,

a power source 6 configured to carry out the selective melting of at least part of the layer of powders deposited on the support 2, a surface treatment assembly 7 for the powders, configured to treat the powders during the additive manufacturing process,

a mechanism 8 to allow the support 2 to be displaced as the layers are deposited, the support being able to be displaced in a vertical direction,

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

The powder inlet 3 can be connected to a powder reservoir which contains the powders forming the material constituting the part P to be produced during additive manufacturing.

The powder reservoir can be internal to the machine or external to the manufacturing zone, and in this case be connected to the powder inlet 3 by means of a pipe.

The powders can be metallic, for example copper, aluminum, silver, iron, or titanium, or ceramic.

The power source 6 may comprise one or more laser sources 10, or one or more sources of electron beams or of particles 11, or else a combination of laser power sources and of beams of electrons and / or particles .

In the example described with reference to FIG. 1, at least one galvanometric mirror 12 makes it possible to orient and move the laser beam coming from the source 10 relative to the object P as a function of the information sent by the unit of control 9.

Deflection 13 and focusing 14 coils make it possible to deflect and locally focus the electron beam on the areas of layers to be sintered or fused.

Any other deviation system can of course be envisaged.

In a variant, the power source 6 comprises several sources 10 of the laser type and the displacement of the different laser beams is obtained by moving the different sources 10 of the laser type above the layer of powder to be fused. A heat shield T can be interposed between the part P and the side wall of the machine 15.

The heat shield is configured to limit the emission of metallic vapors (“fumes”) from the molten part P on the other internal components of the additive manufacturing machine.

The components of the device 1 are arranged inside a sealed enclosure 15, which can optionally be connected to a vacuum pump 16.

The surface treatment assembly 7 comprises an etching agent reservoir 18 connected to an etching agent spraying element 19.

The etching agent can be a fluid which reacts chemically with the surface of the powder grains when the etching agent comes into contact with the powder, for example a solution comprising halides, and / or sulphides, or any other substance having an effect. oxidizing on metal or ceramic.

Thus, the chemical attack superficially degrades the surface state of the powder grains, thereby increasing the roughness of the powder grains.

The surface treatment assembly 7 can optionally be mounted on an actuator 20 such as a robotic arm or any other device making it possible to move the etching device over the layers of powders.

The actuator 20 can be controlled by the control unit 9.

The etching agent contained in the reservoir 18 is injected into the etching agent spraying element 19, which projects a controlled amount of etching agent onto the powders situated opposite the spraying element 19.

The displacement of the surface treatment assembly 7 by means of the actuator 20 makes it possible to treat the powder on any zone of the surface 26 of the powder layer, which in particular makes it possible to treat only the surface of the grains of powder which will subsequently be merged, and for example exposed to laser radiation. Optionally, the actuator 20 causes the spraying element 19 to move, the reservoir 18 being fixed so as to limit the mass displaced by the actuator 20. The spraying element 19 and the reservoir 18 can in this case be connected by a flexible pipe.

The speed of movement of the surface treatment assembly 7 and the rate of injection of the etching agent into the spraying spraying element 19 are controlled by means of the control unit 9 so as to control the quantity of etching agent sprayed onto the powder and thus controlling the quantity of reagents consumed during the chemical reaction between the etching agent and the powder grains.

The depth of the chemical attack of the powders produced by the etching agent is thus controlled, making it possible to obtain the desired roughness with precision.

Optionally but advantageously, the spraying element 19 disperses the etching agent in the form of micro- or nanometric droplets (the droplets having at least one of their dimensions of an average size less than lpm for a micrometric droplet, or at 100nm for a nanometric droplet) or in gaseous form (aggregates or molecules). This makes it possible in particular to produce reliefs of small dimension (at least one of the dimensions of which has an average value of less than lpm), which makes it possible to improve the absorption of light without significantly modifying the size and / or the shape. grains of powder. Advantageously, the quantities of etching agent used being minimal, this process also limits the insertion of dopants or impurities in the powders, preserving the initial nature (because this chemical attack surface state, most of the etching agent s 'evaporates during the fusion of the powders).

Optionally, it is possible to control the injection rate of the etching agent by means of an electrostatic device or a microfluidic system. For example, Ang et al. ¹ mention that the fraction of energy absorbed by an aluminum target exposed to a red laser with a wavelength of 690 nm increases with roughness. In this example, the roughness is defined as an aspect ratio h / d, h and d representing the average values of the dimensions of a relief in two directions, here for example the height (or depth) h and the diameter d. The absorption rate has a value of 2% for a roughness of 1 (depth to width ratio, h / d, Fig. 1), and has a value of 9% for a roughness of 5.

In this example, the roughness is defined as an aspect ratio h / d, h and d representing the average values of the dimensions of a relief in two directions, here for example the height (or depth) h and the diameter d.

A relief is considered in a conventional model illustrated in FIG. 1b as being a cylindrical crevice with a depth h and a diameter d. In this model, the relief comprises a substantially cylindrical wall having a diameter d, the wall extending between a bottom and an opening which are distant by a height (or depth) h.

This type of attack can be produced, for example, by ion etching (or plasma), also known as anisotropic etching, because the energy of the ions (of active agent) is much greater and oriented perpendicular to the surface relative to to atoms or molecules of neutral etching agent. In fact, the well created is deep (large aspect ratio) with appreciably vertical sides.

Optionally, the surface treatment assembly 7 may comprise several reservoirs 18 comprising the same etching agent or which may include different etching agents depending on the powder used for manufacturing.

These different reservoirs 18 can each be connected to a spray device 19 which is specific to them, by a pipe which is specific to them or even by a single pipe. Optionally,

¹ LK Ang et al, Appl. Phys. Lett. 70 (6), 1997, p. 696 tanks 18 are connected to an inlet element common to the different tanks 18, the inlet element being connected on the one hand to the different tanks 18 and on the other hand to the spraying device 19.

Optionally, the laser source 10 of the power source 6 has a wavelength chosen as a function of the roughness obtained on the powder grains, so as to optimize the energy transfer between the laser beam and the powder grains.

For example, Ang et al. describe that the fraction of energy absorbed by an aluminum target exposed to an ultraviolet laser with a wavelength of 248 nm increases with roughness, the absorption rate having a value of 4% for a roughness of 1, and having a value of 16% for a roughness of 5.

In this example, the ultraviolet laser has better heating capacity (energy transfer) than the red laser. Depending on the materials and wavelengths used, these results may vary and are in no way limiting.

Optionally, a step of heating the powders is carried out, locally or over the entire surface 26 of the powder layer disposed on the support 2, before carrying out the selective melting, and after having carried out the surface treatment of the powders making it possible to obtain the roughness desired for the grains of powder. By heating the rough surface, absorption is further improved.

For example, Ang et al. describe that the fraction of energy absorbed by a surface having a roughness value of 5 in solid silver exposed to a red laser with a wavelength of 690 nm increases with temperature, the absorption factor varying between a rate about 5% at room temperature and a rate of around 25% for a temperature of about 900 ° C.

In a similar situation but for a roughness of 6, the absorption factor varying between a rate of around 5% at room temperature and a rate around 30% for a temperature of around 900 ° C.

In a second similar situation but for a roughness of 4, the absorption factor varying between a rate of around 5% at temperature ambient and a rate of around 20% for a temperature of around 900 ° C.

Optionally, the surface of the powder grains is treated to present a nanostructure of optimal size, relative to the wavelength of the laser source to cause resonant phenomena of absorption of laser radiation.

It is understood by nanostructure that at least one of the parameters representing the average values of the dimensions of a relief has a value between 1 and 100 nanometers.

Liquid spraying

In an embodiment shown in FIG. 3, the etching agent is a liquid contained in the reservoir 18. It can be conveyed to the discharge by a flexible conduit and using a micro-injector.

In another embodiment, the liquid is entrained through a bubbler (that is to say by bubbling a gas into the etching agent which it is desired to inject). The flow of the mixture of gas and liquid droplets can be monitored by a flow meter.

The spraying device 19 comprises a nozzle 21 configured to project droplets of etching agent onto the powders.

Optionally, the nozzle 21 is a micro-nozzle or an electro-nozzle configured to control the size of the drops of etching agent, so as to control the depth of the chemical attack regardless of the size of the powder grains.

The use of a nozzle 21 allows local application of the chemically active substances. It can lead to isotropic roughness, like those presented in Fig. 1 C).

In a preferred embodiment, the liquid chosen for surface engraving of the powder grains is volatile at high temperature.

In this way, the traces of etching agent which could exist on the surface are eliminated during the melting of the powder grains and subsequently evacuated in the form of fumes, with the other elements released during the formation of the liquid metal bath. Plasma spray

In an embodiment illustrated in FIG. 4, the etching agent is a gas contained in the reservoir 18.

The spraying device 19 comprises a plasma spraying device 22.

The etching agent is injected in the form of molecular gas or very fine droplets (aerosols, for example) into the plasma projection device 22, the plasma ensuring the activation and the projection of the etching agent on the powders.

In another embodiment, the liquid is entrained through a bubbler (that is to say by bubbling the plasma gas into the etching agent which it is desired to inject). The flow of the mixture of gases and liquid droplets can be controlled by a flow meter in order to keep the total pressure of the enclosure 15 in the standard process parameters. Of course, the plasma gas can also act as an etchant, or not. The use of a plasma projection device 22 makes it possible to precisely control the surface exposed to the plasma jet as well as the activation of gaseous species by the plasma, in particular as a function of the flow rate of etching agent injected into the plasma projection 22 and as a function of the power applied to maintain the discharge.

The action of the plasma on the etching agent can cause the formation of radicals and thus improve the efficiency of the etching agent, making it possible to reduce the quantities of etching agent consumed during the surface treatment of the powders.

In addition, the use of a plasma spraying device 22 makes it possible to carry out the step of heating the powders prior to the selective melting simultaneously with the surface treatment of the powders, and therefore to reduce the duration of the process.

In a first variant, the plasma projection device 22 is configured to produce a plasma jet, making it possible to generate a plasma at atmospheric pressure or under primary vacuum (the pressure being between lOmbar and lbar). By plasma jet, it is understood that the section of the plasma jet is substantially circular and has a low lateral dispersion. It can be produced inside a capillary tube, for example.

Optionally, the plasma projection device 22 includes a dielectric barrier discharge device supplied by a high voltage pulse system, allowing the creation of a "clean" plasma, without internal electrodes, and with a high gas activation efficiency. .

Optionally, the plasma projection device 22 includes a microwave power coupling device.

Such a microwave power coupling device is effective from 1 mbar and up to atmospheric pressure, with the particularity of operating continuously, that is to say in non-pulse mode.

Such a device therefore makes it possible to reduce the ambient pressure during the surface treatment of the powders, and makes it possible to carry out the selective melting operation at low pressure (lower than atmospheric pressure) without there being any need to modify the pressure. between the powder processing step and the selective melting step. This allows in particular to reduce the cycle time and improve the productivity of the additive manufacturing process.

Carrying out the selective melting step at low pressure makes it possible to minimize the losses by energy transfer between the beam and the gaseous medium of the enclosure 15, which improves the energy efficiency of the selective melting operation.

Optionally, a plurality of plasma projection devices 22 are arranged to form a plasma projection network, the projection network comprising a plurality of parallel plasma jets.

The plasma projection devices 22 are connected to a common reservoir 18 or each plasma projection device 22 is connected to a dedicated reservoir 18.

In a second variant illustrated in FIG. 5, the plasma projection device 22 includes an elongated electrode 23 supplied by an electrical excitation source itself controlled by the control unit 9.

This electrode 23 generates, under the effect of said excitation source, electric discharges between said electrode 23 and the powders and creates a plasma by the supply of energetic particles of positive and negative charge, allowing effective activation of the molecules of plasma neutral gas, including that of the etching agent.

The etching agent is injected in the form of gas near the electrode 23, the plasma ensuring the projection of the etching agent on the powders through the slot 25, the width of which is of the order of 1 mm (capillary) , in order to preserve the lateral precision of the treatment.

The electrode 23 extends substantially parallel to the powder layer. It is moved parallel to the surface 26 of the powder layer, perpendicular to the direction in which the electrode extends.

Such a configuration allows a uniform projection of the etching agent on a surface 26 of the powder layer corresponding to the length of the electrode 23 and to its displacement distance.

This solution for generating an electric discharge by an elongated electrode is effective over a wide range of pressures ranging from 1 mbar to a few hundred millibar.

Optionally, by modifying the structure of the electrodes, it is possible to extend the operation of such a slit device for a range of pressures around atmospheric pressure.

The distance between the electrode 23 and the surface 26 of the powder layer must be as small as possible, so that the electrical discharge (plasma) develops only between the electrode 23 and the surface 26 of the powder layer. powder.

A mechanism (not shown) allows the adjustment of this distance in addition to the mechanism 8.

In the above-mentioned pressure ranges, the electrode 23 is spaced from the surface to be heated by a space (gas) of the order of a millimeter.

The electrode 23 is preferably made of a metal which has a high melting temperature (By high temperature, it is understood that the melting temperature of the material of the electrode is at least equal to or greater than the melting temperature of the powders).

The electrode 23 can be made of dielectric material, or of semiconductor material or ceramic.

Preferably, the electrode 23 is made of a material which is resistant to the action of the etching agent.

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

In another embodiment (not shown), a cooling system for the elongated electrode can be installed.

The powder layer is for example connected to ground.

The electrical excitation source allows the application of a high voltage (typically> 0.5 kV, for a heating power of some 100 W to a few kW) between the electrode 23 and the powder layer.

The power supply thus produced by the source can be alternated, either sinusoidal low frequency, or any other signal profile, (square or triangular for example) or radio frequency, or pulse.

The operation of the radio frequency excitation discharge ensures perfect neutrality of the surface 26 of the powders and the mutual repulsion of the powders is thus avoided.

It should be noted that by modifying the excitation mode, for example in high-voltage pulse mode, it is possible to accelerate the ions (in particular those originating from the etching agent, for example iodine or chlorine) to very high energies. In this case, these ions are directed in a parallel beam and they can produce reliefs with vertical walls, such as that illustrated in FIG. 1b.

Also, in the case of an ionized droplet, it can cross the surface layer (the “skin”) of a grain of powder and once the kinetic energy is lost, attack the grain of powder to create a relief in the form of drop, as shown in FIG.

Also, the electrode 23 is in turn subjected, in all cases, to ion bombardment. Consequently, a minute quantity of material from this electrode 23 will be sprayed, in the neutral state. This subject will redeposit, essentially, just below, so on the powder layer.

One way to overcome this drawback is to construct the electrode 23 in the same material as the powder to be preheated.

Optionally, the electrode 23 is constructed from a material making it possible to improve certain characteristics of the material constituting the part to be produced when the material constituting the electrode is mixed with the powders.

The electrode 23 can also - as illustrated in FIG. 5 in the particular case of an electrode 23 with a substantially circular section - be protected by a metal sheath 24 (“guard electrode”), floating or connected to the mass, provided with a slot 25 opposite the powder layer.

The etching agent is then injected between the electrode 23 and the sheath 24, and is projected through the slot 25 onto the powder layer under the action of ejecting the plasma.

The electrode 23 may alternatively have a different geometry, for example having a substantially annular section, or a knife-like section, or in an arc of a circle or in an arc of a ring. The electrode can also be provided with a slot.

In the case of an electrode 23 with an annular section and comprising a slot, or a ring-shaped section, the electrode 23 has a wall delimiting an internal cavity.

The etching agent is introduced into the cavity internal to the electrode 23, and is projected by the slit 25 onto the powder layer under the action of the ejection of the plasma by the slit 25.

Such a variant makes it possible to obtain a very strong and localized action of surface corrosion of the gains, and it is possible to quickly treat the entire surface 26 of the powder layer.

Method for surface treatment of powders

The associated method proposes to surface attack the extreme surface of the grains constituting the powder bed, after its layering, but before the micro-fusion by electron beam / laser. A chemical action is carried out on the surface of the powder grains, producing minute corrosion (of the order of pm) but controlled, localized and of random distribution. Thus, the surfaces of the powder grains - initially smooth - will gain a micrometric roughness, compatible with the wavelength of the laser radiation (infrared, ultraviolet or visible).

It is understood by micrometric roughness that the diameter of the relief, as shown in FIG. 1, has a value of the order of a micrometer, between 0, lpm and lOpm.

In addition to the increase in the energy absorption of the laser beam by the powders (ie the decrease in the reflection coefficient of the powders), it is possible to cause resonant absorption phenomena through surface plasmons, if the surface has a nanostructure.

Several methods can be envisaged for chemically attacking the surface of the powder grains.

Wet etching involves sending droplets to the surface of the powders after layering.

Dry etching is carried out by plasma using a locally acting etching gas (linear plasma for example, with a gas supply or a mixture of chemically active gases on the powders).

The precise dosage of the amount of etching agent stops surface corrosion, typically micrometric in depth, and therefore makes it possible to control the surface condition of the grains, without significantly modifying their size and with perfect control of any possible doping.

By dopants is meant trace elements which modify the properties of the initial material. In the case of etching agents (eg Phosphorus for Copper), if the amount exceeds 1%, then the electrical conductivity of the Copper drops a lot. So this control and especially the limitation of the amount of etching agent are very important.

According to the additive, laser, electron beam or hybrid manufacturing method, in other words the pressure range lbar, 0.1 Pa or 1 mbar respectively, either of the surface treatment methods described can be used.

Claims

1. Manufacturing process by adding material comprising the steps of:

Depositing a layer of powder,

Selective fusion of at least one zone of the powder layer, in which the process comprises, after deposition and

prior to the selective melting, a surface treatment step of the powder grains carried out on site and comprising a surface attack step during which an etching agent is sprayed onto the surface of the powder grains, the etching agent reacting chemically with the powder grains and altering the surface of the powder grains so that the surface of the powder grains has a micrometric roughness.

2. Manufacturing process by adding material according to claim 1, in which the etching agent alters the surface of the powder grains to produce a nanostructure on the surface thereof.

3. Manufacturing method by adding material according to claim 1 or 2, wherein the selective melting step is carried out by means of a power source (6) comprising a laser source (10), the wavelength of said source and the roughness of the grains after surface treatment being adapted to the generation of phenomena of absorption of laser radiation by said grains.

4. Manufacturing process by adding material according to one of claims 1 to 3, further comprising a step of heating the powders carried out during and / or after surface treatment and prior to the selective melting step of the powders.

5. Manufacturing process by adding material according to claim 4, in which the surface treatment step of the powder grains is carried out by means of a surface treatment treatment of the powders (7) comprising a plasma spraying device ( 22) configured to spray the etching agent onto the powder grains, and in which the step of heating the powders is carried out by means of the plasma spraying device (22) simultaneously with the surface treatment step.

6. Apparatus for additive manufacturing (1) comprising:

a support (2) such as a horizontal plate on which various layers of powder are successively deposited,

powder supply (3),

a distribution arrangement (4) configured to distribute the powder on the support (2), this distribution arrangement (4) comprising for example a squeegee (5) or a layering roller for spreading the different successive layers of powder, a power source (6) configured to carry out the selective melting of at least part of the layer of powder deposited on the support (2),

a mechanism (8) to allow the support (2) to be displaced as the layers are deposited, the support being able to be displaced in a vertical direction,

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

characterized in that the apparatus (1) further comprises a surface treatment assembly (7) of the powders comprising an etching agent reservoir (18) connected to a spraying element (19) of etching agent, the element spray (19) being disposed opposite a surface (26) of a powder layer and being configured to spray the etching agent on the powder grains so as to carry out a manufacturing process by adding material according to one of claims 1 to 5 comprising a surface treatment step of the powder grains.

7. Apparatus for additive manufacturing according to claim 6, in which the etching agent is a liquid, and in which the spraying device (19) comprises a nozzle (21) configured to project droplets of etching agent onto the grains of powder.

8. Apparatus for additive manufacturing according to claim 7, wherein the nozzle (21) is a micro-nozzle or an electro-nozzle configured to control the size of the drops of etching agent.

9. Apparatus for additive manufacturing according to one of claims 6 to 8, in which the etching agent is a gas, and in which the spraying device (19) comprises a plasma spraying device (22) configured to spray the agent etching on grains of powder.

10. Apparatus for additive manufacturing according to claim 9, wherein the plasma spraying device (22) is configured to project a plasma jet and comprises an excitation source configured to operate in pulse mode and / or in continuous mode.

11. Apparatus for additive manufacturing according to one of claims 9 or 10, wherein the plasma projection device (22) comprises an electrode (23) extending in a longitudinal direction inside a sheath (24 ) extending longitudinally and into which the etching agent is injected, the sheath comprising a slot (25) extending longitudinally opposite the surface (26) of the powder layer, the electrode (23) being excited by so as to generate a linear plasma projected through the slot (25) on the powder, the ejection of the plasma causing the projection of the etching agent on the powder.