FR3057794B1 - IMPROVEMENTS IN SELECTIVE ADDITIVE MANUFACTURING - Google Patents

Abstract

The invention relates to an apparatus for manufacturing a three-dimensional object by additive manufacturing comprising in an enclosure: a support for the deposition of successive layers of additive manufacturing powder; a distribution arrangement adapted to apply a layer of powder on said tray; on a layer previously consolidated, - at least one energy source adapted to the selective consolidation of a powder layer applied by the distribution arrangement, characterized in that it comprises an ionization chamber situated in the vicinity of at least one module and / or optical / electronic component to protect deposits, in the path of the charged vapor going up to said module and / or component in the enclosure.

Description

IMPROVEMENTS IN SELECTIVE ADDITIVE MANUFACTURING

The present invention relates to selective additive manufacturing.

GENERAL TECHNICAL FIELD AND PRIOR ART

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

It has also recently been proposed hybrid machines in which several energy sources are used to achieve selective fusion. For example, the primary source is an electron gun, which is used to perform the selective fusion at the heart of the object. It is supplemented by a secondary source, which is a laser source and which is used, layer after layer, to carry out the selective fusion at the level of the skin or border zones. In this way, it is possible to obtain an object having different mechanical or metallographic properties, for example at its periphery (edge or skin) and in its volume (heart). An example of this is described in patent application WO2013 / 092997.

In selective additive manufacturing processes, the vapor, in the atomic state or in the form of clusters of atoms up to the powder (also called "clusters"), is produced by the vaporization of the surface under the effect of the primary beam (electrons or laser) intense. This vapor is essentially neutral, because the evaporation process takes place, in general, with thermodynamic equilibrium.

However, at atmospheric pressure or under vacuum, the charged vapor thus formed has a high capacity to deposit (condensation) on any solid material with which this vapor comes into contact, and in particular on all metals but also on dielectric materials (ceramics, glass, plastic, etc.) or semiconductors (silicon, germanium, GaAs, etc.).

The particles of this vapor thus propagate to the walls in a ballistic manner at low pressure or diffusive up to atmospheric pressure.

The deposits that result are particularly harmful.

They lead to the formation, on the optical elements inside the manufacturing enclosures (mirrors, lenses, optics of cameras, etc ...) of thin layers which are opaque for wavelengths ranging from ultraviolet to infrared, so including the visible.

More generally, these deposits foul all other components and are not desirable.

In addition, these deposition formations are all the more important at low pressure because the average free path of the species is then very large, or comparable with the dimensions of the enclosure of the machine.

To combat the effects of these deposits, it is already known to provide in front of the optics of the film protection films and sacrificial droplet, that an operator can advance as and when their fouling.

This solution is not fully satisfactory. From a mechanical point of view, it is complex to implement in an additive manufacturing enclosure.

In addition, the protective films placed in front of the optics prevent obtaining optimized images.

GENERAL PRESENTATION OF THE INVENTION

A general object of the invention is to overcome these problems of deposition.

More particularly, the invention provides a solution for greatly limiting the deposits of charged vapors in selective additive manufacturing enclosures.

It also provides a solution to protect against these deposits optics used inside the speakers and more generally to protect any other sensitive surface regardless of its nature. Also, the invention proposes a solution that does not have the disadvantages of the solutions of the prior art.

In particular, according to a first aspect, the invention proposes an apparatus for manufacturing a three-dimensional object by selective additive manufacturing comprising in an enclosure: a support for the deposition of successive layers of additive manufacturing powder, a distribution arrangement adapted to apply a layer of powder on said plateau or on a layer previously consolidated, - at least one source adapted to the selective consolidation of a layer of powder applied by the distribution arrangement, characterized in that it comprises an ionization chamber located in the vicinity of at least one module and / or optical / electronic component to protect deposits, in the path of the vapor charged back to said module and / or component in the enclosure.

Such an apparatus advantageously finds application in the case where the enclosure is a vacuum enclosure, but also applies in the case where the manufacture is carried out at atmospheric pressure or at lower pressures. Ionization can be carried out by an electron source or a photon source.

PRESENTATION OF THE FIGURES Other features and advantages of the invention will become apparent from the description which follows, which is purely illustrative and nonlimiting, and should be read with reference to the appended figures in which: FIG. 1 is a diagrammatic representation of FIG. a selective additive manufacturing apparatus according to a possible embodiment of the invention; FIG. 2 generally illustrates a possible configuration for the heat shield and the ionization chamber of an apparatus of the type of that of FIG. 1; FIGS. 3 and 4 illustrate two possible embodiments for the ionization chamber of an apparatus of the type of FIG. 1.

DESCRIPTION OF ONE OR MORE MODES OF IMPLEMENTATION AND REALIZATION General The selective additive manufacturing apparatus 1 of FIG. 1 comprises: a support such as a horizontal plate 3 on which the various layers of powder are deposited successively; additive manufacturing (metal powder, ceramic powder, etc.) making it possible to manufacture a three-dimensional object (object 2 in the shape of a fir tree in the figure), - a powder reservoir 7 situated above the plate 3, - an arrangement 4 for the distribution of said metal powder on the plate, this arrangement 4 comprising in particular a squeegee 5 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) spread thin layers, - a control unit 9 which controls the various components of the device 1 according to pre-stored information (memory M), a mechanism 10 for allowing 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 two sources of consolidation: an electron beam gun 11 and a laser source 12.

As a variant, the assembly 8 may comprise only one source, for example a source of energy located under vacuum or at low pressure: electron gun, laser source, etc.

A galvanometric mirror 14 makes it possible to orient and move the laser beam coming from the source 12 with respect to the object 2 as a function of the information sent by the control unit 9.

Any other deflection system can of course be considered.

Deflection and focusing coils 15 and 16 locally deflect and focus the electron beam on the layer areas to be sintered or fused.

The components of the apparatus 1 are arranged inside a sealed enclosure 17 connected to a vacuum pump 18 which maintains a vacuum inside said enclosure 17 (typically about 10'2 / 10'3 mbar, even 10'4 / 10'6 mbar).

The walls of the enclosure 17 are preferably made of steel and are sufficiently thick to protect the operator against X-rays. The enclosure 17 furthermore includes portholes (not shown) enabling the operator to visualize the different areas inside the device, while providing protection against X-rays emitted by the electron gun and against the light rays emitted by the laser source. The apparatus 1 may further comprise temperature measuring means, such as an IR camera. or CCDs which are able to communicate to the control unit 9 information concerning the temperature of the powder layer and thus make it possible to adjust the operating parameters of the electron gun 11 or the laser source 12.

In an example of possible use, the laser beam 19 from the source 12 consolidates, layer by layer, the skin or outer edge of the object 2. The electron beam 20 generated by the barrel 11 is meanwhile used to consolidate the inner core of object 2 (heart).

The consolidation carried out by the electron beam 20 can be done layer by layer, at the same time as the consolidation at the periphery by the laser beam 19. The rapid displacement of the electron beam 20 makes it possible to sweep and consolidate the central portion of the layer, while the displacement of the laser beam, slower, occurs simultaneously on a shorter path, which is that of the contour of said central portion. Reverse operation can also be envisaged (scanning of the core by the electron beam and an area of periphery by the laser beam).

Alternatively, the consolidation by the electron beam 20 can be done in several layers, after each of these layers have been fused at the periphery by the laser beam 19.

The operation of such an apparatus, as well as the sizing and parameterization of its various components are for example of the type envisaged in the application WO2013 / 092997. The apparatus 1 further comprises a heat shield T.

This screen T is a material for absorbing radiation from the impact of electron beams on the powder layers. By way of illustration, it may have a parallelepipedal shape provided with an opening in the upper part allowing the passage of the primary beam of energy (electrons, laser, etc.) and which extends by flaring out of said opening towards the support plate.

This form is for example a truncated-pyramidal or frustoconical formed by the assembly of several plates or sectors in the material for absorbing radiation, for example steel.

It can be arranged above the plate 2 and the zone where the powder layers are applied, with a space allowing the passage of the squeegee 5.

Ionization chamber

Referring more particularly to FIG. 2, reference is made to 21 its wide base located above the deposition plane of the powder bed and 22 to its small base which defines an opening 22 intended to be traversed by the energy source. 19 of the laser type and / or the electron beam 20 when they are sent on the bed of powder.

An ionization chamber 23 is disposed at said opening 22 at the top of the heat shield T.

This chamber 23 is defined by the inner walls of a carcass 25.

It opens through an opening 26 inside the heat shield T, and through an opening 27 outside thereof.

These openings 26, 27 are facing each other.

The walls of said chamber 23 and said openings 26, 27 are oriented to allow a direct path (optical, laser, etc.), through said chamber 23 and said openings 26, 27, between an element 24 to protect (transparent optical window , semiconductor sensor, etc.) located opposite the opening 27 (for example an element which extends substantially normal to the axis of the opening 27), outside the heat shield , and a bed of powder on the tray 3.

Various components or optical / electronic modules may be arranged at this optical window 24. This may be the case of the laser 12 and / or the mirror 14, or a camera, possibly associated with optical lenses, allowing to observe the plateau 3 and the progress of additive manufacturing.

Furthermore, as illustrated in Figures 3 and 4, the ionization chamber 23 comprises at least two inner electrodes 28, 29 and a power supply 31 which polarizes said electrodes.

The electric field E created between these electrodes 28, 29 makes it possible to collect the ions produced in the charged vapor which goes up to the ionization chamber 23.

When charged steam released from the surface during a melting operation rises to the ionization chamber 23, this vapor is ionized in said chamber.

The electric field E acts on charged vapor ions (monoatomic ions, aggregates, whether created by this ionization or initially present) with a force of electrostatic type (F = qE) perpendicular to the electrodes. This force induces the deflection of the ionized vapor with respect to its initial ejection trajectory. The ionized vapor is then mainly intercepted by the electrodes 28 and 29: the positive ions are guided by the field E to the electrode having the lowest potential ('cathode'); the negative ions, just like the free electrons, are guided towards the other electrode ('anode').

This electric field E is continuous or variable in time.

Many configurations can be envisaged for the power supply 31: this can be a battery, a source of voltage or direct current, a low or high frequency power supply, or a bipolar, multipolar or pulse power supply.

In this way, the optics and components (lenses, cameras, lasers, etc.) placed opposite the outer opening 27 (at the level of the window 24) are protected and preserved from significant deposits.

The carcass 25 can be mounted directly on the heat shield T. It can be removably mounted thereon or can be fixed non-releasably.

The carcass 25 can serve as a potential reference for the source 31. It can be connected to the mass or kept floating. These walls are electrically isolated from the electrodes 28 and 29 by dielectrics 30. They also play a role of heat shield with respect to the additional heat that can be released in the ionization chamber itself. The heat shield thus constituted by the steel or other material of said walls makes it possible to avoid disturbing the additive manufacturing, which can be particularly sensitive to temperature drifts.

The carcass 25 acts as a Faraday cage, allowing the electrical shielding outside of this ionization chamber, and the interference-free operation of the electron beam 20 of the barrel 11.

Ionization by electron source

As illustrated in FIG. 3, the ionization can be obtained thanks to an electron source 32 accelerated by a voltage supplied by the power supply 31.

This source of electrons 32 is for example a filament. Other types of electron sources can be envisaged (cold emission or field emission, Schottky emission, etc.).

The electrons thus emitted are accelerated by the electric field which is established by the polarization of at least one electrically insulated wall with respect to the other surfaces of the ionization chamber 23.

The energetic electrons thus obtained by this acceleration ionize by electronic impact the charged vapor (atomic or in the form of aggregates) released from the molten surface and which passes through the ionization chamber 23 up through the opening 26. Once ionized, the vapor is deflected by the electric field E and captured as a deposit on the electrodes 28, 29.

In the case of aggregates of nanometric size or greater, some of these electrons can also be captured by these aggregates without necessarily ionize them, which leads to the creation of negative ions.

The acceleration voltage is chosen so that a single ionization is possible, at most two, during the interaction with the vapor, before touching one of the walls of the ionization chamber.

Moreover, the lower the pressure, the more the number of interactions will be too. On the other hand, by increasing the pressure it will be necessary to also increase the polarization, so that the energy transmitted to the electrons by the electric field on a mean free flight path between two successive interactions remains substantially the same.

The new electrons created by ionization of the vapor must be limited in number so as to avoid the creation of a plasma inside the ionization chamber. Such a plasma could indeed disturb the EBM beam, for example, and more generally the operation of the apparatus.

Typically, the acceleration voltage is 10 to 100V.

Ionisation by photoionization

Alternatively, the ionization can be obtained by photoionization (FIG. 4) by means of a photonic source 33.

The photoionization source 33 may be a lamp emitting at wavelengths corresponding to the Ultra-Violet range.

The transmission power of the source 33 is for example 50 to 100 W. The wavelength may be more specifically of the order of 250 nm, which corresponds to photons of about 5 eV energy.

The photon source is a lamp whose emission is very intense in the Ultra-Violet (UV) range of the spectrum.

The photons of a source of this type effectively excite the atoms that constitute the charged vapor, as well as the possible aggregates. If during the lifetime of an excited level a second photon is absorbed, then the absorbing particles are ionized. In addition, some metals and aggregates have ionization energies of 5 eV and lower and can be ionized by absorption of a single photon.

In order to promote the absorption of photons, it is expected that the source 33 is placed between at least two curved mirrors 34, 35 facing each other which together define an optical cavity. The radii of curvature of these mirrors and their positions are chosen so that the photons of the source 33 undergo multiple reflections and that they are concentrated in the zone of interest of the chamber 23. Other pairs of mirrors 36 are in further disposed facing two by two, along the walls of the carcass 25, in the length of the optical cavity defined between the two curved mirrors 34, 35. In this way, the photons are kept as long as possible in the optical cavity. ; the chances of photo-ionization are increased. The electrodes 28, 29 of the chamber 23 can themselves also act as mirrors.

A heat shield 37 made of ceramic or refractory material may also be interposed between the various mirrors and the walls of the carcass 25.

The electrons emitted during the photoionization are accelerated towards the positive electrode (in this case the electrode 28 in the figure). In their path, these free electrons gain energy and if they interact with a vapor, additional ionization can also take place.

The new electrons created by photoionization or ionization of the vapor must nevertheless be limited in number so as to avoid the creation of a plasma inside the chamber 23.

Claims (9)

Apparatus for manufacturing a three-dimensional object by additive manufacturing comprising in an enclosure: a support for the deposition of successive layers of additive manufacturing powder, a distribution arrangement adapted to apply a layer of powder on said support or on a previously consolidated layer at least one energy source adapted to the selective consolidation of a layer of powder applied by the distribution arrangement, characterized in that it comprises an ionization chamber situated in the vicinity of at least one module and or optical / electronic component to protect deposits, in the path of the vapor charged back to said module and / or component in the enclosure, and in that it comprises a heat shield which has an opening allowing the passage of radiation and / or the electron beam and which extends from said opening to the support plate, around the zone of the powder bed and in that the chamber of ionization is disposed at said opening. 2. Apparatus according to claim 1, characterized in that the ionization chamber is integrated in a carcass mounted on a heat shield. 3. Apparatus according to claim 2, characterized in that said carcass is removably mounted on said screen. 4. Apparatus according to one of the preceding claims, characterized in that the ionization chamber comprises two electrodes and a power supply which polarizes them in order to collect the ions created in the ionization chamber or initially present in the vapor charged, when it goes up to said room. 5. Apparatus according to one of the preceding claims, characterized in that the ionization source is a source of accelerated electrons. 6. Apparatus according to claim 5, characterized in that the electrons of the ionization source are accelerated by a voltage of between 10 and 100 V. 7. Apparatus according to one of claims 1 to 4, characterized in that the ionization source is a photonic source. 8. Apparatus according to claim 7, characterized in that said source is a UV lamp. 9. Apparatus according to one of the preceding claims, characterized in that an optical / electronic component or module is a lens, a camera, a sensor or a laser-type radiation source.