WO2018078057A1

WO2018078057A1 - Appliance for manufacturing a three-dimensional object by means of an additive manufacturing method, and associated additive manufacturing method

Info

Publication number: WO2018078057A1
Application number: PCT/EP2017/077522
Authority: WO
Inventors: Gilles WALRAND; Tiberiu Minea; Didier VALENTIN; Jean-Claude Aperce
Original assignee: Addup
Priority date: 2016-10-26
Filing date: 2017-10-26
Publication date: 2018-05-03
Also published as: FR3057793B1; FR3057793A1

Abstract

The invention relates to an appliance for manufacturing a three-dimensional object by means of selective additive manufacturing, comprising, in a housing: a support for depositing successive layers of additive manufacturing powder; a distribution arrangement designed to apply a layer of powder to said support or to a previously consolidated layer; and at least one source for the selective consolidation of a layer of powder applied by the distribution arrangement, characterised in that it comprises at least one protection element designed to trap, by electrical polarisation, ions of loaded vapour in the housing, said element consisting of a material designed to be electrically polarised and arranged in the vicinity of at least one optical/electronic module and/or component to be protected from the deposits, the appliance also comprising a polarisation assembly designed to ensure the electrical polarisation of said protection element during additive manufacturing operations.

Description

MANUFACTURING APPARATUS BY ADDITIVE MANUFACTURING METHOD OF A THREE DIMENSIONAL OBJECT AND ASSOCIATED ADDITIVE MANUFACTURING METHOD

GENERAL TECHNICAL FIELD AND PRIOR ART

The present invention relates to selective additive manufacturing. Selective additive manufacturing consists in producing three-dimensional objects by consolidating selected areas on successive layers of powder material (metal powder, ceramic powder, etc.). The consolidated areas correspond to successive sections of the three-dimensional object. The consolidation is done, 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 at its periphery (edge or skin) and in its volume (heart). An example in this sense is for example described in the 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 providing the energy necessary for the melting of the powders. This steam It is essentially neutral, because the evaporation process takes place, in general, at 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 ultraviolet light. '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 vapor loaded into the selective additive manufacturing enclosure.

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.

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 the successive layers of additive manufacturing powder,

A dispensing arrangement adapted to apply a layer of powder to said support or a previously consolidated layer, - at least one energy source adapted for the selective consolidation of a layer of powder applied by the dispensing arrangement, characterized in it comprises at least one protection element adapted to trap by electric polarization the charged vapor (in the form of positive or negative ions) in the chamber, said element being made of a material capable of being electrically polarized and being located in the vicinity of at least one module and / or optical / electronic component to protect deposits, the apparatus further comprising an electrical polarization fitting adapted to ensure the establishment of an electric field in and around said protection element during additive manufacturing operations.

In one embodiment, said polarization protection element is a plate or sector of a heat shield that extends at least partially around the area on which the powder layers are applied. In particular, said heat shield may comprise a conductive frame on which plates or sectors are reported on the one hand isolated from said chassis and on the other mutually isolated, said chassis being connected to ground or constituting a potential reference for the polarization assembly.

According to another aspect, the invention relates to a selective additive manufacturing process in which a layer of additive manufacturing powder is applied to a previously consolidated plate or layer and a selective consolidation is implemented by total or partial fusion of the layer of powder applied by means of at least one consolidation source, characterized in that a protective element is electrically biased, said element being made of a material capable of being electrically polarized and being situated in the vicinity of at least one module and / or optical / electronic component to protect deposits between at least two sectors or at least two of said sectors, said polarization trapping vapor ions charged into the enclosure.

The method is for example implemented using such a device. The apparatus and / or the method may comprise the following features, taken alone or in any of their technically possible combinations:

said polarization protection element is a plate or sector of a heat shield which extends at least partially around the area on which the powder layers are applied,

said heat shield comprises a conductive frame on which plates or sectors are reported on the one hand electrically insulated from said chassis and on the other mutually isolated, said chassis being connected to ground or constituting a potential reference for mounting of polarization, the frame is of truncated-pyramidal shape and comprises four uprights interconnected at their ends by two frames and in that the sectors comprise four plates attached to the uprights of said chassis,

the voltage between two plates or sectors is less than 100

V

the voltage between two plates or sectors is less than 75 V,

the voltage between two plates or sectors is such that it can transmit to the free electrons an energy of 15 eV or greater,

the electric field generated by the polarization circuit is substantially parallel, for example parallel, to the general plane of the support plate,

the manufacturing chamber is at atmospheric pressure or at a lower pressure or is under vacuum,

it comprises both a radiation source and an electron beam source.

PRESENTATION OF FIGURES

Other characteristics and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and should be read with reference to the appended figures in which:

- Figure 1 is a schematic representation of a selective additive manufacturing apparatus according to a possible embodiment of the invention;

FIGS. 2 and 3 illustrate two possible embodiments for the heat shield and the polarization circuit of an apparatus of the type of FIG. 1. DESCRIPTION OF ONE OR MORE MODES OF IMPLEMENTATION AND REALIZATION

Overview

The selective additive manufacturing apparatus 1 of FIG. 1 comprises: a support such as a horizontal plate 3 on which are deposited successively the various layers of additive manufacturing powder (metal powder, ceramic powder, etc.) allowing to make a three-dimensional object (object 2 in the shape of fir in the figure),

a reservoir 7 of powder 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 total or partial melting) of the spread thin layers,

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

a mechanism 10 for enabling the support of the plate 3 to be lowered as the layers are deposited (displacement along the double arrow B).

In the example described with reference to FIG. 1, the set 8 comprises two sources of consolidation:

an electron beam gun 11 and

a source 12 of the laser type.

As a variant, the assembly 8 may comprise only one source, for example a source of energy operating 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 around 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 furthermore comprise temperature measuring means, such as an IR or CCD camera, which are capable of communicating to the control unit 9 information concerning the temperature of the powder layer and making it possible to adjust thereby the operating parameters of the electron gun 11 or the source 12 of the laser type.

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 shape that has an opening allowing the passage of a radiation and / or beam and which extends by flaring from said opening to 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.

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

The apparatus 1 further comprises at least one polarized protective element located in the vicinity of at least one module and / or optical / electronic component to be protected, in the path of the vapor (for example charged vapor) that emerges in the vacuum chamber following the consolidation of the powder.

This element or these polarized protection elements are intended to trap the vapor ions that rise in the chamber before they reach the module and / or optical / electronic component to be protected.

Such a protection element is for example a plate or a sector (or a pair of plates or sectors) which can simultaneously fulfill the function of heat shield T.

It can be any material likely to be polarized. In the example of FIG. 2, this screen T comprises a frame 25 and four flat plates 21 to 24 attached thereto and electrically insulated on the one hand from said chassis 25 and on the other hand from each other.

The frame 25 is of generally pyramidal shape. It consists of four uprights 25a assembled at the corners of a large frame 25b and a small frame 25c.

The frame 25 as the plates 21 to 24 are made of an electrically conductive material, for example steel.

The plates 21 to 24 are of a shape corresponding to the shape of the faces of the frame and are attached to the frame 25 while being isolated from it by dielectric shims 26.

They are two by two opposite and are polarized by a power supply 31.

This polarization creates between the plates an electric field E which deflects the charged vapor which comprises at least one elementary charge released from the molten surface, so that it is captured by the plates 21 to 24 and that this vapor is deposited on these instead of being deposited on the various components inside the enclosure 17.

This electric field E has a principal component oriented parallel to the general plane of the bed of powder and layers deposited on the plate 3.

During the vaporization of the deposited material (metal, ceramic, etc.) under the effect of a beam or energy radiation, a more or less significant fraction of the vapor released is in ionized form (positive or negative ions).

The electric field E of polarization acts on the charged vapor ions (monoatomic ions, aggregates) with a force of the electrostatic type (F = qE), substantially parallel to the plateau. This force adds a velocity component parallel to the plate 3, that is to say horizontal, inducing the deflection of the ionized vapor with respect to its initial trajectory of ejection of the surface (during vaporization). The ionized vapor is then mostly intercepted by the sectors 21 to 24 of the thermal screen T: the positive ions are guided by the E field towards the sector (s) 21 to 24 where the surface (including the frame) of the screen T is at the lowest potential ('cathode'); the negative ions, just like the free electrons, are guided towards the area or sectors where the surface is at the highest potential ('anode').

The fraction of vapor that escapes and passes through the upper opening of the frame (frame 25c) is in any case diverted towards the walls of the enclosure. The optical surfaces of the laser and the various electronic components facing this opening are all the more protected.

Note also that when the source of consolidation is an electron gun (source 11), the rising vapor intersects this beam and is itself ionized. Also, the acceleration caused by the field E on the free electrons (other than those of the EBM primary electron beam) present in the volume delimited by the polarized elements induces itself a vacuum ionization of the vapor at the same time. interaction with it.

This increases the fraction of ionized vapor and the capture efficiency of the whole.

For this purpose, the voltage between the plates is chosen to correspond for the electrons to an energy greater than 15 eV and preferably of the order of 50 eV.

The voltage between two plates 21-24 facing each other is nevertheless chosen so as not to disturb the trajectory of the electrons of the beam EMB 20.

It is for this purpose typically less than 100 V, and more particularly less than 75 V.

The electric field E is continuous or variable in time.

Many configurations are for this purpose possible for the power supply 31: it can be a battery, a DC voltage source, a low or high frequency power supply, or a bipolar, multipolar or pulse power.

An alternative power supply has the advantage of making it possible to limit the impact of the electric field E on the trajectory of the electrons of the source An impulse supply has the advantage of applying the electric field between the plates only on limited time fractions. For this purpose, for example, a low frequency function generator (GBF with a TTL type output) is used.

For a thermal screen T of a height of the order of 50 cm, the transit time to go back into the vacuum chamber through this heat shield is estimated at 1 ms in the case of charged fine particles. For droplets or large clusters of atoms, this rise time should be lower because the mass is greater than that of fine particles.

Thus, a frequency of 1 kHz or less makes it possible to effectively attract the ionized atomic vapor and the charged clusters to the polarized plates during the pulses.

For a repetition frequency of 1 kHz, the duty cycle of the pulses is for example chosen of the order 1/10, ie a time gate of 0.1 ms. Thus, 90% of the time the side plates 21 to 24 are not polarized; the electron beam 20 from the barrel 11 operates without disturbance.

It will be noted that the pulsed supply of the two pairs of polarized plates 21 to 24 can be achieved by means of two GBF generators operating in synchronous mode. They can furthermore be used together to generate polarization pulses of the positive or negative isolated plates.

In the example illustrated in FIG. 2, the chassis 25 is maintained at the ground of the supply circuit, while different voltages are applied to the various plates 21 to 24 to generate the electric field E.

It may, however, be provided for the grounding of insulated plates 21 to 24, at least during the phase during which the pulse is not applied. This can be achieved by a programmable symmetrical power supply or with programmable switches, allowing the insulated plates to be short-circuited and connected to the ground for certain configurations. Other configurations than that described with reference to Figure 2 are of course conceivable.

In particular, the chassis may not be connected to ground and serve as a floating potential with respect to the voltages applied to the various plates 21 to 24.

Alternatively also, as illustrated in Figure 3, one of the plates or sectors can itself (itself) be electrically isolated thereby taking a floating potential. In the latter case, the frame 25 is not necessary since the plates or sectors 21 to 24 are assembled electrically isolated from each other. This insulation is for example provided by the amounts used to assemble said plates or said sectors.

In the example of this FIG. 3, the heat shield is not trapezoidal, but in the form of a truncated cone, sectors 21 to 24 being sectors of corresponding shape.

Moreover, in still other variants, the electric field can be created between two adjacent sectors; it can also be created between sectors separated from one or more sectors.

In addition, the above has mainly been the case in the case of selective additive manufacturing in a vacuum chamber.

More generally, working pressures lower than atmospheric pressure, or even equal to it, can be envisaged. Lower working pressures, however, facilitate the ionization of the vapor due to the application of an electric field.

Claims

Apparatus for manufacturing a three-dimensional object by selective additive manufacturing comprising in an enclosure:

A dispensing arrangement adapted to apply a layer of powder on said support or on a previously consolidated layer,

at least one source adapted to the selective consolidation of a layer of powder applied by the distribution arrangement, characterized in that it comprises at least one protective element adapted to trap by electric polarization ions of charged vapor lying in the enclosure, said element being made of a material capable of being electrically polarized and being situated in the vicinity of at least one module and / or optical / electronic component to protect deposits, the apparatus further comprising a suitable polarization mounting for providing electrical polarization of said protection element during additive manufacturing operations.

Apparatus according to claim 1, characterized in that said polarization protection element is a plate or sector of a heat shield which extends at least partially around the area on which the powder layers are applied.

Apparatus according to claim 2, characterized in that said heat shield comprises a conductive frame on which plates or sectors are reported being on the one hand electrically insulated from said frame and on the other hand insulated from each other, said frame being connected to the ground or constituting a potential reference for the polarization circuit. Apparatus according to claim 3, characterized in that the frame is of truncated-pyramidal shape and comprises four uprights interconnected at their ends by two frames and in that the sectors comprise four plates attached to the uprights of said frame.

Apparatus according to one of claims 2 to 4, characterized in that the voltage between two plates or sectors is less than 100 V.

Apparatus according to claim 5, characterized in that the voltage between two plates or sectors is less than 75 V.

Apparatus according to one of claims 2 to 6, characterized in that the voltage between two plates or sectors is such that it can transmit to the free electrons an energy of 15 eV or higher.

Apparatus according to one of the preceding claims, characterized in that the electric field generated by the polarization circuit is substantially parallel to the general plane of the support plate.

Apparatus according to one of the preceding claims, characterized in that the manufacturing chamber is at atmospheric pressure or at a lower pressure or is under vacuum.

Apparatus according to one of the preceding claims, characterized in that it comprises both a radiation source and an electron beam source.

A selective additive manufacturing process in which a layer of additive manufacturing powder is applied to a previously consolidated support or layer and a selective consolidation is implemented by total or partial melting of the applied powder layer by means of at least one a source of consolidation, characterized in that a protection element is electrically biased, said element being made of a material capable of being electrically polarized and being situated in the vicinity of at least one module and / or optical / electronic component to protect deposits between at least two sectors, said polarization trapping vapor ions from the manufacturing powder in the chamber.