FR3097798A1 - additive manufacturing device and its implementation - Google Patents

Abstract

The invention relates to an additive manufacturing device (10) for the manufacture of objects by successive addition of fused layers comprising:- a plate (20) on one face of which, called the front face (20a), a bed of powder is intended to be formed;- vibration means (50) configured to vibrate the plate at a frequency ν between 10 Hz and 10,000 Hz, and a vibration amplitude between 1 µm and 2 mm. Figure for the abstract: Figure 1a.

Description

additive manufacturing device and its implementation

This application concerns the technical field of additive manufacturing, and more particularly that of additive techniques based on the implementation of powder beds. Among these processes, we find in particular those where the powder is melted and resolidified locally, designated as powder bed fusion or by the acronym “PBF” for “Powder Bed Fusion”. So-called PBF processes include processes involving complete melting of the powder grains (e.g. SLM™ for "Selective Laser Melting" according to Anglo-Saxon terminology or "EBM" for "Electron Beam Melting" according to Anglo-Saxon terminology) . By misuse of language, the acronym PBF is used for processes where the cohesion of the material is ensured by sintering the material (“SLS” processes for “Selective Laser Sintering” according to Anglo-Saxon terminology). Powder bed processes also include those based on the local injection of a binder on the bed, we then speak of the binder jetting process (“Binder Jetting” according to Anglo-Saxon terminology).

In particular, the present application aims to propose a device and a method making it possible to control the layering phenomena of the successive powder beds necessary for the production of parts by additive manufacturing.

Additive manufacturing processes based on the implementation of a powder bed known from the state of the art generally comprise the following steps:
i) a step of forming a bed of powder on a front face of a plate,
ii) for PBF processes, a localized melting or sintering step intended to define a layer of the part during manufacture.

Steps i) and ii) are then repeated as many times as necessary for the production of the part.

Step i) of forming the powder bed comprises in particular the spreading of the powder with a layering system, such as for example a doctor blade or a roller (hereinafter “blade”).

However, such an implementation is not satisfactory.

Indeed, coating systems are extremely sensitive to surface roughness.

In particular, in PBF processes, the fused zones commonly present prominences (e.g. due to expansion or thermal stresses) likely to cause degradation of the layering system which affects the quality of the bed of powder.

In particular, such degradation can be the source of the formation of a furrow on the surface of the powder bed generating defects in the part being manufactured. It also happens that such contact, single or repeated, tilts or even tears the part in the powder bed.

Moreover, layering systems require very fine alignment, which is complex to obtain.

In addition, depending on the systems, the layering time can be significant, reducing the productivity of the equipment.

Squeegee-type layering devices do not make it possible to obtain significant compactness due to the absence of vertical force on the powder bed. In this respect, a large quantity of air or gas between the powder grains generates more frequent porosities.

Furthermore, the doctor blade, due to repeated contact with the powder intended to form the powder bed, as well as with the large ejecta resulting from the instabilities of the molten bath in the techniques involving passage through a liquid phase, wears out and makes controlling step i) complicated and requires frequent maintenance operations.

In particular, these wear phenomena result in irregularities in the surface of the doctor blade likely to leave an imprint that remains visible on the surface of the powder bed.

This lack of control over the formation of the powder bed generally leads to inhomogeneities in the distribution, or even lack of material, with the consequence of the formation of porosities or defects in the part being manufactured, likely to render the latter defective, or even unusable.

Additive manufacturing devices based on the formation of a powder bed generally comprise a small-sized plate, in particular of a size of less than 50 cm on a side, and accordingly limit the size of the parts likely to be manufactured with this type. of device. The difficulty of controlling the formation of powder beds is one of the factors that limit the increase in the size of the plates.

An object of the present invention is therefore to propose an additive manufacturing device making it possible to better control the formation of a homogeneous powder bed, or even to obtain greater compactness.

Another object of the present invention is to propose an additive manufacturing device for which the phenomena of wear by contact with the powder for the formation of the powder bed remain limited.

Another object of the present invention is to provide a manufacturing device allowing more effective control of additive manufacturing processes.

The aims of the present invention are, at least in part, achieved by an additive manufacturing device for the manufacture of objects by successive addition of layers comprising:
- A plate on one face of which, called the front face, a powder bed is intended to be formed;
- vibration means configured to vibrate the plate at a frequency ν between 10 Hz and 10000 Hz, advantageously between 100 Hz and 1000 Hz, and a vibration amplitude between 1 μm and 2 mm, preferably between 10 μm and 500 μm, even more preferably between 50 μm and 200 μm.

According to one mode of implementation, the plate has side edges configured to confine the successive powder beds.

According to one mode of implementation, the device further comprises one or more distribution means configured to pour a controlled quantity of powder onto the front face of the tray.

According to one mode of implementation, one or more distribution means comprises at least one of the elements chosen from: nozzle, hopper, sieve.

In particular, the powder can be deposited as a pile of sand (point source) or by rain (passing through sieves). By passing, for example, through several sieves (by adjusting the mesh and the distance between sieves), the powder can be distributed over almost the entire surface in a quasi-homogeneous manner before vibrating.

According to one mode of implementation, the vibration means are configured to vibrate the plate in a direction perpendicular to the front face.

According to one mode of implementation, the vibration means are configured to set the plate in vibration along at least one direction contained in the plane defined by the front face.

According to one mode of implementation, the vibration means comprise at least one vibrating pot, advantageously arranged facing a face of the plate opposite the front face.

According to one mode of implementation for PBF technologies, the device comprises at least one energy source configured to locally cause melting or sintering of the powder bed.

According to one mode of implementation, the energy source comprises at least one of the elements chosen from: a laser, a plasma source, an electron beam source.

According to one mode of implementation, the device also comprises means for shaping the powder bed, advantageously this means comprises a doctor blade or a roller.

According to one mode of implementation, the device also comprises an additional element making it possible to improve the quality of the powder bed. For example the additional element can be configured to evacuate an excess quantity of powder. In this case, the additional element advantageously comprises a doctor blade, or even a roller. Alternatively or additionally, the additional element can also be configured to carry out additional compaction of the bed of powders, in which case the additional element advantageously comprises a roller.

According to one mode of implementation, the device is also provided with a weir configured to recover the unused powder.

According to one mode of implementation, the plate has a characteristic dimension greater than 50 cm, or even advantageously greater than 1 m.

The invention also relates to a method of manufacturing a part implementing the device according to the present invention.

According to one mode of implementation, the method comprises the following steps:
a) a step of forming a bed of powder on the front face of the plate;
b) for PBF technologies, localized melting or sintering of the powder bed;
steps a) and b) being repeated so as to form the part by stacking fused layers.

According to one mode of implementation, step a) comprises the following steps:
a1) a step which consists in pouring powder onto the front face of the plate;
a2) a step which consists in spreading the powder in the form of a powder bed by imposing at least one vibration cycle on the plate at a frequency ν between 10 Hz and 10000 Hz, advantageously between 100 Hz and 1000 Hz, and an amplitude of vibration between 1 μm and 2 mm, preferentially between 10 μm and 500 μm, even more preferentially between 50 μm and 200 μm.

According to one mode of implementation, step a2) is executed for a period of between 1 second and 60 seconds, advantageously between 2 seconds and 30 seconds, even more advantageously between 5 seconds and 10 seconds.

According to one mode of implementation, the at least one vibration cycle comprises a first sequence executed at a first frequency ν ₁ and a first vibration amplitude, followed by a second sequence executed at a second frequency ν ₂ and a second vibration amplitude, so that the acceleration induced by the second vibration sequence is less than the acceleration induced by the first vibration sequence.

By “acceleration”, we conventionally mean the product of the amplitude of vibration by the square of the frequency of vibration.

According to one mode of implementation, step a2) is followed by a step a3) intended to compact the powder bed and/or evacuate an excess of said powder.

This step a3) therefore makes it possible to improve the quality of the powder bed.

According to one embodiment, the grains of powder forming the powder bed have a D50 of between 5 μm and 100 μm, advantageously of between 10 μm and 40 μm.

Other characteristics and advantages will appear in the following description of an additive manufacturing device, given by way of non-limiting examples, with reference to the appended drawings in which:

is a schematic representation of the device according to the present invention, in particular, FIG. 1a represents the device with a pile of powder deposited on the front face of the plate;

is a schematic representation of the device according to the present invention, in particular, FIG. 1b represents the device with a bed of powder formed on the front face of the plate, and the energy source facing the bed of powder;

is a schematic representation of the device according to the present invention, in particular, FIG. 2a represents the device with a layering system and a mechanical actuator for vertical translation of the plate and the vibration system positioned under the mechanical actuator;

is a schematic representation of the device according to the present invention, in particular, FIG. 2b represents the device with a part being manufactured surrounded by powders not transformed in the previous steps, a pile of powder corresponding to the bed to be formed in the current step as well as an excess powder spillway system;

is a schematic representation of the device according to the present invention, in particular, FIG. 2c represents the device with a vibration system positioned directly on the rear face of the plate.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

The present invention relates to an additive manufacturing device for manufacturing objects by successive addition of layers (FIGS. 1a, 1b, 2a to 2c).

The device 10 comprises, in particular, a plate 20 optionally mounted on a mechanical actuator 30 (FIGS. 2a to 2c), for example and without limitation a jack or a motorized system with linear guidance, intended to adjust the height of said plate 20 according to a ZZ' axis.

The plate 20 comprises one face, called the front face 20a. The tray may include side edges 21 to confine the powder beds (FIG. 1a). In this case, the height of the edges 21 of the plate is preferably chosen to be at least equal to that of the piece of greatest height to be produced on said plate.

According to one embodiment, the edges 21 are integral with the plate (FIGS. 1a and 1b). According to another embodiment, the edges 21 are removable and can be removed at the end of the manufacturing process (FIGS. 2a to 2c).

The mechanical actuator 30 can be secured to a support 31 on one face of which the plate 20 rests (Figure 2a to 2c).

The device 10 further comprises one or more dispensing means 40, for example a single dispensing means, configured to pour powder onto the front face 20a of the plate 20.

One or more distribution means 40 may in particular comprise at least one of the elements chosen from: nozzle, hopper, sieve.

The device according to the present invention also comprises vibration means 50 configured to set the plate to vibrate at a frequency ν between 10 Hz and 10000 Hz, advantageously between 100 Hz and 1000 Hz, and a vibration amplitude between 1 μm and 2 mm, preferably between 10 μm and 500 μm, even more preferably between 50 μm and 200 μm.

These vibration means 50 are implemented to form the powder bed after pouring the powder onto the front face 20a of the plate 20.

The vibration can preferably be applied in a direction perpendicular to the front face 20a. Thus, the alignment of the plate 20 with respect to the at least one energy source 60 (described in the following description) is little or not affected.

In PBF technologies, the energy source 60 is in particular configured to locally cause melting or sintering of the powder bed.

However, a vibration of the plate 20 along at least one direction of the plane defined by the front face 20a can also be envisaged.

According to an advantageous mode of implementation, the vibration means 50 comprise at least one vibrating pot, advantageously arranged opposite a face of the plate opposite the front face 20a.

A vibrator, or exciter, or vibrator, is a device for vibrating a structure in a controlled manner.

The vibrating pot can comprise a coil intended to be traversed by a magnetic field.

The vibrating pot is chosen according to the total mass (in addition to the powder deposited in the current step, the plate 20 and the part being manufactured with the powders (100) not transformed in the previous steps, the support 31 and the mechanical actuator 30, Figure 2b) intended to be vibrated. The vibrating pot can in particular be adapted to vibrate masses of up to 1000 Kg.

Alternatively to the vibrating pot, it is also possible to use a vibrating device based on a stack of layers made of a piezoelectric material.

The implementation of the vibration means 50 according to the terms of the present invention makes it possible to obtain a uniform distribution of the powder grains in the powder bed.

This effect nevertheless remains unexpected, and the implementation of the means of vibration counter-intuitive. Indeed, for thin powder beds, a segregation of the powder grains is generally observed when the plate on which they rest is vibrated. This segregation can notably take the form of Chladni figures.

The inventors have however been able to observe, under certain vibration frequency and amplitude conditions mentioned above, that it is possible to form a relatively homogeneous powder bed in terms of solid fraction in the bed.

The formation of a powder bed by vibrating the plate avoids the need for a doctor blade or a roller to spread the powder. The implementation of such a means is however not excluded to further improve the quality of the bed (elimination of any excess powder or additional compaction of the powder bed).

In practice, one or more heaps of powders can be deposited by one or more nozzles, hoppers or sieves, and the whole transformed into a powder bed with a solid fraction controlled by vibrating the plate.

As soon as a PBF technology is considered, the device 10 can comprise at least one energy source 60 configured to locally cause melting or sintering of the powder bed.

The energy source can comprise at least one of the elements chosen from: a laser, a plasma source, an electron beam source.

The energy source is associated with a scanning system 61 of the energy beam 60a, moving the point of impact of the energy beam to the powder bed surface (FIG. 1b). The element(s) 40 must be positioned so as not to obstruct the beam as it scans the surface of the powder bed.

The device can also comprise an additional element 70 making it possible to improve the quality of the powder bed. For example to evacuate a quantity of excess powder, in this case the additional element is advantageously a doctor blade, or even a roller. Alternatively or additionally, the additional element 70 can be implemented to achieve additional compaction of the powder bed, in which case the additional element is advantageously a roller.

In other words, the additional element 70 (squeegee or roller) is implemented after formation of the powder bed.

The device can also be provided with a weir 80 configured to recover the unused powder (FIG. 2b).

The vibration means according to the terms of the present invention make it possible to envisage a large plate, and in particular of a characteristic dimension greater than 50 cm, advantageously greater than 1 m.

The characteristic dimension of a tray can be associated with the length of a side if it is a polygon such as a square or a rectangle, or with a diameter if it is a disk.

The invention also relates to the implementation of the additive manufacturing device for the manufacture of an object.

In particular, the method comprises a step a) of forming a bed of powder on the front face 20a of the plate 20.

Step a) may include a first step a1) which consists in pouring powder onto the front face 20a of the plate 20.

The powder can be discharged using one or more hoppers or nozzles under one or more piles of powder (Figure 1a).

The quantity of powder poured onto the front face 20a of the plate 20 is generally calculated so as to obtain a bed of powder with a thickness of between 20 μm and 100 μm.

The powder grains forming the powder bed can have a D50 of between 5 μm and 100 μm, advantageously of between 10 μm and 40 μm.

Thus, for a median gain diameter D50 equal to 37 μm and assuming compactness of the powder bed close to 50%, the quantity of powder discharged can be adjusted so as to form a powder bed with a thickness close to 50 µm.

Step a) can also include a second step a2) of spreading the pile or piles of powder on the front face 20a of the plate 20 (FIG. 1b).

The second step a2) is intended to impose at least one vibration cycle on the plate at a frequency ν between 10 Hz and 10000 Hz, advantageously between 100 Hz and 1000 Hz, and a vibration amplitude between 1 μm and 2 mm, preferentially between 10 μm and 500 μm, even more preferentially between 50 μm and 200 μm (FIGS. 1b and 2c).

The plate can be subjected to a vibration in a direction perpendicular to the front face 20a, and/or in a direction contained in the plane defined by said front face 20a.

Step a2) can be performed for a period of between 1 second and 60 seconds, advantageously between 2 seconds and 30 seconds, even more advantageously between 5 seconds and 10 seconds.

In a particularly advantageous manner, the at least one vibration cycle can comprise a first sequence executed at a first frequency ν ₁ and a first amplitude of vibration, followed by a second sequence executed at a second frequency ν ₂ and a second amplitude of vibration, so that the acceleration induced by the second vibration sequence (conventionally measured as the product of the amplitude times the square of the frequency) is less than the acceleration induced by the first vibration sequence.

The first sequence thus makes it possible to carry out a first rough mixing of the powder grains, and leads to the shaping of the powder bed. The second sequence makes it possible to homogenize and increase the density (solid fraction) of the powder bed.

Step a) can, optionally, comprise a third step a3), performed after the second step a2), of final shaping of the powder bed.

The third step a3) may in particular comprise the implementation of a roller. The uniform distribution of grains in the form of a powder bed obtained at the end of the second step a2) allows compaction, via contact with a roller, without movement of the grains, and reduced abrasion of the tool used to compaction.

Moreover, the means implemented both for the formation of the powder bed and for its compaction are not affected by these operations, so that it is possible to form several powder beds having equivalent properties in a repeatable manner.

In PBF technologies, step a) is followed by a step b) of melting or localized sintering of the powder bed.

More particularly, localized melting or sintering draws a stratum of the object in process 90 (FIG. 2b).

Steps a) and b) are repeated as many times as necessary to form the object by stacking layers.

The presentation of the present invention has focused on PBF techniques with localized melting (or sintering) of the powders. However, the present invention is not limited to this mode of implementation alone. In particular, step b), as described previously, can be replaced by a binder jetting step (“Binder Jetting” according to Anglo-Saxon terminology), intended to be debinded during a subsequent step.

Claims (19)

Additive manufacturing device (10) for manufacturing objects by successive addition of layers comprising:
- a plate (20) on one face of which, called the front face (20a), a powder bed is intended to be formed;
- vibration means (50) configured to vibrate the plate at a frequency ν between 10 Hz and 10000 Hz, advantageously between 100 Hz and 1000 Hz, and a vibration amplitude between 1 μm and 2 mm, preferably between 10 μm and 500 μm, even more preferably between 50 μm and 200 μm. Device according to Claim 1, in which the plate has lateral edges (21) configured to confine the successive powder beds. Device according to Claim 1 or 2, in which the device further comprises one or more distribution means (40) configured to discharge a controlled quantity of powder onto the front face (20a) of the tray (20). Device according to Claim 3, in which one or more distribution means (40) comprises at least one of the elements chosen from: nozzle, hopper, sieve. Device according to one of Claims 1 to 4, in which the vibration means (50) are configured to put the plate (20) into vibration in a direction perpendicular to the front face. Device according to one of Claims 1 to 4, in which the vibration means (50) are configured to put the plate (20) into vibration in at least one direction contained in the plane defined by the front face (20a). Device according to one of Claims 1 to 6, in which the vibration means (50) comprise at least one vibrating pot, advantageously arranged opposite one face of the plate (20) opposite the front face (20a). Device according to one of Claims 1 to 7, in which the device (10) comprises at least one energy source configured to locally cause melting or sintering of the powder bed. Device according to claim 8, in which the energy source comprises at least one of the elements selected from: a laser, a plasma source, an electron beam source. Device according to one of Claims 1 to 9, in which the device (10) also comprises means for shaping the bed of powder, advantageously this means comprises a doctor blade or a roller. Device according to one of Claims 1 to 10, in which the device is also provided with a weir configured to recover the unused powder. Device according to one of Claims 1 to 11, in which the plate has a characteristic dimension greater than 50 cm, advantageously greater than 1 m. Method of manufacturing a part implementing the device according to one of Claims 1 to 12. A method according to claim 13 which comprises the following steps:
a) a step of forming a bed of powder on the front face (20a) of the plate (20);
b) localized melting or sintering of the powder bed;
steps a) and b) being repeated so as to form the part by stacking fused layers. Method according to claim 14, wherein step a) comprises the following steps:
a1) a step which consists in pouring powder onto the front face of the plate;
a2) a step which consists in spreading the powder in the form of a powder bed by imposing at least one vibration cycle on the plate at a frequency ν between 10 Hz and 10000 Hz, advantageously between 100 Hz and 1000 Hz, and an amplitude of vibration between 1 μm and 2 mm, preferentially between 10 μm and 500 μm, even more preferentially between 50 μm and 200 μm. Method according to claim 15, in which step a2) is carried out for a duration comprised between 1 second and 60 seconds, advantageously comprised between 2 seconds and 30 seconds, even more advantageously between 5 seconds and 10 seconds. A method according to claim 15 or 16, wherein the at least one vibration cycle comprises a first sequence performed at a first frequency ν ₁ and a first vibration amplitude, followed by a second sequence performed at a second frequency ν ₂ and a second vibration amplitude such that the acceleration induced by the second vibration sequence is less than the acceleration induced by the first vibration sequence. Process according to one of Claims 15 to 17, in which step a2) is followed by a step a3) intended to compact the bed of powder and/or to evacuate an excess of said powder. Process according to one of Claims 14 to 18, in which the grains of powder forming the bed of powder have a D50 of between 5 µm and 100 µm, advantageously of between 10 µm and 40 µm.