Additive manufacturing process by adding plasma-activated thermoplastic layers

Abstract

Additive manufacturing method by adding plasma-activated thermoplastic layers One aspect of the invention relates to an additive manufacturing method by adding layers (14) based on thermoplastic material (8), superimposed on each other, in which the thermoplastic material of each layer of rank n of the superposition is activated by plasma before being covered by the layer of rank n+1, this activation being carried out before, during or after the addition of the layer of rank n. Another aspect of the invention relates to an additive manufacturing machine (1) allowing the implementation of this method, which comprises a device (7) for producing the layers based on thermoplastic material, and an activation device (15) comprising at least one plasma nozzle (16) arranged so as to activate the thermoplastic material of each layer of rank n before it is covered by the layer of rank n+1. Figure to be published with the abstract: Figure 1

Description

Title of the invention: Additive manufacturing method by adding plasma-activated thermoplastic layers TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of additive manufacturing by adding successive layers of polymer or composite materials. The invention relates both to additive manufacturing by extrusion, in particular by deposition of filaments, and to manufacturing by deposition of strips, or even to the sintering of powders by laser.

[0002] The present invention relates to a manufacturing method by adding successive thermoplastic layers activated by plasma. It also relates to a machine allowing the implementation of this method. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] To manufacture parts from thermoplastic polymer materials or composite thermoplastics, numerous additive manufacturing processes have been developed. These are iterative processes for adding superimposed layers, which allow the parts to be produced layer by layer. With each new layer, the heat of the newly added material causes welding with the previous layer, thus giving overall cohesion to the parts produced. The parts obtained are thus made up of a stack of superimposed layers of material welded to each other.

[0004] However, regardless of the additive manufacturing process used, it is found that the mechanical properties of the part obtained are not identical in all directions. They are greatly reduced when the part is stressed in the axis of stacking of the layers, rather than in a direction belonging to the deposition plane, the reduction being able to be up to 30 to 50%.

[0005] This degradation of the mechanical properties is due to the poor quality of the welding between the layers. Indeed, during manufacturing, the lower layer is not sufficiently heated by the contact of the hot material of the following layer for the welding to be satisfactory.

[0006] The situation is even worse with semi-crystalline thermoplastic polymer materials that crystallize and consolidate upon cooling. The heat provided by the next layer is also not sufficient to melt the crystallites or spherulites formed during cooling, which block the mobility of the polymer chains and hinder welding. Summary of the invention

[0007] The invention teaches an additive manufacturing method by adding layers successive thermoplastic polymers, which improves the mechanical properties of the product obtained in directions not belonging to the deposition plane, in particular its resistance to inter-laminar shear and fatigue.

[0008] The invention also teaches an additive manufacturing machine for carrying out this process.

[0009] A first aspect of the invention relates to a method of additive manufacturing by adding layers based on thermoplastic polymer material, said layers being added on top of each other so as to form a superposition of N layers, with N> 2, each layer having a rank in the superposition ranging from 1 to N. According to this method, the thermoplastic polymer material of each layer of rank n, with l <n<N, est activé par plasma avant d’être recouvert par la couche de rang n+1, cette activation se faisant avant, pendant ou après l’ajout de la couche de rang n.

[0010] N and n, being numbers of layers, are obviously whole numbers.

[0011] Plasma is an electrically neutral ionized gas, which, when projected onto a layer of thermoplastic polymer material, increases the surface energy of this layer. This plasma activation causes the breaking of certain molecular bonds on the surface of the treated layer, thus creating highly reactive sites which bind much more easily with the molecules of the following layer when they are brought into contact. The bond between the two layers of thermoplastic polymer material is thus greatly promoted and the resulting weld is of much better quality.

[0012] This plasma activation of the thermoplastic polymer material results in an increase in the surface tension of the material which improves the adhesion between the layers.

[0013] In addition, plasma treatment creates surface nano or microporosities which further increase this adhesion.

[0014] Thus, there is increased cohesion between the adjacent layers, which improves the overall mechanical properties of the resulting part in the direction of stacking of the layers.

[0015] Advantageously, in the case of semi-crystalline polymer materials, plasma activation allows, in addition to the creation of reactive sites in the material, to at least partially melt the interface crystallites and spherulites which may have appeared during the cooling of the material. By making these crystalline phases disappear, plasma activation allows greater mobility of the polymer chains, improving their reactivity, and promotes welding between the layers.

[0016] When the material contains fibers, especially carbon fibers, plasma activation also makes it possible to eliminate the transcrystallinity zones which tend to form around these fibers. The free volume is increased and a greater mobility of the polymer chains is obtained, improving their reactivity and thus the quality of inter-layer welding.

[0017] In the context of the invention, the plasma treatment of the layers based on thermoplastic polymer material is not a simple cleaning of these layers, which consists of breaking the molecules of polluting substances located on the surface of the layers to detach them, but a real activation of the material constituting the layers themselves, that is to say of the thermoplastic polymer material belonging to these layers.

[0018] The thermoplastic polymer material used in the method according to the invention can be any, as long as it is compatible with additive manufacturing and is capable of being activated by plasma. Preferred examples include polyaryletherketones (PAAEK), polyetherimides (PEI), polyethersulfones (PESU), polyphenylenesulfides (PPS), polyphenylenesulfones (PPSU), polycarbonates (PC) or polyamides (PA).

[0019] The layers may be composed solely of one or more thermoplastic polymer materials.

[0020] These layers may also contain other elements in addition, for example fillers and / or fibers, in particular glass, carbon or aramid fibers, conferring additional properties to the part manufactured according to the intended applications.

[0021] These layers can also be made from composite strips, formed from any suitable material impregnated with thermoplastic polymer resin.

[0022] Once a layer is plasma activated, it is covered by the next layer so that the reactive sites created in the thermoplastic polymer material of that layer react and bond with the molecules of the next layer.

[0023] If the treated layer is left free, the reactive sites gradually disappear, because they react with each other and with their environment. However, the plasma activation treatment advantageously has a long duration of effectiveness, of the order of one or more hours with a thermoplastic polymer material, which is much greater than the operational durations encountered in additive manufacturing. Once the plasma activation of the thermoplastic polymer material has been carried out, it is therefore not necessary for the activated layer to be immediately covered by the next layer.

[0024] The period of time that begins at the time of plasma activation and lasts as long as the activation is sufficient for satisfactory welding is called the effectiveness time.

[0025] The plasma activation treatment of the thermoplastic polymer material can therefore be carried out indifferently before, during or after the addition of the layer concerned.

[0026] During the process, the thermoplastic polymer material of the n-th layer may be plasma activated prior to the step of adding the n-th layer.

[0027] In this case, the activation can advantageously be carried out on the material before it reaches the layer-making device, for example at the exit from the storage area or just before it passes into the layer-making device.

[0028] The duration of effectiveness of the activation treatment is largely sufficient for the material to then reach the layer production device, for layer n to be added by the latter, then to be covered by layer n+1, without losing the benefit of the activation treatment, all of these steps lasting only a few seconds to a few minutes depending on the type of additive manufacturing and the size of the part produced.

[0029] Thus, the activation device can advantageously be fixed, independent of the layer-making device and placed far from it, in a less cluttered area where it will not hinder the movement of the layer-making device. The activation device will be technically simpler to produce and less expensive.

[0030] Alternatively, the thermoplastic polymer material of the n-rank layer may be plasma activated during the step of adding the n-rank layer to an already added portion of the n-rank layer.

[0031] Alternatively, the thermoplastic polymer material of the layer of rank n can be activated by plasma during the step of adding the layer of rank n+1 on a portion not yet covered with the layer of rank n.

[0032] In these last two cases, the plasma activation is advantageously carried out after the thermoplastic material has passed through the layer manufacturing device. The effectiveness of the activation is therefore not likely to be reduced by the treatment undergone by the material in this device.

[0033] In addition, the plasma activation is also carried out after the thermoplastic material has started to cool. If the thermoplastic polymer material is semi-crystalline or contains fibers, the plasma activation treatment advantageously reduces the crystalline phases or transcrystallinity zones, which form a few hundredths of a second to a few seconds after the start of cooling.

[0034] Furthermore, the activation processing is carried out simultaneously with the step of adding a layer, whether it is that of rank n or of rank n+1. The activation device can then advantageously be coupled to the layer-making device, for example integrated thereon and / or placed on the same robotic arm. The two devices can be controlled simultaneously, which facilitates the control operation and simplifies the machine.

[0035] During the process, plasma activation can be performed only on the face of the layer of rank n intended to be in contact with the layer of rank n+1.

[0036] In this case, activation is only done on one side of each layer, which is easy to achieve with simple and inexpensive equipment, such as a bar-type plasma nozzle for example.

[0037] The activation is nevertheless sufficient because it creates reactive sites in the part of the n layer which will be in contact with the n +1 layer. At each interface between two successive layers, one of the layers therefore has reactive sites on its contact face improving the welding between the two layers.

[0038] According to another example, the plasma activation can be carried out on all faces of the layer of rank n.

[0039] In this case, activation is complete on all the outer faces of the layers. At each interface between two successive layers, the two layers have reactive sites on their contact face. Welding between the two layers is therefore further improved.

[0040] The method according to the invention is advantageously compatible with any type of additive manufacturing by adding superimposed layers based on thermoplastic polymer material.

[0041] This may be, for example, an additive manufacturing process by extrusion (“Extrusion Additive Manufacturing” in English), whether by deposition of filaments, also called deposition of fused filaments (“Fused Filament Fabrication” or “Filament Deposition Molding”™ in English), or by extrusion from other types of solid or liquid material, in particular from cylindrical cartridges, paste or granules (fabrication by fused granules or “Fused Granular Fabrication” in English).

[0042] It may also be a method of additive manufacturing by strip deposition, that is to say a layer-by-layer deposition of strips of any width previously formed, in particular composite strips impregnated with thermoplastic polymer resin, such as an automated fiber placement method ("Automated Fiber Placement" or "micro Automated Fiber Placement" in English), or an automated tape layup or superposition method ("Automated Tape Layup" in English).

[0043] This may also be, for example, an additive manufacturing process by sintering powders such as selective laser sintering.

[0044] A second aspect of the invention relates to an additive manufacturing machine enabling the implementation of such a method. This machine comprises a layer-making device capable of adding layers based on thermoplastic polymer material on top of each other so as to form a superposition of N layers, with N> 2, each layer having a rank in the superposition ranging from 1 to N, and an activation device which comprises at least one plasma nozzle arranged so as to be able to activate the thermoplastic polymer material of each layer of rank n, with the <n<n, avant que ce matériau soit recouvert par la couche de rang n+1.

[0045] cette machine peut être exemple une fabrication additive extrusion, notamment dépôt filaments, fils fondus ou granulés fondus, encore bandes préalablement formées, placement fibres automatisé, micro-placement automatisé superposition frittage sélectif laser.

[0046] Advantageously, the plasma nozzle of this machine can be a rotary nozzle or an annular nozzle.

[0047] In a rotary nozzle the plasma exit angle can be modified, which advantageously makes it possible to treat a greater width of material and to distribute the effect of the plasma uniformly over the entire surface to be treated. With a single rotary nozzle, it is thus possible to treat wide strips or several strips or filaments simultaneously, in particular if the machine has several extrusion heads, or the forward and return cords of the same filament. This avoids having to use several plasma nozzles.

[0048] An annular nozzle advantageously makes it possible to carry out an activation treatment on all the faces of the layer to be treated. In fact, the annular nozzle projects the plasma from its circumference towards the inside of the ring where the thermoplastic material passes, thus activating all the faces of the corresponding layer.

[0049] Alternatively, a rotating nozzle capable of rotating around the thermoplastic material also makes it possible to carry out such treatment on all faces of the layer concerned.

[0050] Advantageously, the plasma nozzle may be connected directly or indirectly to the layer-forming device, such that the plasma nozzle moves with the layer-forming device.

[0051] The plasma nozzle is thus controlled with the layer production device, which simplifies the machine.

[0052] The plasma nozzle can for example be placed directly on the layer-making device or on the same robotic arm as it. It is generally fixed there by standard means, in particular screwing or clipping. In the event of space requirement, the plasma nozzle can also be offset from the layer-making device.

[0053] When connected to the layer-forming device, the plasma nozzle may, for example, be positioned upstream of this device. In this case, the nozzle projects plasma onto the part not yet covered with the previously added layer n, while the layer realization device adds layer n+1.

[0054] According to another example, the plasma nozzle can be positioned downstream of the layering device. In this case, the nozzle projects plasma onto the portion of the layer n that the layering device has just added.

[0055] According to yet another example, the plasma nozzle can be positioned alternately upstream and downstream of the layer-forming device.

[0056] This situation occurs when the plasma nozzle is connected to a layer-forming device which does not pivot when it reaches the end of its travel, but moves back in the opposite direction after being shifted laterally.

[0057] Upstream and downstream are defined relative to the direction of movement of the layer-forming device.

[0058] Advantageously, the plasma nozzle of this machine can also be arranged so as to be able to activate the thermoplastic polymer material before it reaches the layer-forming device.

[0059] In this case the plasma nozzle can advantageously be fixed and independent of the layer production device.

[0060] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0061] The figures are presented for information purposes only and in no way limit the invention.

[0062] [Fig.l], [Fig.2] and [Fig.3] are schematic perspective views of three variants of a filament deposition additive manufacturing machine with an extrusion head, with respectively a plasma nozzle upstream of the layer production device, a plasma nozzle downstream of the layer production device, and an annular plasma nozzle.

[0063] [Fig.4] is a schematic perspective view of an additive manufacturing machine by deposition of filaments with two extrusion heads with a plasma nozzle upstream of the layer production device.

[0064] [Fig.5], [Fig.6] and [Fig.7] are schematic side views of an automated fiber placement additive manufacturing machine, with a plasma nozzle that activates a layer already deposited respectively upstream for [Fig.5] and downstream for [Fig.6] of the layer production device, and a plasma nozzle that activates a layer not yet deposited for [Fig.7].

[0065] [Fig.8] and [Fig.9] are schematic perspective views of two variants of a selective laser sintering additive manufacturing machine, with respectively a plasma nozzle that activates a layer already solidified by laser in the build tank and a plasma nozzle that activates the powder in the reserve tank. DETAILED DESCRIPTION

[0066] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0067] The figures show several examples of additive manufacturing machines 1 according to the invention: an additive manufacturing machine by filament deposition 2 in figures 1 to 4, an automated fiber placement machine 3 in figures 5 to 7 and a selective laser sintering machine 31 in figures 8 and 9.

[0068] Although the invention has only been illustrated in this context, it is obviously possible to implement it with other types of additive manufacturing machine.

[0069] The filament deposition additive manufacturing machine 2 shown comprises an enclosure 4 containing a vertically movable plate 5 on which an object 6 is manufactured.

[0070] A layer-making device 7, which is here a deposition device, deposits layer by layer, on the plate 5, the material constituting the object 6. This material, based on a thermoplastic polymer material 8, is in this example in the form of a filament 9 unwound from a reel 10 and pulled to an extrusion head 11 of the layer-making device 7.

[0071] The extrusion head 11 comprises heating elements 12 which melt the filament material and an extrusion nozzle 13 through which the molten material is extruded.

[0072] By moving above the plate 5 in the horizontal plane, the extrusion head 11 deposits a bead of material which forms by juxtaposition a layer 14 of the object 6.

[0073] The transition from one layer to the upper layer of the superposition is done by a vertical movement of the plate 5 downwards or of the extrusion head 11 upwards. By moving in the horizontal plane, the extrusion head 11 then deposits the bead of material constituting the upper layer n+1 over the previous layer n. This process is repeated until the object 6 is completely manufactured.

[0074] In the example shown, the layers 14 of the object 6 are horizontal. However, with more sophisticated tooling, it is possible to make them non-planar by superimposing them according to the same principle on the surface of a non-planar support, until the desired object is completely manufactured.

[0075] The filament deposition additive manufacturing machine 2 further comprises an activation device 15 comprising a plasma nozzle 16 which emits a plasma jet 17 capable of activating the thermoplastic polymer material 8.

[0076] Different plasma nozzles 16 can be used, for example a bar-type nozzle, an annular nozzle 18 or even a rotary nozzle 19.

[0077] In the examples of Figures 1 and 2, the plasma nozzle 16 is connected to the extrusion head 11 so as to follow the movement symbolized by arrow 20.

[0078] In [Fig. 1], the plasma nozzle 16 is placed upstream of the extrusion head 11. It projects its plasma jet 17 onto the layer n-1 previously deposited, just before it is covered by the new bead emerging from the extrusion head 11 which carries out the deposition of the next layer n of the superposition.

[0079] In [Fig.2], the plasma nozzle 16 is arranged downstream of the extrusion head 11. It projects its plasma jet 17 onto the bead that the extrusion head 11 has just extruded, and therefore onto the layer n that the extrusion head 11 is in the process of depositing.

[0080] In the example of [Fig.3], the plasma nozzle 16 is independent of the extrusion head. It is an annular nozzle 18 which delimits a hollow interior volume 20 in which the plasma jet is generated. The filament 9 coming from the spool 10 passes through this hollow interior volume 21 and undergoes plasma activation of its thermoplastic polymer material 8 there, before reaching the extrusion head 11.

[0081] In the example of [Fig.4], the layer production device 7 of the additive manufacturing machine by filament deposition 2 is a deposition device which comprises two extrusion heads 11, each with heating elements 12 and an extrusion nozzle 13, each of these extrusion heads 11 being supplied with a filament 9a, 9b coming from a different reel 10a, 10b.

[0082] Such a machine makes it possible, for example, to produce more complex objects 6 with overhanging parts. One of the filaments, called the main filament 9a, is used to print the object 6, while the second filament, called the support filament 9b, makes it possible to print a support structure 22 serving as a support for the overhanging layers of the object 6. Once manufacturing is complete, this support structure 22 is removed from the object 6, for example by dissolving it in a suitable solvent.

[0083] The machine further comprises an activation device 15 comprising a plasma nozzle 16 which activates the thermoplastic polymer material 8 of the main filament 9a.

[0084] Advantageously, the plasma nozzle 16 may be a rotary nozzle 19, capable of activating the thermoplastic polymer material of the two filaments 9a and 9b by a variation of the exit angle of the plasma jet 17.

[0085] Alternatively, it is possible to provide two plasma nozzles 16, one for each of the filaments 9a and 9b, or a wide jet plasma nozzle capable of simultaneously activating both filaments 9a and 9b.

[0086] In the example of [Fig.4], the plasma nozzle 16 is linked to the extrusion heads 11 and arranged upstream of them.

[0087] The automated fiber placement additive manufacturing machine 3 shown in Figures 5 to 7 comprises a support tool 23 on which a layer production device 7 stacks strips 24 impregnated with thermoplastic polymer material in order to constitute the different layers 14 of the object 6 to be manufactured.

[0088] The layer-forming device 7 comprises a laser source 25 and a compacting roller 26 which move in the direction of the arrow 27.

[0089] During the step of adding a strip 24 belonging to layer n of the stack, the laser source 25 heats, by its laser radiation 28, the lower face 29 of the strip 24 of the layer n being added and the upper face 30 of the strip 24 of the layer n-1 previously added, to locally melt the thermoplastic polymer material of these strips.

[0090] The lower face 29 of the strip 24 of layer n and the upper face 30 of the strip of layer n-1 are then brought into contact and pressed against each other by the compacting roller 26 to weld them together.

[0091] The machine 3 also comprises an activation device 15 with at least one plasma nozzle 16.

[0092] In the example of [Fig.5], the plasma nozzle 16 moves with the layer-forming device 7. It is for example fixed to the arm carrying the laser source 25.

[0093] The plasma nozzle 16 is arranged upstream of the layer production device 7 and activates by its plasma jet 17 the upper face 30 of the strip 24 of the layer n-1 already added, before it is heated by the laser radiation 28 and covered by the strip 24 of the layer n being added.

[0094] In the example of [Fig.6], the plasma nozzle is arranged downstream of the layer production device 7 and activates by its plasma jet 17 the upper face 30 of the strip 24 of the layer n being added.

[0095] The plasma nozzle 16 is connected to the layer-forming device 7 and moves with it. It is for example fixed to the support of the compacting roller 26.

[0096] In the example of [Fig.7], the plasma nozzle 16 activates a portion of the strip 24 which has not yet reached the layer-forming device 7 and therefore before it has been heated by the laser radiation 28 and pressed by the compacting roller 26.

[0097] The additive manufacturing machine by laser sintering of powders 31 (“Selective Laser Sintering” or SLS in English) shown in FIGS. 8 and 9 makes it possible to construct layer by layer the object 6 to be manufactured from a thermoplastic polymer material 8 in the form of powder 32.

[0098] The machine 31 comprises a reserve tank 33 which serves as a storage reservoir for the powder not yet used, a construction tank 34 which is the main tank in which the additive manufacturing takes place and a recovery tank 35 in which the surplus powder is recovered.

[0099] The bottoms, respectively 36, 37 and 38, of the reserve 33, construction 34 and recovery 35 tanks are vertically movable in order to increase or decrease the capacity of the tank concerned.

[0100] The layer production device 7 comprises a laser source 25, the beam 39 of which is precisely oriented by an inclined mirror 40 towards the surface of the construction tank 34, and a scraper 41 which moves horizontally on the surface of the tanks pushing the powder.

[0101] To produce the layer 14 of rank n of the manufacturing, the scraper 41 begins by spreading powder 32 coming from the reserve tank 33 on the surface of the construction tank 34. Then the laser source 25 comes to solidify this layer of rank n by heating and locally melting the thermoplastic polymer material 8 of the powder 32 only along the outline of the layer n of the object 6.

[0102] The bottom 37 of the construction tank then descends by the thickness of a layer 14, just like that 38 of the recovery tank, while the bottom 36 of the reserve tank 33 rises. The process can then start again in the same way for the next layer n+1.

[0103] The machine 31 also comprises an activation device 15 with at least one plasma nozzle 16.

[0104] In the example of [Fig.8], the plasma nozzle 16 activates by its plasma jet 17 the thermoplastic polymer material 8 which is located in the construction tank 34.

[0105] The plasma nozzle 16 can, as shown, be placed downstream of the laser beam 39 and activate the layer 14 of rank n already solidified by the laser source 25. In this case, the activation is therefore done after the addition of the layer of rank n.

[0106] Alternatively, the plasma nozzle can be arranged upstream of the laser beam 39 and activate the powder 32, already put in place by the scraper 40 to form the layer 14 of rank n, but before its solidification by the laser source 25. In this case, the activation takes place during the addition of the layer of rank n.

[0107] In the example of [Fig.9], the plasma nozzle 16 activates the thermoplastic polymer material 8 of the powder 32 which is in the reserve tank 33, before the scraper 40 takes it into the construction tank 34. The activation therefore takes place before the addition of the layer of rank n.

[0108] Advantageously, the invention is not limited to a particular type of plasma and different plasma sources can be used satisfactorily. One example is the Openair-Plasma® solution marketed by the company PLASMATREAT as being perfectly suitable.

[0109] The power of the plasma source being generally fixed and different depending on the device used, the person skilled in the art will be able to easily optimize the other activation parameters, namely the distance between the plasma nozzle 16 and the material 8 to be activated, as well as the running speed (speed of advance of the filament, of depositing the strip or of movement of the plasma nozzle, etc.), in order to adapt them to the power of the plasma source used and to the nature of the thermoplastic polymer material 8 considered in order to to obtain satisfactory activation of the latter.

[0110] To do this, it will be sufficient, for example, to compare the initial surface tension of the material with that of the same material after plasma treatment by varying these parameters and then to apply, for additive manufacturing, the parameter setting conferring the highest surface tension. This surface tension can be measured in a conventional manner using calibrated inks or a goniometer.

[0111] As an example, with a thermoplastic polymer material 8 in polyetherimide (PEI) and a plasma source of the Openair-Plasma® type with approximately 5 kW of power, a preferential distance of between 15 and 25 mm was determined, with a running speed of 10 to 50 mm per second for treatment with a conventional nozzle of 3 to 5 mm (quasi-“point” treatment) or 100 mm per second with two juxtaposed nozzles (treatment over a greater length).

[0112] With such parameters, the surface tension of the PEI advantageously increases from a value of 56 mN / m measured initially to a value greater than 75 mN / m measured after treatment.

Claims

Claims

1. Additive manufacturing method by adding layers (14) based on thermoplastic polymer material (8) on top of each other so as to form a superposition of N layers (14), with N> 2, each layer (14) having a rank in the superposition ranging from 1 to N, method characterized in that the thermoplastic polymer material (8) of each layer (14) of rank n, with l <n<N, est activé par plasma avant d’être recouvert par la couche de rang n+1, cette activation pouvant se faisant avant, pendant ou après l’ajout de la couche de rang n

2. 11. Additive manufacturing method according to claim 1 characterized in that the thermoplastic polymer material (8) of the layer (14) of rank n is activated by plasma before the step of adding the layer (14) of rank n.

3. Additive manufacturing method according to claim 1 characterized in that the thermoplastic polymer material (8) of the layer (14) of rank n is activated by plasma during the step of adding the layer (14) of rank n on an already added portion of the layer (14) of rank n.

4. Additive manufacturing method according to claim 1 characterized in that the thermoplastic polymer material (8) of the layer (14) of rank n is activated by plasma during the step of adding the layer (14) of rank n+1, on a portion not yet covered by the layer (14) of rank n.

5. Additive manufacturing method according to one of the preceding claims, characterized in that the plasma activation is carried out on all the faces of the layer (14) of rank n or only on the face of the layer (14) of rank n which is intended to be in contact with the layer (14) of rank n+1.

6. Additive manufacturing method according to one of the preceding claims, characterized in that it is an additive manufacturing method by extrusion, preferably by deposition of filaments, or an additive manufacturing method by deposition of strips, or an additive manufacturing method by sintering of powders by laser.

7. Additive manufacturing machine (1) allowing the implementation of the method according to one of the preceding claims, characterized in that it comprises a layer production device (7) capable of adding layers (14) based on thermoplastic polymer material (8) on top of each other so as to form a superposition of N layers (14), with N> 2, each layer (14) having a rank in the su- perposition ranging from 1 to N, and an activation device (15) which comprises at least one plasma nozzle (16) arranged so as to be able to activate the thermoplastic polymer material (8) of each layer (14) of rank n, with the <n<n, avant qu’il ne soit recouvert par la couche de rang n+1.

8. Additive manufacturing machine (1) according to claim 7 characterized in that the plasma nozzle (16) is a rotary nozzle (19) or an annular nozzle (18).

9. Additive manufacturing machine (1) according to claim 7 or 8 characterized in that the plasma nozzle (16) is connected directly or indirectly to the layer production device (7), so that the plasma nozzle (16) moves with the layer production device (7).

10. Additive manufacturing machine (1) according to claim 9 characterized in that the plasma nozzle (16) is positioned upstream or downstream or alternately upstream and downstream of the layer production device (7), relative to the direction of movement of the layer production device (7).

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