Method and compaction system for layer-by-layer manufacturing of a part using additive manufacturing technology

Abstract

The invention relates to a method for manufacturing a part layer by layer using additive manufacturing techniques. The method comprises the following steps: - printing the part with an elastomer enclosure shaped thereon, leaving a gap free of material between the part and the elastomer enclosure, the elastomer enclosure comprising at least one opening; - subjecting the whole of the printed part and the elastomer enclosure to a heating or holding operation at the printing temperature; - applying a vacuum through the at least one opening of the elastomer enclosure, causing the elastomer enclosure to deflate, thereby applying a pressure to the printed part; and - maintaining the printed part under vacuum and heating during a predetermined time. The invention also relates to a compacting system for a printed part manufactured layer by layer using additive manufacturing techniques.

Description

TECHNICAL FIELD

[0001] The present invention belongs to the field of manufacturing, in particular the field of manufacturing parts using additive manufacturing techniques. More specifically, the present invention has a particular application in the manufacturing of printed parts with complex shapes for structural applications. BACKGROUND

[0002] In the past, aircraft parts with structural applications have always been made of aluminum alloys. Over the past decades, with the development of composite manufacturing techniques, such structural parts have been manufactured using different techniques, such as co-bonding or co-curing of parts composed of carbon fiber reinforced plastics (CFRP).

[0003] However, all these manufacturing techniques require the part to go through different stages of operation in order to manufacture separately different constituent parts which will subsequently be assembled together. This is a time-consuming process and determines the production rate of the aircraft. As a result, the final part is obtained after a series of different manufacturing steps which increase the manufacturing cost and time.

[0004] This drawback, together with the high recurring / non-recurring costs associated with these conventional manufacturing techniques, has facilitated the emergence of additive manufacturing (AM) techniques in the aeronautical field.

[0005] Generally, these AM techniques use a computer with 3D modeling software (computer-aided design or CAD), an additive manufacturing tool (e.g. a machine device) and a filament of layered material. The CAD sketch is a 3D electronic model of the final 3D object construction. The AM tool is able to read the data (both cross-sectional geometry and surface pattern) from the CAD file and, through at least one head, lay or deposit successive filaments (which then form the layers) of liquid, powder, sheet, etc. in a layer-by-layer manner to manufacture the 3D object.

[0006] Thus, while enabling rapid prototyping, the possibility of reducing the buy-to-fly ratio (i.e. the ratio between the mass of material needed to produce a part and the mass of material in the final aeronautical structure) sets a promising roadmap for layer-by-layer printing of polymer parts.

[0007] However, it is well known that the mechanical properties of printed composite parts are still far from those of aluminum parts or composite parts manufactured by conventional techniques. This is due to the inherent defects present in conventional printed parts, such as voids, porosities or poor adhesion between successive filaments from the same layer or different layers.

[0008] The formation of pores or voids is mainly due to the stacking of the long filaments forming the layers with a substantially circular cross-section, and typically these voids extend along the printing direction. Another typical local defect is the lack of polymer chain intermingling between adjacent long filaments, which makes the interlaminar shear strength ('ILSS') very low and can cause the printed part to be weak when subjected to certain stresses.

[0009] Therefore, when these conventional printed parts are tested or put into use, these voids and printing defects can act as stress concentrators, causing the parts to fail prematurely.

[0010] The current solution provides an in-situ compacting mechanism based on a roller that generally applies pressure to the deposited layers against the printing bed to mitigate these undesirable phenomena. This solution can be easily applied to printed parts with simple geometries or with soft curvatures, in which the roller can roll extensively and uniformly.

[0011] However, the most remarkable feature of printing parts layer by layer using additive manufacturing techniques is precisely the ability to manufacture economic and fast parts with complex geometries, making this roller-based compacting technique useless for most printed parts.

[0012] Therefore, there is a need in the industry for a simple, fast, reliable and effective method of manufacturing structural printed parts that can be applied extensively regardless of the expected geometry, while ensuring the mechanical properties imparted to meet the structural requirements. SUMMARY

[0013] The present invention provides a solution to the above-mentioned problems through a method for manufacturing a part layer by layer using additive manufacturing techniques according to the invention and a compacting system for a printed part according to the invention.

[0014] In a first inventive aspect, the present invention provides a method for manufacturing a part layer by layer using additive manufacturing techniques, the method comprising the steps of:

[0015] - printing the part together with an elastomeric enclosure shaped thereon, leaving a gap free of material between the part and the elastomeric enclosure, the elastomeric enclosure comprising at least one opening;

[0016] - heating or maintaining the printed part and the whole piece of elastomeric enclosure at the printing temperature;

[0017] - applying a vacuum through the at least one opening of the elastomeric enclosure, causing the elastomeric enclosure to deflate, thereby applying pressure to the printed part; and

[0018] - maintaining the printed part under vacuum and heating for a predetermined period of time.

[0019] Throughout this entire document, the "additive manufacturing technique" (AM) will be understood as those techniques that build 3D objects by adding material layer by layer, where the material (in the case of reinforced materials, a meltable material or a matrix material) becomes liquid when heat is applied and solidifies (or hardens) into a solid when it cools.

[0020] Depending on the form of the material and machine technology used, a number of techniques are included in additive manufacturing techniques. Among them, mention can be made of selective laser sintering (SLS), stereolithography (SLA), multi-jet modeling (MJM) or fused filament fabrication (FFF).

[0021] In a preferred embodiment of the method of the application, the part and the elastomer envelope are printed using fused filament fabrication (FFF). As is known, FFF is a particular example of 3D printing (3DP).

[0022] Fused filament fabrication (FFF) is a process-oriented manufacturing that includes the use of material in the form of long filaments injected through at least one indexing nozzle onto a build sheet. The nozzle(s) trace the surface pattern of each particular layer, the material hardening before the next layer is deposited. The process is repeated until the piece is complete, i.e. printed. Preferably, the material is a thermoplastic or elastomeric material, or a fibrous material reinforcement embedded in a thermoplastic material.

[0023] In FFF, each deposited layer can be formed by a set of oriented filaments.

[0024] It is noted that the process of printing the part together with the elastomer envelope is performed by repeating the following steps, as many times as necessary:

[0025] - depositing at least one layer of material of the part onto a build sheet,

[0026] - leaving a gap without material, and

[0027] - depositing at least one layer of elastomer material for the elastomer envelope following the shape of the part.

[0028] Since the first printed layer (lower layer) of both the elastomer envelope and the printed part is deposited directly on the build sheet, and the elastomer envelope follows the shape of the printed part, the first printed layer of the elastomer envelope forms the edge of at least one opening.

[0029] As a result, the elastomer envelope completely surrounds the printed part, except for this at least one opening.

[0030] Due to the strong dependence on temperature when forming bonds (diffusion-based fusions) between adjacent filaments / layers, typical printing tools preheat their printing chamber or surroundings in order to reach and maintain the operating printing temperature determined by the selected material.

[0031] Thus, according to the application, there is a step of heating the integral piece formed by the printed part and the elastomer envelope resulting from the previous printing step to an operating temperature. Optionally, during the printing process, the integral piece can also be heated and maintained at the operating temperature. The operating temperature can be constant or can vary with the process.

[0032] This operating temperature is advantageously the glass transition temperature of the printed part material, so as to soften the layers and slightly enable shaping. For example, typical values for the glass transition temperature are 143°C for PEEK (polyether ether ketone), 50°C for PA66 (e.g. nylon), 105°C for ABS (acrylonitrile butadiene styrene copolymer). Although the exact value of the glass transition temperature depends on the measurement technique, all known results provide values sufficiently similar to apply the application.

[0033] Another step of the application is to apply a vacuum on the integral piece by communicating a vacuum system airtightly to at least one opening of the elastomer envelope, so that air is removed from the gap between the printed part and the elastomer envelope, causing the elastomer envelope to deflate.

[0034] As the elastomer envelope is shaped to the printed part, this vacuuming causes the elastomer envelope to exert a pressure on the printed part, the elastomer envelope thus acting as an in-situ printing thermoforming film or vacuum bag for consolidation.

[0035] For the term "envelope", it is understood that for each wall of the printed part (internal or external), there is a corresponding wall of elastomer material separated by a gap. Only when the internal wall of the printed part is not open to the outside (for example, to introduce voids intentionally to lighten the part), the elastomer material does not cover such a wall, as it is not possible to apply a vacuum first and then to remove the elastomer material second.

[0036] If this combination of operating temperature and vacuum is maintained for a predetermined time, the printed part is considered to be just consolidated.

[0037] Advantageously, the elastomer material is flexible and stretchable enough to change their geometry under vacuum and heating, so as to tightly cover the printed part. In particular, it has been found that the elastomer material printed as an envelope can be easily inflated and deflated without damaging, and is then particularly suitable to exert a pressure (i.e. compact) on the printed part and improve its mechanical properties.

[0038] Further, due to the swelling / shrinking properties inherent to the flexible elastomer material, the printed part can be easily removed from this envelope without being damaged.

[0039] As mentioned, since the part is made of a polymeric material, heat sufficiently softens the printed part and the compaction relieves the voids between the filaments, thus promoting the polymer fusion to improve the interlayer mutual adhesion. As a result, not only the mechanical properties of the printed part, such as ILSS, tensile strength, compressive strength, etc., are greatly improved, but also the dimensional tolerances are improved. Incidentally, therefore, any warping effects are eliminated.

[0040] Advantageously, since the elastomer enclosure prints the parts to be consolidated while printing step by step, i.e. they are "printed together" or simultaneously, there are no limitations on the shape or geometry of the printed part.

[0041] In short, the consolidated printed part manufactured by the method according to the present application has a high-resolution surface, a smaller pore volume or voids and no interfaces compared to a conventional printed part.

[0042] For example, an aeronautical part, which is usually made in pieces and then assembled together (thus having interfaces), can be manufactured integrally in one piece and meet any structural specifications.

[0043] In a preferred embodiment, the printed part is an aeronautical part.

[0044] This last remarkable feature of the interface-free (i.e. integral or self-sealing) part manufactured according to the present application has additional advantages, such as improved water ingress and debonding issues. Moreover, since the printed part has better structural performance, the handling can be enhanced.

[0045] In a particular embodiment, the method further comprises the steps of:

[0046] - cooling down the printed part and the integral piece of elastomer enclosure at a predetermined cooling rate; and

[0047] - removing the printed part from the elastomer enclosure manually or by applying air through the gap between the part and the elastomer enclosure.

[0048] Cooling down the consolidated printed part from the operating temperature (usually defined in °C / min) causes its solidification and, therefore, an impact on its final mechanical properties as a result of the material shrinkage and the onset of internal stresses.

[0049] If the cooling rate is slow enough, residual thermal stresses on the printed part can be mostly avoided. A suitable cooling rate depends on the specific case, usually considering both the material type and the geometry, with typical values around 16 °C / min or lower.

[0050] Cooling down is usually performed by gradually stopping working or switching off the heating means through convection and then applying cooling air.

[0051] In a preferred embodiment, the cooling speed is chosen as a function of the printed part material to reach a crystallinity of at least 32%.

[0052] Contrary to amorphous polymers, semi-crystalline polymers comprise an ordered arrangement of their polymer molecular chains, in particular these chains tend to align, further densifying the printed part.

[0053] Thus, in this embodiment, the final consolidation is produced by the combination of the thermo-mechanical effect and the crystallization effect, enlarging the possible mechanical properties of the final product.

[0054] Promoting a certain degree of crystallization in the printed product advantageously improves the mechanical properties conferred to it.

[0055] Once the printed part is cooled, for example to ambient temperature, the monolithic piece can be removed from the printing tool, if still there, and the printed part can be further removed from the elastomer envelope, either manually or by disconnecting the vacuum system and connecting a compressed air system for the application of air through the interstices.

[0056] Due to the flexible nature of the elastomer material, it can be removed without damage due to its easy inflation.

[0057] It is important to note that, once cooled, there is no need to remove the elastomer envelope immediately, since it can act as a cushioning protection for the printed part during storage.

[0058] In a preferred embodiment, the elastomer envelope is made of silicone rubber and / or elastomeric polyurethane.

[0059] Advantageously, these elastomer materials are flexible and elastic materials that can be printed according to the geometry of the part around them. Preferably, the elastomer envelope is printed taking into account the expected deformations and / or adaptability.

[0060] In a preferred embodiment, the printed part is made of a fibrous material reinforcement embedded in a meltable material.

[0061] By depositing the fibrous material reinforcement with a meltable material, a lightweight design is achieved, since less material is needed to meet the structural requirements compared to using only a meltable material.

[0062] According to the invention, the fibrous material reinforcement can be in the form of, for example, fibrils (very short and / or irregular fibers), nanofibers, carbon fillers, short fibers (length < 1 mm) or continuous fibers (continuous along the entire filament and thus along the entire length / width of the part when manufactured). Preferably, the fibrous material reinforcement is in the form of continuous fibers and / or short fibers, with continuous fibers being preferred.

[0063] Additionally, the fibrous material reinforcement can be glass fibers, carbon fibers, polymer fibers or any other conventional material used as reinforcement. Among these, carbon fibers are preferred.

[0064] According to the present application, the meltable material can be a thermoplastic material, such as PA (polyamide), PA66, ABS (acrylonitrile-butadiene-styrene), PEEK (polyether ether ketone), PAEK (polyaryletherketone) or PEKK (polyether ketone ketone). In a preferred embodiment, the meltable material is in the form of filaments for better storage and handling.

[0065] In a preferred embodiment, the meltable material is any of the following thermoplastic materials: PEKK, PAEK, or PEEK. More preferably, the meltable material is PAEK or PEEK. And most preferably, the meltable material is PEEK.

[0066] In a preferred embodiment, this fibrous material reinforcement is deposited to better adapt to future load requirements during operation and service. Thus, an optimized structural arrangement is achieved.

[0067] In a particular embodiment, the elastomer enclosure comprises at least one external rib formed of additional elastomer material.

[0068] That is, the elastomer enclosure is printed with at least one external rib configured and arranged so that the pressure applied to the printed part under vacuum for consolidation takes into account the mechanical properties to be applied on the printed part.

[0069] When the vacuum is applied, the elastomer material deflates by removing the air between itself and the printed part and compacts the printed part. Since it is not possible to compact in three axes, to further optimize the mechanical properties, the elastomer enclosure can be designed according to the expected mechanical properties of the printed part.

[0070] In particular, the concentration of elastomer material on both sides of the walls of the printed part provides a higher local pressure, thus, during operation and service, the compaction can be applied according to the expected load requirements.

[0071] Since the AM technology allows both to vary the thickness of the elastomer enclosure and to provide ribs (understood as local concentration of elastomer material), the compaction can also be locally varied according to the expected mechanical properties. Likewise, for complex geometries, controlling the direction of the applied pressure, a more homogeneous consolidation can be achieved.

[0072] In a particular embodiment, the part and the elastomer enclosure are printed on a porous build sheet that is connected to a vacuum system for the application of the vacuum.

[0073] Conventional additive manufacturing tools for printing a part layer by layer comprise a print chamber that accommodates a build sheet and at least one head that is configured to move over said build sheet and deposit material.

[0074] The conventional build sheet can be replaced by a porous build sheet, or this porous build sheet can be placed on top of the conventional build sheet. In either way, in this embodiment, a vacuum system is connected underneath to apply a vacuum through at least one opening of the elastomer enclosure.

[0075] Advantageously, by hermetically closing the print chamber, if not already closed, and then activating the vacuum system for a predetermined time, the printed part can be consolidated in situ immediately after printing.

[0076] Advantageously, the method according to the invention can easily be implemented in a conventional additive manufacturing tool, such as a FFF printer.

[0077] In a preferred embodiment, the printed part and the integral piece of elastomer enclosure are kept at an operating temperature inside the print chamber.

[0078] Since the vacuum extraction can be performed immediately after printing, the print chamber is already at an operating temperature, so the heater therein only needs to maintain such temperature for a predetermined compacting time.

[0079] In a particular embodiment, the method further comprises the steps of:

[0080] - printing an elastomer connector layer by layer, the elastomer connector being configured to hermetically connect with the at least one opening of the elastomer enclosure, wherein said elastomer connector is printed together with the part and the elastomer enclosure, or in a separate printing step;

[0081] And, the step of applying a vacuum further comprises:

[0082] o hermetically connecting the elastomer connector with the at least one opening of the elastomer enclosure; and

[0083] o connecting a vacuum system to said elastomer connector.

[0084] That is, the elastomer connector is printed in situ and specifically according to the geometry of the printed part, and in particular according to the at least one opening of the elastomer enclosure. The additional non-structural material is printed as a vacuum connection between the elastomer enclosure opening and a valve of the vacuum system.

[0085] Likewise, based on the same CAD file, the elastomer connector can be printed in a separate printing step, if the print chamber is not large enough to print this connector and the integral piece at the same time.

[0086] In either way, the elastomeric connection comprises a first connection point shaped to at least one opening of the elastomer envelope, and further comprises at least one second connection point configured to distribute one or more vacuum valves of the vacuum system thereon.

[0087] Then, according to the invention, the elastomer connection is airtightly connected to the at least one opening of the elastomer envelope through the first connection point; and to the vacuum system through the second connection point.

[0088] Advantageously, the invention can use a conventional external vacuum system.

[0089] As mentioned, for efficient compacting, the printed part needs to be warm enough, preferably above its glass transition temperature. Then, one option is to introduce a vacuum connection inside the printing chamber and perform compacting there.

[0090] Alternatively, once the part and the elastomer envelope are printed, the method further comprises the step of moving them into an oven or autoclave, so as to be kept at an operating temperature therein.

[0091] In a second inventive aspect, the invention provides a compacting system for a printed part manufactured layer by layer using an additive manufacturing technique, wherein the system comprises:

[0092] - an elastomer envelope printed layer by layer with the part and adapted to be shaped to leave a gap therebetween, wherein this envelope comprises at least one opening;

[0093] - heating means configured to heat and keep the whole of the printed part and the elastomer envelope at an operating printing temperature;

[0094] - means to apply a vacuum through the at least one opening of the elastomer envelope, and

[0095] - a controller,

[0096] wherein the controller is configured to operate the means to apply a vacuum and the heating means simultaneously at least during a predetermined time, so that the elastomer envelope deflates, thereby applying a pressure to the printed part.

[0097] Advantageously, a conventional additive manufacturing printing tool, such as a FFF printer, can be improved by including this compacting system.

[0098] If this combination of operating temperature and vacuum is maintained for a predetermined time, the printed part is considered to be just consolidated or compacted.

[0099] In embodiments, the compacting system further comprises the printed part.

[0100] Preferably, the heating means is arranged inside a printing chamber in which the printed part and the elastomer enclosure will be printed. In this embodiment, the controller can be the same as the controller incorporated in the printing chamber for coordinating the movement of the head and / or the build sheet.

[0101] Otherwise, the heating means can be an oven or an autoclave. In this embodiment, the controller can be a software-based component for coordinating the temperature of the oven / autoclave and the vacuum applied by the vacuum system.

[0102] In a particular embodiment, the means for applying a vacuum comprises a porous build sheet on which the printed part and the elastomer enclosure are printed and a vacuum system connected to such porous build sheet.

[0103] In an alternative embodiment, the means for applying a vacuum comprises an elastomer connector configured to be airtightly connected to at least one opening of the elastomer enclosure and a vacuum system connected thereto.

[0104] In this embodiment, the means for applying a vacuum can further comprise an airtight seal at the connection between the elastomer connector and the at least one opening of the elastomer enclosure to ensure airtightness.

[0105] To effectively compact, in a particular embodiment, the elastomer enclosure comprises at least one external rib arranged so that the pressure applied under vacuum to the printed part for consolidation takes into account the mechanical properties to be applied on the printed part.

[0106] In a third inventive aspect, the present invention provides an additive manufacturing tool for printing and consolidating a printed part layer by layer using an additive manufacturing technique, the additive manufacturing tool comprising:

[0107] - a printing chamber housing a build sheet and at least one head configured to move on said build sheet and deposit a material for printed parts and / or an elastomer material; and

[0108] - a compacting system according to any embodiment of the second inventive aspect.

[0109] The additive manufacturing tool according to the present third inventive aspect can be used in the method according to any embodiment of the first inventive aspect comprises a printing chamber, preferably a closable printing chamber.

[0110] Inside the printing chamber, a build sheet and at least one head are arranged. This build sheet can be planar or curved, reproducing any outer surface of the product to be printed.

[0111] At least one head is configured to move over the build sheet and simultaneously deposit the stored material, which tracks the surface pattern of each particular layer, the material hardens after application before a subsequent layer is applied.

[0112] If material in the form of filaments is used, the tool can further comprise spool(s) for storing the meltable material of the part and separate fibrous material reinforcement, or fibrous material reinforcement already embedded into the meltable material, or even elastomeric material. Preferably, all in the form of filaments.

[0113] The material stored in the spool(s) is guided to the head(s). The head additionally comprises an extruder that uses a torque and clamping system to feed and retract the fed material in order to drive the deposition of the required amount of material. The head(s) can also comprise a heating block for heating the meltable material or elastomeric material to any precise temperature. Once the material is heated, its diameter is reduced, thereby forcing the material to be deposited more accurately.

[0114] The additive manufacturing tool can have one head configured to deposit the meltable material for the part and / or elastomeric material, and another head configured to deposit the fibrous material reinforcement to be embedded in the meltable material, or only one head configured to transform the material to be deposited. Alternatively, the additive manufacturing tool has one head configured to deposit the meltable material for the part, and another head for depositing the elastomeric material.

[0115] Furthermore, the fibrous material reinforcement can be:

[0116] • embedded into the material of the part before entering the head (similar to pre-impregnated composite materials), or

[0117] • embedded into the material of the part in situ in the head, or

[0118] • embedded into the material of the part in situ on the part, depositing the fibrous material reinforcement and the meltable material separately, and applying heat to melt the meltable material once deposited.

[0119] In embodiments, the head is configured to move and / or rotate (around X, Y, Z) along three translational axes (X, Y, Z) over the build sheet to print more complex geometries. Optionally, the head(s) can be limited to move over the build sheet only in the horizontal directions (X, Y), while the movement in the vertical Z direction is performed by the build sheet, thereby enabling so-called 2.5D manufacturing. These movements are typically performed by actuators and / or servos, one for each direction and / or rotation.

[0120] In a fourth inventive aspect, the present application provides a layer- wise manufacturable part using additive manufacturing technology according to any embodiment of the first inventive aspect. In a preferred embodiment, the part is an aerospace part.

[0121] All features and / or steps described in the present specification (including the claims, the description and the drawings) can be combined in any combination, except combinations where at least some of the features and / or steps are mutually exclusive. BRIEF DESCRIPTION OF DRAWINGS

[0122] These and other characteristics and advantages of the present application will become apparent from the detailed description, the claims, and the accompanying drawings, and unless otherwise defined, all technical and scientific terms used herein are intended to have their common meanings, and not their most restrictive or legal meanings.

[0123] Figure 1 This figure shows an example of an additive manufacturing tool with a printed part of different geometry.

[0124] Figure 2 This figure shows a schematic representation of an additive manufacturing tool, where both the first layer of the part and the elastomer enclosure have been printed.

[0125] Figure 3a , Figure 3b These figures show cross-sectional views of a cylindrical printed part (5a) and a hemispherical printed part (5b) with respective elastomer enclosures. Figure 3a ) and a hemispherical printed part ( Figure 3b ) with respective elastomer enclosures.

[0126] Figure 4a , Figure 4b These figures show plan and cross-sectional views of a cylindrical printed part, where the corresponding elastomer enclosure further comprises at least one external rib for localised compaction control.

[0127] Figures 5a to 5c These figures show cross-sectional views of a cylindrical printed part with a corresponding elastomer enclosure and another elastomer connection at three instants: (5a) just after printing, (5b) after assembly, and (5c) after disconnection from the vacuum system. DETAILED DESCRIPTION

[0128] The skilled person will appreciate that the aspects described herein can be embodied as a method of manufacturing a part 1, a compaction system, or an additive manufacturing tool.

[0129] The present application defines a method of layer-wise manufacturing a part 1 using additive manufacturing technology. Essentially, the method comprises the following steps:

[0130] - printing the part 1 with an elastomer envelope 2 shaped thereon, leaving a gap free of material between the part and the elastomer envelope, the elastomer envelope comprising at least one opening 2.1 ;

[0131] - heating or maintaining the operating printing temperature of the whole piece of printed part 1 and elastomer envelope 2;

[0132] - applying a vacuum through the at least one opening 2.1 of the elastomer envelope 2, causing the elastomer envelope to deflate, thereby applying pressure to the printed part 1; and

[0133] - maintaining the printed part 1 under vacuum and heating during a predetermined time.

[0134] Figure 1 An embodiment of an additive manufacturing tool 10 according to an aspect of the application is depicted, having a set of printed parts 1’, 1”, 1”’ of different geometrical shapes.

[0135] The printing chamber is not shown for illustrative reasons. However, this printing chamber typically houses the build sheet 3.1 and the head(s) 5 that can move horizontally (X, Y) on this build sheet 3.1. As with 2.5D manufacturing, the movement in the vertical Z direction is performed by the build sheet.

[0136] During the printing step, layers of material are deposited on this build sheet 3.1. Moreover, this build sheet is a porous build sheet from which air can be extracted, i.e. a vacuum is transmitted.

[0137] To apply a vacuum, this porous build sheet 3.1 is connected to a conventional vacuum system (not shown) arranged underneath (see Figure 2 ).

[0138] Moreover, although not shown, the printing chamber houses heating means or “heater” (e.g. resistors) for heating and maintaining the interior at an operating temperature during both the printing and the compacting steps.

[0139] These printing and compacting operating temperatures can be identical or different. Thus, if different, the heating means are configured to warm up and maintain the interior of the printing chamber at least up to a maximum temperature, which is typically an operating temperature above the glass transition temperature of the material of the printed part. Otherwise, two different heaters or heating means can be provided for each step.

[0140] Thanks to the additive manufacturing tool having combined the vacuum system 3 and the vacuum transmission means through the porous build sheet 3.1 and the heating system, the steps of printing, heating and vacuum extraction can be subsequently performed in situ within the printing chamber.

[0141] As a result, the part 1 ', 1 ", 1 "' is printed simultaneously with the elastomer envelope 2', 2", 2"' shaped onto it but separated by a gap. Figure 1 The geometries shown are half-cylinders 1 ', 2', tubular profiles 1 ", 2" and quarter-spheres 1 "' 2"'.

[0142] These basic geometries are for illustrative purposes and the method according to the invention can be extended to any other geometry, no matter how complex it will be. Indeed, the invention is particularly suitable for cases where the geometry of the printed part is too complex to be compacted with conventional means.

[0143] As mentioned above, no matter how pronounced the curvature of the outer wall of the printed part 1 will be, there should always be a corresponding wall made of elastomer material 2 separated by a gap, unless the wall of the printed part is not open outwardly, for example in the case of an internal void.

[0144] Figure 2 A similar process is depicted in Figure 1 a schematic representation of an embodiment of the additive manufacturing tool 10, where both the first layer of the part 1 and of the elastomer envelope 2 have been printed.

[0145] In short, the process of printing a part 1 together with an elastomer envelope 2 is performed by repeating the following steps, as many times as necessary:

[0146] - depositing at least one layer of material of the part 1 onto a build sheet,

[0147] - leaving a gap without material, and

[0148] - depositing as many layers of elastomer material 2 as possible as intended walls of the part for the elastomer envelope.

[0149] As can be seen, the first layer of the part 1 surrounded by a layer of the elastomer envelope 2 following the shape of the part is printed directly on a build sheet, for example a porous build sheet 3.1. This printed layer of the part 1 will form an edge with two exposed sides, for example a cylindrical wall.

[0150] These printed layers of the elastomer envelope 2 on both sides of the first layer of the part will then form the edges of the opening 2.1 through which air can escape by vacuum extraction.

[0151] If more layers are deposited layer by layer, the printing process will result in a printed part 1 and an elastomer envelope 2 as shown in Figure 3a and Figure 3b

[0152] ​In particular, these figures show cross-sectional views of a cylindrical printed part 1 and a hemispherical printed part 1, each having its specifically printed elastomer envelope 2.

[0153] The elastomer material 2 and the composite / polymeric part 1 can be printed together in a similar way as a regular printer. In a regular printing process (e.g. 2.5D), for each deposition step, the height of the overall piece formed by the part and the elastomer envelope is the same, so that both pieces are “printed together”. That is, at any printing step, the part 1 and the elastomer envelope 2 can have the same or similar number of deposited layers, to avoid the print head colliding with any printed piece.

[0154] Regarding the cylindrical geometry of the part 1 ( Figure 3a ), at the end of the printing process, considering that the printed part 1 is open on one or more faces, it is important to join the inner and outer walls of the elastomer material 2 to provide a closure (also with a gap left) for the part 1 in all the open areas except the areas in direct contact with the build sheet. Then, it allows the removal of the air inside the gap during the vacuum extraction process through the open area 2.1 in the bottom of the overall piece, to compact the piece.

[0155] In the case of a spherical geometry of the part 1 ( Figure 3b ), the process is the same as explained in Figure 3a , but the completion of the printing process results in a part that is closed, so there is no need - and it is not possible - to join the inner and outer walls of the elastomer envelope 2. Therefore, both the inner and outer walls of the elastomer envelope 2 are closed to avoid air escaping.

[0156] Figure 4a and Figure 4b depict a plan view and a cross-sectional view A-A’ of a cylindrical printed part 1, respectively, wherein the corresponding elastomer envelope further comprises rib(s) 2.2, 2.2’ for local compacting control.

[0157] As can be observed, this elastomer envelope 2 comprises: ribs, e.g. a seating ledge 2.2’ for providing a stable base, e.g. through a porous build sheet, when vacuum is applied; and four radial protrusions 2.2, uniformly (that is, every 90°) distributed at an intermediate height.

[0158] Further, the elastomer material accumulation on both sides of the part wall can similarly act, thus providing a higher local applied pressure compared to a constant thickness, so, during operation and maintenance, compacting can be done according to the expected load requirements.

[0159] As the compaction cannot be applied on the three axes X, Y, Z, the elastomer enclosure 2 needs to be designed taking into account the expected mechanical properties the printed part 1 will have. Regarding the cylindrical geometry (for example in Figure 3a herein the arrows have been drawn to show how these ribs change the direction of the compaction, thus providing a roughly radial force on the cylindrical part. In particular, because the ribs can avoid any unwanted crease formation, a more uniform pressure is applied radially.

[0160] Figures 5a to 5c A cross-sectional view of a cylindrical printed part 1 is drawn, with a corresponding elastomer enclosure 2 and another elastomer connector 4.

[0161] The cylindrical printed part 1 can be equivalent to those cylindrical printed parts drawn in Figure 3a or Figure 4a The elastomer connector 4 is an additional non-structural flexible elastomer material that allows the distribution of the vacuum valve 3.2 to the opening 2.1 of the elastomer enclosure 2, in order to apply a vacuum by an external source.

[0162] This elastomer connector 4 comprises a first connection point 4.1 shaped to the at least one opening 2.1 of the elastomer enclosure 2, and further comprises at least one second connection point 4.2 configured to distribute the vacuum valve(s) 3.2 of the vacuum system 3 thereon. In this particular example, only one valve 3.2 is used.

[0163] Then, according to the invention, the elastomer connector 4 is hermetically connected to the at least one opening 2.1 of the elastomer enclosure 2 by the first connection point 4.1 ; and to the vacuum system 3 (not shown) by the second connection point 4.2.

[0164] As seen in Figure 5a The elastomer connector 4 can be printed in situ and in particular according to the geometry of the printed part 1, and in particular according to the at least one opening 2.1 of the elastomer enclosure 2.

[0165] Then, as seen in Figure 5b This elastomer connector 4 is assembled to the whole by hermetically connecting its first connection point 4.1 to the at least one opening 2.1 of the elastomer enclosure.

[0166] It is also noted that in this embodiment, the elastomeric connector 4 is formed by two superimposed cups (i.e. an inner cup 4.4 and an outer cup 4.5) forming a receptacle 4.3 for insertion of a mushroom-type sealant counterpart. The outer cup 4.5 comprises a second connection point 4.2 in the form of a through hole for insertion of a vacuum valve 3.2 of the vacuum system 3 thereon. Furthermore, the rim of the inner cup 4.4 and the outer cup 4.5 form a first connection point 4.1 adapted to the opening 2.1 of the elastomeric enclosure.

[0167] During assembly, a hermetic seal can be required at the connection between the elastomeric connector 4 and at least one opening 2.1 of the elastomeric enclosure to ensure the hermeticity. This hermetic seal is preferably a gum sealant tape or other similar tape, such as those conventionally used in vacuum systems.

[0168] Figure 5c The situation after compression is depicted, wherein the monolithic piece 1, 2 is still assembled to the elastomeric connector 4 after just being disconnected from the vacuum system valve 3.2. It can further be seen that the mushroom-type sealant counterpart is inserted into the receptacle 4.3 to cooperate with the vacuum valve 3.2 and improve the vacuum extraction.

Claims

1. A manufacturing method for layer-by-layer manufacturing of a printed part (1) using an additive manufacturing technique, the manufacturing method comprising the steps of: - printing the printed part (1) together with an elastomeric enclosure (2) shaped thereon, leaving a gap free of material between the printed part and the elastomeric enclosure, the elastomeric enclosure comprising at least one opening (2.1); - subjecting the whole of the printed part (1) and elastomeric enclosure (2) to a heating or holding operation at a printing temperature; - applying a vacuum through the at least one opening (2.1) of the elastomeric enclosure (2) so that the elastomeric enclosure (2) deflates, thereby applying pressure to the printed part (1); and - maintaining the printed part (1) under vacuum and heating for a predetermined time period.

2. The manufacturing method according to claim 1, further comprising the steps of: - subjecting the whole of the printed part (1) and elastomeric enclosure (2) to a cooling at a predetermined cooling rate; and - removing the printed part from the elastomeric enclosure manually or by applying air through the gap between the printed part (1) and the elastomeric enclosure (2).

3. The production method according to claim 1 or 2, wherein The elastomeric enclosure comprises at least one external rib (2.2) formed of additional elastomeric material.

4. The production method according to claim 1 or 2, wherein The printed part (1) and the elastomeric enclosure (2) are printed on a porous build sheet (3.1) connected to a vacuum system (3) for applying the vacuum.

5. The production method according to claim 1 or 2, wherein The whole of the printed part (1) and elastomeric enclosure (2) is maintained at an operating temperature inside a printing chamber.

6. The manufacturing method according to claim 4, further comprising the step of: - printing an elastomeric connector (4) layer-by-layer, the elastomeric connector being configured to be airtight connected to the at least one opening (2.1) of the elastomeric enclosure (2), wherein the elastomeric connector (4) is printed together with the printed part (1) and the elastomeric enclosure (2) or in a separate printing step; and wherein the step of applying a vacuum further comprises: o airtight connecting the elastomeric connector (4) to the at least one opening (2.1) of the elastomeric enclosure (2); and o connecting the vacuum system to the elastomeric connector (4).

7. The manufacturing method according to claim 6, further comprising the step of: - once the printed part (1) and the elastomeric enclosure (2) are printed, moving them into an oven or autoclave to be maintained at an operating temperature therein.

8. The production method according to claim 1 or 2, wherein The elastomeric enclosure (2) is made of silicone rubber and / or elastomeric polyurethane.

9. The production method according to claim 1 or 2, wherein The printed part (1) is made of a fibrous material reinforcement embedded in a meltable material.

10. The manufacturing method according to claim 9, wherein, The meltable material is a thermoplastic material.

11. The manufacturing method according to claim 9, wherein, The fibrous material reinforcement is a continuous fiber and / or a short fiber.

12. The manufacturing method according to claim 2, the predetermined cooling rate being selected for such printed part (1) to reach a crystallinity of at least 32%.

13. A compaction system for a printed part (1) manufactured layer by layer using an additive manufacturing technique, wherein, The compaction system comprises: - an elastomer enclosure (2) printed layer by layer with the printed part (1) and adapted to be shaped onto the printed part with a gap between them, wherein the elastomer enclosure (2) comprises at least one opening (2.1); - a heating means configured to heat the whole of the printed part (1) and the elastomer enclosure (2) and to keep them at an operating printing temperature; - a means (3) to apply vacuum through the at least one opening (2) of the elastomer enclosure (2.1), and - a controller, wherein the controller is configured to operate the means to apply vacuum (3) and the heating means simultaneously at least during a predetermined time, so that the elastomer enclosure deflates, thereby applying pressure to the printed part, after which a compacted printed part is obtained.

14. The clamping system of claim 13, wherein, The elastomer enclosure (2) comprises at least one external rib (2.2) formed of additional elastomer material.

15. A compression system according to claim 13 or 14, wherein, The heating means is arranged inside a printing chamber in which the printed part and the elastomer enclosure will be printed; or is an oven or an autoclave.

16. The clamping system of claim 13 or 14, wherein, The means to apply vacuum comprises a porous build sheet (3.1) on which the printed part (1) and the elastomer enclosure (2) are printed, and a vacuum system (3.1) connected to such porous build sheet (3.2).

17. The clamping system of claim 13 or 14, wherein, The means to apply vacuum comprises an elastomer connector (4) configured to be airtight connected to the at least one opening (2.1) of the elastomer enclosure (2) and a vacuum system (3) connected thereto.

18. The clamping system of claim 17, wherein, The means to apply vacuum further comprises an airtight seal at the connection between the elastomer connector (4) and the at least one opening (2) of the elastomer enclosure (2) to ensure airtightness.

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