Apparatus and method for three-dimensional printing of continuous fibre composite materials

An apparatus and method for three-dimensional printing of composite materials of continuous fibre, in which a feed head for feeding a compound material of continuous fibre is moved so as to print a three-dimensional object; a means for relative movement between the feed head and the three-dimensional object exerts a drawing force on the compound material of continuous fibre, so as to bring about the feeding of the material; this material is realized at a station arranged upstream of the feed head.

This application is the National Phase of International Application PCT/IB2016/056912 filed Nov. 17, 2016 which designated the U.S.

This application claims priority to Italian Patent Application No. 102015000073191 filed Nov. 17, 2015, which application is incorporated by reference herein.

The object of the present invention is an apparatus and method for three-dimensional printing of continuous fibre composite materials.

As is known, three-dimensional printing or 3D printing is a process that makes it possible to create objects based on digitized models using suitable modelling software.

Among 3D printing apparatuses, extrusion 3D printers are the ones most used and they have seen widespread distribution. These printers realize the object to be printed by means of the extrusion of specific materials, generally thermoplastic and thermosetting polymeric materials, metal materials and ceramic materials.

Such apparatuses are based on the extrusion of material that passes from a liquid state to a solid state. For example, for 3D printing using thermoplastic materials, the polymer is extruded in the molten state and then, as it cools, it solidifies, producing the final form of the object.

Production of the object takes place by means of the movement of the extrusion head and/or the plate supporting the object to be printed, so as to enable the deposition of overlapping layers of material that results in the creation of the desired form

To enable this movement and thus enable deposition of the material along a predefined path (determined by the digitized model), mechanical movement systems with three axes are generally used for moving the extrusion head.

Also known are three-dimensional printing apparatuses that are capable of realizing objects, again by extrusion printing, using composite materials constituted by a polymeric matrix and by metal or ceramic fillers. However, the latter are in the form of particulate matter or short fibres that are dispersed in the matrix prior to the printing process.

Accordingly, such apparatuses are limited as concerns the use of composite material, as they cannot be used to extrude continuous fibre composite material, that is to say, material having a long fibre that is deposited in the extrusion stage.

In this regard, it should be specified that 3D printing of continuous fibre composite material offers numerous advantages, mainly deriving from the possibility of realizing any 3D form, using resins, including thermosetting resins, optimizing fibre orientation, thus maximizing performance of the printed object and not necessarily using supports for the hollow and/or projecting parts.

In fact, in the case of 3D printing of objects reinforced with long or short fibres for example, the use of thermoplastic matrices leads to intrinsic limitations regarding the mechanical performance and the durability of these objects.

To realize objects having hollow internal parts, printing with a conventional composite material (i.e., with short fibres) necessarily calls for the use of supports that define the cavity of the form and on which the extruded material is deposited. This support is eliminated upon completion of the printing process for the object.

Generally, long-fibre composite material is used to realize hollow portions, or sections spaced away from the supporting base, owing to the supporting capacity of the fibre, thus eliminating the use of the above-mentioned supports.

To enable the printing of continuous fibre material, apparatuses such as those described in patent application US2014/0061974 are used for example; they have a continuous long-fibre feed system, suitable for conveying the fibre to the extrusion head.

In particular, in this solution, the extrusion head has a lateral inlet (with respect to the feed direction) for the fibre, which comes out from the extrusion opening together with the respective polymeric matrix.

The material is thus realized directly in the extrusion head, joining the fibre with the matrix during extrusion of the composite material.

Moreover, in this solution, extrusion of the matrix determines an outlet flow of the matrix, which, as it joins with the fibre, directs the fibre out from the extrusion head.

In other words, the fibre is supplied by the effect of the advancement of the matrix (in the liquid state), which has a suitable viscosity capable of adhering and directing the fibre out of the print head.

Although this solution is capable of printing a continuous fibre composite material with thermosetting matrices, it does, however, have a significant drawback.

In the first place, it should be considered that the step of joining the fibre with the matrix does not ensure proper distribution of the liquid matrix along the entire extension of the continuous fibre.

This inconvenience originates precisely from the fact that the fibre is supplied simultaneously with the matrix only in the extrusion stage. Accordingly, the contact between the fibre and the matrix is not always sufficient for proper impregnation of the fibre.

This drawback becomes even more serious with the use of continuous fibres obtained from very compact strands that thus block internal impregnation of the fibre. In this case, the matrix is deposited only on the external surface of the fibre, creating a composite material the final structure of which is not homogeneous.

Additionally, the material making up the matrix (polymer resin) also makes proper impregnation of the fibre difficult. In fact, as defined above, in this case the resin must necessarily have a particularly high viscosity in order to be extruded.

As a result, proper impregnation of the fibre proves to be even more difficult with high-viscosity resins, which thus have greater difficulty in penetrating between the fibre filaments.

By contrast, the use of a resin that is less viscous and therefore capable of impregnating the fibre to a greater degree would lead to a significant disadvantage in the procedures for drawing the fibre. In this situation, the fibre would not be drawn by the resin, which, because it has a very low viscosity, would not be capable of adhering to the fibre itself.

In this context, the technical task underlying the present invention is to offer an apparatus and a method for three-dimensional printing of continuous fibre composite materials which overcome the above-mentioned drawbacks of the prior art cited hereinabove.

In particular, an aim of the present invention is to make available a three-dimensional printing device and relative method that are capable of printing using continuous fibre composite materials, with the consequent advantages resulting precisely from the use of a long fibre and from the use of thermosetting resins.

Specifically, an aim of the present invention is to make available a device and a relative method for three-dimensional printing using continuous fibre composite materials which are capable of properly realizing the composite material, uniformly impregnating the fibre with the respective matrix.

Even more specifically, an aim of the present invention is make available a device and a relative method for three-dimensional printing of continuous fibre composite materials, said device and method being versatile and thus usable with any type of fibre and matrix, without jeopardizing the structural characteristics of the material itself.

A further aim of the present invention is to offer an apparatus and method for three-dimensional printing using continuous fibre composite materials, said apparatus and method being versatile and simple and in terms of structure and the costs of realization.

The defined technical task and the specified aims are substantially achieved by an apparatus and method for printing continuous fibre composite material, comprising the technical characteristics set forth in one or more of the appended claims.

In particular, the present invention comprises an apparatus for three-dimensional printing of continuous fibre composite materials that has a feed head for feeding a continuous fibre compound material and that is configured to print a three-dimensional object. Also provided is a means for relative movement between the feed head and the three-dimensional object so as to exert a drawing force on the continuous fibre compound material and thus feed the material out from the head. The compound material is realized in a station arranged upstream of the feed head.

In a similar manner, the present invention also comprises a method for three-dimensional printing of continuous fibre composite materials, in which the material is realized by immersing a continuous fibre in a resin. Subsequently, the compound material thus formed is supplied from the print head so as to print the three-dimensional object.

This feeding process is implemented by exerting a drawing force on the compound material by means of relative movement between the feed head for feeding the material and the three-dimensional object

With reference to the attached figures, an apparatus for three-dimensional printing of continuous fibre composite materials3is indicated in its entirety by the number1.

In particular, the present invention is suited to printing a compound material2made up of at least two steps: at least one continuous fibre3(or long fibre), which has the task of sustaining the fillers; the matrix, which keeps the fibres3joined together, protecting them from the external environment; and possibly other additives and reinforcements.

Referring toFIG. 1, a number of fibres3, suitably joined together in a step of realizing the compound material2, can be processed so as to constitute a single body. The fibres3can also be constituted by different materials, including for example glass fibre, carbon fibre, Kevlar fibre, basalt fibre, natural fibres, etc.

The fibres3, which must be supplied continuously, are preferably collected on an element4, such as a cylindrical spool5around which the fibre3is wound. Advantageously, during the printing stages, the spool5is unwound for continuous feeding of the fibre3. As illustrated inFIG. 1, in the case of a plurality of different fibres3, a spool5is provided for each fibre.

As regards the matrix, a resin6in the liquid state is used, particularly a thermosetting resin6for example an epoxy, acrylic, polyester resin etc., that can be reticulated by using various stimuli added to the system (light radiation, heat energy, chemical stimuli including contact between reactive components etc.).

In particular, the apparatus1comprises a station7for realizing the compound material2.

The station7is arranged upstream of a feed head8for feeding the compound material2suitable for printing a three-dimensional object10, as shall be clarified in further detail herein below in this description.

In further detail, the station7for realizing the compound material2has at least one basin9for containing the above-mentioned resin6and inside of which at least one fibre3is immersed.

Advantageously, the continuously fed fibre3that is unwound from the respective spool5is passed inside the basin9. In this situation, the fibre3is completely immersed in the resin6.

Passage of the fibre3in the resin6thus ensures proper impregnation of the fibre3, guaranteeing homogeneous distribution of the resin6on the respective fibre3. In this regard, it should be specified that a longer or shorter length of time for the fibre3to remain in the basin9can be pre-established as a function of the viscosity of the resin6and the structure of the fibre3.

Advantageously, for particularly viscous resins6and/or for fibres3constituted by very compact filaments, passage inside the basin9is prolonged so as to ensure proper (homogeneous) impregnation of the fibre3with the resin6.

In this regard, a plurality of basins9can also be provided, arranged in a series so as to implement a repeated passage of the fibre3inside each basin9containing the resin6, and/or even chemically different resins, useful for example for chemical activation using bicomponent systems. This solution, which is not illustrated in the attached figures, is also aimed at providing greater and homogeneous impregnation of the fibre3with the resin6, as well as at providing for versatility in the production of composites having different and optimized matrixes.

With reference to the attached figures, the station7for realizing the compound material comprises a feed line11for feeding the continuous fibre3and that is suitable for guiding the same fibre3from the above-mentioned collection element4, through the basin9, and to the feed head8.

In particular, according to the first embodiment shown inFIG. 1, the feed line11is made up of a plurality of idler rollers12that are mounted idly or motorized, as a function of the complexity of the fibre feed line.

It should be specified that there may be any number of rollers12and any arrangement thereof, as a function of the extension of the line11and as a function of the length and the path that the fibre3must travel during its advancement.

In the solution illustrated by way of example inFIG. 1, which is thus non-limiting, three rollers12are provided, arranged between the collection elements4and the basin9, inside the basin9, and between the basin9and the feed head8, respectively.

In particular, the first roller12arranged upstream of the basin9correctly directs the fibre3inside the basin9. The second roller12arranged in the basin9is suited to keeping the fibre3immersed in the resin6during advancement of the same fibre3.

The third roller downstream of the basin9directs the compound material2formed in the basin9to the feed head8.

Note also that in this solution, the basin9is detached from the feed head8. This basin9, which is open inFIG. 1in order to show the resin6contained therein, is preferably shielded from any source of interference with the activation of the resin6and/or degradation of the resin itself (e.g. light radiation, heat, moisture, oxygen, etc.).

This shielding is of a known type and therefore not described in detail herein; it is necessary in that the resin6, for example in the case in which it is a photopolymer that can be polymerized, transitioning from a liquid to a solid state, by the action of light.

In accordance with a second embodiment shown inFIG. 2, the basin9containing the resin is constituted by a feeder13that has a first open inlet end13afor the continuous fibre3, and opposite the first end13a, a second open exit end13b(partially visible inFIG. 2) for the compound material2.

In this situation, the feed line11may not have idler rollers in that the fibre3can be directly supplied inside the first open end13aof the feeder13containing the resin6.

Moreover, in the present embodiment, the second open end13bdefines the above-mentioned feed head8for feeding the compound material2.

In other words, the feed head8is in fact constituted by the second end13bof the feeder13from which the compound material2realized inside the same feeder13exits.

In particular, the feed head8comprises an outlet nozzle14for the compound material2, and which in the embodiment shown inFIG. 2is constituted by the second end13bof the feeder13.

The nozzle14has a section for passage of the compound material2dimensioned as a function of the cross section of the fibre3. In fact, the fibre3must have cross-sectional dimensions that are identical to the section for passage of the nozzle14so as to prevent excess resin6from dripping from the nozzle14or drops of resin6from forming on the fibre3, thus creating defects in the final product.

The head8further comprises a polymerization member15arranged at the nozzle14, for polymerizing the material leaving the above-mentioned nozzle14and for defining the composite material.

The polymerization member15can be of various types, according to the resin6and the respective reticulation characteristics.

According to a first embodiment, the polymerization member15can be of a type using electromagnetic radiation.

In this case, the member15can for example be constituted by at least one UV light LED, or a laser emitter (FIG. 1a), or any other source of electromagnetic radiation positioned on the feed head8and directed in an exit zone for the material2leaving the nozzle14.

In a second embodiment, the polymerization member15can be constituted by a heat-emitting source provided to heat the material2leaving the nozzle14. Polymerization members15of this type are used in the case of heat-activated resins and they are generally based on the supply of a flow of warm air or a laser source.

According to a further embodiment, the polymerization member15can also be constituted by an activator of a chemical type, which, in contact with the resin6, reacts by polymerizing the same resin6. In particular, in this case the resin6is a bicomponent resin in that the two components of the resin6are joined so as to implement the above-mentioned reaction.

Advantageously, the chemical reaction step can be implemented upstream of the feed head8through passage of the fibre in a series of tanks containing respective components, which, in contact with each other, activate the polymerization reaction. In this case, the step of reticulating the resin6continues during extrusion of the material2from the head8and it is completed once the material has been deposited so as to form the object10.

Alternatively, the chemical substance for activating polymerization can be sprayed on the fibre along the above-mentioned feed line11.

Additionally, the polymerization member15can be of a combined type and thus implement different steps of resin reticulation.

For example, the polymerization step can be constituted by a first step of a type with electromagnetic radiation to activate only one part of the resin6, obtaining a semi-finished product, and a second step of a thermal type to complete the polymerization process. The second reticulation step can be implemented following deposition of the material2.

The type of polymerization (thermal and/or light and or chemical polymerization) and the sequence of partial activation of the reticulation steps are defined as a function of the reticulation times of the resin and the need to obtain a semi-finished product.

Advantageously, in the case of photo-activated and/or heat-activated resins, to prevent reticulation of the resin6before the latter is actually extruded, a nozzle14is used that is capable of shielding the same resin from the polymerization apparatus (e.g. a nozzle made of metal but also of a shielding polymer material, of a ceramic material etc.).

The kinetics of the reticulation of the resin6influences the printing speed (generally on the order of seconds) and therefore the time needed to realize the object10is directly dependent upon the reticulation rate of the resin6.

The position, distance, intensity and wavelength of the light radiation, in the case of photo-activated resins, are thus essential parameters for the optimal realization of a manufactured article, as is the intensity of the heat radiation in the case of heat-activated resins. Advantageously, in the case of photo-activated resins, to optimize the reticulation process, the wavelength of the light emitted by the source is made to coincide with the absorption peak of the initiator of the photo-reticulable resin.

According to the embodiment shown inFIG. 1, the feed head8also has an inlet hole8aof the compound material2, arranged on the opposite end with respect to the nozzle14; said feed line11feeding the material2inside said hole8a.

The feed head8can further comprise a cutting member16for cutting the compound material2and configured to interrupt the supply of the material2leaving the nozzle14.

As illustrated in greater detail in the enlargement appearing inFIG. 1a, the cutting member16is preferably constituted by a pair of blades17that are movable towards/away from each other to cut the compound material2upon completion of the feeding step and to obtain single pieces of material2.

In this case as well, the movement system for moving the blades17is not described in detail as it is of a known type.

The feed head8is advantageously supported by respective means18for relative movement between the same feed head8and the three-dimensional object10.

During the feeding of the compound material2, the movement means18exerts a drawing force on the compound material2and thus also on the continuous fibre3.

In other words, the relative movement between the head8and the object10determines a drawing action on the material2during the extrusion process thereof. Accordingly, this drawing force is also transferred to the fibre3, which is unwound from the respective spool5(mounted rotatably or adequately motorized, to unwind the fibre). Note that this drawing force brings about the feeding of the same fibre along the feed line11, through the basin9and inside the head8. Accordingly, the greater the relative speed, the faster the advancement of the fibre along the line (and thus the shorter the time that the fibre3will remain in the resin6).

In further detail, the movement means18comprises at least one machine19having numerically controlled movement along at least three axes.

According to the first embodiment shown inFIG. 1, the numerically controlled machine19comprises a motorized arm20for supporting the above-mentioned feed head8at a respective end portion21.

The motorized arm20, which is not described or illustrated in detail in that it is of a known type, is suitable for moving the head in the three spatial axes, orienting the head8according to any position with respect to the object10and with respect to a support surface22on which the object10is positioned in the printing process.

In the embodiment appearing inFIG. 2, the numerically controlled machine19has a frame23within which the above-mentioned support surface22extends.

The frame23has suitable carriage slide guides for moving a carriage24along a first direction. The carriage24, in turn, movably supports an actuator25for advancing the same actuator25along a second axis perpendicular to the first axis.

The actuator25sustains the feeder13and therefore the respective feed head8and it is in turn equipped with a movement system for moving the feeder13and the head8along a third axis perpendicular to the first and the second axis.

In this manner, the head8is pivotable along the three spatial axes for realization of the object10.

Note that the support surface22, which is arranged below the feed head8, can, in turn, be movable towards/away from the feed head8. In this case, the actuator25can sustain the feeder13in a fixed manner, in that the movement along the third axis is determined by the movement of the support surface22with respect to the head8.

The present invention also regards a method for three-dimensional printing of continuous fibre composite materials which comprises the steps of: realizing a compound material2by immersing the continuous fibre3in the resin6; and feeding the previously formed continuous fibre compound material2.

This feeding process is implemented by exerting a drawing force on the compound material by means of relative movement between the feed head8and the three-dimensional object10.

In other words, by moving the head8by means of the action of the numerically controlled machine19, the material2that is gradually deposited so as to form the object10is drawn with consequent feeding of the material2and the fibre3.

Advantageously, drawing of the material2also involves feeding the fibre3, which is suitably directed so as to pass into the basin9containing the resin6.

In further detail, to implement the printing process, the compound material2leaving the head8is initially distributed on the respective support surface22. At this point, the material2is polymerized by the member15on the support surface22so as to define an anchoring point26for anchoring the compound material2.

In other words, at the beginning of the process of depositing the compound material2, part of the material2is already projecting out of the nozzle14. When the apparatus1begins the printing process, the member15polymerizes the resin6, enabling adhesion of the fibre3to be support surface22. The anchoring point26is thus formed and it enables the material2that has already been deposited and polymerized to draw, as the numerically controlled machine19moves, the fibre3upstream of the head8.

The material2that is gradually supplied from the head8is polymerized and made to adhere to the other layers already deposited (by virtue of the adhesive characteristics of the resin6), thus enabling the continuous drawing action affecting the fibre3.

The feed head to8is thus moved by the machine19according to a predetermined path that defines the object10to be printed. This path is determined by suitable management software that is not described in the present description in that it does not fall within the scope of the invention.

At the end of the printing process, or in any case when continuous feeding of the material2must be interrupted, the material is cut by the blades17as described above (and then it continues to be deposited in another point of the printing plate).

Advantageously, the method described hereinabove makes it possible to realize manufactured articles without necessarily having to carry out conventional linear “slicing”, that is to say, the division of the object to be printed into layers in a manner parallel to the printing plane. There being no constraints imposing the use of conventional slicing for construction of the object10, any form in three-dimensional space can be followed in the present invention. The impregnated fibres3that are extruded are particularly suited to this implementation in that when the head8traces a line in the space, by feeding the material2, simultaneous reticulation of the resin6toughens the fibre3, which is capable of sustaining deformations in the subsequent steps of the process.

Moreover, by using optimized software for non-linear “slicing”, it is possible to design and realize objects10orienting the fibres3along the direction of maximum stress. In this situation, the apparatus can be advantageously equipped with additional axes of rotation or even with robotic arms to increase its capacity to produce three-dimensional forms.

As regards the structure of the material2, the method can also comprise a pre-impregnation step for pre-impregnating the fibres when the latter are in the form of thin filaments and then assemble the filaments to form the fibre3or more complex structures like cords, braids, etc.

This solution entails the use of a system of idler rollers and basins through which the thin filaments are passed before being conveyed to the feed head8. The fibres3can also be pre-treated so as to improve chemical adhesion with the resin6.

Moreover, the step of realizing the compound material2can comprise the additional substep of mixing particulate and/or fibrous fillers into the compound material2following passage of the fibre3inside the basin9. In this manner, the formation of the compound material2proves to be more versatile in that it can be obtained with any type of substance according to various needs regarding realization. For example, owing to the use of fibrous fillers, the joining of the layers in the step of depositing the material2can be improved.

In addition, in a further, alternative embodiment, the resin is partially reticulated before the whole material2is deposited.

In this manner, the fibre3obtained can be more easily managed compared to a filament impregnated only with a liquid resin, and at the same time, it is sufficiently flexible to be extruded and deposited without problems.

This solution is particularly advantageous in the case in which the fibres3processed are of a material that obstructs to a greater degree the reticulation of liquid photo-reticulable resins6such as carbon, Kevlar, etc.

The present invention resolves the problems observed in the prior art and leads to the significant advantages.

Firstly, it should be noted that the apparatus1and the relative method for three-dimensional printing make it possible to realize the continuous fibre composite material properly. In other words, the present invention enables proper and homogeneous impregnation of the fibre3with the respective liquid resin6.

This advantage is offered precisely by the step of realizing the material in which the fibre3is immersed in the basin9containing the resin6. The time the fibre3remains inside the basin9is defined and measured as a function of the characteristics of the materials used, so as to ensure proper formation of the material at all times, regardless of the structure of the fibre3and/or the viscosity of the resin6.

A further advantage of the present invention is determined by the step of feeding the compound material2, which ensures proper dispensing and deposition of the material2that will constitute the object10.

As described above, the feeding of the material2is determined by the relative movement between the head8and the object10, which involves a drawing action affecting the fibre3. Accordingly, the material2is supplied from the head8only after movement of the same head8and the feeding thereof does not depend on the structure (viscosity) of the resin.

Accordingly, the printing apparatus1and the relative method prove to be versatile and they can be used for any type of continuous fibre composite material.