Method and apparatus for impregnating a fiber bundle and system for producing a structure

Abstract

The present invention comprises a method for impregnating at least one fiber bundle (12) with a plastic material, wherein the method comprises the following steps: - Providing at least one fiber bundle (12) to be impregnated, which is formed from a plurality of continuous fibers, and a plastic material which is melted at a specified process temperature, - Impregnating the fiber bundle (12) with the plastic material by passing the fiber bundle (12) to be impregnated through an impregnation cavity (19) filled with the molten plastic material (13) with a certain fiber tension, wherein - the fiber tension of at least the part of the fiber bundle (12) which is passed through impregnation cavity (19) is varied during the passage.

Description

[0001] The invention relates to a method for impregnating at least one fiber bundle with a plastic material. The invention also relates to a device for this purpose.

[0002] The invention also relates to a system for producing a three-dimensional structure formed from two or more different materials, using a 3D print head.

[0003] Due to their exceptional strength-to-weight ratio and stiffness, fiber-reinforced composites have become indispensable as modern materials. The combination of fiber and polymer materials in 3D printing also opens up new possibilities for the production of complex structures without the need for isotropic materials. Both in the production of fiber-reinforced composite components and in 3D printing with fiber reinforcement, fiber rovings are very frequently used. These rovings are a type of fiber bundle composed of numerous continuous fibers, also known as filaments.

[0004] German patent application DE 10 2017 124 352.6 discloses a system for producing three-dimensional structures made of two or more different materials. In this system, a 3D print head is fed both a quasi-continuous fiber material, for example in the form of rovings, and a thermoplastic polymer material. These materials then enter a mixing chamber where the fiber material is impregnated with the thermoplastic polymer material. The resulting material mixture is then extruded through an outlet of the 3D print head to produce the three-dimensional structure.

[0005] However, the impregnation of quasi-endless fiber rovings with thermoplastic material is currently unsatisfactory due to the high viscosity of the thermoplastic material and the low permeability of the continuous fibers, especially when the fiber material is to be continuously conveyed and extruded.

[0006] It is a well-known and widely used practice to first spread the fiber rovings, i.e., to fan them out horizontally. For this, the fiber roving is typically guided over several specially shaped rollers, which are designed to increase the cross-section of the fiber bundle and thus the distance between the individual filaments. This reduces the required penetration depth of the molten plastic material and increases the permeability of the fibers. Subsequently, the molten plastic material is brought into contact with the spread fiber under pressure at one or more points for an extended period to impregnate it.

[0007] For example, EP 0 712 716 A1 discloses a method for impregnating continuous fibers or fiber bundles with a molten thermoplastic polymer, wherein the fibers or rovings pass through an impregnation zone which has the form of a damped vibration.

[0008] From US patent 2012 / 0040106 A1, a method and a device for impregnating a fiber material with a matrix material are known, in which the fiber material is placed in a mold and subsequently infused with the matrix material. During the infusion of the fiber material with the matrix material, vibrations are generated using loudspeakers or sound generators to improve the impregnation result.

[0009] From DE 102016 107 956 A1, a process for impregnating continuous fibers for the production of fiber-reinforced semi-finished products is known, wherein several individual fibers are first combined to form a common fiber bundle and impregnated with the plastic material. Subsequently, the fiber material impregnated with the plastic material is extruded onto a cooled roller, where it is in operative contact with a sonotrode in such a way that the fiber material is excited by ultrasonic vibration in conjunction with the matrix material by means of the sonotrode.

[0010] JP 2003 / 039430 A describes a method for impregnating a fibrous material continuously passed through a container filled with plastic, wherein a plate-shaped ultrasonic generator is arranged at the bottom of the container. The vibration excitation is intended to improve the impregnation and reduce the occurrence of air bubbles in the plastic.

[0011] The methods known from the prior art for impregnating fiber material, especially fiber bundles, with a highly viscous polymer material, such as a thermoplastic polymer, have several disadvantages. For example, fiber spreading processes require a relatively large amount of installation space because the fibers must be redirected multiple times. To prevent damage to the fibers, maximum permissible bending radii must be observed. Furthermore, the multiple redirections increase friction and thus require a greater tensile force on the fiber. This force must be ensured by the process to allow for continuous fiber guidance. The applied tensile force must not exceed a maximum permissible value to prevent individual filaments of the fiber roving from breaking.

[0012] Processes that operate without or with very little fiber spreading reduce the risk of fiber damage, but require long processing times to achieve sufficient fiber impregnation, which is particularly true for highly viscous plastic materials. This is because high fiber roving conveying speeds typically generate high tensile forces, which reduce the roving's permeability. Reducing the permeability, i.e., the penetrability of the dry fiber roving, makes reliable impregnation more difficult. In practice, the conveying speed is reduced to address this problem, resulting in a longer residence time of the fiber roving in the melt. However, this leads to longer processing times and higher unit costs.

[0013] Against this background, the object of the present invention is to provide an improved method and an improved device with which, in particular, fiber rovings can be impregnated quickly and reliably with a plastic material.

[0014] The problem is solved by the method for impregnating a fiber bundle according to claim 1 according to the invention. Advantageous embodiments of the invention are then found in the corresponding dependent claims.

[0015] According to claim 1, a method for impregnating at least one fiber bundle with a plastic material, in particular a high-viscosity plastic material, is proposed, wherein first, at least one fiber bundle to be impregnated, which is formed from a plurality of continuous fibers, and a plastic material that has been melted at a predetermined process temperature are provided. Subsequently, the fiber bundle is impregnated with the plastic material by passing the fiber bundle to be impregnated through an impregnation cavity filled with the molten plastic material under a certain fiber tension.

[0016] A high-viscosity plastic material is defined here as one that has a viscosity of significantly more than 8000 mPas (millipascal-seconds) at a given process temperature. This is distinct from low-viscosity plastic materials, which have a viscosity up to 300 mPas. Viscosities between 300 mPas and 8000 mPas are considered medium. Thermoplastic materials, commonly used in hybrid 3D printing, often exhibit a viscosity of 300 Pa to 10,000 Pa. Depending on the degree of shear stress exerted on the plastic material when it comes into contact with the fiber, the viscosity can also be significantly below the typical zero viscosity (3000–10,000 Pa). The given process temperature refers to the temperature at which the plastic material is used for impregnation.In the case of thermoplastic materials, this is in particular the temperature at which the plastic material is melted and can thus impregnate the fiber bundle accordingly.

[0017] The provided fiber bundle is then impregnated with the plastic material by continuously passing the fiber bundle to be impregnated, for example a roving, through an impregnation cavity. Continuous passing means, in particular, that at the exit of the impregnation cavity, the fiber bundle impregnated with the plastic material is dispensed and conveyed without interruption at a certain speed for a predetermined process time.

[0018] The impregnation cavity contains the tempered and molten plastic material, so that when the fiber bundle is passed through the cavity, it is completely encased in the molten plastic. The cavity can be filled with the plastic material in such a way that no air is present during the impregnation process. Naturally, the system can be designed to continuously supply fresh plastic material to the impregnation cavity as the fiber bundle is passed through, thus ensuring a continuous impregnation process. Furthermore, the impregnation cavity can also be equipped with a temperature control device to heat it to the specified process temperature of the highly viscous plastic material.It is therefore advantageous if, during the continuous passage of the fiber bundle through the impregnation cavity, new plastic material is continuously added to the impregnation cavity and / or the plastic material in the impregnation cavity is continuously tempered, in order to keep it at the desired process temperature.

[0019] It can advantageously be provided that during the impregnation of the fiber bundle, the molten plastic material located in the impregnation cavity is in contact with a surface of at least one vibration generator in such a way that sound energy is introduced into the molten plastic material of the impregnation cavity by means of the vibration generator.

[0020] According to the invention, it is now provided that the fiber tension of at least the part of the fiber bundle which is passed through the impregnation cavity is varied during the passing process.

[0021] By varying the fiber tension of at least the portion of the fiber bundle currently in the impregnation cavity, the permeability of that portion is temporarily increased, thus improving the impregnation process due to better penetration by the plastic material. This allows for higher conveying speeds without compromising impregnation quality. Furthermore, the mechanical spreading of the fiber bundles can either be completely eliminated or significantly reduced.

[0022] Furthermore, in combination with a vibration generator and the introduction of sound energy into the molten plastic material, it has been shown that this results in a significantly better impregnation of the part of the fiber bundle where the fiber tension is temporarily reduced, for example.

[0023] Varying the fiber tension refers specifically to a continuous, cyclical decrease and increase of the fiber tension throughout the entire conveying process. The fiber bundle is continuously guided through the impregnation cavity, with the variation of the fiber tension—i.e., the cyclical decrease and increase—occurring during this continuous passage through the impregnation cavity, without interrupting the actual continuous conveying process.

[0024] Besides reducing fiber tension to increase permeability, it is also possible to increase fiber tension so that the natural frequency of the fiber bundle lies within the range of the oscillation frequency of a vibration generator. The vibration generator introduces sound energy into the molten plastic material, causing it to pulsate at the generator's frequency. It has been shown that impregnation can be improved when the fiber bundle's natural frequency lies within a range of the pulsating plastic material's frequency, which typically corresponds to the vibration generator's frequency. The fiber bundles, or even the individual fibers within the bundle, also begin to oscillate strongly, which significantly enhances the impregnation process.

[0025] It is conceivable that the clamping distance of the fiber bundle is reduced. This clamping distance is limited by the clamping points and defines the freely vibrating length of the fiber bundle. If this clamping distance is shortened in the impregnation cavity, for example by reducing the distance between the clamping points, this also increases the vibration frequency of the fiber bundle.

[0026] Therefore, according to one embodiment, the clamping distance of the fiber bundle, which is limited by two clamping points, is varied in order to vary the freely oscillating clamping length of the fiber bundle. This ensures that the natural frequency of the fiber bundle is adapted to the frequency present in the molten plastic material or, with (continuous or alternating) variation of the free clamping length, is at least temporarily within the correct frequency range.

[0027] The clamping points can be, for example, the entry and exit points of the impregnation cavity.

[0028] According to one embodiment, the fiber bundle is introduced into the impregnation cavity at an entry point and led out of the impregnation cavity at an exit point, with the fiber tension of the fiber bundle being varied between the entry point and the exit point during the passage.

[0029] In this embodiment, the fiber tension within the impregnation cavity is varied by a suitable device, i.e., increased or decreased, so that at least temporarily (for example, cyclically at discrete intervals) the fiber tension of the fiber bundle in the impregnation cavity is reduced to such an extent that an improvement in impregnation is achieved. This reduction can be so significant that essentially no fiber tension remains and the fiber bundle is essentially loose in the impregnation cavity for a period of time.

[0030] According to one embodiment, the length of the fiber bundle between the entry point and the exit point is varied during the fiber routing process in order to vary the fiber tension.

[0031] In this process, the length of the fiber bundle between the inlet and outlet of the impregnation cavity is temporarily increased and then reduced again to the minimum length (defined by the conveying path between the inlet and outlet), whereby the fiber bundle has a higher permeability during the temporarily increased length and thus the impregnation is better.

[0032] In combination with a vibration generator, the maximum possible vibration of the roving or fiber bundle as well as the individual fibers is increased, which also leads to an improvement in impregnation.

[0033] An increase in the length of the fiber bundle between the entry and exit points of the impregnation cavity is defined as an increase in length compared to the minimum length defined by the conveying path between these points. The conveying path is defined as the distance the fiber bundle must travel through the impregnation cavity without any variation or increase in length. This includes the path the fiber bundle must take due to deflection rollers. It is therefore the path the fiber bundle is forced to take through the impregnation cavity when the conveying-induced fiber tension is applied to the fiber bundle within the cavity.

[0034] According to one embodiment, it is provided that the fiber bundle is deflected between a first point and a second point, in particular orthogonally to a connecting line between the points, by a deflection force acting on the fiber bundle until a maximum deflection is reached, wherein the deflection force acting on the fiber bundle is then reduced in such a way that the fiber tension of the fiber bundle between the two points is reduced.

[0035] This first point and this second point can be the entry and exit points of the impregnation cavity.

[0036] The fiber bundle is deflected between these two points to a maximum deflection, which typically lengthens the path the fiber bundle travels between the points. This results in a temporary increase in fiber tension. Subsequently, the deflection force required is reduced to such an extent that the fiber tension decreases below the normal, conveying-related fiber tension. This can be achieved, for example, by a sudden or rapid, continuous decrease in the deflection force required, creating a kind of material-free state.

[0037] This deflection of the fiber bundle, especially orthogonal to the connecting path between the points, leads to an extension of the conveying path, whereby when the deflection ends, there is an excess length of the fiber bundle, which reduces the fiber tension and improves the impregnation through increased permeability.

[0038] According to one embodiment, the fiber bundle is guided between the points via an eccentrically mounted deflecting roller, which rotates around a center point in such a way that the fiber bundle is deflected, in particular orthogonally to the connecting path between the points.

[0039] Due to the eccentricity of the eccentrically mounted deflection pulley, the fiber bundle is continuously deflected in one direction as the pulley rotates around its center point. This causes the distance traveled by the fiber bundle between the two points to vary continuously as the pulley rotates around its center point. Consequently, the fiber tension also continuously increases and decreases, thus varying as well.

[0040] The frequency of the fiber tension variation can be adjusted by changing the rotational speed. The prevailing fiber tension can be adjusted by changing the distance of the eccentrically mounted deflection pulley from the center point.

[0041] According to one embodiment, the fiber bundle is guided between the points over a translationally moving deflecting roller, which moves in particular orthogonally to the connecting section such that the fiber bundle is deflected in particular orthogonally to the connecting section between the points.

[0042] The direction of the translational movement alternates, so that the distance traveled by the fiber bundle during the cycle increases and decreases. When the distance traveled decreases, the tensile stress is reduced, thereby improving the impregnation.

[0043] According to one embodiment, it is provided that the fiber bundle is gripped at a gripping point by an intermittent advance and pulled forward in such a way that the fiber tension in the conveying direction is increased in front of the gripping point and reduced behind the gripping point, and / or that the fiber bundle is gripped at a gripping point by an intermittent retraction and retracted in such a way that the fiber tension in the conveying direction is reduced in front of the gripping point and increased behind the gripping point.

[0044] In this process, the fiber material is either accelerated or decelerated at the gripping point, resulting in a lower fiber tension in the fiber bundle, depending on the outcome.

[0045] According to one embodiment, the fiber bundle is guided over a deflecting roller that rotates with or against the conveying direction.

[0046] This dynamically varies the rope friction (eytelwein) at the pulley, thereby reducing and varying the fiber tension accordingly in front of or behind the pulley.

[0047] According to one embodiment, the variation of the fiber tension is provided for at intervals of more than 1 millisecond and less than 5 seconds and / or that the variation of the fiber tension is between 0 Newtons and 100 Newtons or between 0 N / mm². 2 and 3000 N / mm 2 , preferably between 0 Newtons and 100 Newtons or between 0 N / mm 2 and 2000 N / mm 2 This occurs. The fiber tension can range from 0 N / mm². 2 and 100 N / mm 2 vary.

[0048] According to one embodiment, it is provided that during the impregnation of the fiber bundle, the molten plastic material located in the impregnation cavity is in contact with a surface of at least one vibration generator in such a way that sound energy is introduced into the molten plastic material of the impregnation cavity by means of the vibration generator.

[0049] The at least one vibration generator can have a surface that is in direct contact with the molten plastic material in the impregnation cavity. The vibration generator is designed to produce a vibration that is then transmitted to the plastic material in the form of sound energy via the surface in contact with the plastic material. The vibrations of the vibration generator thus generate sound waves or pressure waves within the molten plastic material, which then cause the plastic material to penetrate deep into the fiber bundle, thereby wetting the individual filaments or continuous fibers. In particular, the spaces between the individual filaments are wetted.The continuous fibers of the fiber bundle are coated with the plastic material, so that a very high impregnation quality can be achieved, even if the fiber bundle is continuously passed through the impregnation cavity.

[0050] According to an advantageous embodiment, the plastic material is a thermoplastic material. Advantageously, the plastic material, which is molten at the specified process temperature, is highly viscous, i.e., has a viscosity of more than 8000 mPas.

[0051] According to a further advantageous embodiment, the vibration generator produces a vibration amplitude between 1 µm and 150 µm and / or a vibration frequency between 100 Hz and 100 kHz, preferably between 20 kHz and 60 kHz. This allows sound energy to be introduced into the highly viscous plastic material, ensuring a very high impregnation performance despite the technical challenges posed by the highly viscous medium.

[0052] According to a further advantageous embodiment, the vibration generator excites real and / or complex eigenmodes of a structure within the impregnation cavity. It has been shown that, despite the viscoelastic effect of the plastic material, sufficient sound power or sound energy can still be introduced into the plastic material to achieve high impregnation performance. In this embodiment, at least a portion of the surface of the vibration generator is formed by a special, preferably modally vibrating structure, whereby the vibration generator can excite real and / or complex eigenmodes of this structure within the impregnation cavity. Preferably, such a structure or structures are completely covered by the plastic material in the impregnation cavity. Such structures can, for example, be modally vibrating plates within the impregnation cavity.It is also conceivable that such structures could be a tube with its own shape, through which the fiber bundle to be impregnated is passed. This can significantly improve the impregnation performance, even with highly viscous plastic materials. The tube itself can form the impregnation cavity or be part of it.

[0053] The resulting vibration maxima and minima of the structure then act as spatially distributed generators for the coupling of sound energy.

[0054] According to a further advantageous embodiment, the surface of the vibration generator in contact with the molten plastic material is pretreated by microstructuring, roughening, and / or plasma treatment to improve the adhesion or wetting of the vibration generator surface with the molten plastic material. It has been shown that such pretreatment measures improve the surface adhesion or wettability to such an extent that, despite the viscoelastic effect of the highly viscous plastic material, sound waves or pressure waves can be introduced into the molten plastic material to achieve the necessary sound energy for impregnation of the fiber bundle.By increasing the adhesion of the surface of the vibration generator that is in contact with the plastic, it is prevented that even at high frequency and / or high amplitude of the vibration generator, cavities form between the surface of the vibration generator and the molten plastic material, which would prevent the transmission of the necessary sound power.

[0055] According to a further advantageous embodiment, the plastic material is materially modified to reduce the cohesive forces, thereby improving the wetting of the surface of the vibration generator and reducing the cohesive forces.

[0056] The problem is also solved according to the invention with the device for impregnating at least one fiber bundle according to claim 11, wherein the fiber bundle is formed from a plurality of continuous fibers and is to be impregnated with a plastic material that is melted at a predetermined process temperature. The device has an impregnation cavity into which the plastic material is filled or can be filled, wherein the impregnation cavity has an inlet and an outlet such that a fiber bundle can be passed through the molten plastic material of the impregnation cavity for impregnation.

[0057] According to the invention, the device is designed in such a way that the fiber tension of at least the part of the fiber bundle which is passed through the impregnation cavity is varied during the passage.

[0058] The device can be designed to perform the method described above. The device possesses the corresponding device-specific features necessary to execute the method.

[0059] The problem is also solved according to the invention with the system for producing a three-dimensional structure according to claim 13, wherein the system has a 3D print head with a first material feed for supplying a quasi-endless fiber bundle of a fiber material and at least a second material feed for supplying a plastic material that is melted at a predetermined process temperature, which open into an impregnation cavity of the 3D print head to impregnate the fiber bundle with the molten, highly viscous plastic material, wherein the impregnation cavity is communicatively connected to an outlet of the 3D print head, which is configured for extruding the impregnated fiber bundle to produce the three-dimensional structure. The fiber bundle is impregnated using the device described above, which is provided in or on the fiber placement head.

[0060] The invention is explained by way of example with reference to the attached figures. They show: Fig. 1. Schematic representation of a device for impregnation; Fig. 2. Schematic representation of the difference between a high fiber voltage and a low fiber voltage in conjunction with a vibration generator; Fig. 3. Schematic representation of a first embodiment; Fig. 4. Schematic representation of a second embodiment; Fig. 5. Schematic representation of a third embodiment; Fig. 6. Schematic representation of a fourth embodiment.

[0061] Fig. Figure 1 shows a schematically simplified representation of an impregnation device 10, in which a dry fiber material in the form of a fiber bundle 12 is first supplied to the impregnation device 10 by means of a material supply 11. This fiber bundle 12, also called fiber roving, is fed by the material supply 11 to an impregnation cavity 19, which is filled with a molten plastic material 13. The impregnation cavity 19 has an inlet 14 and an outlet 15 for this purpose, through which the fiber bundle 12 can be inserted into and removed from the impregnation cavity 19. Subsequently, the impregnated fiber bundle 12 is wound onto a material storage unit 16 and can thus be used accordingly.

[0062] The Fig. The impregnation device 10 shown in Figure 1 has a vibration generator 17 which is in contact with the molten plastic material 13 via a surface 18. In the case of the Fig. The vibration generator 17 shown in Figure 1 is a longitudinal oscillator which, to introduce sound energy into the plastic material 13 at a predetermined frequency, performs a reciprocating movement in the form of an amplitude. In the exemplary embodiment, the direction of the reciprocating movement is Fig. 1 essentially perpendicular to the fiber bundle 12.

[0063] Due to the fact that the vibration generator 17 with its surface 18 is in direct contact with the molten plastic material 13, the vibrations generated by the vibration generator 17 can be introduced into the plastic material 13 in the form of sound energy in order to improve the impregnation of the fiber bundle 12.

[0064] Using a method only in Fig. In the schematically indicated fiber tension variation device 20, which is located within the impregnation cavity 19, the fiber tension of the fiber bundle 12 is varied, particularly cyclically, during the continuous passage of the fiber bundle 12 through the impregnation cavity 19, so that at certain time intervals the fiber tension of the fiber bundle 12 is reduced to such an extent that improved impregnation within the impregnation cavity 19 can be achieved.

[0065] The underlying core idea here is in Fig. Figure 2 shows an impregnation cavity 19 in which the fiber bundle 12 is guided through with conveying-induced fiber tension. This conveying-induced fiber tension is determined, among other things, by the fact that the impregnated fiber bundle 12 must ultimately be wound onto the material storage 16 and pulled through the impregnation cavity 19. The tensile and frictional forces involved in this process result in the conveying-induced fiber tension.

[0066] The tensile stress applied to the fiber bundle 12 is so high that any vibrations of the fiber bundle 12 or of the individual fibers within the fiber bundle 12 are greatly reduced. As a result, particularly with highly viscous plastic materials, impregnation between the individual fibers of the fiber bundle 12 is insufficient. The energy required for vibration is introduced into the impregnation cavity 19 by means of the vibration generator 17.

[0067] The lower figure shows an impregnation cavity 19 in which the fiber tension has been reduced to such an extent that the fiber bundle can exhibit a larger amplitude during vibration when the corresponding sound energy is introduced into the plastic material 13 of the impregnation cavity 19 using the vibration generator 19. In particular, highly viscous plastic material can now penetrate between the individual fibers of the fiber bundle 12, thereby achieving comprehensive impregnation.

[0068] In the impregnation cavity 19, a pulsating pressure level preferably prevails due to the sound wave introduced by the vibration generator 17 and a related movement of the molten plastic material 13.

[0069] Fig. Figure 3 shows a first embodiment of the fiber tension variation device 20, which is arranged in the impregnation cavity 19. The fiber bundle 12 is guided in the impregnation cavity 19 over an eccentrically mounted deflecting roller 21, which is mounted on a rotary device 22 that rotates about a central point. By rotating the eccentrically mounted deflecting roller 21 with the help of the rotary device 22, the fiber bundle 12 is, in the exemplary embodiment, adjusted with each rotation. Fig. 3 is deflected upwards, which briefly results in an elongation of the fibers of the fiber bundle 12 present in the impregnation cavity 19. Up to this point, the fiber tension of the fiber bundle 12 will increase.

[0070] If the rotational movement continues, the mechanical stroke achieved by the eccentrically mounted deflection roller 21 is reversed, causing the fiber tension to decrease significantly due to the previously generated extension of the path. At this moment, the fiber bundle 12 can be set into optimal vibration using the vibration generator 17 to achieve optimal impregnation.

[0071] When the fiber bundle 12 has regained its conveying-related fiber tension, a new cycle begins in which the eccentrically mounted deflection roller 21 deflects the fiber bundle upwards again, thereby increasing the distance the fiber bundle must travel between the inlet point 14 and the outlet point 15 (path extension). Once the maximum stroke is reached, the deflection is reduced due to the rotation of the eccentrically mounted deflection roller 21, and the process begins anew.

[0072] This achieves a continuous variation of the fiber tension during the passage of the fiber bundle 12, in which a path lengthening and subsequent path shortening of the fibers of the fiber bundle located in the chamber is cyclically effected.

[0073] Fig. Figure 4 shows an embodiment in which the change in path length of the fiber bundle 12 is not controlled by an eccentrically mounted deflection pulley, as Fig. 3, but is realized using a translationally moving deflection pulley 23. This translationally moving deflection pulley 23 has an alternating direction of movement, i.e., in the exemplary embodiment of the Fig. 4 the deflection pulley 23 moves alternately up and down.

[0074] During the upward translational movement, the conveying path of the fiber bundle 12 within the impregnation cavity 19 is increased, the conveying path being defined by the distance the fiber bundle 12 must travel between the inlet point 14 and the outlet point 15. Once the maximum stroke is reached at the upper endpoint by the deflecting roller 23, the deflecting roller 23 moves downwards translationally, thereby reducing the distance traveled again. This movement also reduces the fiber tension, resulting in improved impregnation.

[0075] Fig. Figure 5 shows an embodiment in which the fiber bundle 12 is gripped by an intermittent feeder 24, thus cyclically reducing the fiber tension. In the intermittent feeder 24, the fiber bundle 12 is gripped at a gripping point, for example by clamping jaws, and then pulled in the conveying direction (i.e., towards the exit point 15), thereby temporarily reducing the fiber tension downstream of the intermittent feeder 24 in the conveying direction.

[0076] Once the endpoint of the advance is reached, the fiber bundle 12 is released and the clamping jaws return to their starting position to begin the next cycle.

[0077] Fig. Figure 6 shows a dynamically excited deflection roller 25, which can rotate forwards or backwards and whose surface friction allows the fiber tension to be varied. For example, if the deflection roller 25 rotates in the conveying direction, an increase in fiber tension is achieved upstream of the deflection roller 25 and a reduction in fiber tension downstream of the deflection roller 25.

[0078] If the deflection roller 25 rotates against the conveying direction, a reduction in fiber tension occurs in front of the deflection roller 25 ( Fig. 6), while this results in an increase in fiber tension behind the deflection pulley 25. Reference symbol list 10 Impregnation device 11. Material provision 12 fiber bundles 13 molten plastic material 14 Entrance / Admission 15 Exit / Outlet 16 material storage 17 Vibration generator 18 Surface of the vibration generator 19 Impregnation cavity 20 Fiber voltage variation device 21 eccentrically mounted deflection pulleys 22 Rotating device of the deflection pulley 23 translationally moving deflection pulley 24 intermittent preference 25 dynamically positioned deflection pulleys QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2017 124 352.6

[0004] EP 0 712 716 A1

[0007] US 2012 / 0040106 A1

[0008] DE 102016 107 956 A1

[0009] JP 2003 / 039430 A

[0010]

Claims

[1] Method for impregnating at least one fiber bundle (12) with a plastic material, the method comprising the following steps: - Providing at least one fiber bundle (12) to be impregnated, which is formed from a plurality of continuous fibers, and a plastic material which is melted at a predetermined process temperature, - impregnating the fibre bundle (12) with the plastic material by passing the fibre bundle (12) to be impregnated through an impregnation cavity (19) filled with the molten plastic material (13) with a certain fibre tension, characterized by , that - the fiber tension of at least the part of the fiber bundle (12) which is passed through the impregnation cavity (19) is varied during the passage. [2] Method according to claim 1, characterized bythat the fiber bundle (12) is introduced into the impregnation cavity (19) at an entry point (14) and is led out of the impregnation cavity (19) at an exit point (15), wherein the fiber tension of the fiber bundle (12) is varied between the entry point (14) and the exit point (15) during the passage. [3] Method according to claim 2, characterized by in that, in order to vary the fibre tension, the length of the fibre bundle (12) between the entry point (14) and the exit point (15) is varied during passage. [4] Method according to one of the preceding claims, characterized bythat the fiber bundle (12) is deflected between a first point and a second point by a deflection force acting on the fiber bundle (12) until a maximum deflection is reached, wherein the deflection force acting on the fiber bundle (12) is then reduced such that the fiber tension of the fiber bundle (12) between the two points is reduced. [5] Method according to claim 4, characterized by that the fiber bundle (12) is guided between the points via an eccentrically mounted deflection roller (21) which rotates about a center point in such a way that the fiber bundle (12) is deflected between the points. [6] Method according to claim 4, characterized by that the fiber bundle (12) is guided between the points over a translationally moving deflection roller (23) which moves alternately in such a way that the fiber bundle (12) is deflected between the points. [7] Method according to one of the preceding claims, characterized by that the fiber bundle (12) is gripped at a gripping point by an intermittent advance (24) and is pulled forward in such a way that the fiber tension in the conveying direction is increased in front of the gripping point and reduced behind the gripping point and / or that the fiber bundle (12) is gripped at a gripping point by an intermittent retraction and is pulled back in such a way that the fiber tension in the conveying direction is reduced in front of the gripping point and increased behind the gripping point. [8] Method according to one of the preceding claims, characterized by that the fiber bundle (12) is guided over a deflection roller which rotates with or against the conveying direction. [9] Method according to one of the preceding claims, characterized by that the variation of the fibre tension occurs at intervals of more than 1 millisecond and less than 5 seconds and / or that the variation of the fibre tension occurs between 0 Newton and 100 Newton or between 0 N / mm2 and 3000 N / mm 2 , preferably between 0 Newton and 100 Newton or between 0 N / mm 2 and 2000 N / mm 2 occurs. [10] Method according to one of the preceding claims, characterized by that during the impregnation of the fiber bundle (12), the molten plastic material (13) located in the impregnation cavity (19) is in contact with a surface of at least one vibration generator (17) in such a way that sound energy is introduced into the molten plastic material (13) of the impregnation cavity (19) by means of the vibration generator (17). [11] Device for impregnating at least one fiber bundle (12) formed from a plurality of continuous fibers with a plastic material that is melted at a predetermined process temperature, wherein the device has an impregnation cavity (19) into which the plastic material is or can be filled, wherein the impregnation cavity (19) has an inlet (14) and an outlet (15) such that a fiber bundle (12) for impregnation can be passed through the molten plastic material (13) of the impregnation cavity (19), characterized by that the device is designed such that the fiber tension of at least the part of the fiber bundle (12) which is passed through the impregnation cavity (19) is varied during the passage. [12] Device according to claim 11, characterized by that the device is designed to carry out the method according to one of claims 1 to 10. [13] A system for producing a three-dimensional structure formed from two or more different materials, comprising a 3D printing head having a first material feed for feeding a quasi-endless fiber bundle (12) of a fiber material and at least one second material feed for feeding a plastic material that is melted at a predetermined process temperature, which open into an impregnation cavity (19) of the 3D printing head in order to impregnate the fiber bundle (12) with the molten, highly viscous plastic material, wherein the impregnation cavity (19) is in communication with an outlet (15) of the 3D printing head, which is designed to extrude the impregnated fiber bundle (12) in order to produce the three-dimensional structure, characterized by that the 3D printing head comprises a device according to one of claims 11 or 12.

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