METHOD AND EXTRUSION DEVICE FOR THE EXTRUSION OF FIBER-REINFORCED PLASTIC MATERIAL FOR THE ADDITIVE MANUFACTURING OF A COMPONENT

Description

[0001] The proposed solution concerns an extrusion process and an extrusion device for extruding fiber-reinforced plastic material for the additive manufacturing of a component.

[0002] Extrusion devices, e.g. in the form of screw extruders, are primarily used in the series production of components by injection molding and die casting. They consist of a conveyor screw, an injection nozzle and a die, usually arranged horizontally to one another. The material, which is mainly in the form of granules or powder, is generally filled in the rearmost part of the screw extruder, in the so-called feed zone. The material is fed vertically onto the conveyor screw via a hopper mounted on a pipe section of the extruder. Thanks to a sufficiently large cross-section in the hopper, which prevents bridging, the material falls onto the conveyor screw under the force of gravity and is drawn in by it. In series production, so-called three-zone screw extruders are generally used, which draw in the material and convey it to the nozzle.The material is compressed, deaerated, and homogenized. Pressure is then built up to fill the die.

[0003] The feed zone of a screw extruder is often designed as a pipe cut within the screw extruder's barrel. A hopper is located on this pipe cut through which the material can be fed to the screw. The pipe cut and hopper must be selected with a minimum cross-section to prevent bridging of the granulated material. This depends heavily on the angle of repose and the coefficient of friction of the bulk material used.

[0004] DE 10 2014 018 081 A1 describes a 3D printing device for the additive manufacturing of metallic components. This device also uses a screw extruder that processes granular material. In a movable print head of the 3D printing device, the thermoplastically deformable material is extruded layer by layer using a vertically arranged screw extruder to produce a three-dimensional component. DE 10 2014 018 081 A1 does not provide any further details on how the material is fed to the extruder screw.

[0005] The use of screw extruders for additive manufacturing is primarily limited by their weight and size, which typically depend heavily on the length of the conveyor screw (extruder screw). The screw extruders must either be designed to be movable or the entire build area must be moved. The latter option, however, requires the entire 3D printing device to be significantly oversized. Furthermore, it is typically observed with previously known extrusion processes for additive manufacturing that the desired or even required material strength of the component to be manufactured is difficult or even impossible to achieve when processing fiber-reinforced plastic.

[0006] DE 10 2017 114 841 A1 describes a process for the extrusion of thermomechanically deformable materials as well as a screw extruder of compact design with a length-diameter ratio of 3 - 10.

[0007] Against this background, the proposed solution is based on the task of further improving the processing of fiber-reinforced plastic material for additive manufacturing in order to overcome or at least reduce the disadvantages known from the state of the art.

[0008] This object is achieved by a method of claim 1 and an extrusion device of claim 8.

[0009] In a proposed process for the extrusion of fiber-reinforced plastic material for the additive manufacturing of a component, it is provided that the fiber-reinforced plastic material is fed to an extrusion device and heated in a heating zone of the extrusion device in order to subsequently feed the fiber-reinforced plastic material to an - optionally replaceable - extrusion nozzle of the extrusion device, at which a material thread with (molten) fiber-reinforced plastic material for the component to be produced is extruded, and to convey the fiber-reinforced plastic material through the heating zone, a conveyor screw of the extrusion device is used, which has a length-diameter ratio of less than 10.

[0010] Furthermore, in the proposed solution, less than 5.5 cm3 of volume is provided for the fiber-reinforced plastic material in the heating zone and the rotational speed of the conveyor screw (around its longitudinal axis) is limited to a maximum of 30 revolutions per minute.

[0011] The proposed solution is based on experimental findings and is based on the fundamental idea that, for the extrusion of fiber-reinforced plastic material for the additive manufacturing of a component, a conveyor screw (extruder screw) with a length-to-diameter ratio of less than 10, combined with a volume limited to 5.5 cm3 or less in the heating zone and a defined maximum speed of the conveyor screw of 30 revolutions per minute or less, is particularly advantageous for additively producing a component with fiber-reinforced plastic material using an extrusion-based process. It has been shown that, based on the proposed solution, degradation of the plastic material during extrusion can be effectively avoided and, at the same time, a particularly advantageous fiber orientation is achieved in the finished component, which has a positive effect on increasing the material strength of the manufactured component.The limited speed of the conveyor screw—especially in combination with a length-to-diameter ratio of less than 10 for the conveyor screw and a volume limited to 5.5 cm3 or less for the fiber-reinforced plastic material in the heating zone—can, for example, also have a positive effect on the shear forces exerted on the plastic material during extrusion via the conveyor screw, resulting in comparatively long and unsheared fibers in the finished component. Thus, the limited speed of the conveyor screw leads to peripheral speeds (which are crucial for the shear rate) that are 50 to 80 times lower than in conventional injection molding machines.

[0012] In this context, it may be advantageous in one embodiment to provide a volume in the range from 2.5 cm 3 to 5.5 cm 3 , in particular 2.5 cm 3 to 4.5 cm 3 , for the fiber-reinforced plastic material in the heating zone. In particular, in one embodiment, a volume in the range from 3.0 cm 3 to 3.5 cm 3 , for example approximately 3.30 cm 3 , is provided. The volume made available for the fiber-reinforced plastic material in the heating zone of the extrusion device is calculated from the volume of a cavity formed in a housing section defining the heating zone and in which the conveyor screw extends, minus the volume in the heating zone occupied by the conveyor screw itself.

[0013] In one embodiment, the feed rate of the screw conveyor for the fiber-reinforced plastic material is set such that the fiber-reinforced plastic material being conveyed toward the extrusion die remains in the heating zone for a maximum of 20 minutes. The feed rate and / or the residence time can be adjusted directly on the extrusion device, taking into account the screw conveyor speed, which is limited to a maximum of 30 revolutions per minute. Alternatively, the feed rate and / or the residence time can be adjusted by changing the screw conveyor speed.

[0014] Depending in particular on the plastic material used and the form of the raw fiber-reinforced plastic material being fed, the feed rate of the screw conveyor can be set for a residence time of at least 1.5 seconds, in particular at least 4.75 seconds or 50 seconds, and a maximum of 20 minutes for the fiber-reinforced plastic material to be conveyed in the heating zone. For example, with certain fiber-reinforced plastic materials, a residence time in the range of 1.5 to approximately 60 seconds or several minutes has proven advantageous when the fiber-reinforced plastic material is fed to the extrusion device in powder or granulate form.

[0015] A feed rate of the plastic material can, for example, be set to a value of at least 5 cm3 per hour and / or a value of a maximum of 7500 cm3 per hour. The screw conveyor can thus have a comparatively high output. For example, the feed rate can be set in the range from 10 cm3 per hour to 5500 cm3 per hour, in particular, for example, in the range from 10 cm3 per hour to 2500 cm3 per hour, from 10 cm3 per hour to 250 cm3 per hour.

[0016] In one embodiment, the feed rate of the screw conveyor for the fiber-reinforced plastic material is set, for example, to a value in the range of 150 cm3 per hour to 220 cm3 per hour, in particular in the range of 150 cm3 per hour to 200 cm3 per hour. For example, for a feed rate of 10 cm3 per hour and a volume of 3.3 cm3 available for the fiber-reinforced plastic material in the heating zone, a maximum residence time of the fiber-reinforced plastic material in the heating zone of less than 20 minutes can be set.

[0017] The fiber-reinforced plastic material can, for example, comprise a thermoplastic matrix material and carbon fibers and / or glass fibers, and / or other aramid fibers and / or synthetic fibers and / or plastic-based fibers and / or natural fibers and / or ceramic fibers. Alternatively or additionally, the matrix material can comprise at least one of the following materials, in particular consist of one of the following materials: polycarbonate, polylactate, polyethylene, polyethylene terephthalate, polymethyl methacrylate, polybutylene terephthalate, acrylonitrile-butadiene-styrene copolymer, polyoxymethylene, polypropylene, polystyrene, polyvinyl chloride, or polyamide.

[0018] In one embodiment, the fiber-reinforced plastic material contains at least one additional reinforcing material, for example, made of flour and / or fragments. In particular, glass fragments can be included as additional reinforcing material.

[0019] In one embodiment, the plastic material is fed into the extrusion device via a material feed at an inlet zone. For example, a funnel-shaped inlet is provided to define the inlet zone. A feed zone of the conveyor screw can be provided at the inlet zone, from which the fiber-reinforced plastic material fed into the inlet zone, for example, in powder or granular form, is conveyed toward the extrusion die by rotation of the conveyor screw about its longitudinal axis. The fiber-reinforced plastic material is carried along via the screw flights of the conveyor screw. The screw flights of the conveyor screw are designed in such a way that the plastic material does not experience any compression until it reaches the heating zone.Compression via the screw conveyor, for example, is then only provided in a melting and compression zone of the screw conveyor, which is located in the area of ​​the heating zone and causes compression and – in combination with the heat supplied to the heating zone – melting of the plastic material. In principle, this can also be achieved by changing the pitch of the screw flights or by changing the diameter of a screw conveyor shaft forming the screw flights.

[0020] In principle, the fiber-reinforced plastic material, as a composite material, can have a volume or mass fraction of reinforcing material, in particular fibers, of at least 10%.

[0021] In principle, within the scope of the extrusion process, an orientation of the fibers can also be controlled by varying process parameters, in particular the extrusion temperature, and / or a deposition of the fibers of the applied fiber-reinforced plastic material can be carried out in such a way that two or more layers of the component to be manufactured, applied via a material thread, are connected to one another.

[0022] Another aspect of the proposed solution concerns an extrusion device for extruding fiber-reinforced plastic material for the additive manufacturing of a component.

[0023] The extrusion device has a heating zone in which the fiber-reinforced plastic material to be extruded is heated in order to subsequently feed the fiber-reinforced plastic material to a (possibly replaceable) extrusion nozzle of the extrusion device, from which a material thread containing (molten) fiber-reinforced plastic material for the component to be produced can be extruded. Furthermore, the extrusion device has a conveyor screw with a length-to-diameter ratio of less than 10 for conveying the fiber-reinforced plastic material through the heating zone and toward the extrusion nozzle. According to the proposed solution, less than 5.5 cm3 of volume is provided for the fiber-reinforced plastic material in the heating zone. Furthermore, the speed of the conveyor screw is limited to a maximum of 30 revolutions per minute via an electronic control device of the extrusion device.

[0024] In principle, the proposed extrusion device can achieve rapid compression of plasticized, fiber-reinforced plastic material, which in turn prevents segregation and thus decomposition of the fiber-reinforced plastic material. Furthermore, advantageous, and therefore comparatively low, shear forces on the extruded plastic material can be achieved during extrusion. Overall, this leads to a significant improvement in the additive manufacturing of a component using a fiber-reinforced plastic filament extruded at the extrusion nozzle.

[0025] A variant of a proposed extrusion device can be used to implement a variant of a proposed extrusion process. Advantages and features described in connection with variants of a proposed extrusion process therefore also apply to variants of a proposed extrusion device, and vice versa.

[0026] The electronic control device of the extrusion device can also be used to specify a conveying rate of the conveyor screw for the fiber-reinforced plastic material such that the fiber-reinforced plastic material to be conveyed in the direction of the extrusion nozzle remains in the heating zone for a maximum of 30 minutes, in particular at least 1.5 seconds and a maximum of 20 minutes.

[0027] For example, a (volumetric) feed rate of the screw conveyor can be specified alternatively or additionally via the control device and set to at least 5 cm 3 per hour and / or limited to a maximum of 7500 cm 3 per hour. This includes, in particular, a design variant in which the feed rate can be set via the electronic control device to no less than 10 cm 3 per hour, but to a maximum of 7500 cm 3 , e.g., limited to a maximum of 5500 cm 3 per hour, 2500 cm 3 per hour, 1000 cm 3 per hour, or 250 cm 3 per hour.

[0028] For example, a specific (volume) conveying rate of the conveyor screw can be preset via the electronic control device of the extrusion device, optionally depending on the plastic material supplied and / or depending on the volume provided within the heating zone for the fiber-reinforced plastic material (particularly in the case of replaceable housing sections for the formation of the heating zones).For example, a user of the extrusion device simply needs to enter the type and shape of the fiber-reinforced plastic material being fed into an operating unit coupled to the control unit. The electronic control unit then uses stored reference values ​​(below the maximum speed of 30 revolutions per minute for the screw conveyor) to set a specific feed rate such that the residence time of the fiber-reinforced plastic material to be extruded in the heating zone remains below 20 minutes. For example, the specified feed rate can vary depending on which thermoplastic matrix material with which type of fibers is being fed into the extrusion device and / or whether the fiber-reinforced plastic material is being fed into the extrusion device as a powder or as granules.

[0029] In one design variant, the heating zone is limited to a maximum length of 40 mm and a maximum diameter of 25 mm. The volume available for the fiber-reinforced plastic material is thus easily less than 5.5 cm3 in this design variant, especially depending on the volume occupied by the screw conveyor within the heating zone.

[0030] In one embodiment, the screw conveyor has a screw blade that rises in the conveying direction of the plastic material. The screw blade can, for example, have a rise of 7 mm to 17 mm, in particular of 8 mm to 15 mm. In particular, with such a configuration of the screw conveyor, in combination with the parameters specified on the basis of the proposed solution, it has been shown that advantageous fiber orientations in the finished component, as well as comparatively long and non-sheared fibers, can be achieved in the finished component, at least when fiber-reinforced plastic material with a thermoplastic matrix is ​​fed in granular form.

[0031] In one embodiment, the heating zone has a conical taper at one end located in the conveying direction of the plastic material, through which fiber-reinforced plastic material can be fed to the extrusion nozzle. For example, this conical taper then has an opening angle in the range of 50° to 65°, particularly in the range of 55° to 60°, for example, 58°. The degree of taper can also be an influencing factor for the material strength and fiber orientation of the component to be manufactured.

[0032] The extrusion device has, as already explained, a feed zone, where the fiber-reinforced plastic material can be fed to the conveyor screw. In one embodiment, the heating zone follows a barrier zone in the conveying direction of the plastic material, which spatially separates the heating zones from the feed zone of the extrusion device. A thermal barrier, for example, is then formed between the feed zone and the heating zone via the barrier zone. It may be advantageous here that the barrier zone is formed by a housing section made of a material which has a lower thermal conductivity than the material from which a housing section adjacent to the barrier zone is formed, by which the heating zone is at least partially formed, and the housing section at least partially forming the heating zone has a greater thermal mass than the housing section forming the barrier zone.

[0033] For example, the housing section of the barrier zone is made of a high-strength or hard, but thermally poorly conductive material, such as ceramic. Cooling can also be provided at the barrier zone if necessary to minimize heating of the feed zone via the heating zone of the extrusion device. In one embodiment, the barrier zone is made of zirconium oxide or aluminum oxide.

[0034] In one embodiment, the diameter of a shaft of the conveyor screw increases at least once within the heating zone in the conveying direction of the plastic material. For example, a conical enlargement of the diameter is provided within the heating zone to assist the compression of the fiber-reinforced plastic material. The aforementioned embodiment thus includes a diameter of the shaft at a first screw section of the conveyor screw having a first (smaller) diameter, while the shaft at a second screw section adjoining it in the conveying direction has a second (larger) diameter. The conveyor screw can therefore be designed, in particular, in the manner of a stuffing screw.For the diameter increase between the first and second screw sections, for example, a conical transition area can be provided at which the diameter of the shaft of the conveyor screw increases in the conveying direction from the first diameter to the second diameter.

[0035] This includes, in particular, a design variant in which the diameter of a screw conveyor shaft within the heating zone, and in particular, for example, in a melting and compression zone of the screw conveyor, is conically enlarged at an angle in the range of 7° to 10° and up to 1.5 to 2 times the smallest (first) diameter of the screw conveyor shaft. In a further development based on this, the diameter is then constant up to an end of the screw conveyor located in the conveying direction, in the region of an ejection zone of the screw conveyor.

[0036] For example, one embodiment provides for the heating zone to extend along a conveying direction of the plastic material (defined by the conveyor screw) and parallel to a longitudinal axis of the conveyor screw, with a length that corresponds to a maximum of half the (total) length of the conveyor screw measured along the longitudinal axis. A heating zone length is thus a maximum of half the length of the conveyor screw. Such a geometric limitation of the heating zone length in relation to the total length of the conveyor screw has proven advantageous in certain configurations, particularly with regard to the intended length-to-diameter ratio of the conveyor screw of less than 10.

[0037] Alternatively or additionally, the conveyor screw can extend within the heating zone with a melting and compression zone and an ejection zone following this in the conveying direction of the plastic material and having an axial end of the conveyor screw. The melting and compression zone and the ejection zone together do not exceed one-third of the length of the conveyor screw measured along the longitudinal axis. The length of the conveyor screw forming the melting and compression zone and the ejection zone within the heating zone of the extrusion device thus does not exceed one-third of the total length of the conveyor screw.

[0038] In this embodiment, in particular, it can be provided that the pitch of the screw conveyor in the melting and compression zone is reduced compared to the feed zone of the screw conveyor, which is followed in the conveying direction by the melting and compression zone and at which the raw material of fiber-reinforced plastic material is fed to the screw conveyor. Relative to the conveying direction of the plastic material within the extrusion device, the melting and compression zone thus follows the feed zone along the screw's longitudinal axis and in the direction of the extrusion nozzle, while the melting and compression zone is followed by the discharge zone.

[0039] In one embodiment, a reservoir is provided in a region between an axial end of the conveyor screw located in the conveying direction of the plastic material and the extrusion nozzle, in which reservoir molten fiber-reinforced plastic material can be maintained in a state of overpressure. The extrusion device thus has a reservoir in said region, which is configured and intended to maintain molten, fiber-reinforced plastic material in a state of overpressure during operation of the extrusion device in order to allow the plastic material to emerge from the extrusion nozzle as a material thread.

[0040] For example, the reservoir extends parallel to the conveying direction and parallel to the longitudinal axis of the screw conveyor with a length that corresponds to a maximum of one-third of the length of the screw conveyor measured along the longitudinal axis. The reservoir length therefore does not exceed one-third of the total length of the screw conveyor. For example, the reservoir has a maximum length of one-fifteenth of the length of the screw conveyor.

[0041] In one embodiment, the extrusion nozzle has a nozzle diameter in the range of 0.25 mm to 2 mm. In particular, the extrusion nozzle can be interchangeable, so that extrusion nozzles with different nozzle diameters, each in the range of 0.25 mm to 2 mm, for example, can be used on the extrusion device.

[0042] A further aspect of the proposed solution further relates to a 3D printing device with at least one embodiment of a proposed extrusion device and / or a 3D printing device with an extrusion device for carrying out an embodiment of the proposed extrusion process. In particular, such a 3D printing device can be configured and provided for a thermoplastic melt deposition process implemented using its extrusion device, wherein the extrusion device is used at least as part of a print head of the 3D printing device on a three-axis kinematic system.

[0043] The attached figures illustrate possible embodiments of the proposed solution Here we show:

[0044] Figure 1 shows a schematic representation of a 3D printing device for the additive processing of fiber-reinforced plastics using a compact screw extruder of the 3D printing device; Figure 2 shows a cross-sectional view of the screw extruder; Figure 3 shows another cross-sectional view of the screw extruder; Figure 4 shows a top view of the screw extruder; and Figure 5 shows a schematic representation of a mechanical interlocking of material threads / webs of extruded fiber-reinforced plastic material deposited using the screw extruder.

[0045] The Figure 1shows a schematic and perspective view of a 3D printing device in which a variant of a proposed extrusion device in the form of a screw extruder 2 is provided as part of a print head of the 3D printing device. With the help of the screw extruder 2, fiber-reinforced plastic material can be used for the additive manufacturing of a component 1 by means of thermoplastic melt deposition. The screw extruder 2 can be moved via a three-axis kinematics above a platform or base 11 on which the component 1 to be manufactured is formed. Material threads made of molten fiber-reinforced plastic material are applied to the base 11 via an extrusion nozzle 10 of the screw extruder 2. The extrusion process is controlled by an electronic control device 20 of the screw extruder 2.

[0046] As can be seen from the enlarged cross-sectional views of the Figures 2 and 3and from the top view of the Figure 4 for the screw extruder 2, the screw extruder 2 has a conveyor screw 3 for conveying fiber-reinforced plastic material 8 supplied in powder or granulate form in the direction of the extrusion nozzle 10. This conveyor screw 3 extends with a total length along a (screw) longitudinal axis over an intake area 31, an adjoining melting and compression zone 32 up to an ejection zone 33. The conveyor screw 3 is rotatably received about its longitudinal axis in a housing 4 of the screw extruder 2 and can be rotated via a motor drive (not shown here).

[0047] The housing 4, which at least partially accommodates the conveyor screw 3, is shown in the cross-sectional view of Figures 2 and 3with different housing sections 41g, 42g, and 43g. The individual housing sections 41g, 42g, 43g can also form independent housing parts that are interconnected and together define the housing 4. A first housing section 41g defines a funnel-shaped inlet 5 for the supply of the powdered or granular fiber-reinforced plastic material 8, which, as a composite material, comprises, for example, a thermoplastic matrix material with fibers embedded therein. The first housing section 41g with the inlet 8, which defines an intake zone 41 for the supply of the plastic material, is followed in a conveying direction to the extrusion nozzle 10 by a second housing section 42g for forming a thermal barrier zone 42. The barrier zone 42 separates the intake zone 41 from a heating zone 43, which is formed by a subsequent third housing section 43g of the housing 4.For the thermal separation of the feed zone 41 from the heating zone 43, the second housing section 42g is made, for example, of a high-strength but thermally very poorly conductive material, such as ceramic, and may optionally have additional feed cooling. For example, the housing section 42g of the thermal barrier zone 42 is made of zirconium oxide or aluminum oxide.

[0048] To form the heating zone 43, the third housing section 43g has one or more heating elements 9 arranged distributed around the circumference. The fiber-reinforced plastic material 8 conveyed toward the extrusion nozzle 10 is melted via the heating elements 9, so that it can be extruded from the extrusion nozzle 10 in a material thread, the thickness of which is determined by the geometry of the extrusion nozzle 10, which is interchangeably attached to the housing 4.

[0049] The conveyor screw 3, which is vertically arranged in the intended installed state, extends within the housing 4 such that the intake area 31 of the conveyor screw 3 is completely enclosed by the first housing section 41g and the intake zone 41 formed thereby. The plastic material 8 is compressed by the conveyor screw 3 via the compression and melting zone 32 of the conveyor screw 3, which adjoins the intake zone 31 within the third housing section 43g and thus within the heating zone 43. For this purpose, the conveyor screw 3 is designed as a stuffing screw, in which the diameter of a shaft 6 of the conveyor screw 3 increases conically in the area of ​​the melting and compression zone 32 at an angle of 7° to 10° and up to 1.5 to 2 times the smallest diameter of the conveyor screw 3.

[0050] In an ejection zone 33 of the conveyor screw 3, which adjoins the melting and compression zone 32 and which also still lies within the heating zone 43, the (larger) diameter of the shaft 6 of the conveyor screw 3 remains constant. Adjoining the ejection zone 33 and thus an axial end of the conveyor screw 3 in the conveying direction of the fiber-reinforced plastic material is a reservoir 7. This reservoir 7 is formed between the axial end of the conveyor screw 3 and the extrusion nozzle 10 and is at least partially defined by a conical taper V of inner lateral surfaces of the third housing section 43g facing the conveyor screw 3 in the heating zone 43. In this reservoir 7, molten fiber-reinforced plastic material is held under excess pressure, wherein the reservoir 7 here has a maximum length of 1 / 15 of a total length of the conveyor screw 3.The conical taper V provided on the inside in the third housing section 43g in the direction of the extrusion nozzle 10 has an opening angle φ in the order of 58° or more.

[0051] In the illustrated screw extruder 2, the plastic material 8 is first received in the funnel-shaped inlet 5 in the intake area 31 of the conveyor screw 3 and transported downwards by the conveyor screw 3 along the conveying direction. Due to the thermal barrier zone 42 in the housing 4, the plastic material 8 is free-flowing up to the second housing section 42g forming the barrier zone 42. Furthermore, it is provided that no compression due to a change in the pitch of the screw flights or the diameter of the shaft 6 of the conveyor screw 3 occurs until the heating zone 43 is reached within the housing 4.

[0052] Only in the heating zone 43, which directly adjoins the barrier zone 42 at the bottom, is the plastic material 8 melted and compressed. For this purpose, the radially arranged heating elements 9 are provided on the housing side of the heating zone 43. These heating elements extend over the entire length of the heating zone 43 and enable a very localized introduction of thermal energy. The heating zone 43 has a maximum length on the housing side that corresponds to half the length of the conveyor screw 3. The third housing section 43g forming the heating zone 43 has a greater thermal conductivity than the second housing section 42g forming the barrier zone 42 and also has a greater thermal mass than this second housing section 42g.

[0053] In the illustrated extrusion device in the form of the screw extruder 2, the volume available in the heating zone 43 for fiber-reinforced plastic material 8 inside the housing 4 is limited to less than 5.5 cm 3 , in this case to approximately 3.30 cm 3 . In other words, a maximum volume of 3.30 cm 3 is available in the heating zone 43 for the plastic material 8 to be conveyed along the longitudinal axis of the conveyor screw 3 in the direction of the extrusion nozzle 10. This volume is calculated from the difference between the hollow space in the third housing section 43g, in which the conveyor screw 3 extends with its melting and compression zone 32 and its ejection zone 33, and the volume occupied by the conveyor screw 3 itself.

[0054] Furthermore, the electronic control device 20 limits the maximum speed of the conveyor screw 3 to 30 revolutions per minute around the (screw) longitudinal axis. Taking this speed limitation into account, a volumetric feed rate of the conveyor screw 3 is set in the present case such that the fiber-reinforced plastic material 8 to be conveyed in the direction of the extrusion nozzle 10 remains in the heating zone 43 for a maximum of 20 minutes, here, for example, at least 1.5 seconds, but a maximum of 20 minutes. In the present case, a simultaneously comparatively high discharge of the conveyor screw 3 in the range of up to 7500 cm 3 per hour, in particular 5500 cm 3 per hour, 2500 cm 3 per hour, 1000 cm 3 per hour or 250 cm 3 per hour is achieved.Combined with a length-to-diameter ratio of the conveyor screw 3 of less than 10, this ensures that the fiber-reinforced plastic material 8 remains in the heating zone 43 for a comparatively short time, thereby preventing degradation of the plastic material 8. This is also promoted by the design of the heating zone 43 with a maximum length of 24 mm and a diameter of less than 18 mm. Furthermore, it has been shown that in an extrusion process implemented with the screw extruder 2 according to the aforementioned process parameters, only a comparatively small proportion of the fibers contained in the powdered or granular plastic material 8 are sheared off, and approximately 70% of the fibers are deposited in the travel direction of the extrusion nozzle 10. This enables the fiber orientation and thus the strength of the component 1 to be produced to be influenced, regardless of the component geometry.During a 3D printing process, only the travel path of the extrusion nozzle 10 needs to be manipulated.

[0055] The throughput time in the heating zone 43 and along the melting and compression zone 32 of the conveyor screw 3 fundamentally depends on the fiber-reinforced plastic material 8 used. According to the proposed solution, the maximum speed of the conveyor screw 3 is limited to a maximum of 30 revolutions per minute. This, in combination with the length-to-diameter ratio of the conveyor screw 3 of less than 10, results in low shear forces, and the throughput time is selected such that the residence time of the plastic material 8 in the heating zone is a maximum of 20 minutes.Due to the short residence time of the quantity of plastic material 8, which is kept small by the predetermined volume of less than 5.5 cm 3<, in the heating zone 43, which is also geometrically designed to be comparatively short (in particular with respect to the length of the conveyor screw 3), which is determined in particular by the conveying rate, the plastic material 8 remains in the hot state for only a short time and the melt held in the melting and compression zone 32 has a sufficiently short throughput time.

[0056] The one in the Figures 1 to 4The compact screw extruder 2 shown is capable of processing fiber-reinforced plastic material 8, which, for example, contains at least one of the following matrix materials: polycarbonate, polylactate, polyethylene, polyethylene terephthalate, polymethyl methacrylate, polybutylene terephthalate, acrylonitrile-butadiene-styrene copolymer, polyoxymethylene, polypropylene, polystyrene, polyvinyl chloride, polyamide. Furthermore, various reinforcing materials in the form of glass fibers, aramid fibers, steel fibers, carbon fibers, synthetic fibers, plastic-based fibers, natural fibers, and / or ceramic fibers can be embedded in the matrix material. Powder or fragments of glass or other materials can also be used as additional reinforcements. The plastic can also be mineral-reinforced.

[0057] In one application scenario, the fiber-reinforced plastic material 8 has a fiber content of greater than or equal to 10%, with no continuous fibers being included.

[0058] With the screw extruder 2 or with the 3D printing device, in which the screw extruder 2 forms part of a print head, a component 1 can be effectively manufactured additively. For component 1, for example, the extrusion process implemented with the screw extruder 2 can be used according to the schematic representation of the Figure 5Using extruded material threads made of fiber-reinforced plastic material, eight layers (material webs) are applied, each containing 70% fibers, which are laid down in the direction of travel of the extrusion nozzle 10. The remaining 30% of the fibers protrude in all spatial directions from the applied (printed) layers, resulting in a mechanical interlocking of the layers deposited on top of one another. In this way, a comparatively high material strength can be achieved in the finished component 1, and the deformation and failure behavior of the finished component 1 can be specifically specified. List of reference symbols

[0059] 1 Component 10 Extrusion nozzle 11 Base 2 Screw extruder (extrusion device) 20 Control device 3 Conveyor screw / extruder screw 31 Feed area 32 Melting and compression zone 33 Discharge zone 34 End area 340 Chamfer 4 Housing 41 Feed zone 42 (thermal) barrier zone 41g, 42g, 43g Housing section 43 Heating zone 5 Inlet 6 Shaft 7 Reservoir 8 Fiber-reinforced plastic material 9 Heating element V Taper φ Opening angle

Claims

1. A method for extrusion of fiber-reinforced plastic material for the additive manufacture of a component (1), wherein - the fiber-reinforced plastic material (8) is supplied to an extrusion apparatus (2) and heated in a heating zone (43) of the extrusion apparatus (2) in order to then supply the fiber-reinforced plastic material (8) to an extrusion nozzle (10) of the extrusion apparatus (2), at which a material thread comprising fiber-reinforced plastic material (8) is extruded for the component to be manufactured, and - in order to convey the fiber-reinforced plastic material (8) through the heating zone (43), a screw conveyor (3) of the extrusion apparatus (2) is utilized, which has a length-diameter ratio of less than 10, characterized in that in the heating zone (43) a maximum of 5.

5. cm3 of volume is provided for the fiber-reinforced plastic material (8) and a rotational speed of the screw conveyor (3) is limited to a maximum of 30 revolutions per minute.

2. The method according to claim 1, characterized in that in the heating zone a volume in the range of 2.5 cm3 to 5.5 cm3 is provided for the fiber-reinforced plastic material.

3. The method according to claim 2, characterized in that in the heating zone a volume in the range of 3.0 cm3 to 3.5 cm3 is provided for the fiber-reinforced plastic material.

4. The method according to any of claims 1 to 3, characterized in that a feed rate of the screw conveyor (3) is set for the fiber-reinforced plastic material (8) in such a way that the fiber-reinforced plastic material (8) to be fed in the direction of the extrusion nozzle (10) remains in the heating zone (43) for a maximum of 30 minutes, in particular for at least 0.5 seconds and a maximum of 20 minutes.

5. The method according to any of the preceding claims, characterized in that a feed rate of the screw conveyor (3) for the fiber-reinforced plastic material (8) is set to a value of at least 5 cm3 / h.

6. The method according to claim 5, characterized in that the feed rate of the screw conveyor (3) for the fiber-reinforced plastic material (8) is set to a value of not more than 7500 cm3 / h.

7. The method according to claim 6, characterized in that the feed rate of the screw conveyor (3) for the fiber-reinforced plastic material (8) is set to a value in the range of less than 250 cm3 / h, in particular in the range of 150 cm3 / h to 220 cm3 / h.

8. An extrusion apparatus for extrusion of fiber-reinforced plastic material for the additive manufacture of a component (1), wherein - the extrusion apparatus (2) includes a heating zone (43) in which the fiber-reinforced plastic material (8) to be extruded is heated in order to then supply the fiber-reinforced plastic material (8) to an extrusion nozzle (10) of the extrusion apparatus (2), at which a material thread comprising fiber-reinforced plastic material (8) can be extruded for the component to be manufactured, and - in order to convey the fiber-reinforced plastic material (8) through the heating zone (43), the extrusion apparatus (2) includes a screw conveyor (3) which has a length-diameter ratio of less than 10, characterized in that in the heating zone (43) a maximum of 5.

5. cm3 of volume is provided for the fiber-reinforced plastic material (8) and a rotational speed of the screw conveyor (3) is limited to a maximum of 30 revolutions per minute via an electronic control device (20) of the extrusion apparatus (2).

9. The extrusion apparatus according to any of claim 8, characterized in that the screw conveyor (3) has a screw blade rising in the conveying direction of the plastic material (8) with a slope of 7 mm to 17 mm.

10. The extrusion apparatus according to any of claim 8 or 9, characterized in that - at an end located in the conveying direction of the plastic material (8) the heating zone (43) has a conical taper (V) via which fiber-reinforced plastic material (8) can be supplied to the extrusion nozzle (10), and the conical taper (V) includes an opening angle (φ) in the range of 50° to 65°, and / or - a diameter of a shaft (6) of the screw conveyor (3) within the heating zone (43) increases at least once in the conveying direction of the plastic material (8), and / or - the heating zone (43) extends along a conveying direction of the plastic material (8) and parallel to a longitudinal axis of the screw conveyor (3) with a length that maximally corresponds to half of a length of the screw conveyor (3) measured along the longitudinal axis, and / or - the screw conveyor (3) with a melting and compression zone (32) and an ejection zone (33) following the same in the conveying direction of the plastic material (8) and including an axial end of the screw conveyor (3) extends within the heating zone (43), and the melting and compression zone (32) and the ejection zone (33) together do not exceed one third of a length of the screw conveyor (3) measured along the longitudinal axis.

11. The extrusion apparatus according to claim 10, characterized in that the diameter of the shaft (6) within the heating zone (43) conically increases with an angle in the range of 7° to 10° and up to 1.5 to 2 times a smallest diameter of the shaft (6) of the screw conveyor (3).

12. The extrusion apparatus according to any of claims 8 to 11, characterized in that the extrusion apparatus (2) includes a feed zone (41) at which the fiber-reinforced plastic material can be supplied to the screw conveyor (3), and in the conveying direction of the plastic material (8) the heating zone (43) follows a barrier zone (42) which spatially separates the heating zone (43) from the feed zone (41) of the extrusion apparatus (2), wherein - the barrier zone (42) is formed by a housing portion (42g) made of a material that has a lower thermal conductivity than the material from which a housing portion (43g) adjoining the barrier zone (42) is made, with which the heating zone (43) is formed at least in part, and - the housing portion (43g) at least partly forming the heating zone (43) has a larger thermal mass than the housing portion (42g) forming the barrier zone (42).

13. The extrusion apparatus according to any of claims 8 to 12, characterized in that in a region between an axial end of the screw conveyor (3), which is located in the conveying direction of the plastic material (8), and the extrusion nozzle (10) a reservoir (7) is provided, in which molten fiber-reinforced plastic material (8) can be maintained in a state of excess pressure.

14. The extrusion apparatus according to claim 13, characterized in that the reservoir extends parallel to the conveying direction and to the longitudinal axis of the screw conveyor (3) with a length that maximally corresponds to one third of the length of the screw conveyor (3) measured along the longitudinal axis.

15. A 3D printing device comprising at least one extrusion apparatus (2) according to any of claims 8 to 14.