Use of plastic powder residues for an extrusion method for additive manufacturing of a component, and extrusion device with a size-reduction unit

Abstract

The proposed solution relates in particular to the use of plastic powder residues (8R), which after a manufacturing method using at least one plastic powder has been carried out, are intended for disposal as an excess remainder, as a plastic material for the additive manufacturing of a component by means of an extrusion device (2).

Description

[0001] Use of plastic powder residues for an extrusion process for the additive manufacturing of a component and extrusion device with comminution device

[0002] Description

[0003] The proposed solution relates in particular to the use of plastic powder residues as a plastic material for the additive manufacturing of a component with an extrusion device as well as to an extrusion process and an extrusion device.

[0004] Extrusion devices, e.g. 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. 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.

[0005] 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 their minimum cross-sections 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.

[0006] 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.

[0007] Typically, during additive manufacturing of a component, granular plastic material is fed into the extrusion device. The granules are then, for example, first crushed by a screw extruder under the application of heat.

[0008] Against this background, the proposed solution is based on the task of further flexibilizing a process for the additive manufacturing of components from a plastic material and, if necessary, also making it more cost-effective.

[0009] This problem can be solved, for example, by using plastic powder residues (in particular, plastic powder residues) that, after at least one manufacturing process involving plastic powder, are actually intended for disposal as surplus residue, but are now used for additive manufacturing in an extrusion device. Accordingly, in this context, it is proposed to use plastic powder residues for additive manufacturing that were previously typically disposed of and for which no further use was intended. It has been recognized that plastic powder residues from other manufacturing processes, in particular other additive manufacturing processes, can still be used for the additive manufacturing of a component using an extrusion device. Corresponding plastic powder residues can thus be put to further use.

[0010] For example, the plastic powder residues can be fed to the extrusion device as the sole starting material or mixed with at least one other material for the additive manufacturing of the component. The at least one other material intended to be mixed with the plastic powder residues can, for example, be a plastic powder, in particular a plastic powder from a different source than the plastic powder residues. For example, the plastic powder residues can originate from an additive manufacturing process that is not based on extrusion. A plastic powder to be mixed with them, on the other hand, can originate from another non-additive or additive manufacturing process or be intended for first-time use. By using plastic powder residues or plastic powder in general, higher packing densities can be achieved in the inlet of the extrusion device.This makes the extrusion more uniform, which in turn is reflected in the very good surface qualities of the components being manufactured.

[0011] For example, it has proven advantageous to utilize plastic powder residues resulting from selective laser sintering or binder jetting in an extrusion process. In such a variant, plastic powder residues resulting from selective laser sintering or binder jetting are used for the additive manufacturing of a component with an extrusion device. For an extrusion process, plastic powder residues that remained as residues during the production of another component and based on a different manufacturing concept are thus utilized.

[0012] Against this background, the proposed solution also relates to a method for extruding plastic material for the additive manufacturing of a component. Within the scope of such a method, the plastic material is fed to an extrusion device and heated in a heating zone of the extrusion device in order to subsequently feed the plastic material to an extrusion nozzle of the extrusion device, at which a material thread containing plastic material for the component to be manufactured is extruded. Within the scope of the proposed solution, at least part of the plastic material fed to the extrusion device consists of plastic powder residues, which were intended for disposal as excess residue after at least one plastic powder-processing manufacturing process.

[0013] As already explained above, the plastic powder residues can be fed into the extrusion device as the sole starting material or mixed with at least one other material. In principle, the plastic powder residues can originate from a non-extrusion-based additive manufacturing process, in particular from selective laser sintering or binder jetting.

[0014] The used plastic powder residues can generally contain at least one filler, for example, fibers and / or particles. Plastic powder residues with or without fibers can also be mixed with separately fed fibers at the extrusion device. If the plastic powder residues to be processed contain fibers or are mixed with fibers, a fiber-reinforced plastic component is produced using additive manufacturing.

[0015] To convey the plastic material through the heating zone, a conveyor screw of the extrusion device can be used, which has a length-to-diameter ratio of less than 10. In the course of a proposed process, the extrusion device can thus comprise a corresponding conveyor screw as part of a screw extruder. Alternatively, the use of a piston extruder or gear extruder is also possible. The use of a screw extruder is therefore not mandatory.

[0016] Furthermore, in one version, the heating zone can be less than 5.5 cm 3 of volume for the plastic material and the speed of a conveyor screw of the extrusion device (around its longitudinal axis) is limited to a maximum of 30 revolutions per minute. A conveyor screw (extruder screw) with a length-to-diameter ratio of less than 10 can also be used with a diameter of 5.5 cm. 3or less limited volume in the heating zone and, alternatively or additionally, a maximum speed of the conveyor screw can be limited to 30 revolutions per minute or less in order to additively manufacture a component with plastic material using an extrusion-based process. This can prevent degradation of the plastic material during extrusion and - in the case of fiber-reinforced plastic material - simultaneously achieve a particularly advantageous fiber orientation 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 diameter of 5.5 cm 3or less limited volume for plastic material in the heating zone – the shear forces applied to the plastic material during extrusion via the conveyor screw can also have a positive effect, resulting in comparatively long and unsheared fibers in the finished component. 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.

[0017] Furthermore, in one design variant it may be advantageous to have a volume in the range of 2.5 cm 3 up to 5.5 cm 3 , especially 2.5 cm 3 up to 4.5 cm 3 for the plastic material. In particular, in one design variant, a volume in the range of 3.0 cm 3 up to 3.5 cm 3 , for example at approx. 3.30 cm 3The volume available for the 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.

[0018] In one embodiment, the feed rate of the screw conveyor for the plastic material is set such that the 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.

[0019] In particular, depending on the plastic material used and the form of the raw 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 plastic material to be conveyed in the heating zone. For example, with certain plastic materials, a residence time in the range of 1.5 to approximately 60 seconds or several minutes has proven advantageous if the plastic material is fed to the extrusion device in powder or granulate form.

[0020] A feed rate of the plastic material can, for example, be set to a value of at least 5 cm 3 per hour and / or to a maximum value of 7500 cm 3per hour. The screw conveyor can therefore have a comparatively high output. For example, the conveying rate can be in the range of 10 cm 3 per hour up to 5500 cm 3 per hour, especially in the range of 10 cm 3 per hour up to 2500 cm 3 per hour, from 10 cm 3 per hour up to 250 cm 3 per hour. In one design variant, the conveying rate of the screw conveyor for the plastic material is, for example, set to a value in the range of 150 cm 3 per hour up to 220 cm 3 per hour, especially in the range of 150 cm 3 hour up to 200 cm 3 per hour. For example, for a flow rate of 10 cm 3 per hour and a volume of 3.3 cm provided for the plastic material in the heating zone 3 a maximum residence time of the plastic material in the heating zone of less than 20 minutes must be set.

[0021] The 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,

[0022] Polymethyl methacrylate, polybutylene terephthalate, acrylonitrile-butadiene-styrene copolymer, polyoxymethylene, polypropylene, polystyrene, polyvinyl chloride, polyamide.

[0023] In one embodiment, the plastic material contains at least one filler, such as an additional reinforcing material, for example, made of flour and / or fragments. In particular, glass fragments can be included as additional reinforcing material.

[0024] 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 area of ​​the conveyor screw can be provided at the inlet zone, from which the 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 plastic material is entrained 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.

[0025] In principle, the plastic material, as a composite material, can have a volume or mass fraction of reinforcing material, in particular fibers, of at least 10%.

[0026] In principle, within the scope of the extrusion process, the orientation of the fibers can also be controlled by varying process parameters, in particular the extrusion temperature, and / or the fibers of the applied plastic material can be deposited 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.

[0027] Furthermore, the proposed solution relates to an extrusion device for extruding plastic material for the additive manufacturing of a component. The extrusion device has a heating zone in which the plastic material to be extruded is heated in order to subsequently feed the plastic material to an extrusion nozzle of the extrusion device, at which a material thread containing plastic material for the component to be produced is extruded. The extrusion device comprises a material feed via which the plastic material can be fed towards the heating zone at an inlet zone of the extrusion device. Furthermore, the proposed extrusion device comprises an additional comminution device with at least one comminution tool. A plastic starting material can be comminuted into a powdered plastic material via the comminution device and conveyed to the material feed.

[0028] By additionally providing a comminution device, powdered plastic material can be prepared before it reaches the actual material feed in the feed zone. This includes, in particular, that powdered plastic material is first generated and prepared via the comminution device and is thus only conveyed to a feed hopper for a screw extruder of the extrusion device after appropriate reduction in size.

[0029] The comminution device can, for example, be configured to comminution the starting material to produce a powdered plastic material with a powder particle size of at least 50 μm and a maximum of 1000 μm. In one embodiment, the comminution device is configured to comminution a starting material in the form of granules, in particular in the form of microgranules, in the form of sticks, or in the form of plastic fragments. The comminution device can thus be provided to process granules, sticks, or plastic fragments fed to it into a plastic powder and to make this plastic powder available at the material feed of the extrusion device for further processing, for example, by a screw extruder.

[0030] In one embodiment, the extrusion device comprises a residue feed through which plastic powder residues can be conveyed to the material feed independently of the comminution device. With such an extrusion device, plastic powder residues can thus be conveyed to the material feed without first having to be fed to the comminution device. The plastic powder residues can thus be conveyed past the comminution device to the material feed via the residue feed. The residue feed thus acts as a type of bypass, allowing the extrusion device to be operated optionally with powdered plastic material with a sufficient powder particle size without the supplied plastic material having to be (further) reduced in size via the comminution device. This enables particularly flexible use of the extrusion device.

[0031] The extrusion device may comprise a conveyor screw having a length-to-diameter ratio of less than 10 for conveying the plastic material through the heating zone and towards the extrusion nozzle.

[0032] Alternatively or additionally, in the heating zone less than 5.5 cm 3 of volume for the plastic material and / or the speed of the conveyor screw can be limited to a maximum of 30 revolutions per minute via an electronic control device of the extrusion device.

[0033] In one variant, several (at least two) powder feeds are provided on the extrusion device, through which powder is fed directly into the feed area of ​​the extrusion device. This allows one or more different powders to be fed more variably to the extruder screw during a printing process. In particular, a dosing unit can be provided for this purpose on at least one of the powder feeds. By dosing the powder(s) via several powder feeds, material gradients (such as color, strength, conductivity, etc.) can then be more precisely adjusted by mixing the material in the extruder during the printing process.

[0034] Alternatively, or in addition, a dosing unit can be integrated into the shredding device. In such a variant, the shredding device can be used to shred, in particular grind, the feed material and then feed it in a metered amount.

[0035] 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.

[0036] A conveying rate of a conveyor screw for the plastic material can also be predetermined by an electronic control device of the extrusion device in such a way that the 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.

[0037] For example, a (volume) conveying rate of the screw conveyor can be specified alternatively or additionally via the control device and can be set to at least 5 cm 3per hour and / or to a maximum of 7500 cm 3 per hour. This includes, in particular, a design variant in which the electronic control device cannot limit the delivery rate below 10 cm 3 per hour, but a maximum of 7500 cm 3 , is adjustable, e.g. 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 is limited.

[0038] For example, a specific (volume) feed rate of the screw conveyor can be preset via the electronic control unit of the extrusion device, optionally depending on the plastic material fed in and / or depending on the volume available within the heating zone for the plastic material (particularly in the case of replaceable housing sections for forming the heating zones). In this way, a user of the extrusion device, for example, only needs to enter the type and shape of the plastic material fed in on an operating unit coupled to the control unit. The electronic control unit then sets a specific feed rate based on stored reference values ​​(below the maximum speed of 30 revolutions per minute for the screw conveyor, which cannot be exceeded) such that the residence time of the 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 and / or whether the plastic material is fed into the extrusion device (only) as a powder or (also) as granules.

[0039] 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 plastic material is thus easily less than 5.5 cm. 3 , especially depending on the volume of the screw conveyor within the heating zone.

[0040] 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 plastic material with a thermoplastic matrix is ​​fed in granular form.

[0041] In one embodiment, the heating zone has a conical taper at one end located in the conveying direction of the plastic material, through which 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.

[0042] The extrusion device has, as already explained, a feed zone, where the 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 is then formed between the feed zone and the heating zone via the barrier zone. It may be advantageous here that

[0043] - 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

[0044] - the housing section which at least partially forms the heating zone has a greater thermal mass than the housing section which forms the barrier zone.

[0045] 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.

[0046] 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 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.

[0047] This includes, in particular, a design variant in which the diameter of a shaft of the conveyor screw within the heating zone, and in particular, for example, in a melting and compression zone of the conveyor screw, is conically enlarged at an angle in the range of 7° to 10° and up to 1.5 to 2 times a smallest (first) diameter of the shaft of the conveyor screw. In a further development based on this, the diameter is then constant up to an end of the conveyor screw lying in the conveying direction, in the region of an ejection zone of the conveyor screw. For example, in one design variant it is provided that the heating zone extends along a conveying direction of the plastic material (specified by the conveyor screw) and parallel to a longitudinal axis of the conveyor screw with a length that corresponds to a maximum of half a (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 relative 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.

[0048] 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.

[0049] In particular, in this embodiment, it can be provided that a pitch of the screw conveyor in the melting and compression zone is reduced compared to a feed area of ​​the screw conveyor, to which the melting and

[0050] Compression zone in the conveying direction and at which the conveyor screw of the

[0051] In relation to the conveying direction of the plastic material within the extrusion device, the feed direction is

[0052] screw longitudinal axis and in the direction of the extrusion nozzle the melt and

[0053] Compression zone follows the feed zone, while the melting and compression zone is followed by the discharge zone.

[0054] 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 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 plastic material in a state of overpressure during operation of the extrusion device in order to allow the plastic material to exit the extrusion nozzle as a material thread.

[0055] 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.

[0056] 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.

[0057] A proposed extrusion device can be configured and provided, in particular, for processing plastic powder residues, making it suitable for implementing a variant of a proposed extrusion process. The advantages and features explained above and below in connection with variants of a proposed extrusion process therefore also apply to variants of a proposed extrusion device, and vice versa.

[0058] 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.

[0059] The attached figures illustrate possible embodiments of the proposed solution

[0060] Herein: Figure 1 shows a schematic representation of a 3D printing device for the additive processing of plastics using a compact screw extruder of the 3D printing device;

[0061] Figure 2 is a cross-sectional view of the screw extruder;

[0062] Figure 3 shows another cross-sectional view of the screw extruder;

[0063] Figure 4 is a top view of the screw extruder.

[0064] Figure 1 shows a schematic perspective view of a 3D printing device in which a variant of a proposed extrusion device is provided with a screw extruder 2 as part of a print head of the 3D printing device. With the aid of the screw extruder 2, plastic material, in particular 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 kinematic system above a platform or base 11 on which the component 1 to be manufactured is formed. Material threads made of molten 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.

[0065] As illustrated by the enlarged cross-sectional views of Figures 2 and 3 and the plan view of Figure 4 for the screw extruder 2, the screw extruder 2 has a conveyor screw 3 for conveying 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 by means of a motor drive (not shown here).

[0066] The housing 4, which at least partially accommodates the conveyor screw 3, is shown in the cross-sectional view of Figures 2 and 3 with 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 plastic material 8, which, as a composite material, comprises, for example, a thermoplastic matrix material with fibers embedded therein. The first housing section

[0067] 41g with the inlet 8, which defines a feed 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

[0068] 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 intake zone 41 from the heating zone 43, the second housing section 42g is made, for example, of a high-strength but thermally poorly conductive material, such as ceramic, and may optionally have additional intake cooling. For example, the housing section 42g of the thermal barrier zone 42 is made of zirconium oxide or aluminum oxide.

[0069] To form the heating zone 43, the third housing section 43g has one or more heating elements 9 arranged circumferentially. The 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.

[0070] 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.

[0071] 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 plastic material 8 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 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 (p) of the order of 58° or more.

[0072] 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.

[0073] 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.

[0074] In the illustrated extrusion device in the form of the screw extruder 2, the volume provided in the heating zone 43 for plastic material 8 inside the housing 4 is limited to less than 5.5 cm3 , in this case about 3.30 cm 3 , limited. In other words, the plastic material 8 to be conveyed along the longitudinal axis of the conveyor screw 3 in the direction of the extrusion nozzle 10 has a maximum volume of 3.30 cm 3 This volume is calculated from the difference between the cavity in the third housing section 43g, in which the conveyor screw 3 extends with its melting and compression zone 32 and its discharge zone 33, and the volume occupied by the conveyor screw 3 itself.

[0075] In addition, 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, the volumetric feed rate of the conveyor screw 3 is set in this case such that the 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 this case, a simultaneously comparatively high discharge of the conveyor screw 3 in the range of up to 7500 cm 3 per hour, especially 5500 cm 3 per hour, 2500 cm 3 per hour, 1000 cm 3 per hour or 250 cm 3per hour. Combined with a length-diameter ratio of the conveyor screw 3 of less than 10, this ensures that the plastic material 8 remains in the heating zone 43 for a comparatively short time, thereby avoiding 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 in accordance with the aforementioned process parameters, any fibers contained in the powdered or granular plastic material 8 are only sheared off to a comparatively small extent and approximately 70% of the fibers are deposited in the travel direction of the extrusion nozzle 10. This makes it possible to influence the fiber orientation and thus the strength of the component 1 to be produced, regardless of the component geometry.During a 3D printing process, only the travel path of the extrusion nozzle 10 needs to be manipulated.

[0076] The throughput time in the heating zone 43 and along the melting and compression zone 32 of the conveyor screw 3 is fundamentally dependent on the 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 results - in combination with the length-to-diameter ratio of the conveyor screw 3 of less than 10 - 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, which is determined in particular by the feed rate, the specified volume of less than 5.5 cm 3Because the amount of plastic material 8 is kept small in the heating zone 43, which is also geometrically comparatively short (in particular with respect to the length of the conveyor screw 3), 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.

[0077] The compact screw extruder 2 shown in Figures 1 to 4 is capable of processing plastic material 8 that contains, for example, 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 fillers, such as 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.

[0078] In one application scenario, the plastic material 8 has a fiber content of greater than or equal to 10%, with no continuous fibers being included.

[0079] 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 example, layers (material webs) for component 1 can be applied using the extrusion process implemented with the screw extruder 2, using extruded material threads made of granular plastic material 8 and / or powdered plastic material 8R.

[0080] The screw extruder 2 shown is designed to process plastic powder residues 8R for additive manufacturing. It has been shown that plastic powder residues originating as excess residue from another manufacturing process that processes plastic powder are generally well suited for processing using the screw extruder 2 described above. The plastic powder residues 8R can, for example, be excess residues intended for disposal and originating from a selective laser sintering process or binder jetting. Plastic powder residues with a powder particle size of at least 50 pm and a maximum of 1000 pm are generally considered suitable.The use of a plastic powder and in particular of plastic powder residues offers the advantage that there are significantly smaller conveying fluctuations during the processing of the plastic material and, in addition, a comparatively dense and thus good filling of the housing space accommodating the screw extruder 2 can be achieved.

[0081] In the screw extruder 2 shown in Figures 1 to 4, a residue feed 2R is provided for feeding plastic powder and plastic powder residues 8R. Via this residue feed, plastic powder residues 8R can be conveyed directly to the funnel-shaped inlet 5 with the feed zone 41 and thus to the material feed for the screw extruder 2.

[0082] The residue feed 2R is provided here as a bypass to a possibly additionally provided comminution device 2Z of the screw extruder 2. This comminution device 2Z is ​​provided, for example, above the intake zone 41 and thus above the funnel-shaped inlet 5. The casing device 2Z has at least one comminution tool for comminuting a starting material, for example in the form of granules, sticks, or fragments of plastic, and for producing a powdered plastic material therefrom (in particular, plastic powder with a powder particle size in the range of 50 μm to 1000 μm).

[0083] In deviation from the schematic representation of Figures 1 to 4, in the illustrated embodiments, it is not mandatory that the residue feed 2R and / or the comminution device 2Z are fixed directly to the screw extruder 2. Rather, the residue feed 2R and / or the comminution device 2Z can be provided as stationary components (assemblies) of a 3D printing device, from which powder is fed to the movable screw extruder 2 for printing the component.

[0084] The 3D printing device comprising the screw extruder 2 can thus be fed with coarser plastic material via the comminution device 2Z, which is processed into a plastic powder via one or more comminution tools of the comminution device 2Z and subsequently conveyed to the conveyor screw of the screw extruder 2. The plastic powder coming from the comminution device 2Z can, of course, be mixed with the plastic powder or the plastic powder residues from the residue feed 2R. Alternatively, the screw extruder 2 can also be operated solely with plastic powder residues 8R from the residue feed 2R or solely with plastic powder from the comminution device 2Z.Irrespective of this, the screw extruder 2 can of course also continue to be operated with granular plastic material which is made available uncomminuted at the feed zone 41 via the residue feed 2R or - in particular when the comminution tool is not active - via the comminution device 2Z.

[0085] In one embodiment, the screw extruder 2 can be provided with several (at least two) powder feeds, through which powder is fed directly into the feed area 31. This allows one or more different powders to be fed more variably to the extruder screw 3 during a printing process. In particular, a dosing unit can be provided for this purpose on at least one of the powder feeds. By dosing the powder(s) via several powder feeds, material gradients (such as color, strength, conductivity, etc.) can then be adjusted more precisely by mixing the material during the printing process.

[0086] Alternatively or in addition, a dosing unit can be integrated into the shredding device. In such a variant, the shredding device 2Z can thus be used to shred, in particular grind, the feed material and then feed it in a metered amount.

[0087] List of reference symbols

[0088] 1 component

[0089] 10 Extrusion nozzle

[0090] 11 Base

[0091] 2 screw extruders (extrusion device)

[0092] 2R residue feed

[0093] 2Z shredding device

[0094] 20 Control device

[0095] 3 Conveyor screw / extruder screw

[0096] 31 catchment area

[0097] 32 Melting and compression zone

[0098] 33 Ejection zone

[0099] 34 End area

[0100] 340 chamfer

[0101] 4 housings

[0102] 41 catchment area

[0103] 42 (thermal) barrier zone

[0104] 41g, 42g, 43g housing section

[0105] 43 heating zones

[0106] 5 Entrance

[0107] 6 Wave

[0108] 7 Reservoir

[0109] 8 Granular (possibly fiber-reinforced) plastic material

[0110] 8R Powdered (possibly fiber-reinforced) plastic material

[0111] 9 Heating element

[0112] V taper P opening angle

Claims

Claims 1. Use of plastic powder residues (8R), which are intended for disposal as surplus residue after carrying out at least one plastic powder processing manufacturing process, as plastic material for the additive manufacturing of a component with an extrusion device (2).

2. Use according to claim 1, characterized in that the plastic powder residues are fed to the extrusion device (2) as the sole starting material or mixed with at least one further material, in particular a plastic powder for the additive manufacturing of the component.

3. Use according to claim 1 or 2, characterized in that the plastic powder residues (8R) originate from an additive manufacturing process not based on extrusion.

4. Use according to claim 3, characterized in that the plastic powder residues (8R) originate from the implementation of a selective laser sintering or a binder jetting.

5. Process for extruding plastic material for the additive manufacturing of a Component (1 ), wherein the plastic material (8) is fed to an extrusion device (2) and heated in a heating zone (43) of the extrusion device (2) in order to subsequently extrude the plastic material (8) to an extrusion nozzle (10) of the Extrusion device (2) on which a material thread with plastic material (8) for the component to be produced is extruded, characterized in that at least part of the plastic material (8) fed to the extrusion device (2) consists of plastic powder residues (8R) which were intended for disposal as excess residue after carrying out at least one plastic powder-processing manufacturing process.

6. Method according to claim 5, characterized in that the plastic powder residues are fed to the extrusion device (2) as the sole starting material or mixed with at least one other material.

7. Method according to claim 5 or 6, characterized in that the plastic powder residues (8R) originate from an additive manufacturing process not based on extrusion.

8. The method according to claim 7, characterized in that plastic powder residues (8R) are used which originate from the implementation of a selective laser sintering or a binder jetting.

9. Method according to one of the preceding claims, characterized in that the used plastic powder residues (8R) contain at least one filler, in particular fibers.

10. Method according to one of the preceding claims, characterized in that the extrusion device (2) comprises a conveyor screw (3) for conveying the plastic material (8) in the direction of the extrusion nozzle (10). 1 1. Method according to claim 10, characterized in that a rotational speed of the conveyor screw (3) is limited to a maximum of 30 revolutions per minute via an electronic control device (20) of the extrusion device (2).

12. The method according to claim 10 or 11, characterized in that a conveyor screw (3) of the extrusion device (2) is used to convey the plastic material (8, 8R) through the heating zone (43), which has a length-diameter ratio of less than 10.

13. Method according to one of claims 10 to 12, characterized in that a conveying rate of the conveyor screw (3) for the plastic material (8, 8R) is set such that the 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.

14. Extrusion device for extruding plastic material for the additive manufacturing of a component (1), wherein the extrusion device (2) has a heating zone (43) in which the plastic material to be extruded is heated in order to subsequently feed the plastic material (8) to an extrusion nozzle (10) of the extrusion device (2), at which a material thread with plastic material for the component to be produced can be extruded, characterized in that the extrusion device (2) comprises a material feed, via which the plastic material (8) can be fed in the direction of the heating zone (42) at a feed zone (41) of the extrusion device (2), and the extrusion device (2) comprises an additional comminution device (2Z) with at least one comminution tool, via which a starting material made of plastic can be comminuted into a powdered plastic material and conveyed to the material feed.

15. Extrusion device according to claim 14, characterized in that the comminution device (2Z) is designed for comminution of the starting material to produce a powdered plastic material with a powder particle size of at least 50 pm and a maximum of 1000 pm.

16. Extrusion device according to claim 14 or 15, characterized in that the comminution device (2Z) is designed to comminute a starting material which is in the form of a granulate, in particular microgranulate, in the form of sticks or in the form of fragments of plastic.

17. Extrusion device according to one of claims 14 to 16, characterized in that the extrusion device (2) comprises a residue feed, via which plastic powder residues (8R) can be conveyed to the material feed independently of the comminution device (2Z).

18. Extrusion device according to one of claims 13 to 17, characterized in that the extrusion device (2) comprises a conveyor screw (3) for conveying the plastic material (8) in the direction of the extrusion nozzle (10).

19. Extrusion device according to claim 18, characterized in that a rotational speed of the conveyor screw (3) is limited to a maximum of 30 revolutions per minute via an electronic control device (20) of the extrusion device (2).

20. Extrusion device according to claim 18 or 19, characterized in that a conveyor screw (3) of the extrusion device (2) is used to convey the plastic material (8, 8R) through the heating zone (43), which has a length-diameter ratio of less than 10. 21 . Extrusion device according to one of claims 18 to 20, characterized in that a conveying rate of the conveyor screw (3) for the Plastic material (8) is predetermined such that the 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.

22. Extrusion device according to one of claims 18 to 21, characterized in that a diameter of a shaft (6) of the conveyor screw (3) within the heating zone (43) changes at least once in the conveying direction of the plastic material (8) is enlarged.

23. Extrusion device according to claim 22, characterized in that the diameter of the shaft (6) within the heating zone (43) increases conically at 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 conveyor screw (3).

24. Extrusion device according to one of claims 18 to 23, characterized in that the conveyor screw (3) with a melting and compression zone (32) and an ejection zone (33) following thereon in the conveying direction of the plastic material (8) and having an axial end of the conveyor screw (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 conveyor screw (3) measured along the longitudinal axis.

25. Extrusion device according to one of claims 18 to 24, characterized in that the extrusion device (2) has a feed zone (41) at which the plastic material (8) can be fed to the conveyor screw (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 device (2), wherein the barrier zone (42) is formed by a housing section (42g) made of a material which has a lower thermal conductivity than the material from which a housing section (43g) adjacent to the barrier zone (42) is made, with which the heating zone (43) is at least partially formed, and the housing section (43g) at least partially forming the heating zone (43) has a greater thermal mass than the housing section (42g) forming the barrier zone (42).

26. Extrusion device according to one of claims 14 to 25, characterized in that the heating zone (43) has a maximum length of 40 mm and a maximum diameter of 25 mm.

27. 3D printing devices with at least one extrusion device according to one of the Claims 14 to 26.

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