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

Abstract

The proposed solution relates in particular to the use of plastic powder residues (8R) that are intended for disposal as excess residue after carrying out at least one plastic powder processing manufacturing process, as plastic material for the additive manufacturing of a component using an extrusion device (2)

Description

[0001] The proposed solution relates in particular to the application of plastic powder residues as a plastic material for the additive manufacturing of a component with an extrusion device, as well as an extrusion process and an extrusion device.

[0002] Extrusion equipment, such as screw extruders, is primarily used in the mass production of components via injection molding and die casting. In these machines, a screw, an injection nozzle, and a die are typically arranged horizontally. The material, usually in granular or powder form, is generally fed into the rearmost part of the screw extruder, the so-called feed zone. The material is fed vertically onto the screw via a hopper mounted on a section of the extruder tube. A sufficiently large cross-section in the hopper prevents bridging, allowing the material to fall onto the screw by gravity and be drawn in. In mass production, three-zone screw extruders are typically used, which draw in the material and convey it to the nozzle.The material is compressed, de-aired, and homogenized. Then, pressure is built up to fill the die.

[0003] The feed zone of a screw extruder is often designed as a pipe section within the extruder housing. A hopper is positioned on this pipe section, through which the material can be fed to the screw. The minimum cross-section of the pipe section and hopper must be selected to prevent bridging of the granular material. This is highly dependent on the angle of repose and the coefficient of friction of the bulk material being used.

[0004] German patent 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 material supplied as granules. In a movable print head of the 3D printing device, the thermoplastic material is extruded layer by layer by means of a vertically arranged screw extruder to create a three-dimensional component. DE 10 2014 018 081 A1 does not contain further details on how the material is fed to the extruder screw.

[0005] Typically, in additive manufacturing of a component, granular plastic material is fed into the extrusion device. The granules are then first broken down, for example, by a screw extruder under the application of heat.

[0006] Against this background, the proposed solution is based on the task of further making a process for the additive manufacturing of components from a plastic material more flexible and, if necessary, also more cost-effective.

[0007] This problem can be solved, for example, by using leftover plastic powder (especially plastic powder residues) that, after at least one manufacturing process involving plastic powder, are typically destined for disposal but can now be used for additive manufacturing in an extrusion device. Accordingly, it is proposed to utilize leftover plastic powder for additive manufacturing that was previously typically disposed of and for which no further use was intended. It has been recognized that leftover plastic powder from other manufacturing processes, particularly other additive manufacturing processes, can still be used for the additive manufacturing of a component with an extrusion device. Such leftover plastic powder can thus be put to further use.

[0008] For example, the plastic powder residue from the extrusion device can be used 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 for mixing with the plastic powder residue can be, for example, a plastic powder, particularly one from a different source than the plastic powder residue. The plastic powder residue, for instance, can originate from a non-extrusion-based additive manufacturing process. Conversely, the plastic powder to be mixed with it can originate from a different non-additive or additive manufacturing process or be intended for initial use. Using plastic powder residue or plastic powder in general allows for higher packing densities in the feed of the extrusion device.This results in a more uniform extrusion, which in turn is reflected in very good surface qualities of the components to be manufactured.

[0009] For example, it has proven advantageous to utilize residual plastic powder in an extrusion process, specifically powder left over from selective laser sintering or binder jetting. In such a design, residual plastic powder, generated as excess material from selective laser sintering or binder jetting, is used for the additive manufacturing of a component with an extrusion device. Thus, the extrusion process utilizes residual plastic powder that remained as byproducts during the production of a different component using a different manufacturing concept.

[0010] Against this background, the proposed solution also concerns a process for extruding plastic material for the additive manufacturing of a component. In this process, the plastic material is fed into an extrusion device and heated in a heating zone of the extrusion device. The plastic material is then fed into an extrusion die of the extrusion device, where a filament of plastic material for the component to be manufactured is extruded. At least part of the plastic material fed into the extrusion device in the proposed solution consists of plastic powder residues that were intended for disposal as excess residue after at least one manufacturing process that utilizes plastic powder.

[0011] As 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, these plastic powder residues can originate from a non-extrusion-based additive manufacturing process, in particular from selective laser sintering or binder jetting.

[0012] The plastic powder residues used can contain at least one filler, such as fibers and / or particles. Similarly, plastic powder residues with or without fibers can be mixed with separately supplied 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.

[0013] To convey the plastic material through the heating zone, a screw conveyor of the extrusion device can be used, which has a length-to-diameter ratio of less than 10. In a given process, the extrusion device can therefore include such a screw conveyor as part of a screw extruder. Alternatively, the use of a piston extruder or gear extruder is also possible, for example. The use of a screw extruder is therefore not mandatory.

[0014] Furthermore, in one version, the heating zone can be less than 5.5 cm. 3 A sufficient volume is provided for the plastic material, and the rotational speed of a screw conveyor in the extrusion device (around its longitudinal axis) is limited to a maximum of 30 revolutions per minute. A screw conveyor (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 screw speed of 30 revolutions per minute or less can be limited to additively manufacture a component with plastic material using extrusion. This prevents degradation of the plastic material during extrusion and – in the case of fiber-reinforced plastic material – simultaneously achieves 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 screw speed – especially in combination with a length-to-diameter ratio of less than 10 for the screw and a length of 5.5 cm – is crucial for optimal performance. 3or a less limited volume for plastic material in the heating zone – this can, for example, have a positive effect on the shear forces applied to the plastic material during extrusion via the screw conveyor, resulting in comparatively long and unsherked fibers in the finished component. The limited rotational speed of the screw conveyor leads to peripheral speeds (which are crucial for the shear rate) that are 50 to 80 times lower than in conventional injection molding machines.

[0015] Furthermore, in one design variant, it may be advantageous to have a volume of approximately 2.5 cm³ in the heating zone. 3 up to 5.5 cm 3 , especially 2.5 cm 3 up to 4.5 cm 3 to provide the plastic material. In particular, one version requires a volume of approximately 3.0 cm³. 3 up to 3.5 cm 3 , for example at approximately 3.30 cm 3, provided. The volume provided 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 conveying screw extends, minus the volume occupied by the conveying screw itself in the heating zone.

[0016] In one version, the feed rate of the screw conveyor for the plastic material is set such that the plastic material being conveyed towards 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 unit, taking into account the screw conveyor's rotational speed, which is limited to a maximum of 30 revolutions per minute. Alternatively, the feed rate and / or residence time can be adjusted by changing the screw conveyor's rotational speed.

[0017] Depending in particular on the type of plastic material used and the form of the raw material being fed, the conveying 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 of the plastic material being conveyed in the heating zone. For example, a residence time in the range of 1.5 to approximately 60 seconds or several minutes has proven advantageous for certain plastic materials when the plastic material is fed to the extrusion device in powder or granule form.

[0018] A conveying rate of the plastic material can, for example, be set to a value of at least 5 cm. 3 be set per hour and / or to a maximum value of 7500 cm 3The feed rate can be set per hour. The screw conveyor can therefore have a comparatively high discharge rate. For example, the conveying rate can be in the range of 10 cm. 3 per hour up to 5500 cm 3 be set per hour, especially e.g. 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

[0019] In one version, 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 area of ​​150 cm 3 hour up to 200 cm 3 set per hour. For example, for a flow rate of 10 cm 3 per hour and a volume of 3.3 cm³ provided for the plastic material in the heating zone 3The maximum dwell time of the plastic material in the heating zone must be set to less than 20 minutes.

[0020] 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: polycarbonate, polylactate, polyethylene, polyethylene terephthalate, polymethyl methacrylate, polybutylene terephthalate, acrylonitrile butadiene styrene copolymer, polyoxymethylene, polypropylene, polystyrene, polyvinyl chloride, polyamide.

[0021] In one version, the plastic material contains at least one filler, such as an additional reinforcing material, for example, made of flour and / or fragments. In particular, fragments of glass may be included as an additional reinforcing material.

[0022] In one embodiment, the plastic material is fed into the extrusion device via a material feeder at a feed zone. For example, a funnel-shaped inlet is provided to define this feed zone. A feed section of the screw conveyor can be provided at the feed zone. From this section, the plastic material fed into the feed zone, for example, in powder or granular form, is conveyed towards the extrusion die by rotating the screw conveyor around its longitudinal axis. The plastic material is carried along by the screw conveyor's flights. These flights are designed such that the plastic material is not compressed until it reaches the heating zone.Compression via the screw conveyor is then provided, for example, only in a melting and compression zone of the screw conveyor, which is located in 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 the screw shaft forming the screw flights.

[0023] 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%.

[0024] In principle, the orientation of the fibers can also be controlled within the extrusion process 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 joined together.

[0025] 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. This heated material is then fed into an extrusion die, where a filament of plastic material is extruded to form the component to be manufactured. The extrusion device includes a material feed through which the plastic material can be fed towards the heating zone at an infeed zone. The proposed extrusion device also includes an additional comminution device with at least one comminution tool. The comminution device reduces the initial plastic material to a powdered form, which can then be conveyed to the material feed.

[0026] By additionally providing a comminution device, powdered plastic material can be supplied before it reaches the actual material feed in the feed zone. This specifically means that the comminution device first produces and supplies powdered plastic material, and only after appropriate reduction in size is it conveyed to a feed hopper for a screw extruder of the extrusion device.

[0027] The comminution device can, for example, be set up to comminute the starting material for the production of a powdered plastic material with a powder particle size of at least 50 µm and a maximum of 1000 µm.

[0028] In one embodiment, the comminution device is configured to comminute a feed material that is in the form of granules, particularly microgranules, sticks, or fragments of plastic. The comminution device can thus be designed to process the supplied granules, sticks, or fragments of plastic into a plastic powder and to supply this plastic powder to the material feed of the extrusion device for further processing, for example, by a screw extruder.

[0029] In one embodiment, the extrusion device includes a residual feeder, allowing plastic powder residues to be conveyed to the material feed independently of the comminution unit. With such an extrusion device, plastic powder residues can thus be conveyed to the material feeder without first having to be fed to the comminution unit. The plastic powder residues can therefore be conveyed to the material feeder via the residual feeder, bypassing the comminution unit. The residual feeder thus functions as a kind of bypass, enabling the extrusion device to be operated with powdered plastic material of a sufficient particle size without the need for the supplied plastic material to be (further) reduced in size by the comminution unit. This allows for particularly flexible use of the extrusion device.

[0030] The extrusion device can have a conveying screw with a length-to-diameter ratio of less than 10 for conveying the plastic material through the heating zone and towards the extrusion die.

[0031] Alternatively or additionally, less than 5.5 cm can be used in the heating zone. 3 a sufficient volume for the plastic material must be provided 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.

[0032] In one embodiment, the extrusion device is equipped with several (at least two) powder feeders through which powder is fed directly into the feed area of ​​the extrusion device. This allows for the variable feeding of one or more different powders to the extruder screw during a printing process. In particular, a dosing unit can be provided at least at one of the powder feeders for this purpose. By dosing the powder(s) via multiple powder feeders, material gradients (such as color, strength, conductivity, etc.) can be more precisely controlled by mixing the material in the extruder during the printing process.

[0033] Alternatively or additionally, a dosing unit can be integrated into the shredding device. In such a design variant, the feed material can thus be shredded, in particular ground, and then metered into the process.

[0034] One embodiment of a proposed extrusion device enables the implementation of one embodiment of a proposed extrusion process. Advantages and features described in connection with embodiments of a proposed extrusion process therefore also apply to embodiments of a proposed extrusion device, and vice versa.

[0035] An electronic control device of the extrusion device can also be used to specify a conveying rate of a screw conveyor for the plastic material such that the plastic material to be conveyed towards 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.

[0036] For example, the control unit can alternatively or additionally specify a (volume) conveying rate of the screw conveyor, with a minimum of 5 cm 3specified per hour and / or up to a maximum of 7500 cm 3 limited per hour. This includes, in particular, a variant in which the electronic control unit does not allow the feed rate to fall below 10 cm. 3 per hour, but a maximum of 7500 cm 3 , 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 is limited per hour.

[0037] The electronic control unit of the extrusion device can, for example, preset a specific (volume) feed rate of the screw conveyor, possibly depending on the type of plastic material being fed and / or the volume available within the heating zone for the plastic material (especially with interchangeable housing sections for creating the heating zones). In this way, a user of the extrusion device only needs to enter the type and shape of the plastic material being fed into a control unit connected to the control unit. The electronic control unit then uses stored reference values ​​(within the maximum screw speed of 30 revolutions per minute, which cannot be exceeded) to set a specific feed rate so 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 to the extrusion device (only) as powder or (also) as granules.

[0038] In one version, 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 in this version is therefore easily less than 5.5 cm³. 3 , especially depending on the volume the screw conveyor occupies within the heating zone.

[0039] In one embodiment, the screw conveyor has a screw blade that rises in the conveying direction of the plastic material. The screw blade can have a rise of, for example, 7 mm to 17 mm, and in particular, 8 mm to 15 mm. Especially with such a screw conveyor configuration, in combination with the parameters specified based on the proposed solution, it has been shown that, at least when using granular plastic material with a thermoplastic matrix, advantageous fiber orientations in the finished component, as well as comparatively long and unsherked fibers, can be achieved.

[0040] In one design variant, the heating zone has a conical taper at one end, located in the conveying direction of the plastic material, through which the plastic material can be fed to the extrusion die. For example, this conical taper then has an opening angle in the range of 50° to 65°, and 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.

[0041] As already explained, the extrusion device has a feed zone where the plastic material can be fed to the screw conveyor. In one design variant, the heating zone follows a barrier zone in the conveying direction of the plastic material. This barrier zone spatially separates the heating zones from the feed zone of the extrusion device. A thermal barrier, for example, is formed between the feed zone and the heating zone via this barrier zone. An advantage of this design can be that... - the barrier zone is formed by a housing section made of a material that has a lower thermal conductivity than the material from which a housing section adjacent to the barrier zone is formed, through which the heating zone is at least partially formed, and - the housing section that at least partially forms the heating zone has a larger thermal mass than the housing section that forms the barrier zone.

[0042] For example, the housing section of the barrier zone is made of a high-strength or hard, but thermally poorly conductive material, such as a ceramic. Optionally, cooling can also be provided at the barrier zone 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.

[0043] In one embodiment, the diameter of a screw conveyor shaft increases at least once within the heating zone in the conveying direction of the plastic material. For example, a conical increase in diameter within the heating zone is provided to aid the compression of the plastic material. This embodiment therefore includes a shaft diameter of a first (smaller) diameter on a first screw section of the screw conveyor, while the shaft of a second (larger) diameter on a subsequent screw section in the conveying direction is also present. Consequently, the screw conveyor can be designed, in particular, as a plugging screw conveyor.For the diameter increase between the first and second screw sections, a conical transition area can be provided, for example, where the diameter of the screw shaft increases from the first diameter to the second diameter in the conveying direction.

[0044] This includes, in particular, a design variant in which the diameter of a screw conveyor shaft within the heating zone, and especially, for example, in a melting and compression zone of the screw conveyor, is conically increased at an angle of 7° to 10° and to a factor of 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 area of ​​an ejection zone of the screw conveyor.

[0045] For example, one embodiment provides that the heating zone extends along a conveying direction of the plastic material (defined by the screw conveyor) and parallel to a longitudinal axis of the screw conveyor, with a length that is at most half the (total) length of the screw conveyor measured along its longitudinal axis. Thus, the heating zone length is at most half the length of the screw conveyor. Such a geometric limitation of the heating zone length in relation to the total length of the screw conveyor has proven advantageous in certain configurations, particularly with regard to the intended length-to-diameter ratio of the screw conveyor being less than 10.

[0046] Alternatively or additionally, the screw conveyor can extend within the heating zone with a melting and compression zone and an ejection zone following this zone in the conveying direction of the plastic material, the ejection zone having an axial end, wherein the melting and compression zone and the ejection zone together do not exceed one-third of the length of the screw conveyor measured along its longitudinal axis. The portion of the screw conveyor 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 screw conveyor.

[0047] In this particular embodiment, the pitch of the screw feeder can be designed so that it is less steep in the melting and compression zone compared to the feed zone. The melting and compression zone follows the feed zone in the conveying direction, and the raw material (plastic) is fed into the screw feeder at this point. Thus, with respect to the conveying direction of the plastic material within the extrusion device, the melting and compression zone follows the feed zone along the screw's longitudinal axis and in the direction of the extrusion die, while the discharge zone follows the melting and compression zone.

[0048] In one embodiment, a reservoir is provided in the area between the axial end of the screw conveyor (located in the conveying direction of the plastic material) and the extrusion die. This reservoir holds molten plastic material under pressure. The extrusion device thus has a reservoir in this area, designed and intended to maintain molten plastic material under pressure during operation, allowing it to exit the extrusion die as a filament.

[0049] For example, the reservoir extends with a length parallel to the conveying direction and parallel to the longitudinal axis of the screw conveyor, which corresponds to a maximum of one-third of the screw conveyor's length measured along its longitudinal axis. The reservoir length therefore does not exceed one-third of the screw conveyor's total length. For example, the reservoir has a maximum length of one-fifteenth of the screw conveyor's length.

[0050] In one version, the extrusion die has a nozzle diameter ranging from 0.25 mm to 2 mm. In particular, the extrusion die can be interchangeable, allowing the use of extrusion dies with different nozzle diameters, e.g., each ranging from 0.25 mm to 2 mm, on the extrusion device.

[0051] A proposed extrusion device can be specifically designed and configured for processing residual plastic powder, making it suitable for carrying out various embodiments of a proposed extrusion process. The advantages and features explained above and below in connection with embodiments of a proposed extrusion process therefore also apply to embodiments of a proposed extrusion device, and vice versa.

[0052] A further aspect of the proposed solution concerns 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 fused deposition modeling 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.

[0053] The attached figures illustrate possible implementation variants of the proposed solution.

[0054] This shows: Fig. 1 a schematic representation of a 3D printing device for the additive processing of plastics using a compact screw extruder of the 3D printing device; Fig. 2 a cross-sectional view of the screw extruder; Fig. 3 another cross-sectional view of the screw extruder; Fig. 4 A top view of the screw extruder.

[0055] The Fig. Figure 1 shows a schematic and perspective view of a 3D printing device in which an embodiment of a proposed extrusion device is provided with a screw extruder 2 as part of a print head of the 3D printing device. Using 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 fused deposition. The screw extruder 2 is movable via a three-axis kinematic system above a platform or substrate 11 on which the component 1 to be manufactured is formed. Material strands of molten plastic material are applied to the substrate 11 via an extrusion die 10 of the screw extruder 2. The extrusion process is controlled by an electronic control unit 20.

[0056] As can be seen from the enlarged cross-sectional views of the Fig. 2 and Fig. 3 and based on the top view of the Fig. As illustrated in Figure 4 for the screw extruder 2, the screw extruder 2 has a conveying screw 3 for conveying powdered or granular plastic material 8 towards the extrusion die 10. This conveying screw 3 extends along a longitudinal axis over a feed area 31, a subsequent melting and compression zone 32, and up to an discharge zone 33. The conveying screw 3 is rotatably mounted about its longitudinal axis in a housing 4 of the screw extruder 2 and is driven by a motor (not shown).

[0057] The housing 4, which at least partially accommodates the auger 3, is shown in the cross-sectional view of the Fig. 2 and Fig. Figure 3 shows different housing sections 41g, 42g, and 43g. The individual housing sections 41g, 42g, and 43g can also form independent housing parts that are connected to each other and together define the housing 4. A first housing section 41g defines a funnel-shaped inlet 5 for feeding the powdered or granular plastic material 8, which, as a composite material, for example, comprises a thermoplastic matrix material with embedded fibers. Adjoining the first housing section 41g with the inlet 8, which defines a feed zone 41 for feeding the plastic material, a second housing section 42g forms a thermal barrier zone 42 in the conveying direction towards the extrusion die 10. The barrier zone 42 separates the feed 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, for example, made of a high-strength but thermally very poorly conductive material, such as a ceramic, and may optionally feature additional intake cooling. For example, the housing section 42g of the thermal barrier zone 42 consists of zirconium oxide or aluminum oxide.

[0058] For the formation of the heating zone 43, the third housing section 43g has one or more heating elements 9 arranged circumferentially. The plastic material 8 conveyed towards the extrusion die 10 is melted by the heating elements 9 so that it can be extruded from the extrusion die 10 in a filament whose thickness is determined by the geometry of the extrusion die 10, which is interchangeably fixed to the housing 4.

[0059] The vertically arranged conveying screw 3, when installed as intended, extends within the housing 4 such that the intake area 31 of the conveying screw 3 is completely enclosed by the first housing section 41g and the intake zone 41 formed therein. The plastic material 8 is compressed by the conveying screw 3 via the compression and melting zone 32 of the conveying 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 conveying screw 3 is designed as a plug screw, in which the diameter of a shaft 6 of the conveying 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 conveying screw 3.

[0060] In an ejection zone 33 of the screw conveyor 3, which adjoins the melting and compression zone 32 and is also located within the heating zone 43, the (larger) diameter of the shaft 6 of the screw conveyor 3 remains constant. A reservoir 7 adjoins the ejection zone 33, and thus an axial end of the screw conveyor 3, in the conveying direction of the plastic material 8. This reservoir 7 is formed between the axial end of the screw conveyor 3 and the extrusion die 10 and is defined, at least partially, by a conical taper V of the inner, screw conveyor 3-facing surfaces of the third housing section 43g in the heating zone 43. Molten plastic material is held under pressure in this reservoir 7, which has a maximum length of 1 / 15 of the total length of the screw conveyor 3.The internally provided conical taper V in the third housing section 43g in the direction of the extrusion nozzle 10 has an opening angle φ on the order of 58° or more.

[0061] In the illustrated screw extruder 2, the plastic material 8 is initially drawn into the funnel-shaped inlet 5 of the feed screw 3 in the feed area 31 and transported downwards along the conveying direction by the feed screw 3. 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, which forms the barrier zone 42. Furthermore, it is ensured that no compression occurs within the housing 4 until the heating zone 43 is reached, due to a change in the pitch of the screw flights or the diameter of the shaft 6 of the feed screw 3.

[0062] Only in the heating zone 43, which directly adjoins the barrier zone 42 below, is the plastic material 8 melted and compressed. For this purpose, radially arranged heating elements 9 are provided on the housing side of the heating zone 43. These elements extend over the entire length of the heating zone 43 and enable a very localized application of heat energy. The heating zone 43 has a maximum length on the housing side that corresponds to half the length of the screw conveyor 3. The third housing section 43g, which forms the heating zone 43, has a higher thermal conductivity than the second housing section 42g, which forms the barrier zone 42, and also has a greater thermal mass than this second housing section 42g.

[0063] In the extrusion device shown, 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 less than 5.5 cm³.3 , presently on approximately 3.30 cm 3 , limited. In other words, the maximum volume of the plastic material 8 to be conveyed along the longitudinal axis of the screw conveyor 3 towards the extrusion die 10 in the heating zone 43 is 3.30 cm³. 3 available. This volume is calculated from the difference between the cavity in the third housing section 43g, in which the conveying screw 3 extends with its melting and compression zone 32 and its discharge zone 33, and the volume occupied by the conveying screw 3 itself.

[0064] Furthermore, the electronic control unit 20 limits the maximum speed of the screw conveyor 3 to 30 revolutions per minute around its longitudinal axis. Taking this speed limitation into account, the volumetric conveying rate of the screw conveyor 3 is set such that the plastic material 8, which is conveyed towards the extrusion die 10, remains in the heating zone 43 for a maximum of 20 minutes, here, for example, at least 1.5 seconds, but no more than 20 minutes. In this case, a comparatively high discharge rate of up to 7500 cm³ is achieved by the screw conveyor 3. 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-to-diameter ratio of less than 10 for the screw conveyor 3, this ensures that the plastic material 8 remains in the heating zone 43 for a comparatively short time, thus preventing degradation of the plastic material 8. This is further enhanced by the heating zone 43 having 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, any fibers potentially 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 direction of travel of the extrusion die 10. This allows for influencing the fiber orientation and thus the strength of the component 1 to be manufactured, independent of the component geometry.During a 3D printing process, only the travel path of the extrusion nozzle 10 needs to be manipulated.

[0065] The throughput time in the heating zone 43 and along the melting and compression zone 32 of the screw conveyor 3 is fundamentally dependent on the plastic material 8 used. According to the proposed solution, the maximum speed of the screw conveyor 3 is limited to a maximum of 30 revolutions per minute. This results – in combination with the length-to-diameter ratio of the screw conveyor 3 being 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. This short residence time, determined in particular by the conveying rate, is further ensured by the specified volume of less than 5.5 cm³. 3The defined small quantity of plastic material 8 in the heating zone 43, which is also geometrically comparatively short (especially in relation to the length of the screw conveyor 3), means that 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.

[0066] The one in the Fig. 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, and 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. Flour or fragments of glass or other materials can also be used as additional reinforcement. The plastic can also be mineral-reinforced.

[0067] In one application scenario, the plastic material 8 has a fiber content of greater than or equal to 10%, without containing any continuous fibers.

[0068] 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 efficiently additively manufactured. For example, layers (material webs) can be applied to component 1 via the extrusion process implemented with the screw extruder 2 using extruded material filaments made of granular plastic material 8 and / or powdered plastic material 8R.

[0069] 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 material from other plastic powder processing methods are generally suitable for processing via the screw extruder 2 described above. These plastic powder residues 8R could, for example, be excess material intended for disposal from a selective laser sintering process or binder jetting. Plastic powder residues with a particle size of at least 50 µm and at most 1000 µm are considered generally suitable.The use of a plastic powder, and especially plastic powder residues, offers the advantage that there are significantly smaller fluctuations in the conveying rate during the processing of the plastic material, and a comparatively dense and therefore good filling of the housing space accommodating the screw extruder 2 can be achieved.

[0070] In the Fig. In screw extruder 2, as shown in figures 1 to 4, a residue feeder 2R is provided for the supply of plastic powder and plastic powder residues 8R. Through this residue feeder, 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 screw extruder 2.

[0071] The residual feed 2R is provided here as a bypass to an optionally provided comminution unit 2Z of the screw extruder 2. This comminution unit 2Z is, by way of example, provided above the feed zone 41 and thus above the funnel-shaped inlet 5. The casing unit 2Z has at least one comminution tool to comminute a starting material, for example in the form of granules, sticks, or fragments of plastic, and to provide a powdered plastic material (in particular, plastic powder with a powder particle size in the range of 50 µm to 1000 µm).

[0072] In deviation from the schematic representation of the Fig.In the illustrated embodiments 1 to 4, it is not mandatory that the residual feed 2R and / or the comminution device 2Z are directly attached to the screw extruder 2. Rather, the residual 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 screw extruder 2, which is movable for printing the component.

[0073] The 3D printing device, which includes the screw extruder 2, can thus be fed coarser plastic material via the comminution unit 2Z. This material is processed into a plastic powder by one or more comminution tools of the comminution unit 2Z and then conveyed to the screw of the screw extruder 2. The plastic powder from the comminution unit 2Z can, of course, be mixed with the plastic powder or plastic powder residues from the waste feeder 2R. Alternatively, the screw extruder 2 can also be operated solely with plastic powder residues 8R from the waste feeder 2R or solely with plastic powder from the comminution unit 2Z.Regardless of this, the screw extruder 2 can of course continue to be operated with granular plastic material, which is supplied unshredded to the feed zone 41 via the residual feed 2R or - especially if the shredding tool is not active - via the shredding device 2Z.

[0074] In one embodiment, the screw extruder 2 can be provided with several (at least two) powder feeders through which powder is fed directly into the feed area 31. This allows for the variable feeding of one or more different powders to the extruder screw 3 during a printing process. In particular, a dosing unit can be provided at least one of the powder feeders for this purpose. By dosing the powder(s) via multiple powder feeders, material gradients (such as color, strength, conductivity, etc.) can then be adjusted more precisely by mixing the material during the printing process.

[0075] Alternatively or additionally, a dosing unit can be integrated into the shredding unit. In such a configuration, the shredding unit 2Z can thus shred, in particular grind, the feed material and then feed it in a metered manner. Reference symbol list 1 component 10 Extrusion die 11 Document 2 screw extruders (extrusion device) 2R Residual Feed 2Z shredding unit 20 Control unit 3 Conveyor screw / extruder screw 31 catchment area 32 Melting and compression zone 33 Ejection zone 34 End area 340 chamfer 4 cases 41 catchment area 42 (thermal) barrier zone 41g, 42g, 43g housing section 43 heating zones 5 Admission 6 wave 7 Reservoir 8 Granular (possibly fiber-reinforced) plastic material 8R Powdered (possibly fiber-reinforced) plastic material 9 Heating element V Rejuvenation φ Opening angle QUOTES INCLUDED IN THE DESCRIPTION

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

[0000] DE 10 2014 018 081 A1

[0004]

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 by 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, in particular a plastic powder for the additive manufacturing of the component. [3] Use according to claim 1 or 2, characterized by that the plastic powder residues (8R) originate from a non-extrusion-based additive manufacturing process. [4] Use according to claim 3, characterized by that the plastic powder residues (8R) originate from selective laser sintering or binder jetting. [5] Method 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 feed the plastic material (8) to an extrusion nozzle (10) of the extrusion device (2), at which a material thread with plastic material (8) for the component to be produced is extruded, characterized by 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 surplus residue after carrying out at least one plastic powder processing manufacturing process. [6] Method according to claim 5, characterized by 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 by that the plastic powder residues (8R) originate from a non-extrusion-based additive manufacturing process. [8] Method according to claim 7, characterized by that plastic powder residues (8R) are used, which come from the implementation of selective laser sintering or binder jetting. [9] Method according to one of the preceding claims, characterized by 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 by that the extrusion device (2) for conveying the plastic material (8) in the direction of the extrusion nozzle (10) comprises a conveyor screw (3). [11] Method according to claim 10, characterized bythat 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] Method according to claim 10 or 11, characterized by 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 by 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 by 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 powdery plastic material and conveyed to the material feed. [15] Extrusion device according to claim 14, characterized by that the comminution device (2Z) is designed to comminute 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. [16] Extrusion device according to claim 14 or 15, characterized by 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 by 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 bythat the extrusion device (2) for conveying the plastic material (8) in the direction of the extrusion nozzle (10) comprises a conveyor screw (3). [19] Extrusion device according to claim 18, characterized by 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 by 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 bythat a conveying rate of the conveyor screw (3) for the plastic material (8) is predetermined via an electronic control device (20) of the extrusion device (2) in such a way 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 by that a diameter of a shaft (6) of the conveyor screw (3) within the heating zone (43) increases at least once in the conveying direction of the plastic material (8). [23] Extrusion device according to claim 22, characterized by 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 bythat 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 by 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 of 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 by that the heating zone (43) has a maximum length of 40 mm and a maximum diameter of 25 mm. [27] 3D printing devices comprising at least one extrusion device according to one of claims 14 to 26.

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