Method and equipment for producing a three-dimensional structure

Abstract

Method for producing a three-dimensional structure from a 3D-printable plastic material (2) using a 3D printing system, the method comprising the following steps: - feeding a 3D-printable plastic material (2) to a 3D print head (1) of the 3D printing system having an extruder unit and - extruding the plastic material (2) fed to the 3D print head (1) from an exit opening (5) of the 3D print head (1) to produce the three-dimensional structure from the plastic material (2), wherein the 3D-printable plastic material (2) is tempered and melted by the extruder unit and then ejected from the exit opening (5) of the 3D print head (1), - wherein the 3D-printable plastic material (2) is tempered by means of a heating device (7) of the 3D printing system, wherein an electrically conductive plastic material (2) is fed to the 3D print head (1). is supplied- wherein the 3D-printable plastic material (2) is electrically contacted with at least two electrodes (8) of the heating device (7) during extrusion, such that a heating section (9) is formed between the electrodes (8) in the 3D-printable plastic material (2), and- wherein, by means of an electrical power supply (10) of the heating device (7), a current flow in the heating section (9) of the 3D-printable plastic material (2) is effected during extrusion by applying an electrical voltage to at least one of the electrodes (8) in such a way that the plastic material (2) is thereby heated, characterized in that- the electrodes (8) of the heating device (7) are provided in the 3D print head (1) and the current flow in the heating section (9) during extrusion is effected in such a way that the plastic material (2) is brought into a molten state,so that the plastic material (2) is only tempered and melted shortly before extrusion from the 3D print head (1).

Description

[0001] The invention relates to a method for producing a three-dimensional structure from a 3D-printable plastic material using a 3D printing system. The invention also relates to a system for carrying out this method.

[0002] Additive manufacturing processes allow for the production of components with almost any shape using a suitable material. 3D printing with a 3D printer is a well-known example of additive manufacturing. In this process, a meltable material, such as a thermoplastic, is printed layer by layer using a 3D printer, resulting in a three-dimensional component or structure at the end of the process.

[0003] Typically, the 3D-printable plastic material, in a solid state (e.g., in the form of plastic filaments), is fed to the 3D print head and guided through an extruder. There, a heating element heats the material above its melting point, causing it to melt. The molten plastic is then extruded under pressure from an opening in the extruder to print the three-dimensional structure. As the molten plastic material exits, it cools and solidifies on the surface of the printed part.

[0004] A 3D printing system of this kind is known from US patent 2015 / 0147472 A1, in which a plastic filament is fed to an extruder. The extruder is arranged in the form of a 3D print head, movable relative to the surface of the component, and has a heating device to heat the plastic filament above its melting temperature. Heating is achieved by means of corresponding heating elements located in the print head.

[0005] German patent DE 10 2015 223 540 A1 discloses a 3D printer for printing liquid metal, in which the metal is heated using an induction coil.

[0006] From Hauke ​​Prüß and Thomas Vietor: “New Design Freedoms Through 3D-Printed Fiber-Reinforced Plastics,” Forum for Rapid Technology, Issue 12 (2015), a 3D print head is described that is fed with a virtually endless fiber material. Furthermore, a plastic material is fed to the 3D print head via two feed channels. The fiber material and the plastic material, which has been heated and melted by a heating element, enter a common mixing chamber, where the fiber material is wetted by the plastic and ejected in this form. This allows for the development of virtually any structure with integrated load paths.

[0007] It has been shown that reducing the weight of such 3D printheads can improve the accuracy of printing with printable plastic materials, such as thermoplastics or thermosets, because the reduced inertia allows for more precise positioning of the build points. However, the heating elements integrated into the 3D printheads, such as induction coils, pelletizing elements, or resistance-based thermocouples, add significant weight, increasing inertia and reducing accuracy.

[0008] Against this background, the object of the present invention is to provide an improved method and an improved device for producing three-dimensional structures in a 3D printing process in which the weight in the 3D print head can be reduced and in which the 3D-printable plastic material can still be tempered above the melting temperature so that it can be extruded.

[0009] The problem is solved according to the invention by the method according to claim 1 and the apparatus according to claim 8.

[0010] According to claim 1, a method for producing a three-dimensional structure from a 3D-printable plastic material using a 3D printing system is proposed, wherein the 3D printing system comprises at least one 3D print head to which the 3D-printable plastic material is fed. The 3D print head further comprises an extruder unit, or extruder, by which the 3D-printable plastic material is typically heated and melted, and then extruded from an outlet of the 3D print head. Advantageously, the 3D-printable plastic material is fed to the 3D print head in solid form, e.g., in the form of a virtually continuous plastic filament or in the form of granules. If the 3D-printable plastic material is fed to the 3D print head in granular form, the extruder typically comprises a screw to convey the plastic material from the outlet by means of the extruder screw.

[0011] The 3D printing system, preferably the 3D print head, therefore has a heating device to temper the 3D-printable plastic material. The plastic material is typically heated to a temperature above its melting point, so that the heating device of the 3D printing system or the 3D print head tempers the solid plastic material and brings it into a molten state.

[0012] According to the inventive method, it is now provided that a 3D-printable plastic material is supplied to the 3D print head for printing, which is electrically conductive and / or contains electrically conductive elements, wherein the heating device has at least two electrodes which are arranged in such a way that the 3D-printable plastic material is electrically contacted with the electrodes during extrusion or during printing, so that a current flow in the 3D-printable plastic material can be effected by applying an electrical voltage to at least one electrode.By contacting the electrodes with the plastic material, a heating path is defined within the plastic material between each pair of corresponding electrodes. Within this path, current flows from one electrode to the other, thus heating the 3D-printable plastic material in a manner similar to electrical resistance heating. This current flow can be such that the heating process heats the plastic material above its specific melting point, causing it to melt. The 3D-printable plastic material exhibits electrical conductivity during this process.This can be achieved by the plastic material being electrically conductive in itself, or by the 3D-printable plastic material containing additional electrically conductive elements or materials that give the plastic material electrical conductivity.

[0013] The inventors have discovered that such an electrically conductive, 3D-printable plastic material can be contacted with electrodes, particularly within a 3D print head, in such a way that an electric current flows through the plastic material, causing it to heat up and melt within the print head. The inventors have specifically recognized that the electrodes can be integrated into the extruder nozzle to temper and melt the fiber material accordingly.

[0014] It was also recognized that by applying an electric current to the plastic material for heating purposes, similar to resistance heating, conventional heating devices, as known from the prior art for such 3D print heads or printing processes, can be replaced, thereby improving the accuracy of 3D printing. This is because eliminating conventional heating devices reduces the moving mass of the 3D print head, thus decreasing the system's inertia and increasing accuracy.

[0015] Another advantage of directly heating the plastic material by applying current in the manner of resistance heating is that the temperature input or heating power can be set very precisely, so that damage to the plastic material due to overheating can be avoided and the energy requirement can be reduced, since the thermal mass to be heated has been fundamentally reduced.

[0016] The 3D print head can be mounted on a motion system within the 3D printing machine, allowing it to move freely within the space. This enables the creation of almost any structural shape. Alternatively, the 3D print head can be fixed in place, while the print bed or surface is movable relative to the print head, allowing it to print at any point on the bed.

[0017] A 3D-printable plastic material is understood to be one that can be printed using 3D printheads. These are primarily thermosetting and thermoplastic plastics. The electrical conductivity of the plastic material can be achieved by adding electrically conductive particles, such as graphite or graphene. It is also conceivable that the plastic material contains carbon fibers that have been added to it. Such carbon fibers can be, for example, quasi-endless or short fibers. Hybrid yarns (commingling yarns) containing a mixture of carbon fibers and thermoplastic fibers are also conceivable and, likewise, constitute a 3D-printable, electrically conductive plastic material within the meaning of the present invention. Finally, it is also conceivable that the electrically conductive plastic material is not a fiber material, such as...Contains carbon fibers.

[0018] In a classic 3D printing process, the 3D-printable plastic material is melted by heating and then extruded using an extruder, with the molten plastic material being extruded in a liquid state during extrusion. Crucially, the continuous feed ensures that the plastic material is continuously heated, melted, and extruded.

[0019] In an advantageous embodiment, the electrodes of the heating device are provided in the 3D print head, preferably in the nozzle of the extruder, so that the plastic material is only tempered and melted shortly before extrusion from the 3D print head.

[0020] In a further advantageous embodiment, the 3D-printable plastic material is heated to a temperature below its melting point by means of a preheating device in the 3D printing system. The heating device according to the invention, based on a type of resistance heating, then raises the temperature from this preheating temperature below the melting point to a temperature above the melting point. This preheating can take place, for example, within the 3D print head or within system components located upstream of the 3D print head.

[0021] In a further advantageous embodiment, additional auxiliary materials are supplied to the 3D-printable plastic material within the heating section, which is formed by at least two spaced-apart electrodes. These auxiliary materials can be, for example, in the form of granules, powders, liquids, or gases. Such auxiliary materials can be, for example, additional fibers and are intended to bond with the melting plastic material.

[0022] In a further advantageous embodiment, the temperature of the 3D-printable plastic material is determined by means of a temperature sensor, and the heating power in the heating section, reduced by the current flow, is adjusted by means of a control device depending on the determined temperature. Thus, the applied electrical voltage can be varied during the extrusion and tempering of the plastic material, thereby varying the current flow in the heating section, which ultimately results in a variation in the heating power.

[0023] Increasing the electrical voltage therefore increases the heating power, while decreasing the electrical voltage reduces the heating power. This variation in heating power occurs depending on the measured temperature, in order to maintain the plastic material at a consistently stable target temperature.

[0024] In a further advantageous embodiment, the heating device has more than two electrodes, so that more than one heating section is formed in the 3D-printable plastic material. The heating sections can be directly adjacent to one another or spatially separated. For example, with three electrodes, two heating sections could be formed: one between the first and second electrodes, and another between the second and third. It is also conceivable that an additional third heating section could be formed in this configuration, namely by the first and third electrodes. The number of electrodes and their arrangement to form the heating section are at the discretion of the person skilled in the art.

[0025] The heating system is designed so that, during extrusion, an electrical current can be generated in each heating section by separately applying an electrical voltage to the respective electrodes. In other words, each heating section can be controlled independently by the heating system, allowing for a separate current flow in each section. This enables precise temperature control.

[0026] In a further advantageous embodiment, a current flow in the respective heating section is induced depending on a temperature profile, thereby enabling a targeted tempering process. Due to the direct heating of the plastic material in the manner of resistance heating, relatively short switching times of a few milliseconds can be achieved, whereby temporal and spatial cascading of the current flow is also possible.

[0027] Moreover, the problem is also solved according to the invention with the system according to claim 8, wherein the system is particularly designed to carry out the method described above.

[0028] According to the invention, at least one of the electrodes can form at least part of the inner wall of an extruder die of the extruder, for example, in the form of a ring electrode. With a ring electrode, the entire inner wall is completely covered by the electrode at a specific position, thus ensuring sufficient contact between the plastic material and the electrode. Alternatively, when granules are fed into the extruder, it is conceivable that the extruder has an extruder screw to convey the fiber material from the exit opening, whereby the extruder screw can be formed partially or completely from the electrode. For example, a first electrode is provided upstream of the extruder screw in the feed direction, while the second electrode is the extruder screw itself.This ensures that the plastic material is in a molten state at the latest when it hits the extruder screw.

[0029] The invention is explained in more detail using the attached figures as examples. They show: Fig. 1 Schematic representation of a 3D print head in a first embodiment; Fig. 2. Schematic representation of a 3D print head in a second embodiment; Fig. 3. Schematic representation of a 3D print head in a third embodiment; Fig. 4. Schematic representation of a 3D print head in a fourth design form.

[0030] Fig. Figure 1 shows a 3D print head 1 to which a 3D-printable plastic material is inserted. 2 is supplied. With the help of opposing rollers. 3 , which extend towards the top of the head 4 moving this will affect the printhead 1supplied plastic material 2 towards the top of the head 4 promoted. At an exit opening. 5 The molten plastic material is then 2 extruded and on a substrate 6 , e.g., printed on a tool.

[0031] In the exemplary embodiment of the Fig. 1. The plastic material is used. 2 in the form of a virtually endless filament in solid form to the print head 1 supplied and within the printhead 1 then melted. The printhead is designed for this purpose. 1 a heating system 7 on, with which the plastic material 2 is transformed from a solid state of matter into a molten or liquid state of matter.

[0032] The plastic material 2 is an electrically conductive plastic material, with the heating device 7 in the exemplary embodiment of the Fig. 2 two electrodes8a and 8b exhibits features that are in the conveying direction of the plastic material 2 are spaced apart. The two electrodes 8a and 8b are located in the printhead 1 arranged so that the plastic material 2 during extrusion with the two electrodes 8a and 8b electrically contacted. Between the two spaced-apart electrodes 8a and 8b This occurs within the plastic material 2 a heating section 9 formed within which the plastic material 2 It is heated in a manner similar to resistance heating. For this purpose, the electrodes are connected to 8a and / or 8b with the help of an electrical power supply 10 an electrical voltage is applied, through which the plastic material 2 in the area of ​​the heating section 9 a current flow is caused because the plastic material 2is electrically conductive. Due to the heating element in the heating section 9 caused current flow in the plastic material 2 The plastic material will be selected based on the electrical power loss. 2 in the area of ​​the heating section 9 It is heated in the manner of a resistance heater and thereby tempered so that it changes from the solid state of matter to the liquid or molten state of matter.

[0033] In the exemplary embodiment of the Fig. 1 are the two electrodes 8a and 8b designed as ring electrodes, with the plastic material 2 in the inner passage of the ring electrodes 8a and 8b through which the cable is routed. This ensures complete and reliable electrical contact.

[0034] Fig. Figure 2 shows an embodiment in which the heating device 7 a total of three electrodes 8a , 8b and8c exhibits, wherein between the first electrode 8a and the second electrode 8b a first heating section 9a and between the second electrode 8b and the third electrode 8c a second heating section 9b is formed.

[0035] The heating system 7 is now designed in such a way that it generates an electrical voltage at the individual electrodes 8a , 8b and 8c so that the heating sections 9a and 9b They can be powered separately and independently of each other. Thus, it is conceivable that the first electrode could be connected to a separate electrode. 8a and to the third electrode 8c a positive electrical voltage is applied while the middle second electrode 8bis connected to the neutral conductor, so that a current flows from the first electrode towards the second electrode and from the third electrode towards the second electrode. However, it is also conceivable that the individual heating sections are energized at different times.

[0036] Finally, it is also conceivable that between the first electrode 8a and the third electrode 8c This results in an overall current flow, generating current through both the first and second heating sections. This allows for control of the heating output not only over time but also spatially.

[0037] In Fig. 2 is also for each heating section 9a and 9b a separate temperature sensor 11 A device is provided that detects the temperature of the plastic material. The detected temperature is then transmitted to the heating device. 7provided, which then, depending on the detected temperature, supply power to the two heating sections 9a and 9b regulates. The heating system can be controlled in this process. 7 be trained in such a way that they can handle the plastic material 2 approximately tempered to a predetermined target temperature, whereby the temperature sensor 11 This provides the corresponding feedback.

[0038] Fig. Figure 3 shows an embodiment in which the electrodes 12a and 12b are designed as plate electrodes, between which the plastic material 2 is passed through it. It is conceivable that the electrodes 12a and 12b are arranged offset from each other.

[0039] According to a fourth embodiment, which is schematically shown in Fig.As shown in Figure 4, a 3D print head is provided, to which a 3D-printable plastic material is added. The area between the two electrodes 8a and 8b trained heating section 9 The temperature is to be regulated by an electric current.

[0040] Within the heating section 9 is an applicator 13 arranged in such a way that auxiliary materials are applied to the 3D-printable plastic material in this area 2 such auxiliary materials can be applied. These materials can serve the purpose of supporting the 3D-printable plastic material. 2 to add further material properties, such as changes in stickiness, dimensional stability, elasticity, or similar. Reference symbol list 1 3D print head 2 3D printable plastic material 3 conveyor rollers 4 Head tip 5 Exit opening 6 Substrat 7 Heating system 8 electrodes 9 Heating section 10 Energy supply 11 Temperature sensor 12 plate electrodes 13 Applicator 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] US 2015 / 0147472 A1

[0004] DE 102015223540 A1

[0005]

Claims

[1] Method for producing a three-dimensional structure from a 3D-printable plastic material (2) using a 3D printing system, the method comprising the following steps: - Feeding a 3D printable plastic material (2) to a 3D print head (1) of the 3D printing system and - Extruding the plastic material (2) fed to the 3D print head (1) from an exit opening (5) of the 3D print head (1) to produce the three-dimensional structure from the plastic material (2), - wherein the 3D-printable plastic material (2) is tempered by means of a heating device (7) of the 3D printing system, characterized by , that - an electrically conductive plastic material (2) is supplied to the 3D print head (1), - wherein the 3D-printable plastic material (2) is electrically contacted with at least two electrodes (8) of the heating device (7) during extrusion, such that a heating section (9) is formed between the electrodes (8) in the 3D-printable plastic material (2), and - wherein, by means of an electrical energy supply (10) of the heating device (7) during extrusion, an electrical voltage is applied to at least one of the electrodes (8) to cause a current flow in the heating section (9) of the 3D-printable plastic material (2) such that the plastic material (2) is thereby heated. [2] Method according to claim 1, characterized by , that the electrodes (8) of the heating device (7) are provided in the 3D print head (1) and the current flow in the heating section (9) during extrusion is caused in such a way that the plastic material (2) is brought into a molten state. [3] Method according to claim 2, characterized by , that by means of a preheating device of the 3D printing system the 3D-printable plastic material (2) is tempered to a temperature below the melting temperature of the plastic material (2). [4] Method according to any one of the preceding claims, characterized by , that additional auxiliary materials are supplied within the heating section (9) of the 3D-printable plastic material (2). [5] Method according to any one of the preceding claims, characterized by , that the temperature of the 3D-printable plastic material (2) is determined by means of a temperature sensor (11), wherein the heating power induced by the current flow is adjusted as a function of the determined temperature by means of a control device. [6] Method according to any one of the preceding claims, characterized by, that the 3D-printable plastic material (2) is electrically contacted with more than two electrodes (8) of the heating device (7) during extrusion, so that two or more heating sections (9) are formed between the electrodes (8), wherein a current flow in the respective heating section (9) is caused by means of the electrical power supply (10) of the heating device (7) during extrusion by separately applying an electrical voltage to the electrodes (8). [7] Method according to any one of the preceding claims, characterized by , that a current flow in the respective heating section (9) is caused depending on a temperature profile. [8] System for producing a three-dimensional structure from a 3D-printable plastic material (2), comprising a 3D print head (1) to which a 3D-printable plastic material (2) can be fed via a feeding device, an extruder unit designed to extrude the plastic material (2) fed to the 3D print head (1) from an outlet opening (5), and a heating device (7) for temperature control of the 3D-printable plastic material (2), characterized by, that the heating device (7) has at least two electrodes (8) arranged such that the 3D-printable, electrically conductive plastic material (2) makes electrical contact with them during extrusion in order to form a heating section (9) between the electrodes (8), wherein the heating device (7) is further configured to cause a current flow in the heating section (9) of the 3D-printable plastic material (2) by means of an electrical power supply (10) during extrusion by applying an electrical voltage to at least one of the electrodes (8) in such a way that the plastic material (2) is thereby heated. [9] Plant according to claim 8, characterized by that the system is designed to carry out the method according to one of claims 1 to 7. [10] Plant according to claim 8 or 9, characterized by , that at least one of the electrodes (8) forms at least part of an inner wall of an extruder nozzle of the extruder. [11] Plant according to claim 10, characterized by , that at least one electrode (8) is designed as a ring electrode. [12] Plant according to any one of claims 8 to 11, characterized by , that at least one of the electrodes (8) is formed by at least part of an extruder screw of the extruder.

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