DEVICE AND METHOD FOR THE ADDITIVE MANUFACTURING OF THREE-DIMENSIONAL COMPONENTS

Description

[0001] The invention relates to a method and a device for the additive or generative manufacturing of three-dimensional components. Besides methods in which three-dimensional components are formed layer by layer from powders by locally defined energy inputs, various printing processes for such additive manufacturing are known.

[0002] Among other methods, a fused deposition modeling (FDM) process, hereinafter referred to as FFF, is used for additive manufacturing. In this process, strands are deposited layer by layer, either on top of or, if necessary, next to each other. After production, the layered material is then cured or sintered.

[0003] The FFF process can be used with thermoplastic polymers containing solids, processed into a strand, at or above their melting point. The system consists of at least one thermoplastic component, into which one or more powdered or fibrous materials are incorporated as solids. At room temperature, the thermoplastic polymer containing the solids is solid. For processing, the thermoplastic polymer is melted by applying heat, and after being deposited, it solidifies again due to cooling.

[0004] This manufacturing method is very well suited for structures with continuous curved sections. A relatively high productivity / build rate can be achieved compared to other additive manufacturing processes. A wide range of commercial systems and manufacturers already exists. Furthermore, systems with very large build volumes are available, enabling the production of large-format components or multiple parts in a single system.

[0005] Components manufactured solely using the FFF process contain voids (porosity) due to the quasi-continuous layer-by-layer deposition of the molten material between two or more adjacent strands. These voids, particularly in brittle materials, can represent fracture-inducing defects. The occurrence of this phenomenon can only be influenced to a limited extent by adjusting the pressure parameters, as this is inherent to the material. The strands used in the melt typically exhibit medium to high viscosity within the operating temperature range. Interruptions in the material flow, such as those that occur when moving the nozzle to a different position, are highly detrimental due to the inertia of the material feed and the cohesive forces within the molten mass.Furthermore, the level of detail in components manufactured using FFF is limited compared to components generated using 3D printing from a nozzle. In the FFF process, strands are deposited along paths, one above the other and possibly also next to each other. In 3D printing, individual droplets with smaller volumes than the strands are printed.

[0006] In FFF processes, the achievable resolution is limited because certain minimum radii must be maintained and the strands applied layer by layer are rounded on their outer surfaces, so that free gussets on and in the volume cannot be avoided.

[0007] Out of Figure 1A schematic example of a device 1 suitable for carrying out the FFF process is shown. It becomes clear that a component 3 can be manufactured layer by layer through three-dimensional movement of the device 1. This is achieved by extruding a strand 4 from a nozzle by moving the nozzle opening and depositing the strand 4 as a layer onto a build platform (not shown) or onto a layer previously formed with a strand, thus enabling the three-dimensional production of a component 3. Figure 3 It is made clear that the individual strands 4 are rounded on the outside, and that this results in the formation of gaps 5 between individual strands, which form cavities that have not been filled with the material. Even with very small dimensions, especially with highly filled strands 4, it is not possible to completely avoid gaps 5.

[0008] Unfortunately, even with post-processing or thermal treatment, it is not possible to sufficiently avoid / eliminate these cavities, so the finished component is not completely free of voids, and its strength is therefore adversely affected. Furthermore, cavities are not always homogeneously distributed and dimensioned within the component material.

[0009] During manufacturing, dimensional deviations from specifications cannot always be avoided, so that the finished component does not have the specified dimensions or a modified geometry, which necessitates very complex post-processing, usually involving machining.

[0010] US 2016 / 0096324 A1 relates to a method and apparatus for manufacturing three-dimensional objects.

[0011] A 3-dimensional printer and a method for printing an object with a curable liquid are disclosed in US 2017 / 0251713 A1.

[0012] Possibilities for colored three-dimensional printing are known from US 2016 / 0096322 A1.

[0013] It is therefore an object of the invention to provide possibilities for the manufacture of three-dimensional components, with which delicate components, with improved contour accuracy, without or with a reduced number and size of cavities present in the component material, can be manufactured with high productivity.

[0014] According to the invention, this problem is solved by a method having the features of claim 1. Claim 8 defines a device for manufacturing three-dimensional components. Advantageous embodiments and further developments of the invention can be realized with features specified in dependent claims.

[0015] An apparatus according to the invention for the additive manufacturing of three-dimensional components comprises a device for carrying out a fused deposition modeling (FDM) process and a device for three-dimensional printing. The device for carrying out the FDM process and the device for three-dimensional printing are both connected to an electronic control system. Both devices and the respective component can be moved relative to each other in at least three degrees of freedom by means of at least one manipulator. The at least one manipulator should be able to move the devices along at least three axes (x, y, and z axes) that are oriented perpendicular to each other.

[0016] Both devices can be designed as conventional, well-known devices. A linear drive, or at least one robot or other multi-axis systems, can be used as the manipulator.

[0017] In electronic control, a computer program can be used to manufacture a component, with which the movement of both devices and the ejection of the material(s) with which the respective component is to be manufactured are controlled and, if necessary, regulated from nozzles.

[0018] The equipment used for the two different application processes can advantageously be designed so that different materials can be processed with each system. A suspension or melt can contain varying proportions of solids or solids with different particle sizes. It can also be advantageous if the equipment for carrying out a fused deposition modeling (FDM) process and the equipment for three-dimensional printing can be moved together by a manipulator. The three-dimensional printing equipment can move along with the FDM process equipment and be attached to it in such a way that movement in at least two degrees of freedom is possible independently of the FDM process equipment.For this purpose, the three-dimensional printing device can advantageously perform a rotational movement around its central longitudinal axis, initiated by electronic control, to carry out a fused deposition modeling (FDM) process. It can thus be rotated to various angular positions relative to the central longitudinal axis or the nozzle of the FDM device and positioned as required. A telescope or other linear actuator can also be used to adjust the distance to the nozzle of the FDM device and adapt it to the specific location where droplets of a suspension of the component material are to be applied.

[0019] In the inventive method, areas of the respective component are formed using a device for carrying out a fused deposition modeling (FDM) process, and other areas of the component are formed using a device for three-dimensional printing. The three-dimensional printing device is preferably used to form areas of the component that fill cavities or voids resulting from the limited material deposition in the FDM process, thus preventing surface depressions and voids in the material of the finished component.

[0020] The 3D printing system fills or compensates for defects, gaps, or deviations from a predefined geometry or dimensions of the respective component, which are detected by a sensor, during the manufacturing process using a fused deposition modeling (FDM) process. For this purpose, a non-contact distance sensor is advantageously connected to the electronic control unit. The electronic control unit allows the 3D printing system to be moved precisely according to the signal detected by the sensor, enabling the material application to be locally controlled and the required material volume to be applied to each area to be adjusted. This can be influenced, for example, by the number and size of the printed droplets.The number and / or size of individual drops applied by the three-dimensional printing device in the area of ​​a defect, gusset or deviation can therefore be adapted to the respective size of the defect, gusset or deviation.

[0021] A component can be manufactured using a thermoplastic polymer, which is cured by cooling after additive manufacturing.

[0022] A component can also be manufactured using a glass, glass-ceramic, hard metal, cermet, metallic and / or ceramic material. In this process, the glass, glass-ceramic, hard metal, cermet, metallic material and / or ceramic material, or mixtures thereof, including fiber-reinforced versions, are applied layer by layer in a melt with a thermoplastic polymer in the form of particles or fibers. This is done using equipment for a fused deposition modeling (FDM) process and equipment for three-dimensional printing. After the completion of a green body for the respective component, a thermal treatment is carried out to remove the organic components and subsequently achieve sintering. The respective suspension may contain thin fibers of short length, ranging from a few millimeters to a maximum of 20 mm. The diameter of the fibers should be kept to a maximum of 1 mm.A melt that is deposited in strands using an FFF process can contain significantly longer fibers.

[0023] In three-dimensional printing, in addition to melts, suspensions containing solids can also be used.

[0024] With the device designed to carry out a fused deposition modeling process and with the device for three-dimensional printing, melts can be applied which are formed with different polymers, in particular polymers with different melting temperatures, wherein preferably the polymer which is used in the device for three-dimensional printing has a lower melting temperature than the polymer which is used for the solid-containing melt which is applied with the device designed to carry out a fused deposition modeling process and is applied for the additive manufacturing of a respective component.

[0025] The solids content in a melt or suspension should in any case be greater than 40 vol%, preferably greater than 60 vol%. A melt, especially one formed solely with polymer, may also contain no solids.

[0026] Thermoplastic polymers suitable for melting include polyolefins. Mixtures of aliphatic hydrocarbons, especially alkanes and / or waxes, are suitable organic binders for a suspension. A suspension can also be formed with water or an organic liquid that does not chemically or physically alter the respective solids.

[0027] With a 3D printing system, selective deposition of individual droplets at precisely defined positions can be achieved. The maximum achievable droplet size can be larger than with an injection molding process. A higher fill level, meaning a higher solids content, is also possible. The resulting resolution is significantly higher than with the FFF process. Locally targeted deposition of very small volumes is possible, and the construction of openwork structures is highly feasible. The lower productivity / build rate of 3D printing can be counteracted by the FFF process.

[0028] In three-dimensional printing, individual droplets of molten material or a suspension are created and can then be printed individually or in groups at intervals in the hertz to kilohertz range. This discrete operation and typically small droplet size make it possible to achieve high detail accuracy with significantly reduced material feed inertia. Advantageously, three-dimensional printing allows the use of melts or suspensions that exhibit significantly lower viscosity at operating temperature than those used in FFF (Fused Flow Fabrication).

[0029] These two processes can be combined in a single component manufacturing step, either in parallel or sequentially, within one or more fixtures using the same or different materials. Preferably, different melting points can be selected for the thermoplastic polymers used in the FFF process and in three-dimensional printing within a single melt, with the thermoplastic polymers in the melt used for three-dimensional printing having a lower melting point. This makes it possible to re-liquefy deposited and potentially already solidified droplets (or droplet chains) during the passage with the higher-melting-point material used in the FFF process and displace them with the resulting mechanical stress. In this way, gaps can be filled, reducing both the surface roughness at the component edge and the pressure-induced porosity resulting from voids in the gap areas.However, it is also possible to work at the same operating temperatures, so that the same material can be used in both melts for both processes.

[0030] Furthermore, the invention makes it possible, with suitable process monitoring hardware and software, to correct misprinted webs using FFF processes by selectively depositing droplets. Upon detection of defects in FFF-printed webs / strands, for example by an online optical measurement method, local material deficiencies can be corrected by selectively depositing significantly smaller elements (droplets). The intervention in the G-code of the control program can be performed during the component manufacturing process.

[0031] The combination of both methods offers the following advantages: Material combinations are possible; high detail accuracy / resolution can be achieved; correction of manufacturing defects in the FFF process is possible through three-dimensional printing of droplets and a reduction in porosity; the quality of the surface roughness can be improved compared to components manufactured solely using the FFF process. With this invention, additive manufacturing of complex polymer, metal, glass, or ceramic components, or even composites of these materials such as glass ceramics, cermets, hard metals, or fiber-reinforced components, can be achieved.

[0032] When solids are used in the FFF process and in three-dimensional printing, melts or melt and suspension should be used that can be sintered together in a joint thermal treatment.

[0033] The invention will be explained in more detail below by way of example.

[0034] This shows: Figure 1 is a schematic representation of a device for carrying out a fused deposition modeling (FDM) process; Figure 2 is a schematic representation of a device for three-dimensional printing; Figure 3 is a schematic representation of a device for carrying out a fused deposition modeling process with a component formed in several superimposed layers; Figure 4 is a schematic representation of an example of a device according to the invention; and Figure 5 is a schematic sectional view of a component produced according to the invention by FDM and with defects filled by 3D printing (right side of the component).

[0035] The in Figure 2The device 2 shown for three-dimensional printing comprises a reservoir 2.1 containing a suspension suitable for printing, a compressor 2.2 for conveying the suspension in the form of individual droplets 6 through a nozzle 2.3. The droplets exiting the nozzle 2.3 can be, as shown in Figure 2 recognizable, individually placed next to each other and layered on top of each other in rows, so that additive manufacturing of three-dimensional components becomes possible.

[0036] With Figure 3 It becomes clear how strands 4 can be deposited on top of each other in layers using a device 1 designed to carry out a fused deposition process. A conveying mechanism 1.1 feeds a strand / filament, thereby generating heated melt, which is then conveyed as a strand 4 of a predetermined length from a nozzle 1.2. This conveying can be achieved using an extruder.

[0037] How to Figure 3If molten metal can also be extracted, gussets 5 form in the end-face areas of adjacent strands 4, which are free of melt and form cavities. Gussets or depressions 7 also form on the outer surface of a component 3 formed with the strands 4 arranged one above the other in layers, which would result in a poor surface quality of a component 3 produced in this way.

[0038] This can be achieved with a device such as the one exemplified in Figure 4This can be counteracted as shown. The gaps 5 or recesses 7 can be filled with droplets 6, which are filled or emptied using a device 2 for three-dimensional printing. For this purpose, the device 2 for three-dimensional printing is positioned accordingly with its nozzle 2.3. The positioning and the respective locally applied droplet volume of the melt or suspension, which is applied from the device 2 for three-dimensional printing, can be influenced by the electronic control system, which is not shown in any of the figures.

[0039] Figure 5It can be determined where and in what quantity a melt or suspension containing component material was applied to a component using a device 2 for three-dimensional printing. Three layers were deposited using the fused deposition modeling (FDM) process, and the resulting gaps were filled by three-dimensional printing. In particular, defects, such as those that occurred on the far right layer deposited using the FDM process, can be corrected by targeted droplet placement via three-dimensional printing. Figure 5 represents component supervision. Example implementation:

[0040] Hybrid manufacturing of a ceramic component using an FFF process and three-dimensional printing

[0041] Based on a CAD model, a component 3 is to be manufactured, partly using the FFF process with a dedicated unit 1 and partly using 3D printing with a unit 2. The CAD model is converted into G-code in a suitable program, containing all processing parameters such as strand diameter, nozzle diameter, processing speed, processing temperature, build chamber temperature, layer height, and path guidance for the respective manufacturing processes of FFF and 3D printing, and then transferred to an electronic control system. Depending on the component portion to be manufactured using the FFF process, the following procedure is followed: Strand 4, for example, is a thermoplastic polymer containing 55 vol% Al₂O₃ (Almatis CT 1200 SG), which can be processed as a melt using an FFF process. The remaining portion of the melt for depositing strands 4 is 45 vol%.-% of a thermoplastic polymer that can be melted at elevated temperatures. A mixture of polyethylene and thermoplastic elastomer and waxes can be used as a suitable polymer blend. Strand 4 is produced continuously using a twin-screw extruder with a die 1.3 with an inner diameter of 1.9 mm at 130 °C. Strand 4 is supplied in sufficient quantity on a spool or other storage container. Strand outer diameters in the range of 1.75 mm to 2.85 mm are typically used. The following processing parameters can be applied: strand outer diameter 1.75 mm, die diameter 0.8 mm, processing speed 30 mm / s, processing temperature 175 °C, build chamber temperature 70 °C, layer height 250 µm. The strands 4 can be deposited quasi-continuously in layers according to the process.

[0042] According to the path defined in the G-code of the control program, the three-dimensional printing process then continues at certain positions during the manufacturing process.

[0043] Depending on the component to be manufactured with three-dimensional prints, the process is as follows: To create a melt, a binder system based on paraffin and beeswax is first melted and homogenized in a dissolver or hot mixer at 90 °C. In the next step, further additives, such as stearic acid, are added. After homogenizing the organic components again, the corresponding solid is finally added to the melted binder system in several steps. Powdered Al₂O₃ is added as the solid at a rate of 67% by volume of the melt.

[0044] For processing, the melt containing the solid is filled into a suitable plastic or metal cartridge, which is then connected to a micro-dosing system of a three-dimensional printing device 2. Using an associated cartridge heater, the mixture formed with thermoplastic feedstock and solid is melted at a temperature of 85 °C, creating a melt. This melt is then conveyed at a pressure of 0.5 bar through a fluidic element into a nozzle compression chamber via a compressed air connection. The micro-dosing system is a jet valve based on piezoelectric technology. After setting the dosing parameters, the melt in the nozzle compression chamber is metered volumewise through the nozzle insert and nozzle 2.3 by the up-and-down movement of a hard metal plunger. This produces free-floating droplets 6 or droplet chains.The following processing parameters are set: nozzle temperature 110°C, working distance 1 mm, and drop frequency 100 Hz. The drop size can be varied by changing the dosing parameters.

[0045] After the complete execution of the control program's G-code, a green body is obtained. This green body undergoes heat treatment at 600 °C in air for debinding. Following the complete removal of organic components, sintering takes place at 1600 °C in air with a holding time of 2 hours.

Claims

1. Method for the additive manufacturing of a three-dimensional component, in which regions of the respective component are designed with a device (1) for performing a fused filament process, and other regions of the component are formed with a device (2) for three-dimensional printing and characterised in that with the device (2) for three-dimensional printing flaws, gussets or deviations from a predetermined geometry or dimensioning of the respective component, which have been detected by a sensor and which have been designed during design with the device (1), which has been designed to perform a fused filament process, are filled or levelled.

2. Method according to the preceding claim, characterised in that the number and / or the size of individual droplets printed with the device (2) for three-dimensional printing in the region of a flaw, a gusset or a deviation is adapted to the respective size of the flaw, the gusset or the deviation.

3. Method according to one of the two preceding claims, characterised in that a component (3) is produced with a thermoplastic polymer which is cured after additive manufacturing.

4. Method according to one of the three preceding claims, characterised in that a component (3) is produced with two different materials.

5. Method according to one of claims 1 or 2, characterised in that a component is manufactured with a polymer, glass, a glass ceramic, a cermet, carbide, a metallic and / or ceramic material, whereby a glass, a metallic material and / or a ceramic material in the form of particles or short fibres is layered in a melt with a thermoplastic polymer with the device (1), which is used for performing a fused filament process, and with the device (2) for three-dimensional printing of a suspension or a melt containing a solid material, and after completion of a green body for the respective component, a thermal process is performed in which the organic components are removed and then sintering is achieved.

6. Method according to the preceding claim, characterised in that a component is produced with fibre-reinforced material and / or with composite material.

7. Method according to one of the two preceding claims, characterised in that the device (1) designed to perform a fused filament process and the device (2) for three-dimensional printing are used to apply suspensions or melts containing solid materials, which are formed with different polymers, in particular polymers with different melting temperatures, whereby the polymer used in the three-dimensional printing device (2) has preferably a lower melting temperature than the polymer contained in the melt applied using the device (1) designed to perform a fused filament process and used for the additive manufacturing of a respective component (3).

8. Device for the additive manufacturing of three-dimensional components using a method according to one of the preceding claims, which is formed with a device (1) for performing a fused filament process and a device (2) for three-dimensional printing, whereby the device (1) for performing a fused filament process and the device (2) for three-dimensional printing are jointly connected to an electronic control system, and the device (1) for performing a fused filament process and the device (2) for three-dimensional printing and the respective component (3) can each be moved with at least one manipulator relative to one another in at least three degrees of freedom and characterised in that a sensor is present to detect flaws, gussets or deviations from a predetermined geometry or dimensioning of the respective component, whereby the sensor is a non-contact distance sensor connected to an electronic control unit.

9. Device according to the preceding claim, characterised in that the device (1) for performing a fused filament process and the device (2) for three-dimensional printing are designed such that different materials can also be processed in the manufacture of a component (3).

10. Device according to one of the preceding claims, characterised in that the device (1) for performing a fused filament process and the device (2) for three-dimensional printing can be moved together with a manipulator, the device (2) for three-dimensional printing moving with the device (1) for performing a fused filament process and being attached thereto in such a way that movement is possible independently of the device (1) for carrying out a fused filament process in at least two degrees of freedom.

11. Device according to the preceding claim, characterised in that the device (2) for three-dimensional printing can be used to perform a rotational movement around the central longitudinal axis of the device (1), initiated by means of the electronic control system, to carry out a fused filament process.