Patent Application
20240375180
The invention relates to an apparatus for manufacturing a component by means of filament or paste extrusion additive manufacturing. The apparatus comprises a build platform, at least one heater, at least one extruder, a monitoring unit and a control unit. In this regard, the extruder is configured to eject building material in layers onto the build platform to form a build part. The heater is configured to heat the build part locally and the monitoring unit is configured to capture data relating the build part. In addition, the control unit is configured to control the extruder and the heater such that a defined ejection point can be driven by the extruder and a defined heating zone and/or heating point can be targeted by the heater.
Furthermore, the invention relates to a method and a use of the apparatus mentioned above for manufacturing a component by means of filament or paste extrusion additive manufacturing.
Additive Manufacturing (AM) is a growing field to produce high-performance functional parts for the aerospace, automobile, biomedical and energetic industries. However, the infancy of the technology today results in an early development stage with multiple parallel techniques being investigated. These can be classified mainly in powder, filament and resin based techniques.
The most common processes for metals, polymers and ceramics include Powder Bed Fusion (PBF), also known as Selective Laser Sintering (SLS) or Selective Laser Melting (SLM), which employs a laser or an electron beam to sinter or melt layers of a 2D sliced object repetitively on a powder bed, until completion of the part. Powder can also be blown into a molten pool, known as Direct Metal Deposition (DMD), where the powder is blown and fused together by means of a laser or an electron beam. On the other hand, Wire Arc Additive Manufacturing (WAAM) employs metal wires instead of powders to Additive Manufacturing large structures, and polymers are typically processed via stereo-lithography, photopolymerization or Fused Filament Fabrication (FFF).
Most additive manufacturing methods do not allow the combination of materials due to their inherent processing method (powder beds and resin basins).
Moreover, although Fused Filament Fabrication (FFF) allows the combination of limited materials, the process disadvantageously requires an uncoupled approach and expensive equipment. Monomaterial metallic or ceramic parts produced through Fused Filament Fabrication ought to be debinded and sintered on a subsequent step. This involves expensive and bulky equipment and is out of reach for most users. In addition, only materials with similar sintering and shrinkage behaviour can be combined in the prior art, limiting the application of this method to few multi-material parts.
In the state of the art, several devices and processes are already known to perform additive manufacturing.
US 2017/0129012 A1 discloses a method for additive manufacturing. A layer is first formed by providing a flowable composition containing a powder and organic material. A unit layer is thereby formed. This is followed by a step of removing the organic material from the unit layer, and then adding energy to obtain a molten layer or sintered layer. The above steps are repeated in a stacking direction. The organic material is removed by applying heat to the unit layer on the front surface side and/or the rear surface side, applying an air flow and/or creating a reduced pressure atmosphere. Overall, the finished component is said to have reduced residue of organic material.
JP 2019094546 A also discloses a method and apparatus for performing additive manufacturing. The apparatus has a layer forming head for forming a new layer on the surface of a substrate or the upper surface of the solidified layer to add the layer to the structure. Further, the apparatus comprises a peening head for intermittently applying an impact force to a predetermined area of a solidified surface of a structure in production formed above the base, the head being in the stacking direction, which is the direction in which layers are deposited.
US 2017/0056974 A1 describes a three-dimensional forming device that provides a three-dimensional article by stacking a layer using a sintering material. The sintering material comprises a metal powder, a binder and a solvent. For this purpose, a material supply region is provided through which the sintering material is supplied into a predetermined material supply region. Furthermore, a first heating section is provided which heats the predetermined material supply region, and a second heating section is provided which heats the sintered material. Further, an energy irradiation section supplies energy for sintering the metal powder.
In EP 3569330 A1, a method and a system for carrying out additive manufacturing are disclosed. For this purpose, a material layer is deposited on a surface of a substrate, the material comprising a sacrificial binder and a powder comprising an oxide dispersion reinforced alloy dispersed in the binder. At least one further layer of material is then deposited to form an additively manufactured component. Sintering of the manufactured component is optional.
U.S. Pat. No. 11,376,788 B2 discloses an apparatus for additively manufacturing an article, wherein the apparatus comprises a thermal spacer defining a feed guide to receive a feed material. A heat block is arranged to heat the feed material and a nozzle is configured to receive the feed material in operable communication with the heat block. Furthermore, a radiator is configured to transfer heat from the heat block, wherein the radiator has inner surfaces defining an inner dimension which is larger than a largest dimension of the heat block. The inner surfaces and an outer diameter of the thermal spacer defining an open volume between the inner surfaces of the radiator and the outer diameter of the thermal spacer.
However, in light of the known state of the art, there is a need for improvements in order to make apparatuses for carrying out additive manufacturing more efficient and to improve the process of additive manufacturing itself.
In light of the prior art the technical problem addressed by the present invention is thus to provide a compact apparatus and a method which simplify the additive manufacturing of components by means of filament or paste extrusion additive manufacturing and, in particular, reduce the costs, while at the same time enabling a particularly precise and, as far as possible, defect-free and resistant manufacture of the component and time-minimized production, while also permitting the combination of different materials.
This problem is solved by the features of the independent claims. Preferred embodiments of the present invention are provided by the dependent claims.
In a preferred embodiment the invention relates to an apparatus for manufacturing a component by means of filament or paste extrusion additive manufacturing characterized in that the apparatus comprises a build platform, at least one heater, at least one extruder, a monitoring unit, and a control unit
The advantages of additive manufacturing are generally known. However, the invention aims to achieve an apparatus which, in particular, comprises all necessary equipment for producing a component by means of filament or paste extrusion additive manufacturing, so that a start-to-finish system is created without the component having to be moved from one machine (or apparatus) to another machine (or apparatus) for various manufacturing steps. Furthermore, the invention allows the production combining different materials, in particular materials that have different properties in terms of sintering and shrinkage.
Such an apparatus according to the invention is neither known nor obvious from the prior art. The combination of production steps and simultaneous automated monitoring advantageously means that certain parameters can be adjusted and optimized during production. In addition, production errors can be eliminated, particularly during the production process. Advantageously, the preferred apparatus enables fully automated production of components (without the manual interaction of a user). In addition, the local heating of a component to be produced allows the components to be designed in great detail. The buildup or production of the components in layers and the subsequent heating, preferably after each layer, leads to a very stable production of the components, since each layer is solidified individually.
The invention is much more than a turn away from the prior art. In fact, the technical innovation of the invention is to debind and sinter the produced build parts locally. Conventionally, green parts must be transported to bulky and expensive facilities, which requires human labor. The ability to debind and sinter locally significantly reduces manufacturing costs. Furthermore, it has been shown that several materials can be combined advantageously in a simple manner in prefabrication. In the prior art, this is only possible with considerable effort.
Since the heater preferably heats the build part only locally and creates a heating zone or heating point, other method steps can be executed simultaneously at other points or location on the build part during heating. It has been shown that simultaneous local heating of the build part on the one hand and extrusion of material onto the build part on the other hand at another location of the build part is possible, wherein the extrusion and heating do not affect each other.
For the purposes of the invention, additive manufacturing by means of filament or paste extrusion preferably means a manufacturing process from the field of 3D printing in which a workpiece or build part is built up layer by layer from a meltable (input) material. The meltable input material can be in the form of filaments or paste (for example embedded with metal or ceramic powders). Additive manufacturing by filament extrusion is known, for example, as fused filament fabrication or fused deposition modeling. Furthermore, additive manufacturing by paste extrusion, on the other hand, is known as PEM (Paste Extrusion Modeling), for example.
It is understood that both solid and hollow components and/or build parts can preferably be produced. However, the producible wall thicknesses for a hollow component and/or a hollow body are preferably at least 1 mm, further preferably at least 0.6 mm and in particular at least 0.2 mm. The aforementioned wall thicknesses enable extremely stable hollow parts. Especially, cracks in the component to be manufactured are already prevented with a wall thickness of at least 0.2 mm.
Preferably, the apparatus comprises a debinding heater and a sintering heater. Preferably, debinding and sintering is performable by the apparatus. Preferably, debinding and sintering is performable by the debinding heater and the sintering heater.
It was completely surprising that an apparatus could be provided which allows both debinding and sintering. In particular, this is unexpected in view of the fact that debinding and sintering fulfill different thermal requirements. For debinding, for example, a temperature of about 350° C. can be introduced, while sintering requires a temperature in the range of about 1200° C.
Preferably, the apparatus comprises a build platform, which forms a planar surface on which a component and/or build part can be manufactured. The build platform is preferably calibrated so that it preferably has a surface that is oriented horizontally over its entire expansion. Therefore, very accurate and detailed components can be produced on this build platform. The build platform is preferably also called as build plate, print bed, or build bed. Preferably, the build platform further comprises means for providing a particularly adhesive first layer of the building material to be applied. In this case, the build platform is for example very clean and has a material or agent on the surface that provides adhesion. Alternatively, the build platform may be preferably preheated for additional adhesion.
In a preferred embodiment, the build platform is effectively bonded to a build platform heater. Preferably, the build platform can be heated starting from the build platform heater. In a preferred embodiment, the build platform is effectively bonded with a heating coil, wherein preferably the build platform heater is a heating coil. The term effectively bonded refers to the fact that the effect of heating can be transferred from the build platform heater to the build platform. Preferably, the build platform heater is a heating coil.
In combination with the possibility of performing sintering and debinding, heating the build platform has surprisingly proven to be particularly advantageous. Advantageously, this considerably improves the formability of the build part and/or individual layers. Furthermore, the formation of thermal gradients is advantageously minimized during sintering and/or melting. The heating of the build platform advantageously and surprisingly results in a synergistic effect. Due to the heat transfer to the build platform starting from a heating coil, this was carried out particularly efficiently without having to accept a loss of heat.
In a further preferred embodiment, the build platform comprises a plate, a crucible (e.g., comprising graphite) and a ceramic shield, wherein the heating coil as the build platform heater is preferably embedded in the ceramic shield, wherein preferably the crucible is positioned between the plate and the ceramic shield.
The preferred arrangement for the build platform has surprisingly proven to be particularly advantageous. The plate (e.g. comprising quartz) provided a component onto which the material for the build platform could be applied with particular precision. The crucible and the ceramic shield made it possible to achieve particularly efficient heat transfer to the build platform.
Further preferred is a heater that allows the build part to be heated to a temperature that can melt or ablate a building material such as polymer and/or sinter a building material such as metal and/or ceramic. Preferably, the heater is variable and allows temperatures to be adjusted over a wide range so that different materials (with different melting points) can be used within a component and/or build part. This makes it advantageous to use a building material that consists of two or more components with different material properties.
The heater preferably heats the build part locally. This preferably means that only the build part is partially heated, while the non-heated part is not or only slightly affected by the heat.
The local heating can preferably be provided by the selection of the heater and/or by other components that limit the spatial effect of the heat along the applied layers. For example, a laser has a particularly precise beam effect so that the laser beams strike an area and thus produce the local heating effect. A surprisingly advantageous local heating effect is achieved by a laser with scan head or a moving laser. Local heating can also be achieved by an induction heater, since the heat that is transferred to the layers does not spread uniformly directly along all the layers.
However, in a further preferred embodiment, the apparatus comprises a plurality of heaters, each heater being arranged to heat the component and/or the build part to a predefined temperature. For example, a heater may be arranged to sinter the component and/or the build part, while another heater is arranged to heat the component and/or the build part such that the binder is removed, for example by ablating. The temperatures that must be reached by the heaters in order to be able to deliver a defined heat (e.g. for sintering) depend on the building materials used.
According to the invention the extruder is configured to eject building material in layers onto the build platform to form a build part, wherein an extruder, on the other hand, is preferably a component that is set up to continuously press solid to viscous masses under pressure out of a shaping opening (also referred to as a nozzle, die or mouthpiece). In the context of the invention, the shaping opening is contained in an extruder end or extruder hot end or extruder head. Preferably, the building material is ejected by the extruder, which can also be ejected under the influence of heat. Furthermore, the extruder and/or the extruder head preferably comprises a heating element in addition to a nozzle.
Moreover, by combining multiple extruders and/or extruder heads, the apparatus allows to 3D print multi-material parts made of a combination of polymers or metal-ceramic composites.
In addition, the extruder can preferably apply dots/points of material to a surface (e.g. build platform) along grids, the extruder being controlled by a preferred control unit. In this case, the dots/points are created by liquefying a filament or paste-like polymer or wax material by heating, applying it by extruding or ejecting it through a nozzle, and then curing it by cooling it at the desired position in a grid of the surface or working plane. A component or a built part is usually built up by repeatedly passing through a working plane line by line and then “stacking” the working plane upwards so that a build part is created layer by layer. The layer thicknesses are substantially in particular in a range from 0.10 mm to 1.25 mm. However, embodiments comprising a layer thickness in a range of preferably 0.01 mm to 3 mm or 0.015 mm to 2 mm are also conceivable. The mentioned layer thicknesses enable excellent stability of a component. In particular, the layer thickness in a range between 0.10 mm to 1.25 mm enables excellent surface quality of the component to be manufactured. In the case of curves, a higher resolution is clearly noticeable. It is understood that the layer thickness depends on the minimum nozzle diameter of the extruder to ensure the flowability of the material. Furthermore, the layer thickness depends on the particle size of the powder, which is preferably in a range of 1 to 20 microns. The process is preferably repeated successively, layer after layer, until completion of the build part. A wide variety of materials can be extruded, with preferably thermoplastics, such as Acrylonitrile Butadiene Styrene (ABS), PolyLactic Acid (PLA), High-Impact Polystyrene (HIPS), Thermoplastic PolyUrethane (TPU), aliphatic PolyAmides (PA, also known as Nylon), and especially high performance plastics such as PolyEther Ether Ketone PEEK or PolyEtherimide (PEI). It is understood that the extruder is controlled via moving means by the control unit. The apparatus preferably comprises moving means suitable to move the extruder, in particular the extruder head, in all spatial directions
In another preferred embodiment highly-filled polymers (HF) with ceramic and metal powders can be printed through the extruder heads (extruder ends), resulting in almost fully dense build parts after a debinding and sintering process. Moreover, by combining multiple extruder heads (extruder ends), the apparatus allows to 3D print multi-material build parts made of a combination of polymers or metal-ceramic composites.
Terms such as “substantially”, “approximately”, “about”, etc. preferably describe a tolerance range of less than +40%, preferably less than +20%, more preferably less than +10%, even more preferably less than +5% and in particular less than +1% and always include the exact value. “Similar” preferably describes quantities that are “approximately equal”. “Partially” preferably describes at least 5%, more preferably at least 10%, and more preferably at least 20%, in some cases at least 40%.
In the preferred layer-by-layer model production, the individual layers thus join together to form a complex component and/or build part. Cantilevered components and/or build parts can preferably be produced with support structures. Alternatively, support structures are preferably created directly during production when building up the component and/or build part from the building material. However, building materials made of a polymer and additionally of metal and/or ceramics are particularly preferred, whereby the support structure (if required) is preferred manufactured directly during production-from the same production material.
In the sense of the invention, a monitoring unit is further preferably a unit comprising means for detecting an object to be monitored. The monitoring unit preferably comprises means for generating, processing, storing, transmitting, and receiving data. It is within the understanding of the invention that the monitoring unit comprises at least one sensor or sensor system. A sensor may detect physical (e.g., heat quantity, temperature, humidity, pressure, sound field quantities, brightness, acceleration) or chemical (e.g., pH, ionic strength, electrochemical potential, analytical methods such as spectral or microbiological) properties and/or the material composition of its environment qualitatively or quantitatively as a measurand. These quantities are detected by physical or chemical effects and converted into an electrical signal that can be further processed. In a preferred embodiment, the monitoring unit comprises a sensor selected from the group consisting of: Temperature sensor, Displacement sensor, Pressure sensor (force sensor), Acceleration sensor, Image sensor, Touch sensor, Humidity sensor, GPS sensor, NFC sensor, RFID sensor, Air quality sensor, Pyrometer, camera, ultrasonic receptor.
The sensors of the monitoring unit are set up to detect and/or analyze a build part or component to be manufactured, preferably automatically, wherein information is preferably obtained, selected from the group: material-related parameters, geometry-related parameters, environment-related parameters, condition-related parameters, operation-related parameters, apparatus-related parameters. The combination of all information preferably results in a comprehensive overall information, from which in particular very detailed knowledge about the component as well as the apparatus according to the invention is obtained.
In a preferred embodiment, the monitoring unit is in a data connection with the control unit. This makes it advantageously possible to generate an effect of the components of the device that were particularly useful for the component on the basis of recorded parameters by the monitoring unit. In this way, the amount of heat supplied for debinding and/or sintering could be determined particularly precisely. Furthermore, the position of the components used for heat transfer for local heating could be determined particularly precisely. The improved results on the component were completely surprising and unexpected. Advantageously, the finished component was characterised by a particularly stable material quality and durability. Thus, the monitoring unit achieved a surprisingly advantageous effect in the context of the invention.
Furthermore, the installation of a preferred monitoring unit had a synergistic effect. On the one hand, by combining the monitoring unit with the other components of the preferred apparatus, the printing process as such and/or the apparatus as such can be monitored. On the other hand, the printing process and/or the effect of the components, such as the heater, could be adjusted particularly well on the basis of the data recorded by the monitoring unit. This in turn made it possible for the finished component to be of particularly good quality. Such an advantageous effect in many areas was not suggested by the prior art.
Another major advantage of the monitoring unit is that the built part can be reproduced by recording process parameters. In addition to monitoring, the monitoring unit is also able to record parameters that greatly improve the overall production through the possibility of reproducibility. Advantageously, the apparatus is thus also suitable in the context of mass production, where the material properties are essentially identical, which is a considerable improvement over the known state of the art. In particular, the monitoring unit makes it possible to provide a digital twin. Furthermore, defects can be detected during production and eliminated more quickly.
A component (manufactured by means of filament or paste extrusion additive manufacturing) within the meaning of the invention is preferably to be understood as a completed or finished build part.
In another preferred embodiment, the feedstock used is a building material that is a solid-liquid mixture with a high solids content, e.g., a paste. The viscosity decreases with increasing heat. The building material can preferably assume several states. An initial paste-like state when extruded from an extruder, and a solid state after the paste has been extruded and possibly subjected to cooling or drying. Alternatively, the starting material can also consist of a solid building material, for example in the form of a filament. In this case, it is preferably heated and brought to a paste-like state and then ejected from the extruder.
In a further preferred embodiment, the control unit comprises a data processing unit and control means, as for example an actuator or heater. The data processing unit preferably comprises means for generating, processing, storing, transmitting, and receiving data. The data processing unit is preferably in data communication with the control means and/or the monitoring unit, whereby data can be transmitted bidirectionally between these system components. In a preferred embodiment, the control means are arranged to control the heater and/or the extruder heads and/or the monitoring unit.
In a preferred embodiment, the data processing unit performs algorithms and calculations by receiving input data from the monitoring unit (e.g., sensors) and, after executing the algorithms, generates output data that is preferably transmitted to control means, e.g., an actuator or heater. The advantage of such an arrangement is that the monitoring unit does not need to be equipped with components for data processing (processor) and data storage. Another advantage is that the data processing unit can include a variety of acquired data from different sensors for its analysis or the execution of the algorithms, so that a wide-ranging analysis is possible.
In a further preferred embodiment, the apparatus is characterized in that the building material comprises binding material and additionally metal and/or ceramics,
By using metal-polymer or ceramic-polymer composite feedstocks, the advantages of two classes of materials can be combined in one component to be manufactured. Specifically for the present purpose, it is advantageous to use two material components, whereby on the one hand the binder is seen as an auxiliary material for the design purpose, while the metal or ceramic used provides the material for the component to be manufactured. The binder is preferably used to bind the metals and/or ceramics present while still in the form of granules and to impart its structural integrity to them in the course of component build up. The fact that the metal and/or ceramic is in the form of powder granules can advantageously ensure that this material is particularly uniformly contained in and surrounded by the binder.
In a preferred embodiment ceramics are preferably selected from the group consisting of: Silicon nitrate (Si3N4), Fused Silica (SiO2), Lead zirconium titanate, Zirconia, Yttria stabilized zirconia, Strontium ferrite (SrFe12O19), Alumina, Mullite+Alumina+MgO, Fused silica+MgO, or Fused silica+MgO.
In another preferred embodiment, metal or metallic alloys are preferably selected from the group consisting of: Stainless steel (17-4PH; 316L or AISI 630), Tungsten carbide-cobalt, Carbonyl iron, Titanium (Ti6Al4V), Chromoly steel 4140, Copper Kovar F-15, Nickel Inconel 625 and 718. Preferably, the metal powder can also consist of a combination of the above compounds.
However, it is possible to conduct the same process with materials that are not commercially available today. In particular, the same process is possible for precious alloys (e.g. gold, bronze, silver or platinum), which would be suitable for the luxury market (e.g. watch & jewellery & luxury industries). Any metallic or ceramic material that can be made into powder is suitable for the process. Even aluminum for the aerospace industry.
Furthermore, a powder (metal and/or ceramics) content of preferably 35% to 90%, more preferably 40% to 80% and in particular 55%-70% is included in the feedstock. The percentages preferably refer to the (total) volume or the (total) mass of the feedstock. A range of 55-70% powder volume loading is advantageous to ensure flowability of the feedstock material.
In another preferred embodiment a high powder volume/packing densities within the feedstock material are desired to decrease the shrinkage of the part after sintering whilst rendering high densities.
In a further preferred embodiment, a binder can be a polymeric mass or a mixture of a polymeric mass. The binder preferably consists of different types of polymers, waxes, and additives. Three main binder groups can preferably be distinguished:
The main binder preferably needs to present low viscosities (e.g. waxes) to be extruded through the extruder head and/or nozzle. One way to make the main binder flexible is preferably to further add elastomers or amorphous polyolefins. The majority of backbones are preferably polyolefins (e.g. polyethylene or polypropylene). Polyolefins are resistant to many solvents used during debinding, add strength to the debound part, and degrade into hydrocarbons only before sintering. Preferably, stearic acid is used as an additive, which facilitates the dispersion of the filler particles.
The main binders can preferably be thermally debinded from the green part by heating to 300-500° C., for 3 to 8 hours. Heating to these temperatures is advantageously a slow process, so that the green compact is not damaged by uncontrolled decomposition and consequent cracking of the part. Careful selection of binder combinations has shown that higher heating rates and lower soak times can be used to thermally debind green compacts. An appropriate combination of binder system heating rates has shown that localized thermal debinding is possible via low intensity lasers or high intensity infrared emitters (infrared lamps).
Although time consuming and complex, removal of the main binder is necessary before sintering to avoid defects such as cracking, blistering, bloating, and the generation of large internal pores. Here, it has been shown that with laser ablation, the polymeric mass can be removed by focusing sufficient energy on the material (build part), which vaporizes the main binder mass. In-situ debinding is achieved by an application of local energy in a layer wise manner, leaving room for the escape of ablated polymers through the open pores, and thus avoiding the detrimental effects of having an increase in vapour pressure within the bulk.
In a further preferred embodiment, the apparatus is characterized in that the apparatus comprises a debinding heater and a sintering heater, wherein
An advantage of microwaves, induction and laser sintering, in contrast to conventional sintering, is the ability to sinter in only a few seconds or minutes rather than hours or days. Low sintering times are possible with microwaves, induction and lasers since high heating rates are easily attained due to internal heating of the build part, as opposed to the external heating of conventional sintering
As always the last/newest layer to be applied is immediately debinded and sintered, little energy is required for the debinding heater and sintering heater, since the respective layer does not exceed a certain thickness. In addition, any defects that occur can be found and eliminated quickly, since the build part or component to be manufactured is not sintered or debinded as a whole, but layer by layer. Detailed component shapes are thus possible.
It is also possible in a further preferred embodiment, if required (with induction and microwave heating), to sinter a component to be manufactured in its entirety at the end of a process—i.e. after building material layer by layer. By using two types of heaters, debinding heater and sintering heater, an optimal heater can be used for both debinding and sintering applications. This promotes precision in production and also reduces the energy required to produce the component.
In a preferred embodiment, the sintering can be performed after the build part has been provided layer by layer. Preferably, the sintering is executable for the entire component. This is of particular advantage because shrinkage of the layers can occur during layer by layer sintering. The latter in turn makes it more difficult to apply a further layer to the sintered layer. Therefore, it is preferred that sintering is performable after all layers have been provided.
In a preferred embodiment, the control unit is in a data link with the sintering heater and/or the debinding heater. In another preferred embodiment, the control unit is configured to cause the sintering heater to sinter the build part after the build part is provided in its entirety.
In a preferred embodiment, the debinding heater is a low intensity laser. Preferably, the low intensity laser is a 1 W, continuous wave diode laser for debinding, with a wavelength of ˜850 nm. The exact wavelength-power combination may depend on the binder selected. Advantageously, the low intensity laser consumes little energy, with the low intensity laser already generating enough heat to debind the build part locally. The low intensity laser needs to achieve an adequate temperature at the focal spot to ablate the main polymeric binder mass.
In a preferred embodiment, the debinding heater is an infrared lamp. The emitted infrared waves enter the build part only a few centimeters, preferentially heating it and thus causing debinding.
In a further preferred embodiment the apparatus is characterized in that the infrared lamp is aligned with the build part and is configured to irradiate the build part until the binding material is at least locally removed from the build part, preferably causing a debinding layer in which the binding material of the last applied material layer is removed from the build part. Infrared lamps are particularly suitable for this purpose, as they generate heat immediately. In addition, it is advantageous to produce a uniform heat, which, among other things, reduces the probability of defects in the build part or component to be manufactured.
In a preferred embodiment, the binder is removable by ablation and/or gasification starting from the binder heater. In the context of the invention, this has proven to be extremely advantageous. In particular, ablation and/or gasification is significantly better than melting and/or vitrification, since other residual components can remain which could have a detrimental effect on the material quality of the build part.
In a further preferred embodiment the sintering heater is a CO2 Laser or a Nd:YAG Laser. With laser sintering, depending on the laser power density, the powder granules preferably begin to melt and form a confined melt pool. The melted phase preferably formed between neighbouring close-packed particles initiate a capillary force that merge particles together. The melt pool forms preferably a rapid way for mass transport and liquid phase sintering.
However, when the laser beam irradiates the powder particles at a given wavelength, it scatters or reflects to a degree proportional to the reflectivity of the material, before it is absorbed. It has been shown both with simulations and experimentally that the heat formation (temperature) is inhomogeneous because of the randomness of the laser interactions. Consequently, lasers with different wavelengths and power densities ought to be selected to match the absorption characteristics of the corresponding powder granules. The laser power, hatch distance, scanning speed and laser beam diameter/spot size determine the laser power density. There are three types of laser sources that are preferably used for laser sintering:
The laser sintering process is preferably combined with an x-y mirror, or scan head/F-theta lens to shape the layer, and is preferably performed under a vacuum or neutral atmosphere such as argon or nitrogen, depending on the processed material.
The wavelength of a Nd:YAG laser, which is ten times shorter than that of CO2 lasers, enables more precise focusing of the laser beam. This property makes the Nd:YAG laser ideal for manufacturing processes where the highest accuracy is required. In addition, high energies can be focused in pulsed mode, which increases the efficiency of the laser. In contrast, the CO2 laser exhibits high process reliability due to its constant power and is also particularly economical with short operating times.
Furthermore, the integration of lasers advantageously opens up new possibilities for processing multi-material components, tailoring metallic microstructures, improving surface properties and thus increasing fatigue life, resulting in high-performance functional build parts or components.
In a preferred embodiment, the sintering heater is a microwave heater. In a microwave heater, high microwave fields are preferably generated (single-mode resonator). The heater preferably contains auxiliary materials which are also heated by the microwave (susceptors). The susceptors thereby preferably transfer the heat energy to the component like a conventional heater. The microwave field is controlled in such a way that the temperature difference is minimized. The sintering time is decisively reduced, and novel material properties can be achieved. Microwave sintering is preferably equally suitable for technical ceramics and hard metals.
In a preferred embodiment, the sintering heater is an induction heater. It is understood that induction heating is a process of heating an electrically conducting object (usually a metal) by electromagnetic induction, through heat generated in the object by eddy currents. By means of a coil, the induction heater preferably generates an alternating magnetic field through which low-frequency (preferably about 50-300 Hz), medium-frequency (preferably 200 Hz-10 kHz or 1 kHz-100 KHz]) or high-frequency alternating current flows, which induces eddy currents in the object (here: build part). The heat is generated directly in the object (here: build part) itself, so it does not need to be transferred by heat conduction. The electrical power comes preferably from special frequency converters or directly from the mains. Induction heating can pass through non-conductive materials, the environment is heated only indirectly. The process can be used under any gases or vacuum. The advantage of induction heating is a clean, energy-efficient and well-controllable sintering or melting process.
Induction heating is very suitable due to the packing density of the build part. Indirect induction heating can advantageously achieve build part densities of 99.79%. Induction heating is preferably combined with a crucible (e.g. graphite) and a ceramic shield (e.g. SiO2). Preferably, induction heating is used to heat graphite crucibles, which provides even better efficiency.
In a further preferred embodiment the apparatus is characterized in that the control unit is configured to focus, via control means, a laser beam of the low intensity laser and/or the CO2 laser or the Nd:YAG laser onto the build part, the laser beams being capable of impacting the build part and causing a heating zone and/or a heating point in the build part;
As already described above, the apparatus according to the invention enables a fully automatic system which, in particular by the control unit and the control means, allows all necessary process steps for the production of a component manufactured by paste or filament extrusion additive manufacturing without human intervention. In particular, the alignment of the laser beams allows a very precise processing of the component, so that not only a heating zone but even a heating point can be generated.
In case of the low intensity laser, the control means preferably also include moving means, so that the low intensity laser can be moved in all spatial directions. Preferably, the low intensity laser can be mounted on a carriage rail system, which is movable in all spatial directions (x, y, z) via an actuator. Such a design allows the low intensity laser to be placed very close over the surface of the build part, so that only minimal energy is lost when the build part is irradiated. Preferably, the low intensity laser can follow the extruder head by its moving means so that immediately after ejecting the building material, the binder is removed.
The CO2 laser or a Nd:YAG laser preferably comprises a stationary laser scan head. The laser scan head is particularly space-saving, since the laser source as such does not have to be moved in a spatial direction. In the scan head, the laser beam is preferably deflected, with the deflection angle being measured and (preferably) electronically controlled. A scan head can preferably have mirrors for deflecting the laser beam. This has the advantage that only a light mirror needs to be moved and the projection can thus be quickly realigned,
In a further preferred embodiment the apparatus is characterized in that the apparatus comprises a pulsed laser, wherein the build part is covered by a solid transparent confinement overlay. The pulsed laser is preferably used for plasticizing the near-surface zone of polycrystalline materials (e.g. metals) in order to increase the fatigue strength, among other things. The solid overlay confines the plasma shock explosion generated from the laser pulses, and plastifies the near surface zone of poly-crystalline metallic layers.
In a further preferred embodiment the apparatus is characterized in that the apparatus includes a monitoring system comprising an optical sensor, preferably a camera, a pyrometer and/or an ultrasonic receptor,
Optical sensors have the advantage of being contactless and have a high measuring accuracy. They also offer the advantage that they cannot be disturbed by ferromagnetic substances or by electric or magnetic fields. In particular, pyrometers have the advantage that they allow very fast temperature measurement. Very large measuring ranges are possible (e.g. 350° C. . . . 3000° C.) and the pyrometers are not subject to wear. Furthermore, there are no errors due to thermal contact and measurement is possible even at high voltages and electromagnetic fields. The presence of the above sensors, in particular a preferred IR camera and preferred ultrasonic receptors, when activated, allows the detection, localization and characterization of defects that occur during the sintering phase. It is understood that the sensors acquire data relating the build part, which are transmitted via an existing data link to the data processing unit of the control unit
The control unit can use these data to evaluate and control the heaters or extruders contained in the apparatus, so that they perform an adapted operation step.
In a further preferred embodiment the apparatus is characterized in that the apparatus comprises a build chamber
The build chamber protects the individual components from damage and exposure to foreign substances or particles such as dust. In addition, the build chamber provides sound insulation. The build chamber can further serve as a load-bearing element to which the individual components are attached and integrated, resulting in a compact apparatus. Preferably, according to the invention, all sensitive parts are housed inside the build chamber. By placing the CO2 or Nd:YAG laser as such outside the build chamber, with the laser beam being guided into the build chamber via a scan head through an opening, very good accessibility is enabled, which simplifies the repair and maintenance of these lasers.
Preferably, debinding and sintering of the build part is performable within one build chamber. In particular, debinding and sintering is performable in the same build chamber. Thus, it is advantageously not necessary to perform debinding and sintering in different chambers. Advantageously, this saves time during the production of the build part, since the transfer of the build part during the process in different chambers is dispensed with. Furthermore, it is of particular advantage that by having one and the same build chamber, a compact apparatus is available which does not require a large storage space for the whole apparatus itself.
In addition, the build chamber advantageously allows to create a vacuum atmosphere and/or optionally add a neutral atmosphere, such as to prevent oxidation of metallic components during sintering (i.e., it is necessary to remove oxygen from the chamber to mitigate the effect of oxidation). In a preferred embodiment the invention relates to a method for manufacturing a component by means of filament or paste extrusion additive manufacturing comprising the following steps:
The combination of the proposed method steps leads to a surprising synergistic effect, which results in the advantageous properties and the associated overall success of the invention, with the individual features interacting with each other. A significant advantage of the method according to the invention is that extremely few process steps and system components are required, and yet an extremely robust and defect-resistant infrastructure is created for manufacturing a component using filament or paste extrusion additive manufacturing. The proposed method leads to an enormous reduction in the time required to manufacture a component, since on the one hand comprehensive aspects (e.g. relating to temperature, geometric shape, etc.) for the manufacture of a component are included simultaneously (with a monitoring unit) from the beginning, so that necessary changes and corrections during manufacture or afterwards are minimized. As a result of the fact that all influencing variables relevant to production are recorded, analyzed and post-processed, an optimized component (in terms of production and use) is advantageously obtained. Advantageously, the method can be automated in the apparatus according to the invention. As already explained, such a method in the context of an all-in-one system (all steps are carried out in one apparatus) is neither known nor proposed in the prior art.
The skilled person will recognize that the advantages, technical effects and preferred embodiments discussed in connection with the apparatus according to the invention apply analogously to the method according to the invention for producing a component by means of filament or paste extrusion additive manufacturing. Likewise, all advantages, technical effects and preferred embodiments described in connection with the method are transferable to the apparatus.
In a further preferred embodiment the method characterized in that the building material comprises binding material and additionally metal and/or ceramics,
In a further preferred embodiment the method characterized in that two heaters are provided, namely a debinding heater and a sintering heater,
In a further preferred embodiment, the method is characterized in that steps b. and c. are repeated until a final component is completely built up, wherein in step b. a single layer of the building material is applied and before applying a next layer the heater heats this layer locally in step c.
This repeated layer-by-layer processing of the component or build part advantageously results in extremely stable and, above all, dense component, whereby defects can be detected and immediately eliminated after each iteration.
In a further preferred embodiment, the method is characterized in that the component (or build part) is built up in layers and each layer is debinded individually. After the component (or build part) is completely built up and no longer contains any binder, it can preferably be completely sintered by means of induction heaters and/or microwave heaters. This has been shown to be advantageous for mono material metallic or ceramic components which are very stable and have few defects.
In a further preferred embodiment, the method is characterized in that
In a further preferred embodiment, the method is characterized in that the control unit regulates or controls the induction heater, comprising induction coil, wherein in the interior of the induction coil, besides the build part, other elements are included, namely a graphite crucible and a SiO2 ceramic shield, for example. This allows even more efficient heating of the build parts. Preferably, other crucibles and ceramic shields are also possible, such as alumina, boron nitride, MgO, molybdenum crucibles, etc.
In another preferred embodiment, the control unit includes control means that control the induction and/or microwave heaters and regulate the combination of output voltage and current to achieve any desired heating profile for a particular material. In the case of induction heating, for example, it is necessary to control the heating rate by regulating the output current and frequency.
In a further preferred embodiment, the method is characterized in that the control unit focuses a laser beam, via control means, of the low intensity laser and/or the CO2 laser or the Nd:YAG laser onto the build part, the laser beam being capable of impacting the build part and causing a heating zone and/or a heating point in the build part
In a further preferred embodiment, the method is characterized in that the apparatus includes a monitoring system comprising an optical sensor, preferably a camera, and/or an ultrasonic receptor,
In a further preferred embodiment, the invention relates to a use of the apparatus of the type mentioned above for manufacturing a component by means of filament or paste extrusion additive manufacturing.
In the following, the invention is explained in more detail with reference to the figures, without being limited to them. Particularly, the following figures contain also illustrations that are not to scale.
a)-c) show several sectional views of the apparatus. Specifically,
d) shows the arrangement of the components for heating the build platform 3. The build part 5, which is applied to the build platform 3, is shown. Below the build part 5 is a graphite crucible 36 which transfers the heat emanating from the induction coil 34. A ceramic shield 35 is arranged between the graphite crucible 36 and the induction coil 34, on which the induction coil 34 is also arranged.
a) shows a setup of the apparatus in an overall view.
The build part is attached to the plate 38. Furthermore, the extruder head 15 is surrounded by a ceramic shield 35, in which an induction coil 34 is present and a graphite crucible 36 is in contact.
a) shows the schematic arrangement of specimens numbered 1-9, having a length and width of 1 cm, arranged along 5 cm in length and width and spaced 2 cm apart. The specimens are mounted on a glass plate. The table on the left shows the laser parameters used to sinter each specimen.
b) shows a photo taken before the laser sintering was performed.
In order to have a flowable feedstock with an embedded powder, the volume ratio of powder to binder in the prior art does not exceed 68%. It is clear from this series of experiments that shrinkage can occur when sintering layer by layer. Sintering for smaller powder packing densities does not render positive results, as shown by the test series.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21192364.4 | Aug 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/072413 | 8/10/2022 | WO |
