The invention relates to a printing system for extrusion-based printing of a three- dimensional object. The invention further relates to a process for printing a three- dimensional object.

Additive manufacturing technologies have become important processes for industrial manufacturing and are used to print three-dimensional objects based on CAD building data. In particular fused deposition modeling systems (FDM) are commonly used for modeling, prototyping, and production applications since they are very advantageous with respect to economic use of the build material and in terms of machinery design. FDM works on an additive principle in that the build material is supplied by a feeding device to a printing device, where it is molten in a nozzle, extruded, and selectively deposited onto a substrate. Despite being a quite flexible technology, FDM printing systems are still limited with respect to the type of build materials that can be used and the option to change the build material during the printing process. It is therefore difficult to vary the build material within the three-dimensional objects in order to create workpieces with a non-uniform structure. It is the task of the present invention to provide a printing system that can easily be equipped with different build materials during the print process. A further task of the present invention is to provide a process with a higher flexilibity for extrusion-based printing of a three-dimensional object. These tasks are solved by a printing system according to claim 1 and a process according to claim 9 for extrusion-based printing of a three-dimensional object. Advantageous developments of the invention are specified in the respective dependent claims, wherein advantageous developments of the first aspect of the invention are to be regarded as advantageous developments of the second aspect of the invention and vice versa.

A first aspect of the invention relates to a printing system, which comprises at least one pretreatment device for selectively modifying the build material prior to melting the build material in the printing device. The printing system according the invention can thus easily be equipped with different build materials during the print process, since a uniform build material can be supplied by the feeding device and selectively modified by the at least one pretreatment device prior to melting, extruding, and depositing the build material by the printing device. The printed three-dimensional object or workpiece can therefore be printed using a selectively modified build material so that the final three-dimensional object can be provided with locally different properties compared to a regular three- dimensional object, which is manufactured from a single or unmodified build material. It is also not necessary to supply different build materials, to change the source of the build material during the printing process, or to provide a printing device with several printing heads, mixing chambers or the like. One of the main advantages is therefore the possibility to create a functional object from a single raw or build material, but with different properties depending on the zone of the object so that the printing system is very flexible and allows for particularly low process costs and rapid printing of objects that are complex both in geometry as well as in their local properties. In addition, the possiblity to use the same raw build material for objects with different properties reduces logistic problems since only one supplier is needed. Furthermore, the printing system according to the invention raises the value of the FDM technology, because it allows the creation of high value workpieces with certain properties, wherein these properties are not just realized on the surface of the workpiece, but embedded within the material of the workpiece. This ameliorates the useful life of the workpiece since erosion of its surface does not eliminate these specific properties.

In an advantageous development of the invention it is provided that the at least one pretreatment device with respect to a supply direction of the build material is arranged downstream of the feeding device and upstream of the printing device. Thus, the build material can consecutively be supplied, selectively modified, and printed, which allows for a very rapid and easy printing process.

In a further advantageous development of the invention it is provided that the at least one pretreatment device is selected from one or more of spray stations, laser application devices, electron beam application devices, coating devices, UV application devices, and liquid baths. This allows for a very flexible modification of the build material. Generally, the at least one pretreatment device can be designed in any way that is necessary to provide the build material with a predetermined property. In a further advantageous development of the invention it is provided that the at least one pretreatment device is configured to modify one or more of antimicrobial properties, hydrophobic properties, hydrophilic properties, electrical conductivity, optical properties, and magnetic properties of the build material. Thus, the final three-dimensional object can be provided with a tailored property distribution.

In a further advantageous development of the invention it is provided that the printing system further comprises a control unit in communication with the at least one pretreatment device for selectively operating the at least one pretreatment device based on modification data. This allows for a very flexible and precise modification of the build material.

In a further advantageous development of the invention it is provided that the control unit is in communication with the at least one printing device and/or with the at least one feeding device. This allows for a very flexible and precise control of the printing process that is carried out by the printing system.

In a further advantageous development of the invention it is provided that the printing system comprises at least two pretreatment devices. By using two or more pretreatment devices or cells, which can generally be configured to modify the build material together and/or in sequence, multifunctional 3D objects can be printed in one piece with minimal mechanical complexity. Thus, the printing system can be manufactured with very low costs. It is generally possible that at least two pretreatment devices modify the chemical and/or physical properties of build material in the same way or differently.

In a further advantageous development of the invention it is provided that the build material comprises a plastic filament and/or a metallic filament. This allows printing of very different 3D objects, for example for different household appliance components so that a household appliance can in principle be assembled at least in large parts from printed household appliance components. The plastic filament may for example comprise or consist of acrylonitrile butadiene styrene (ABS) or polylactic acid (polylactide, PLA, Poly). A second aspect of the invention relates to a process for extrusion-based printing of a three-dimensional object. According the invention the process comprises at least the steps of supplying a build material by at least one feeding device to at least one pretreatment device, selectively modifying the build material by the pretreatment device, supplying the selectively modified build material to at least one printing device and selectively melting, extruding, and depositing the build material onto a substrate to form the three-dimensional object based on building data by the printing device. Thus, the printing device is selectively supplied with modified or unmodified build material so that the resulting three-dimensional object can easily and without the need of additional raw build material be provided with different local properties. Further features and their advantages can be gathered from the description of the first aspect of the invention.

In an advantageous embodiment of the invention it is provided that the at least one pretreatment device selectively modifies the build material based on modification data. This allows for a very precise modification of the build material's properties depending on the current printing stage.

In a further advantageous embodiment of the invention it is provided that the modification data are comprised in the building data. In other words the geometry and the local material properties of the three-dimensional object are coded in a single data file or data stream. This allows for a very precise synchronization of the printing process so that very precise objects with different local properties can be printed at high printing speeds.

In a further advantageous embodiment of the invention it is provided that the at least one pretreatment device modifies one or more of antimicrobial properties, hydrophobic properties, hydrophilic properties, electrical conductivity, optical properties, and magnetic properties of the build material. Thus, the printed object can be optimally provided with one or more functional properties, depending on its later use. In a further advantageous embodiment of the invention it is provided that the at least one pretreatment device coates and/or impregnates the build material with one or more of silver zeolite, zinc pyrithione, 4,5-Dichloro-2-octyl-4-isothiazolin-3-one (DCOIT), methyl nonafluoroisobutyl ether, methyl nonafluorobutyl ether, a polysaccharide, a dye, silver, in particular nanosilver, and graphene. Silver zeolite, zinc pyrithione, 4,5-Dichloro-2-octyl-4- isothiazolin-3-one (DCOIT), and nanosilver provide the build material with antimicrobial properties, methyl nonafluoroisobutyl ether and methyl nonafluorobutyl ether provide the build material with hydrophobic properties, one or more polysaccharides provide the build material with hydrophilic properties, and silver and/or graphene to provide the build material with electrical conductivity.

In a further advantageous embodiment of the invention it is provided that at least two pretreatment devices selectively modify different properties of the build material. The build material can thus be equipped simultaneously or consecutively with two or more functional properties. This allows for a particularly fast and easy manufacturing of multifunctional 3D objects.

In a further advantageous embodiment of the invention it is provided that the three- dimensional object is a household appliance component. Thus, the advantages of the 3D object, which is manufactured by means of the inventive process and/or by means of the inventive printing system, can be advantageously used for the construction of a household appliance. The household appliance component can for example be designed as part of a dishwasher, a dryer, a washing machine, a microwave oven, a steam oven, and the like. Further features of the invention derive from the claims as well as based on the following embodiments. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the embodiments are usable not only in the respectively specified combination, but also in other combinations without departing from the scope of the invention. There are thus also variations of the invention possible that are not explicitly shown and described in the embodiments but can be formulated through different combinations of separated features from the described embodiments. Also variations and combinations of features are possible that do not contain all the features of an originally formulated independent claim. In the following, embodiments of the invention are shown in more detail by referring to schematic drawings. These show in: a principle schematics of a printing system according to the invention; and Fig. 2 a perspective view of a three-dimensional object which has been produced by the printing system of Fig. 1.

Fig. 1 shows a principle schematics of a printing system 1 according to the invention. The printing system 1 comprises a feeding device 2 for supplying build material 3 to a printing device 4. The printing device 4, which generally can also be denominated FDM printer, extrusion 3D printer, or FDM 3D printer, selectively melts, extrudes, and deposits the build material 3 onto a substrate 5 in order to form a three-dimensional object 6 (Fig. 2) based on respective building data, e. g. CAD data. In order to be able to modify one or more properties of the build material 3 and thus of the resulting 3D object 6, the printing system 1 further comprises two pretreatment devices 7, which are located between the feeding device 2 and the printing device 4, i. e. between the raw build material 3 supply and the point where the build material 3 is fused by the FDM printer 4. Usually, in a common FDM printer, the build material 3 is supplied directly from the raw input or feeding device 2 to the printing device 4 without any pretreatment. The build material 3 may be a PLA plastic filament. According to the invention, the build material 3 before entering the printing device 4 passes through one or more pretreatment devices or cells 7, which selectively modify the build material 3, depending on the desired properties of the 3D object 6. These pretreatment devices 7 can generally comprise or consist of a spray station, a laser application device, an electron beam application device, a coating device, an UV application device, or a liquid bath, i.e. any device that is capable of modifying the build material 3 in a desired way. Each pretreatment device 7 can generally provide a different property to the build material 3 which gives the flexibility of using the same raw build material 3 and changing its properties depending on the phase of the making process which the printing device 4 is currently conducting. Thus, respective modification data may be comprised in the building data to synchronize geometry and property of the 3D object 6. In the present embodiment, the first pretreatment device 7, which is located upstream of the second pretreatment device 7, comprises a cell with an antibacterial liquid bath. Thus, the build material 3 passes through the first pretreatment device 7 and may be coated or impregnated such that antimicrobial compounds adhere to its surface, thereby generating the modified build material 3'. The modified build material 3' may then be further modified by the second pretreatment device 7 (build material 3") before entering the printing device 4.

Different changes of the chemical or physical properties of the build material 3 are therefore possible. For example, the hydrophobic, hydrophilic, and/or electrical conductivity properties of the base material 3 may be modified, depending on the desired properties of the final 3D object 6. As a list of possible pretreatments which may be used to achieve different functionalities are: - Antibacterial: Silver Zeolite, Zinc Pyrithione, 4,5-Dichloro-2-octyl-4- isothiazolin-3-one (DCOIT);

Hydrophobic: methyl nonafluoroisobutyl ether, methyl nonafluorobutyl ether;

Hydrophilic: Polysaccharide(s); and

- Electrical conductivity: Silver, Graphene.

One of the main advantages of the printing system 1 is the possibility of creating a functional object 6 with the same raw build material 3, but with different properties depending on the zone or location within the object 6.

Further, it is for example also possible to equip the first pretreatment device 7 with a first coloring agent (e. g. methylene blue) and the second pretreatment device 7 with a second coloring agent or dye (e. g. rhodamine B). Depending on the amount of dye that is applied to the build material 3, at least three different colors (build material 3, build material 3', build material 3") as well as color mixtures, gradients or transitions may be generated. This can be gathered from Fig. 2, which shows a perspective view of the three- dimensional object 6 which has been produced by the printing system 1 of Fig. 1. The object 6 has a cylindrical shape, wherein a base part 6' has a first color (e. g. white, i. e. regular PLA), a middle part 6" has a second color, for example blue (methylene blue), and a top part 6"' has a third color, for example pink (rhodamine B). Depending on the control of the pretreatment devices 7, the colors of the base, middle, and top part 6', 6", 6"' can be sharply seperated or may be merged or blended together. It is of course also possible to change the color distribution within the object 6. For example, the object 6 may be white inside and only colored on the outside. The same is possible with other modifications. It will be understood by those skilled in the art that while the present invention has been disclosed above with reference to preferred embodiments, various modifications, changes and additions can be made to the foregoing invention, without departing from the spirit and scope thereof. The parameter values used in the claims and the description for defining process and measurement conditions for the characterization of specific properties of the invention are also encompassed within the scope of deviations, for example due to measurement errors, system errors, weighing errors, DIN tolerances and the like.

LIST OF REFERENCES printing system

feeding device

build material

printing device

substrate

object

pretreatment device