Device for the production of three-dimensional objects

Abstract

Device (1) for producing three-dimensional objects (9) by successively solidifying layers of a build-up material (4), in particular a powder form, which can be solidified by means of electromagnetic radiation or particle radiation, at the locations corresponding to the respective cross-section of the object (9), comprising a carrying device for carrying the object with a height-adjustable support (6) arranged in a build-up chamber (5), an application device (11) for applying the build-up material (4), and an irradiation device (13) for irradiating the applied layers of the build-up material (4) at the locations corresponding to the respective cross-section of the object (9), wherein a build-up plate (7) is arranged on the support of the carrying device, which can be heated by means of a heating device (18), characterized in that the heating device (18) comprises a plate-like support (20),the upper side of which is provided with a recess (24) facing the building plate (7), in which a heating element (22) is floatingly mounted, the heating element (22) being formed by a heating plate (23) and heating rods (25) and the heating element (22) being supported at its edges by flexible insulating sealing elements (21).

Description

The invention relates to a device for producing three-dimensional objects according to the features of the preamble of claim 1. In such devices, powder is applied layer by layer in a build chamber, with predetermined areas in the last layer being solidified by energy input, for example, using a laser. In this way, a three-dimensional object is built layer by layer, making it particularly easy to create complex cavities within the object or very fine structures. One challenge with these generic processes is that the build material for sintering or melting must be heated to a specific temperature at precisely defined locations in order to complete the sintering or melting process. Due to the spatial extent of, for example, the laser spot on the surface, the energy input cannot be controlled with arbitrary precision; in particular, a laser beam does not only heat the covered area, but also heats the surrounding material through heat exchange processes. To prevent distortions in the object due to differing energy inputs and thus different solidification stages of the building material, one known method is to heat the building material. If the building material has a temperature close to its melting point, less energy is required to reach that point. This also reduces the impact of heat transfer processes, resulting in a more homogeneous three-dimensional object overall. To heat the build material, it is known to install heating elements above or around the build chamber. An arrangement of heating elements below the support within the build chamber is also known. Typically, the heating elements are arranged above or at the edge of the build chamber, as this design ensures the most direct influence on the top layer of build material, which is always located at the top edge of the build chamber. On the other hand, a heating device below the support is advantageous in that the upper part of the construction chamber remains fully accessible. However, placing a heater below the support is problematic because the materials deform when heated. Devices of this type are known from documents EP 0 759 848 B1 , DE 103 42 880 A1 , DE 10 2008 031 587 A1 and US 2011 / 0 256 253 A1. The invention is therefore based on the objective of further developing a device for producing three-dimensional objects with the features of the preamble of claim 1 in such a way that the use of a heating device is improved. This objective is achieved by the features of claim 1; advantageous further developments of the invention are set forth in the dependent claims. The core of the invention lies in the fact that the heating element itself is not rigidly connected to the support structure, and that expansion of the heated element is also ensured. This design makes it possible to position the heating device between the support and the base plate, thereby achieving higher temperatures than previously possible. A floating mounting means that the heating element is not fixed in the recess, especially not by the side walls. To reduce heat dissipation from the heating element towards the support or into the assembly chamber below the support, the heating device is designed to include a plate-shaped support made of insulating material, which has a recess. The heating device can thus be mounted within the support of the assembly chamber, with the insulating support shielding the heat output of the heating device from the surrounding environment in the direction of the assembly chamber support. To ensure a certain degree of positioning of the heating element despite its floating mounting, the element is supported at its edges by flexible insulating sealing elements. These sealing elements fix the heating element in such a way that it does not move uncontrollably within the recess; however, expansion of the heating element due to heat generation during the heating process is still possible. Due to their insulating effect, the sealing elements prevent heat transfer from the heating element to the side walls of the heating device or to the plate-like support in which the heating element is floatingly mounted. Advantageously, the base of the recess can be provided with a grooved structure on which the heating element rests. This grooved structure reduces heat conduction between the heating element and the rest of the heating device. For heat generation, the heating element advantageously has at least two heating rods, which can, for example, have a rectangular cross-section. The heating rods are elongated rods that extend over most of the length of the heating element. For energy input, one end of each heating rod is connected to a power source. Due to the electrical resistance present in the heating rods, resistance heating is thus achieved. To allow this end of the heating rods to connect to the power source, the heating device has openings at the bottom of the recess through which the heating rods are guided. In the area passing through the opening, the heating rods are bent or angled. To achieve a symmetrical distribution of the heating elements, the openings for the heating elements can be arranged on the two different halves of the base of the recess. Since the recesses must be spaced a certain distance apart and the heating elements have a smaller cross-section than the recesses, this allows for a higher density of heating elements in the central area of ​​the heating element. The heating elements can be potted, which offers a particular advantage. The potting compound used for this purpose homogenizes the heat output of the heating elements. Instead of embedding the heating elements in a potting compound, a coupling element with slots or recesses can be used. The heating elements can be inserted into the coupling element or its recesses and even fixed within them. In particular, good thermal coupling can be achieved between the heating elements and the coupling element. Above the recesses, towards the base plate, the coupling element can have several layers of different materials. These layers can have different thermal conductivities to further homogenize heat dissipation. The plate-like support itself can be placed on a trough-shaped insulating tray. This double insulation improves the insulating function of the entire structure. A particular advantage is that the building plate can rest on insulating sealing elements that surround the heating element laterally. Advantageously, the building panel with its plate-like support can be held in place at the corners by bolt-like elements. This secures the building panel and support to the extent that displacement between the support and the building panel is prevented. However, the heating element between the support and the building panel can expand and thus move, as it is mounted on a floating bearing. Due to this design, there is no mechanical force acting between the heating element and the building panel, nor between the support and the heating element. The invention is explained in more detail with reference to embodiments shown in the drawings. These show: Fig. 1 a schematic representation of a laser sintering device, Fig. 2 a cross-sectional view of the build chamber, Fig. 3 a perspective view of the build chamber in a first view, Fig. 4 a perspective view of the build chamber in a second view, Fig. 5 a perspective view of the build chamber in a third view, Fig. 6 a perspective view of the build chamber in a fourth view, Fig. 7 a heating plate in a first embodiment, and Fig. 8 a heating plate in a second embodiment. Fig. 1 shows a purely schematic representation of a laser sintering device 1 comprising a metering chamber 2 with a carrier 3 for storing the build material 4. The build chamber 5 adjoins the metering chamber 2. A heating device 8 is located in the build chamber 5 between the carrier 6 and the build plate 7. The object 9 is built on the build plate 7. A build chamber 5 is connected to an overflow chamber 10. A feed device 11 for transporting the build material 4 from the dosing chamber 2 to the build chamber 5 is arranged above the dosing chamber 2, the build chamber 5, and the overflow chamber 10. The dosing chamber 2, the build chamber 5, and the overflow chamber 10 are arranged in a gas-tight, inert gas-filled chamber, the process chamber 12. The irradiation device 13, which consists of a number of components, such as a laser and deflecting mirrors, is usually located outside the process chamber. The dosing chamber 2, the application device 11, the overflow chamber 10, the process chamber 12 and the irradiation device 13 as well as all other elements of the laser sintering device not shown can be designed arbitrarily; they have no influence on the design of the heating device 8, the carrier 6 or the build plate 7. The illustration of a laser sintering system 1 is purely exemplary; a laser melting system could also be used instead. Fig. 2 shows the assembly chamber 5 in a perspective cross-sectional view. The support 6 is arranged in the housing 14 of the assembly chamber 5. It consists of a trough-shaped support plate 15 and seals 16 on the outside. The support is driven by spindles 17. The number of spindles 17 is relatively arbitrary; one spindle 17 or several, in particular four spindles 17, can be used. The heating device 18 is at least partially inserted into the support plate 15. The heating device 18 comprises an insulating tray 19, a plate-like support 20, insulating sealing elements 21, and a heating element 22. The heating element 22 comprises a heating plate 23 with recesses 24 and heating rods 25, the heating rods 25 being insertable into the recesses 24. The heating plate 23 is floatingly mounted in the recess 26 of the plate-like support 20. The sandwich-like structure shown in Fig. 2 is shown in more detail in Figs. 3-6. Fig. 3 shows the assembly chamber 5 from a perspective view. The trough-shaped support plate 15, into which the heating device 18 can be inserted, is shown. Wedge-shaped projections 28 are located on the side walls 27, which allow the insulation tray 19 to be fixed in place. It should be noted that not the entire heating device 18, but only the heating element 22, is intended to be floating. Otherwise, displacement of the assembly plate 7 could occur, which would impair the quality of the object 9. Mounting brackets 29, in which the spindles 17 are mounted, are located on the base of the support plate 15. The support plate 15 is adjusted in height by four spindles 17, thus ensuring stable mounting and support of the support plate 15. This is particularly advantageous with regard to the additional weight of the heating device 18 placed on the support plate 15. Fig. 4 shows the assembly chamber 5 as in Fig. 3, with the difference that the insulation tray 19 is inserted into the tray-shaped support plate 15. Recesses 30 for receiving the brackets 29 are located at the bottom of the insulation tray 19. Furthermore, a wall-like support element 31 and several column-like support elements 32 are arranged in the center of the insulation tray. To provide further support for the plate-like support 20 that follows the insulation tray 19, the side walls 33 of the insulation tray 19 are indented or provided with U-shaped recesses. Instead of the recesses, further column-like or wall-like support elements 31 and 32 can also be provided. Fig. 5 shows the assembly chamber 5, in which the plate-like support 20 is placed on the insulation tray 19. The support 20 is also tray-like on its upper side and accordingly has the recess 26. The bottom side of the recess 26 is provided with a grooved structure 34. The heating rods 25 are mounted on these grooves. The heating rods 25 are guided through recesses 42 so that one end can be connected to a power source. The heating rods 25 are made of metal, so that they heat up when an electric current is applied. The recesses 42 are located at opposite ends of the base of the recess 26. This offers two advantages. Firstly, depending on the design of the recesses 42 for the heating elements 25, a denser packing of the heating elements 25 can be achieved, since the recesses 42 must be spaced a certain distance apart. If all the recesses 42 were in a row, the number of usable heating elements 25 would be limited. Secondly, only half the number of heating elements 25 on each side below the recess 26 need to be provided with power supply connections, which simplifies handling the connections. The carrier 20 has further recesses for inserting pressure springs 43. The pressure springs 43 can each be fitted with circular or square cover plates at their ends to better distribute the spring force. The recesses in the carrier 20 can either be continuous. In this case, the pressure springs 43 are supported, for example, by the U-shaped indentations of the insulation tray 19 or by column-like support elements 31. The pressure springs 43 press the heating element 22 against the base plate 7 to optimize or ensure contact between the heating element 22 and the base plate 7. The spring-supported contact of the heating rods 25 with the heating plate 23 by the plurality of four pressure springs in this embodiment ensures that the heating rods 25 remain in contact with the heating element 22 even when the heating element 22 is lifted. Fig. 6 shows the heating plate 23, which is placed on the plate-like support 20. The heating plate 23 has recesses 24 on its underside, into which the heating rods 25 are inserted. However, it is also possible that the heating rods 25 are cast into the heating plate 23, in which case the free ends of the heating rods 25 must be guided through the recesses 42 when the heating plate 23 is inserted. The heating element 22 is formed by the heating plate 23 and the heating rods 25. Finally, the building plate 7 is placed on the heating plate 23, thus completing the building chamber 5. Fig. 7 shows an embodiment of the heating plate 23 with which improved homogenization of heat output can be achieved. The heating plate 23 is designed to have at least two layers, one of which has a higher thermal conductivity than the other. In the simplest embodiment, the heating plate 23 comprises layers 35 and 36. The heating rods 25 are cast into or can be inserted into the recesses 24 of layer 35. Layer 35 has a higher thermal conductivity than layer 36. Preferably, the layer closest to the heating rods 25 has a higher conductivity than the layer that follows it. Layer 35 already homogenizes the heat output of the heating rods 25 to a certain degree. The subsequent layer 36, due to its lower thermal conductivity, provides further homogenization. Any number of additional layers 37 and 38 can follow layers 35 and 36, with layers 37 having a higher conductivity and layers 38 having a lower conductivity.In particular, layers 37 and 38 can have different conductivities than layers 35 and 36; any sequence of layers with different conductivities is conceivable. Fig. 8 shows a further embodiment of a heating plate 23. In this embodiment, the layer on the heating elements 25 consists of elements with different thermal conductivities. The elements 41 directly above the heating elements 25 have a lower thermal conductivity, and the elements 40 arranged laterally above them have a higher conductivity than the elements 41. By selecting suitable thermal conductivities for the elements 40 and 41 depending on the heating power of the heating elements 25, an almost homogeneous temperature distribution can be achieved on the upper surface of the layer 39. Layer 39 can be followed by any further layers 36 - 38 with thermal conductivities identical or different to those of elements 40 and 41. In addition, it is of course possible that layer 39 is followed by further layers, which in turn have sections with different thermal conductivities. In particular, it can also be provided that the subsequent layers are arranged in a checkerboard pattern, with areas of higher thermal conductivity surrounded by areas of lower thermal conductivity. REFERENCE MARK LIST 1 Laser sintering device 2 Dosing chamber 3 Carrier 4 Build material 5 Build chamber 6 Carrier 7 Heating device 8 Heating device 9 Object 10 Overflow chamber 11 Application device 12 Process chamber 13 Irradiation device 14 Housing 15 Tray-shaped carrier plate 16 Seal 17 Spindle 18 Heating device 19 Insulation tray 20 Plate-shaped carrier 21 Insulation sealing element 22 Heating element 23 Heating plate 24 Recess 25 Heating rod 26 Recess 27 Side wall 28 Projection 29 Holder 30 Recess 31 Wall-like support element 32 Column-like support element 33 Side wall 34 Grooved structure 35 Layer 36 Layer 37 Layer 38 Layer 39 Layer 40 Element 41 Element 42 Recess 43 Pressure spring

Claims

Device (1) for producing three-dimensional objects (9) by successively solidifying layers of a build-up material (4), in particular a powder form, which can be solidified by means of electromagnetic radiation or particle radiation, at the locations corresponding to the respective cross-section of the object (9), comprising a carrying device for carrying the object with a height-adjustable support (6) arranged in a build-up chamber (5), an application device (11) for applying the build-up material (4), and an irradiation device (13) for irradiating the applied layers of the build-up material (4) at the locations corresponding to the respective cross-section of the object (9), wherein a build-up plate (7) is arranged on the support of the carrying device, which can be heated by means of a heating device (18), characterized in that the heating device (18) comprises a plate-like support (20).the upper side of which is provided with a recess (24) facing the building plate (7), in which a heating element (22) is floatingly mounted, the heating element (22) being formed by a heating plate (23) and heating rods (25) and the heating element (22) being supported at its edges by flexible insulating sealing elements (21). Device according to claim 1, characterized in that the bottom of the recess (24) is provided with a grooved structure (34) on which the heating element (22) rests. Device according to one of claims 1 or 2, characterized in that heating rods (25) are integrated into the heating element (22) and are arranged in downwardly open recesses (42) of the heating device (18). Device according to one of claims 1 - 3, characterized in that the plate-like support (20) is an insulating element which is mounted on a trough-like insulating tray (19). Device according to claim 4, characterized in that the plate-like support (20) is held on the insulation tray (19) by a central support element (31). Device according to one of the preceding claims 4 or 5, characterized in that the carrying device comprises a support plate (15) and the support plate (15) of the carrying device is designed in a trough-like manner and accommodates the insulation trough (19). Device according to claim 6, characterized in that the plate-like insulating element (20) is supported at the upper edge of the support plate (15). Device according to one of the preceding claims 6 or 7, characterized in that the insulation tray (19) is arranged floating in the tray-like recess of the support plate (15). Device according to one of the preceding claims, characterized in that the building plate (7) rests on the insulating sealing elements (21) that laterally surround the heating element (22). Device according to one of the preceding claims, characterized in that the insulating sealing elements (21) are surrounded by a circumferential sealing element which runs around the edge of the plate-like support (20) in a circumferential groove on the top side. Device according to one of the preceding claims, characterized in that the building plate (7) with the plate-like support (20) is held in the corner area by bolt-like elements. Device according to one of the preceding claims 4 to 11, characterized in that the insulation tray (19) is provided in the area of ​​its side walls with u-shaped indentations and / or in its interior with column- or wall-like support elements (31, 32). Device according to claim 12, characterized in that the column- or wall-like support elements (31, 32) hold the center of the plate-like support (20) and the latter rests floating on the edge of the insulation tray (19). Device according to any one of the preceding claims 4 to 13, characterized in that the plate-like support (20) and the insulation tray (19) supporting it are made of insulation material consisting of a resin and glass fiber elements or comprising such materials. Device according to one of the preceding claims, characterized in that the carrier (20) has at least one recess for receiving at least one pressure spring (43), wherein the pressure spring (43) presses the heating element (22) from below against the base plate (7). Device according to claim 15, characterized in that the recess extends over the entire height of the support (20) and the pressure spring (43) is supported downwards on an underlying element, in particular an area of ​​the insulation tray (19). Device according to claim 15, characterized in that the recess is not continuous, so that the support (20) supports the pressure spring (43).

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