Heating device with infrared radiator

Abstract

To provide a heating device equipped with an IR radiator for heating a powder during manufacturing a 3D molded article in a constituent space, which ensures an optimized heat transfer to a sintered or molten powder with a particularly homogeneous temperature distribution.SOLUTION: The invention relates to a heating device for heating a powder P during the production of a 3D molded part 5, comprising an IR radiating element 3; 3' and a housing 12. A construction space 1 is provided in the housing 12. The construction space 1 is bounded at the bottom by a construction platform 4 for receiving the molded part 5. The construction platform 4 rests on a carrier plate 9. In the heating device, a separating wall 2 made of a material that is transparent for IR radiation is arranged between the construction space 1 and the infrared radiating element 3;3'.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heating device for heating powder during the production of 3D molded parts, comprising an IR radiator and a housing, in which a construction space is provided, the construction space being defined below by a structural platform for placing the molded part, the structural platform resting on a support plate.

[0002] Furthermore, the present invention relates to a method for producing a 3D molded article using a heating device.

[0003] Three-dimensional (3D) mouldings are usually produced using the so-called selective laser sintering or laser melting technique in the layer construction and hardening of loose powders, or in the case of plastic powders, the abbreviated s elective l aser s The name SLS is used for intering, or in the case of metal powders, s elective l aser m The term SLM is also used for melting. When heating the powder, whether it is plastic or metal powder, a homogeneous temperature distribution is required to avoid thermal stresses (cracks, distortion) in the finished part.

[0004] Infrared radiators (abbreviated as IR radiators) within the meaning of the present invention are radiation units comprising several radiator tubes, so-called arc tubes, usually made of quartz glass, inside which are arranged heating filaments (also called glow wires), which determine the radiation spectrum of the IR radiator.

[0005] IR-A radiation has a wavelength in the range of 0.78 μm to 1.4 μm, IR-B radiation has a wavelength in the range of 1.4 μm to 3.0 μm, and IR-C radiation has a wavelength in the range of 3 μm to 1000 μm. [Background technology]

[0006] German Patent Application Publication No. 102015006533 discloses the production of 3D molded parts from plastic sintered powder. To heat the construction platform, an electrically resistively heated silicone-based planar heating sheet is used, which rarely reaches temperatures above 200°C. While this heating power is sufficient to heat the plastic sintered powder when producing 3D molded parts, it is insufficient when producing metal 3D molded parts, which require significantly higher overall process temperatures. Additionally, radiators mounted on the sides of the construction space are preferred.

[0007] Instead of a silicone-based heating sheet, German Patent Application Publication No. 102015006533 proposes temperature regulation of the construction platform or the sintered powder on the construction platform by means of a heating coil through which tempering oil flows, the heating coil being arranged below the assembly plate and on the side of the construction platform. The temperatures that can be achieved by the heating coil are not much higher than 200°C, and heat transfer to the sintered powder is inefficient (slow) due to this design. For the tempering oil, a storage tank and possibly a pump must also be provided to pump the tempering oil through the heating coil. These additional devices make the heating system expensive overall and do not result in increased efficiency or an expanded temperature range in terms of rapid heat transfer.

[0008] German Patent No. 102012012344 discloses a method and an apparatus for producing workpieces by radiative melting of powdered material. To reduce the temperature gradients conditioned by the process, the powdered construction material is preheated by heating elements, instead of by platform heating, which are arranged on or in the side walls of the storage chamber and / or the process chamber.

[0009] From DE 10 2015 211 538 A1, a construction cylinder assembly for a machine for the layer-by-layer production of three-dimensional objects by laser sintering or laser melting of powdered material is known, in which a layer of powdered material is heated by a heating device with an infrared heating coil. Summary of the Invention [Problem to be solved by the invention]

[0010] The problem underlying the present invention is to provide a heating device with IR radiators for heating powder during the production of 3D molded parts in a construction space, which ensures optimized heat transfer to the sintered or molten powder with a particularly homogeneous temperature distribution. The heating device should also function as a high-temperature heating device and allow for simple retrofitting into existing construction spaces, so that the heating device can be used in a corresponding method for producing 3D molded parts. [Means for solving the problem]

[0011] According to the invention, this object is achieved in that a separating wall made of a material that is transparent to IR radiation is arranged between the construction space and the infrared radiator.

[0012] The construction spaces are separated from the infrared radiators by a separating wall made of a material transparent to IR radiation.

[0013] At least one IR emitter is mounted on the outside of the separation wall and emits IR radiation in the direction of the powder or 3D molded part on a construction platform in the construction space, which is located directly above a height-adjustable support plate or is indirectly connected to the support plate via a so-called assembly plate.

[0014] The heating device additionally comprises a separating wall, which surrounds the construction space at its sides as a surrounding wall that is transparent to IR radiation (side wall).

[0015] When manufacturing 3D molded parts using the SML method, a laser scans powder piled on a building platform and melts it locally, layer by layer. Especially with metallic materials with high melting points, a high temperature gradient can occur between the melted area and the surrounding powder. During the uneven heating and cooling of the workpiece, stress cracks often occur during the construction process.

[0016] The heating device according to the present invention averages out or completely avoids the temperature difference between the already partially hardened molded part and the new layer of powder when heating the powder before or during the laser treatment for local melting or before applying a new powder layer. Rather, the powder and the 3D molded part are heated particularly uniformly and without temperature gradients, which makes it possible to eliminate the need for thermal post-treatment of the molded part, which is sometimes performed after the molded part is completed to relieve thermal stress. This makes the manufacturing method relatively fast and economical.

[0017] A further advantage of the heating device is that the separating wall can be easily replaced in the event of repairs, and that the heating device according to the invention can also be retrofitted into existing construction spaces.

[0018] Typically, multiple IR radiators are arranged on the separating walls of the construction space, and preferably the IR radiators are part of a radiator assembly that includes multiple IR radiators, and the IR radiators of the radiator assembly can be individually electrically controlled. Multiple IR radiators can be provided, so that individual radiators can be deactivated or activated to obtain a desired radiation spectrum and simultaneously a preset total radiation output.

[0019] It has been found that at least one infrared radiator has a radiation spectrum in the IR-A range that is adapted to the absorption characteristics of the powder, i.e., an IR-A radiator. A suitable short-wave radiation spectrum in the IR-A range has a peak wavelength of 0.9 μm to 1.3 μm. IR radiation in the IR-A range has a higher radiation energy than IR-B radiation. Essentially, the higher the radiation energy, the shorter the radiation process can be selected. Therefore, the IR-A radiation component contributes to an efficient method using the heating device.

[0020] It has proven advantageous if the IR-transparent separating wall is made of quartz glass or glass ceramics. Quartz glass is highly transparent to IR radiation, electrically insulating even at relatively high temperatures, has good corrosion resistance, heat resistance, and temperature change resistance, and can be used in high purity. Therefore, quartz glass is used particularly in high-temperature and heating processes. In addition to quartz glass, glass ceramics can also be used as IR-transparent materials for forming the side walls.

[0021] It has proven particularly advantageous if the construction space is radially surrounded by a preferably cylindrical sleeve-shaped side wall, which is at least partially, in particular over the entire circumference, configured as a separation wall. The separation wall may be configured as a side wall extending to surround the construction space. The separation wall may have the shape of a hollow cylinder with a circular or rectangular base and may be adapted to the geometric shape of the construction platform surface. This configuration optimizes heat transfer to the powder bed or molded part.

[0022] In a preferred configuration of the heating device, the IR emitter is provided with at least one reflector on the side opposite the molded part, which directs the infrared radiation towards the powder on the build platform and / or the 3D molded part, thereby increasing the efficiency of the heating device.

[0023] The reflector can be configured as a primary reflector, with the IR radiator having a covering tube which is covered on the side facing away from the molded part by a primary reflector in the form of a reflector layer applied to the covering tube. Preferably, the reflective inner surface of the housing wall of the housing facing the molded part additionally forms a secondary reflector or possibly also a tertiary reflector.

[0024] In order to limit the heat generation in the region of the housing, the housing wall may be formed with cooling and / or thermal insulation means which insulate the IR radiator from the external environment and may be provided as a thermal insulation layer and / or as a cooling plate.

[0025] In a preferred embodiment of the heating device, the IR radiator and the side wall are arranged in a frame of the heating unit, which can be inserted into the housing. The frame has an outer frame wall with a reflective inner surface facing the molded part, which inner surface forms a secondary reflector. The frame preferably encloses a closed interior chamber in which the IR radiator is arranged. This configuration of the heating device is particularly advantageous in relation to retrofitting existing equipment for producing 3D molded parts.

[0026] Preferably, the construction space has at least one measuring cell for detecting the temperature of the powder and / or the molded part. The temperature in the construction space can be continuously measured. For this purpose, a pyrometer, a thermal imaging camera, or a thermal sensor, such as a thermocouple or a resistance sensor, can be used as a measuring means.

[0027] In another preferred configuration of the heating device, the separating wall is double-walled to form at least one intermediate chamber, and at least one IR radiator is arranged in the intermediate chamber.

[0028] The IR radiator in the side wall of the double wall or in the middle chamber of the separating wall includes at least one heating filament with an emission spectrum in the IR-B range. The individual heating filaments can be mechanically and electrically isolated from one another by webs in the side wall of the double wall of the construction space.

[0029] IR radiation in the IR-B range has a lower radiation energy than IR-A radiation. Given the appropriate duration of the radiation process and in many cases where the powder or molding has a high absorption of IR-B radiation, good radiation results can also be achieved with IR-B radiation. Furthermore, the separation of the individual heating filaments by the webs in the double-walled side walls or separating walls allows for targeted control, whereby the individual heating filaments can be deactivated or activated, thereby simultaneously achieving the desired total radiation output in the appropriate radiation spectrum.

[0030] The heating device is preferably used in a method for producing a 3D molded part, in which the 3D molded part is preferably produced by sintering a metal powder at least partially in a construction space using a laser, the powder and / or the 3D molded part being heated during sintering by at least one IR radiator, and a separating wall made of a material transparent to IR radiation is arranged between the construction space and the infrared radiator.

[0031] The present invention will now be described in detail with reference to the drawings and examples. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a schematic side view showing an embodiment of a heating device according to the present invention. [Figure 2] 10 is a schematic view of another embodiment of the heating device with a partial view showing the construction space. DETAILED DESCRIPTION OF THE INVENTION

[0033] FIG. 1 shows a schematic representation of one embodiment of the heating device. In this embodiment, a construction space 1 has a circular cylindrical side wall or separating wall 2 made of quartz glass. A number of IR emitters 3, 3′ are attached to the outside of the separating wall 2 and emit IR radiation toward a powder P or a 3D molded part 5 lying on a construction platform 4 in the construction space 1. A process chamber 6 is located above the construction space 1 and houses a unit (not shown here) for controlling the construction process of the molded part 5. A diagrammatically shown laser unit 7 is located at the top end of the process chamber 6 and is suitable for selectively sintering and / or melting the powder P by means of a high-energy laser beam emitted from the laser unit 7 to produce the 3D molded part 5.

[0034] The powder P is typically a metal powder, although plastic powders can also be used. The powder P rests on a construction platform 4, which is in turn placed on a height-adjustable support plate 9, indicated by a double arrow 8, which is provided with a plunger 9.1.

[0035] The structural platform 4 is mounted on a mounting plate 10 which allows for easy replacement of the structural platform 4 .

[0036] The infrared emitters 3; 3' emit radiation in the IR-A range and are equipped with a reflector 11 on the side of the infrared emitters 3; 3' facing away from the molded part 5. The reflector 11 directs the infrared radiation toward the powder P and / or the 3D molded part on the build platform 4. The reflector 11 is configured as a so-called primary reflector in the form of a reflector layer applied to the jacket (not shown) of the IR emitter 3; 3'. The reflector layer is, for example, a gold layer or a layer made of white, opaque quartz glass. Alternatively, the primary reflector may be provided as a separate sheet metal part that contacts the jacket of the IR emitter.

[0037] Furthermore, a reflective inner surface 12.2 of the housing wall 12.1 of the housing 12 facing the molding 5 additionally forms a secondary reflector. The reflective inner surface 12.2 is formed by a gold or aluminum layer.

[0038] Correspondingly, in the case of a truly cylindrical construction space 1 with a truly circular construction platform 4 and a truly cylindrical side wall 2 surrounding the construction space, the IR radiator 3; 3' has two sections of a ring radiator (also called an omega radiator) arranged to surround the outside of the cylindrical side wall 2, as can be seen in Figure 1.

[0039] If the construction space 1 has a construction platform 4 with a rectangular base, the IR radiators 3; 3' can be understood as individual linear radiators which are attached to the outside of the separation wall 2 in multiple planes, the separation wall 2 having the shape of a rectangular parallelepiped.

[0040] In order to limit the heat generation in the region of the housing 12, the housing wall 12.1 is further provided with a cooling plate and / or a heat insulating layer, not shown here.

[0041] FIG. 2 shows a variant of the heating device. In this variant, the construction space 1 with the separating wall 2 is shown only diagrammatically. The separating wall 2 is formed as a double-walled side wall 22 made of quartz glass with an intermediate chamber 23. Kanthal wire heating filaments 30 are arranged in the intermediate chamber 23 of the double-walled side wall 22. These heating filaments 30 emit IR radiation in the IR-B range. The double-walled side wall 22 functions as a sheath for the heating filaments 30. The heating filaments can be formed as individual long filaments spirally arranged from bottom to top in the intermediate chamber 23 of the double-walled side wall 22, or they can be provided in the form of several individually electrically controllable rings. Separating the rings or spirals are provided webs 40 made of a heat-resistant, electrically insulating material. These webs 40 consist of quartz glass, glass ceramics, or ceramics, such as calcium silicate ceramics under the trade name Calcast®. A gold reflector layer 24 is applied to the outside of the double-walled side wall 22, which reflects the IR-B radiation of the heating filament 30 towards the powder P and the molded article 5, thereby allowing the heating device to operate efficiently.

Claims

1. A heating device for heating powder (P) during the production of a 3D moulded part (5), comprising an infrared radiator (3; 3'; 30) and a housing (12), in which a construction space (1) is provided, the construction space (1) being defined below by a construction platform (4) for placing the 3D moulded part (5), the construction platform (4) resting on a support plate (9), a separating wall (2) made of a material transparent to IR radiation is arranged between the construction space (1) and the infrared radiator (3; 3'; 30), a plurality of infrared radiators (3; 3'; 30) are arranged on the sides of the construction space (1), The separating wall (2) is arranged on the side of the construction space (1), each of the infrared emitters (3; 3'; 30) has a sheath tube which, on the side opposite the 3D moulded part (5), is covered by a primary reflector in the form of a reflector layer applied to the sheath tube; heating device.

2. 2. The heating device according to claim 1, wherein the material of the separating wall (2) that is transparent to IR radiation consists of quartz glass or glass ceramics.

3. 3. The heating device according to claim 1, wherein the construction space (1) is radially surrounded by a cylindrical sleeve-shaped side wall, which is at least partially formed as a separating wall (2).

4. 4. The heating device according to claim 1, wherein a reflective inner surface (12.2) of the housing wall (12.1) of the housing (12) facing the 3D molded part (5) forms a secondary reflector.

5. 5. Heating device according to claim 4, characterized in that the housing wall (12.1) is formed with cooling means and / or thermal insulation means.

6. 6. The heating device according to claim 1, wherein the construction space (1) comprises at least one measuring cell for detecting the temperature of the powder and / or the 3D molded part.

7. 7. The heating device according to claim 1, wherein the separating wall (2) is double-walled to form at least one intermediate chamber (23), and the at least one infrared radiator (3; 3'; 30) is arranged in the intermediate chamber (23).

8. 8. The heating device according to claim 7, wherein the double-walled separating wall (2) comprises a double-walled side wall (22) of the construction space (1), and the individual heating filaments are mechanically and electrically separated from one another by webs (40) within the double-walled side wall (22).

9. 9. Heating device according to any one of claims 1 to 8, wherein the at least one infrared radiator (3; 3'; 30) comprises an IR-B radiator with at least one heating filament having a radiation spectrum in the IR-B range.

10. 10. Heating device according to any one of claims 1 to 9, characterized in that the heating device comprises a radiator assembly comprising a plurality of infrared radiators (3; 3'; 30), the infrared radiators of the radiator assembly being individually electrically controllable.

11. 8. Heating device according to claim 1, wherein at least one of the infrared radiators (3; 3'; 30) comprises an IR-A radiator having a radiation spectrum in the IR-A range adapted to the absorption properties of the powder (P).

12. 12. Heating device according to any one of claims 3 to 11, characterized in that the at least one infrared radiator (3; 3'; 30) and the side wall are arranged in a frame of a heating unit which is insertable into the housing (12).

13. 13. The heating device according to claim 12, wherein the frame has an outer frame wall with a reflective inner surface (12.2) facing the 3D moulded part (5), the inner surface (12.2) forming a secondary reflector.

14. 14. Heating device according to claim 12 or 13, wherein the frame surrounds a closed interior chamber in which the infrared radiator is located.

15. 15. Heating device according to any one of the preceding claims, characterized in that the infrared radiators (3; 3'; 30) are arranged at different levels.

16. 16. A method for producing a 3D moulded part using a heating device according to any one of claims 1 to 15.

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