Method for cooling a three-dimensional object

Abstract

A method for cooling a three-dimensional object (2) produced by selectively solidifying a powdered starting material layer by layer is described, wherein the three-dimensional object (2) is arranged in a chamber (4) having at least one opening (5), wherein an overpressure P1 or a vacuum P2 is alternately generated in the chamber (4) by supplying a medium (6) to the chamber (4) or removing medium (6) from the chamber (4) through the at least one opening (5).

Description

[0001] The invention relates to a method for cooling a three-dimensional object produced by selectively solidifying a powdered starting material layer by layer. Furthermore, the invention also relates to a cooling device for cooling such a three-dimensional object, comprising a chamber in which the three-dimensional object is arranged.

[0002] Particularly in the production of prototypes or small series, processes have been used for several years in which the desired three-dimensional object is produced by selectively solidifying a powdered starting material layer by layer. In such processes, powdered materials are processed, with the desired structures of the three-dimensional object being created layer by layer through selective melting and solidification. One such process is selective laser sintering (SLS). In this process, plastic powders are selectively exposed to a laser beam in a chamber, causing the powder particles struck by the laser beam to fuse before solidifying into a solid mass. By repeatedly irradiating newly applied layers of the plastic powder, three-dimensional objects can be produced simply and quickly using this method.

[0003] Such a method for producing a three-dimensional object using selective laser sintering is known, for example, from DE 195 14 740 C1.

[0004] After the three-dimensional object has been manufactured, both the object and the unsolidified base material in which it is embedded must be cooled. Cooling can be achieved by at least partially passing a fluid through the unsolidified base material.

[0005] DE 10 2017 211 381 A1 discloses a corresponding method and a cooling device in which the fluid medium flows through the unsolidified starting material, also referred to as a powder cake, preferably in a direction opposite to gravity. For this purpose, the chamber of the cooling device, in which the three-dimensional object is arranged in the powder cake, has a plate permeable to the fluid medium at its bottom and an outlet in its lid opposite the bottom, through which the fluid medium can exit the chamber. A problem with this method for cooling the three-dimensional object is that the object located in the powder cake cools unevenly.

[0006] The present invention is therefore based on the objective of providing a method and a cooling device for cooling a three-dimensional object that has been produced by selectively solidifying a powdered starting material layer by layer, with which improved cooling of the three-dimensional object is made possible.

[0007] This problem is solved in the method described above with the features of claim 1. In the method according to the invention, the three-dimensional object is arranged in a chamber having at least one opening, wherein an overpressure P1 or a vacuum P2 is alternately generated in the chamber by supplying a medium to the chamber or removing medium from the chamber through the at least one opening. The method according to the invention is not limited to a sequence in which an overpressure or a vacuum is generated in the chamber, but encompasses both possibilities. Thus, in the method according to the invention, an overpressure or a vacuum can be generated in the chamber first.

[0008] The chamber is designed to be so pressure-tight that the desired maximum overpressure or underpressure can be generated within it without damage. If overpressure is generated in the chamber, a cooling effect can occur because the chamber is flooded with a medium that is cooler than the three-dimensional object. If underpressure is generated in the chamber, a cooling effect can occur due to the enthalpy of vaporization.

[0009] In the method according to the invention, the chamber is not continuously permeated by a medium, but rather is subjected to repeated, discontinuous pressure changes, alternating between overpressure and underpressure. The resulting pressure differences within the chamber cause the medium to distribute itself largely homogeneously and not simply along the path of least resistance. This ensures that even hard-to-reach, concealed areas of the three-dimensional object are exposed to the medium, leading to more homogeneous cooling of the object and thus preventing unwanted stresses within it.

[0010] In the inventive method, the three-dimensional object is generally located in the unsolidified starting material, the so-called powder cake, during cooling. The medium then flows through the powder cake, thereby cooling both the powder cake and the object.

[0011] The medium supplied through the chamber's at least one opening can be, in particular, a liquid or gaseous medium. This medium could be, for example, air, nitrogen, water, glycol, ethanol, a hydrocarbon compound, or oils. Alternatively, it could be a solid medium, such as small particles consisting of water ice crystals or dry ice crystals, which can accelerate the cooling process.

[0012] The temperature of the medium supplied to the chamber is generally chosen to be lower than the temperature of the relatively hot three-dimensional object after selective solidification. However, it is also conceivable that the temperature of the medium initially matches or even exceeds the temperature of the object in order to first homogenize the temperature within the powder cake.

[0013] It has been previously explained that, unlike in the prior art, the chamber is not continuously permeated by a medium, but is alternately pressurized with an overpressure P1 or a negative pressure P2. A pause can be provided between pressurizing the chamber and subsequently pressurizing it with a negative pressure, or between pressurizing it with a negative pressure and subsequently pressurizing it with an overpressure, during which the pressure in the chamber is held constant for a period of time. The generation of an overpressure and the generation of a negative pressure in the chamber therefore do not have to follow each other immediately. The duration during which the chamber is pressurized with an overpressure can also differ from the duration during which it is pressurized with a negative pressure.

[0014] This allows a pressure to be generated in the can that differs from the pressure that was in the chamber at the beginning of the process.

[0015] According to an advantageous embodiment of the method, an overpressure or a vacuum is alternately generated in the chamber in several successive process steps, so that the method comprises several process cycles. A process cycle includes at least two process steps: flooding the chamber with a medium and vacuuming the chamber, i.e., supplying the medium to the chamber or removing the medium from the chamber. A third process step can be provided between these two process steps, in which no medium is supplied to or removed from the chamber. In this third process step, the pressure in the chamber can be kept constant. The third process step can also be considered a pause between the other two process steps.

[0016] If the process comprises multiple process cycles, the duration for which a medium is supplied to the chamber or the duration for which the medium is discharged from the chamber can be varied in the individual process steps. If the duration for which a medium is supplied to the chamber differs from the duration for which the medium is discharged from the chamber, the pressure in the chamber can be increased or decreased over several process cycles.

[0017] If the process has multiple cycles, the temperature and / or pressure of the medium supplied to the chamber can be varied in each step. This allows the rate at which the three-dimensional object is cooled to be controlled. For example, the temperature and / or pressure of the medium can be set at the beginning of the process to initially cause rapid cooling. After a certain period, the temperature and / or pressure of the medium can then be changed to slow down the further cooling of the object.

[0018] If the procedure has several process cycles, different media can be supplied to the chamber in the individual process steps.

[0019] According to a further embodiment of the invention, depending on the choice of medium and its temperature, an overpressure or a vacuum can be alternately generated in the chamber, such that the medium in the chamber changes its state of matter, for example from liquid to gaseous. This can be achieved, for example, by reducing the pressure in the chamber to such an extent that a liquid medium evaporates. This leads to a significant cooling of the medium and thus also to a significant cooling of the object or the powder cake surrounding the object.

[0020] The aforementioned problem is solved in the cooling device described at the outset by the features of claim 10. In the cooling device, the chamber in which the three-dimensional object is arranged has at least one opening through which an overpressure P1 or a negative pressure P2 is alternately generated in the chamber according to the method described above. The three-dimensional object is generally surrounded in the chamber by the unsolidified starting material, the powder cake.

[0021] It has been previously stated that the chamber has at least one opening. According to one embodiment of the cooling device according to the invention, the chamber has exactly one opening, which can be used alternately as an inlet or outlet. A medium is thus alternately supplied to and discharged from the chamber through this single opening. In this embodiment of the cooling device, the chamber is particularly easy to manufacture, since only the single opening needs to be sealed to ensure the required pressure tightness.

[0022] Alternatively, the chamber can also have multiple openings, which are likewise used alternately as inlet or outlet openings. Thus, a medium is alternately supplied to or discharged from the chamber via these openings.

[0023] According to another embodiment of the cooling device according to the invention, the chamber has at least one inlet opening and at least one outlet opening, wherein medium can be alternately supplied to the chamber through the at least one inlet opening or discharged from the chamber through the at least one outlet opening. The chamber can also have several inlet openings and several outlet openings. The inlet openings and the outlet openings are arranged on the chamber in such a way as to achieve the most homogeneous flow possible through the chamber or the powder cake arranged in the chamber and the object surrounded by the powder cake. Preferably, the inlet openings and the outlet openings are not arranged opposite each other in pairs.

[0024] According to a further preferred embodiment of the cooling device, the at least one opening can be closed so that the pressure in the chamber can be kept constant for a time t.

[0025] In detail, there are several ways to design and further develop the inventive method or cooling device. Reference is made to the dependent claims as well as to the following description of preferred embodiments in conjunction with the drawing. The drawing shows Fig. 1 a simplified, schematic representation of a cooling device according to the prior art, Fig. 2 a simplified, schematic representation of a first embodiment of a cooling device according to the invention, Fig. 3 the cooling device according to Fig. 2 with a schematic representation of the process step of applying an overpressure P1, Fig. 4 the cooling device according to Fig. 2 with a schematic representation of the process step of applying a negative pressure P2, Fig. 5 a simplified, schematic representation of a second embodiment of a cooling device according to the invention, Fig. 6 the cooling device according to Fig. 5 with a schematic representation of the process step of applying an overpressure P1, Fig. 7 the cooling device according to Fig. 5 with a schematic representation of the process step of applying a negative pressure P2

[0026] Fig. Figure 1 shows a simplified, schematic representation of a cooling device 10 according to the prior art. The cooling device 10 serves to cool a three-dimensional object 2, which is produced by selectively solidifying a powdered starting material layer by layer and is surrounded by unsolidified starting material 3, the so-called powder cake. The known cooling device 10 has a chamber 40 with two openings 50, the lower of which serves as an inlet and the upper as an outlet for a fluid medium 60 that flows through the unsolidified starting material 3 in one direction, essentially opposite to gravity. Because the fluid medium 60, which has a temperature T1 upon entering the chamber 40 that is lower than the temperature of the three-dimensional object 2, flows through the powder cake 3, both the powder cake 3 and the three-dimensional object 2 are cooled. The fluid medium 60, or rather the powder cake 3, cools the powder cake 3.whose flow through chamber 40 is in . Fig. 1 is represented by arrows. This shows that the fluid medium 60 does not flow homogeneously through the chamber 40 or the powder cake 3, so that the three-dimensional object 2 enclosed in the powder cake is not cooled uniformly everywhere.

[0027] The Fig. Figures 2 to 4 show a first embodiment of a cooling device 1 according to the invention for cooling a three-dimensional object 2, which has been produced by selectively solidifying a powdered starting material layer by layer, for example by selective laser sintering. Here too, the three-dimensional object 2, surrounded by unsolidified starting material 3, is located in a chamber 4 of the cooling device 1. In the illustrated embodiment, the chamber 4 has only one opening 5, which is used alternately as an inlet opening 51 or as an outlet opening 52, as shown in the figures. Fig. 3 and Fig. 4 is evident.

[0028] At the beginning of the process, the hot, three-dimensional object 2, surrounded by the powder cake 3, is located in chamber 4, in which an atmospheric pressure P0 prevails ( Fig. 2) No medium 6 is supplied to or discharged from chamber 4 through opening 5. According to the inventive method, an overpressure P1 is then alternately applied in chamber 4 ( Fig. 3) or a negative pressure P2 ( Fig. 4) generated.

[0029] To create an overpressure P1 in chamber 4, chamber 4 is flooded with a medium 6 through opening 5, as described in Fig. Figure 3 shows the flowing medium 6. The opening 5 of chamber 4 acts as the inlet opening 51. Since chamber 4 has no further opening through which the medium 6 can exit during the supply of the medium 6, the pressure in chamber 4 increases. Furthermore, flooding chamber 4 with the medium 6 ensures that the medium 6 is distributed more homogeneously within chamber 4 and the powder cake 3, leading to more uniform cooling of the three-dimensional object 2 within the powder cake 3.

[0030] In a second procedural step, which takes place in Fig. As indicated in Figure 4, a negative pressure P2 is created in chamber 4 by drawing medium 6 out of chamber 4 through opening 5. Opening 5 serves as the outlet opening 52 for the medium 6. This also results in a homogeneous exchange of the medium 6 in chamber 4, ensuring that even areas 21 of the three-dimensional object 2, which are difficult to access, are surrounded by the medium 6, thus promoting the uniform cooling of the three-dimensional object 2.

[0031] Fig. Figure 5 shows a second embodiment of a cooling device 1 according to the invention for cooling a three-dimensional object 2. In contrast to the cooling device 1 shown in Fig. As shown in Figure 2, in this embodiment the chamber 4 has several openings 5 ​​which alternately serve as inlet openings 51 ( Fig. 6) or as exit openings 52 ( Fig. 7) can be used. By arranging the openings 5 ​​at different positions in the chamber 4, the flow of the medium 6 in the chamber 4, and thus also the flow of the medium 6 around the three-dimensional object 2, can be influenced. The alternating generation of overpressure or underpressure in the chamber 4 is carried out essentially as described previously in connection with the first embodiment and the Fig. 3 and Fig. 4 has been described.

[0032] To generate an overpressure P1 in chamber 4, chamber 4 is flooded with a medium 6 through the openings 5, as described in Fig. The flowing medium 6 is shown by the arrows in Figure 6. The openings 5 ​​of chamber 4 all function as inlet openings 51. Because chamber 4 has several openings 5, in this case four, and because medium 6 cannot escape from chamber 4 through any of the openings 5, not only does the pressure in chamber 4 increase, but the medium 6 also becomes more homogeneous within chamber 4 and in the powder cake 3, leading to a uniform cooling of the three-dimensional object 2 within the powder cake 3.

[0033] In the second procedural step, which takes place in Fig.As indicated in Figure 7, medium 6 is discharged from chamber 4 through the openings 5, with all openings 5 ​​serving as outlet openings 52 for the medium 6, thereby creating a negative pressure P2 in chamber 4. This also results in a homogeneous exchange of medium 6 within chamber 4, ensuring that even areas 21 of the three-dimensional object 2, which are more difficult to access, are surrounded by the medium 6. Reference sign 1. Cooling device 2. 3-D object 21. hard-to-reach areas 3. Powder cake 4th Chamber 5. Opening 51. Opening 52. Exit opening 6. Medium 10. Cooling device 40th Chamber 50th opening 60. fluid medium T1 Inlet temperature T2 Outlet temperature P0 output pressure P1 Overpressure P2 negative pressure QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 195 14 740 C1

[0003] DE 10 2017 211 381 A1

[0005]

Claims

[1] Method for cooling a three-dimensional object (2) produced by selectively solidifying a powdered starting material layer by layer, wherein the three-dimensional object (2) is arranged in a chamber (4) having at least one opening (5), wherein an overpressure P1 or a vacuum P2 is alternately generated in the chamber (4) by supplying a medium (6) to the chamber (4) or removing medium (6) from the chamber (4) through the at least one opening (5). [2] Method according to claim 1, characterized by , that between generating an overpressure P1 and generating an underpressure P2 in chamber (5) the pressure in chamber (4) is kept constant for a time t. [3] Method according to claim 1 or 2, characterized by , that in several successive process steps in the chamber (4) an overpressure P1 or a negative pressure P2 is alternately generated. [4] Method according to claim 3, characterized by , that in individual process steps the duration during which a medium (6) is supplied to the chamber (4) or the duration during which the medium (6) is discharged from the chamber (4) varies. [5] Method according to claim 3 or 4, characterized by , that in individual process steps the temperature and / or pressure of the medium (6) supplied to the chamber (4) varies. [6] Method according to any one of claims 3 to 5, characterized by , that different media (6) are supplied to the chamber (4) in the individual procedural steps. [7] Method according to any one of claims 1 to 6, characterized by , that in the chamber (4) an overpressure P1 or a underpressure P2 is alternately generated, such that the medium (6) in the chamber (4) changes its state of matter. [8] Method according to any one of claims 1 to 7, characterized by, that the three-dimensional object (2) is surrounded by unsolidified starting material (3) during cooling. [9] Method according to any one of claims 1 to 8, wherein the chamber (4) has exactly one opening (5), characterized by , that the opening (5) is used alternately as an inlet opening (51) or as an outlet opening (52). [10] Cooling device (1) for cooling a three-dimensional object (2) produced by selectively solidifying a powdered starting material layer by layer, comprising a chamber (4) in which the three-dimensional object (2) is arranged, wherein the chamber (4) has at least one opening (5) in which an overpressure P1 or a vacuum P2 is alternately generated according to the method of any one of claims 1 to 9. [11] Cooling device (1) according to claim 10, characterized by, that the three-dimensional object (2) together with unsolidified starting material (3) surrounding the three-dimensional object (2) is arranged in the chamber (4). [12] Cooling device (1) according to claim 10 or 11, characterized by that the chamber (4) has exactly one opening (5) which can be used alternately as an inlet opening (51) or as an outlet opening (52). [13] Cooling device (1) according to claim 10 or 11, characterized by , that the chamber (4) has several openings (5) which can each be used alternately as an inlet opening (51) or as an outlet opening (52). [14] Cooling device (1) according to claim 10 or 11, characterized by, that the chamber (4) has at least one inlet opening (51) and at least one outlet opening (52), wherein medium (6) can be alternately supplied to the chamber (4) through the at least one inlet opening (51) or medium (6) can be discharged from the chamber (4) through the at least one outlet opening (52). [15] Cooling device (1) according to any one of claims 10 to 14, characterized by , that at least one opening (5) can be closed so that the pressure in the chamber (4) remains constant for a time t.

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