TRANSPORTING POWDERED BUILDING MATERIAL FOR THE MANUFACTURE OF THREE-DIMENSIONAL OBJECTS

Description

[0001] The invention generally relates to the field of manufacturing three-dimensional objects by additive manufacturing. In particular, the invention relates to methods and devices for transporting powdered build material used in the manufacture of three-dimensional objects.

[0002] Additive manufacturing processes are well known in the art. Examples include laser melting, mask sintering, drop-on-powder / drop-on-bed, stereolithography, and the like. Objects are typically constructed by selectively solidifying a build-up material applied layer by layer. Systems that perform this type of layered construction process are also known as rapid prototyping systems. These layered construction processes are used to produce layered components from solidifiable materials such as resin, plastic, metal, or ceramic, and are used, for example, to manufacture technical prototypes. Using an additive manufacturing method, three-dimensional objects can be created directly from CAD data.

[0003] In such a layered construction process, the objects are built up layer by layer, i.e. layers of the building material are applied successively on top of one another. Before the next layers are applied, the areas in the respective layers corresponding to the object to be manufactured are selectively solidified. Solidification is achieved, for example, by locally heating the usually powdered building material using a radiation source. By specifically applying radiation to the desired areas in a suitable manner, a precisely defined object structure of any type can be created. The layer thickness is also adjustable. Such a process is particularly suitable for producing three-dimensional objects by creating several thin, individually designed layers one after the other.

[0004] During the production of the objects, the powdered build material used must be transported at least once, but several times in the rack, from one location to another, spatially separate location, or in other words, from one room to another. This applies both to transport within the layered build system itself and to transport to systems for treating the build material, i.e., for use in ancillary processes such as sieving, mixing, cleaning, drying, etc. Particularly critical is the transport of the build material for the purpose of supplying the powder to the layered build system, especially during the filling and emptying of the process chamber in which the layer-by-layer construction of the three-dimensional object takes place.

[0005] The process chamber and other rooms (storage vessels, supply and discharge lines, etc.) often have different atmospheres. In other words, the gas composition, temperature, humidity, pressure, etc., can differ in the individual rooms. For example, the first room may contain normal air, while the second room contains dried air or a protective gas. The rooms may contain comparatively inexpensive gases, such as nitrogen, or expensive gases, such as argon. In these cases, a change of room always involves a change of atmosphere. To prevent mixing of the individual atmospheres, for example to avoid atmospheric contamination or the loss of an expensive gas, gas separation between the rooms is required.The goal is to achieve 100% gas separation, i.e., to prevent mixing of the atmospheres as completely as possible. In practice, it is often sufficient to ensure that no gas exchange relevant to the operation of the system or that no gas exchange exceeding a tolerable level occurs between the rooms.

[0006] In order to transport material from room to room while maintaining gas separation between the rooms, various lock and / or sealing designs are known from the state of the art, such as rotary valves, pendulum flap locks, and valves of various designs. Techniques in which a powder material is transported in this or similar ways, sometimes while maintaining gas separation between the rooms, are described in GB 2 520 161 A, DE 199 50 101 C1, and EP 1 514 622 A1. All of these solutions are structurally complex, especially when reliable gas separation is required. As additional, usually moving mechanical components, they also increase the susceptibility to failure of the overall system. The powdery construction material can become trapped between moving parts of the locks and block them.If cleaning or repair is necessary, the lock must be removed and the operation of the shift construction system must be interrupted.

[0007] An object of the present invention is therefore to provide a simple, reliable and maintenance-free solution for material transport from room to room, wherein either the first room or the second room is the process chamber of the production plant, while simultaneously influencing the gas exchange between the two rooms, in particular while maintaining the gas separation of the rooms.

[0008] This object is achieved by the methods and devices specified in the independent claims.

[0009] Advantageous embodiments of the invention are specified in the subclaims.

[0010] In this context, protection is claimed for a method for additive manufacturing in which such material transport takes place (claim 1), for a manufacturing plant for additive manufacturing in which such material transport takes place (claim 4), and for a method for transporting powdered building material in a manufacturing plant for additive manufacturing (claim 5).

[0011] The advantages and embodiments explained below in connection with the methods also apply mutatis mutandis to the devices according to the invention and vice versa.

[0012] A core idea of the invention is to allow the build-up material to form a powder column during transport from one chamber to the other, which influences a gas exchange between the two chambers, whereby either the first chamber or the second chamber is the process chamber of the production plant. The height of the powder column can then be specifically changed to influence this gas exchange. If gas separation of the chambers is desired, this is ensured by an appropriately designed powder column, in which the transport path of the build-up material and thus the gas path from one chamber to the other is sealed gas-tight by the build-up material itself. Instead of gas separation of the chambers, a defined gas transfer or gas transport between the two chambers can also take place by appropriately designing the powder column. In particular, the gas leaving the chamber through the transport path of the build-up material or entering the chamber canThe gas volume entering the room in this way can be specifically influenced, in particular regulated or controlled. The following primarily describes the variant in which gas separation is desired. The explanations in this context also apply accordingly to the variant with a targeted gas transfer.

[0013] According to the invention, no additional, particularly no moving mechanical parts, such as locks or the like, are used to separate the gases between the chambers. Instead, the powdered building material itself, in the form of a powder column, serves as a gas-tight seal for the building material's transport path. In other words, the powder itself seals the transport path of the powder in a gas-tight manner. The powder column serves as a gas barrier, i.e., it prevents gas exchange between the two chambers between which the material is transported.

[0014] To create gas separation using the powder column, no additional barrier material is used, for example, one not required for additive manufacturing. Instead, the buildup material already required in the chamber or to be transported into the chamber is used. This material also serves as a sealing material for the transport path and thus to close the transition between the two chambers.

[0015] For this purpose, a transport device (not part of the claimed invention) is provided which enables the formation of a powder column. The powder column is preferably formed purely by gravity, i.e., by the powder falling downwards due to the effect of gravity. The powder is then subjected only to the pressure of its own weight and is correspondingly compacted in the powder column, so that it exerts the desired gas barrier function. The powder column slides downwards towards an exit or outlet opening solely under the effect of gravity and then enters the target space. The exit or outlet opening is provided with a closure mechanism which, when closed, prevents build-up material from escaping from the powder column. For this purpose, a controllable closure element is provided, which can preferably be moved by a motor from a closed position to an open position and back.

[0016] The transport path between the chambers provided by the transport device is closed off by the powder column. The transport device or the transport path can be designed as a separate connection between the two chambers. Among other means, pipelines, funnels and the like with a constant or changing cross-section are suitable for forming the powder column. The transport device or the transport path can also be designed as part of one of the two chambers. In both cases, a defined space for the formation of the powder column is provided either by the boundaries of the chamber itself or by an additional suitable construction means. The transport device can, particularly when implemented using separate elements, have a defined feed opening in addition to an outlet or discharge opening.

[0017] The transport device can also comprise conveyors or be connected to such conveyors. Such conveyors serve to supply or remove the powdered building material, for example, for pneumatic powder conveying using a carrier gas.

[0018] The material transport serves to introduce and / or discharge, or to supply and / or remove, or to fill and / or empty, or to let in and / or discharge, powdered building material. In other words, the material transport taking place in this manner occurs, for example, from a storage container or a conveyor line into a process chamber, or from such a process chamber into a storage container or a conveyor line. In other words, the material transport proposed by the invention can be used for both a powder introduction device and a powder discharge device, generally speaking, for powder supply.

[0019] The powdered build-up material can be any suitable material, in particular metal powder or plastic powder. The build-up material is preferably a fine powder with a grain size of less than 0.5 mm. The finer the powder used, the denser the powder column formed by the material.

[0020] To ensure gas separation, a minimum amount of build-up material is always maintained in the powder column. In other words, the addition of build-up material to the powder column, on the one hand, and the removal of build-up material from the powder column, on the other, always occur in such a way that a minimum fill level is maintained in the powder column. Both the addition of build-up material to the powder column and the removal of build-up material from the powder column can occur discontinuously, continuously, or quasi-continuously.

[0021] The powder fill level is regulated to ensure a minimum height of the powder column, depending in particular on the pressure difference between the two chambers and / or the grain size of the powder and / or other parameters. Using suitable fill level sensors, the fill level of the powder column is monitored continuously or at suitable intervals. If the fill level falls below a defined limit, the powder column is refilled until the desired fill level is reached. The powder fill level is preferably regulated by controlling the powder conveying speed.

[0022] The filling level of the powder column can be monitored directly, for example using level sensors, or indirectly, for example by determining the current pressure difference in the spaces connected to each other via the powder column.

[0023] Any discharge of build-up material from the powder column, for example, the addition of build-up material to the process chamber or the removal of build-up material from the process chamber, always only occurs to the extent that a certain fill level, namely a minimum fill height, is maintained. At the same time, such removal of build-up material from the powder column only occurs when a certain fill level (minimum fill height plus X) is present or reached.

[0024] To ensure gas separation, a minimum fill level is always maintained, which maintains the gas-tightness between the chambers and prevents or minimizes the passage of gases through the powder column, thus preventing or minimizing gas exchange between the chambers. However, by regulating or changing the fill level of the powder column, which is most easily controlled by changing the defined limit value of the fill level of the powder column, gas separation can just as easily be reduced or even completely eliminated. This can be used advantageously to achieve a defined, pressureless supply of additives or the admixture of reaction gases, etc., into the atmosphere of the target chamber in a particularly simple manner. In other words, gas exchange between the chambers can not only be prevented, but also controlled.Such a targeted adjustment of the gas exchange is realized, for example, by increasing or decreasing the height of the powder column by filling or draining build-up material as soon as a lower fill level limit is undershot or an upper fill level limit is exceeded, whereby instead of the fill level limit values, other limit values, in particular those corresponding to the fill level, such as pressure limit values, can be used for control.

[0025] If a layered assembly plant or a plant for processing the build material contains several process chambers connected to a common supply line or a common discharge line for the build material, not only can different atmospheres exist within the different process chambers within the same plant. With a suitable design of the supply and discharge lines and strict gas separation of the rooms, different atmospheres can also exist in different sections of the lines.

[0026] The invention is applicable in connection with the powder supply of a layer construction system, wherein the build material is transported into and / or out of the process chamber in which the actual build process takes place using the invention. When the invention is used in secondary processes, the process chamber serving as the target or exit chamber can be the cleaning chamber, mixing chamber or the like. Preferably, the transport path for the build material used by the invention is the only possible transport path for the build material into the target chamber. In other words, the system is preferably designed such that the method of transporting build material according to the invention is the only way to supply build material to the process chamber or to remove build material from the process chamber. The system can therefore be of particularly simple construction.

[0027] Preferably, the transport path is also the only available path for gas transport or gas exchange between the chambers. The powder column closing the transport path according to the invention thus represents the only way to seal the connection between the two chambers in a gas-tight or pressure-tight manner. This preferably also applies if a closure mechanism is provided to close the outlet or exit opening. In other words, this closure mechanism does not have to be gas-tight or pressure-tight.

[0028] In contrast to the systems known from the prior art, in which each powder column formed between two spaces influences the gas exchange between these spaces by its nature, namely, depending on its height, either prevents it or allows it to a greater or lesser extent, the present invention does not merely concern an unwanted, arbitrary influence on the gas exchange, but an intentional, targeted control of the height of the powder column of the building material for the purpose of a targeted influence on the gas exchange between spaces with different atmospheres.

[0029] An exemplary embodiment of the invention is explained in more detail below with reference to the drawing. The single figure shows part of a layered construction system. The figure is not to scale, but merely shows the invention schematically and with only its essential components.

[0030] A layer construction system 1, which operates, for example, according to the laser sintering process, comprises a process chamber 2 filled with a special process atmosphere, in which a build platform 3 is arranged in an xy plane, on which a three-dimensional object 4 is produced layer by layer in a known manner. The build material is a suitable plastic powder. After the production of a layer n, in order to produce a new layer n+1, the build platform 3 with the already created and hardened layers is moved downwards by a certain distance. For this purpose, a drive device (not shown), for example an electric motor, is used to generate a movement of the build platform 3 in the z-direction, i.e. perpendicular to the build plane.

[0031] The layer builder 1 comprises at least one solidification radiation source 5, which provides radiation energy for locally heating build material in order to selectively solidify it. The radiation source is, for example, a laser that emits a guided laser beam 6 extending into the process chamber 3.

[0032] The layer building system 1 also comprises an application device 7, with which build material is applied and distributed as a thin layer onto the build platform 3 or an existing build layer from time to time during the system's operation. The application device 7 is, for example, a device for applying a powder bed that extends into the process chamber 2 or is connected to the process chamber 2 via a transport path for build material. The powdered build material is fed to the application device 7 via a connected supply device. The supply device is, for example, a supply line 8, wherein the supply is achieved by pneumatic powder conveyance using a carrier gas.

[0033] Between the solidification of a layer n and the application of new build material for a subsequent layer n+1, it may be provided to remove excess build material from the build platform 3. In this case, a suitable device (not shown) is provided for this purpose, for example in the form of a doctor blade or the like. In any case, after completion of the build of the object 4, the process chamber 2 contains excess or unused, loose build material that can be removed from the process chamber 2. For this purpose, a removal device 9 is provided, which is connected to the process chamber 2 via a transport path for build material or extends into the process chamber 2. Connected to the removal device 9 is a removal device, for example in the form of a removal line 10, with the aid of which the build material can be removed, which in turn takes place by means of a pneumatic powder conveyance.

[0034] The supply device 8 and the application device 7 on the one hand, as well as the removal device 10 and the removal device 9 on the other, are each connected to a corresponding control system (not shown) that controls the material supply into the process chamber 2 and the material application or removal from the process chamber 2 and its removal. These controls are preferably implemented in the form of computer programs that carry out the steps relevant for the control, in particular regulating the conveying capacity of the powder supply or removal, when the computer program is executed on a computer with a processor. This is preferably the central control or process computer (not shown) of the layer-by-layer production system 1.

[0035] During the supply of build material as part of the powder supply to the layer building system 1, the powdered build material is transported from time to time under the sole effect of gravity, i.e. in the z-direction, from a first chamber, the supply line 8, into a second chamber spatially separated from the first chamber, the process chamber 2, wherein the atmospheres in these chambers differ from one another, for example with regard to their gas composition. During this transport of the build material, a powder column 11 is formed, which prevents gas exchange between the two chambers 8, 2. The application device 7 serves as a transport device for the build material and is designed such that the build material forms a powder column 11 as soon as the application device 7 is supplied with build material via the supply device 8.For this purpose, the application device 7 comprises a cylindrical tube section 12 in which the powder column 11 is built up in a defined manner.

[0036] During the removal of build-up material as part of the powder disposal of the layered construction system 1, the powdered build-up material is transported from time to time under the sole effect of gravity, i.e. in the z-direction, from a first space, the process chamber 2, to a second space spatially separated from the first space, the discharge line 10, whereby the atmospheres in these spaces also differ from one another. During this transport of the build-up material, a powder column 11 is formed, which prevents gas exchange between the two spaces 2, 10. The removal device 9 serves as a transport device for the build-up material and is designed such that the build-up material forms a powder column 11 as soon as the removal device 9 is fed with build-up material via the process chamber 2. For this purpose, the removal device 9 comprises a cylindrical tube section 12, in which the powder column 11 builds up in a defined manner.

[0037] The removed build-up material can then be cleaned or otherwise processed in a processing plant (not shown) and fed back into the production process in a circuit via the supply device 8. The processing plant can also comprise transport devices 7, 9 operating according to the invention.

[0038] In both cases, the tube section 12 defines the transport path between the two chambers, which can be blocked with the help of the powder column 11 to prevent gas transport or gas exchange, while simultaneously allowing the build-up material to be transported from chamber to chamber. In both cases, the tube section 12 ends with an outlet or exit opening 13 through which the build-up material is transported further. This opening 13 can be closed with a non-pressure-tight closure element 14. The tube section 12 does not have to be cylindrical; other designs are also possible, for example, in the shape of a funnel (truncated cone).

[0039] In both cases, i.e. during powder supply as well as powder disposal, the height of the powder column 11 is monitored using a number of suitable fill level sensors (not shown) and can be changed using the controls, with the fill level being set so that no gas exchange occurs between the chambers. This is achieved by constantly controlling the supply of powder material to the powder column 11 and the removal of powder material from the powder column 11 in such a way that a minimum fill level of the powder column 11 is always guaranteed. For this purpose, the controls regulate the pneumatic powder conveyance in the supply line 8 and the discharge line 10 as well as the motor drive of the closure elements 14. The respective minimum fill level for reliable gas separation depends, among other things, on the pressure difference between the two chambers. For this reason, suitable pressure sensors (not shown) connected to the controls can be provided.The controls then determine the required minimum filling level, taking into account the material required for the build-up process to be supplied to the process chamber 2, the pressure difference between the chambers and other parameters, for example the grain size of the build-up material used, and during operation of the layer build-up system 1, they provide the required minimum filling level by means of corresponding control commands for filling the powder column 11 with build-up material and / or control commands for removing build-up material from the powder column. 11 Ensure that this filling level is always maintained. If necessary, the height of the powder column can be 11 to enable a targeted gas exchange between the two spaces, it can also be changed in a defined manner, in particular reduced. List of reference symbols

[0040] 1Layer construction system 2Process chamber 3Building platform 4Object 5Radiation source 6Laser beam 7Deployment device 8Provision device, supply line 9Removal device 10Removal device, discharge line 11Powder column 12Pipe section 13Opening 14Closing element

Claims

1. A method for additive manufacturing, in which powdered build material is transported from a first space (8; 2) into a second space (2; 10) of a manufacturing system (1) for additive manufacturing, wherein either the first space or the second space is the process chamber (2) of the manufacturing system (1), wherein the atmospheres in those spaces are different from one another, wherein the build material forms a powder column (11) that influences a gas exchange between the two spaces, characterized in that the height of the powder column (11) is specifically modifiable in order to influence that gas exchange; wherein the height of the powder column (11) is adjusted in order to suppress a gas exchange between the two spaces; or wherein the height of the powder column (11) is modified in order to enable a targeted gas exchange between the two spaces.

2. The method according to claim 1, wherein the height of the powder column (11) is monitored.

3. The method according to claim 1 or 2, wherein transportation of the build material occurs during the runtime of the manufacturing system (1).

4. A manufacturing system (1) for additive manufacturing, having a first space (8; 2) and a second space (2; 10), wherein either the first space or the second space is the process chamber (2) of the manufacturing system (1), wherein the spaces are configured to contain atmospheres that differ from one another, and having a transportation device (7; 9) for transporting powdered build material from the first space (8; 2) into the second space (2; 10), wherein the transportation device (7; 9) comprises a tube section (12) having an opening (13), which opening (13) is closable by a closure element (14), and having a control for filling the tube section (12) with build material and / or for actuating the closure element (14), and having a powder column (11) formed in the tube section (12) by the build material by means of the transportation device (7; 9) during transport, which influences a gas exchange between the two spaces, characterized by sensors for monitoring the height of the powder column (11), wherein the height of the powder column (11) is specifically modifiable with the aid of the control in order to influence that gas exchange, wherein the height of the powder column (11) is adjusted in order to suppress a gas exchange between the two spaces or wherein the height of the powder column (11) is modified in order to enable a targeted gas exchange between the two spaces.

5. A method for transporting powdered build material from a first space (8; 2) into a second space (2; 10) of a manufacturing system (1) for additive manufacturing, wherein either the first space or the second space is the process chamber (2) of the manufacturing system (1), wherein the atmospheres in those spaces are different from one another, wherein the build material forms a powder column (11) that influences a gas exchange between the two spaces, characterized in that the height of the powder column (11) is specifically modifiable in order to influence that gas exchange, wherein the height of the powder column (11) is adjusted in order to suppress a gas exchange between the two spaces or wherein the height of the powder column (11) is modified in order to enable a targeted gas exchange between the two spaces.