Device and method for constructing a laminar body comprising at least one position adjustable body defining the working area

The invention relates to a device (13) for constructing a laminar body (5) from a plurality of superimposed layers of free-flowing material, in particular particulate material, an a build platform (6) within a working area (11). The layers are solidified in locally predetermined regions by the action of binders and are joined together so that at least one molded body (4) is formed by the solidified and joined regions of the layers. The device comprises a discharging device (1) movable back and forth over the working area (11) in at least one discharge direction and having at least one discharge opening (14) from which the free-flowing material can be discharged in individual superimposed layers during the movement of the discharging device (1). According to the invention at least one body (8, 8a) defining the working area (11) in at least one discharge direction of the discharging device (1) and the build platform (6) are adjustable vertically relative to each other in accordance with the specific progress with which the laminar body (5) is being constructed, in such a manner that a surface of the at least one body (8, 8a) facing the discharge opening (14) is aligned flush with a laminar body (5) topmost layer that is yet to be produced or has already been produced, in order to dose the discharge opening (14) of the discharging device (1) and prevent the discharging device from discharging free-flowing material or in order to discharge free-flowing material not used for laminar construction into a collecting container (7) when the discharge opening (14) is located above the body (8, 8a).

BACKGROUND INFORMATION

The invention relates to a device and a method for constructing a layer body from a plurality of superimposed layers of free-flowing material. In particular particulate material, on a build platform within a build space, the layers being solidified and joined together in locally predetermined areas by the action of a tender so that at least one molding is formed fey the solidified and joined areas of the layers, the device comprising a discharging device which is movable back and forth over the build space in at least one discharge direction and which has at least one discharge opening from which the free-flowing material is dischargeable in individual superimposed layers during the movement of the discharging device, according to the definition of the species in the alternative independent Patent Claims1and12.

A computer-controlled method for producing three-dimensional moldings is described in EP 0 431 924 B1. Free-flowing particulate material is applied in a thin layer to a build space which is surrounded, as appropriate, by container walls and applied to a build platform, and a binder is selectively printed thereon, using a print head, according to computer data. The particle area onto which the binder is printed sticks together and solidifies under the influence of the binder and, if necessary, an additional hardener. The build platform is then lowered by a distance of one layer thickness into a build cylinder and provided with a new layer of particulate material, which is also printed as described above.

These steps are repeated until the desired height of the molding is achieved. A three-dimensional object is thus produced from the printed and solidified areas.

After it is completed, the molding produced from solidified particulate material is embedded in loose particulate material and is subsequently removed therefrom. This is done, for example, using an extractor. This leaves the desired molding from which the remaining adhering particles are removed, for example by brushing.

Other powder-supported rapid prototyping processes work in an identical or similar manner, for example, selective laser sintering or electron beam sintering, in which a loose particulate material is also applied in layers and selectively solidified with the aid of a controlled physical radiation source. The aforementioned method is summarized under the term, “three-dimensional printing” or “3D printing.”

However, the provision of a build container or build cylinder having a build platform which may be lowered vertically into the build container requires a high degree of technical complexity for sealing the build container wall against the build platform to prevent uncontrolled outflow of the particulate material through the gap between the build platform and the build container wall. Another disadvantage of a lowerable build platform is the constantly increasing weight to be moved on the build platform as the building process progresses. In particular during application of another layer, it may be necessary to lower the build platform by a distance of more than one layer thickness and then to raise it again to the dimension required in order to adjust the layer thickness with sufficient accuracy.

In a reversing operation of this type, not only does the entire weight of the power feedstock, including the build platform, need to be overcome but also the friction forces between the power bed and the build container wall. This results in high stresses on the guides and drives of a vertically moving build platform, in particular in the case of large build spaces and high feedstock densities.

In contrast, EP 1 872 928 A1 proposes to raise the discharging device and the print head relative to the build platform instead of lowering the build platform relative to the discharging device and print head for building larger three-dimensional moldings as the layering process progresses. This publication furthermore proposes to construct solid walls made of particulate material by solidifying the edge areas of the applied particulate material and by forming, from these walls, a build space-delimiting build container in whose inner chamber moldings of a selective size and shape may be constructed. It is alternatively proposed to construct moldings on the build space in a free-standing manner without using a build container for encompassing and supporting previously applied layers. For this purpose, the discharging device is designed as a dosing device which may undergo controlled activation and deactivation for the controlled output of a predetermined, preferably constant, linear volume flow of particulate material per length unit and per time unit, so that particulate material is not unnecessarily strewn around the molding to be built or is not “emptied” prematurely and thus does not lose its function while the layer is being deposited. However, such dosing-controlled and “intelligent” discharging devices have a relatively complex structure and are correspondingly expensive.

“Unintelligent” discharging devices of a simpler design, on the other hand, are unable to selectively dose particulate material or are not switchable. For example, they include a scraper moving in the discharge direction or a counter-rotating roller or an oscillating blade.

These devices then distribute a quantity of material in front of the discharging device on the build space in the discharge direction. The amount of particulate material then has to be sufficiently measured before the discharging device travels over the build space.

Other design shapes may guide a quantity of material in two directions around the surface to be coated. These include discharging devices which comprise a simple, elongated hopper which has a slot on the underside as the discharge opening for discharging particulate material. In another embodiment, at least one of the two hopper walls, for example, is replaced by a counter-rotating roller.

In order for the process to progress as described, the discharging device must pass completely over the area to be coated. However, a discharging device according to the aforementioned, simple and “unintelligent” design, loses a remaining quantity of material in front of the discharging device in the discharge direction once the edge of the build space has been reached. This quantity of material would then be unavailable for the remaining building process. Nevertheless, it would be desirable to return this lost material to the discharging device for further layering.

A possibility for largely avoiding lost material is known for example, from U.S. 2005/0230185 A. In this publication, the quality of particulate material in the discharging device is predetermined by a sensor system.

The discharging device carries along a predetermined material quantity which is sufficient for coating the desired surface without producing too many waste particles after passing over the edge of the build space. In this case, however, the quantity must be very precisely determined to avoid too small a dosing in each cases, which would result in insufficient layering. The continuous decrease in the quantity of material in the discharging device during travel has proven to be another disadvantage of this method, resulting in an unsteady coating process. This may cause the feedstock density to be greater at the beginning of discharging device travel than at the end of the travel, due to the greater weight of the material, when a residual amount is left over in the discharging device.

In contrast, the object of the invention is to refine a method and a device of the aforementioned type in such a way that a variable and coating material-saving adjustment of the build space size is possible while simultaneously maintaining high coating quality, despite a simple and cost-effective design of the discharging device.

SUMMARY OF THE INVENTION

The invention is based on the idea that no free-flowing material or particulate material may flow out or be discharged through the discharge opening of a non-switchable discharging device, i.e., an “unintelligent” discharging device which has no way to turn the material flow through the discharge opening on and off, when the discharge opening is closed by a body which is located on an appropriate level and over which the discharging device passes.

A body of this type then simulates an already discharged layer of free-flowing material, which prevents further discharge of material when this layer reaches the same level as the discharge opening of the discharging device. In this case, after all, the discharge opening has already been closed by the already discharged layer.

By designing the body or the build platform to be able to change at least the vertical position of the body in relation to the build platform, the size of the build space may be easily limited by the body without requiring a build container which is laboriously adjusted to the particular size of the build space. When the discharging device with its discharge opening comes into contact with the surface of the body, which is suitably placed on the edge of the build space in the vertical direction, the body closes the discharge opening, whereby no more free-flowing material is dischargeable at the edge of the build space.

Alternatively or additionally, the body is designed in such a way that it does not close the discharge opening but instead has means such as an opening to be controllably opened or closed, for example, for the purpose of discharging or conducting free-flowing material that is not used for layering from the discharge opening into a collecting container, so that it may be fed back into the layering process.

According to the invention, it is therefore proposed that at least one body delimiting the build space in at least one discharge direction of the discharging device and the build platform are vertically adjustable relative to each other according to the particular progress with which the layer body is being constructed, in such a way that a surface of the body facing the discharge opening is aligned flush with a topmost layer of the layer body which is yet to be produced or has already been produced, in order to close the discharge opening of discharging device and to prevent the discharging device from discharging free-flowing material or to discharge free-flowing material not used for layering into a collecting container when the discharge opening is located above the body.

It is advantageous that, even when using an “unintelligent,” non-switchable, non-dosing and only displacement-controlled discharging device, it is possible to discharge free-flowing material only within the build space delimited by the body and to avoid, in particular, discharging material in the area of the build platform located outside the build space. As a result, it is not necessary to remove residual material located outside the build space, which has a positive effect on the costs. The option of using an “unintelligent,” non-switchable, non-dosing and only displacement-controlled discharging device in connection with the invention also helps lower costs because a discharging device of this type is much more cost-effective than an “intelligent” discharging device. An only displacement-controlled and “unintelligent” discharging device is understood to be a discharging device which travels a certain computers-controlled discharge route, for example from a starting position to a reversing position, and which discharges or permits the outflow of free-flowing material along this discharge route and through the always open discharge opening onto the build space. In particular, the discharging device does not have any means of closing the discharge opening or, for instance, dosing the quantity of free-flowing material to be discharged, depending on the traveling distance.

Advantageous refinements of and improvements to the invention specified in the independent claims are made possible by the measures discussed in the dependent claims.

It is particularly advantageous if the at least one body is designed to foe adjustable within a horizontal plane parallel to the build platform for the purpose of variably delimiting the build space. The areal extension of the build space may then be delimited by the at least one body, in particular if one body is disposed in one discharge direction of the discharging device (e.g., the X direction) and another body is displayed in a discharge direction perpendicular thereto (e.g., the Y direction) in order to achieve a delimited build space in both directions.

This ensures that a discharge of free-flowing material, beyond the edges of the build space no longer occurs in both directions.

As mentioned above, the discharging device is preferably an “unintelligent” discharging device and only displacement-controlled with regard to a predefined discharge distance extending from a starting position at one edge of the build space to a reversing position at the opposite edge of the build space. This additionally lowers costs.

The reversing position may be predefined by the particular position of the at least one body, and the starting position is stationary. In this case, the coating operation is started from a stationary starting position, and the reversing position is defined as a function of the position of the at least one body on the horizontal plane.

Conversely, however, the starting position may be predefined by the particular position of the at least one body, and the reversing position is stationary. In this case, the coating operation is started from the at least one body and its direction is reversed at the stationary reversing position. In both cases, the length of the discharge route to be traveled by the discharging device and thus the extension of the build space in this direction depends on the position of the at least one body.

The starting position of the discharging device, i.e., the place from which the discharging operation is started, is particularly preferably a filling position in which the discharging device may be filled or refilled with free-flowing material by means of a filling device. Depending on whether the starting position is or is not dependent on the position of the at least one body, the position of the filling device on a horizontal plane parallel to the build platform is therefore also dependent on the position of the body. The filling device is then positioned, for example, above the discharging device.

The container for collecting excess material is disposed, for example, at the reversing position or at the starting position. One body may then be disposed at the starting position and at least one other body may be disposed at the reversing position, means being provided in the one body or in the other body for introducing free-flowing material into the collecting container or for conducting it thereto. The one body closing the discharge opening of the discharging device is then used to prevent a discharge of free-flowing material at the edge of the build space, while the purpose of the other body on the opposite edge of the build space is to introduce excess, i.e., unused, free-flowing material into the collecting container, so that it may be supplied for reuse in the layering process.

The at least one body is preferably a flat, plate-shaped body, for example a metal plate with or without a through-opening, depending on whether it is to prevent a discharge from the discharge opening of the discharging device or whether it is to discharge material into the collecting container.

It is therefore particularly preferable to design the build platform to be adjustable vertically relative to the body and discharging device and to design the body and the discharging device to be adjustable horizontally relative to the build platform, in order to flexibly adapt the build space to the particularly requirements and, in particular, to the particular molding to be constructed, while minimizing the loss of free-flowing material.

The invention additionally relates to a method for constructing a layer body from a plurality of superimposed layers of free-flowing material on a build platform within a build space.

Additional measures which improve the invention are illustrated in greater detail below together with the description of one exemplary embodiment of the invention on the basis of the drawing.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a preferred embodiment of a device13for constructing a layer body5from a plurality of superimposed layers of, for example, powdered, initially loose, particulate material on a build platform6within a build space11athrough11d.

Build spaces11athrough11dof different sizes illustrated inFIG. 1extend over a wide area inFIG. 1parallel to build platform8in the horizontal X and Y directions, layer body5being constructed in the vertical Z direction, which is perpendicular to the drawing plane inFIG. 1.

Device13comprises a discharging device1which is movable back and forth over build space11athrough11din at least one discharge direction, in this case, for example, in the X direction and/or the Y direction, discharging device1having at least one discharge opening14, which is not visible in this view and from which the particulate material, may be discharged in individual superimposed layers during the movement of discharging device1.

Discharging device1is preferably a non-switchable discharging device, i.e., without the option of turning the material flow through discharge opening14on and off, so that free-flowing material or particulate material may or may not flow out. Instead, particulate material continuously flows through discharge opening14in discharging device1unless discharge opening14is closed by means belonging to discharging device1or if no (more) particulate material is present in a reservoir of discharging device1.

Device13furthermore comprises a print head2which is moveable back and forth over build space11, for example, in the X and V directions for the selective application of binder onto at least one discharged layer in order to solidify and join together discharged layers in locally predetermined areas of build space11athrough11dby the action of binders, so that at least one molding4is formed by the solidified and joined areas of the layers of layer body5in a known manner.

Alternatively, print head2could be replaced with a radiation source if the discharged, free-flowing material already contains a binder which is then hardened by selective irradiation with the radiation source for the purpose of creating molding4. Or the free-flowing material itself is fused or slightly melted by the irradiation and joined thereby.

The extension of build space11athrough11din the X and Y directions is predefined by the application of material to build platform6, different sizes of build spaces11athrough11dbeing illustrated inFIG. 1. If build space11athrough11dis described in the illustrated orthogonal coordinate system9, each extension or size of build spaces11athrough11dmay be displayed as a rectangle, starting from origin10. The dimensions of build platform6in the X and Y directions then correspond to a maximum displayable size of one build space11a.

One rectangular side of a build space11of this type is generally determined, for example, by the discharge route or discharge travel of discharging device1in discharge direction X, so that, in the present case, the size of the build space is dependent on the length of this discharge route. Based on the example inFIG. 1, the discharge route of discharging device1thus increases from11dto11ain the X direction.

The other rectangular side of a build space11athrough11dis determined, for example, by the width of discharge opening14of discharging device1in the Y direction, which may be formed in particular, by a an elongated slot. In the present case, different lengths of discharge openings14of discharging device1are provided to obtain the variable-length rectangular side of build spaces11athrough11din the Y direction. In the present case, therefore, one layer of layer body5may, on the whole, be completely produced in one pass of the discharge route in the X direction.

Only one rectangular side of a build field11is visible in the cross-sectional side representation inFIGS. 2athrough2dand3athrough3g. In these illustrations, the edges of build space11are preferably formed by printed walls3in the X and Y directions, i.e., the particulate material is selectively solidified here by print head2so that loose particulate material of layer body5located within the edges of build space11is hot able to flow off in areas outside build space11. For this purpose print, head2suitably prints, the edge areas of each discharged layer. Alternatively, however, a separate build container or separate build walls could be used to delimit build space11.

In the embodiments illustrated herein, build platform6is preferably lowered as the height of layer body5increases in the Z direction, in particular using drives and guides which are not illustrated. Discharging device1therefore remains on its initial level for each new layer to be discharged and is therefore movable relative to build platform6, for example only in the X direction and/or the Y direction. Alternatively, build platform6could, be designed to be stationary, and at least discharging device1could be designed to be movable relative to stationary build platform6in both the X and Y directions as well as the Z direction.

In the specific embodiments inFIGS. 2athrough2dand3athrough3g, build platform6is vertically adjustable relative to, for example, two bodies8,8adelimiting the build space in discharge direction X of the discharging device according to the particular progression of construction, in such a way that surfaces of bodies Bf8afacing discharge opening14of discharging device1are aligned flush with a topmost layer of layer body5yet to be produced or already produced.

The purpose of the two bodies8,8ais to close discharge opening14of discharging device1and to prevent discharging device1from discharging free-flowing material (body8) or to discharge free-flowing material that is not used for layering into a collecting container7(body8a) when discharge opening14of discharging device1is located above particular body8,8a.

At least one of bodies8,8a, in this case preferably body8, is designed to be adjustable within a horizontal plane parallel to build platform6and, in particular, in the X direction, for the purpose of variably delimiting build space11. The areal extension of build space11is then delimited by body8at least in the X direction, in particular when the position of body8is designed to be movable in discharge direction X of discharging device1.

Build platform6is therefore particularly preferably designed to be adjustable relative to bodies8,8a, discharging device1and print head2in the vertical Z direction, and body8, discharging device1and print head2are designed to be movable relative to build platform6in the horizontal X direction. The position of body8is adjusted in the X direction in order to flexibly adapt build space11to the particular requirements and, in particular, to the one or more moldings4to be constructed, while minimizing losses of free-flowing material.

The two bodies8,8aare consequently always on the same level in the Z direction, in particular through attachment to or guidance on a stationary frame of device13, which is not illustrated herein, while build platform6is being lowered as the construction of layer body5continues to progress.

Bodies8,8aare preferably flat, plate-shaped bodies, for example metal plates with and without through-openings12, depending on whether the particular body8or8ais to prevent material from being discharged from discharge opening14of discharging device1or to permit or cause material to be discharged into collecting container7. Body8ais therefore preferably formed by a perforated plate having at least one through-opening12. Body8amay furthermore also comprise means for conducting particulate material into collecting container7. Not least, at least one through-opening12of body8amay be controllable, i.e., the at least one through-opening12may be opened or closed as a function of external electrical, pneumatic and/or mechanical control signals in order to discharge or conduct free-flowing material not used for layering from discharge opening14info collecting container7for the purpose of returning it to the layering process.

As indicated above, discharging device1is displacement-controlled, for example, by an electronic control unit, which is not illustrated here, with regard to a predefined discharge route in the X direction, extending from an initial, starting or idle position14at one edge of build space11to a reversing position16at the opposite edge of build space11; i.e., in response to a starting command, it first moves from its starting or idle position14in the X direction to reversing position16, at which the direction of movement is automatically reversed, if necessary upon expiry of a certain dwell time at reversing position16.

During the movement of discharging device1along the discharge route, which simultaneously forms the length of the rectangular side of build space11visible herein, particulate material is preferably continuously applied to build platform6or to a previously layered part of layer body5via discharge opening14.

Prior to this, discharging device1, which in this case is, for example, a discharging hopper of a filling device which is not illustrated herein but is easy to picture, is preferably filled with a quantity of particulate material corresponding to a multiple of layers to be applied.

According to the embodiment inFIGS. 2athrough2d, starting position15is predefined by the position of body8adjustable in the X direction, while reversing position16, at which body8ais located, is stationary. In this case, the coating operation is started from the particular set position of body8, body8closing discharge opening14of discharging device1precisely at starting position15and preventing particulate material from being discharged, as is easily pictured on the basis ofFIG. 2a. Only after discharging device1has moved a distance from body8is free space the height or thickness of one layer provided below discharge opening14, into which particulate material may be discharged to form a single layer. Specifically, the following method steps are carried out in the embodiment inFIGS. 2athrough2d;

Build platform6is first positioned in the vertical direction relative to bodies8and8a, to discharging device1and to print head2, in such a way that the surfaces of body8,8afacing discharge opening14, discharge opening14of discharging device1and print head2are disposed higher than the current topmost layer of layer body5by a distance of one layer thickness.

When discharging device1is located in its starting position right above body8, its discharge opening14is closed by body8, as is easily pictured on the basis ofFIG. 2a. Print head2is then preferably located on the far side of opposite reversing position16of discharging device1, i.e., outside build space11, in order to avoid colliding later on with discharging device1once it has reached reversing position16.

At the same time or thereafter, discharging device1is filled with free-flowing material at starting position15in a quantity sufficient to produce, for example, a single layer of layer body5. The filling device, which is not illustrated herein, is then positioned, for example, above discharging device1.

The control unit then activates discharging device1so that it moves from starting position15to reversing position16while discharging particulate material to construct one layer. This situation is illustrated inFIG. 2a.

When discharging device1has reached body8aat reversing position16, discharge opening14is located right above opened through-opening12in body8a, so that any excess particulate material still remaining in discharging device1for producing a layer is able to flow into collecting container7, which is disposed, for example, below through-opening12in body8a. The control unit then returns emptied discharging device1to its starting position15, whereby it is followed by print head2in order to provide or print binder onto a locally predetermined area of the discharged layer. Since discharging device1is empty during this movement, i.e., it is moved without particulate material, an unwanted application of particulate material to layer body5is avoided. This operation is illustrated inFIG. 2c.

Once discharging device1has reached starting position15, it is refilled with particulate material for one layer, and the described cycle begins all over again (FIG. 2d). The cycle according toFIGS. 2athrough2dare repeated until the entire layer body5is created. Print head2also prints the areas that represent walls3of layer body5.

In the specific embodiment illustrated inFIGS. 3athrough3g, in contrast to the specific embodiment inFIGS. 2athrough2d, reversing position16is determined by the position of body8set in the X direction, and starting position25, where body8ais located, is stationary. In this case, the coating operation is started at a stationary starting position15, and reversing position16is defined depending on the position of body8in the X direction.

Specifically, the following method steps are carried out in the embodiment inFIGS. 3athrough3g:

Build platform6is first positioned vertically (in the Z direction) relative to bodies8,8a, to discharging device1and to print head2, in such a way that, on the one hand, the surfaces of body8,8afacing discharge opening14and, on the other hand, discharge opening14are disposed higher than the current topmost layer of layer body5by a distance of one layer thickness. Body8a, which has the at least one through-opening12, and collecting container7located thereunder are positioned at starting position15, and body8, which does not have a through-opening12of this type, is positioned at reversing position16.

To prevent particulate material from flowing through through-opening12in body8ainto collecting container7in starting position15, discharging device1is filled by a filling device, which is not illustrated herein, for example in a position located a short distance from starting position15in the X direction, in which a part of body8afacing build space11is able to close discharge opening14in discharging device1, as shown inFIG. 3g. Discharging device1is filled with particulate material for producing, for example, two layers of layer body5.

Print head2is located in the starting position, preferable on the near side of body8a, so that it does not collide with discharging device1. Discharging device1is then activated by the control unit in order to move from starting position15to reversing position16for the purpose of discharging particulate material in this matter to construct a layer (FIG. 3a). Once reversing position16at the edge of build space11has been reached, body8closes discharge opening14in discharging device1. Print head2is subsequently activated by the control unit in order to print binder onto a locally determined area of the discharged layer as well as the areas that form walls3of layer body5(FIG. 3b). Afterwards, print head2returns to its starting position.

Once a layer has been discharged and selectively printed, build platform6is lowered by a distance of one layer height or one layer thickness so that the surfaces of bodies8and8afacing discharge opening14, discharge opening14of discharging device1and print head2are again disposed higher than the current topmost layer of layer body5by a distance of one layer thickness.

Discharging device1is then activated by the control unit in order to move from reversing position16back to starting position15while discharging particulate material for constructing another layer, as illustrated inFIG. 3c.

After starting position15is reached, any particulate material that is not used for the two discharged layers may flow through the at least one through-opening12of body8ainto collecting container7(FIG. 3d).

Print head2is subsequently activated so that it prints binder onto the areas of molding4and walls3of the additional discharged layer. Emptied discharging device1may then move in front of print head2, as shown inFIG. 3e.

According toFIG. 3f, discharging device1and print head2are moved back to their starting position15after the printing operation, build platform6preferably being simultaneously lowered by a distance of one layer height or one layer thickness for the purpose of making space in the vertical direction for a subsequent layering operation.

After discharging device1has been refilled with particulate material in the position according toFIG. 3g, the described cycle begins all over again and is repeated until complete layer body5is created. Finally, loose particulate material is removed from the layer body in the unprinted areas, leaving molding4behind.

Instead of lowering build platform6vertically relative to bodies8,8a, to discharging device1and to print head2as the construction continues to progress, bodies8,8a, discharging device1and the print head could, of course, also be designed to be movable relative to a stationary build platform6in the vertical2direction, according to another embodiment,

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