# Patent

## Title
Method and device for conveying particulate material during the layer-wise production of patterns

## Abstract

The present invention relates to apparatus, devices and methods for conveying particulate material during the manufacture of patterns in layers, wherein powder is conveyed out of a reservoir into a spreader unit and, if applicable, excess powder fed to the spreader unit is again conveyed back into the reservoir and wherein this conveying takes place in a closed conveying circuit.

## Background
CLAIM OF PRIORITY
This application is divisional patent of U.S. patent application Ser. No. 12/681,961 (filed Apr. 7, 2010), which is incorporated herein by reference in its entirety. U.S. patent application Ser. No. 12/681,961 is a national phase of PCT application No. PCT/DE2008/001602, filed Oct. 6, 2008, which claims priority to German Application No. DE 10 2007 050 679.3, filed Oct. 21, 2007, all of which are incorporated herein by reference. This patent application claims priority to U.S. patent application Ser. No. 12/681,961, filed Apr. 7, 2010, PCT application No. PCT/DE2008/001602, filed Oct. 6, 2008, and German Application No. DE 10 2007 050 679.3, filed Oct. 21, 2007


FIELD OF THE INVENTION
The invention relates to a method and to a device for conveying particulate material during the manufacture of patterns in layers.
BACKGROUND
Methods for producing three-dimensional components have already been known for a long time.
European patent specification EP 0 431 924 B1, for example, describes a method for producing three-dimensional objects from computer data. A particulate material is thereby applied onto a platform in a thin layer and said platform is selectively imprinted with a binder material by means of a print head. The particulate area, which is imprinted with the binder, adheres and solidifies under the impact of the binder and an additional hardener, if applicable. The platform is subsequently lowered by a layer thickness in a construction cylinder and is provided with a new layer of particulate material, which is also imprinted, as is described above. These steps are repeated until a certain, desired height of the object is reached. A three-dimensional object is thus created from the imprinted and solidified areas.
After its completion, this object, which is produced from solidified particulate material, is embedded in the loose particulate material and is subsequently freed therefrom. This takes place, for example, by means of a vacuum cleaner. Thereafter, the desired objects, which are then freed from the residual powder, e.g., by means of brushing, remain.
Other powder-supported rapid-prototyping processes, such as the selective laser sintering or the electron beam sintering, e.g., in the case of which a loose particulate material is also in each case applied in layers and is selectively solidified by means of a controlled physical source of radiation, also operate in a similar manner.
All of these methods will be combined herein below under the term “three-dimensional print processes”.
In the case of the three-dimensional print process known from the state of the art, the particulate material is typically applied by means of a spreader unit. In the case of a low fill level, this spreader unit must be filled with particulate material from a reservoir.
Different methods and device are known from the state of the art for this purpose.
WO 98/28124 A1, for instance, describes a method, in the case of which the powder material is pushed onto a workspace via a piston and is applied from there via rollers onto the area, which is to be coated.
A device for filling a spreader device is further known from WO 00/78485 A2, in the case of which a reservoir is arranged in an end position of the spreader device thereabove, with said reservoir encompassing a sliding closure, wherein this sliding closure can be opened, if needed, and the spreader device can thus be filled.
A device, in the case of which the conveying of the particulate material out of the reservoir into the spreader device takes place via a conveyor belt, is furthermore known from the same patent application.
WO 2003/97518 further describes the conveying of the particulate material out of the reservoir into the speeder system via a slider.
A conveying device, which uses a belt transport system comprising conveyor cages for transporting particulate material to the spreader device, is further known from US 2004/0012112 A1.
A further possibility for conveying particulate material out of a reservoir into a spreader system is described in DE 10 2005 056 260 A1. In the case of a low fill level, the spreader unit is hereby filled with particulate material from a reservoir in such a manner that the fill level in the spreader unit reaches a predetermined level across the entire length of the spreader device even in the case of a previously irregular fill level.
In the case of these methods and devices for filling a spreader unit for fluids, which are known from the state of the art, it has proven to be disadvantageous that one fill level control is always necessary. An uneven filling across the length of the spreader device can furthermore only be compensated or to an unsatisfactory degree with the methods from the state of the art.
SUMMARY OF THE INVENTION
It is thus the objective of the present invention to provide a method and a device to refrain from using a fill level control and to evenly fill the spreader device across the entire length.
This objective is solved by means of a method for conveying particulate material during the manufacture of patterns in layers, wherein powder from a reservoir is conveyed into a spreader unit and, if applicable, excess powder fed to the spreader unit is again conveyed back into the reservoir and wherein this conveying takes place in a closed conveying circuit.
In the case of such a method according to the invention, it is now possible for particulate material to be conveyed out of a reservoir into the spreader system and for excess powder to again be conveyed back to the reservoir by means of conveying the particular material in a conveying circuit.
The spreader system is thus filled until it is filled completely and excess particulate material is again fed back directly to the reservoir. This means that the filling runs for a certain (reliable) period and that one can be sure that the spreader device is filled completely. In the event that the spreader device is full, the excess particulate material is simply conveyed back to the reservoir.
Accordingly, pursuant to a first aspect of the present invention, there is contemplated a method for conveying particulate material during the manufacture of patterns in layers, wherein powder is conveyed out of a reservoir into a spreader unit and, if applicable, excess powder fed to the spreader unit is again conveyed back into the reservoir and wherein this conveying takes place in a closed conveying circuit.
The first aspect of the present invention may be further characterized by one or any combination of the features described herein, such as the powder conveying takes place via screw conveyors; the powder conveying takes place via low pressure; the powder conveying of the conveying circuit takes place via an individual conveying systems; the powder conveying of the conveying circuit takes place via a plurality of conveying systems; the powder conveying of the conveying circuit takes place via conveyor belts and/or conveyor cages; the powder conveying out of the reservoir into the spreader system takes place via an ejection system; the conveying circuit conveys excess powder material back into the reservoir after the coating process.
Accordingly, pursuant to a second aspect of the present invention, there is contemplated a device for conveying particulate material during the manufacture of patterns in layers, encompassing a reservoir, a spreader unit and a powder conveying system, wherein at least the reservoir and the spreader unit are contained in a closed conveying circuit.
The second aspect of the present invention may be further characterized by one or any combination of the features described herein, such as provision is furthermore made for an ejection system; the reservoir is arranged below the spreader unit in vertical direction, thus viewed in the direction at right angles to the coating direction, at least during filling process; the powder conveying system encompasses at least one conveyor belt; the powder conveying system encompasses screw conveyors; the powder conveying system encompasses a suction device for low pressure conveying; the ejection system encompasses two covers comprising slits; the ejection system encompasses two tubes located within one another and comprising boreholes, which are arranged so as to be offset; provision is furthermore made for a junction for introducing new powder material into the reservoir.



DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a common method for applying particulate material in layers;
FIG. 2 shows a device according to the invention according to a preferred embodiment;
FIG. 3 shows a device according to the invention according to a further preferred embodiment;
FIG. 4 shows a particularly preferred embodiment of a conveying system;
FIG. 5 shows a further preferred embodiment of a conveying system;
FIG. 6 shows yet a further preferred embodiment of a conveying system;
FIG. 7 shows a preferred embodiment of the ejection system;
FIG. 8 shows a further preferred embodiment of the ejection system according to the invention;
FIG. 9 shows yet a further preferred embodiment of the ejection system;
FIG. 10 shows a further preferred embodiment of a conveying system; and
FIG. 11 shows a refilling device according to a preferred embodiment of the invention.



DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, a closed conveying system thus refers to a system, in the case of which a conveying to the spreader device system takes place and from there also back into the reservoir, if applicable.
According to a preferred embodiment of the present invention, the conveying of powder could take place via screw conveyors.
Apart from this or in addition thereto, it would also be possible for the conveying of powder to take place via low pressure.
A conveying via low pressure can be advantageous in particular when the conveying is to take place in a conveying system, which is closed off from the environment.
In the case of the method according to the invention, it can furthermore be advantageous when the conveying of powder of the conveying circuit takes place via an individual conveying system. The different conveying systems must then possibly not be coordinated.
However, it is also possible for the conveying of powder of the conveying circuit to take place via a plurality of conveying systems in the case of the method according to the invention.
The conveying of the particulate material out of the reservoir into the spreader system and back to the reservoir can take place via all possible conceivable individual or a plurality of conveying methods in the case of a method according to the invention. In addition to screw conveyors and low pressure, this could be conveyor belts and/or conveyor cages, for example.
According to the present invention, it can furthermore also be advantageous when the conveying of powder out of the reservoir into the spreader system takes place via an ejection system.
Such an embodiment of the present invention has thus proven to be particularly advantageous, because an even filling can take place in the spreader system due to the use of the ejection device.
According to a preferred embodiment it can be advantageous in the case of the method according to the invention when the conveying circuit also conveys excess powder material back into the reservoir after the spreading process. If applicable, this excess particulate material from the coating method could also be cleaned before it is conveyed back to the reservoir. A conveying could thus take place through a screen, for example.
The objective of the present invention is further solved by means of a device for conveying particulate material during manufacture of patterns in layers encompassing a reservoir, a spreader unit and a powder conveying system, wherein at least the reservoir and the spreader unit are contained in a closed conveying circuit.
According to a preferred embodiment of the device according to the invention, provision is furthermore made for an ejection system. Such an ejection system can be suitable to attain a particularly even level distribution of the particulate material in the spreader system.
It can be advantageous in particular with reference to the machine geometry when the reservoir in the case of the device according to the invention is arranged below the spreader unit in vertical direction, thus viewed in the direction at right angles to the coating direction, at least during a filling process.
It can furthermore be advantageous for the device according to the invention when the powder conveying system encompasses at least one conveyor belt.
In addition, it would also be possible, however, for the device as a powder conveying system to encompass screw conveyors and/or a suction device for the low pressure conveying.
In the event that the device according to the invention encompasses an ejection system according to a preferred embodiment, it may be advantageous for the ejection system to encompass two covers comprising slits.
In addition, it is also possible for the device to be provided in such a manner that the ejection system encompasses two tubes located within one another and comprising boreholes or slits, which are arranged so as to be offset.
In the event a junction for introducing new powder material into the reservoir is provided according to the invention, the refilling of particulate material into the reservoir is possibly particularly simple and clean.
To elaborate in more detail, the invention will be described in more detail below by means of preferred exemplary embodiments with reference to the drawing.
FIG. 1 generally describes a particulate coating process.
The method according to the invention and the device according to the invention are to be explained in the following in an exemplary manner for the use during the assembling of casting patterns in layers from particulate material, binding material and hardener in the case of a rapid-prototyping method.
In the case of an assembling method of a component, which is described with reference to FIG. 1, such as of a casting pattern, for example, a build platform 9 on which the casting pattern is to be set up, is lowered by a layer thickness of the particulate material 2. Particulate material 2 is subsequently applied from a spreader system 4 onto the build platform 9 in a desired layer thickness.
The selective application of hardener onto areas, which are to be hardened, then takes place between the set-up of the individual layers.
At the onset of the coating process, the spreader system 4 is moved from a starting position across the workpiece platform. This is illustrated in FIG. 1a).
The spreader system 4 now moves across the build platform 9 at a constant speed. It thereby releases particulate material 2 in precisely the correct quantity and creates thin layers 5 of the particulate material 2 on the build platform 9. This is shown in FIG. 1b).
The spreader system 4 is subsequently moved back into the starting position and can be newly filled from a particulate reservoir 1 via a filling device by opening the ejection slider 3. This is shown in FIG. 1c).
The filling of the spreader system 4 via a circuit system according to the invention is illustrated in FIG. 2.
As can be seen from the figure, the particulate material 2 is conveyed out of a reservoir 17, which is located below the level of the movement plane of the spreader device and below the machine table 8, via a first conveying system 12 to a level above the spreader device 4 for this purpose. This means that the reservoir is arranged below the spreader unit in vertical direction, thus viewed in the direction at right angles to the coating direction at least during a filling process.
The particulate material according to the shown preferred embodiment is realized via a shiftable ejection system 15 via a further conveying system 13 (separately or part of the first system). Excess powder is guided back again into the reservoir or into the reservoir chamber 17, respectively, via a bypass system 16.
In the case of the illustrated preferred embodiment of the invention, the component parts of the device, comprising conveying devices 12, 13, reservoir 17, ejection system 15, bypass 16 and spreader device 4 are arranged in a vertical plane parallel to the spreader device in response to the filling process. The advantage of this configuration lies in that excess powder or leakage can flow directly back into the reservoir.
FIG. 3 illustrated a further preferred embodiment of the invention. As can easily be seen in this figure, two openings 19, 18 are arranged in the machine table 8 comprising the build platform 9. A first opening 16 hereby serves for the powder return in the conveying circuit, in the case of which particulate material is conveyed from the reservoir 17 to the spreader device 4 and a second opening 19 for accommodating excess particulate material 11 of the coating process. This powder can have been contaminated by the building process. It can thus be advantageous for it to be discharged into a separate container. In addition, however, it could also be the case that it is directly subjected to a cleaning.
As is shown in FIG. 4, the conveying systems 12, 13 can be embodied according to a preferred embodiment by means of screw conveyors 21, which are embodied in tubes. Likewise, however, it is also possible to use conveyor belts, conveyor belts comprising conveyor cages or vacuum devices.
In the event that screw conveyors are used, it can be advantageous two separate systems 12, 13 are provided. A first screw conveyor takes over the transport of the powder to a level above the spreader device 4. Curved or beveled systems provide advantageous powder absorption from the reservoir 17, are particularly suitable. A second screw conveyor runs horizontally above the spreader device 4. It takes over the transport to the spreader device 4 and to the bypass 16.
For filling, the spreader device 4 moves into a position below the filling system. The coating reservoir is thereby preferably embodied in a funnel-shaped manner. As is illustrated in FIG. 3, only a narrow gap is located in the position between spreader device 4 and ejection system 15.
An ejection system 15 according to the present invention can be operated in all conceivable manners. As an example, two different systems are to be described herein with reference to FIGS. 4, 5 and 6.
For example, an ejection device 15 can be opened according to a method, which is known from the state of the art, in response to a filled transport system and the available powder can thus be shaken off. The conveying device is thereby not active. In the case of this method, a defined powder quantity is refilled into the spreader device. This is illustrated in FIG. 7 using reference numeral 20. Level differences within the spreader device, which are created during the building process, can only be compensated to a limited extent in the case of this type of operation. Such a filling is called impact filling.
According to a preferred embodiment of the present invention, the spreader device can be filled in that the ejection device 15 is opened and the conveying system 12, 13 is activated. As is illustrated in FIG. 5, the spreader device 4 is filled with particulate material 2 in transport direction of the transport device. In the case of an excessive filling time, excess powder falls past the spreader device 4 and back into the reservoir 6. This is illustrated in FIG. 6 by means of reference numeral 24. It would furthermore also be possible for the excess powder to be fed back to the powder circuit via the bypass opening 16. This is illustrated by means of reference numeral 22 in FIG. 5. Such a filling is called level filling.
An advantage of such a level filling is that, in connection with the circuit system, the filling can take place without a sensor. Due to the fact that a resupply can on principle take place without any disadvantages for any amount of time in the case of a completely filled spreader device, no particular actions must be taken to protect all involved aggregates. The fill level can be secured via a simple preselection of the filling period.
A further advantage lies in the even filling across the length of the spreader device.
In many cases, the fill level can change across the length during the building process due to uneven powder outflow out of the spreader device. An even refilling can be guaranteed in the case of each refilling by means of the level filling.
According to a preferred embodiment of the invention shown in FIG. 7, the ejection device is embodied as a cover system. In the case of such an embodiment, two thin disks 25, 26 comprising boreholes 29 or slits are used in the ejection system. The hole pattern of the one disk corresponds to the second hole pattern, but is shifted to one another. Powder can escape 28 in the event that the disks are moved against one another 27 so that the hole patterns coincide. Gravity forces it to flow into the spreader device.
The embodiment of such a system can be as a rectangular tube, for example, wherein the underside encompasses a hole pattern. An additional displaceable disk comprising a hole pattern completes the system.
An embodiment of the ejection system, in the case of which the described hole patterns are realized on two tubes 31, 32, which run into one another, is particularly preferred. Such an embodiment can be seen in FIG. 8. In the case of this system, the opening for the powder discharge is attained by means of rotating the tubes against one another. The inner tube 31 encompasses a row of boreholes 29A at the lowermost location. The system is open in the event that the row of boreholes 29B of the outer tube 32 is also brought into this position.
A tube cover system comprising a screw conveyor 21 in the interior is furthermore particularly preferred. The above-described level filling can be realized in a particularly advantageous manner by means of such a system.
The afore-described systems can be activated in different manners. According to a preferred embodiment, pneumatic electromagnetic and hydraulic actuators 33 are suitable. See FIG. 9.
In addition, provision can be made in the powder circuit for a connection for fresh powder. This is illustrated in FIG. 10. Such a fresh powder connection 14 is advantageously connected to one of the already necessary conveying systems 12, 13.
The advantage as compared to the simple refilling into the reservoir 6 lies in the constructively possible lower dust exposure for the user.
A system, in the case of which closed powder kegs 36 are placed onto a connecting spigot comprising a funnel tube 14 and supply the system with fresh powder is particularly preferred.
As is illustrated in FIG. 11 in an exemplary manner, the kegs can be provided with a membrane 38, which is opened only when placed onto the funnel 37. Plastic, metal or paper are suitable as membrane substances.
The method according to the invention thus uses a powder circuit for filling purposes, which makes it possible to fulfill the posed demands. Powder loss can be avoided by means of the embodiment of the powder conveyance in a circuit-like manner. A return of excess powder makes it possible to fill the spreader device carriage at high speed to an even level. A refilling device, which provides for a low-dust refilling, can be used at the circuit. On the one hand, this benefits the safety and the comfort of the user and, on the other hand, the explosion protection requirements.

## Claims

1. An apparatus for the manufacture of a three dimensional object in layers comprising
i) a device for conveying a particulate material during the manufacture of the object in layers, wherein the devise comprises
a) a reservoir,
b) a spreader unit, and
c) a plurality of particulate material conveying systems including a first particulate material conveying system and a second particulate material conveying system; and

ii) a build platform on which the object is built;
wherein
the first particulate material conveying system conveys the particulate material from the reservoir to the spreader;
the spreader is adapted for being filled with the particulate material, releasing the particulate material while moving over the build platform, and spreading the particulate material over the build platform; and
the second particulate material conveying system conveys excess particulate material that was fed to the spreader back to the reservoir;
so that at least the reservoir and the spreader unit are contained in a closed conveying circuit.

2. The apparatus according to claim 1, wherein provision is furthermore made for an ejection system.

3. The apparatus according to claim 1, wherein the reservoir is arranged below the spreader unit in a vertical at least during a filling process.

4. The apparatus according to claim 1, wherein the particulate material conveying system comprises at least one conveyor belt.

5. The apparatus according to claim 1, wherein the particulate material conveying system comprises screw conveyors.

6. The apparatus according to claim 1, wherein the particulate material conveying system comprises a suction device for low pressure conveying.

7. The apparatus according to claim 2 wherein the ejection system comprises two covers comprising slits.

8. The apparatus according to claim 2 wherein the ejection system comprises two tubes located within one another and comprising boreholes, which are arranged so as to be offset.

9. The apparatus according to claim 1, wherein a provision is furthermore made for a junction for introducing a new particulate material into the reservoir.

10. The apparatus according to claim 1, wherein the reservoir is maintained in a fixed position and the spreader unit is movable relative to the reservoir.

11. The apparatus according to claim 1, wherein the build platform is movable in the vertical direction.

12. An apparatus for the manufacture of a three dimensional object in layers comprising
i) a first device for conveying a particulate material during the manufacture of the object in layers, wherein the devise comprises
a) a reservoir,
b) a spreader unit, and
c) a plurality of particulate material conveying systems including a first particulate material conveying system and a second particulate material conveying system, wherein the particulate material conveying system comprises screw conveyors; and

ii) a build platform on which the object is built;
the first device includes a junction for introducing new particulate material into the reservoir;
the first particulate material conveying system conveys the particulate material from the reservoir to the spreader;
the spreader is adapted for carrying the particulate material, releasing the particulate material while moving over the build platform, and spreading the particulate material onto the build platform; and
the second particulate material conveying system conveys excess particulate material that was fed to the spreader back to the reservoir;
so that at least the reservoir and the spreader unit are contained in a closed conveying circuit.

13. The apparatus according to claim 12, wherein
the reservoir is maintained in a fixed position and the spreader unit is movable relative to the reservoir; and
the build platform is movable in the vertical direction.

14. An apparatus for the manufacture of a three dimensional object in layers comprising
i) a first device for conveying a particulate material during the manufacture of the object in layers, wherein the devise comprises
a) a reservoir,
b) a spreader unit, and
c) a plurality of particulate material conveying systems including a first particulate material conveying system and a second particulate material conveying system, wherein the particulate material conveying systems comprises at least one conveyor belt;

ii) a build platform on which the object is built
the first device includes a junction for introducing new particulate material into the reservoir;
the first particulate material conveying system conveys the particulate material from the reservoir to the spreader;
the spreader is adapted for being filled with the particulate material, releasing the particulate material while moving over the build platform, and spreading the particulate material onto the build platform; and
the second particulate material conveying system conveys excess particulate material that was fed to the spreader back to the reservoir;
so that at least the reservoir and the spreader unit are contained in a closed conveying circuit.

15. The apparatus according to claim 14, wherein
the reservoir is maintained in a fixed position and the spreader unit is movable relative to the reservoir; and
the build platform is movable in the vertical direction.

16. The apparatus of claims 1, wherein the build platform is movable in the vertical direction by a layer thickness of one of the layers.

17. The apparatus of claim 16, wherein the apparatus includes an ejection system for evenly refilling the spreader unit with the particulate material.

18. The apparatus of claim 17, wherein the ejection system includes a pair of tubes that rotate against one another two provide an opening for discharge of the particulate material into the spreader unit.

19. The apparatus of claim 16, wherein the reservoir is maintained in a fixed position and the spreader unit is movable relative to the reservoir.

20. The apparatus of claim 16, wherein the apparatus includes an opening for removing the particulate material from the apparatus.

21. The apparatus of claim 16, wherein the apparatus includes an opening for recovering excess particulate material during a filling of spreader unit.