ACTIVE AIR CONDITIONING IN SLM PROCESSES

Abstract

An apparatus for carrying out a method for producing an object using selective powder melting and by building up layers of powder material. The apparatus includes a build chamber configured to accommodate the object being produced and a powder delivery device equipped with a powder storage container and configured to supply material powder into the build chamber, a powder layer preparation unit to prepare successive layers of the supplied material powder on a substrate arranged in the build chamber, an irradiation device configured to irradiate a prepared powder layer to thereby melt the prepared powder layer locally, and a protective gas circulation device configured to circulate a protective gas present in the build chamber. At least one air conditioning device is also included and is configured to condition one or more of a temperature or a humidity of the protective gas circulated by the protective gas circulation device.

Claims

1. An apparatus for carrying out a method for producing an object according to the process of selective powder melting, by building up layers of powder material, the apparatus comprising: a build chamber configured to accommodate the object being produced; a powder delivery device equipped with a powder storage container and configured to supply material powder into the build chamber; a powder layer preparation unit configured to prepare successive layers of the supplied material powder on a substrate arranged in the build chamber (102); an irradiation device configured to irradiate a prepared powder layer and thereby melt the prepared powder layer locally; a protective gas circulation device configured to circulate a protective gas present in the build chamber; and at least one air conditioning device configured to condition, in an air conditioning operation, one or more of a temperature or a humidity of the protective gas circulated by the protective gas circulation device.

2. The apparatus of claim 1, wherein the protective gas circulation device is further configured to maintain an overpressure in the build chamber.

3. The apparatus of claim 1, wherein the air conditioning device comprises a cooling unit for cooling the protective gas.

4. The apparatus of claim 3, wherein the cooling unit is assigned a condensate discharge system configured to discharge condensate produced due to the cooling of the protective gas.

5. The apparatus of claim 1, further comprising a powder return for returning unmelted material powder to the powder storage container, wherein the powder return forms part of the powder delivery device.

6. The apparatus of claim 1, wherein the powder delivery device further comprises at least one filter device for the material powder.

7. The apparatus of claim 1, further comprising a powder extraction device configured to extract material powder remaining in the build chamber, the powder extraction device comprising a circulating pump for extracting the material powder remaining in the build chamber, wherein a flow of protective gas driven by the circulating pump conveys the remaining material powder through a separator.

8. The apparatus of claim 1, wherein the air conditioning device comprises a control unit configured to adapt parameters of the air conditioning operation.

9. The apparatus of claim 8, further comprising at least one sensor unit which is operatively coupled to the control unit of the air conditioning device and is configured to supply data relating to at least one process parameter of the apparatus.

10. The apparatus of claim 9, wherein the at least one process parameter includes one or more of (A) a temperature or (B) a relative or absolute humidity of the protective gas.

11. The apparatus of claim 1, wherein the at least one air conditioning device is at least partially arranged in the build chamber, in order to condition the protective gas therein.

12. The apparatus of claim 1, wherein the at least one air conditioning device is at least partially arranged in the powder storage container in order to condition the protective gas therein.

13. The apparatus of claim 1, wherein the at least one air conditioning device is at least partially arranged in a gas line which is part of the protective gas circulation device in order to condition the protective gas therein.

14. The apparatus of claim 1, wherein the at least one air conditioning device is at least partially arranged in a gas or powder line which is part of the powder delivery device in order to condition the protective gas therein.

15. The apparatus of claim 1, wherein the at least one air conditioning device is at least partially arranged in in a gas line which is part of the powder extraction device in order to condition the protective gas therein.

16. The apparatus of claim 3, wherein the cooling unit comprises a heat exchanger.

17. The apparatus of claim 16, wherein the heat exchanger comprises a counter-flow heat exchange.

18. The apparatus of claim 7, wherein the separator comprises a cyclone separator.

Description

[0021] Further features and advantages of the present invention will become even clearer from the following description of an embodiment, when said embodiment is considered together with the accompanying drawings, in which:

[0022] FIG. 1 is a schematic illustration of a protective gas circulation device in an embodiment of an apparatus according to the invention;

[0023] FIG. 2 is a schematic illustration of a powder extraction device in an embodiment of an apparatus according to the invention;

[0024] FIG. 3 is a schematic illustration of a powder supply device in an embodiment of an apparatus according to the invention; and

[0025] FIG. 4 is a schematic illustration of a possible embodiment of an air conditioning device from the apparatus of FIGS. 1 to 3.

[0026] A schematic illustration of an embodiment of an apparatus according to the invention is shown in a cross-sectional view in each of FIGS. 1 to 3, and is designated as a whole by reference sign 100. Different circuits are shown in FIGS. 1 to 3, but these are used in the same apparatus 100 and have only been divided between FIGS. 1 to 3 for reasons of clarity.

[0027] The apparatus 100 comprises a build chamber 102 which accommodates an object G being produced, which object is produced by the method of selective powder melting by building it up in layers from a powder material P, wherein a protective atmosphere with elevated pressure prevails in the build chamber 102.

[0028] The irradiation device used to produce the object G is not shown in FIGS. 1 to 3, for reasons of clarity; however, a powder layer preparation device 104 is provided in the build chamber 102, and is configured to prepare sequential layers of supplied material powder P on a substrate 106 arranged in the build chamber 102.

[0029] This substrate 106 is accommodated in the build chamber 102 in a manner allowing height adjustment by a lifting device 108, which is shown in rough, schematic form. In the state shown in FIG. 1, it is presently held at such a height that the powder P prepared by the powder layer preparation device 104 is spread out at a suitable level for a subsequent, further irradiation step which serves the purpose of building up a further layer of the object G.

[0030] Furthermore, FIG. 1 shows a protective gas circulation device 110 in which a protective gas flow is driven by a circulating pump 112, which flow is indicated schematically by the arrows S. The protective gas circulated by the protective gas circulation device 110 is maintained at an overpressure relative to the environment of the apparatus 100, and the protective gas circulation device 110 removes flue gas and spatter particles from the build chamber 102. These can be collected in a filter 114 through which the gas to be circulated passes in the circulation device 110.

[0031] Since heat is introduced into the build chamber 102 as a result of the process during operation of the irradiation device (not shown), the protective gas circulating in the apparatus 100 will inevitably heat up—this also applies to numerous other components of the apparatus 100. Since such heating of components of the apparatus 100 will lead to a thermal expansion of these components, the accuracy of the production process of the object G in the apparatus 100 can suffer as a result. Because of this, cooling of various components, such as individual components of the irradiation device itself, is known in the prior art. Furthermore, it has been shown that moisture remaining in the protective gas or the material powder can also lead to deterioration of the objects G produced in the apparatus 100.

[0032] According to the invention, the apparatus 100 of FIGS. 1 to 3 therefore comprises at least one of the air conditioning devices described below in conjunction with FIG. 4, which can first of all be provided at various positions in the apparatus 100 of FIG. 1, for example in the protective gas circulation device 110 behind the circulating pump, i.e. at the position indicated with P1, at a position P2 inside the protective gas circulation device 110, in front of the filter 114, or directly assigned to the build chamber 102, i.e. at position P3. In this case, position P1 is preferred to position P2, since the protective gas flow at position P1 is better suited for cooling operation than at position P2, where the protective gas flow can still contain impurities that could damage the air conditioning device.

[0033] Furthermore, at least one sensor unit can be operationally assigned to the air conditioning device, which unit, in a known manner, supplies data regarding at least one process parameter, for example a temperature and/or a relative humidity or absolute humidity of the protective gas, to a control unit (not shown) of the air conditioning device so as to establish a control loop. This at least one sensor unit can also be provided at one of the three positions P1 to P3 within the apparatus 100, for example.

[0034] FIG. 2 now shows a powder extraction device 120 which also forms part of the apparatus 100. By means of this powder extraction device 120, after the end of the production process of the object G, an operator can extract remaining material powder P in the build chamber 102 that was not melted during the production process, and return it to a powder storage container 122. In order to illustrate that in FIG. 2 the production process of the object G is substantially complete, in the state shown there the lifting device 108 has raised the substrate 106 into an upper stop position, and the object G is now ready to be removed from the build chamber 102.

[0035] For the process of extracting the remaining powder, on the one hand an extraction hose 124 is provided inside the build chamber 102 and can be guided by the operator from outside the build chamber 102 to the material powder P to be extracted, and on the other hand, a circulating pump 126 is provided which draws protective gas from the build chamber 102 and thus generates a gas flow which results in the extraction of the material powder P. The material powder extracted in this way and following the arrow F is guided through a cyclone separator 128 in which it is separated from the gas flow and collects in the powder storage container 122.

[0036] A filter 130 can also be assigned to the powder extraction device 120, as can at least one of the air conditioning devices described below in connection with FIG. 4, which accordingly can also be provided at further positions P4 and P5 inside the powder extraction device 120, in addition to position P3 inside the build chamber 102 as mentioned above, wherein position P5 again is preferred to position P4 since already-filtered protective gas arrives at it, or at position P6 within the powder storage container 122.

[0037] FIG. 3 also shows a schematic illustration of the powder supply device 200 of the apparatus 100 according to the invention. Here again, the build chamber 102 is shown with the powder layer preparation device 104 provided therein, and with an irradiation device (not shown).

[0038] In the build chamber 102, an object G made of a material powder P has also already been built up on the substrate 106, but the production of the object G is not yet fully completed, analogously to FIG. 1, so that the lifting device 108 again holds the substrate 106 at the height shown in FIG. 1.

[0039] In addition to a powder storage container 212, which can be identical to the powder storage container 122 already mentioned above, and a cyclone separator 214, the powder delivery device 200 also includes an ultrasonic sieve 215 for sieving the material powder to be supplied, a buffer container 216 with an associated screw conveyor 217 for the sieved material powder, and a loading unit 218 which ultimately feeds the material powder supplied by the screw conveyor 217 from below into the build chamber 102, where it is then prepared by the preparation device 104 for a subsequent irradiation step.

[0040] Furthermore, the powder delivery device 200 comprises a powder return 219 through which material powder that has not been melted in an irradiation process can be transferred back to the powder storage container 212, and consequently, in a subsequent step of re-supply into the build chamber 102, after again passing through the cyclone separator 214, the ultrasonic sieve 215, the buffer tank 216 and the screw conveyor 217, is guided again into the build chamber 102 by the loading unit 218. In addition, the powder storage container 212 is assigned a refilling device 212a through which material powder can be fed into the powder storage container 212 during ongoing operation of the device 200.

[0041] The powder delivery device 200 is again coupled to a protective gas circulation device 220, specifically in such a way that the protective gas circulated by a circulating pump 222, the flow of which is indicated by the arrow S, carries the material powder which is conveyed by a screw conveyor 212b out of the powder storage container 212, as indicated by the arrow F, to the cyclone separator 214.

[0042] At least one air conditioning device as shown in FIG. 4 can also be provided in the powder delivery device 200 of FIG. 3 to condition the protective gas, it being possible for this air conditioning device to be likewise provided at different points in the powder delivery device 200—for example, also at a point P6 in the powder storage container 212 or a point P3 inside the build chamber 102.

[0043] In addition to these possible positions for the air conditioning device already mentioned above in conjunction with FIGS. 1 and 2, it could also be located in FIG. 3 in the region of the ultrasonic sieve 215 at a position P7, at a position P8 assigned to the buffer container 216, or at a position P9 assigned to the loading device 218 or the powder return 219.

[0044] Again, the positions P1 to P9 mentioned can also or alternatively serve as installation positions for at least one sensor unit for detecting at least one process parameter, for example the temperature and/or the moisture content of the protective gas.

[0045] A possible embodiment of an air conditioning device is shown schematically in FIG. 4, indicated overall by reference sign 300. In this case, warm and humid protective gas is fed into a counter-flow heat exchanger 306 at a point 302, and temperature-controlled, dry protective gas is removed from this heat exchanger 306 again at point 304 after the heat exchanger has undertaken a first pre-cooling of the warm and humid protective gas according to the counter-flow principle.

[0046] The heat exchanger 306 is also assigned a cooling circuit 314 coupled via a cooling unit 312, as is known from the prior art, in which cooling circuit a heated coolant is initially compressed and heated at point 316 by a compressor 318, and then cooled by a cooler 320 and liquefied. Subsequently, the cooled coolant is decompressed by a throttle 322 and is thereby cooled considerably further. With the coolant thus cooled acting on the pre-cooled protective gas flow at point 324, the latter also cools down and can be sent to point 304 as a dry and cold gas flow, and moisture originally present therein will condense in the region of the cooling unit 312. This condensed moisture can be removed from the air conditioning device 300 by a condensate drainage system 326, which is also known from the prior art, without protective gas being able to escape from the apparatus or gas from outside being able to penetrate the apparatus.

[0047] The protective gas flow can be conditioned in this way, and this is carried out by the heat exchanger 306 and the cooling unit 312, which consequently act together as a cooling unit within the meaning of the present invention. Process parameters, such as the temperature or the cooling power of the coolant of the cooling circuit, can be adjusted by a control device (not shown) of the air conditioning device 300, for example, using sensor units supplying the above-mentioned sensor data. By way of example, an increased detected temperature of the protective gas at one of the measuring points can lead to the control unit of the air conditioning device increasing the cooling power of the cooling circuit.

[0048] The active air conditioning of protective gases in apparatuses for carrying out a method for producing an object using the process of selective powder melting, as described here, allows excellent adjustment of the relevant process parameters of temperature and humidity of the protective gas inside the build chamber 102, and thus makes it possible to achieve improved accuracy and increased efficiency of the production process.