Active atmosphere control in the SLM process

Abstract

The present invention relates to an apparatus (100) for carrying out a method for fabricating an object (G) from a powdered material (P) by layer-by-layer construction according to a selective powder fusion technique, the apparatus comprising: a fabrication chamber (102) configured to accommodate the object (G) to be fabricated; a powder supply device (200) with a powder stock container (212) configured to supply material powder (P) to the fabrication chamber (102); a powder layer preparation device (104) configured to prepare overlapping layers of the supplied material powder (P) on a support (106) arranged in the fabrication chamber (102); an irradiation device configured to irradiate the last prepared powder layer and thereby locally melt it; and a shielding gas circulation device configured to circulate a shielding gas present in the fabrication chamber (102). According to the present invention, the apparatus (100) further comprises at least one atmosphere conditioning device configured to atmospherically condition the temperature and / or humidity of the shielding gas circulated by the shielding gas circulation device during an atmosphere conditioning operation.

Description

[Technical field]

[0001] The invention relates to an apparatus for carrying out a method for producing an object from a powdered material by layer-by-layer construction according to a technique of selective powder fusion, the apparatus comprising a construction chamber configured to accommodate the object to be produced, a powder supply device with a powder stock container configured to supply material powder to the construction chamber, a powder layer preparation unit configured to prepare overlapping layers of the supplied material powder on a support arranged in the construction chamber, an irradiation device configured to irradiate and thereby locally melt the last prepared powder layer, and a shielding gas circulation device configured to circulate a shielding gas present in the construction chamber.

[0002] The present invention particularly relates to an apparatus for producing shaped bodies according to the principle of selective laser melting or selective laser sintering.For the prior art related to the field of selective laser melting, see DE 19905067 A1, DE 10112591 A1, WO 98 / 24574 A1, DE 102009038165 A1, DE 102012221641 A1, EP 2052845 A1, DE 102005014483 A1, WO 2017 / 084781 A1.

[0003] It is known that using the method of selective laser melting, shaped bodies, such as machine parts, tools, prosthetics, decorative objects, etc., can be produced by layer-by-layer formation from metallic or ceramic material powder in accordance with the geometric shape specification data of the corresponding shaped body, in which during the production process, multiple powder layers are deposited one on top of the other, and before depositing the next powder layer, each powder layer is heated by a focused laser beam in predetermined areas corresponding to selected cross-sectional areas of the shaped body model, so that the material powder is melted in the irradiated areas and connected into hardened parts.

[0004] In this case, the laser beam is guided to the respective powder layer in accordance with the geometric specification data of the selected cross-sectional area of ​​the shaped body or, if appropriate, data derived therefrom.

[0005] In such processes of selective laser melting, the material powder is applied as a generally binder-free and flux-free, metallic, ceramic or mixed metal / ceramic material powder and heated to its melting temperature by a laser beam whose energy is selected, on the one hand, in order to melt the material powder as completely as possible over its entire layer thickness at the location where the laser beam hits, but on the other hand, in order to avoid such an amount of heat entering the powder that adjacent areas of the powder would also be melted, which would result in a decrease in the precision of the production process and an undesirably large wall thickness of the object to be produced.

[0006] Over the zone of interaction between the laser beam and the material powder, an inert shielding gas atmosphere, for example an argon atmosphere, is generally maintained, having a pressure higher than the ambient pressure, in order to preclude oxidation of the material or other undesirable chemical reactions between the material and the molecules of the atmosphere, and also to prevent the ingress of air from the surroundings. The shielding gas used for this is filtered in a gas circulation process and fed back into the production chamber.

[0007] In some circumstances, furthermore, in order to remove residual moisture remaining in the shielding gas or in the material powder from the shielding gas atmosphere, for example in EP 2 992 986 A1 it is proposed to use a purely passive gas drying device, in which silica gel is present, for example, in a stock container in the gas exchange section with the shielding gas atmosphere, which removes the moisture from the shielding gas in a known manner. Furthermore, WO 2017 / 220744 A1 proposes to provide a drying gas flow by means of a separate gas system, which is guided through the preparation chamber in order to absorb moisture from the top layer of material powder.

[0008] However, it has become apparent that the two proposed drying devices are either inflexible in that they operate solely passively or uncontrolled and therefore do not allow the setting of predetermined process parameters of the shielding gas atmosphere, or they are costly and component intensive due to the inclusion of components for generating the drying gas flow.

[0009] It also became clear that the heating of the shielding gas, which always occurs due to the effect of the laser beam, is not eliminated by the two proposed drying devices and can therefore further lead to a thermal expansion of all components in the production chamber.

[0010] Such fluctuating process parameters of the humidity and temperature of the shielding gas are associated with a decrease in process stability and component quality, since moisture in the fabrication chamber makes powder transport and processing much more difficult, for example by reducing the flowability of the fabrication chamber, its stratification and its distribution, and even preventing powder transport into the fabrication chamber, which can further lead to the formation of agglomerates and decomposition of water from residual moisture in the atmosphere, which in extreme cases can lead to uncontrollable explosions and flying particles, or at least to a worse surface quality of the fabricated components.

[0011] The object of the present invention is therefore to develop an apparatus of the type mentioned at the beginning for carrying out a process of selective powder fusion in such a way that constant process conditions can prevail in the production chamber, which can lead to improved component quality and higher efficiency in the flow and production of the corresponding objects.

[0012] To solve this problem, the apparatus according to the present invention has at least one atmospheric conditioning device configured to atmospherically condition the shielding gas circulated by the gas circulation device with respect to its temperature and / or its humidity in the atmospheric conditioning operation, which not only eliminates the above-mentioned drawbacks of the prior art, but also contributes to a reduction in the cooling capacity required for other machine components, such as optical components of the irradiation device, and to a faster cooling of the hot powder, which in itself can increase the process speed in producing the object, thereby increasing the efficiency of the apparatus.

[0013] Furthermore, in the device according to the invention, the shielding gas circulation device can be configured in such a way that a positive pressure is maintained in the preparation chamber. Maintaining a constant positive pressure is also an operating parameter that can positively influence the resulting part quality, the positive pressure being set to prevent, in particular, the ingress of air from the surroundings.

[0014] According to the invention, the atmospheric conditioning device of the device according to the invention may comprise a cooling unit for cooling the shielding gas, in particular a heat exchanger, more particularly a counterflow heat exchanger, so that a high energy efficiency of the atmospheric conditioning device is achieved in a known manner in its atmospheric conditioning operation. In such a counterflow heat exchanger, the shielding gas already cooled in the first cooling stage is fed in a counterflow to the shielding gas to be cooled, so that a thermal coupling between the two gas flows is formed.

[0015] In order to allow atmospheric regulation of both the temperature and the water content of the shielding gas, the cooling unit may be associated with a condensate discharge system that is configured to discharge condensate resulting from the cooling of the shielding gas, where it should be noted that the condensate discharge system must be capable of discharging the condensate from the apparatus without pressure loss; suitable discharge systems for this are known to those skilled in the art from the prior art.

[0016] Furthermore, the apparatus according to the invention may include a powder return device for returning unmelted powder of material to the powder stock container, the powder return device forming part of the powder feeding apparatus.

[0017] Alternatively or additionally, the powder feed device may further advantageously comprise at least one filter device for the material powder.The device according to the invention may further comprise a powder suction device which is arranged for suctioning the material powder remaining in the preparation chamber and for this purpose comprises a circulation pump, the flow of shielding gas swept by the circulation pump carrying the remaining material powder through a separator, in particular a cyclone separator.

[0018] Although various devices are conceivable for directing the atmosphere adjustment operation of the atmosphere adjustment device, for example for directing intermittent operation with a predetermined cycle time based on other process parameters, for example exposure time, in a preferred embodiment the atmosphere adjustment device may include a control unit configured to adapt the parameters of the atmosphere adjustment operation, which may be integrated into a higher-level control unit controlling other processes of the flow of the production of the object or may be connected thereto for data exchange during operation.

[0019] In another preferred embodiment, the above-mentioned device may include at least one sensor unit that is operatively connected to a control unit of the atmosphere conditioning device and configured to provide data on at least one process parameter of the device. The sensor unit may measure, for example, the temperature or humidity of the shielding gas at a suitable point in the shielding gas circulation device and output corresponding data to the control unit, thereby forming a closed control loop for this at least one process parameter or one or more process parameters derived therefrom, which allows the control unit to set a time-optimized operation and the corresponding process parameter as accurately as practical. As already indicated, the at least one process parameter may therefore include the temperature and / or the relative or absolute humidity of the shielding gas.

[0020] In the apparatus according to the invention, the at least one atmospheric conditioning device can be provided in very different positions, but it can, for example, be arranged at least partially in the production chamber, or in the powder stock container, or in a gas line belonging to a shielding gas circulation device, or in a gas line or powder line belonging to a powder circulation path, or in a gas line belonging to a powder suction device, so that the shielding gas present there is atmospherically conditioned.

[0021] Other features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention when considered in conjunction with the accompanying drawings. [Brief description of the drawings]

[0022] [Figure 1] 1 is a schematic diagram of a shielding gas circulation device in an embodiment of the apparatus according to the present invention. [Diagram 2] 1 is a schematic diagram of a powder inhalation device in an embodiment of the device according to the present invention. [Diagram 3] FIG. 2 is a schematic diagram of a powder feeding device in an embodiment of the device according to the invention; [Figure 4] FIG. 4 is a schematic diagram of a possible embodiment of an atmosphere conditioning device for the apparatus of FIGS. 1 to 3.

[0023] 1-3 each show a schematic diagram of an embodiment of an apparatus according to the present invention in cross-section and is generally designated by the reference numeral 100. Here, different circuits are shown in each of FIGS. 1-3 which are used in the same apparatus 100 and which have been separated into FIGS. 1-3 for clarity.

[0024] The apparatus 100 includes a fabrication chamber 102 housing an object G to be fabricated, the object G being fabricated from a powdered material P by layer-by-layer construction according to a selective powder melting technique, the fabrication chamber 102 being occupied by a shielded atmosphere having a high pressure.

[0025] The irradiation device used to prepare the target object G is not shown in Figures 1 to 3 for the sake of clarity, but the preparation chamber 102 is provided with a powder layer preparation device 104, which is configured to prepare successive layers of material powder P to be supplied to a support 106 arranged in the preparation chamber 102.

[0026] The support 106 is accommodated in the production chamber 102 so as to be movable in the vertical direction by a roughly illustrated lifting device 108, and in the state shown in FIG. 1, the support 106 is held at a height such that the powder P currently prepared by the powder layer preparation device 104 is spread to an appropriate level for a subsequent irradiation step to form another layer of the target G.

[0027] 1 further shows a shielding gas circulation system 110 in which a circulation pump 112 drives a flow of shielding gas, indicated generally by arrows S. Here, the shielding gas circulated by the shielding gas circulation system 110 is maintained at a positive pressure relative to the surroundings of the apparatus 100, and the shielding gas circulation system 110 exhausts smoke and splash particles from the production chamber 102, where they can be captured in a filter 114 through which the gas circulated in the circulation system 110 passes.

[0028] In operation of the irradiation device, not shown, the heat generated by the process is introduced into the production chamber 102, which inevitably leads to heating of the shielding gas circulating in the device 100, and also of many other components of the device 100. Such heating of the components of the device 100 leads to their thermal expansion, which affects the accuracy of the production process of the object G in the device 100, and for this reason it is known from the prior art to cool various components, for example individual parts of the irradiation device themselves. Furthermore, it has been found that moisture remaining in the shielding gas or in the material powder can likewise lead to a deterioration of the object G produced in the device 100.

[0029] According to the invention, the apparatus 100 of Figures 1-3 therefore includes at least one atmospheric conditioning device, which will be further explained below in connection with Figure 4, which can be arranged in different positions in the apparatus 100 of Figure 1, for example in the shielding gas circulation device 110 after the circulation pump, i.e. in the position indicated by P1, in the shielding gas circulation device 110 in front of the filter 114 in position P2, or even directly in the preparation chamber 102, i.e. in position P3. Here, position P1 is preferred over position P2, since due to the preceding filter, the shielding gas flow in position P1 is more suitable for the cooling operation than position P2, where the shielding gas flow may still contain impurities that may damage the atmospheric conditioning device.

[0030] Furthermore, the atmospheric conditioning device can be associated in operation with at least one sensor unit, which in a known manner supplies data on at least one process parameter, for example the temperature and / or the relative or absolute humidity of the shielding gas, to a control unit (not shown) of the atmospheric conditioning device in order to enable the formation of a control loop. This at least one sensor unit may also be provided, for example, at one of the three positions P1-P3 in the device 100.

[0031] 2 shows a powder suction device 120 which also forms part of the apparatus 100. By using this powder suction device 120, the operator can suck the material powder P which is not melted during the production process and which still remains there after the production process of the object G in the production chamber 102 and return it to the powder stock container 122. In order to clearly show that the production process of the object G is substantially completed in FIG. 2, in the state shown there, the support 106 has been raised by the lifting device 108 to an upper abutment position and the object G is prepared for its removal from the production chamber 102.

[0032] For the suction process of the remaining powder, on the one hand, a suction hose 124 is provided in the preparation chamber 102, which can be guided by the operator from outside the preparation chamber 102 to the material powder P to be sucked in, and on the other hand, a circulation pump 126 is provided, which sucks in shielding gas from the preparation chamber 102, so that a gas flow is formed which causes the suction of the material powder P. The material powder thus sucked in and following the arrow F is guided through a cyclone separator 128, in which it is separated from the gas flow and collected in the powder stock container 122.

[0033] The powder aspirator 120 may likewise be associated with a filter 130 and at least one atmospheric conditioning device, which will be further described below in connection with FIG. 4, and which may therefore be provided in addition to the already mentioned position P3 in the preparation chamber 102, also at other positions P4 and P5 in the powder aspirator 120, or at a position P6 in the powder stock container 122, with position P5 again being preferred over position P4, since at position P5 already filtered shielding gas enters.

[0034] 3 further shows a schematic diagram of a powder feeding device 200 of the apparatus 100 according to the invention. Here again, a production chamber 102 is shown with a powder layer preparation device 104 arranged therein and an irradiation device (not shown).

[0035] In the preparation chamber 102, the object G has likewise already been formed from the material powder P on the support 106, and like in FIG. 1, the preparation of the object G has not yet been fully completed, so the lifting device 108 likewise holds the support 106 at the height shown in FIG. 1.

[0036] In this embodiment, the powder feeding device 200 comprises, in addition to a powder stock container 212, which may be the same as the powder stock container 122 already mentioned above, a cyclone separator 214, and further comprises an ultrasonic sifter 215 for sifting the material powder to be fed, a buffer container 216 with an associated screw conveyor 217 for the sifted material powder, and a loading unit 218 for finally depositing the material powder fed by the screw conveyor 217 from below into the preparation chamber 201, where it is then prepared by the preparation device 104 for the subsequent irradiation step.

[0037] The powder feeding device 200 further comprises a powder return section 219, through which the material powder not melted in the irradiation process can be conveyed back to the powder stock container 212 and thus fed again to the production chamber 102 by a loading unit 218, after passing again through a cyclone separator 214, an ultrasonic sieve 215, a buffer container 216 and a screw conveyor 217, in a subsequent step of feeding again to the production chamber 102. Furthermore, a top-up device 212a is associated with the powder stock container 212, by means of which material powder can be added to the powder stock container 212 during operation of the device 200.

[0038] The powder feeder 200 is again connected to a shielding gas circulation system 220, and in such a manner that the shielding gas, circulated by a circulation pump 222 and whose flow is indicated by arrow S, transports the material powder pumped out of the powder stock container 212 by the screw conveyor 212b to the cyclone separator 214, as indicated by arrow F.

[0039] In order to regulate the shielding gas atmosphere, the powder feeding apparatus 200 of FIG. 3 may also be provided with at least one atmospheric conditioning device as shown in FIG. 4, which may again be provided at different locations in the powder feeding apparatus 200, for example at point P6 in the powder stock container 212 or at point P3 in the preparation chamber 102.

[0040] In addition to these possible positions for the atmospheric conditioning device, already mentioned further above in connection with Figures 1 and 2, the atmospheric conditioning device can also be arranged in Figure 3 in the region of the ultrasonic sieve 215 at position P7, in the region of position P8 associated with the buffer container 216, or at position P9 associated with one of the loading device 218 or the powder return section 219.

[0041] The abovementioned positions P1 to P9 may also or alternatively be used as mounting positions for at least one sensor unit which detects at least one process parameter of the shielding gas, for example the temperature and / or the moisture content.

[0042] Finally, one possible embodiment of the atmosphere conditioning device is shown diagrammatically in Figure 4 and is most generally designated by the reference numeral 300. Here, hot and moist shielding gas is admitted at point 302 into a counter-flow heat exchanger 306, by means of which a first pre-cooling of the hot and moist shielding gas takes place according to the counter-flow principle, after which the temperature-conditioned and dried shielding gas is removed again from said heat exchanger 306 at point 304.

[0043] A cooling circuit 314, as known from the prior art, is further connected to the heat exchanger 306 via a cooling unit 312, in which a heated coolant is first compressed and heated at point 316 by a compressor 318, then cooled and liquefied by a cooler 320, and the cooled coolant is then decompressed by a throttle 322, whereby it is further cooled. The thus cooled coolant acts on the pre-cooled shielding gas flow at point 324, which is likewise cooled and directed as a dry and cool gas flow to point 304, whereby the moisture originally present there can condense in the region of the cooling unit 312. This condensed moisture can be removed from the atmosphere-conditioning device 300 by a condensate removal system 326, also known from the prior art, so that the shielding gas cannot escape from the device or gas cannot enter the device from the outside.

[0044] In this way, atmospheric conditioning of the shielding gas flow can be achieved, which is carried out by the heat exchanger 306 and the cooling unit 312, which act together as a cooling unit within the meaning of the present invention, and a control unit (not shown) of the atmospheric conditioning device 300 can set process parameters, such as the temperature of the coolant in the cooling circuit or the cooling performance, for example based on a sensor unit supplying the above-mentioned sensor data, such that, for example, determining a higher temperature of the shielding gas at one of the multiple measuring points can lead to the control unit of the atmospheric conditioning device increasing the cooling performance of the cooling circuit.

[0045] In an apparatus for carrying out a method for fabricating objects according to the technique of selective powder fusion, active atmospheric conditioning of the shielding gas as described in the present invention allows for better setting of the relevant process parameters, temperature and humidity, of the shielding gas in the fabrication chamber 102, thus improving the accuracy and increasing the efficiency of the fabrication process.

Claims

1. A device (100) for carrying out a method for producing an object (G) from a powdered material (P) by layer-by-layer construction according to a method of selective powder fusion, said device (100) comprising: a fabrication chamber (102) configured to accommodate said object (G) to be fabricated; - a powder supply device (200) equipped with a powder stock container (122; 212) configured to supply a material powder (P) to said preparation chamber; a powder layer preparation device (104) configured to prepare overlapping layers of said powder of material (P) supplied on a support (106) arranged in said preparation chamber (102); - an irradiation device arranged to irradiate and thereby locally melt the last prepared powder layer; a shielding gas circulation device (110) configured to circulate the shielding gas present in said preparation chamber (102), The apparatus (100) further comprises at least one atmospheric conditioning device (300) configured to atmospherically condition the shielding gas circulated by the shielding gas circulation device (110) with respect to the temperature of the shielding gas and / or the humidity of the shielding gas in an atmospheric conditioning operation; The atmospheric control device (300) includes a counterflow heat exchanger (306) for pre-cooling the shielding gas, and a cooling circuit (314) is connected to the counterflow heat exchanger (306) via a cooling unit (312), and in the cooling circuit (314), a heated refrigerant is first compressed and heated by a compressor (318), and then cooled and liquefied by a cooler (320). The cooled refrigerant is then decompressed by a throttle (322), the cooled refrigerant acts on the pre-cooled shielding gas flow, and moisture present in the shielding gas flow is condensed in the area of ​​the cooling unit (312); The atmospheric conditioning apparatus (300) is further provided with a condensate exhaust system (326) for removing the condensed water from the atmospheric conditioning apparatus (300).

1. An apparatus (100).

2. The apparatus (100) of any preceding claim, wherein the shielding gas circulation system (110) is further configured to maintain a positive pressure in the fabrication chamber (102).

3. 3. The apparatus (100) of claim 1 or 2, further comprising a powder return section (219) for returning unmelted powder of material to the powder stock container (122; 212), the powder return section (219) forming part of the powder feeding device (200).

4. The apparatus (100) according to any one of claims 1 to 3, characterized in that the powder feeding device (200) further advantageously comprises at least one filter device (215) for the material powder (P).

5. The apparatus (100) according to any one of claims 1 to 4, characterized in that it further comprises a powder suction device (120) configured for suctioning the material powder (P) remaining in the preparation chamber (102) and comprising a circulation pump (126) for said suction, and that the remaining material powder (P) is carried through a separator (128), in particular a cyclone separator (128), by a flow of shielding gas swept by the circulation pump (126).

6. The apparatus (100) as described in claim 5, wherein at least one of the atmospheric conditioning devices (300) is at least partially arranged in the preparation chamber (102), or in the powder stock container (122; 212), or in a gas line belonging to the shielding gas circulation device (110), or in a gas line or powder line belonging to a powder supply device (200), or in a gas line belonging to the powder suction device (120), whereby the atmosphere of the shielding gas present therein is conditioned.

7. The apparatus (100) according to any one of the preceding claims, characterized in that the atmosphere conditioning device (300) comprises a control unit configured to adapt parameters of the atmosphere conditioning operation.

8. The apparatus (100) of claim 7, further comprising at least one sensor unit operatively connected to the control unit of the atmospheric conditioning device (300) and configured to provide data on at least one process parameter of the apparatus (100).

9. The apparatus (100) of claim 8, wherein the at least one process parameter comprises a temperature and / or a relative or absolute humidity of the shielding gas.

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