DE102021110137A1 - METHOD OF MEASURING INFLOW LEAKAGE RATE OF AGRICULTURAL MANUFACTURING DEVICE AND AGGREGATIVE MANUFACTURING DEVICE - Google Patents

Abstract

A method for measuring an inflow leak rate in a gas circulation system (41) of a device (1) for the additive manufacturing of a component (3) made of a powder material (5) is provided on the construction platform (27) in a manufacturing chamber (13). The gas circulation system (41) comprises a pump (47), a protective gas connection (53), a pressure sensor (S_P) and a gas sensor (S_G) for circulating a gas through the production chamber (13) and is also designed to create a production atmosphere with a Adjust overpressure in the production chamber (13). The method comprises the following steps, which are carried out before starting additive manufacturing of the component (3): - circulating the gas in the gas circulation system (41), - setting an initial overpressure in the manufacturing chamber (13), - setting an initial volume fraction of a Gas component of the circulated gas, - measuring an increase over time in the volume fraction of the gas component in the production chamber (13), - comparing the measured increase in the volume fraction over time with a test threshold value which indicates an allowable inflow leak rate, and- generating a leak rate test value based on the comparison.

Description

The present invention relates to methods and devices for the, in particular laser-based, additive manufacturing of components made of powder. In particular, the invention relates to methods for determining an inflow leakage rate of gas, in particular a specific measurable gas component, in a gas circuit of a device for additive manufacturing.

The generative manufacturing of, in particular metallic or ceramic, components is based on solidifying a starting material present in powder form on a construction platform in a manufacturing chamber by irradiation with an energy beam, in the case of laser-based generative manufacturing with laser light. This concept - also known as selective laser melting (SLM) or powder bed fusion - is used in machines for (metallic) 3D printing, among other things. In the case of 3D printing based on a metallic powder, one also speaks of laser metal fusion (LMF) systems. An exemplary machine for additive manufacturing of three-dimensional products is in EP 2 732 890 A2 disclosed. Aspects of a gas cycle are in the WO 2017/220744 A1 disclosed.

The present disclosure relates in particular to the provision of a manufacturing atmosphere—(protective) gas atmosphere—in the manufacturing chamber, which avoids influences such as oxidation on generatively manufactured component layers, melted powder material or surrounding powder material.

Revealed for this EP 3 209 446 B1 an additive manufacturing method in which an inert atmosphere is established in a process chamber using a gas recirculation circuit with a getter before the build process begins such that oxygen, nitrogen and/or hydrogen in the recirculating gas is absorbed by the getter.

One aspect of this disclosure is based on the object of proposing a method that makes it possible to ensure in manufacturing processes that an actual z. B. Oxygen absorption in a manufactured component and powder material during the manufacturing process remains within a tolerable extent that does not negatively affect the quality of the component. This assumes that e.g. B. an oxygen content in the manufacturing atmosphere during manufacturing remains below a predetermined limit level.

At least one of these objects is achieved by a method for measuring an inflow leak rate in a gas circulation system of a device for additive manufacturing according to claim 1, a method for checking a manufacturing atmosphere according to claim 11 and a device for additive manufacturing of a three-dimensional component according to claim 12. Further developments are in specified in the dependent claims.

• - Zirkulieren das Gases im Gaskreislaufsystem,
• - Einstellen eines initialen Überdrucks in der Fertigungskammer,
• - Einstellen eines initialen Volumenanteils einer Gaskomponente des zirkulierten Gases,
• - Messen eines zeitlichen Anstiegs des Volumenanteils der Gaskomponente in der Fertigungskammer,
• - Vergleichen des gemessenen zeitlichen Anstiegs des Volumenanteils mit einem Prüf-Schwellwert, der eine zulässige Einströmleckrate, insbesondere einen Bereich für eine zulässige Einströmleckrate, angibt, und
• - Erzeugen eines Leckraten-Prüfwertes basierend auf dem Vergleich.

In one aspect, a method for measuring an inflow leak rate in a gas circulation system of an apparatus for the additive manufacturing of a component made of a powder material that is provided on a construction platform in a manufacturing chamber, the gas circulation system for circulating a gas through the manufacturing chamber with the manufacturing chamber fluidly connected Pump, an inert gas connection which is fluidly connected to an inert gas tank for a controllable supply of inert gas, a pressure sensor for measuring a pressure present in the gas circulation system, and in particular in the production chamber, and a gas sensor for measuring a volume fraction of a gas component of the circulated gas. The gas circuit system is also designed to set a manufacturing atmosphere with an overpressure in the manufacturing chamber. The method includes the following steps, which are carried out in particular before the start of additive manufacturing of the component:

• - circulate the gas in the gas circulation system,
• - setting an initial overpressure in the production chamber,
• - setting an initial volume fraction of a gas component of the circulated gas,
• - measuring a temporal increase in the volume fraction of the gas component in the manufacturing chamber,
• - Comparing the measured increase in the volume proportion over time with a test threshold value, which specifies a permissible inflow leak rate, in particular a range for a permissible inflow leak rate, and
• - Generating a leak rate test value based on the comparison.

• - vor einem Beginn der generativen Fertigung des Bauteils Durchführen des zuvor zusammengefassten Verfahrens,
• - Durchführen des Fertigungsprozesses mit der Vorrichtung, wenn ein initial erzeugter Leckraten-Prüfwert eine Durchführung des Fertigungsprozesses freigibt,
• - optional Deaktivieren einer Wärmequelle zum Temperieren des Pulvermaterials nach Abschluss des Fertigungsprozesses,
• - Abkühlen der Fertigungsatmosphäre unter einen Temperatur-Schwellwert,
• - erneutes Durchführen des Verfahrens, wobei der nach der Durchführung des Fertigungsprozesses erneut erzeugte Leckraten-Prüfwert mit einem Leckraten-Schwellwert verglichen wird, der eine zulässige Fertigungsprozess-Einströmleckrate angibt, und
• - Erzeugen eines Fertigungsprozess-Prüfwertes basierend auf dem Vergleich, wobei der Fertigungsprozess-Prüfwert zur Überprüfung der Fertigungsatmosphäre angibt, ob der Fertigungsprozess unter der zulässigen Fertigungsprozess-Einströmleckrate durchgeführt wurde.

In a further aspect, a method for checking a manufacturing atmosphere that was present during a manufacturing process with a device for the additive manufacturing of a component from a powder material, the powder material being provided on a construction platform in a manufacturing chamber, the gas circulation system for a circulation of a gas through the production chamber, a pump fluidly connected to the production chamber, a protective gas connection, which is used for the controllable supply of protective gas a protective gas tank, a pressure sensor for measuring a pressure present in the gas circulation system, and in particular in the production chamber, and a sensor for measuring a volume fraction of a gas component of the circulated gas. The gas circuit system is also designed to provide the manufacturing atmosphere with an overpressure in the manufacturing chamber. The procedure includes the following steps:

• - before starting the additive manufacturing of the component, carrying out the previously summarized method,
• - Carrying out the manufacturing process with the device if an initially generated leak rate test value enables the manufacturing process to be carried out,
• - optional deactivation of a heat source for tempering the powder material after completion of the manufacturing process,
• - Cooling of the production atmosphere below a temperature threshold,
• - Re-performing the method, wherein the leak rate test value generated again after the manufacturing process has been carried out is compared with a leak rate threshold value which indicates a permissible manufacturing process inflow leak rate, and
• - generating a manufacturing process check value based on the comparison, the manufacturing process check value for checking the manufacturing atmosphere indicating whether the manufacturing process was performed below the allowable manufacturing process inflow leak rate.

In a further aspect, a device for the additive manufacturing of a three-dimensional component from a powder material comprises a manufacturing chamber, a construction platform in the manufacturing chamber, with the powder material being provided on the construction platform, an irradiation system for generating an energy beam for irradiating the powder material for the layer-by-layer production of the component , and a gas circulation system for circulating a gas through the processing chamber. The gas circuit system includes a pump that is fluidly connected to the production chamber, a protective gas connection that is/can be fluidly connected to a protective gas tank for the controllable supply of protective gas, a pressure sensor for measuring a pressure present in the gas circuit system, and in particular in the production chamber, and a gas sensor for measuring a Includes volume fraction of a gas component of the circulated gas. The gas circuit system is also designed to set a manufacturing atmosphere with an overpressure in the manufacturing chamber. The manufacturing device further comprises a control device with at least one microprocessor and a memory device, wherein the memory device is set up to store instructions which, when executed by the microprocessor, carry out partial steps of one of the methods disclosed herein.

In some embodiments, the powder material can be tempered with a heat source during additive manufacturing. In particular, it is provided on a construction platform that can be heated with a heating device in the production chamber and/or can be heated by a radiant heater. During the measurement of the increase in the volume fraction over time, the gas in the gas circulation system can be circulated under a thermal boundary condition in which absorption of the gas component in the powder material and/or in the component essentially does not affect the increase in the volume fraction over time.

• - Bereitstellen der thermischen Randbedingung durch Deaktivierung der Wärmequelle oder durch Aktivierung der Wärmequelle, bis maximal eine Grenztemperatur im Pulvermaterial vorliegt, bei der eine Absorption der Gaskomponente im Pulvermaterial und/oder im Bauteil den zeitlichen Anstieg des Volumenanteils im Wesentlichen nicht beeinflusst.

In some embodiments, the method may further include the step of:

• - Provision of the thermal boundary condition by deactivating the heat source or by activating the heat source until a limit temperature is present in the powder material at most, at which absorption of the gas component in the powder material and/or in the component essentially does not affect the increase in the volume fraction over time.

The initial volume fraction of the gas component can be set to a value in the measuring range of the gas sensor. In particular, the initial volume fraction of the gas component can be assigned to an oxygen gas component and/or the initial volume fraction can be adjusted by feeding inert gas into the gas circulation system.

• - Regeln des Überdrucks in der Fertigungskammer während des Messens des zeitlichen Anstiegs des Volumenanteils, insbesondere durch Zuführen von Schutzgas in das Gaskreislaufsystem.

In some embodiments, the method may further include the step of:

• - Regulating the overpressure in the production chamber while measuring the increase in the volume fraction over time, in particular by feeding protective gas into the gas circulation system.

The gas can be circulated in the gas circulation system under an unregulated boundary condition with regard to the overpressure in the production chamber.

In some embodiments, the increase in the volume fraction of the gas component over at least 5 minutes or at least 10 minutes and in particular in a time window can be measured in a range of 5 to 15 minutes. In particular, it can be measured before activating a heat source for tempering the powder material.

• - Bestimmen des Prüf-Schwellwerts spezifisch für Prozessbedingungen, die einen Typ des Pulvermaterials und ein Ausmaß eines temperierbaren Oberflächenanteils in der Fertigungskammer umfassen, und wobei der Prüf-Schwellwert für Sauerstoff als der Messung zugrunde liegende Gaskomponente in einem Bereich von 10 ppmv/h bis 300 ppmv/h liegt.

In some embodiments, the method may further include the step of:

• - Determining the test threshold specific to process conditions that include a type of powder material and an amount of temperature controllable surface area in the processing chamber, and wherein the test threshold for oxygen as the gas component underlying the measurement is in a range from 10 ppmv/h to 300 ppmv/hr.

• - Bestimmen, dass der Leckraten-Prüfwert eine Durchführung eines Fertigungsprozesses erlaubt, und
• - Aktivieren der Einnahme der Prozessbedingungen, wobei insbesondere einer Wärmequelle zum Temperieren des Pulvermaterials aktiviert wird.

In some embodiments, the method may further include the steps of:

• - determining that the leak rate test value allows a manufacturing process to be carried out, and
• - Activation of taking the process conditions, in particular a heat source for tempering the powder material is activated.

• - Bestimmen, dass der Leckraten-Prüfwert einer Durchführung eines Fertigungsprozesses entgegensteht, und
• - Ausgeben eines Prüfsignals, das angibt, dass eine Überprüfung des Gaskreislaufsystems hinsichtlich der Leckrate von einem Bediener vorzunehmen ist.

In some embodiments, the method may further include the steps of:

• - determining that the leak rate test value prevents a manufacturing process from being carried out, and
• - Issuance of a test signal, which indicates that a check of the gas circulation system with regard to the leak rate is to be carried out by an operator.

• - die Pumpe Gas durch die Fertigungskammer zirkuliert,
• - Messdaten des Drucksensors eingelesen werden,
• - Volumenanteildaten des Gassensors eingelesen werden, die eine zeitliche Entwicklung des Volumenanteils der Gaskomponente über mindestens 5 Minuten oder mindestens 10 Minuten und insbesondere in einem Zeitfenster in einem Bereich von 5 bis 15 Minuten angeben,
• - eine zeitliche Entwicklung des Volumenanteils der Gaskomponente mit einem Prüf-Schwellwert, der eine zulässige Einströmleckrate angibt, verglichen wird und basierend auf dem Vergleich ein Leckraten-Prüfwert erzeugt wird, und/oder
• - ein Fertigungsprozess mit der Fertigungsvorrichtung (1) gemäß einem Fertigungsplan durchgeführt wird.

In some embodiments of the manufacturing device, the controller may be configured to process instructions that, when executed by the microprocessor, cause

• - the pump circulates gas through the manufacturing chamber,
• - measurement data of the pressure sensor are read in,
• - volume fraction data of the gas sensor are read in, which indicate a time development of the volume fraction of the gas component over at least 5 minutes or at least 10 minutes and in particular in a time window in a range of 5 to 15 minutes,
• - a development over time of the volume fraction of the gas component is compared with a test threshold value, which indicates an allowable inflow leak rate, and a leak rate test value is generated based on the comparison, and/or
• - A manufacturing process with the manufacturing device (1) is carried out according to a manufacturing plan.

• - die Wärmequelle aktiviert, teilaktiviert oder deaktiviert wird und optional
• - thermische Randbedingung bereitgestellt werden, indem die Wärmequelle deaktiviert oder derart aktiviert wird, sodass maximal eine Grenztemperatur im Pulvermaterial vorliegt, bei der eine Absorption der Gaskomponente im Pulvermaterial und/oder im Bauteil den zeitlichen Anstieg des Volumenanteils im Wesentlichen nicht beeinflusst, und Volumenanteildaten des Gassensors bei Vorlage der thermischen Randbedingung eingelesen werden.

The manufacturing device can optionally include a heat source for tempering the powder material, in particular a heating device for heating the construction platform and/or a radiant heater for irradiating the powder material, and the control device can be set up to process commands that are executed by the microprocessor , cause that

• - the heat source is activated, partially activated or deactivated and optional
• - Thermal boundary conditions are provided by the heat source being deactivated or activated in such a way that there is a maximum limit temperature in the powder material at which absorption of the gas component in the powder material and/or in the component does not essentially affect the increase in the volume fraction over time, and volume fraction data of the gas sensor be read in if the thermal boundary condition is presented.

Further aspects relate to a computer program/computer program product and a computer-readable medium. The computer program/computer program product and the computer-readable medium are respectively provided for executing one of the methods described herein. The computer program can be stored on a non-volatile memory, which is used in particular as part of a control device for operating a device for the additive manufacturing of a three-dimensional component.

The embodiments disclosed herein may include: have the advantage that oxygen absorption in a manufactured component and powder material remains within a tolerable extent during the manufacturing process, so that the quality of a generatively manufactured component is not adversely affected and powder material that has not been melted can be reused. In particular, "aging" of the powder material usually used in several manufacturing processes can be delayed.

As a further advantage, better control of the manufacturing atmosphere can improve component quality in manufacturing processes that are carried out without preheating, since e.g. B. also an oxidation in a molten pool during the production of the energy beam generated in the powder bed can be (better) controlled.

• 1 eine schematische räumliche Darstellung einer beispielhaften generativen Fertigungsvorrichtung,
• 2 eine schematische Schnittansicht der generativen Fertigungsvorrichtung aus 1 parallel zur XY-Ebene durch die Fertigungskammer,
• 3 eine schematische Schnittansicht der generativen Fertigungsvorrichtung aus 1 parallel zur XZ-Ebene,
• 4 eine schematische Schnittansicht der generativen Fertigungsvorrichtung aus 1 parallel zur YZ-Ebene,
• 5 eine Skizze zur Verdeutlichung eines beispielhaften Gaskreislaufs einer generativen Fertigungsvorrichtung und
• 6 ein beispielhaftes Flussdiagramm zur Erläuterung des erfindungsgemäßen Verfahrens zum Messen einer Einströmleckrate.

Concepts are disclosed herein that allow at least some aspects of the prior art to be improved. In particular, further features and their usefulness result from the following description of embodiments with reference to the figures. From the figures show:

• 1 a schematic spatial representation of an exemplary additive manufacturing device,
• 2 a schematic sectional view of the additive manufacturing device 1 parallel to the XY plane through the manufacturing chamber,
• 3 a schematic sectional view of the additive manufacturing device 1 parallel to the XZ plane,
• 4 a schematic sectional view of the additive manufacturing device 1 parallel to the YZ plane,
• 5 a sketch to illustrate an exemplary gas circuit of an additive manufacturing device and
• 6 an exemplary flowchart to explain the method according to the invention for measuring an inflow leak rate.

Aspects described here are based in part on the knowledge gained in additive manufacturing that, for very small O2/N/H2O volume fractions, a measurement e.g. B. a volume fraction of an oxygen gas component of the gas in the manufacturing chamber does not allow reliable statements about how high an actual oxygen uptake in a component and / or in a powder material is during a manufacturing process. A statement on the content of O2/N/H2O gas can also be made more difficult by conventional preheating of the construction platform, since preheating has a binding rate of e.g. B. oxygen in the component and powder material can increase.

The inventors have further recognized that despite a slight overpressure in the manufacturing chamber, an inflow leak rate into the gas circulation system can lead to an increase in the oxygen content in the manufacturing atmosphere. The inventors now propose measuring an inflow leakage rate into the gas circulation system, detached from processes that affect the oxygen content, such as increased oxygen absorption in the case of a heated construction platform or a heated powder bed in general, whether due to an energy input during production or an external heat source . According to the invention, a measurement and evaluation of an effective leak rate of oxygen, nitrogen or water, measured z. B. in ppmv / min, after a (protective) gas atmosphere has been built up in the manufacturing chamber, the additive manufacturing process itself does not take place and z. B. a preheating at the time of measurement is inactive or active to a tolerable extent.

The following explanations regarding the measurement of an inflow leak rate usually refer to the measurement of an oxygen content in the production chamber as an example. However, the leakage rate can be equally performed based on other types of gas/gas components (ingredients) of the gas constituting the manufacturing atmosphere (also commonly referred to as protective gas atmosphere). For example, the development of a proportion of nitrogen or a proportion of water in the production atmosphere can be measured.

In manufacturing processes z. For example, very small oxygen contents are always necessary when a component can bind oxygen through oxidation, which can impair component quality, or when powder material can bind oxygen through oxidation during the manufacturing process, which can impair reusability of the powder material.

The tendency to bind oxygen depends both on the material (powder material) and on the temperature. For example, titanium alloys that can be used for the powder material on which a manufacturing process is based, e.g. B. have a high oxygen affinity. In this way, oxygen can be incorporated into a crystal lattice of a titanium alloy without a passivating oxide layer forming, as is the case, for example, in B. is the case with aluminum alloys. The affinity can increase with increasing temperature. Higher temperatures in the range of z. B. greater than 473 K can occur in the production chamber and in particular in the component or powder bed if energy (e.g. as a laser beam) is irradiated, the construction platform and/or the powder material is preheated or a process-induced heat build-up in the component during of the layer structure occurs.

The recording of z. B. Oxygen in the component/powder material can result in all of the oxygen present in the gas circuit being bound in the heated component and/or powder material. The oxygen removed from the production atmosphere includes the initial residual oxygen content that is initially present in the gas composition of the production atmosphere, ie after the production atmosphere has built up as a “protective gas atmosphere”. became. On the other hand, the oxygen continuously flowing in due to leaks in the gas circulation system (given by a "mechanical" existing inflow leakage rate of the gas circulation system) can be removed from the production atmosphere. Depending on the process conditions (temperature, component size, powder type, powder surface), an oxygen content (volume mixing ratio) that can be measured during the production process can drop to a few ppmv, in particular zero ppmv. The latter is the case in particular when the inflow leakage rate of oxygen into the gas circuit is lower than the binding rate in the component, powder material, heated components of the production device, etc. Ie, a residual oxygen content in the production atmosphere can become so low that a sensitivity of conventional oxygen sensors can no longer grasp. The same situation can arise with very low initial oxygen levels and very low leak rates. As a result, a measurement during a production process can show virtually no oxygen content, although oxygen is still continuously being absorbed by the component and powder material.

• (1) Wird ein Restsauerstoffgehalt im Gaskreislauf während des Fertigungsprozesses gemessen - d.h., liegt ein Restsauerstoffgehalt vor, der größer als die Messgrenze ist, hier z. B. größer Null ppmv -, ist das Messergebnis nicht ausreichend, um eine nachteilige/ungewollte Sauerstoffaufnahme im Bauteil und Pulvermaterial zu vermeiden. Vielmehr ist die Leckrate sogar größer als die Bindungsrate. Eine Vergrößerung des Sauerstoffgehalts bis zum Umgebungssauerstoffgehalt könnte zwar in diesem Fall durch die Zufuhr von frischem Schutzgas mit einem geringen Sauerstoffanteil unterbunden werden, dies erhöht allerdings die Prozesskosten.
• (2) Wird kein Restsauerstoffgehalt im Gaskreislauf während des Fertigungsprozesses gemessen - d.h., es wird eine Einhaltung eines maximal zulässigen Restsauerstoffgehalts (oder auch z. B. Null ppmv) im Gaskreislauf während des Fertigungsprozesses gemessen -, ist dies Messergebnis nicht zwingend dahingehend aussagekräftig, dass eine nachteilige/ungewollte Sauerstoffaufnahme im Bauteil und Pulvermaterial vermieden wird. Die Leckrate ist nun zwar kleiner als die Bindungsrate, aber trotzdem kann die Menge an absorbierten Sauerstoff zu hoch sein. Insbesondere in Fertigungsprozessen mit Vorwärmung kann eine Bindungsrate so groß sein, dass auch bei gemessenen Null ppmv in der Fertigungsatmosphäre eine Zunahme des Sauerstoffgehalts im Bauteil/Pulvermaterial feststellbar sein kann. D.h., je höher die Bindungsrate in der Fertigungskammer, desto höher kann eine vorliegende Leckrate sein, ohne dass ein Sauerstoffgehalt (von größer Null ppmv) in der Fertigungskammer gemessen würde.

Assuming that a sensitivity of the measuring device (gas sensor) for measuring a volume fraction of a gas component such as oxygen is suitable to measure a (oxygen) content of zero ppmv (where "zero ppmv" can be exchanged for a minimum measurable value of the measuring device ), given the above analysis, the following conclusions can be drawn:

• (1) If a residual oxygen content is measured in the gas circuit during the manufacturing process - ie the residual oxygen content is greater than the measurement limit, here e.g. B. greater than zero ppmv -, the measurement result is not sufficient to avoid disadvantageous / unwanted oxygen absorption in the component and powder material. Rather, the leak rate is even greater than the binding rate. In this case, an increase in the oxygen content up to the ambient oxygen content could be prevented by supplying fresh protective gas with a low oxygen content, but this increases the process costs.
• (2) If no residual oxygen content is measured in the gas circuit during the manufacturing process - i.e. compliance with a maximum permissible residual oxygen content (or e.g. zero ppmv) is measured in the gas circuit during the manufacturing process - this measurement result is not necessarily meaningful in that a disadvantageous/unwanted oxygen absorption in the component and powder material is avoided. The leak rate is now smaller than the binding rate, but the amount of oxygen absorbed can still be too high. In particular in manufacturing processes with preheating, a binding rate can be so high that an increase in the oxygen content in the component/powder material can be detected even when the measured ppmv in the manufacturing atmosphere is zero. That is, the higher the binding rate in the processing chamber, the higher an existing leak rate can be without an oxygen content (greater than zero ppmv) being measured in the processing chamber.

To an impermissible increase in z. B. to prevent oxygen content in the component, powder material, etc., the inventors have now recognized that the leak rate of oxygen, which is a parameter of the gas cycle in the gas cycle system to a first approximation, should be below a defined limit value. However, as explained, an inflow leak rate cannot be meaningfully measured during the manufacturing process, since the penetrating oxygen is at least partially bound directly and can therefore no longer be measured. In other words, the inventors have recognized that during the manufacturing process, a statement about the situation of z. B. oxygen content can not be met.

The inventors now propose carrying out a (separate) measurement of the inflow leak rate after the protective gas atmosphere has been built up, but the manufacturing process and in particular the preheating have not yet started. At this time, the measurement of the inflow leakage rate can be performed uncontaminated by absorbing effects. The proposed procedure makes it possible to adhere to experimentally and/or theoretically determined limit values for a leak rate (also referred to herein as test threshold value) in manufacturing processes. The test threshold value can be set specifically for process conditions, which include a powder type and an extent of a temperature-controlled surface area in the production chamber, etc. For example, a test threshold value for, for example, oxygen as the gas component on which the measurement is based can be in a range from 10 ppmv/h to 300 ppmv/h.

A start of a production process is only released if an inflow leak rate measured under the above conditions is less than a respectively specified limit value or an explicit release is given by the operator.

In addition, the inflow leak rate can be determined again after the end of the manufacturing process and after the build platform/the manufactured component has cooled down in order to check for a possible change in the leak rate during the process and thus to assess the quality of the components produced with regard to e.g. B. the feature oxygen contamination to classify. Such a development of the leak rate during the manufacturing process cannot be determined during the manufacturing process or can only be determined if a measured volume fraction changes significantly during the manufacturing process, e.g. B. increases from 0 ppmv to 10 ppmv.

The following is with reference to the 1 until 4 an exemplary embodiment of a manufacturing device 1 for the generative manufacturing of a component 3 from a powdered construction material present in a powder bed is explained, in which the concepts disclosed herein for the manufacturing atmosphere can be implemented. An associated gas circuit is exemplified in 5 sketched.

The construction material is z. B. a metallic powder of a titanium alloy or a refractory alloy and is referred to herein generally as powder material 5. In a generative manufacturing process, the powder material 5 is solidified in layers with an energy beam. The energy beam is generated with an irradiation system 7, for example as a laser beam from a laser beam source. The irradiation system 7 also includes z. B. a scanner device that is set up to guide the energy beam over the powder bed. The energy beam melts the powder material 5 so that a (further) material layer of the component 5 is formed after the melt has solidified. Accordingly, energy and thus heat is introduced into the powder bed or the component during the manufacturing process.

The manufacturing device 1 comprises a main housing 11 which provides a manufacturing chamber 13 for the manufacturing process (for example an LMF process). In the 2 and 3 the already partially manufactured component 3 is indicated, component layers of the component 3 that have already been produced being embedded in the powder bed of the powder material 5 .

The main body 11 has a front wall 15, a rear wall 17, side walls 19A, 19B and a ceiling 21 which define the processing chamber 13 together with a work surface 23 (as a floor). A door 15A in the front wall 15 allows access to the processing chamber 13. An operator can e.g. B. carry out the necessary preparatory steps such as cleaning the production area 13 and (re)filling a powder storage container through the door 15A or remove the finished component 3 through the door 15A after the production process.

The manufacturing process takes place in a construction area 23A on the work surface 9 . Construction area 23A is in 1 located between a powder storage area 23B and a powder collection area 23C (optional). In 1 For example, the powder storage portion 23B, the building portion 23A, and the powder collecting portion 23C are staggered in the X direction.

The irradiation process for producing the component 3 takes place in the construction area 23A. For this purpose, a construction platform 27 is arranged on a base plate 29A of a construction cylinder 29 in the construction area 23A in order to increase the height (in 1 in ±Z-direction). In general, a heat source can be installed in the production chamber 13, which heats the processing plane, in particular the powder material in the construction area 23A, and in particular the uppermost powder layer in a temperature range of z. B. 673 K to 873 K for the manufacturing process (preheat) can provide. For temperature control, in particular for preheating, the powder material in the powder bed, the base plate 29A z. B. be equipped with a heater 31. An example is in 1 furthermore, an optional radiant heater 31A on the ceiling 21 of the production chamber 13 is indicated, which can be operated in addition to or as an alternative to the heating device 31 . Further embodiments of the heat source include laser radiation sources such as surface emitters (VCSEL) and diode lasers, infrared lasers and infrared radiators in general, etc. The heating device 31 is z. B. set up to heat the powder material 5 in the construction cylinder 29 and thus also the top layer of powder.

1 1 also shows a slide 25 for distributing the powder material 5 during the manufacturing process. The powder storage area 23B serves to provide fresh powder from a storage cylinder 32, which is transferred to the construction area 23A with the slide 25 for the layer-by-layer production of the component 3.

In summary, a generative manufacturing process comprises repeated lowering of the construction platform 27 in the construction cylinder 29, application of a fresh powder layer in the construction area 23A and fusion of the powder material 5 according to an irradiation plan of the component 5 based on a layer model structure.

The manufacturing process takes place in a manufacturing atmosphere that is set in the manufacturing chamber 13 with a gas circulation system 41 and can be regulated. Parameters of the manufacturing atmosphere include a suitable composition of the gas mixture present in the manufacturing chamber 13 (generally also referred to as protective gas) and an overpressure to be set in the manufacturing chamber 13. B. inert gas such as argon or nitrogen during the manufacturing process. A controlled manufacturing atmosphere can improve the quality of the manufactured component if z. B. oxidation in the melt bath can be better controlled, in particular kept to a minimum. In general, the gas circulation system 41 is designed to circulate gas through the processing chamber at a slight positive pressure relative to the ambient atmosphere.

In the 2 and 4 a laminar flow 43 over the construction area 23A is indicated by way of example. For the establishment of the flow 43, the gas is discharged into the processing chamber 13, for example, through outlet opening structures 45A provided in the door 15A and sucked out through suction opening structures 45B in the rear wall 17.

For the circulation of the gas, the gas circulation system 41 comprises a pump 47 (fan/blower) which is fluidly connected to the processing chamber 13, in particular the outlet opening structures 45A and the suction opening structures 45B. The pump 47 generates a pressure increase on a pump outlet side 47A such that the manufacturing chamber 17 has an overpressure of, for example, a few 100 Pa (for example 500 Pa to 1,000 Pa, for example 2,000 Pa, generally less than 10,000 Pa) above the ambient pressure.

The gas circulation system 41 further comprises a filter unit 49. In the exemplary arrangement shown, the filter unit 49 is fluidly connected to the suction opening structure 45B in the rear wall 17 and the pump 47 via lines 51. The filter unit 49 has z. B. an ultra-fine filter for removing particles from the circulating gas. Optionally, additional moisture z. B. be removed by a cold trap in the filter unit 49 from the gas flow. Alternatively, moisture can be removed from the gas by passing the gas over a drying medium.

The various components and the piping lead to a pressure drop along the gas circuit, with a (slight) negative pressure compared to the ambient pressure possibly also occurring—in particular on a suction side 47B of the pump 47.

Furthermore, the gas circulation system 41 comprises a protective gas connection 53 which is fluidly connected to an internal or external source of protective gas, see e.g. B. an inert gas tank 55 in 5 . The protective gas connection 53 is set up to enable controllable feeding of protective gas into the gas circuit of the gas circuit system 41 .

To set and monitor the production atmosphere, the gas circuit system 41 includes a pressure sensor S_P for measuring a pressure present in the gas circuit system 41. The gas circuit system 41 also includes a gas sensor S_G for measuring a volume fraction of a gas component of the circulated gas and a temperature sensor S T. In 3 the measurements are carried out with the pressure sensor SP, the gas sensor S_G and the temperature sensor ST in the production chamber 13, for example, in order to be able to monitor the production atmosphere in the area of the production process in particular.

In some embodiments, additional valves such as a bleed valve 57 may also be provided.

To control the methods disclosed herein, the manufacturing device 1 comprises a control device 61 (schematically in 5 shown). The control device 61 comprises at least one microprocessor 61A and at least one memory device 61B. The control device 61 is preferably selected from a group consisting of a computer, in particular a personal computer (PC), a plug-in card or control card, and an FPGA board.

As in 5 the control device 61 is indicated via data connections 63 (wireless or wired) with the various components of the production device 1 (e.g. the heating device 31, the heat radiator 31A (generally the heat source) and/or the irradiation system 33) and in particular with components of the gas circulation system 41 (e.g. the pump 47, the pressure sensor S_P, the gas sensor S_G and the temperature sensor S_T as well as the inert gas connection 53 and the drain valve 57) for receiving (e.g. measurement) data sets and/or for sending (e.g B. tax) records connected.

The at least one storage device 61B stores e.g. B. Instructions which, when executed by the at least one microprocessor 61A, cause the manufacturing device 1 to perform steps of the methods proposed herein. In the memory device 61B for this purpose, e.g. B. stored an irradiation plan that includes cross-sectional information of the component 3, so that a finished treatment process can be processed according to the radiation plan. The at least one storage device 61B stores e.g. B. also predetermined control values such as a test threshold or leak rate threshold and the manufacturing atmosphere characterizing values such as a leak rate test value and / or a manufacturing process test value. Stored instructions may include, but are not limited to, instructions that, when executed by the at least one microprocessor 61A, cause a manufacturing process to be performed according to a manufacturing plan and, in particular, the heat source to be activated, partially activated, or deactivated, the pump 47 to circulate gas through the manufacturing chamber, measurement data from the Pressure sensor SP are read in, volume fraction data of the gas sensor S_G are read in, a development over time of the volume fraction of the gas component is compared with a test threshold value that indicates a permissible inflow leak rate, and/or a leak rate test value is generated based on the comparison.

The additive manufacturing is significantly influenced by the parameters of the powder material 5 with regard to the interaction with the energy beam. Since the powder material 5 as well as layers of the component 3 that have already been produced are exposed to the production atmosphere during the production process, additive manufacturing can—as already mentioned at the outset—be influenced by gas components being absorbed by the finished component 3 or the powder material 5 during the production process. this is in 5 indicated by an arrow 69 as an example. This relates in particular to the oxygen content that is present in the production atmosphere. Furthermore, the moisture content of the powder can affect the manufacturing process.

During additive manufacturing, an overpressure of a few 100 Pa (for example 500 Pa to 1,000 Pa, for example 2,000 Pa, generally less than 10,000 Pa) can be maintained in the manufacturing chamber in a control circuit. In 5 relative pressures along the gas circuit are given as examples: 1,500 Pa directly after the pump 47, 1,000 Pa before the processing chamber 13, 500 Pa after the processing chamber 13 and -500 Pa on the suction side of the pump 47. If the overpressure in the processing chamber 13 falls due to From leaks in the gas circuit system 41, protective gas from the protective gas tank 55 can be added.

The aim is also to reduce the oxygen content in the production chamber to generally less than 1,000 ppmv, e.g. B. less than 300 ppmv or less than 150 ppmv to limit. An excessively high proportion of oxygen can also be compensated for from the protective gas tank 55 by adding fresh protective gas which has a lower oxygen content (for example less than 10 ppmv).

In addition to the loss of circulating gas, a leak in the gas circuit system 41 can also lead to gas from the environment, including oxygen, diffusing into the gas circuit. this is in 5 indicated by arrows 71 by way of example. Particularly on the suction side of the pump 47, gas from the environment can be absorbed due to a possible negative pressure. As a result, it may become necessary to quantify an inflow leak rate of the gas circuit system 41 . The aim is to limit an inflow leak rate in such a way that an oxygen content within a target ppmv range can be guaranteed throughout the entire manufacturing process.

As explained at the beginning, the oxygen absorption in the component/powder material (titanium heating plate) occurs at an undefined rate during production and especially when heated. It is correspondingly difficult to quantify. A sufficiently low proportion of oxygen (e.g. zero ppmv) can be measured during a manufacturing process, in particular with an activated heat source. However, an oxygen proportion that appears to be sufficiently low can occur, although oxygen diffuses into the gas circulation system 41 to an undesirable extent, since the oxygen entering is directly absorbed in the component/powder material. Correspondingly, as explained at the outset, a measurement that is carried out during the production process does not necessarily allow a conclusion to be drawn as to the oxygen content present in the production chamber 13 .

In connection with the flowchart of 6 the method of measuring an inflow leak rate into the gas cycle system 41 will be explained.

The method is carried out before the start of additive manufacturing of a component. In other words, before the process conditions are set, a heat source such as a radiant heater, a laser, an infrared radiator or a (pre-)heating device of the construction platform is activated in particular; in other words, the measurement takes place in the cold state of the production device. It is noted that the heat source can alternatively also be activated or partially activated as long as a limit temperature is not exceeded, below which absorption of a gas component is negligible. For example, for a powder material (eg, a titanium alloy or a refractory alloy), the limit temperature be selected in a range from 373 K to 473 K, which at such temperatures of the powder material the absorption can be largely neglected under certain circumstances.

In a step 101 (activation of pure gas circulation), the control unit 61 activates the pump 47 so that the gas in the gas circulation system 41 circulates in the gas circulation system 41 and flows through the production chamber 13 .

In a step 103 (setting an initial overpressure), the control unit 61 (or an operator) sets a predetermined overpressure in the gas circulation system 41 and thus in the production chamber 13 in particular. The pressure sensor S_P delivers a corresponding pressure value to the control unit 61, so that it recognizes that a desired overpressure is present in the gas circuit system 41 and the leak rate-specific steps of the measurement can be started. Alternatively, the latter can be monitored by an operator before initiating the leak rate specific steps of the measurement.

In a step 105 (setting an initial volume fraction), the control unit 61 (or an operator) sets an initial volume fraction of a gas component of the circulated gas, for example, a starting volume fraction of oxygen in the circulated gas. Measurements required for this can be carried out with the gas sensor S_G, which outputs corresponding measured values to the control unit 61 . The set initial volume fraction is in an easily accessible measuring range of the gas sensor S_G. The setting can be accompanied, for example, by adding argon as a protective gas to the gas circulation system 41 to reduce the volume fraction. The set initial volume fraction is, for example, in particular above an operating value that represents an upper limit for a permissible volume fraction during the additive manufacturing of the component. This is possible because there is no production at this time. The aim of the set initial volume fraction is to enable a precise measurement of a development over time.

In a step 107 (measuring an increase in the volume fraction over time), the gas sensor S_G continuously or at time intervals detects the volume fraction of the gas component (e.g. the oxygen volume fraction in ppmv) in the production chamber 13. The gas is circulated in the gas circulation system 41 under thermal boundary conditions continued, in which an absorption of the gas component in the powder material does not affect the temporal increase in the volume fraction substantially. Based on the measured volume fractions, an increase in the volume fraction over time can be measured (e.g. X ppmv/min). The measurement takes place over a few minutes, for example 5, 10 or 15 minutes.

It is noted that the time rise measurement can be performed with controlled or uncontrolled positive pressure in the manufacturing chamber. Regulation is not disadvantageous in particular if the volume fraction of the gas component to be measured that is supplied as a result of the regulation with the inert gas tank is negligible.

However, it is essential that the volume fraction is not regulated, since the volume fraction is to be developed on the basis of a mechanically present leakage situation in the gas circuit system 41 .

In a step 109 (comparison with test threshold value), the control unit 61, in particular the processor 61A, compares the measured increase in the volume fraction over time with a test threshold value. The test threshold value specifies a permissible inflow leak rate and is determined, for example, in preparation for the specific parameters of the manufacturing process (process conditions such as the type of powder material and type of manufacturing device, in particular an extent of a temperature-controlled surface area) and stored in the memory device 61B.

In a step 111 (generating a leak rate test value), the control unit 61, in particular the processor 61A, generates a leak rate test value based on the comparison and outputs it (e.g. for verification by an operator) and/or stores it in the storage device 61B away.

In a step 113 (evaluation of the leak rate test value), it can be determined whether or not the leak rate test value allows a manufacturing process to be carried out.

If this is not the case, in a step 115 (output of a test signal) a test signal can be output which indicates that the gas circuit system must be checked for possible leaks.

If execution of a manufacturing process is released, the control unit 61 causes the process conditions to be accepted in step 117 (complete activation of the manufacturing device 1); In particular, a volume fraction of the gas component in the manufacturing atmosphere to a target value by adding protective gas can be reduced and an optional heat source can be activated.

In a step 119 (additive manufacturing of a component), the control unit 61 initiates an additive manufacturing process according to an irradiation plan.

After completion of the manufacturing process, the manufacturing atmosphere/manufacturing chamber 13 is cooled below a temperature threshold value in a step 121 (cooling of components and powder bed). For this purpose, the control unit 61 receives from the temperature sensor S_T z. B. Measurement data on the temperature of the production atmosphere. The temperature threshold value is selected in such a way that absorption of the gas component in the powder material essentially does not affect the increase in the volume fraction over time.

Optionally, the inflow leak rate can now be measured again according to steps 101 to 111 (step 123).

A leak rate check value newly generated in this way can be compared in step 109, which is carried out again, with a leak rate threshold value which specifies a permissible manufacturing process inflow leak rate. The leak rate threshold value can correspond to the test threshold value or, for example, can be selected to be slightly larger than this.

In a step 125 (evaluate the leak rate check value), the control unit 61 (or the operator) determines a manufacturing process check value based on the comparison. The manufacturing process check value indicates whether the manufacturing process was performed below the allowable (manufacturing process) inflow leak rate or not. The manufacturing process test value accordingly allows a statement to be made about the quality of the manufactured component 3 .

Devices for additive manufacturing (e.g. LMF machines) in which the concepts described here can be used include, for example, the "mysint 100", "TruPrint 1000" and "TruPrint 3000" systems.

It is explicitly emphasized that all features disclosed in the description and/or the claims are to be regarded as separate and independent from each other for the purpose of original disclosure as well as for the purpose of limiting the claimed invention independently of the combinations of features in the embodiments and/or the claims must. It is explicitly stated that all indications of ranges or groups of units disclose every possible intermediate value or subgroup of units for the purpose of original disclosure as well as for the purpose of limiting the claimed invention, in particular also as a limit of a range indication.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 2732890 A2 [0002]
• WO 2017/220744 A1 [0002]
• EP 3209446 B1 [0004]

Claims (13)

Method for measuring an inflow leakage rate in a gas circuit system (41) of a device (1) for the additive manufacturing of a component (3) from a powder material (5) which is provided on a construction platform (27) in a production chamber (13), the gas circuit system (41) for circulating a gas through the processing chamber (13) - a pump (47) fluidly connected to the processing chamber (13), - a protective gas connection (53) which is fluidly connected to a protective gas tank (55) for a controllable supply of protective gas, - A pressure sensor (S_P) for measuring a pressure present in the gas circulation system (41), and in particular in the production chamber (13), and - a gas sensor (S_G) for measuring a volume fraction of a gas component of the circulated gas and is also designed to set a manufacturing atmosphere with an overpressure in the manufacturing chamber (13), and wherein the method comprises the following steps, which are carried out before starting a generative Production of the component (3) are carried out: - circulate the gas in the gas circulation system (41), - setting an initial overpressure in the production chamber (13), - setting an initial volume fraction of a gas component of the circulated gas, - Measuring an increase over time in the volume fraction of the gas component in the production chamber (13), -comparing the measured increase in the volume fraction over time with a test threshold value which indicates an allowable inflow leak rate, and - Generating a leak rate test value based on the comparison. procedure after claim 1 , wherein the powder material (5) can be temperature-controlled during additive manufacturing with a heat source, in particular is provided on a construction platform (27) that can be heated with a heating device (31) in the manufacturing chamber (13) and/or with a radiant heater (31A), a Laser radiation source or an infrared radiator can be heated, and wherein during the measurement of the increase in the volume fraction over time, the gas in the gas circulation system (41) is circulated under a thermal boundary condition in which absorption of the gas component in the powder material (5) and/or in the component (3) essentially does not affect the temporal increase in the volume fraction. procedure after claim 2 , also with: - Providing the thermal boundary condition by deactivating the heat source or by activating the heat source until a maximum temperature limit is present in the powder material (5) at which absorption of the gas component in the powder material (5) and/or in the component (3) occurs essentially unaffected by the increase in volume over time. Method according to one of the preceding claims, wherein the initial volume fraction of the gas component is set to a value in the measuring range of the gas sensor (S_G), and wherein in particular the initial volume fraction of the gas component is assigned to an oxygen gas component and the initial volume fraction by supplying protective gas to the gas circuit system ( 41) is adjustable. A method according to any one of the preceding claims, further comprising: - Regulating the overpressure in the production chamber (13) while measuring the increase in the volume fraction over time, in particular by supplying protective gas to the gas circulation system (41). Procedure according to one of Claims 1 until 3 , wherein the gas in the gas circulation system (41) is circulated under an unregulated boundary condition with regard to the overpressure in the production chamber (13). Method according to one of the preceding claims, wherein the increase over time in the volume fraction of the gas component is measured over at least 5 minutes or at least 10 minutes and in particular in a time window in a range from 5 to 15 minutes and in particular before activation of a heat source for tempering the powder material ( 5) is measured. A method according to any one of the preceding claims, further comprising the step of: - Determining the test threshold value specifically for process conditions, which include a type of powder material (5) and an extent of a temperature-controlled surface area in the production chamber (13), and wherein the test threshold value for oxygen as the gas component on which the measurement is based is in a range from 10 ppmv/hr to 300 ppmv/hr. A method according to any one of the preceding claims, further comprising the steps of: - determining that the leak rate test value allows a manufacturing process to be carried out, and - Activation of taking the process conditions, in particular a heat source for tempering the powder material (5) is activated. Procedure according to one of Claims 1 until 8th , further with the steps: - determining that the leak rate test value prevents a production process from being carried out, and - outputting a test signal which indicates that the gas circulation system (41) is to be checked by an operator with regard to the leak rate. Method for checking a manufacturing atmosphere that was present during a manufacturing process with a device (1) for the additive manufacturing of a component (3) from a powder material (5), the powder material (5) being on a construction platform (27) in a manufacturing chamber (13) is provided, wherein the gas circulation system (41) for a circulation of a gas through the production chamber (13) - a pump (47) fluidly connected to the processing chamber (13), - a protective gas connection (53) which is fluidly connected to a protective gas tank (55) for a controllable supply of protective gas, - A pressure sensor (S_P) for measuring a pressure present in the gas circulation system (41), and in particular in the production chamber (13), and - a sensor (S_G) for measuring a volume fraction of a gas component of the circulated gas and is also designed to provide the manufacturing atmosphere with an overpressure in the manufacturing chamber (13), and wherein the method comprises the following steps: - Before starting the additive manufacturing of the component (3), performing the method according to any one of the preceding claims, - Carrying out the manufacturing process with the device (1) if an initially generated leak rate test value enables the manufacturing process to be carried out, - optional deactivation of a heat source for tempering the powder material (5) after completion of the manufacturing process, - Cooling of the production atmosphere below a temperature threshold value, - Re-performing the method according to any one of the preceding claims, wherein the leak rate test value generated again after the manufacturing process has been carried out is compared to a leak rate threshold value which indicates an allowable manufacturing process inflow leak rate, and - generating a manufacturing process check value based on the comparison, the manufacturing process check value for checking the manufacturing atmosphere indicating whether the manufacturing process was performed below the allowable manufacturing process inflow leak rate. Device (1) for the additive manufacturing of a three-dimensional component (3) from a powder material (5), having: a manufacturing chamber (13), a construction platform (27) in the manufacturing chamber (13), the powder material (5) being on the construction platform (27 ) is provided, an irradiation system (7) for generating an energy beam for irradiating the powder material (5) for producing the component (3) in layers, and a gas circulation system (41) for circulating a gas through the production chamber (13), the Gas circulation system (41) comprises - a pump (47) fluidly connected to the production chamber (13), - an inert gas connection (53), which is fluidly connected to an inert gas tank (55) for the controllable supply of inert gas, - a pressure sensor (S_P) for measuring a pressure present in the gas circulation system (41), and in particular in the production chamber (13), and - a gas sensor (S_G) for measuring a volume fraction of a gas component of the circulated gas it and is also designed to set a manufacturing atmosphere with an overpressure in the manufacturing chamber (13), and wherein the manufacturing device (1) further comprises a control device (61) with at least one microprocessor (61A) and a memory device (61B), wherein the Storage device (61B) is set up to store instructions which, when executed by the microprocessor (61A), sub-steps of a method according to one of Claims 1 until 11 execute. Manufacturing device (1) after claim 12 , wherein the controller (61) is adapted to process instructions which, when executed by the microprocessor (61A), cause - the pump (47) to circulate gas through the processing chamber (13), - measurement data from the pressure sensor (S_P) are read in, - volume fraction data of the gas sensor (S_G) are read in, which indicate a development over time of the volume fraction of the gas component over at least 5 minutes or at least 10 minutes and in particular in a time window in a range of 5 to 15 minutes, - a time Development of the volume fraction of the gas component is compared with a test threshold value, which specifies a permissible inflow leak rate, and a leak rate test value is generated based on the comparison, and/or - a manufacturing process is carried out with the manufacturing device (1) according to a manufacturing plan, and wherein the manufacturing device (1) optionally a heat source for tempering the powder material (5), in particular a heating device (31) for heating the construction platform (27) and/or a radiant heater (31A) for radiating the powder material (5), and the control device (61) arranged to process instructions which, when executed by the microprocessor (61A), cause - the heat source to be activated, partially activated or deactivated, and optionally - to provide thermal boundary conditions by deactivating the heat source or such is activated, so that there is a maximum temperature limit in the powder material (5) at which absorption of the gas component in the powder material (5) and/or in the component (3) essentially does not affect the increase in the volume fraction over time, and volume fraction data of the gas sensor (S_G) be read in if the thermal boundary condition is presented.

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