DE102016220949B3 - Method for rapidly inerting a chamber of an additive component manufacturing machine and associated machine - Google Patents

Abstract

The inventive method for inerting a chamber (2) of a machine (1) for the additive production of components, in particular an LMF or SLS machine, comprises the following method steps: expanding an expansion body (10) in the chamber (2) in an open Chamber outlet (4) by filling the expansion body (10) with a pressurized fluid (17) to at least partially, in particular completely, displace the gas volume in the chamber (2) out of the chamber (2) through the chamber outlet (4); and then filling the chamber (2) with an inert gas (17) through an open chamber inlet (3) while simultaneously deflating the expansion body (10).

Description

The invention relates to a method for inerting a chamber of a machine for the additive production of components, in particular a LMF (Laser Metal Fusion) or SLS (Selective Laser Melting) machine, as well as an associated machine for the additive production of components. Such a machine is for example in EP 3 023 228 A1 or in DE 10 2009 006 189 A1 described.

In machines for the additive production of components, reactive materials are processed by applying a powder layer (metal, ceramic, thermoplastics) to a substrate plate in a construction or process chamber and solidifying it with a laser beam. When the powder layer is melted with the laser beam, it is called Laser Metal Fusion (LMF) or Selective Laser Melting (SLM). If the powder layer is only sintered with the laser beam, this is called Selective Laser Sintering (SLS). Subsequently, the substrate plate is lowered by a powder layer thickness and a new powder layer is applied and solidified again until a 3-dimensional component has been produced.

For reactive materials in the form of easily oxidizable and combustible metal dusts, usually after closing the machine, an inert gas under overpressure, e.g. Nitrogen or argon, passed through the process chamber ("inerting"), so that due to the overpressure no impurities can penetrate from the outside into the process chamber. The oxygen content and, if necessary, also the proportion of other impurities (water, organic residues) in the process chamber is gradually "diluted" by displacement until the laser beam can safely begin to melt it, without causing unwanted reactions of the powder, such as eg An explosion or reproduction of combustion occurs, which can lead to a disruption of the process, associated with losses in the quality of the components down to the rejects. However, this dilution process has the disadvantage that it takes a long time, since not only reactive gas, but also already existing in the process chamber inert gas is displaced by the incoming inert gas.

Today's LMF construction process requires a defined protective gas atmosphere (eg O ₂ or H ₂ O content). The inerting today takes place almost exclusively in the machine main time. With increasing demand for high inert gas quality (eg residual O ₂ content <50 ppm) and larger installation spaces, the machine set-up or downtime increases exponentially due to the duration for the inertization. Due to the concept, the machines are regularly opened when the job is changed, which causes the chambers to fill with air. The inertization is carried out by continuous supply of inert gas and monitoring of the controlled variables for the atmosphere (eg O ₂ content) until the target value in the chamber has been reached. There is a risk that areas of the machine (eg docked overflow tank) due to the flow are not sufficiently inertized and air masses from "dead" zones, if necessary, only in the process (by displacement by powder) in motion and interfere with the construction process.

In order to accelerate the inerting of the process chamber, it is known to apply vacuum prior to inerting to the process chamber. This has the advantage that reactive gases are removed from the process chamber very quickly and after the subsequent filling of the process chamber with inert gas make up only a very small proportion. This process can be repeated in order to further reduce the proportion of reactive gases. By a slight overpressure of the inert gas, the ingress of impurities from the outside into the inertized process chamber can be prevented. This saves inert gas and time in the production of the inert atmosphere in the process chamber, but has the disadvantage that the machine must be designed both for pressures near 0 bar and for a slight atmospheric pressure. Although the vacuumization of the process chamber is significantly more efficient than the mere flooding with inert gas, it may still be time consuming.

From the DE 37 19 395 A1 For example, an expandable bag for shutting off a pipeline is known, which can be filled with liquid, thereby shutting off the pipeline.

From the DE 10 2007 015 909 A1 Furthermore, a method for producing fiber-reinforced hollow bodies with integrally molded elements in a mold is known. In this case, a fiber mat is laminated in two halves of the hollow mold, which respectively form the negative mold for the fiber-reinforced hollow body to be produced with integrally molded elements. The fiber mat is pressed by means of an introduced into the mold inflatable element form fit into the mold by the inflatable element is inflated after joining the halves of the mold.

Finally, out of the DE 195 12 753 A1 nor a buoyancy aid for watercraft known, which has a inflatable by a gas bag or floating bag with pressure relief valve and a, to be opened at least one place enclosure.

In contrast, the present invention has for its object to provide an alternative method for rapid and gas-saving inerting a chamber of the machine, without the Chamber must be designed for greater negative pressures.

1. a. Expandieren eines Expansionskörpers in der Kammer bei einem geöffneten Kammerauslass durch Befüllen des Expansionskörpers mit einem Druckfluid, um das in der Kammer befindliche Gasvolumen zumindest teilweise, insbesondere vollständig, durch den Kammerauslass aus der Kammer zu verdrängen; und
2. b. anschließend Befüllen der Kammer mit einem Inertgas durch einen geöffneten Kammereinlass bei gleichzeitigem Entleeren (Inflation) des Expansionskörpers.

This object is achieved by a method for inerting a chamber of a machine for the additive production of components, in particular an LMF or SLS machine, with the following method steps:

1. a. Expanding an expansion body in the chamber at an open chamber outlet by filling the expansion body with a pressurized fluid to at least partially, in particular completely, displace the volume of gas in the chamber through the chamber outlet from the chamber; and
2. b. then filling the chamber with an inert gas through an open chamber inlet with simultaneous emptying (inflation) of the expansion body.

Instead of diluting the atmosphere in the process chamber time consuming with inert gas until a predetermined oxygen content is reached, according to the invention, a flexible, gas-tight expansion body, such. a balloon or bladder, inflated in the chamber until it fills almost all of the free volume present in the chamber and so has almost completely expelled the contaminated or oxidizing atmosphere from the chamber through the chamber outlet. Subsequently, the chamber is filled with inert gas and emptied of the expansion body, so that only a small amount of reactive gases / impurities in the chamber is present. As in the case of vacuum, this process can be repeated one or more times to further reduce the proportion of reactive gases in the chamber. The expansion of the expansion body is most easily done by filling with compressed air or inert gas. Preferably, the chamber inlet and the chamber outlet are equipped with valves, which are controlled by a machine control accordingly.

• - kürzere Inertisierungsdauer und dadurch reduzierte Rüst- bzw. Nebenzeiten;
• - geringerer Inertgasverbrauch;
• - einfaches Monitoring ohne aufwendige O_2-Sensorik in der Kammer;
• - Inertisierung schlecht zugänglicher Maschinenbereiche (z.B. Überlaufbehälter) effizient und unabhängig von der Füllhöhe des Pulvers in der Kammer.

In particular, the inertization process according to the invention has the following advantages over the conventional processes:

• - shorter duration of inertization and thus reduced set-up times or idle times;
• - lower inert gas consumption;
• - simple monitoring without elaborate O ₂ sensors in the chamber;
• - Inerting of poorly accessible machine areas (eg overflow tank) efficiently and independently of the filling level of the powder in the chamber.

Preferably, the filling of the chamber with the inert gas takes place with the chamber outlet closed, the filling of the chamber with inert gas and the emptying of the expansion body being carried out in the opposite direction. Due to the closed chamber outlet, the inert gas excess pressure built up in the chamber can then be maintained during the entire process duration.

Alternatively, the filling of the chamber with the inert gas can also be carried out with the chamber outlet open, as long as the inert gas in the chamber is always under overpressure.

In particular, in order to protect the expansion body from excessive temperatures in the chamber and not to influence the protective gas flow during the process, the expansion body does not remain permanently in the chamber, but is advantageously housed in its non-expanded initial position outside the actual chamber, e.g. in an open to the chamber storage space, which can be closed off with a cover of the chamber. By filling with the pressurized fluid, the expansion body can be expanded out of the stowage space into the chamber. After the chamber has been filled with inert gas and the emptied expansion body has been accommodated in the storage space again by the inflowing inert gas or manually by means of gloves, the stowage space can be closed again with the cover. Without extensive monitoring, the chamber is completely inertized when the expansion body has been emptied again.

In a further aspect, the invention also relates to a machine for the additive production of components, in particular an LMF or SLS machine, having an inertizable chamber which has an inlet opening for inert gas and an outlet opening, wherein the machine according to the invention can be filled with a pressurized fluid the chamber has expandable expansion body which at least partially, in particular completely fills the free volume present in the chamber in an expanded position in the chamber.

Further advantages and advantageous embodiments of the subject invention will become apparent from the description, the claims and the drawings. Likewise, the features mentioned above and the features listed further can be used individually or in combination in any combination. The embodiment shown and described is not to be understood as an exhaustive list, but rather has exemplary character for the description of the invention.

• 1a-1c schematisch die Prozesskammer einer LMF-Maschine zur additiven Fertigung von Bauteilen mit einem Expansionskörper, der in 1a in einer nicht-expandierten Ausgangsstellung, in 1b in einer expandierten Endstellung und in 1c in einer teilexpandierten Zwischenstellung gezeigt ist.

Show it:

• 1a - 1c schematically the process chamber of an LMF machine for the additive production of components with an expansion body, which in 1a in a non-expanded starting position, in 1b in an expanded end position and in 1c is shown in a partially expanded intermediate position.

In the 1a - 1c shown LMF machine 1 serves for the additive production of components and includes an inertizable process chamber 2 with an inlet opening 3 for inert gas and with an outlet opening 4 , In the process chamber 2 is a powder layer (metal, ceramic, thermoplastics) on a substrate plate 5 applied and melted with a laser beam (not shown) and thereby solidified. Subsequently, the substrate plate 5 lowered by a powder layer thickness and applied a new layer of powder and solidified again until a 3-dimensional component was manufactured.

Due to the reactive powder materials in the form of easily oxidizable and flammable metal dusts, the process chamber 2 be inertized before the layer buildup process, so filled with an inert gas under pressure (eg nitrogen or argon), so that there can be no undesirable reactions of the powder and due to the overpressure no contamination from the outside into the process chamber 2 can penetrate. This inertization takes place in the machine off-time.

The inlet opening 3 is via an inlet valve 6 to an inert gas line 7 and the outlet opening 4 via an exhaust valve 8th to the atmosphere 9 connected. Furthermore, the machine points 1 a gas-tight expansion body 10 on that in 1a in its non-expanded starting position and in 1b is shown in its expanded end position. Instead of the balloon as shown in the embodiment shown, the expansion body 10 also be designed as a bellows. The expansion body 10 can via a 3/2-way switching valve 11 either to a compressed air line 12 (or to the inert gas line 7 ) or with the atmosphere 9 get connected.

In the starting position is the unexpanded expansion body 10 outside the process chamber 2 in a storage space 13 housed, extending over a chamber opening 14 in the process chamber 2 opens. In 1a is the chamber opening 14 through a cover 15 locked.

For fast and gas-saving inerting of the process chamber 2 the procedure is as follows:

The cover 15 is removed, manually via glove intervention or in the case of a motor-driven cover by driving the motor. With inlet closed 6 and with the exhaust valve open 8th is activated by operating the changeover valve 11 the expansion body 10 to the compressed air line 12 connected and with compressed air 16 filled. This will be the expansion body 10 through the chamber opening 14 through into the process chamber 2 into it, until that in the process chamber 2 located gas volume through the chamber outlet 4 from the process chamber 2 almost completely displaced ( 1b ). In the construction of the process chamber 2 is preferably dispensed with sharp edges, for example. On the powder coater, at the inlet opening 3 and the outlet opening 4 or at the transition to the overflow tank or to the substrate plate 5 , Then the outlet valve 8th closed and the inlet valve 6 open, eliminating the process chamber 2 to the inert gas line 7 is connected and with inert gas 17 is filled. At the same time by pressing the changeover valve 11 the expansion body 10 with the atmosphere 9 connected and thus emptied ( 1c ). When the expansion body 10 is completely emptied, the inerting process is complete, and the process chamber 2 is complete with the inert gas under inert pressure p 17 filled. Due to the inflowing inert gas 17 or manually via glove procedures (not shown) becomes the deflated expansion body 10 again in the storage room 13 accommodated. Finally, the chamber opening 14 again with the cover 15 manually or motor-closed.

The control of the individual valves 6 . 8th . 11 is preferably automated by means of a machine control, but can in principle also be done manually.

Claims (13)

Method for inerting a chamber (2) of a machine (1) for the additive production of components with the following method steps: a. Expanding an expansion body (10) in the chamber (2) at an open chamber outlet (4) by filling the expansion body (10) with a pressurized fluid (16) to at least partially expose the volume of gas in the chamber (2) through the chamber outlet (4 ) to displace from the chamber (2); and b. then filling the chamber (2) with an inert gas (17) through an open chamber inlet (3) with simultaneous emptying of the expansion body (10). Method according to Claim 1 , characterized in that the filling of the chamber (2) with the inert gas (17) takes place with the chamber outlet (4) closed. Method according to Claim 1 , characterized in that the filling of the chamber (2) with the inert gas (17) takes place with the chamber outlet (4) open. Method according to one of the preceding claims, characterized in that the steps a. and b. be repeated. Method according to one of the preceding claims, characterized in that the expansion body (10) is accommodated in its unexpanded starting position in a stowing space (13) and by filling with the pressurized fluid (16) from the stowage space open to the chamber (2) ( 13) is expanded into the chamber (2). Method according to one of the preceding claims, characterized in that in step a. that in the chamber (2) located gas volume is completely displaced by the chamber outlet (4) from the chamber (2). Method according to one of the preceding claims, characterized in that the method for inerting a chamber (2) of an LMF or SLS machine (1) is used. Machine (1) for the additive production of components with an inertizable chamber (2), which has an inlet opening (3) for inert gas and an outlet opening (4), characterized by a filling with a pressure fluid (16) in the chamber (2) expandable expansion body (10) which at least partially fills the free volume present in the chamber (2) in a position expanded in the chamber (2). Machine after Claim 8 , characterized in that the expansion body (10) is a balloon or a bellows. Machine after Claim 8 or 9 , characterized in that the expansion body (10) is housed in its non-expanded initial position in a chamber (2) open storage space (13). Machine after Claim 10 , characterized in that the storage space (13) with a cover (15) from the chamber (2) can be shut off. Machine after one of the Claims 8 to 11 , characterized in that the expansion body (10) in the in the chamber (2) expanded position completely in the chamber (2) existing free volume fills. Machine after one of the Claims 8 to 12 , characterized in that the machine is an LMF or SLS machine (1).

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