GB2569520A

GB2569520A - Method for fast inertization of a chamber of a machine for additive production of components and associated machine

Info

Publication number: GB2569520A
Application number: GB1905713.2A
Authority: GB
Inventors: Haugk Ben
Original assignee: Trumpf Laser und Systemtechnik GmbH
Current assignee: Trumpf Laser und Systemtechnik GmbH
Priority date: 2016-10-25
Filing date: 2017-10-24
Publication date: 2019-06-19
Anticipated expiration: 2037-10-24
Also published as: CN109862978A; GB201905713D0; DE102016220949B3; CN109862978B; GB2569520B; WO2018077894A1

Abstract

The invention relates to a method for inertization of a chamber (2) of a machine (1) for additive production of components, in particular a LMF or SLS machine, comprising the following method steps: a. expanding an expansion body (10) in the chamber (2), when a chamber outlet (4) is opened, by filling the expansion body (10) with a pressure fluid (17) in order to displace the gas volume located in the chamber (2) out of the chamber (2), at least in part, in particular completely, through the chamber outlet (4); and b. subsequently filling the chamber (2) with an inert gas (17) through an opened chamber inlet (3) while simultaneously emptying the expansion body (10). The associated machine (1) according to the invention has an expansion body (10), which can be filled with pressure fluid (16) and can be expanded in the chamber (2) and which, in an expanded position in the chamber (2), fills the available free volume in the chamber (2) at least in part, in particular completely.

Description

Englisch Translation of PCTEP2017077195

Method for quickly inerting a chamber of a machine for the additive manufacturing of components and associated machine

The invention relates to a method for inerting a chamber of a machine for the additive manufacturing of components, in particular an LMF (Laser Metal Fusion) or SLS (Selective Laser Melting) machine, and also to an associated machine for the additive manufacturing of components. Such a machine is described for example in EP 3 023 228 A1.

In machines for the additive manufacturing of components, reactive materials are processed, in that a layer of powder (metal, ceramic, thermoplastics) is applied to a substrate plate in a building chamber or process chamber and is solidified with a laser beam. If the layer of powder is melted by the laser beam, this is referred to as Laser Metal Fusion (LMF) or Selective Laser Melting (SLM). If the layer of powder is only sintered by the laser beam, this is referred to as Selective Laser Sintering (SLS). Subsequently, the substrate plate is lowered by an amount corresponding to the thickness of the layer of powder and a new layer of powder is applied and once again solidified, until a three-dimensional component has been manufactured.

In the case of reactive materials in the form of readily oxidizable and combustible metal dusts, usually after closing the machine a pressurized inert gas, for example nitrogen or argon, is passed through the process chamber (“inerting”), so that the overpressure prevents impurities from penetrating into the process chamber from the outside. The oxygen content, and any fraction of other impurities (water, organic residues) there may be, in the process chamber is gradually “diluted” by displacement to the extent required until it is safe to begin with the melting by the laser beam, without undesired reactions of the powder occurring, such as for example an explosion or propagation of a combustion, which can lead to a disturbance of the process together with losses of quality of the component, even to the extent that it is rejected. However, this diluting process has the disadvantage that it takes a very long time, because the inflowing inert gas displaces not only reactive gas but also inert gas that is already present in the process chamber.

The present-day LMF building process requires a defined inert gas atmosphere (for example an 02 or H2O content). Inerting is today performed almost exclusively in the primary processing time of the machine. With the increasing demand for a high quality of inert gas (for example residual 02 content < 50 ppm) and larger building spaces, the time taken for the inerting is having the effect that the machine setting-up time or downtime is increasing exponentially. The concept of the process means that, when changing from one job to another, the machines are regularly opened, as a result of which the chamber is filled with air. The inerting is performed by continuously supplying inert gas and monitoring the controlled variables for the atmosphere (for example 02 content) until the target value is achieved in the chamber. There is the risk here that, for flow-related reasons, regions of the machine (for example attached overflow containers) are not sufficiently inerted and air masses from dead zones can possibly only begin moving during the process (due to being displaced by powder) and disturb the building process.

In order to speed up the inerting of the process chamber, it is known to apply a vacuum to the process chamber before the inerting. This has the advantage that reactive gases are removed very quickly from the chamber and only make up a very small fraction after subsequent filling of the process chamber with inert gas. This operation can be repeated, in order to reduce the fraction of reactive gases still further. A slight overpressure of the inert gas allows the penetration of impurities into the inerted process chamber from outside to be prevented. This saves inert gas and time when producing the inert atmosphere in the process chamber, but has the disadvantage that the machine has to be designed both for pressures close to 0 bar and for a pressure slightly above atmospheric pressure. Although evacuating the process chamber to create a vacuum is much more efficient than just filling with inert gas, it can still sometimes be very timeconsuming.

Against this background, the present invention is based on the object of providing an alternative method for inerting a chamber of the machine quickly and while saving gas, without having to design the chamber for great overpressures.

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

a. expanding an expansion body in the chamber with an opened chamber outlet by filling the expansion body with a pressure fluid, in order to displace the gas volume located in the chamber out of the chamber at least partially, in particular completely, through the chamber outlet; and

b. subsequently filling the chamber with an inert gas through an opened chamber inlet while simultaneously emptying the expansion body (deflation).

Instead of the time-consuming procedure of diluting the atmosphere present in the process chamber with inert gas to the extent required until a predetermined oxygen content is achieved, according to the invention a flexible, gas-tight expansion body, such as for example a balloon or bellows, is inflated in the chamber until it virtually fills the entire free volume present in the chamber, and so has displaced the contaminated or oxidizing atmosphere out of the chamber almost completely through the chamber outlet. Subsequently, the chamber is filled with inert gas and the expansion body is emptied, so that there is only a small amount of reactive gases/impurities left in the chamber. As in the case of a vacuum, this operation can be repeated one or more times in order to keep reducing the fraction of reactive gases in the chamber. The expanding of the expansion body is performed most easily by filling with compressed air or inert gas. Preferably, the chamber inlet and the chamber outlet are fitted with valves, which are activated appropriately by the machine control system.

The inerting method according to the invention has in particular the following advantages over the conventional methods:

- shorter inerting time, and as a result reduced setting-up or non-productive times;

- lower inert gas consumption;

- easy monitoring without complex 02 sensor equipment in the chamber;

- inerting regions of the machine that are difficult to access (for example overflow containers) efficiently and independently of the filling level of the powder in the chamber.

Preferably, the filling of the chamber with the inert gas is performed with the chamber outlet closed, the filling of the chamber with inert gas and the emptying of the expansion body correspondingly taking place counter to one another. On account of the closed chamber outlet, inert gas overpressure built up in the chamber can then be maintained throughout the entire duration of the process.

Alternatively, the filling of the chamber with the inert gas may also be performed with the chamber outlet opened, as long as the inert gas in the chamber is constantly under overpressure.

In particular to protect the expansion body from excessive temperatures in the chamber, and not to influence the flow of inert gas during the process, the expansion body does not remain permanently in the chamber but in its nonexpanded starting position is advantageously kept outside the actual chamber, for example in a stowage space that is open to the chamber and can be shut off from the chamber by a cover. By filling with the pressure fluid, the expansion body can be expanded out of the stowage space into the chamber. Once the chamber is filled with inert gas and the emptied expansion body has been returned to the stowage space by the inert gas flowing in or manually by using glove ports, the stowage space can be closed again with the cover. Without complex monitoring, the chamber is completely inerted when the expansion body has been emptied again.

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

Further advantages and advantageous refinements of the subject matter of the invention are evident from the description, the claims and the drawing. Similarly, the features mentioned above and those set out below can be used each on their own or together in any desired combinations. The embodiment shown and described should not be understood as a definitive list, but rather is of exemplary character for portraying the invention.

In the figures:

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

The LMF machine 1 shown in Figs 1a-1c serves for the additive manufacturing of components and comprises an inertable process chamber 2 with an inlet opening 3 for inert gas and with an outlet opening 4. In the process chamber 2, a layer of powder (metal, ceramic, thermoplastics) is applied to a substrate plate 5 and melted with a laser beam (not shown) and thereby solidified. Subsequently, the substrate plate 5 is lowered by an amount corresponding to the thickness of the layer of powder and a new layer of powder is applied and once again solidified, until a three-dimensional component has been manufactured.

On account of the reactive powder materials in the form of readily oxidizable and combustible metal dusts, the process chamber 2 must be inerted before the process of building up layers, that is to say must be filled with a pressurized inert gas (for example oxygen or argon), so that no undesired reactions of the powder can occur and, as a result of the overpressure, no impurities can penetrate into the process chamber 2 from outside. This inerting is performed in the non-productive time of the machine.

The inlet opening 3 is connected via an inlet valve 6 to an inert gas line 7 and the outlet opening 4 is connected via an outlet valve 8 to the atmosphere 9. Furthermore, the machine 1 has a gas-tight expansion body 10, which in Fig. 1a is shown in its non-expanded starting position and in Fig. 1b is shown in its expanded end position. Instead of being designed as a balloon, as shown in the exemplary embodiment, the expansion body 10 may also be designed as a bellows. The expansion body 10 may be connected via a 3/2-way changeover valve 11 either to a compressed air line 12 (or to the inert gas line 7) or to the atmosphere 9.

In the starting position, the non-expanded expansion body 10 is kept outside the process chamber 2 in a stowage space 13 which opens via a chamber opening 14 into the process chamber 2. In Fig. 1a, the chamber opening 14 is closed by a cover 15.

For inerting the process chamber 2 in a way that is quick and saves gas, the following procedure is adopted:

The cover 15 is removed, to be precise manually by using glove ports or in the case of a motorized cover by activating the motor. With the inlet valve 6 closed and the outlet valve 8 opened, the expansion body 10 is connected to the compressed air line 12 by actuating the changeover valve 11 and is filled with compressed air 16. As a result, the expansion body 10 is expanded through the chamber opening 14 into the process chamber 2, until the gas volume located in the process chamber 2 has been displaced almost completely out of the process chamber 2 through the chamber outlet 4 (Fig. 1 b). The structural design of the process chamber 2 preferably does not have any sharp edges, for example on the powder charger, at the inlet opening 3 and the outlet opening 4 or at the transition to the overflow container or to the substrate plate 5. Then, the outlet valve 8 is closed and the inlet valve 6 is opened, whereby the process chamber 2 is connected to the inert gas line 7 and is filled with inert gas 17. At the same time, by actuating the changeover valve 11, the expansion body 10 is connected to the atmosphere 9 and is thereby emptied (Fig. 1c). When the expansion body 10 has been emptied completely, the inerting operation is completed, and the process chamber 2 is filled completely with the inert gas 17 under slight overpressure p.

The emptied expansion body 10 is returned to the stowage space 13 by the inert gas 17 flowing in or manually by using glove ports (not shown). Finally, the chamber opening 14 is closed again with the cover 15 manually or in a motorized manner.

The activation of the individual valves 6, 8, 11 is preferably performed in an automated manner by means of a machine control system, but in principle may also be performed manually.

Claims

Patent claims

1. A method for inerting a chamber (2) of a machine (1) for the additive manufacturing of components, in particular an LMF or SLS machine, with the following method steps:

a. expanding an expansion body (10) in the chamber (2) with an opened chamber outlet (4) by filling the expansion body (10) with a pressure fluid (16), in order to displace the gas volume located in the chamber (2) out of the chamber (2) at least partially, in particular completely, through the chamber outlet (4); and

b. subsequently filling the chamber (2) with an inert gas (17) through an opened chamber inlet (3) while simultaneously emptying the expansion body (10).

2. The method as claimed in claim 1, characterized in that the filling of the chamber (2) with the inert gas (17) is performed with the chamber outlet (4) closed.

3. The method as claimed in claim 1, characterized in that the filling of the chamber (2) with the inert gas (17) is performed with the chamber outlet (4) opened.

4. The method as claimed in one ofthe preceding claims, characterized in that steps a. and b. are repeated.

5. The method as claimed in one ofthe preceding claims, characterized in that the expansion body (10) in its non-expanded starting position is kept in a stowage space (13) and is expanded out of the stowage space (13) that is open to the chamber (2) into the chamber (2) by filling with the pressure fluid (16).

6. A machine (1) for the additive manufacturing of components, in particular an LMF or SLS machine, with an inertable chamber (2), which has an inlet opening (3) for inert gas and an outlet opening (4), characterized by an expansion body (10) that can be filled with a pressure fluid (16) and can be expanded in the chamber (2) and which, in the position in which it is expanded in the chamber (2), fills the free volume present in the chamber (2) at least partially, in particular completely.

7. The machine as claimed in claim 6, characterized in that the expansion body (10) is a balloon or a bellows.

8. The machine as claimed in claim 6 or 7, characterized in that the expansion

10 body (10) in its non-expanded starting position is kept in a stowage space (13) that is open to the chamber (2).

9. The machine as claimed in claim 8, characterized in that the stowage space (13) can be shut off from the chamber (2) with a cover (15).