BE1027305B1 - DEPOWING PROCESS - Google Patents

Abstract

The subject of the invention is a method (1) for manufacturing a part, the method (1) comprising: an additive manufacturing operation (10) by melting powder beds and a depouding operation (20), remarkable in terms of that the dusting operation (20) is at least partially carried out simultaneously with the additive manufacturing operation (10), and in that the dusting operation (20) comprises the injection of an air flow in the room and / or the air intake contained in the room. Advantageously, channels dedicated to depolding are manufactured at the same time as the part to create an air supply or suction path.

Description

, Ç BE2019 / 5335 Description

TECHNICAL FIELD The invention relates to a method for manufacturing a part comprising an additive manufacturing operation by melting powder beds. In particular, the invention relates to a dusting operation in conjunction with production. PRIOR ART In an additive manufacturing process by melting powder beds, successive layers of powder are deposited on a platform. A laser beam scans part of the powder layer to merge the grains which, when they solidify, create, layer after layer, the desired geometry for the part to be manufactured. Part of each layer is intentionally not reached by the beam to create cavities in the part to be produced. || there is therefore a part of the powder which is not fused. This unfused powder should be removed from the room. The usual technique is to fabricate the part and then remove any grains of powder that have not been fused until the part is finished and the additive manufacturing operation is complete. This so-called dusting step can be done using a workshop vacuum cleaner or using a brush.

This technique is not always sufficient for parts with complex internal shapes or with small cavities. This is the case, for example, for heat exchangers which are made up of a multitude of pipes, often small sections to maximize the heat exchange surfaces for a given flow. Post-production dusting does not always ensure that the internal ducts are free of unfused powders. However, a part whose powder has not been correctly removed has drawbacks. First, from a dimensional point of view, the powder that has not been removed can create amalgams, the part therefore not meeting its nominal dimensions, thus inducing assembly or operating problems. In the case of a heat exchanger, the efficiency of

> BE2019 / 5335 the exchanger can be affected by partially or completely blocked ducts. Next, the presence of metal powders in finished parts is undesirable for reasons of health risks for the operators handling these parts. The operator is usually protected by a coverall when handling powders but is no longer protected once he handles the finished part, which is supposed to be free of powders. Summary of the Invention Technical Problem The object of the invention is to overcome the above drawbacks and in particular to provide a depolding process that is more reliable and allows better control of the dimensions produced.

Technical solution The subject of the invention is a method for manufacturing a part comprising: an additive manufacturing operation by melting powder beds and a powder coating operation, remarkable in that the powder coating operation is at least partially carried out simultaneously. in the additive manufacturing operation, the depolding operation comprising the injection of an air flow into the part and / or the suction of air contained in the part.

Thus, by carrying out the powdering throughout the manufacture of the part, it is possible to ensure that no non-fused powder remains encapsulated in the finished part.

In practice, the room is built in an airtight enclosure. Air injection or suction therefore means that a suitable system is provided inside this chamber.

By “additive manufacturing operation” is meant the sequence of steps which allow the same machine to produce a part without external intervention (for example, without putting a semi-finished part back into position, and without human intervention). The term “depouding operation” is understood to mean a set of depouding steps which can be spaced out over time, and which take place on the same machine.

By "at least partially simultaneous" is meant that the dusting operation begins even though the additive manufacturing operation as a whole has not been completed. In order to remove dust, air is injected and / or sucked. The injection can take place alternately or simultaneously with the aspiration. According to advantageous modes of the invention, the method can comprise one or more of the following characteristics, taken in isolation or according to all the technically possible combinations: - the operation of additive manufacturing by melting powder beds comprises a channel manufacturing step dedicated to dusting, said channels preferably being cut after the additive manufacturing operation. Thus, channels are manufactured by additive manufacturing during the same operation and in the same machine as the manufacture of the part in question. These channels have no function for the finished part and are simply intended to bring in air for dusting during manufacturing. In other words, these temporary channels create an air intake or suction path; - The channels are semi-cylindrical in shape, formed directly on a platform on which the first layer of powder is deposited. This technique avoids consuming too much powder for the sole manufacture of the channels; - The channels open onto respective end pieces which form manufacturing inserts. The end pieces can be of materials other than powder and in particular more resistant to temperature; - The method comprises a preliminary step before the deposition of the first layer of powder, step during which the end pieces are positioned on the manufacturing platform and air injection and / or suction pipes are connected to the end pieces. Thus, suction and pressurizing means - for example a fan and a compressor - are connected to the end pieces before the start of production. The connection between the part and these end caps is made during manufacture through the channels.

This technique makes it possible to manufacture several types of parts while having the same air injection and suction device.

Only the shape of the channels will be adapted and therefore integrated into the programming of the machine on a case-by-case basis;

- air suction in one channel is simultaneous with air injection in another channel.

This makes it possible to multiply the efficiency of the depoudment; the part comprises cavities or pipes and the air is injected and / or the air is sucked into / from these cavities or pipes, optionally via the channels dedicated to depouding.

Indeed, it is advantageous for the channels to be fluidly connected to the internal cavities or pipes of the part; - the operation of additive manufacturing by melting powder beds comprises a succession of steps of depositing a layer of powder followed alternately by steps of melting part of the layer of powder by application of a beam energetic, the depouding operation consisting of at least one depouding step following a melting step, preferably of a plurality of depouding steps respectively succeeding several melting steps; the pressure of the injected air flow and / or the vacuum of the sucked air increases in absolute value with the number of layers, preferably up to approximately 10 bar; the quantity of powder sucked in or discharged by injection of air outside the room is measured and the injected air pressure and / or the vacuum of the sucked air is controlled in response to said quantity of powder.

Thus, when there is a regular decrease in the amount of powder, the pressure / vacuum can be gradually increased and vice versa, so as not to block the suction ducts in particular; - depoudment comprises air injection or suction cycles, and / or cycles of air injection followed by suction or vice versa, and / or cycles of injection and simultaneous aspiration, the cycles having a frequency which increases with the number of layers deposited.

For example, at the start of manufacturing, powdering can be done after melting every tenth layer and at the end of manufacturing, powdering can be done every two layers.

This allows a compromise between the manufacturing time and the reliability of the powder coating process; the part is substantially cylindrical, defining a vertical axis around which the channels are angularly irregularly distributed.

The asymmetry of the arrangement of the channels makes it possible to create more turbulence and therefore to improve the suction or separation of the non-fused powder from the part; - Compressed air comprises a suspension of an active agent such as a detergent, a lubricant, a colorant and / or an anti-oxidant.

The air injection during additive manufacturing is an opportunity to also carry out various treatments on the part; the part is a fuel-oil heat exchanger for a turbojet engine, the exchanger comprising pipes intended to be traversed by fuel or oil and whose diameter is preferably of the order of 0.6 mm, the powder preferably being a aluminum powder; - the channels have a section which is at least 3 times greater than the section of the pipes of the exchanger.

This scale makes it possible to increase the speed of the air entering the exchanger and therefore to promote the evacuation of the powders, at a given inlet pressure.

Advantages Provided The process according to the invention makes it possible to obtain unparalleled removal of unfused powders.

The post-manufacturing depolding operation is eliminated.

The surface finishes are also of better quality and the dimensions obtained are more precise.

On the other hand, the method does not require expensive equipment.

Brief description of the drawings FIG. 1 represents a diagram (Gantt type) of the method according to the invention; FIG. 2 represents an isometric view of a part being manufactured according to the method of the invention.

Figures 3 and 4 show examples of pressure or depression cycles that can be applied during the process according to the invention.

FIG. 5 illustrates the control of the pressure / depression as a function of the quantity of powder detected.

Description of the Embodiments FIG. 1 represents a diagram illustrating the progress of the method according to the invention as a function of time.

The horizontal axis represents the passage of time.

The additive manufacturing operation as a whole is rated 10. This is made up, among other things, of powder deposition steps 11 followed by melting steps 12. The melting results from the scanning of an energy beam on the powder, in particular a laser beam, which targets the portions of the layer which must be melted in order, after cooling, to constitute the part.

According to an advantageous embodiment of the invention, a step 13 at the start of manufacture is provided for the production of channels (denoted 38 in FIG. 2) which are dedicated to depouding.

This step 13 can extend over several printing of layers.

The example of Figure 1 shows an overlap on two layers of steps 13 and 11/12 but the overlap may be greater.

Optionally, these channels 38 are separated from the rest of the part manufactured during a sectioning operation 15 subsequent to the additive manufacturing 10. After certain powder melting steps, a depouding step 22 can take place. 22 forms the powder coating operation 20. The powder coating operation 20 overlaps the manufacturing operation 10 in time. There is thus a simultaneity of the manufacturing and the powder coating, although at the scale of the manufacturing steps. (and not operations), a layer deposition or fusion step is not simultaneous with the evacuation of the powders.

FIG. 1 represents schematically and only by way of illustration, the number and the arrangement in time of the various stages.

In practice, tens or even hundreds of layers of powder are deposited and merged. The frequency of the depoding steps is also purely indicative in FIG. 1. It can take place more often as the production progresses (and therefore less often at the start of production).

FIG. 2 describes an example of a part 30 produced with the method according to the invention. In this example, part 30 is a fuel / oil heat exchanger for a turbojet engine. This part is only used here as an illustration of the manufacturing process. The manufacturing process cannot be limited to the manufacture of this particular part.

The exchanger 30 is generally cylindrical in shape around a vertical axis A. The exchanger comprises a cylindrical body 32 containing pipes 34. The pipes 34 and the design of the heat exchange surfaces in this exchanger 30 may be similar to the exchanger disclosed in application BE2018 / 5931. Openings 36 allowing the arrival and the exit of the oil or fuel can be provided at the base of the exchanger 30. The complexity of the pipes 34 is such that only an additive manufacturing process makes it possible to produce the part. The exchanger 30 is shown here in a semi-finished state, during manufacture.

The deposition of the powder layers takes place on a platform 40. This platform is flat and is located in a hermetic enclosure.

According to an advantageous embodiment of the invention, channels 38 are manufactured. These are dedicated to the depolding steps and are not part of the finished part. They are intended to be separated from the part once the additive manufacturing operation is complete. The channels 38 can be rectilinear pipes of square or circular section, completely manufactured by additive manufacturing. Alternatively, to save manufacturing time for these channels, they can be formed from a half-cylinder manufactured directly from the platform 40. The channels 38 are in fluid communication with the cavities or pipes 34 of the exchanger 30. Thus, when air is blown in or sucked in through these channels 38, the cavities or pipes 34 of the exchanger 30 are traversed by an air flow which circulates the unfused powders to evacuate them.

End caps 50, for example metal or plastic, can be provided on the platform 40. These make it possible to fix compressed air or suction pipes (not shown). The channels 38 are made so as to connect the tubes 34 to the compressed air / suction lines.

End caps 50 and their associated conduits can be attached to platform 40 before the additive manufacturing operation 10 begins, during a step denoted 14 in FIG. 1. The same end caps 50 and conduits can be used to manufacture different. rooms. Only the geometry of the channels 38 will be adapted so that the end pieces 50 are connected to the areas of the part which are to be dusted.

In a way, the end pieces 50 can be considered as manufacturing inserts although they are not intended to be part of the finished part, in the sense that the material will come to conform to the end pieces 50 during manufacture.

The channels 38 are arranged around the axis A to distribute the air flows in the room during the depolding. Advantageously, the distribution of the channels 38 is not angularly regular around the axis λ to promote the generation of turbulence in the air flow and thus promote dusting. Advantageously, the section of the channels 38 is greater than the section of the tubes 34, for example with a ratio of approximately 3. This makes it possible, for a given air pressure, to multiply the effects of the compressed air or of suction in the pipes 34.

According to an advantageous embodiment, the compressed air blown into the room can comprise droplets of an active agent suspended in the air. For example, a detergent or a lubricant can promote the release of powders which would adhere to the part. A dye makes it possible to observe with the naked eye that the dusting takes place during manufacture. An anti-oxidant makes it possible to treat the part as early as possible during its manufacture.

Figure 3 shows an example of overpressure or depression cycles that can be used. A cycle can include several oscillations. A cycle can be repeated several times per step 22, interrupted by pauses.

Cycle T1 shows a cycle of compressed air.

Any type of cycle can be used, but pressure variations with pulses are sometimes more effective than constant value overpressure.

Square, triangular, or rectilinear variations may replace or overlap the sinusoidal variations shown.

The T2 cycle is a cycle of depression.

It can take place simultaneously (in a channel 38 other than that which is overpressed) with cycle T1 as shown in FIG. 3. Alternatively, the cycles follow one another or partially overlap in time.

The cycles T1 and T2 can be of different periods, or of the same period, in phase or not.

The period of the oscillations can vary for the same cycle.

The cycle period is advantageously shorter as the part manufacturing progresses.

FIG. 4 illustrates another example of an overpressure / depression cycle.

This can take place in a single channel.

In this example, the overpressure and the underpressure are part of the same T3 cycle. To perform the different cycles, the part 30, and possibly the channels 38 and / or the end pieces 50, is / are connected / connected to conduits supplied in a controlled manner with compressed air and suction.

Appropriate valves and control means (sensors, etc.) are provided.

In each of the examples, the pressure p can reach approximately 10 bar.

The depression dp may be less (in absolute value), for example -2 bar.

FIG. 5 illustrates a final aspect of the invention.

Sensors can be provided to estimate the quantity q of powder sucked into the ducts or expelled by the compressed air.

For example, inductive sensors, cameras or the like, judiciously placed in the manufacturing chamber or in the suction / compression ducts make it possible to detect the powder particles.

In an advantageous embodiment of the invention, the level of pressure or depression of the air flow is controlled as a function of the quantity of particles detected.

For example, the variations Aq of the quantity of particles q measured can be analyzed.

When there is a decrease in the quantity of particles measured, it can be considered that the quantity of powder which remains to be discharged into the room decreases.

The pressure or depression can be reduced so as not to use energy unnecessarily.

When the quantity increases, the pressure or depression can also be reduced to avoid clogging the ducts, if the quantity of powder exceeds a given threshold.

The duration of the depoudment steps can be adjusted according to the quantity of particles detected and thus not be predefined but adjusted in real time during manufacture.

The deposition of a layer of powder will not begin until after the previous depolding step is completed.

Claims (15)

Claims 1. Method (1) for manufacturing a part (30), the method (1) comprising: an operation (10) of additive manufacturing by melting powder beds and an operation (20) of depouding, characterized in that the powdering operation (20) is at least partially carried out simultaneously with the additive manufacturing operation (10), and in that the powdering operation (20) comprises the injection of an air flow into the room (30) and / or the air intake contained in the room (30). 2. Method (1) according to claim 1, characterized in that the operation (10) of additive manufacturing by melting powder beds comprises a step (13) of manufacturing channels (38) dedicated to depolding, said channels ( 38) being preferably sectioned after the additive manufacturing operation (10). 3. Method (1) according to claim 2, characterized in that the channels (38) are of semi-cylindrical shape, formed directly on a platform (40) on which is deposited the first layer of powder. 4. Method (1) according to claim 2 or 3, characterized in that the channels (38) open onto respective end pieces (50) which form manufacturing inserts. 5. Method (1) according to claim 4, characterized in that it comprises a preliminary step (13) before the deposition of the first layer of powder, step (13) during which the end pieces (50) are positioned on the manufacturing platform (40) and injection and / or air suction lines are connected to the nozzles (50). 6. Method (1) according to one of claims 2 to 5, characterized in that the suction of air into one channel (38) is simultaneous with an injection of air into another channel (38). 7. Method (1) according to one of claims 1 to 6, characterized in that the part comprises cavities or pipes (34) and air is injected and / or air is drawn into / from these cavities. or pipes (34), optionally via the channels (38) dedicated to dusting. 8. Method (1) according to one of claims 1 to 7, characterized in that the operation (10) of additive manufacturing by melting powder beds comprises a succession of steps (11) of depositing a layer of powder. followed alternately by steps (12) of melting part of the powder layer by application of an energy beam, the depouding operation (20) consisting of at least one subsequent depouding step (22) in a step (12) of melting, preferably of a plurality of steps (22) of depouding respectively succeeding several steps (12) of melting. 9. Method (1) according to one of claims 1 to 8, characterized in that the pressure (p) of the injected air flow and / or the depression (dp) of the sucked air increases in absolute value with the number of layers, preferably up to about 10 bar. 10. Method (1) according to one of claims 1 to 9, characterized in that the quantity (q) of powder sucked in or discharged by injection of air outside the room (30) is measured and the pressure (p) d the injected air and / or the vacuum (dp) of the sucked air is controlled in response to said quantity (q) of powder. 11. Method (1) according to one of claims 1 to 10, characterized in that the depolding comprises cycles (T1, T2) of air injection or suction, and / or cycles (T3) d air injection followed by aspiration or vice versa, and / or cycles (T1, T2) of simultaneous injection and aspiration, the cycles having a frequency which increases with the number of layers deposited. 12, A method (1) according to one of claims 1 to 11, characterized in that the part (30) is substantially cylindrical, defining a vertical axis (A) around which the channels (38) are angularly irregularly distributed. 13. Method (1) according to one of claims 1 to 12, characterized in that the compressed air comprises a suspension of an active agent such as a detergent, a lubricant, a dye and / or an anti-oxidant. 14. Method (1) according to one of claims 1 to 13, characterized in that the part (30) is a fuel-oil heat exchanger for a turbojet engine, the exchanger (30) comprising pipes (34) intended for be traversed by fuel or oil and whose diameter is preferably of the order of 06 mm, the powder preferably being an aluminum powder. 15. The method (1) according to claim 14 in combination with claim 2, characterized in that the channels (38) have a section which is at least 3 times greater than the section of the pipes (34) of the exchanger (30). ).