FR3088837A1 - SCRAPER FOR ADDITIVE MANUFACTURE OF METAL PARTS BY POWDER BED PROCESS - Google Patents

Abstract

A scraper (17) designed for additive manufacturing processes of mechanical parts (25) by transporting powder, depositing layers of the powder, melting the layers then solidifying the agglomerated powder, comprises successive scraping elements (18), only one is active at a time by the transport of the powder: as their rigidities are different, one is used which is appropriate to the local rigidity of each piece of the part in order to avoid excessive deformations of the part or on the contrary of the element, which would adversely affect manufacturing accuracy. Figure for the abstract: Fig. 2.

Description

Description

Title of the invention: SCRAPER FOR A MANUFACTURE

ADDITIVE OF METAL PARTS BY POWDER BED PROCESS The subject of the invention is a scraper, which can be applied in particular to the transport of powders for manufacturing metal parts by additive manufacturing by the powder bed process.

A process that the invention can improve is described in document FR 2980380 AL The manufacture of a metal part is described by deposition and agglomeration of successive layers of a powder. The installation includes a powder supply container, a production tray, a container for collecting excess powder, these three stations being aligned and contiguous, with the tray between the two containers; and it also includes a scraper capable of passing over these three stations in order to move the powder from the feed tank to the recovery tank while depositing a layer of powder on the production plate. The scraper can take various aspects in the art, but it always includes a main face directed in a direction of advance, in which the scraper is moved to transport the powder, i.e. a face extending at least essentially perpendicular to this direction of advance, and on which the transported powder accumulates.

The plate is movable vertically under the effect of an adjustable cylinder, and the bottom of the powder feed tank is also mobile under the effect of another adjustable cylinder, independent of the previous one. It is also possible that the bottom of the powder collecting tank is also mobile under the effect of another cylinder. Indeed, in certain configurations, and in order to optimize the consumption of powder, the supply bin can become a recovery bin and vice versa. The scraper then changes direction of movement.

The feed tank cylinder is periodically deployed to lift the powder contained therein and to bring out a small part above an upper edge of the tank. The scraper can then be moved, and it intercepts at least part of this quantity of powder and moves it to let it flow and spread over the surface of the tray; any powder remaining in excess on the scraper falls into the collecting tank.

These operations are repeated so as to deposit the powder in successive layers and stacked on the tray. As soon as a layer is deposited, it can be melted in successive plots, by a laser for example, which gradually give an agglomerated layer by solidifying, then the scraper is returned to its original position, the cylinder of the tank feed is raised to release a new quantity of powder and the cylinder of the tray is lowered to allow the material of the next layer to settle. A part can thus be manufactured layer by layer, after successive passes of the scraper. Such methods include those known as LBM (Laser Beam Melting) or EBM (Electron Beam Melting). The known scrapers are of different types: roll or blade, steel, silicone, brush, etc.

The rigidity of the scrapers can become problematic on certain parts. Hard material scrapers have good wear resistance, but are normally very rigid, and they can deform certain thin parts when passing over them. Wipers made of softer materials have the opposite disadvantages of being subject to rapid wear and being very sensitive to variations in the height of the part. Finally, brushes composed of flexible bristles are also flexible, with the additional disadvantages of being able to lose bristles during scraping, which pollutes the powder bed, and to risk disturbing the powder bed in the case of a movement stopped. Manufacturing defects can ensue in any case. The least harm would be a scraper just flexible enough not to deform the workpiece, depending on the flexibility thereof. However, the choice of a scraper well suited to a part to be manufactured remains problematic if it has a complex shape having both rigid and flexible portions, all the scrappers then appear to be ill-suited to at least some of these portions.

The invention was designed to reduce these drawbacks by avoiding or reducing the use of scrapers that are too rigid or, on the contrary, too flexible. In general form, it relates to a scraper for a machine for the additive manufacturing of metal parts by transporting powder, comprising a support designed to be movable in a direction of advance during said manufacturing, characterized in that the support carries a plurality of scraping elements facing the powder, the scraping elements being aligned in the direction of advance with main faces directed in the direction of advance (i.e. having a normal directed, at least essentially, in this direction), movable independently of each other in a vertical direction (at least essentially perpendicular to the direction of advance, which and normally horizontal) and provided with different rigidities.

Indications such as "horizontal", "vertical", "top", "bottom", "upper", "lower", etc. given in this text refer to a normal orientation of the apparatus during the manufacturing processes.

It then becomes possible to choose, for each pass or each pass portion, the scraping element which is most suitable as a function of the local rigidity of the part to be manufactured, by associating for example the most rigid scrapers. to the most rigid parts of the part, and vice versa the less rigid scrapers to the less rigid parts of the part.

In a plausible embodiment, the scraping elements are each movable in the vertical direction between a position retracted towards the support and an active position, said scraping element extending lower than the other scraping elements are found in the retracted position, the retracted position of each scraper element being an upper position and the active position, associated with the transport of powder, a lower position.

According to a preferred embodiment of the invention, the scraping elements can be constructed from different materials, at least one of which can for example be metallic, the other or the others which can be of polymer, such as silicone, brush made of bristles, etc.

The rigidities considered here relate to the ability of the scraping element to yield in the vertical direction when a friction force on a workpiece is applied to it during a pass in the direction of advanced. In the case of a scraper in the form of a blade or plate, the deformation can result mainly from a bending towards the rear of the support; in the case of a roller, it can consist mainly of compression of the roller in its radial direction.

One of the scraping elements may be metallic, the other or the other non-metallic.

Another aspect of the invention is a pigging installation comprising a support plate for a workpiece, a powder supply container adjacent to the plate, and a scraper for transporting the powder from the container. feeding to the plate, characterized in that the scraper conforms to the above.

Yet another aspect is a method of manufacturing a part by means of the scraper or the installation in accordance with the above, the method comprising deposits of layers stacked with powder, associated with successive passes where the scraper provides the powder of each layer, and agglomeration (or sintering) of each layer between the deposition of said layer and the deposition of the next layer, characterized in that at each instant of said successive passes, only one of the elements of The scraper of the row is lowered to transport the powder, the other or the other scraping elements being lifted above the workpiece.

In a particularly preferred embodiment, the method comprises permutations of the scraping element which is lowered, certain scraping elements, more rigid than others of the elements, being lowered onto relatively rigid parts of the part, the other elements being lowered over relatively non-rigid parts of the part.

The various aspects, characteristics and advantages of the invention will now be described by means of the following figures, which represent certain detailed embodiments thereof and given purely by way of illustration:

[Fig-1] illustrates an installation for manufacturing a metal part from a powder comprising a scraper according to the invention;

[Fig.2] and [fig.20] [fig.3] illustrate the scraper according to the invention in longitudinal section and cross section;

[Fig.4] and [fig22] [fig.5] illustrate metal parts particularly suited to the application of the invention; and [Fig. 6] is an alternative embodiment.

The invention schematically represents an installation for manufacturing a part from powder, comprising a supply tank 1, a tray 2, a recovery tank 3 and a scraper 4. The supply tank 1, the plate 2 and the recovery tank 3 are aligned in a horizontal direction Y called the direction of advance. A first jack 5 makes it possible to adjust the height of the plate 2, which is disposed between the tanks 1 and 3 and a second jack 6 allows to adjust the height of a bottom 7 of the feed tank 1 and therefore the depth of this bin. The plate 2 is oriented in X-Y, that is to say horizontal plane. A laser 8 overhangs it, which can be moved in the same directions X and Y by a mechanism not shown, so that its beam can be directed towards any point of the tray 2. The feeding tray 1 is filled with powder 9 until 'at its upper edge 10, and its top is open. The scraper 4 can be moved along rails 11 extending in the horizontal direction of advance Y. During the production of a part 27 in the installation, it passes successively above the upper edge 10 of the tank feed 1, tray 2 and upper edge 12 of the collecting tank 3. The bottom 7 having been raised to make a quantity of powder 9 exceed the upper edge 10, this quantity is at least partly intercepted by the scraper 4 and transported on the plate 2, where it is deposited by forming a layer 13. The laser 8 is then activated to heat at least a portion 14 of the layer 13 and melt it, after which it is left to solidify. The coalescence of the powder grains in the solidified portions 14 of the successively deposited layers 13 gradually produces a piece 27 of agglomerated powder. The excess powder from each layer 13 ends up in the collecting tank 3 when the scraper 4 reaches it. The plate 2 is lowered before each passage of the scraper 4 to allow the deposition of the next layer, the surface of which is usually limited by the lower edge of the scraper 4.

The scraper 4 is described in more detail by means of Figure 2. It comprises a support 17 sliding on the rails 11 and scraper elements 18 extending under the support and each of which is retained by a fixed frame 19 on the underside of the support 17. The scraping elements 18 slide in a vertical direction Z in slots 20 of the frames 19 which open downwards, along vertical slides 21, and their vertical position can be ensured by a any lifting element, for example worms 22 rotated by motors 23 installed on the support 17, these motors 23 being controlled by a general system 24 sensitive to position sensors, not shown, associated with each scraping element 18 Their heights can be adjusted independently of one another by the general control system 24. Their main faces, of larger area, are directed in the direction of advance Y.

It is according to the invention to have a plurality of scraping elements 18 aligned in a row in the direction of advance Y of the scraper 4. In addition, it is expected that the scraping elements 18 have similar widths in the horizontal transverse direction X and perpendicular to the direction of advance Y, but that they are of different rigidities, which can be ensured either by differences in structure, or by differences in materials. If for example there are three scraping elements 18, denoted 18A, 18B and 18C as in FIG. 2, one of them 18A could be constructed in the form of a metal blade, in steel for example, another 18B in the form of a polymer blade, in silicone for example, and the third 18C in the form of a blade or a parallelepipedal block of brush bristles. During the manufacture of the part, only one of the scraping elements 18 (18A in FIG. 2) is lowered onto the free surface 25 of the part 27 to be manufactured, while the others are lifted above it, retracted into the fittings 19.

Indeed, the scraping elements 18A, B and C of the scraper 4 are all capable of traversing the same strip 26 of the part 27 when the scraper 4 is moved. However, to make contact with the free surface 25, the scraping element 18 is chosen which has the rigidity locally adapted to that of the part 27. In fact, a scraping element 18 which is too rigid could deform the part 27 if it is locally flexible, of small thickness for example, while a flexible scraping element 18 would have the disadvantage of undergoing faster wear and of being sensitive to variations in height of the free surface 25. Irregularities in the deposition of powder and manufacturing layers could thus appear. This is why it is advisable to choose, for each portion of the part 27 to be manufactured, that of the scraping elements 18 which is the most suitable, just flexible enough not to excessively deform the part 27.

The flexibility considered here for the scraping elements 18 can be correlated with the deformation component ΔΖ in the vertical direction which they present in a concrete situation of displacement on a determined strip 26, independently of their overall deformation mode. of flexion or compression, in their lowered position on the free surface 25, at a height determined by the general system 24 according to the setting of the machine. In practice, we will rather be interested in the order of the flexibilities, or the rigidities, of the scraping elements 18 of the row.

The differences in rigidity will be produced, in the preferred embodiments of the invention, by different materials for the scraping elements 18, but without excluding other factors, such as differences in thickness or shape of the scraping elements 18.

The scraping elements 18 are not limited to blades but can take other forms, such as cylindrical rollers 28, as shown in Figure 6. They rotate freely around a horizontal axis 29 mounted on a linkage 30 sliding in vertical bore cannons 31 of the support 17. As before, a motor 23 rotates an endless screw 22, which engages on a threaded socket 32 at the top of the linkage 30 to control the height of the latter. . The rest of the embodiment will be identical to that of FIG. 2: there will be found in particular other scraping elements aligned on the support 17 in a row in the direction of advance Y, and an identical control system, make it possible to lower one of the scraping elements on the part 27, while the others are lifted, so as to choose the scraping element best suited to the part 27. The flexibility of the roller 28 is correlated with the radial compression ΔΖ which it undergoes at its lower generator.

A part for which we can recommend the use of the invention is a turbomachine blade shown in Figure 4 and composed of three main parts: a long and thin blade 34 between a blade root 35 and a flat - upper form 36, both, especially the first, more massive and rigid. The large difference in rigidity between these three parts can justify their manufacture by different scraping elements with regard to rigidity, for example the most flexible scraping element for manufacturing the blade 34 and another scraping element, more rigid, for the blade root 35 and the upper platform 36; or a more rigid scraping element for the blade root 35 and a scraping element of intermediate stiffness by the upper platform 36. Other choices are possible on a case-by-case basis. Each plot of dawn 33 can therefore be constructed with an appropriate scraper element and possibly different from a neighboring plot. In addition, the scraping elements provided for any location of the blade 33 can be replaced by others, when the scraper passes through the same locations for depositing subsequent layers, when certain predetermined thicknesses of the draft 'dawn 33 were reached during manufacturing.

Another kind of interesting part for the invention, represented in FIG. 5, is a ferrule, or a sector of cylindrical or conical ferrule, such as a wall of combustion chamber 37 of a turbomachine, thin but limited by a thick and rigid flange 38 at at least one end. The same comments as above apply.

Claims (1)

Claims [Claim 1] Scraper for a machine for the additive manufacturing of metal parts (27) by transporting powder, comprising a support (17) designed to be movable in a direction of advance (Y) during said manufacture, characterized in that the support carries a plurality scraping elements (18) facing the powder, the scraping elements being aligned in the direction of advance with main faces directed in the direction of advance, movable independently of each other in a vertical direction (Z ) and with different stiffnesses in the vertical direction. [Claim 2] Scraper according to Claim 1, characterized in that the scraping elements are constructed from different materials. [Claim 3] A scraper according to claim 2, characterized in that one of the scraping elements is metallic, the other or the other of the scraping elements being non-metallic. [Claim 4] Scraper according to either of Claims 2 and 3, characterized in that the scraping elements comprise a polymer element. [Claim 5] Scraper according to any one of Claims 2 to 4, characterized in that the scraping elements comprise a brush. [Claim 6] Scraper according to any one of Claims 1 to 5, characterized in that the scraping elements comprise at least one blade-shaped element (18). [Claim 7] Scraper according to any one of Claims 1 to 6, characterized in that the scraping elements comprise at least one roller-shaped element (28). [Claim 8] Scraper according to any one of the preceding claims, characterized in that the scraper elements are each movable in the vertical direction (Z) between a position retracted towards the support and an active position, said scraper element extending lower than the other scraping elements are in the retracted position. [Claim 9] Scraper installation comprising a tray (2) for supporting a workpiece (15) to be produced, a powder supply container (1), adjacent to the tray, and a scraper (4) for transporting the powder from the container 'tray feeding, characterized in that the scraper conforms to any one of the preceding claims. [Claim 10] Method of manufacturing a mechanical part (27) by means of the scraper or the installation according to any one of the preceding claims cedents, the process comprising deposits of layers (13) stacked with powder, associated with successive passes where the scraper (4) provides the powder for each layer, and sintering of each layer between the deposition of said layer and the deposition of the next layer, characterized in that at each instant of said successive passes, only one of the scraping elements (18A) of the row is lowered to transport the powder, the other or the other scraping elements (18B, 18C) being lifted above the workpiece (27). [Claim 11] Method of manufacturing a part according to claim 10, characterized in that it comprises modifications of the scraping element which is lowered, certain scraping elements, more rigid than others of the elements, being lowered on more rigid parts of the part, the other elements being lowered on less rigid parts of the part.