WO2016102876A1

WO2016102876A1 - Tool for manufacturing parts by selective melting or selective sintering on a powder bed, and manufacturing method implementing such a tool

Info

Publication number: WO2016102876A1
Application number: PCT/FR2015/053702
Authority: WO
Inventors: Guillaume Fribourg; Stéphane LAVIGNOTTE; François PICHOT
Original assignee: Snecma
Priority date: 2014-12-23
Filing date: 2015-12-22
Publication date: 2016-06-30
Also published as: FR3030323A1; FR3030323B1

Abstract

The invention relates to a tool (1) for manufacturing three-dimensional metal, metal alloy or ceramic parts, using a method of selective melting or selective sintering on a powder bed, comprising: a manufacturing table (22) on which a part is intended to be manufactured, a means (14) for spreading a layer of powder on the manufacturing table (22) intended to deposit a layer of powder on the manufacturing table, and a heating means (30) intended for melting or sintering at least one portion of a layer of metal, metal alloy or ceramic powder deposited on the manufacturing table. The manufacturing table (22) comprises: a base (24) comprising a refractory material, and a coating (26) at least partially covering the base, the coating consisting of at least one layer (26a) of a material having a thermal expansion coefficient with a value between the value of the thermal expansion coefficient of the refractory material of the base and five times the value of said thermal expansion coefficient, the part being intended to be manufactured on said coating. The invention also concerns a method implementing such a tool.

Description

Title of the invention

Tooling for the manufacture of parts by selective melting or selective sintering on a powder bed, and manufacturing method using such tools.

Background of the invention

The present invention relates to the general field of manufacture of metal parts, metal alloys or ceramic additive manufacturing.

Today it is common to use additive manufacturing techniques to easily and quickly make complex parts.

When it comes to the manufacture of metal parts, metal alloys or ceramics, the selective melting process (it is called selective sintering when it comes in particular to ceramics) on a bed of powder makes it possible to obtain complex parts that are difficult to achieve or not feasible with conventional processes such as foundry, forging or machining. The aeronautical field is particularly suited to the use of this method.

In addition, this method has the advantage of being fast and not requiring specific tools unlike most conventional processes, which significantly reduces the costs and parts manufacturing cycles.

Such a method generally comprises a step during which a first powder layer of a metal, metal alloy or ceramic of controlled thickness is deposited on a production plate (for example a metal plate), then a step consisting of heating with a heating means (for example a laser or an electron beam) a predefined zone of the powder layer, and proceeding by repeating these steps for each additional layer, until a slice is obtained, of the final piece.

However, in the known processes of selective melting or selective sintering on a powder bed, the parts have an anisotropic microstructure, the grains being directed in particular in the direction of the maximum thermal gradient, which happens to be in the normal direction to the production plate on which parts are made. The strategy of The construction of the parts must be developed taking into account this anisotropy so that the grains are oriented in the preferred directions of stress of the part, which poses a major manufacturing constraint.

Moreover, a part manufactured by selective melting or selective sintering on a powder bed has strong residual stresses capable of inducing deformation phenomena or even cracking in the part and at the interface between the part and the production plate.

There is therefore a need for a tool and a method for manufacturing parts made of metal, metal alloy or ceramic by selective melting or selective sintering on a powder bed which make it possible to obtain parts having more favorable properties. isotropic and reduce internal stresses in the part, to limit its deformation and its risk of cracking.

Object and summary of the invention

The anisotropy and internal stresses observed on parts manufactured by traditional processes of selective melting or selective sintering on a powder bed are mainly due to too rapid dissipation and in a preferred direction of heat at the time of melting or sintering powder.

The inventors have studied the dissipation of heat and have noted that it operates in several ways: by convection at the gas constituting the atmosphere of the manufacturing chamber, by radiation, and by thermal conduction at the level of the surrounding powder and manufacturing platform supporting the part in progress.

It has been observed that the solidification front of the melted or sintered zone progresses in the opposite direction to the heat flow directed perpendicularly to the production plate, which results in grain growth in the same direction. During the solidification of the N layer, the crystalline orientation of the Nl layer is maintained by epitaxy. This results in elongated grains in the direction of this thermal gradient. It is this phenomenon which is thus mainly responsible for the final anisotropy of the piece. And among the factors mentioned above is the production plate, traditionally metal or metal alloy, which is the source of the strongest heat dissipation.

Consequently, it would be conceivable to reduce these phenomena by using a production plate comprising a material having a lower thermal conduction than metals or metal alloys traditionally used, for example ceramic, or more generally a refractory material.

However, the inventors have noticed that the production trays made of refractory material have adhesion problems with the parts, which are made of metal or metal alloy, mainly because the metals and the metal alloys hardly adhere with the ceramic of a metal. on the other hand, and expand more than the most refractory materials when heated on the other hand. However, there must be a so-called "dilution" zone in which the manufacturing plate and the first layers of powder can merge so that the part adheres properly on the plate.

The main object of the present invention is therefore to overcome such disadvantages by proposing tools for the manufacture of three-dimensional parts made of metal, metal alloy or ceramic by a selective melting process or selective sintering on a powder bed, comprising:

a production tray on which is intended to be manufactured a part,

means for spreading a layer of powder on the production platform for depositing a layer of powder on the production plate, and

heating means for melting or sintering at least a portion of a layer of metal, metal alloy or ceramic powder deposited on the production tray,

characterized in that the production tray comprises:

a base comprising a refractory material, and

a coating at least partially covering the base, the coating consisting of at least one layer of a material having a coefficient of thermal expansion having a value between the value of the coefficient of thermal expansion of the refractory material of the base and five times the value of said coefficient of thermal expansion, the part being intended to be manufactured on said coating.

The term refractory material is understood to mean a material which minimizes heat exchange, for example a material having a sufficiently low thermal effusivity and preferably less than or equal to 4 kJ · K · m · m · s · ¹ · ^2. Examples of refractory materials may be find among the ceramics, but also among the alloys such as for example the TA6V.

The coefficient of thermal expansion considered is defined throughout the temperature range to which the production plate is subjected, generally between the ambient temperature and the lowest melting point of the materials present in the coating (for example between 20 ° C. and 900 ° C).

Note that the part is intended to be manufactured directly on the coating, even when it covers the base only partially. In other words, the part is intended to be in contact only with the coating of the production plate. Thus, the plate makes it possible, on the one hand, to limit the thermal conduction responsible for the anisotropy in the direction normal to the production plate because it comprises a base made of refractory material, and, on the other hand, to provide a adhesion of the workpiece to the work platform by means of a coating having at least one layer of material having the value of a higher coefficient of thermal expansion and sufficiently close to that of the coefficient of thermal expansion of the base. In other words, this coating makes it possible to make the interface between the part and the base on which it can adhere, while ensuring the adhesion of the part on the production plate by allowing a dilution zone.

Preferably, the coating comprises a plurality of layers, each layer of the plurality of layers having above an underlying layer having a coefficient of thermal expansion greater than the coefficient of thermal expansion of said underlying layer.

With such an arrangement, it is possible to progressively adapt the properties of the coating so that they approach those of the base at the level of the first layer of material by ensuring adhesion therewith, and that they are also close to those of the of the powder at its upper layers to secure the piece.

More preferably, a layer of the coating has a thickness of between 0.1 mm and 5 mm.

As the layers forming the coating may be more thermally conductive than the base, limiting their thickness thus limits the thermal losses due to the coating.

Also preferably, the coating has a thickness of less than or equal to 15 mm.

Similarly, by limiting the total thickness of the coating, it limits the thermal losses due to the manufacturing platform.

The base may be made of one of the following materials: Zirconia, SiO ₂ , TA6V alloy.

A layer of the coating may be made of one of the following materials: an iron-based alloy, a cobalt-based alloy, a nickel-based alloy, a titanium-based alloy, a molybdenum-based alloy, an aluminum-based alloy, silicon carbide, tungsten carbide.

The invention also relates to a method for manufacturing three-dimensional parts made of metal, metal alloy or ceramic by selective melting or selective sintering on a powder bed, the method comprising successively the following steps:

depositing at least one powder layer of a metal, a metal alloy or a ceramic intended to constitute the part, and melting or sintering at least a portion of the powder layer by a heating means. According to the invention, the preceding steps are carried out on a production platform comprising:

a base comprising a refractory material, and

a coating at least partially covering the base, the coating consisting of at least one layer of a material having a coefficient of thermal expansion having a value between the value of the coefficient of thermal expansion of the refractory material of the base and five times the value of said coefficient of thermal expansion.

Preferably, the coating comprises a plurality of layers, each layer of the plurality of layers present above an underlying layer having a coefficient of thermal expansion greater than the coefficient of thermal expansion of said underlying layer.

Also preferably, the layer of the coating intended to be in contact with the workpiece is made of the same material as the powder. Thus, as this layer is made of a material identical to that of the powder, the adhesion of the workpiece to the production plate is maximal since the last layer of the coating and the part of the first layer of powder intended to form the first portion of the part can merge optimally in a dilution zone.

Brief description of the drawings

Other features and advantages of the present invention will emerge from the description given below, with reference to the accompanying drawings which illustrate an embodiment having no limiting character. In the figures:

FIG. 1 is a schematic view of a tool according to one embodiment of the invention,

FIG. 1A is an enlarged view of the tool of FIG. 1 at the level of the production plate, and

FIG. 2 is a flowchart illustrating the steps of a method according to the invention. Detailed description of the invention

An example of tooling 1 for the manufacture of metal or metal alloy parts by selective melting or selective sintering on a powder bed according to one embodiment of the invention is illustrated in FIGS. 1 and 1A.

In a manner known per se, the tool 1 comprises a powder reservoir 10 and a hollow portion in which the workpiece 3 is manufactured.

The reservoir 1 and the portion 20 are located at the same level.

The powder reservoir 10 contains the metal powder 2 or a metal alloy which will be used to manufacture the part 3, while the part 20 is able to contain the part 3 to be manufactured as well as the unfused powder 4. For example, it is possible to use a powder of a metal, a metal alloy or a ceramic to make the part. For example an alloy based on Iron (for example XC48 Steel, Inox®), a cobalt-based alloy (for example: MAR-M-509®), a nickel-based alloy (for example: Inconel®625 , Hastelloy C276®, Hastelloy-X®, Hastelloy-W®), a titanium-based alloy (for example: TA6V, ΤΊ6-2-4-2, Til7, T40), an alloy based on molybdenum, an alloy aluminum-based (for example of one of the following grades: 1050, 6061, 7075, 5053, 2024, 2618, 2219), silicon carbide, tungsten carbide, etc.

The size of the grains of the powder may vary for example from

From 5 pm to 150 pm.

At the bottom of the tank 10 is a movable platen 12 that can move vertically to push the powder up the tank.

Similarly, at the bottom of the portion 20 is a manufacturing plate 22 adapted to move vertically, and in particular to go down as the workpiece is manufactured.

According to the invention, the production plate 22 comprises a base 24 (FIG. 1A).

The base 24 may be ceramic and constituted for example by

Zirconia, Silica (SiO ₂ ), etc. Alternatively, the base 24 may be made of a sufficiently refractory alloy, for example of the TA6V type.

This base 24 is covered with a coating 26, composed for example of two layers 26a, 26b. The part 3 is intended to be manufactured directly on the coating 26 of the production plate 22, even when the coating 26 partially covers the base 24. Thus, the part 3 is in contact only with the coating 26 during its manufacture .

Preferably, the first layer 26a has a value of thermal expansion coefficient greater than or equal to the value of the coefficient of thermal expansion of the refractory material of the base 24, and less than or equal to five times the value of this coefficient. The last layer 26b has a coefficient of thermal expansion greater than that of the first layer 26a. Advantageously, the coefficient of thermal expansion of the materials of the layers forming the coating is less than that of the material constituting the powder. It is also possible to use for the last layer 26b, intended to be in contact with the piece 3, the same material as that of the powder.

The layers 26a, 26b have a thickness of between 0.1 and

5 mm.

The deposition of these layers 26a, 26b can be carried out by various methods known to those skilled in the art such as: plasma or laser deposition, physical vapor phase deposition (PVD), chemical vapor deposition (CVD), fusion selective or selective sintering on powder bed, welding of prefabricated plates, injection of powdered metal Powder Injection Metal), extrusion, etc.

At the end of these deposits, it is possible to perform thermal diffusion treatments on the layers 26a, 26b forming the coating 26 so that diffusion takes place between these layers, so that the properties of the coating follow a vertical gradient and that there is no significant discontinuity between the layers, including the coefficient of thermal expansion. In other words, these heat treatments make it possible to limit the differential thermal expansion between the layers of the coating.

For example, for layers comprising a nickel-based alloy or steel, it will be possible to perform a diffusion heat treatment at a temperature between 1000 ° C and 1250 ° C for 1 hour to 10 hours, and preferably under vacuum or protective atmosphere (under Argon).

In the case where the coating 26 consists of more than two layers, the total thickness e of the coating 26 must not exceed 15 mm to limit heat losses in the coating.

Before the process starts, the production plate 22 is in the up position and the mobile plate 12 is in the low position.

The first step of the process (E1) consists in depositing a first layer of powder on the production plate 22, and in particular on the coating 26. To do this, the mobile plate 12 is mounted on a controlled length in order to push a quantity sufficient powder out of the tank 10, simultaneously the manufacturing plate 22 will lower on a controlled length (that chosen for a layer of powder, for example between 10 pm and 200 μητι) then a spreading means 14 will distribute the powder extracted from the tank on the plateau manufacturing 22, and in particular on the coating 26, moving horizontally from the reservoir 10 to the production plate 22. The excess powder can be discharged on the side opposite the reservoir, for example in an additional recovery tank.

The spreading means 14, which may for example be a roller or a scraper, thus makes it possible to uniformly deposit and distribute the powder layer on the production plate 22, and in particular on the coating 26.

Once the first layer has been deposited, a heating means 30 will make it possible to selectively melt or sinter a portion of the powder corresponding to a first portion of the piece (step E2).

This first layer may merge with the last layer 26b of the coating in a dilution zone 28 shown in Figure 1A, which will ensure the position of the part during the entire manufacturing process.

The heating means 30 may for example consist of a CO ₂ laser, an Nd-YAG laser, or an electron beam generator, associated with means 32 for directing the beam 34 coming from the heating means to a surface precise layer of powder. The heating means that can be used in a selective melting process or selective sintering on a powder bed are known to those skilled in the art and will not be detailed here.

In the case where the heating means 30 is a laser, the tool 1 is generally placed in a neutral gas atmosphere. Alternatively, if the heating means 30 is an electron beam generator, the tool 1 is placed in a secondary vacuum chamber.

When the melted or sintered powder has cooled, and if necessary solidified (step E3), the above operations can be repeated for each successive slice of the piece by depositing a layer of powder on the preceding one, until it's over.

Once manufacture is complete, the piece 3 is extracted from the production plate 22 of which it is integral, and can undergo conventional finishing treatments (step E4), such as machining, polishing, etc.

In this presentation, the phrase "between ... and ..." should be understood to include the bounds. First example

An alloy piece of Inconel® 718 type is produced from a powder of this alloy.

The production tray has a zirconia base, and a layer of metal alloy material.

The layer, of a thickness of 3 mm, consists of an alloy of Inconel®718 type and is deposited by plasma deposition or by selective melting on a powder bed on the ceramic plate.

To finalize the deposition of the coating, the production plate is imposed a temperature of 1230 ° C for 1 hour.

Table 1 groups together the main components of the alloys used in this first example, and the orders of magnitude of the thermal expansion coefficient (CDT) values of the materials constituting the plate.

Table 1

Second example

A titanium alloy piece of the TA6V type is produced from a powder of this alloy.

The production tray has a base S1O2, and two layers of metal alloy material.

The first layer consisting of an Invar®-type alloy is deposited by plasma deposition on the ceramic plate and has a thickness of 2 mm.

The second layer consisting of an alloy of TA6V type, identical to that of the powder, is deposited by plasma deposition on the first layer and has a thickness of 5 mm.

To finalize the deposition of the coating, the production plate is imposed a temperature of 1180 ° C for 1 hour to allow the layers to diffuse into the coating. Table 2 groups together the main components of the alloys used in this second example, and the orders of magnitude of the thermal expansion coefficient (CDT) values of the materials constituting the plate.

Table 2

TA6V Invar® Si0 ₂

Ti (base)

Fe (64%) Si (47%)

Al mass composition (6%)

Neither (36%) 0 (53%) Va (4%)

CDT at 200 ° C (1CT ⁶ I ¹ ) 9 2 0.4

Claims

Tooling (1) for manufacturing three-dimensional metal, metal alloy or ceramic parts by a selective melting process or selective sintering on a powder bed, comprising:

a production tray (22) on which is intended to be manufactured a part,

means for spreading (14) a layer of powder on the production platform (22) for depositing a layer of powder on the production platform, and

heating means (30) for melting or sintering at least a portion of a powdery layer of metal, metal alloy, or ceramic deposited on the production tray, characterized in that the production tray (22) ) includes:

a base (24) comprising a refractory material, and a coating (26) at least partially covering the base, the coating consisting of at least one layer (26a) of a material having a coefficient of thermal expansion having a value of between the value of the coefficient of thermal expansion of the refractory material of the base and five times the value of said coefficient of thermal expansion, the part being intended to be manufactured on said coating.

2. Tooling according to claim 1, characterized in that the coating (26) comprises a plurality of layers (26a, 26b), each layer of the plurality of layers present above an underlying layer having a coefficient of thermal expansion greater than the coefficient of thermal expansion of said underlying layer.

3. Tooling according to claim 1 or 2, characterized in that a layer (26a, 26b) of the coating (26) has a thickness of between 0.1 mm and 5 mm.

4. Tooling according to any one of claims 1 to 3, characterized in that the coating (26) has a thickness (e) less than or equal to 15 mm.

5. Tooling according to any one of claims 1 to 4, characterized in that the base (24) consists of one of the following materials: Zirconia, Si0 ₂ , TA6V alloy.

6. Tooling according to any one of claims 1 to 5, characterized in that a layer of the coating (26a, 26b) is made of one of the following materials: an alloy based on iron, an alloy based on Cobalt, a nickel-based alloy, a titanium-based alloy, a molybdenum-based alloy, an aluminum-based alloy, silicon carbide, tungsten carbide.

7. A process for manufacturing three-dimensional metal, metal alloy or ceramic parts by selective melting or selective sintering on a powder bed, the process comprising successively the following steps:

depositing at least one powder layer of a metal, a metal alloy or a ceramic intended to constitute the part, and melting or sintering at least a portion of the powder layer by a heating means (30),

characterized in that the preceding steps are carried out on a production platform comprising:

a base (24) comprising a refractory material, and a coating (26) at least partially covering the base, the coating consisting of at least one layer (26a) of a material having a coefficient of thermal expansion having a value of between the value of the coefficient of thermal expansion of the refractory material of the base and five times the value of said coefficient of thermal expansion.

8. Method according to claim 7, characterized in that the coating (26) comprises a plurality of layers (26a, 26b), each layer of the plurality of layers present above an underlying layer having a coefficient of thermal expansion greater than the coefficient of thermal expansion of said underlying layer.

9. Method according to any one of claims 7 and 8, characterized in that the layer (26b) of the coating (26) intended to be in contact with the workpiece is made of the same material as the powder.