FR3040645A1 - PROCESS FOR MANUFACTURING A PIECE BY SELECTIVE FUSION OR SELECTIVE FRITTAGE ON BED OF POWDER - Google Patents

Abstract

The invention relates to a method of manufacturing a piece (20) of metal, metal alloy or ceramic by selective melting or selective sintering on a powder bed, the part comprising a stack of powder layers fused or sintered by a energy beam, the method comprising the steps of: depositing at least one layer of powder of a metal, a metal alloy or a ceramic intended to constitute the part, and the melting or sintering of at least a part of the powder layer by the energy beam, the conditions of the melting or sintering step being defined by a group of parameters comprising: the beam power, the beam diameter, and the beam displacement speed . The melting or sintering conditions are modified during the manufacturing process by varying at least one of said parameters, said beam power being, if it is modified, increased from a first value to a second value, said diameter of said beam being, if modified, reduced from a first value to a second value, said beam moving speed being, if it is modified, decreased from a first value to a second value, so as to introduce locally into the piece of residual stresses.

Description

Background of the invention

The present invention relates to the general field of the manufacture of three-dimensional parts by a process of the additive manufacturing type, and more precisely to selective sintering or selective melting processes on a powder bed. The invention applies particularly, but not exclusively, to the manufacture of parts for aeronautics (that is to say, parts that can be used in a jet engine propelling an aircraft).

It is now common to use additive manufacturing techniques to easily and quickly produce complex three-dimensional parts. These manufacturing techniques have many advantages over traditional foundry or mass machining processes.

Among the additive manufacturing techniques, there may be mentioned, for example: selective melting on a powder bed, or selective sintering on a powder bed, by means of a laser or an electron beam (for example of the type : "Laser Metal Deposition", "Selective Laser Sintering", "Selective Laser Melting", or "Electron Beam Melting"). In these manufacturing processes, powder layers are successively sintered or fused using an energy beam (laser or electron), in order to manufacture the part.

Some parts to manufacture may have several parts that will be solicited differently during their use. For example, the same part can be stressed in creep in one part, and fatigue in another part. We thus seek the optimal microstructure for the piece that can respond to these two modes of ruin. In other words, we seek a judicious distribution of the microstructure in terms of grain size and metallurgical structure.

To ensure a good creep resistance of the part, it is sought to obtain a microstructure having grains of larger size, while to ensure good fatigue performance, smaller grains are preferable. Indeed, creep deformation occurs because of grain boundary slips, increasing grain size reduces the number of grain boundaries and their cumulative length. Conversely, to reduce the propagation of a crack, it is sought to increase the number of grain boundaries by reducing their size.

When a part is produced by selective sintering or selective melting on a powder bed, the microstructure can be adapted during a heat treatment performed after manufacture of the part. The conditions of this heat treatment will allow to control the microstructure homogeneously throughout the room. More precisely, the duration and the temperature of such a treatment will make it possible to enlarge the grains throughout the room.

However, the current manufacturing processes do not allow to control the different grain sizes within the same room, and thus optimize its resistance to creep or fatigue locally. There is thus a need for a process for manufacturing by selective melting or selective sintering on a powder bed, which makes it possible to obtain different microstructures within the same part.

Object and summary of the invention

The main purpose of the present invention is therefore to overcome such drawbacks by proposing a method of manufacturing a piece of metal, metal alloy or ceramic by selective melting or selective sintering on a powder bed, the part comprising a stack of layers of powder fused or sintered by an energy beam, the method comprising the steps of: depositing at least one layer of powder of a metal, a metal alloy or a ceramic intended to constitute the part, and the melting or sintering of the powder layer by the energy beam, the conditions of the melting or sintering step being defined by a group of parameters comprising: the beam power, the beam diameter, and the traveling speed of the beam, characterized in that the melting or sintering conditions are modified during the manufacturing process by varying at least one of said parameters, said beam power being, if it is changed, increased from a first value to a second value, said beam diameter being, if modified, decreased from a first value to a second value, said speed of the displacement of the beam being, if it is modified, reduced by a first value to a second value, so as to introduce residual stresses locally into the piece.

The method according to the invention differs from the processes of the prior art in that the manufacturing parameters are varied during the process, from one layer to another but also during the deposition of the same layer, to introduce residual stresses in certain parts of the room. To introduce these residual stresses, the parameters of the energy beam are modified in order to increase the energy density that is introduced into a part of the part at the time of melting or sintering. These local stresses are equivalent to additional energy that is stored in the material at the time of manufacture of the part.

When the parameters are modified so as to introduce more energy into a part of the part in the form of residual stresses, this part will have, after heat treatment, grains of larger size than the parts of the part in which these constraints residuals are lower. Indeed, the energy required for the growth of the grains in the part comprising residual stresses will be less than in a part where the residual stresses are lower.

In other words, with a method according to the invention, it is possible to create within the same room, areas with large grains, and areas with small grains. Therefore, it is now possible to increase creep resistance in some parts of the room, while increasing the fatigue strength in other parts of the room.

The method is advantageous in that it makes it possible to benefit from the advantages associated with an additive manufacturing process, while making it possible to confer on a part different mechanical properties in several parts thereof by modifying the manufacturing parameters.

In certain exemplary embodiments, the melting or sintering conditions are modified during the manufacturing process by varying two parameters.

In this case, the two parameters to be varied may be the beam power and the beam displacement speed, said beam power being increased from a first value to a second value, said beam displacement speed being decreased by a first value at a second value.

As a variant, the two parameters to be varied may be the beam power and the beam diameter, said beam power being increased from a first value to a second value, said beam diameter being decreased from a first value to a first value. second value.

The parameter group may further comprise a thickness of a powder layer, said thickness of a powder layer being decreased from a first value to a second value during the manufacturing process.

The parameter group may further comprise a beam scanning strategy, said beam scanning strategy being modified during the part manufacturing process, said scanning strategy of the beam being selected from: bands, checkerboard. By a strip type strategy (or "stripe"), it is meant that the scanning of a layer is carried out by a succession of parallel lines. By a checker-like strategy (or "chess"), it is meant that the sweep of a layer forms a checkerboard, a checkerboard box having parallel strips in a first direction, another adjacent checkerboard box having parallel strips in a a direction different from the first (and generally perpendicular to the first direction).

The parameter group may further comprise a pattern direction, said pattern direction being changed during the manufacturing process. Scanning patterns typically include parallel bands, both in band-type strategy and in checkerboard-style strategy (in checkerboard boxes). These strips are oriented in a certain direction, and it is possible to vary this direction during the manufacturing process to introduce residual stresses, especially between two successive layers. Other reasons are of course conceivable.

Preferably, the energy beam is a laser or an electron beam.

Also preferably, the method further comprises a step of heat treatment of the part. During this step, the densification of the part is finalized, and the microstructure of the part is controlled.

Finally, the invention relates to the method described above, in which the part to be manufactured is a part for aeronautics. "Aeronautical part" means a part that can be used in a jet engine intended to propel an aircraft, for example: an aeronautical turbine engine blade, turbine ring sectors, a turbine disk, a turbine system injection of an aircraft combustion chamber, an aeronautical injection system component, a flange, a clamping system, a motor equipment support a hood, etc.

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 embodiments having no limiting character. In the figures: FIG. 1 is a schematic view of an elongated piece manufactured by a method according to the invention; FIGS. 2 to 6A-6B are diagrammatic views of layers making up the part of FIG. 1 according to different modes; embodiment of the invention, and FIG. 7 is a schematic view of a low-pressure turbine disk for an aviation turbomachine produced by a method according to the invention.

Detailed description of the invention

A method according to the invention will now be described in its application to the manufacture of an elongated piece 10 comprising two openings 11 at each of its ends (Figure 1). The part 10 thus comprises two parts 12 which will be stressed in fatigue (that is to say likely to crack in use), and a portion 13 which will be biased creep when the part will be used. The process according to the invention makes it possible locally to define different microstructures in the parts 12 and 13 of the part, in order to increase their resistance to creep or fatigue, during the manufacture of the part by selective melting or sintering on powder bed.

The part 10 is made from a vertical stack (along the Z axis) of layers 14 integral with each other (Figures 2 to 6B). Each layer is manufactured, in a manner known per se, from a layer of deposited powder which is then fused or sintered by an energy beam (of the laser or electron beam type, for example). In the illustrated example, the openings 11 may be made by machining after manufacture of the piece by melting or selective sintering on a powder bed.

The powder may comprise a metal, a metal alloy or a ceramic.

During the manufacture of a layer, the beam merges or sintered successively the portions 12 and 13 of the layer. Parts 12, intended to hold more effectively in fatigue, must have a microstructure characterized by small grains. Conversely, the part 13, intended to hold more efficiently in creep, must have a microstructure characterized by larger grains.

According to the invention, a group of parameters is fixed for the energy beam as it traverses the portions 12 of a layer 14. This parameter group comprises in particular: the diameter of the beam Di2, the speed of displacement of the beam vi2, and the power of the beam Pi2. The portions 12 are fused or sintered using this group of parameters.

Then, when the beam passes through the portion 13 of the layer 14, at least one of these parameters is changed to introduce more residual stresses in this part, and subsequently allow the formation of grains of larger size. In order to introduce more constraints into the B part, it is then necessary to choose a new beam diameter Di3 <Di2 (FIG. 2), a new beam displacement speed vi3 <vi2 (FIG. 3), or a new beam power. Pi3> Pi2 (Figure 4). It should be noted that the diameter of the beam in the figures has voluntarily been enlarged for more readability.

It is of course conceivable to vary two of these parameters simultaneously, or all three simultaneously. For example, in part 13, the beam diameter can be reduced and the speed of beam movement reduced; or increase the power of the beam and reduce the speed of movement of the beam.

It is also possible, to introduce residual stresses into the layer, to change the scanning strategy of the beam between the parts 12 and the part 13. Indeed, a stripe-type scanning strategy (or "stripe") makes it possible to introduce more constraints than a checkerboard (or chess) strategy. In the example of layer 14 illustrated in FIG. 5, the strategy is of the band type for part 13, and of the checker type for parts 12.

Pattern rotation between two successive layers can also introduce additional constraints within the part. By "pattern" is meant the pattern formed by the energy beam when it fuses or sinter a layer of powder. By "pattern rotation" is meant that the orientation of the pattern changes from one layer to another, i.e. the direction or orientation of the pattern is changed from one layer to the other. other.

FIGS. 6A and 6B illustrate such pattern rotation between two successive layers 14a and 14b at the portion 13, the scan strategy being of the strip type. Indeed, in the layer 14a, the strips of the portion 13 are parallel to those of the portion 12, while in the next layer 14b, the strips of the portion 13 are perpendicular to those of the portion 12.

Note that the pattern rotation can also be applied to patterns obtained from a checker-type scan strategy.

A manufacturing method according to the invention has been described to manufacture a part 10 in which the parameters of the beam are modified within the same layer, it is however possible to keep the same parameters in a set of layers, and the vary in another set of layers (as will be the case in the example described below with reference to Figure 7).

In addition, the thickness of the layer can also be varied between different layers, or between different sets of layers. Indeed, a lower layer thickness will introduce more residual stresses compared to a thicker layer, all things being equal.

Finally, a heat treatment is carried out once all the layers of the part have been fused or sintered. This heat treatment makes it possible to enlarge the grains in the room. In particular, parts of the part in which greater stresses have been induced will have a larger grain size than those with fewer stresses. The conditions and the duration of such heat treatment depend in particular on the material and the properties of the powder used.

Example

An aerospace turbine engine low-pressure turbine disk 20 such as that shown diagrammatically in FIG. 7 has been manufactured by a selective melting process on a powder bed according to the invention. The disc 20 has fastening holes 21, a portion 23 which will be biased in creep during operation of the turbomachine, and a portion 22 which will be stressed in fatigue (at the fixing holes 21 in particular).

The disk 20 is made from fused powder layers stacked along the Z axis, the Z axis being parallel to the axis of the low pressure turbine disk. The powder used in the manufacturing process is identical throughout the disc 20. The powder has an average particle size of 30 μm and comprises an alloy of the NiCrigFeigNbsMos type, better known under the name Inconel® 718 (In718).

The conditions of the powder bed selective melting process in parts 22 and 23 of the part are summarized in the table below. It will be noted that the parts 22 and 23 each comprise a set of several layers, and that the operating parameters of the method will remain constant in each of the parts 22 and 23.

In this example, the part 22 is manufactured before the part 23, and the conditions of the process vary between these two parts. Indeed, the power is notably increased and the scanning speed is reduced from part 22 to part 23, in order to introduce more residual stresses in part 23 than in part 22. In addition, the strategy of Scanning is also changed between parts 22 and 23, from a checker strategy 24 to a strip type strategy 25. It will be noted that the thickness of a layer of the portion 23 is greater than the thickness of the strip. a layer of the part 22, the increase in the power makes it possible to compensate for this difference and to introduce despite all, and thanks to the reduction of the speed and the change of strategy, additional stresses in the layer 23 with respect to the layer 22.

Following the manufacture of the disc 20 by a method according to the invention, the disc 20 is heat-treated in an oven at 1095 ° C for 2 hours (for Inconel® 718). During this heat treatment, the part 23 undergoes a recrystallization greater than the part 22 because of the residual stresses introduced during the manufacture of the disk 20. Thus, a disk 20 is obtained comprising two parts 22 and 23 having different microstructures and conferring a combination of fatigue and creep.

Claims (10)

1. A method of manufacturing a piece (10; 20) of metal, metal alloy or ceramic by selective melting or selective sintering on a powder bed, the part comprising a stack of layers (14, 14a, 14b) of powder fused or sintered by an energy beam, the method comprising the steps of: depositing at least one layer of powder of a metal, a metal alloy or a ceramic intended to constitute the part, and the melting or sintering the powder layer by the energy beam, the conditions of the melting or sintering step being defined by a group of parameters comprising: the beam power, the beam diameter, and the beam moving speed characterized in that the melting or sintering conditions are varied during the manufacturing process by varying at least one of said parameters, said beam power being, if modified , increased from a first value to a second value, said beam diameter being, if changed, decreased from a first value to a second value, said beam moving speed being, if changed, decreased by a first value to a second value, so as to locally introduce into the room residual stresses. 2. Method according to claim 1, characterized in that the melting or sintering conditions are modified during the manufacturing process of the part by varying two parameters. 3. Method according to claim 2, characterized in that the two parameters to be varied are the power of the beam and the speed of displacement of the beam, said beam power being increased from a first value to a second value, said speed of beam displacement being decreased from a first value to a second value. 4. Method according to claim 2, characterized in that the two parameters to be varied are the beam power and the beam diameter, said beam power being increased from a first value to a second value, said beam diameter being decreased from a first value to a second value. 5. Method according to any one of claims 1 to 4, characterized in that the parameter group further comprises a thickness of a powder layer, said thickness of a powder layer being reduced from a first value to a second value during the manufacturing process. 6. Method according to any one of claims 1 to 5, characterized in that the parameter group further comprises a beam scanning strategy, said scanning strategy of the beam being modified during the manufacturing process of the part, said beam scanning strategy being selected from: bands, checkerboard. The method according to any one of claims 1 to 6, characterized in that the parameter group further comprises a pattern direction, said pattern direction being changed during the manufacturing process. 8. Method according to any one of claims 1 to 7, characterized in that the energy beam is a laser or an electron beam. 9. Method according to any one of claims 1 to 8, characterized in that it further comprises a step of heat treatment of the workpiece. 10. Method according to any one of claims 1 to 9, characterized in that the part to be manufactured is a part for aeronautics.