Method for additive manufacturing of a part

Abstract

The present invention relates to a method for additive manufacturing of a part, comprising the following successive steps: forming a layer of powder on a construction support; using a high-energy device to perform a melting step in which the layer of powder thus formed is illuminated by means of at least one beam and the at least one beam is moved in order to form a temperature profile at each point of the layer, said profile including successively: a first, positive thermal gradient G1 for gradually preheating the powder, a melting peak for melting the powder, and a second, negative thermal gradient G2 for gradually cooling the powder.

Description

Description Title: Additive manufacturing process of a part Technical field

[0001] The invention relates to the field of additive manufacturing.

[0002] More specifically, the invention relates to an additive manufacturing device, as well as a method for manufacturing at least one part, implementing this device. Prior art

[0003] Additive manufacturing is increasingly used in the aeronautics sector and tends to replace the historical foundry process.

[0004] The method of producing parts by additive manufacturing has, in fact, many advantages in terms of mechanical properties. The elastic limit is pushed back and the fatigue resistance on polycrystalline materials is improved. The size of dendrites produced by additive manufacturing is of the order of a micron, whereas with a foundry process, the size of dendrites reaches a hundred microns. This explains the mechanical advantages conferred by additive manufacturing. In addition, the absence of a mold in the case of additive manufacturing allows the production of more complex geometries with a greater degree of freedom. By additive manufacturing, manufacturing internal channels is also easier because these internal channels will not be subjected to high stresses during demolding, which would be the case with a foundry process.

[0005] An additive manufacturing method consists of manufacturing at least one part, in particular one or more metal part(s), by melting successive layers of powder using a laser beam controlled by an information processing system in which the three-dimensional coordinates of the points of the successive layers to be produced to form said parts have been recorded.

[0006] Figure 1 illustrates a manufacturing device 1 intended to implement such a method.

[0007] The manufacturing device 1 comprises a reservoir 3 containing a metal powder 5 and whose bottom 7 is movable, movable in translation vertically by a rod 9 of a jack, and a neighboring tank 11, substantially parallelepiped, whose bottom is constituted by a movable plate 13, movable in translation vertically by a rod 15 of a second jack.

[0008] The manufacturing device 1 further comprises a scraper 17 for bringing powder from the reservoir 3 to the tank 11, the scraper 17 being movable in translation along a horizontal plane A substantially parallel to the plate 13. The manufacturing device 1 further comprises means 18 for generating a laser beam 19, coupled to a device 20 for moving said laser beam 19, making it possible to orient it and / or move it to reach any point of the tank 11.

[0009] To manufacture one or more parts 21, a first layer of powder is placed in the tank 11 using the scraper 17.

[0010] The layer then has a lower surface corresponding to the surface of the plate 13 and an upper surface on which the laser beam 19 is directed and moved. The energy provided by this beam causes the local melting of the powder which, by solidifying, forms a first layer of the or each part 21.

[0011] After formation of this first layer, the plate 13 is lowered by a distance corresponding to the thickness of a layer of powder, while the bottom 7 of the reservoir 3 is raised by a corresponding height, so that a certain quantity of powder 22 is located above the horizontal plane A.

[0012] Then, this quantity of powder 22 is brought by the scraper 17, from the reservoir 3 into the tank 11, to form a second layer over the previous layer. In the same way as previously, a second layer of each part 21 is formed using the laser beam 19. The quantity of powder and the positions of the bottom 7 and the plate 13 are determined so as to form layers of powder of a chosen and constant thickness.

[0013] These operations are repeated until the parts 21 are completely manufactured.

[0014] Today, the laser beam shapes used are simple. These simple laser beam shapes result in very rapid melting and solidification of the powder layer. The energy distribution of the laser beam over the powder layer may not be uniform across the entire fused powder layer. The thermal gradient of the fused powder layer and the solidification rate of this powder layer are therefore poorly controlled and can lead to poor mechanical strength with an inappropriate crystalline microstructure. Summary

[0015] The present disclosure improves the situation and relates to a method of additive manufacturing of a part comprising the following successive steps: - the formation of a layer of powder on a construction support, - carrying out by a high-energy device generating at least one energy beam of a fusion step in which said layer of powder thus formed is illuminated by means of said at least one beam and said at least one beam is moved to form at each point of said layer a temperature profile, successively comprising: -- a first positive thermal gradient G1 for progressive preheating of the powder; -- a powder melting peak and -- a second negative thermal gradient G2 for progressive cooling of the powder, and in that, -- the temperature profile and the displacement speed V of at least one moving beam on the surface of the construction support being adapted to generate a dendritic equiaxed crystalline microstructure of said layer, and - depositing at least one new layer of powder on the previous layer and repeating the previous melting step for each new layer deposited until said part is obtained.

[0016] The high-energy device simultaneously emits several beams with different powers.

[0017] The overall temperature profile is adapted using a plurality of laser beams with powers adapted according to what the operator has available. N beams are temporally shifted by a time EVN / V to ensure the formation of a thermal gradient G1 or G2, where V is the speed of movement of the N beams and EVN is a distance separating the melting peaks of two successive beams, the temperature profile and the speed of movement V of at least one beam moving on the surface of the construction support being adapted to generate a dendritic equiaxed crystalline microstructure of said layer.

[0018] The present disclosure makes it possible to control the temperature of the area to be solidified by modifying the shape of the deposit by the at least one energy beam. The area irradiated by said at least one beam receives a variable power. The thermal gradient generated by said at least one beam is controlled by a suitable and modulated energy source. The temperature profile is more spread out over time than in the prior art, which allows better control of the crystalline microstructure and therefore to manufacture parts with better mechanical strength.

[0019] The grain size, like the microstructure obtained, depends on the thermal gradient and the solidification rate. An increase in the thermal gradient results in an increase in grain size compared to an initial state, without this thermal gradient. Therefore, the particular temperature profile of the invention makes it possible to obtain an equiaxed dendritic crystalline microstructure with grains of suitable size.

[0020] A diameter of the at least one beam of the high energy device may be between 20 pm and 500 pm.

[0021] A power of the at least one beam may be between 50 W and 2000 W, more particularly between 50 and 1000 W.

[0022] The heating power can vary during the first thermal gradient G1 between 0 and 100% of the power associated with the melting peak P*.

[0023] The cooling power during the second thermal gradient G2 can be less than or equal to the power associated with the melting peak P*.

[0024] A thickness of the powder layer can be between 10 pm and 120 pm, more particularly between 20 and 60 pm.

[0025] A melting speed of the powder layer can be between 0.1 ms -1 and 10 ms -1 , more particularly between 0.1 ms -1 and 2.8 ms -1 .

[0026] The beam can be a laser beam and / or an electron beam. Brief description of the drawings

[0027] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which:

[0028] [Fig. 1] shows an additive manufacturing device, according to the prior art.

[0029] [Fig. 2] shows, at the top, an additive manufacturing build support with a powder layer including a point M through which a plurality of laser beams pass, and, at the bottom, a temperature profile generated by the plurality of laser beams in solid lines and according to the prior art in dotted lines.

[0030] [Fig. 3] shows a prediction of a microstructure of the manufactured part, according to the invention, with on the abscissa axis, a thermal gradient G in K / m applied to the manufactured part and on the ordinate axis, a solidification speed Vs in m / s.

[0031] [Fig. 4] shows the evolution of the width of the heat-affected zone ZAT and the melted zone ZF as a function of the heating temperature of the prior art, without preheating.

[0032] [Fig. 5] shows the evolution of the width of the heat-affected zone ZAT and the melted zone ZF as a function of the heating temperature with a first positive thermal gradient G1 of preheating, according to the invention. Description of the embodiments

[0033] Reference is now made to Figure 2.

[0034] Figure 2 schematically represents, at the top, an additive manufacturing construction support 24 receiving a layer of powder passing through a point M. This layer of powder is melted by a high-energy device according to the method of the present disclosure.

[0035] The high energy device emits one or more energy beams such as electron beams, laser beams

[0036] The following example is described considering a laser device as a high-energy device, but other types of devices generating other types of beams can be used as mentioned above. The melting of the powder layer is represented over time. Four times are represented: T, T+1, T+2, T+3. A laser device emits ten moving laser beams 26 on the surface of the construction support melting the powder layer: four successive laser beams denoted C, then a laser beam denoted B and finally, five laser beams denoted A. These laser beams 26 can be of the Gaussian type. The laser beams 26 are configured to form, during their movement at each point of the surface of the powder layer and in particular at M, a temperature profile.

[0037] At time T, the laser device therefore successively emits four laser beams of increasing power and lower than a melting power P* of the powder layer. These four laser beams are configured to form a first positive thermal gradient G1 for progressive preheating of the powder layer. This first thermal gradient makes it possible to pass from 0 to 80% of the melting temperature in less than 1 ms. The first positive thermal gradient G1 is visible on the temperature profile noted in solid line, below the construction support represented at the four times T, T+1, T+2, T+3. The temperature profile represented in dotted line is that which would be had without the invention. The temperature profile obtained without the invention, in dotted line, is a Gaussian profile characteristic of a single laser beam.

[0038] At time T+1, this same laser device emits a laser beam at a melting power P*. This laser beam is configured to form a melting peak of the powder layer. This melting peak is visible on the temperature profile in solid line.

[0039] At times T+2 and T+3, the laser device emits five laser beams denoted A. These laser beams have a decreasing power and are lower than P*. The laser beams are configured to form a second negative thermal gradient G2 for progressive cooling of the powder layer. This second thermal gradient G2 makes it possible to go from the melting temperature to less than 5% of the melting temperature in a time of approximately 2.4 ms.

[0040] In a particular embodiment, the laser device emits a single beam of variable power. This laser beam is configured to form a temperature profile similar to that shown in Figure 2, in solid lines. This temperature profile successively comprises a first positive thermal gradient G1 for progressive preheating of the powder layer, a melting peak of the powder layer and a second negative thermal gradient G2 for progressive cooling of the powder layer.

[0041] In a particular embodiment, the laser device simultaneously emits several laser beams having different powers. The laser device can emit Cn laser beams with n>1 configured to form a temperature profile comprising a first positive thermal gradient G1 for progressive preheating of the powder layer. These Cn laser beams have powers varying from 0 to 100% of the melting power P*, with Pen è P*. The laser device can emit a laser beam B configured to form a melting peak of the powder layer. This laser beam B has a power equal to the melting power P*. The laser device can emit A n laser beams with n>1 configured to form a temperature profile comprising a second negative thermal gradient G2 for progressive cooling of the powder layer. These A nLaser beams have powers varying from 0 to 100% of the fusion power P* with P An è P*. The time between passes of the laser beams follows the following formula: t = , where Lb represents a bandwidth and V a speed set by the operator, identical for all powder layers.

[0042] In a particular embodiment, the power of the at least one laser beam is between 50 W and 2000 W, more particularly between 50 and 1000 W. A thickness of the powder layer is between 10 pm and 120 pm, more particularly between 20 and 60 pm. A melting speed of the powder layer is between 0.1 ms -1 and 10 ms -1 , more particularly between 0.1 ms -1 and 2.8 ms -1 .

[0043] In a particular embodiment, ten laser beams can be emitted with the following powers: Pi = 50W, P2= 70W, P3= 90W, P4= 100W, P5= 250W, Pe = P* = 370W, P7= 200W, P8= 150W, P9= 100W, Pio = 50W, Where P n is the power associated with n ième laser beam.

[0044] Reference is now made to Figure 3.

[0045] Figure 3 represents a prediction of a microstructure of the part manufactured with the method of the present disclosure. The abscissa axis represents a thermal gradient G in K / m 30 applied to the manufactured part and the ordinate axis represents a solidification rate Vs in m / s 28. Depending on the position in this graph, the microstructure of the manufactured part can be either planar 32, cellular 34, dendritic columnar 36 or equiaxed dendritic 38. Two curves are represented. The curve, at the top, representing a higher cooling rate 40, changes from a planar microstructure to a cellular microstructure and then to a dendritic columnar microstructure. In contrast, the curve at the bottom, representing a slower cooling rate 42, changes from a planar microstructure to an equiaxed dendritic microstructure.Therefore, the temperature profile and the displacement speed V of the moving laser beams on the surface of the construction support are adapted to generate a dendritic equiaxed crystalline microstructure whereas in the prior art, a cellular crystalline microstructure is obtained.

[0046] Reference is now made to Figures 4 and 5.

[0047] Figure 4 represents the evolution of the width 42 of the heat-affected zone ZAT and of the melted zone ZF as a function of the heating temperature 44 of the prior art, without preheating. Figure 5 represents the evolution of the width 46 of the heat-affected zone ZAT and of the melted zone ZF as a function of the heating temperature 48 with a first positive thermal gradient G 1 of preheating, according to the invention. It can be seen that the ZAT obtained is wider in the case where preheating is carried out, according to the invention. Preheating the powder makes it possible to reduce the energy required to manufacture the part by reducing the temperature difference between the ZF and the end of the ZAT.

[0048] The present invention therefore relates to a method for additive manufacturing of a part, implementing a high-energy device of the aforementioned type, the method comprising the following successive steps: - formation of a layer of powder on a construction support, - carrying out by a high-energy device a melting step in which said layer of powder thus formed is illuminated by means of at least one energy beam such as an electron beam or a laser beam and said at least one beam is moved to form at each point of said layer a temperature profile, successively comprising: -- a first positive thermal gradient G1 for progressive preheating of the powder; -- a powder melting peak and -- a second negative thermal gradient G2 for progressive cooling of the powder, and in that, -- the temperature profile and the displacement speed V of the at least one moving beam on the surface of the construction support being adapted to generate a dendritic equiaxed crystalline microstructure of said layer, and - deposit at least one new layer of powder on the previous layer and repeat the previous fusion step for each new layer deposited until the said part is obtained.

[0049] In a particular embodiment, the plurality of N laser beams, where N = C n or N = An, are temporally shifted by one time EVN / V to ensure the formation of a thermal gradient G1 in the case of Cn laser beams or G2 in the case of A n laser beams, where V is the speed of movement of the N laser beams and EVN is a distance separating the fusion peaks of two successive laser beams. The diameter of the at least one beam of the device is varied during the formation of the part between 20 pm and 500 pm

[0050] In a particular embodiment, a single beam is emitted on the surface of said construction support. The power of said beam is modulated as it moves on the surface of said construction support.

Claims

Claims

1. Method for additive manufacturing of a part comprising the following successive steps: - the formation of a layer of powder on a construction support, - carrying out by a high-energy device generating at least one energy beam of a fusion step in which said layer of powder thus formed is illuminated by means of said at least one beam and said at least one beam is moved to form at each point of said layer a temperature profile, successively comprising: -- a first positive thermal gradient G1 for progressive preheating of the powder; -- a powder melting peak and -- a second negative thermal gradient G2 for progressive cooling of the powder, and, - the deposition of at least one new layer of powder on the previous layer and a repetition of the previous melting step for each new layer deposited until said part is obtained, characterized in that the high-energy device simultaneously emits several beams having different powers temporally offset by a time EVN / to ensure the formation of said thermal gradient G1 and / or said thermal gradient G2, where V is the speed of movement of the N beams and EVN is a distance separating the melting peaks of two successive beams, the temperature profile and the speed of movement V of at least one beam moving on the surface of the construction support being adapted to generate a dendritic equiaxed crystalline microstructure of said layer.

2. An additive manufacturing method according to claim 1, wherein a diameter of the at least one beam of the high-energy device is between 20 pm and 500 pm.

3. Additive manufacturing method according to claim 1 or 2, wherein a power of the at least one beam is between 50 W and 2000 W, more particularly between 50 and 1000 W.

4. Additive manufacturing method according to any one of the preceding claims, in which the heating power varies during the first thermal gradient G1 between 0 and 100% of the power associated with the melting peak P*.

5. Additive manufacturing method according to any one of the preceding claims, in which the cooling power during the second thermal gradient G2 is less than or equal to the power associated with the melting peak P*.

6. Additive manufacturing method according to any one of the preceding claims, wherein a thickness of the powder layer is between 10 pm and 120 pm, more particularly between 20 and 60 pm.

7. An additive manufacturing method according to any preceding claim, wherein a melting rate of the powder layer is between 0.1 ms- 1 and 10 ms -1 , more particularly between 0.1 ms -1 and 2.8 ms -1 .

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