Additive manufacturing process of a part
The method addresses the issue of thermal gradient control in additive manufacturing by using a controlled temperature profile to create a dendritic equiaxed crystalline microstructure, improving mechanical strength and grain size in manufactured parts.
Patent Information
- Application Number
- FR2023002634
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-03-21
- Publication Date
- 2025-10-10
- Estimated Expiration
- 2043-03-21
AI Technical Summary
Existing additive manufacturing methods face issues with poor control over thermal gradients and solidification rates, leading to inadequate mechanical strength and crystalline microstructure in manufactured parts due to non-homogeneous energy distribution and rapid melting/solidification processes.
A method involving a high-energy device that uses a controlled temperature profile with a first positive thermal gradient for preheating, a melting peak, and a second negative thermal gradient for cooling, combined with adjustable beam power and speed, to create a dendritic equiaxed crystalline microstructure.
This approach enhances mechanical strength by controlling the crystalline microstructure, resulting in parts with improved mechanical properties and controlled grain size.
Smart Images
Figure 00000011_0000 
Figure 00000011_0001 
Figure 00000012_0000
Abstract
Description
Title of the invention: Method for additive manufacturing 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 field 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 and with a greater degree of freedom. By additive manufacturing, the production of 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] [Fig.l] 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 allowing it to be oriented and / or moved 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 shapes of the laser beams 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 on the powder layer may not be homogeneous over the entire melted powder layer. The thermal gradient of the melted 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. Abstract
[0015] The present disclosure improves the situation and relates to a method for additively manufacturing 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 of progressive preheating of the powder; — a peak of fusion of the powder and — a second negative thermal gradient G2 of 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 - 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 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 having better mechanical strength.
[0017] The size of the grains, like the microstructure obtained, depends on the thermal gradient and the solidification speed. An increase in the thermal gradient has the consequence of increasing the size of the grains 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.
[0018] The high energy device can emit a single beam onto the surface of said building support and the power of said beam is modulated as it moves across the surface of said building support.
[0019] By using only one beam, the ease of use of the high energy device is increased.
[0020] The high-energy device can simultaneously emit several beams having different powers.
[0021] The general temperature profile can thus be adapted by using a plurality of laser beams with powers adapted according to what the operator has at his disposal.
[0022] N beams can be 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 can be a distance separating the fusion peaks of two successive beams.
[0023] A diameter of the at least one beam of the high energy device may be between 20 qm and 500 qm.
[0024] A power of the at least one beam may be between 50 W and 2000 W, more particularly between 50 and 1000 W.
[0025] The heating power can vary during the first thermal gradient G1 between 0 and 100% of the power associated with the melting peak P*.
[0026] The cooling power during the second thermal gradient G2 may be less than or equal to the power associated with the melting peak P*.
[0027] A thickness of the powder layer may be between 10 μm and 120 μm, more particularly between 20 and 60 μm.
[0028] A melting speed of the powder layer may be between 0.1 ms 1 and 10 ms ', more particularly between 0.1 ms 1 and 2.8 ms
[0029] The beam may be a laser beam and / or an electron beam. Brief description of the drawings
[0030] Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which: Fig.l
[0031] [Fig.l] shows an additive manufacturing device, according to the prior art. Fig. 2
[0032] [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. Fig. 3
[0033] [Fig.3] shows a prediction of a micro structure 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. Fig. 4
[0034] [Fig.4] shows the evolution of the width of the heat-affected zone ZAT and of the melted zone ZF as a function of the heating temperature of the prior art, without preheating. Fig. 5
[0035] [Fig.5] shows the evolution of the width of the heat-affected zone ZAT and of 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
[0036] Reference is now made to [Fig.2].
[0037] [Fig. 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.
[0038] The high energy device emits one or more energy beams such as electron beams, laser beams
[0039] 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 one 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.
[0040] 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 go 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.
[0041] 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.
[0042] 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.
[0043] 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 [Fig.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.
[0044] 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 PCn< 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 An 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 An laser beams have powers varying from 0 to 100% of the melting power P* with PAn< P*.The time between passes of the laser beams follows the following formula: . / — Lè, where Lb represents a strip width and V a speed set by the operator, identical for all layers of powder.
[0045] In a particular embodiment, the power of 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 qm and 120 qm, more particularly between 20 and 60 qm. A melting speed of the powder layer is between 0.1 ms 1 and 10 ms ', more particularly between 0.1 ms 1 and 2.8 ms '.
[0046] In a particular embodiment, ten laser beams can be emitted with the following powers: P! = 50W, P2 = 70W, P3= 90W, P4 = 100W, P5 = 250W, P6 = P* = 370W, P7 = 200W, P8= 150W, P9 = 100W, P10 = 50W, Where Pn is the power associated with the nth laser beam.
[0047] Reference is now made to [Fig.3].
[0048] [Fig. 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. On the other hand, 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.
[0049] Reference is now made to Figures 4 and 5.
[0050] [Fig.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. [Fig.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 G1 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.
[0051] 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 of progressive preheating of the powder; — a peak of fusion of the powder 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.
[0052] In a particular embodiment, the plurality of N laser beams, where N = Cn or N = An, are temporally offset by a time EvN / V to ensure the formation of a thermal gradient G1 in the case of the Cn laser beams or G2 in the case of the An 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 pins and 500 pins
[0053] 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. A method of additive manufacturing a part comprising the following successive steps: - the formation of a layer of powder on a construction support, - the 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 melting peak of the powder 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 / V 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 the at least one mobile beam 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 qm and 500 qm.
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. An additive manufacturing method according to any one of the claims- preceding indications, 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 qm and 120 qm, more particularly between 20 and 60 qm.
7. Additive manufacturing method according to any one of the preceding claims, wherein a melting rate of the powder layer is between 0.1 ms 1 and 10 ms ', more particularly between 0.1 ms 1 and 2.8 ms '.