METHOD AND DEVICE FOR THE ADDITIVE PRODUCTION OF A COMPONENT FROM A POWDER LAYER

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a method for additively manufacturing an object from a layer of powder, as well as a device suitable for implementing such a method. STATE OF THE ART

[0002] Additive manufacturing involves creating an object by fusing layers of powder superimposed on each other. These layers correspond to different sections of the object to be manufactured.

[0003] To fuse a layer of powder, a source projects an energy beam onto the surface of the powder layer, at a spot where such fusion occurs. The energy beam is then controlled to sweep across the surface to spread this fusion over the entire surface of the layer.

[0004] Conventionally, the energy beam scans different areas of the surface in a longitudinal direction and in a forward and return direction, alternately.

[0005] In particular, it has been proposed to control the energy source so that the spot does not travel through each zone in a perfectly rectilinear translational movement in the longitudinal direction, but in a movement composed of a translation in the longitudinal direction and an oscillatory movement ("wobbling" in English). The oscillatory movement oscillates in a transverse direction, in order to widen the molten pool.

[0006] Different oscillatory movements have been proposed.

[0007] One of them, which is generally called "circular mode", is such that the spot follows a trajectory comprising loops offset from each other in the longitudinal direction. Such a circular mode was notably proposed in document WO2019207239.

[0008] There Figure 1shows a trajectory followed by the spot during the implementation of a process using such a circular mode. On the Figure 1 , the longitudinal direction is horizontal, and the transverse direction is vertical. The forward direction is from left to right and the return direction is from right to left. Four successions of loops, located in four distinct zones, are represented on the Figure 1 . Two of the four zones were traversed in the forward direction, and the other two in the reverse direction, as shown by the four dotted arrows. The spot travels through each loop in a constant direction of rotation. The direction of rotation is the same for each of the four zones, and in particular for each loop. As a result, two successions of adjacent loops are head to tail. STATEMENT OF THE INVENTION

[0009] One aim of the invention is to distribute the energy supplied by an energy beam more evenly over a layer of powder during additive manufacturing, without reducing the manufacturing time.

[0010] For this purpose, according to a first aspect, a method of additive manufacturing of an object from a layer of powder is proposed, comprising steps of: projecting an energy beam onto a surface of the powder layer into a spot so as to fuse the powder, scanning, by the energy beam, a first area of ​​the surface in a longitudinal scanning direction and in a forward direction, and, during the scanning of the first area, orienting the energy beam so that the spot travels through the first area along a trajectory comprising first loops offset from each other in the longitudinal scanning direction, the spot traveling through each first loop in a first direction of rotation, scanning by the energy beam a second area of ​​the surface in the longitudinal scanning direction and in a return direction opposite to the forward direction, the second area being adjacent to the first area in a transverse scanning direction perpendicular to the longitudinal scanning direction, and during the scanning of the second area,orienting the energy beam so that the spot travels through the second zone along a trajectory comprising second loops offset from each other in the longitudinal scanning direction, the spot traveling through each second loop in a second direction of rotation opposite to the first direction of rotation.

[0011] The inventors noticed that, due to the asymmetrical shape of the loops traversed by the spot, more energy was deposited at the base of the loops than at their top. Consequently, when two successions of adjacent loops are head to tail as shown in Figure 1 , the energy deposited on the layer varies strongly in the transverse direction: this energy is high near the bases of the facing loops, and lower near the tops of the facing loops.

[0012] Changing the direction of the loops between the first zone and the second zone ensures that the succession of first loops and the succession of second loops are no longer head to tail, as in the Figure 1 , but are oriented in the same direction in the transverse direction. Thus, the bases of the first loops are close to the tops of the second loops, or the tops of the first loops are close to the bases of the second loops, which in both cases reduces the energy variations in the transverse direction. This is why the energy deposition is more homogeneous.

[0013] Furthermore, scanning the first zone in a forward direction and the second zone in a return direction makes it possible to scan both of these zones quickly. This is why the gain in homogeneity offered by the method according to the first aspect does not compromise its execution speed.

[0014] The method according to the first aspect may further comprise the following optional features, taken alone or combined with each other when technically possible.

[0015] Preferably, at least two of the first loops and / or at least two of the second loops intersect.

[0016] Preferably, at least two of the first loops and / or at least two of the second loops are of the same dimension.

[0017] Preferably, the succession of second loops is spaced from the succession of first loops in the transverse scanning direction.

[0018] Preferably, at least one of the loops extends over an amplitude measured in the transverse scanning direction of between 100 micrometers and 2 millimeters.

[0019] Preferably, the energy beam oscillates in the transverse scanning direction at a frequency of at least 1 kHz.

[0020] Preferably, the energy beam is a laser beam or an electron beam.

[0021] Also provided, according to a second aspect, is a device for additively manufacturing an object from a layer of powder, the device comprising an energy source configured to: projecting an energy beam onto a surface of the powder layer in a spot so as to fuse the powder, controlling a scan, by the energy beam, of a first area of ​​the surface in a longitudinal scanning direction and in a forward direction, and, during the scanning of the first area, orienting the energy beam so that the spot travels through the first area along a trajectory comprising first loops offset from each other in the longitudinal scanning direction, the spot traveling through each first loop in a first direction of rotation, controlling a scan by the energy beam of a second area of ​​the surface in the longitudinal scanning direction and in a return direction opposite to the forward direction, the second area being adjacent to the first area in a transverse scanning direction perpendicular to the longitudinal scanning direction, and, during the scanning of the second area,orienting the energy beam so that the spot travels through the second area along a trajectory comprising second loops offset from each other in the longitudinal scanning direction, the energy beam traveling through each second loop in a second direction of rotation opposite to the first direction of rotation. DESCRIPTION OF FIGURES

[0022] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which: There Figure 1 , already discussed, represents a trajectory followed by a spot resulting from the projection of an energy beam onto a surface using a method known in the state of the art. Figure 2 is a schematic view of an additive manufacturing device according to a first embodiment. The Figure 3is a perspective view of the additive manufacturing device already shown in Figure 2 . There Figure 4 is a perspective view of an additive manufacturing device according to a second embodiment. The Figure 5 is a flowchart of steps of an additive manufacturing process according to one embodiment. The Figure 6 represents a trajectory followed by a spot resulting from the projection of an energy beam onto a surface during the implementation of the method to which the Figure 4 .

[0023] Throughout the figures, similar elements have identical references. DETAILED DESCRIPTION OF THE INVENTION Additive manufacturing device

[0024] In reference to the figures 2 And 3 , an additive manufacturing device comprises an energy source 1 according to a first embodiment, and a support 140.

[0025] The support 140 has a free surface, typically flat, extending in two directions: a longitudinal direction and a transverse direction perpendicular to the longitudinal direction. In the following, the longitudinal direction is conventionally denoted X, and the transverse direction Y.

[0026] The free surface of the support 140 is intended to serve as a support surface 140 for a layer 150 of powder or a plurality of layers 150s stacked on top of each other.

[0027] Generally, the energy source 1 is adapted to project an energy beam towards the support 140. When a layer 150 of powder is deposited on the support 140, this energy beam is projected onto an upper surface of this layer 150 in a spot.

[0028] The energy source 1 comprises in particular a generator 110 configured to generate the energy beam. The generator 110 is for example a laser source; the beam generated is then a laser beam comprising photons, in other words a light beam. Alternatively, the generator 110 is of the EBM (“Electron Beam Melting”) type, that is to say of a type adapted to generate a beam of electrons. In the following, we will consider the non-limiting case of a laser beam.

[0029] The energy source 1 further comprises a focuser adapted to adjust a focus of the light beam. This focuser thus makes it possible to vary the size of the spot into which the beam is projected on the upper surface of a layer 150 of powder deposited on the support 140.

[0030] The focuser comprises for example a focusing element 1102 and a focusing lens 1101 movable relative to the focusing element in translation parallel to an optical axis of the lens. The focusing lens 1101 is arranged downstream of the beam generator 110. In the following, the terms “upstream” and “downstream” will implicitly refer to a direction of propagation of the energy beam on an optical path going from the generator 110 to the support 140.

[0031] The focuser includes an actuator for moving the focusing lens 1101 relative to the focusing element 1102.

[0032] The energy source 1 further comprises a scanning device 130 adapted to orient the energy beam so that the spot where this beam is projected is movable relative to the support 140, on the surface of the layer 150, in the longitudinal direction and in the transverse direction.

[0033] The scanning device 130 is arranged downstream of the focusing device.

[0034] The scanning device 130 comprises for example a first scanning mirror 131 rotatable relative to the support 140 about a first axis of rotation 133, and a second scanning mirror 132 rotatable relative to the support 140 about a second axis of rotation 134 different from the first axis of rotation. For example, the first axis of rotation 133 is in the longitudinal direction, and the second axis of rotation 134 is in the transverse direction. One of the two scanning mirrors 131, 132 is arranged downstream of the other scanning mirror, such that an energy beam from the generator 110 is reflected on the two scanning mirrors sequentially, before being redirected towards the support 140.

[0035] Alternatively, the scanning device 130 comprises a single scanning mirror movable in rotation relative to the support 140, around the first axis of rotation 133 and around the second axis of rotation 134. In this case, this single scanning mirror is arranged so that an energy beam coming from the generator 110 is reflected on this scanning mirror before being redirected towards the support 140.

[0036] The scanning device 130 further comprises at least one actuator (one per scanning mirror used). Each actuator has the function of moving a scanning mirror in rotation over a range of scanning angles.

[0037] The scanning angle ranges are for example adapted to allow the spot to cover the entire surface of the layer 150, or at least a majority of it.

[0038] For a given configuration of the scanning device, the central axis of a beam emanating from the generator 110 intersects the surface of the support 140 at a specific point. There is thus a mathematical relationship between the coordinates (x, y) of this point and the angular position of the scanning mirrors 131, 132.

[0039] The scanning device 130 is in particular configured to cause a translation of the spot projected onto the surface of the layer 150 of powder in a longitudinal scanning direction, in a forward direction and in a return direction opposite to the forward direction, and this alternately, the longitudinal scanning direction being chosen independently of the longitudinal and transverse directions of the support 140.

[0040] In the first embodiment, the energy source 1 further comprises an oscillation device 120, adapted to oscillate an energy beam emanating from the generator 110, and consequently also to oscillate the spot where the energy beam is projected in at least one oscillation direction, on the surface of a layer 150 of powder deposited on the support 140.

[0041] The oscillation device 120 comprises, for example, an oscillation mirror which can rotate relative to the support 140 around two different oscillation axes 122, 123. The oscillation device 120 further comprises an actuator arranged to oscillate the oscillation mirror at a given frequency, fixed or variable.

[0042] The actuator of the oscillation device 120 is configured to oscillate the oscillation mirror around the oscillation axes 122, 123 over two oscillation angle ranges smaller than the scanning angle ranges over which each scanning mirror 131, 132 is rotatable around the axes 133, 134. The oscillation angle ranges used by the oscillation device 120 are adapted to allow the projected spot to oscillate over an amplitude of between 100 micrometers and 2 millimeters.

[0043] The scanning device 130 and the oscillation device 120 are configured to cooperate so that the spot can move on the surface of the layer 150 of powder deposited on the support 140 according to a movement composed of a translation induced by the scanning device 130 and an oscillatory movement induced by the oscillation device 120. In other words, the oscillatory movement modulates the translation induced by the scanning device 130.

[0044] The oscillation device 120 is arranged upstream of the scanning device 130. In other words, an energy beam from the generator 110 is reflected on the oscillation mirror before reaching the scanning device 130.

[0045] The oscillation device 120 is for example arranged downstream of the focuser.

[0046] The laser source 110, the modulation device 120 and the scanning device 130 are for example arranged so as to allow a surface melting rate, that is to say the surface of the layer 150 of powder covered by the laser spot per unit of time, greater than 1000 cm 2 < / min, for example greater than 2000 cm 2 < / min, for example greater than 4000 cm 2 < / min, for example less than 15000 cm 2 < / min, for example less than 10000 cm 2 < / min, for example of the order of 6000 cm 2 < / min.

[0047] The modulation device 120 and the scanning device 130 are for example configured to allow a speed of movement of the spot of between 0.5 and 10 m / s, for example between 1 and 5 m / s, for example equal to 1 or 2 m / s.

[0048] The energy source 1 further comprises a control unit configured to control the focuser, the scanning device 130 and the oscillation device 120 (not shown). This control unit is in particular configured to control the respective actuators of these different devices.

[0049] The control unit may comprise or be coupled to a memory storing a table of pre-calculated focusing parameter values ​​for different pairs of coordinates (x, y) in the plane of the free surface of the support 140. Thus, when the spot is centered at a point of coordinates (x, y) of the surface of the support, the control unit is configured to control the focuser using the focusing parameter value associated with this pair in the table of pre-calculated values.

[0050] Is represented in Figure 4a second embodiment of the energy source 1. This second embodiment differs from the first embodiment in that it does not comprise an oscillation device 120. On the other hand, in the second embodiment, the device 130 is configured to, by itself, ensure that the spot can move on the surface of the layer 150 of powder deposited on the support 140 according to a movement composed of a translation induced by the scanning device 130 and an oscillatory movement which would be induced by the oscillation device 120 if it were present in this second embodiment. This is possible by oscillating the scanning mirror(s). Additive manufacturing process

[0051] In reference to the Figure 4 , an additive manufacturing process using the device described above comprises the following steps.

[0052] At least one layer 150 of powder is deposited on the support 140, as shown in Figure 1 The powder layer 150 has a free surface extending in two longitudinal and transverse directions of the support 140.

[0053] The powder grains have, for example, a particle size between 10 and 100 µm, for example between 20 and 60 µm, for example equal to 40 µm.

[0054] The material of the or each layer 150 of powder has for example a fluence of between 0.5 and 10 J / mm 2< , for example of between 1 and 5 J / mm 2< , for example equal to 2 J / mm 2< .

[0055] The material of the or each powder layer 150 may comprise titanium and / or aluminum and / or inconel and / or stainless steel and / or maraging steel. The material of the or each powder layer 150 may consist of titanium and / or aluminum and / or inconel and / or stainless steel and / or maraging steel.

[0056] The generator 110 is activated, so as to emit an energy beam. This energy beam passes through the focuser, the oscillation device 120 (if present in the energy source 1), and the scanning device 130 before being projected onto the free surface of the layer 150 of powder in a spot (step 200). The layer 150 of powder then heats up at this spot, to the point of causing its grains to melt.

[0057] The focuser also adjusts the focus of the beam in order to reduce the size of this spot, and therefore to further concentrate the energy carried by the energy beam.

[0058] The scanning device 130 orients the beam so that the spot moves in translation in a longitudinal scanning direction, in a forward direction, over a first area of ​​the surface. This translational movement is shown in the Figure 6 by dotted arrows (step 202).

[0059] During step 202, the scanning device 130 or the oscillation device 120 oscillates the beam, so that this translation is modulated by an oscillatory movement. This oscillatory movement comprises a transverse oscillation component in a transverse scanning direction perpendicular to the longitudinal scanning direction and a longitudinal oscillation component in the longitudinal scanning direction. In other words, this oscillatory movement causes an oscillation of the spot on the surface of the powder layer 150 not only in the transverse scanning direction, but also in the longitudinal scanning direction.

[0060] When the source 1 is in accordance with the first embodiment, the oscillatory motion is induced by the oscillation device 120. When the source 1 is in accordance with the second embodiment, the oscillatory motion is induced by the scanning device 130.

[0061] Preferably, both oscillation components oscillate at the same frequency. The oscillatory motion can then be ellipsoidal if both components are sinusoidal in shape.

[0062] Due to the composition of this oscillatory movement and the translation in the forward direction, the spot follows, in the first zone, a trajectory comprising a succession of first loops offset from each other in the longitudinal scanning direction.

[0063] Each loop has a node, which is a point through which the spot passes twice. Each loop also includes an upstream portion, an intermediate hairpin portion, and a downstream portion. The spot travels through the different portions of a loop in this order: the upstream portion, the node, the intermediate hairpin portion, the node again, and finally the downstream portion. This downstream portion is connected to the upstream portion of a subsequent loop. While traveling through a loop, the spot rotates around a central point of the loop always in the same direction of rotation, called the first direction of rotation.

[0064] Each loop has a base formed by its upstream portion, its downstream portion, and the node. Each loop has a top formed by its intermediate portion. Due to its asymmetrical shape, the amount of energy deposited by the beam at the base of a loop (especially near the node) is higher than the amount of energy deposited at the top of that loop.

[0065] On the Figure 5 , the longitudinal scanning direction is horizontal, and the forward direction is from left to right, and the first rotation direction is a counterclockwise rotation direction. It follows that the respective bases of the first loops are below the tops of these first loops.

[0066] If both components of the oscillatory motion have the same amplitude, the oscillatory motion becomes circular. As a result, each first loop has a shape that tends more towards a circle.

[0067] Preferably, at least one first loop extends over a height, measured in the transverse scanning direction, of between 100 micrometers and 2 millimeters. This height corresponds to the amplitude of the transverse component of the oscillatory movement.

[0068] Furthermore, it is preferable that the scanning device 130 (in the second embodiment of the energy source 1) or the oscillation device 120 (in the first embodiment of the energy source 1) oscillates the spot in the transverse direction at a frequency of at least 1 kHz. This frequency is typically between 1 kHz and 10 kHz when the energy beam is a laser beam, or between 1 kHz and 100 kHz when the energy beam is an electron beam.

[0069] All first loops are traversed by the task in the first direction of rotation.

[0070] All first loops are preferably of the same dimension (of the same height between their base and their top, measured in the transverse direction, and / or of the same width, measured in the longitudinal direction).

[0071] At least two of the first loops intersect, that is, a current first loop crosses a previous loop at at least two intersection points. Preferably, all the first loops intersect in pairs.

[0072] The succession of first loops extends over a certain length in the longitudinal scanning direction, and over a certain width in the transverse scanning direction.

[0073] Then, the scanning device 130 orients the energy beam so as to move the spot in the transverse scanning direction, for example in translation, so that the spot reaches a second zone which is adjacent to the first zone (for example above the first zone in the case illustrated in the Figure 5 ).

[0074] Then, the scanning device 130 orients the beam so that the spot moves over the second zone in translation in the longitudinal scanning direction, but this time in a return direction opposite to the forward direction (step 204).

[0075] During step 204, the scanning device 130 or the oscillation device 120 oscillates the beam, so that this translation is modulated by an oscillatory movement, such that the spot follows, in the second zone, a trajectory comprising a succession of second loops offset from each other in the longitudinal scanning direction. All the first loops are this time traveled by the spot in a second direction of rotation.

[0076] As for step 202, the oscillatory movement is induced by the oscillation device 120 when the source 1 is in accordance with the first embodiment, or by the scanning device 130 when the source 1 is in accordance with the second embodiment. The second direction of rotation is opposite to the first direction of rotation. This change in the loop travel direction is typically obtained by adjusting the oscillation parameters used to oscillate the beam.

[0077] On the Figure 5 , the return direction is from right to left, and the second direction of rotation of the spot on the second loops is a clockwise direction of rotation. It follows that the respective bases of the second loops are below the peaks of these same second loops, as was already the case for the first loops discussed previously. As a result, the energy transported by the energy beam on the layer 150 of powder is distributed more homogeneously over the whole consisting of the first zone and the second zone.

[0078] Preferably, at least one second loop extends over a height, measured in the transverse scanning direction, of between 100 micrometers and 2 millimeters. This height corresponds to the amplitude of the transverse component of the oscillatory movement.

[0079] Furthermore, it is preferable that the source 1 oscillates the spot in the transverse scanning direction and in the second zone at a frequency of at least 1 kHz. This frequency is typically between 1 kHz and 10 kHz when the energy beam is a laser beam, or between 1 kHz and 100 kHz when the energy beam is an electron beam.

[0080] All second loops are preferably of the same dimension (of the same height between their base and their apex, measured in the transverse scanning direction, and / or of the same width, measured in the longitudinal scanning direction).

[0081] At least two of the second loops intersect. Preferably, all of the second loops intersect in pairs.

[0082] Preferably, the succession of second loops is at a distance from the succession of first loops (as shown in the Figure 5). Alternatively, at least one second loop intersects a first loop.

[0083] The preceding steps, in particular steps 202 and 204, are repeated alternately. In order to cover a greater number of areas adjacent to each other in the transverse scanning direction (four areas being shown on the Figure 5 ).

Claims

1. Method for additively manufacturing an object from a powder layer, the method comprising the steps of: • projecting (200) an energy beam onto a surface of the powder layer as a spot so as to fuse the powder, • scanning (202), by the energy beam, a first zone of the surface in a longitudinal scanning direction and in a forward direction, and, during scanning of the first zone, directing the energy beam so that the spot traverses the first zone along a trajectory comprising first loops offset with respect to one another in the longitudinal scanning direction, the spot traversing each first loop in a first direction of rotation, • scanning (204), by the energy beam, a second zone of the surface in the longitudinal scanning direction and in a return direction opposite to the forward direction, the second zone being adjacent to the first zone in a transverse scanning direction perpendicular to the longitudinal scanning direction, and during scanning of the second zone, directing the energy beam so that the spot traverses the second zone along a trajectory comprising second loops offset with respect to one another in the longitudinal scanning direction, the spot traversing each second loop in a second direction of rotation opposite to the first direction of rotation.

2. Method according to any of the preceding claims, wherein at least two of the first loops and / or at least two of the second loops intersect.

3. Method according to either of the preceding claims, wherein at least two of the first loops and / or at least two of the second loops are of the same size.

4. Method according to any of the preceding claims, wherein the succession of second loops is at a distance from the succession of first loops in the transverse scanning direction.

5. Method according to any of the preceding claims, wherein at least one of the loops extends over an amplitude measured in the transverse scanning direction of between 100 micrometers and 2 millimeters.

6. Method according to any of the preceding claims, wherein the energy beam oscillates in the transverse scanning direction at a frequency of at least 1 kHz.

7. Method according to any of the preceding claims, wherein the energy beam is a laser beam or an electron beam.

8. Device for additively manufacturing an object from a powder layer, the device comprising an energy source configured to project a beam of energy onto a surface of the powder layer as a spot so as to fuse the powder, the energy source comprising a control unit configured to: • control a scan, by the energy beam, of a first zone of the surface in a longitudinal scanning direction and in a forward direction, and, during the scan of the first zone, direct the energy beam so that the spot traverses the first zone along a trajectory comprising first loops offset with respect to one another in the longitudinal scanning direction, the spot traversing each first loop in a first direction of rotation, • control a scan, by the energy beam, of a second zone of the surface in the longitudinal scanning direction and in a return direction opposite to the forward direction, the second zone being adjacent to the first zone in a transverse scanning direction perpendicular to the longitudinal scanning direction, and, during scanning of the second zone, direct the energy beam so that the spot traverses the second zone along a trajectory comprising second loops offset with respect to one another in the longitudinal scanning direction, the energy beam traversing each second loop in a second direction of rotation opposite to the first direction of rotation.