Method for additive manufacturing of an object from a powder layer

Abstract

A method for additive manufacturing of an object from a powder bed, the method comprising: projecting (200) an energy beam onto a surface of the powder bed to form a spot for melting the powder; scanning the energy beam in a longitudinal scan direction and a forward scan direction across a first zone of the surface, wherein during the scan of the first zone, the energy beam is orientated such that the spot travels through the first zone in a trajectory consisting of first loops offset from one another in the longitudinal scan direction, and the spot travels through each of the first loops in a first rotational direction. and (202) scanning the energy beam through a second zone of the surface in a longitudinal scan direction and a return direction opposite to the forward scan direction, the second zone being adjacent to the first zone in a lateral scan direction perpendicular to the longitudinal scan direction, and during scanning of the second zone, orienting the energy beam so that the spot travels through the second zone in a trajectory consisting of second loops offset from one another in the longitudinal scan direction, and the spot travels through each of the second loops in a second rotational direction opposite to the first rotational direction.

Description

Technical Field

[0001] The present invention relates to a method for additive manufacturing of an object from a powder bed and an apparatus configured to perform a method of that kind.

Background Art

[0002] Additive manufacturing manufactures an object by melting layers of powder stacked on top of each other. These layers correspond to different sections of the object being manufactured. To melt the powder bed, a source projects an energy beam onto the surface of the powder bed to form a spot where such melting occurs. Subsequently, the energy beam is controlled to scan the surface in order to propagate the melting across the entire surface of the layer.

[0003] Conventionally, the energy beam has scanned different zones of the surface longitudinally, alternating between the outward sense and the return sense. In particular, it has been proposed to control the energy source such that the spot progresses in a movement consisting of a longitudinal translational movement and an oscillatory movement (also called "wobbling") rather than a complete linear movement where the spot translates longitudinally across each zone. The oscillatory movement oscillates laterally, in particular so as to widen the melt pool.

[0004] Various wobbling movements have been proposed. One of them is generally called the "circular mode", in such a way that the spot follows a trajectory consisting of loops offset from each other longitudinally.

[0005] Figure 1 shows the trajectory traced by a spot during the execution of a method using this type of circular mode. In 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. Figure 1 shows a series of four loops located in four zones. Four dashed arrows indicate that two of the four zones proceed in the forward direction and the remaining two proceed in the return direction. The spot proceeds through each loop in a constant rotation sense. The rotation sense is the same in the four zones and, in particular, the same in each loop. As a result, two adjacent series of loops are in a head-to-tail relationship. SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0006] An object of the present invention is to distribute more uniformly the energy supplied to a powder layer by an energy beam during additive manufacturing, without thereby shortening the manufacturing time. MEANS FOR SOLVING THE PROBLEM

[0007] For this purpose, in a first aspect, there is provided a method for additive manufacturing of an object from a powder layer, the method comprising: - projecting an energy beam onto the surface of the powder layer to form a spot for melting the powder; - the energy beam scanning a first zone of the surface in a longitudinal scanning direction and a forward direction, during the scanning of the first zone, orienting the energy beam such that the spot proceeds along a trajectory composed of first loops that are offset from each other in the longitudinal scanning direction in the first zone, and the spot proceeds through each of the first loops in a first rotation sense; - A step in which an energy beam scans a second zone on the surface in a return direction opposite to the longitudinal scanning direction and the forward path direction, the second zone being adjacent to the first zone in a transverse scanning direction orthogonal to the longitudinal scanning direction, and during the scanning of the second zone, the energy beam advances along a trajectory in which spots are configured in a second loop offset from each other in the longitudinal scanning direction of the second zone, and the spots are oriented to advance each of the second loops in a second rotation direction opposite to the first rotation direction. It is proposed to include.

[0008] The inventors have noticed that since the shape of the loop along which the spot advances is asymmetric, more energy is accumulated at the base than at the top of the loop. As a result, as shown in FIG. 1, when two adjacent series of loops are in a head-to-tail relationship, the energy accumulated in the layer varies greatly in the transverse direction. This energy is large near the base of the opposing loops and small near the top.

[0009] Changing the direction in which the loop advances between the first zone and the second zone enables the series of first loops and the series of second loops to be oriented in the same direction laterally, rather than in a head-to-tail relationship as in FIG. 1. Therefore, the base of the first loop can be close to the top of the second loop or the top of the first loop can be close to the base of the second loop, and in either case, the lateral energy variation can be reduced. Thus, the energy accumulation becomes more homogenized.

[0010] Furthermore, by scanning the first zone in the forward path direction and the second zone in the return direction, it becomes possible to scan all of these two zones at high speed. Therefore, the improvement in homogeneity provided by the method according to the first aspect does not impair its execution speed.

[0011] The method according to the first aspect can have any of the following features, separately or in combination, if technically possible. Preferably, at least two of the first loops and / or at least two of the second loops intersect.

[0012] Preferably, at least two of the first loops and / or at least two of the second loops have the same dimensions.

[0013] Preferably, a series of second loops is separated from a series of first loops by a predetermined distance in the lateral scanning direction.

[0014] Preferably, at least one of the loops spreads with an amplitude ranging from 100 micrometers to 2 millimeters as measured in the lateral scanning direction.

[0015] Preferably, the energy beam oscillates in the lateral scanning direction at a frequency of at least 1 kHz.

[0016] Preferably, the energy beam is a laser beam or an electron beam.

[0017] Also, in a second aspect, an apparatus for additive manufacturing of an object from a powder layer, the apparatus comprising an energy source, the energy source - projects an energy beam in the form of a spot onto the surface of the layer so as to melt the powder, - scans a first zone of the surface in the longitudinal scanning direction and the forward path direction, and during the scanning of the first zone, commands the energy beam such that the spot travels along a trajectory composed of first loops that are offset from each other in the longitudinal scanning direction in the first zone, and the spot travels through each of the first loops in the first rotational direction. - The second zone on the surface is scanned by the energy beam in the longitudinal scanning direction and the return path direction opposite to the forward path direction, and the second zone is adjacent to the first zone in the transverse scanning direction perpendicular to the longitudinal scanning direction. During the scanning of the second zone, the energy beam is made to travel along a trajectory in which the spots are configured in a second loop offset from each other in the longitudinal scanning direction in the second zone, and the energy beam is commanded to travel along each of the second loops in a second rotational direction opposite to the first rotational direction. An apparatus configured as such is proposed.

[0018] Other features, objects, and advantages of the present invention will become apparent from the following merely illustrative and non-limiting description that needs to be read with reference to the accompanying drawings.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0020] In all the drawings, similar elements are given the same reference numerals. Additive manufacturing apparatus Referring to FIGS. 2 and 3, the additive manufacturing apparatus includes an energy source 1 and a support 140 in the first embodiment. The support 140 has a typically planar free surface that extends in two directions, a longitudinal direction and a transverse direction perpendicular to the longitudinal direction. Hereinafter, by convention, X indicates the longitudinal direction and Y indicates the transverse direction.

[0021] The function of the free surface of the support 140 is to serve as a support surface 140 for the powder layer 150 or a plurality of layers 150 stacked on one another. In principle, the energy source 1 is adapted to project an energy beam towards the support 140. When the powder layer 150 is deposited on the support 140, this energy beam is projected onto the upper surface of the layer 150 to form a spot.

[0022] The energy source 1 specifically includes a generator 110 configured to generate an energy beam. The generator 110 is, for example, a laser light source, and the generated beam is a laser beam composed of photons, that is, an optical beam. Alternatively, the generator 110 is of the EBM (electron beam melting) type, that is, a type adapted to generate an electron beam. Hereinafter, the non-limiting situation is that of the laser beam.

[0023] The energy source 1 further includes a focusing device configured to adjust the focusing of the optical beam. Accordingly, the size of the spot in the form in which the beam is projected onto the upper surface of the powder layer 150 deposited on the support 140 can be changed by this focusing device.

[0024] The focusing device includes, for example, a focusing element 1102 and a focusing lens 1101 that can be translated parallel to the optical axis of the lens with respect to the focusing element. The focusing lens 1101 is disposed downstream of the beam generator 110. Hereinafter, the terms "upstream" and "downstream" implicitly refer to the propagation direction of the energy beam on the optical path from the generator 110 to the support 140. The focusing device includes an actuator for moving the focusing lens 1101 relative to the focusing element 1102.

[0025] The energy source 1 further includes a scanning device 130 configured to orient the energy beam such that the spot on which the beam is projected moves longitudinally and transversely relative to the support 140 on the surface of the layer 150. The scanning device 130 is arranged downstream of the focusing device.

[0026] The scanning device 130 includes, for example, a first scanning mirror 131 that is rotatably movable relative to the support 140 about a first rotation axis 133, and a second scanning mirror 132 that is rotatably movable relative to the support 140 about a second rotation axis 134 different from the first rotation axis. For example, the first rotation axis 133 is in the longitudinal direction and the second rotation axis 134 is in the transverse direction. One of the two scanning mirrors 131, 132 is arranged downstream of the other scanning mirror, and the energy beam from the generator 110 is sequentially reflected by the two scanning mirrors before being redirected towards the support 140.

[0027] Alternatively, the scanning device 130 includes a single scanning mirror that is rotatably movable relative to the support 140 about the first rotation axis 133 and the second rotation axis 134. In this case, the single scanning mirror is configured such that the energy beam from the generator 110 is reflected by this scanning mirror before being redirected towards the support 140.

[0028] Furthermore, the scanning device 130 includes at least one actuator (one for each scanning mirror used). The function of each actuator is to rotate the scanning mirror over a range of scanning angles. The range of scanning angles is such that, for example, the spot can cover the entire surface of the layer 150, or at least most of it.

[0029] Regarding a predetermined configuration of the scanning device, the central axis of the beam generated from the generator 110 intersects the surface of the support 140 at a specific point. Therefore, there is a mathematical relationship between the coordinates (x, y) of that point and the angular positions of the scanning mirrors 131 and 132.

[0030] The scanning device 130 is configured to cause translational movement in the forward path direction, which is the longitudinal scanning direction of the spot projected onto the surface of the powder layer 150, and in the return path direction opposite to the forward path direction, and to perform these alternately. The longitudinal scanning direction is selected independently of the longitudinal and transverse directions of the support 140.

[0031] In the first embodiment, the energy supply source 1 further includes a vibration device 120 configured to cause vibration of the energy beam generated from the generator 110, and as a result, to cause vibration of the spot projected onto the surface of the powder layer 150 deposited on the support 140 in at least one vibration direction.

[0032] The vibration device 120 includes, for example, a vibration mirror that is rotatable relative to the support 140 around two different vibration axes 122 and 123. The vibration device 120 further includes an actuator configured to cause vibration of the vibration mirror at a predetermined fixed or variable frequency.

[0033] The actuator of the vibration device 120 is configured to vibrate the vibration mirror around the vibration axes 122 and 123 over two ranges of vibration angles that are smaller than the range of scanning angles over which each of the scanning mirrors 131 and 132 rotates around the axes 133 and 134. The range of vibration angles used by the vibration device 120 is such that the projected spot can vibrate over an amplitude that includes the range between 100 micrometers and 2 millimeters.

[0034] The scanning device 130 and the vibration device 120 are configured to cooperate such that the spot can move on the surface of the powder layer 150 deposited on the support 140 by a movement composed of a translational movement caused by the scanning device 130 and a vibration movement caused by the vibration device 120. In other words, the vibration movement modulates the translational movement caused by the scanning device 130.

[0035] The vibration device 120 is arranged upstream of the scanning device 130. In other words, the energy beam from the generator 110 is reflected by the vibration mirror before reaching the scanning device 130. The vibration device 120 is arranged, for example, downstream of the focusing device.

[0036] The laser light source 110, the vibration device 120, and the scanning device 130 are arranged such that, for example, the surface melting rate, that is, the surface area of the powder layer 150 covered by the laser spot per unit time, is 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, less than 6000 cm 2 / min.

[0037] The vibration device 120 and the scanning device 130 are configured to enable a movement speed of the spot, for example, including between 0.5 and m / s, for example, including between 1 and 5 m / s, for example, equal to 1 or 2 m / s.

[0038] The energy supply source 1 further includes a control unit (not shown) configured to control the focusing device, the scanning device 130, and the vibration device 120. This control unit is specifically configured to control the respective actuators of these various devices.

[0039] The control unit can comprise or be connected to a memory storing a table of focusing parameter values pre-calculated for different pairs of coordinates (x, y) in the plane of the free surface of the support 140. Thus, the control unit is configured to control the focusing device using the focusing parameter value associated with that pair in the pre-calculated value table when the spot is centered at a point with coordinates (x, y) on the surface of the support.

[0040] FIG. 4 shows a second embodiment of the energy source 1. This second embodiment differs from the first embodiment in that it does not comprise a vibration device 120. On the other hand, in the second embodiment, the scanning device 130 is itself configured to move on the surface of the powder layer 150 deposited on the support 140 with a movement consisting of the translational movement caused by the scanning device 130 and the vibrational movement that would be caused if the vibration device 120 were present in this second embodiment. This is made possible by vibrating a scanning mirror or a mirror.

[0041] Additive manufacturing method Referring to FIG. 4, an additive manufacturing method using the above-described apparatus includes the following steps. As shown in FIG. 1, at least one powder layer 150 is deposited on the support 140. The powder layer 150 has a free surface extending in the longitudinal and transverse directions of the support 140. The powder particles have a particle size, for example, equal to 40 μm, including, for example, from 20 to 60 μm, for example, from 10 to 100 μm.

[0042] The material of each powder layer 150 has a fluence, for example, equal to 2 J / mm, including, for example, between 1 and 5 J / mm, including, for example, between 0.5 and 10 J / mm. 2 The material of each powder layer 150 has a fluence, for example, equal to 2 J / mm, including, for example, between 1 and 5 J / mm, including, for example, between 0.5 and 10 J / mm. 2 The material of each powder layer 150 has a fluence, for example, equal to 2 J / mm, including, for example, between 1 and 5 J / mm, including, for example, between 0.5 and 10 J / mm. 2 The material of each powder layer 150 has a fluence, for example, equal to 2 J / mm, including, for example, between 1 and 5 J / mm, including, for example, between 0.5 and 10 J / mm. The material of the powder layer 150 or each of them can include titanium and / or aluminum and / or inconel and / or stainless steel and / or maraging steel. The generator 110 is operated to emit an energy beam. The energy beam passes through a focusing device, a vibration device 120 (if present in the energy source 1), and a scanning device 130, and is projected onto the free surface of the powder layer 150 in the form of a spot (step 200).

[0043] Therefore, the powder layer 150 is heated to the melting point of its particles at the level of this spot. Furthermore, the focusing device adjusts the focus of the beam so as to reduce the size of this spot and thus concentrate the energy transmitted by the energy beam more.

[0044] The scanning device 130 orients the beam so that the spot translates in the longitudinal scanning direction in the forward direction across the first zone of the surface. This translational movement is represented by the dashed arrow in FIG. 6 (step 202).

[0045] During step 202, the scanning device 130 or the vibration device 120 vibrates the beam so that this translational movement is modulated by the vibratory motion. This vibratory motion consists of a lateral vibratory component in the lateral scanning direction perpendicular to the longitudinal scanning direction and a longitudinal vibratory component in the longitudinal scanning direction. In other words, this vibratory motion generates the vibration of this spot on the surface of the powder layer 150 not only in the lateral scanning direction but also in the longitudinal scanning direction.

[0046] When the source 1 conforms to the first embodiment, the vibratory motion is caused by the vibration device 120. When the source 1 conforms to the second embodiment, the vibratory motion is caused by the scanning device 130. The two vibratory components preferably vibrate at the same frequency. When the two components are in the form of sine waves, the vibratory motion can be elliptical.

[0047] Due to this oscillatory motion and the component of the translational motion in the forward direction, in the first zone, the spot follows a trajectory composed of a series of first loops that are offset from each other in the longitudinal scanning direction.

[0048] Each loop has a node, which is the point where the spot passes twice. Further, each loop is composed of an upstream portion, a hairpin-shaped intermediate portion, and a downstream portion. The spot progresses through each portion of the loop in the order of the upstream portion, the node, the hairpin-shaped intermediate portion, the node again, and finally the downstream portion. This downstream portion connects to the upstream portion of the next loop. When moving through the loop, the spot always rotates in the same rotational direction (the first rotational direction) about the center point of the loop.

[0049] 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 the asymmetric shape, the amount of energy accumulated by the beam at the base of the loop (especially near the node) is greater than the amount of energy accumulated at the top of that loop.

[0050] In FIG. 5, the longitudinal scanning direction is horizontal, the forward direction proceeds from left to right, and the first rotational direction is counterclockwise. As a result, each base of the first loop will be below the top of those first loops. When the two components of the oscillatory motion have the same amplitude, the oscillatory motion becomes circular. As a result, each first loop has a shape closer to a circle.

[0051] At least one first loop preferably extends to a height measured in the lateral scanning direction that includes the range from 100 micrometers to 2 millimeters. This height corresponds to the amplitude of the lateral component of the oscillatory motion.

[0052] Furthermore, the scanning device 130 (in the second embodiment of the energy supply source 1) or the vibration device 120 (in the first embodiment of the energy supply source 1) preferably vibrates the spot laterally at a frequency of at least 1 kHz. This frequency typically ranges from 1 kHz to 10 kHz when the energy beam is a laser beam and from 1 kHz to 100 kHz when the energy beam is an electron beam.

[0053] In all of the first loops, the spot travels in the first rotational direction. All of the first loops preferably have the same dimensions (the same height between their base and top when measured laterally and / or the same width when measured longitudinally).

[0054] At least two of the first loops intersect, i.e., the latest first loop intersects the preceding loops at at least two intersection points. All of the first loops preferably intersect in pairs. A series of first loops extends to a predetermined length in the longitudinal scanning direction and to a predetermined width in the lateral scanning direction.

[0055] Next, the scanning device 130 orients the energy beam so that the spot reaches a second zone adjacent to the first zone (e.g., above the first zone in the situation shown in FIG. 5), and moves the spot in the lateral scanning direction, e.g., translationally. Next, the scanning device 130 orients the beam so that the spot translates over the second zone in the longitudinal scanning direction, but this time in the return direction opposite to the forward direction (step 204).

[0056] During step 204, the scanning device 130 or the vibration device 120 vibrates the beam so that the translational movement is modulated by an oscillatory movement as the spot follows a trajectory composed of a series of second loops that are offset from each other in the longitudinal scanning direction in the second zone. This time, in all of the first loops, the spot travels in the second rotational direction.

[0057] Regarding step 202, the oscillatory movement is caused by the vibration device 120 when the supply source 1 is adapted to the first embodiment, and by the scanning device 130 when the supply source 1 is adapted to the second embodiment. The second rotational direction is opposite to the first rotational direction. The change in the direction in which this loop progresses is typically obtained by acting on the oscillation parameters used to oscillate the beam.

[0058] In FIG. 5, the return path direction progresses from right to left, and the second rotational direction of the spot on the second loop is the clockwise rotational direction. As a result, similar to the case of the first loop described above, the respective bases of the second loop will be below their respective tops of the second loop. As a result, the energy carried onto the powder layer 150 by the energy beam is distributed in a more homogeneous manner by the combination of the first zone and the second zone.

[0059] At least one second loop preferably extends to a height including between 100 micrometers and 2 millimeters when measured in the lateral scanning direction. This height corresponds to the amplitude of the lateral component of the oscillatory movement.

[0060] Furthermore, in the second zone, the supply source 1 preferably oscillates the spot in the lateral scanning direction at a frequency of at least 1 kHz. This frequency typically includes between 1 kHz and 10 kHz when the energy beam is a laser beam, and between 1 kHz and 100 kHz when the energy beam is an electron beam.

[0061] All second loops preferably have the same dimensions (the same height between their bases and tops when measured in the lateral scanning direction, and / or the same width when measured in the longitudinal scanning direction). At least two of the second loops intersect. Preferably, all second loops intersect in pairs.

[0062] A series of second loops are spaced apart from the series of first loops (as shown in FIG. 5). Alternatively, at least one second loop crosses the first loop. The above steps, particularly steps 202 and 204, are alternately repeated in a manner that covers more zones adjacent to each other in the horizontal scanning direction (four zones are shown in FIG. 5).

Claims

1. A method for additive manufacturing of an object from a powder layer, comprising: - projecting an energy beam onto the surface of the powder layer to form a spot for melting the powder (step 200); - scanning the energy beam in a longitudinal scanning direction and a forward path direction across a first zone of the surface (step 202), during which scanning of the first zone, orienting the energy beam to travel along a trajectory formed by a first loop in which the spots are offset from each other in the longitudinal scanning direction across the first zone and the spots travel through each of the first loops in a first rotational direction; - scanning the energy beam in a longitudinal scanning direction and a return path direction opposite to the forward path direction across a second zone of the surface (step 204), the second zone being adjacent to the first zone in a transverse scanning direction orthogonal to the longitudinal scanning direction, during which scanning of the second zone, orienting the energy beam to travel along a trajectory formed by a second loop in which the spots are offset from each other in the longitudinal scanning direction across the second zone and the spots travel through each of the second loops in a second rotational direction opposite to the first rotational direction. A method characterized by the above.

2. At least two of the first loops and / or at least two of the second loops intersect. The method according to claim 1.

3. At least two of the first loops and / or at least two of the second loops have the same dimensions. The method according to claim 1 or 2.

4. A series of the second loops are spaced apart from a series of the first loops by a predetermined distance in the transverse scanning direction. The method according to any one of claims 1 to 3.

5. At least one of the loops spreads with an amplitude ranging from 100 micrometers to 2 millimeters as measured in the transverse scanning direction. The method according to any one of claims 1 to 4.

6. The energy beam vibrates in the transverse scanning direction at a frequency of at least 1 kHz. The method according to any one of claims 1 to 5.

7. The energy beam is a laser beam or an electron beam. The method according to any one of claims 1 to 6.

8. An apparatus for additive manufacturing of an object from a powder layer, the apparatus comprising an energy source configured to project an energy beam in the form of spots onto the surface of the powder layer so as to melt the powder, the energy source being - scanning a first zone of the surface with the energy beam in a longitudinal scanning direction and a forward path direction, and during the scanning of the first zone, orienting the energy beam such that the spot travels along a trajectory formed by a first loop in which the spots are offset from each other in the longitudinal scanning direction in the first zone, and the spot travels through each of the first loops in a first rotational direction, - scanning a second zone of the surface with the energy beam in the longitudinal scanning direction and a return path direction opposite to the forward path direction, the second zone being adjacent to the first zone in a transverse scanning direction orthogonal to the longitudinal scanning direction, and during the scanning of the second zone, orienting the energy beam such that the spot travels along a trajectory formed by a second loop in which the spots are offset from each other in the longitudinal scanning direction in the second zone, and the energy beam travels through each of the second loops in a second rotational direction opposite to the first rotational direction, and comprising a control unit configured as such. An apparatus characterized by the above.

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