Adaptive trajectories for additive manufacturing using laser sources

Abstract

The present invention relates to a method (P) for determining a trajectory followed by a laser beam for selective additive manufacturing of a three-dimensional object, the laser beam being intended to be emitted towards a powder layer and to move along a trajectory consisting of a plurality of adjacent paths so as to melt the powder layer, characterized in that the paths are determined by performing the following steps: a) determining a plurality of reference points (T i ) on a predetermined reference path (T ij ), b) determining a plurality of adjacent points (T i+1j ) located on the same side of the reference path, each adjacent point (T i+1j ) being associated with a reference point (T ij ) and such that a simulated adjacent melting zone around the adjacent point (T i+1j ) and a simulated reference melting zone around the reference point (T ij ) have an overlap corresponding to a fraction of the lateral width of the simulated reference melting zone between a predetermined minimum fraction and a predetermined maximum fraction, c) determining an adjacent path (T i+1 ) passing through the determined plurality of adjacent points, d) iterating steps a) to c) with the adjacent path defined as the new reference path in order to determine a new adjacent path in each iteration, the set of adjacent paths thus determined defining the trajectory to be followed by the laser beam, which trajectory is stored and / or sent to the control unit of the selective additive manufacturing device.

Description

Technical Field

[0001] The present invention relates to the general field of selective additive manufacturing. Background Art

[0002] Selective additive manufacturing consists in building a three-dimensional object by consolidating selected areas in successive layers of powdered material (metal powder, ceramic powder, etc.). The consolidated areas correspond to successive cross-sections of the three-dimensional object. Consolidation is performed layer by layer, for example, by selectively melting all or part of the material using a power source.

[0003] Typically, a high power laser source or an electron beam source is used as the source for melting the powder layer.

[0004] In the case of a process for manufacturing three-dimensional objects using a high-power laser source, the laser scanning trajectory can be defined as all adjacent paths traveled by the laser beam in each layer of powder, along which the material melts to define the contours and fill the interior of the part.

[0005] The laser scanning trajectory plays an important role: it affects the geometric quality and mechanical properties of the component on the one hand, and the efficiency of the manufacturing process, i.e. speed and productivity, on the other hand.

[0006] The scan spacing is an important parameter defined together with the laser scanning strategy. The scan spacing is the distance that separates two adjacent passes of the trajectory.

[0007] Typically, during the manufacture of components using a selective-laser-melting (SLM) process, using a trajectory consisting of adjacent paths separated by a set scanning pitch can lead to certain problems.

[0008] Depending on the shape of the track or the geometry of the component, there may be thermally isolated areas, which can lead to heat buildup and hot spots.

[0009] The increased temperature in these localized areas leads to high thermal gradients. These gradients, in turn, cause residual stresses, which can negatively affect the mechanical properties of the component.

[0010] In addition, in case of overheating, a "keyhole" condition may occur. This phenomenon causes porosity to form in the component. Specifically, in this case, the depth of the molten pool becomes deeper and the temperature reaches the vaporization temperature of the material. This causes vaporization and the formation of gas at the bottom of the molten pool, which creates recoil pressure in it. Due to the instability and rapid cooling of the molten pool, the formed gas cannot escape and is trapped in the material. Given the depth of the formed porosity, melting the next layer will not melt the surrounding material and release the gas.

[0011] Furthermore, the recoil pressure in the melt pool leads to the Marangoni effect, which causes spattering and ejection of material from the melt pool. The beads of material thus ejected can then be redeposited on the already solidified surface and can prevent the deposition of the next layer or even damage the powder deposition device and hinder the manufacturing process.

[0012] Using very high scan pitches, especially in the case of low thermal conductivity materials, can create unmelted zones between adjacent passes, leading to porosity in the part. This problem directly affects the mechanical properties of the obtained part and the quality of its surface.

[0013] In the case of a process of melting a powder bed by laser, the scanning pitch (p) is usually calculated based on the laser beam diameter (D) according to the formula p=(1-λ)×D, where λ is the overlap factor. The overlap factor has a value comprised between 0 and 1.

[0014] Representation of two adjacent paths

[0015] Figure 1 is a schematic diagram showing a laser scanning trajectory 1 consisting of two adjacent paths 3 and 5 in the case of a constant scanning pitch 2 and a laser beam of constant diameter 24. Figure 1 This corresponds to an overlap factor λ equal to 30%. For a diameter 24 of the laser beam equal to 100 μm, the scanning pitch 2 is equal to 70 μm.

[0016] The laser beam is emitted towards the powder layer and moves along the adjacent path so that a point 9 of the adjacent path 5 is illuminated by the laser spot 11 at a certain moment.

[0017] The laser spot is a laser spot corresponding to a cross section of the laser beam located at the interface between the laser beam and the powder layer.

[0018] The laser locally provides sufficient energy to melt the powder layer. During scanning, the powder melts in the melting area 12 of the powder layer around the adjacent path 3 and in the melting area 14 of the powder layer around the adjacent path 5.

[0019] The lateral width of the region 12 can be characterized as the total width 13a in a direction transverse to the scanning direction of the laser beam. The lateral width of the region 12 enables assessment of the size of the region 12 in a direction orthogonal to the direction of the reference path (which is also the direction of the laser scanning).

[0020] The lateral width of region 14 is characterized by an overall width 15a.

[0021] Adjacent paths are separated by a scan pitch 2. At point 20 of adjacent path 3, a tangent 19 to adjacent path 3 is shown. Vector 21 is orthogonal to tangent 19 and the length of vector 21 is equal to the scan pitch 2. Vector 21 can go from point 20 of adjacent path 3 to point 22 of adjacent path 5. Path 3 and path 5 are connected as a whole by this type of local construction and enable the length of the vector from a point on path 3 to a point on path 5 to remain constant and equal to the pitch 2.

[0022] Taking into account the spacing 2 separating the path 3 from the path 5 and taking into account the width 13 b of the region 12 and the width 15 b of the region 14 , there is an overlap 23 between the region 12 and the region 14 .

[0023] The overlap 23 is the lateral length of a portion of a melted area or zone. The overlap 23 is the lateral length of a portion of the powder layer that is melted during the passage of the laser beam through the first path 3 and melted again during the passage of the laser beam through the second path 5. In other words, the overlap is the lateral length of the common portion between two melted areas around two adjacent paths. Since the overlap does not present a constant value everywhere along adjacent paths, it should be evaluated locally.

[0024] exist Figure 1 In FIG. 2 , overlap 23 is the lateral length of the common portion of melt region 12 and melt region 14 .

[0025] The degree of overlap between two adjacent paths is equal to the ratio of the overlap 23 to the lateral width (here the total width 13a) of the adjacent path first scanned by the laser beam.

[0026] In general, adjacent paths can be scanned in the order of time by the laser beam, with T indexed by i. i expressed in the form of .

[0027] Path T i The jth point of can be expressed as T ij and is identified by the following position vector:

[0028]

[0029] In the case of a constant scanning pitch p, the points T facing each other ij With T i+1j The associated relations have the following form:

[0030]

[0031] in,

[0032]

[0033] At point Tij Location and path T i A locally orthogonal unit vector which is contained in the plane of the powder layer and extends from the path T i Pointing to path T i+1 .

[0034] In the case of tracks with a set pitch, the value of the overlap and the unevenness depend on the material, process parameters and track geometry.

[0035] For example, scanning one area of ​​a first material and scanning another area of ​​a second material with a higher conductivity may result in different degrees of overlap in different situations, based on the same trajectory parameters (specifically, the same set pitch corresponding to the same overlap factor).

[0036] In the case of the second material, the melt zone is wider, thus resulting in a greater degree of overlap.

[0037] Regarding the non-uniformity of overlap, the presence of curvature causes heat accumulation, which results in an increase in the lateral width of the melted area. This results in a greater overlap in the local area of ​​the curvature.

[0038] The case of a trajectory formed by concentric circles

[0039] Figure 2 Schematically shows a laser scanning trajectory selected to produce a component having a disc shape. The laser scanning trajectory is a trajectory consisting of circular and concentric adjacent paths. The adjacent paths are evenly spaced apart with a constant spacing equal to 70 μm.

[0040] Figure 3 Schematic diagram of the laser beam moving along Figure 2 The maximum temperature field reached by the powder during the laser scanning trajectory is shown. The first adjacent path scanned by the laser beam is located at the center of the part.

[0041] The scanning speed and laser power were kept constant during the scanning process.

[0042] Figure 3 It is generated by digitally simulating the temperature during the manufacturing process.

[0043] For each investigated point, a time series can be generated of the temperature reached by the powder at that point in the manufacturing process.

[0044] The maximum of its values ​​can be extracted from this time series, which corresponds to the highest temperature reached by the powder at the investigated point during the manufacturing process.

[0045] Figure 3The maximum temperature field at various points within the area shown presents the influence of the trajectory on the thermal behavior during manufacturing. The mapping of the maximum temperature field shows that the maximum temperature is higher in the center of the component and lower at the edge of the component. The highest temperature recorded is equal to 3300K and the lowest value is equal to 2000K.

[0046] The overlap obtained by this laser scanning trajectory can be determined: Figure 3 In the case of , the overlap varies between 100% at the center and 39% at the edges.

[0047] The observed results can be explained by the effect of the trajectory on the pre-consolidation powder temperature, which is an estimate of the temperature of the powder layer before the laser passes through it. This estimate characterizes the spread of the energy delivered by the laser beam at a point in the powder layer before the laser passes through it, during the scanning of a portion of the laser scanning trajectory located upstream of this point.

[0048] At the beginning of laser scanning of the powder layer in the center of the part, the length of the adjacent pass is short, so little time elapses between the laser passing from one adjacent pass to the next, and the temperature of the powder before consolidation is high.

[0049] This results in higher maximum temperatures and leads to remelting with each scan of the adjacent path over the entire area of ​​the component center.

[0050] Further along the laser scanning trajectory, away from the center, the length of the adjacent path is longer, so more time passes between the laser from one adjacent path to the next adjacent path, and the temperature of the powder before consolidation is lower.

[0051] This results in lower maximum temperatures, which results in a more stable lateral width of the melt zone (ie, less material splashing), and ultimately in lower overlap.

[0052] Overlap quality indicators

[0053] To characterize the overlap along the trajectory, metrics may be defined whose purpose is to identify and evaluate optimal overlap regions, overheated regions (ie, excessive overlap regions), and regions where there is not enough melting between adjacent melt regions (ie, insufficient overlap regions).

[0054] Best Quality Index I qop An optimal overlap region can be evaluated. The overlap is considered optimal when the degree of overlap is included in a tolerance interval defined between a predetermined minimum score and a predetermined maximum score.

[0055] It can be estimated that an overlap equal to 15% is sufficient to ensure continuity of melting of the powder layer of a path adjacent to the next adjacent path.A tolerance interval centered on a target overlap equal to 15% with a predetermined minimum fraction equal to 12% and a predetermined maximum fraction equal to 18% can be selected.

[0056] Best Quality Index I qop It is calculated by finding the ratio of the length of adjacent path segments whose overlap is within the allowable interval to the total length of the trajectory.

[0057] Super Quality Index I sq It is calculated by finding the ratio of the length of adjacent path segments with an overlap greater than the allowable interval to the total length of the trajectory.

[0058] Non-Quality Indicators I nq It is calculated by finding the ratio of the length of adjacent path segments whose overlap is less than the allowable interval to the total length of the trajectory.

[0059] For a given laser scanning trajectory, the sum of these three indicators is always equal to 100%. qop +I sq +I nq =100%.

[0060] When the indicator I qop Equal to 100% and other indicators I sq and I nq When it is equal to 0, the laser scanning trajectory is optimal in terms of overlap.

[0061] In the corresponding Figure 3 The minimum overlap measured is equal to 39% for a laser scanning track and a constant spacing of 70 μm. sq =100% and the other indicators = 0. In other words, there are overheated areas anywhere along the trajectory.

[0062] To improve the quality of the trajectory, the first option is to increase the scanning spacing. This preserves the shape of the trajectory formed by concentric circles that are closer to each other than Figure 2 In order to obtain the area where the overlap is within the allowable interval and avoid the area where the overlap is outside the allowable interval, a new value of the constant scanning pitch can be calculated.

[0063] The calculated value of the new scanning pitch is 95 μm, which is larger than Figure 2 Laser scanning trajectory.

[0064] At this time, the highest temperature recorded is equal to 3200K and the lowest temperature is equal to 1750K.

[0065] Measuring the overlap makes it possible to determine the value of the indicator: Isq =50.91% and I qop =49.09%.

[0066] There are only two types of regions, supermassive regions and optimal mass regions. There are no non-massive regions.

[0067] Increasing the scan spacing improved the overlap, but it was not satisfactory.

[0068] It is worth noting that by using a constant spacing value greater than 95 μm, non-mass regions appear, which can create unmelted areas in the powder layer.

[0069] It is worth noting that in addition to causing overheated areas, high overlap can also cause spatter and defects in the part, as well as lead to longer production times.

[0070] Therefore, in order to ensure a more uniform heat distribution within the powder layer, while avoiding unmelted areas and reducing production time, the overlap of adjacent paths needs to be optimized. Summary of the invention

[0071] A general object of the present invention is to overcome the disadvantages of prior art additive manufacturing processes.

[0072] In particular, it is an object of the present invention to provide a method for better controlling the temperature field during selective additive manufacturing and ensuring a more uniform heat distribution within the powder layer.

[0073] Another object of the present invention is to provide a method for optimizing the overlap of adjacent paths in a laser scanning trajectory while avoiding unmelted areas.

[0074] Another object of the present invention is to provide a method that reduces production time.

[0075] Within the scope of the present invention, this object is achieved by a method for determining a trajectory followed by a laser beam for the selective additive manufacturing of a three-dimensional object, the laser beam being intended to be emitted towards a powder layer and moving along a trajectory consisting of a plurality of adjacent paths in order to melt the powder layer, the paths being determined by carrying out the following steps:

[0076] a) determining a plurality of reference points on a predetermined reference path,

[0077] b) determining a plurality of adjacent points located on the same side of the reference path, each adjacent point being associated with the reference point and such that a simulated adjacent melt zone around the adjacent point and a simulated reference melt zone around the reference point have an overlap corresponding to a fraction of the lateral width of the simulated reference melt zone between a predetermined minimum fraction and a predetermined maximum fraction,

[0078] c) determining an adjacent path passing through the determined plurality of adjacent points,

[0079] d) iterating steps a) to c) using the neighboring paths defined as new reference paths to determine new neighboring paths in each iteration, all neighboring paths thus determined defining a trajectory to be followed by the laser beam, said trajectory being stored and / or sent to a control unit of the selective additive manufacturing device.

[0080] This approach advantageously complements the following features implemented alone or in combination:

[0081] The step of determining a plurality of adjacent points comprises performing the following steps in sequence for each adjacent point along a direction of travel of the trajectory:

[0082] - estimation of the lateral width of the simulated reference melt zone for a reference point in relation to its neighbours,

[0083] - determining a possible position of an adjacent point, the possible position of the adjacent point being separated from the position of the reference point by a distance equal to the product of a lateral width of the simulated reference melt zone and a predetermined target overlap, the adjacent point being arranged relative to the reference point in a direction orthogonal to the reference path, the direction orthogonal to the reference path at the reference point being included in the plane of the powder layer and pointing from the reference path to the adjacent path,

[0084] - A loop that performs the following sub-steps:

[0085] -- Estimate the possible lateral width of the simulated adjacent melt zone,

[0086] -- estimate the possible overlap between the simulated reference melt zone and the simulated adjacent melt zones,

[0087] - if the estimated possible overlap corresponds to a fraction of the simulated reference melt zone that is less than a predetermined minimum fraction or greater than a predetermined maximum fraction, executing again a cycle of the secondary steps while modifying the possible positions of the neighboring points;

[0088] determining a deviation between the estimated possible overlap and a target overlap, the target overlap being equal to the product of the lateral width of the simulated reference melt zone and the target overlap;

[0089] The target overlap is equal to 15%, the minimum score is equal to 12%, and the maximum score is equal to 18%;

[0090] To estimate the possible overlap between the simulated reference melt zone and the simulated adjacent melt zone, determine the distance separating the possible location of the adjacent point and the location of the reference point minus half the sum of the lateral width of the simulated reference melt zone and the possible lateral width of the simulated adjacent melt zone;

[0091] When the cycle of the secondary step is executed again, the possible position of the neighboring point is modified so that the distance separating the possible position of the neighboring point from the position of the reference point is replaced by the difference between the distance and a deviation, the deviation being the deviation between the estimated possible overlap and the product of the lateral width of the simulated reference melt zone and the target overlap;

[0092] The step of estimating the lateral width of the simulated melt zone around the investigation point located on the powder layer comprises the following steps:

[0093] - determining a plurality of calculation points, said calculation points being points of the powder layer situated in the neighborhood of the investigation point,

[0094] - an estimation of the maximum temperature reached at each calculated point, the estimation being dependent on the temperature variation caused by emitting a laser beam to consolidate a region of the powder layer around a point upstream of a plurality of paths of the laser beam passing upstream of the point under investigation, and the estimation being dependent on the temperature variation of the powder at the calculated point caused by emitting a laser beam to consolidate a region of the powder layer around the point under investigation,

[0095] - compare the maximum temperature thus estimated to be reached with the melting point of the powder,

[0096] - identifying, among the calculated points, a melting point for which the estimated value of the maximum temperature reached is greater than or equal to the melting point of the powder,

[0097] - estimating the lateral width of the area occupied by said melt point;

[0098] The procedure for estimating the maximum temperature at a calculation point includes the following steps:

[0099] - for each upstream point, calculating an estimate of the temperature change of the powder at the calculation point resulting from the emission of the laser beam to consolidate the region of the powder layer surrounding the upstream point,

[0100] - calculating an estimate of the temperature change of the powder at the calculation point resulting from firing the laser beam to consolidate a region of the powder layer surrounding the upstream point,

[0101] - calculate an estimate of the temperature change of the powder at the calculated point due to the emission of the laser beam to consolidate the area of ​​the powder layer surrounding the investigated point,

[0102] - calculating an estimate of the temperature of the powder at the point of calculation from an estimate of the temperature variation caused by emitting a laser beam to consolidate a region of the powder layer surrounding the point of investigation or upstream of the point of calculation,

[0103] - Calculate an estimate of the maximum temperature at the calculation point;

[0104] The step of estimating, for each upstream point, an estimated value of a temperature change of the powder at the calculation point resulting from emitting a laser beam so as to consolidate a region of the powder layer surrounding the upstream point comprises the following steps:

[0105] - calculating for each upstream point the distance separating the study point from said upstream point,

[0106] - comparing said distance with a predetermined spatial neighborhood distance,

[0107] - for each upstream point spaced at a distance greater than the spatial neighborhood distance from the studied point, the temperature variation of the powder at the calculated point resulting from firing the laser beam to consolidate the region of the powder layer surrounding the upstream point is estimated to be zero;

[0108] The step of estimating, for each upstream point, an estimated value of a temperature change of the powder at the calculation point resulting from emitting a laser beam to consolidate a region of the powder layer surrounding the upstream point comprises the following steps:

[0109] - for each upstream point, calculating the duration of firing the laser beam so as to consolidate the area of ​​the powder layer surrounding the upstream point until the laser beam passes through the investigated point,

[0110] - comparing said duration with a duration of a predetermined time neighbourhood,

[0111] - For each upstream point whose calculated duration is greater than the duration of a temporal neighbour, the temperature change of the powder at the calculated point due to firing the laser beam to consolidate the region of the powder layer surrounding the upstream point is estimated to be zero.

[0112] The invention also relates to a process for selective additive manufacturing of a three-dimensional object based on powder layers, said process comprising the steps of performing in a selective additive manufacturing device:

[0113] - applying the additively manufactured powder layer to a carrier or a previously consolidated layer,

[0114] - emitting a laser beam onto the powder layer along a trajectory consisting of a plurality of adjacent paths, the passage of the laser beam causing the powder layer to melt,

[0115] The trajectory is determined by implementing, for example, the trajectory determination method mentioned above, and the trajectory is stored and / or sent to a control unit of the selective additive manufacturing device.

[0116] The invention also relates to a selective additive manufacturing device for a three-dimensional object based on a powder layer, the selective additive manufacturing device comprising:

[0117] The powder tank is located above the horizontal plate.

[0118] Arranging means for distributing the metal powder onto the plate and configured to successively spread a plurality of powder layers,

[0119] A laser source, a control unit and a memory, wherein the control unit is configured to control the laser source to emit a laser beam onto a powder layer along a trajectory composed of a plurality of adjacent paths, wherein the laser beam causes the powder layer to melt through the paths, and the memory communicates with the control unit and stores a trajectory determined by implementing, for example, the trajectory determination method mentioned above.

[0120] The device may advantageously be supplemented by a computer suitable for implementing a trajectory determination method such as that mentioned above.

[0121] Finally, the invention relates to a computer program comprising instructions suitable for implementing at least one of the steps of the trajectory determination method, for example mentioned above, when said program is executed on a computer. BRIEF DESCRIPTION OF THE DRAWINGS

[0122] Other features and advantages of the present invention will become more apparent from the following description which is intended to be illustrative only and not limiting and which should be read in conjunction with the accompanying drawings, in which:

[0123] Presented Figure 1 is a schematic diagram of a laser scanning trajectory including two adjacent paths;

[0124] Presented Figure 2 is a schematic diagram of a laser scanning trajectory according to known prior art;

[0125] Presented Figure 3 Schematically shows the maximum temperature field reached by the powder when a powder layer is scanned with a laser beam according to the known prior art;

[0126] Figure 4 is a schematic diagram of a method for determining a laser scanning trajectory according to the present invention;

[0127] Figure 5 is a schematic diagram of a method for determining a laser scanning trajectory according to the present invention;

[0128] Figure 6 The laser scanning trajectory is schematically shown;

[0129] Figure 7 The overlap associated with the laser scanning trajectory is schematically shown;

[0130] Figure 8 The scanning pitch associated with the laser scanning trajectory is schematically represented;

[0131] Fig. 9The maximum temperature field reached by the powder when the laser beam scans the powder layer along the laser scanning trajectory is schematically shown;

[0132] Fig.10 is a schematic diagram of a laser scanning trajectory according to known prior art;

[0133] Fig.11 and Fig.12 schematically illustrates the overlap associated with the laser scanning trajectory according to the known prior art;

[0134] Fig.13 is a schematic diagram of the laser scanning trajectory;

[0135] Fig.14 The scanning pitch with respect to the laser scanning trajectory is schematically represented;

[0136] Fig.15 The overlap associated with the laser scanning trajectory is schematically shown;

[0137] Fig.16 is a schematic diagram of a laser scanning trajectory according to known prior art;

[0138] Fig.17 schematically illustrates the overlap associated with the laser scanning trajectory according to the known prior art;

[0139] Fig.18 is a schematic diagram of the laser scanning trajectory;

[0140] Fig.19 The scanning pitch associated with the laser scanning trajectory is schematically represented;

[0141] Fig. 20 and Fig.21 is a schematic diagram of the simulated melting zone in two different overlapping configurations;

[0142] Fig. 22 A method of determining the spatial and temporal neighborhood of a point of a powder layer is schematically shown;

[0143] Fig.23 The spatial and temporal neighborhoods of a point of a powder layer are schematically shown;

[0144] Fig.24 is a schematic diagram of an additive manufacturing apparatus according to a possible embodiment of the present invention. DETAILED DESCRIPTION

[0145] Adaptive trajectories formed from adjacent paths

[0146] like Figure 4As shown, a method is provided that is capable of constructing a trajectory formed by a plurality of adjacent paths determined in a recursive manner. The method is capable of determining a trajectory followed by a laser beam for selective additive manufacturing of a three-dimensional object, the laser beam being intended to be emitted toward a powder layer and moving along a trajectory composed of a plurality of adjacent paths to melt the powder layer, the path being determined by executing the following steps:

[0147] a) On the predetermined reference path T i Determine multiple reference points T ij ,

[0148] b) Determine multiple adjacent points T on the same side of the reference path i+1j , each adjacent point T i+1j With reference point T ij Related and so that around the adjacent point T i+1j The simulation of adjacent melting zones and around the reference point T ij The simulated reference melt zone has an overlap corresponding to a fraction of the lateral width of the simulated reference melt zone between a predetermined minimum fraction αmin and a predetermined maximum fraction αmax,

[0149] c) Determine an adjacent path T passing through the determined plurality of adjacent points i+1 ,

[0150] d) iterating steps a) to c) using the neighboring paths defined as new reference paths to determine new neighboring paths in each iteration, all neighboring paths thus determined defining a trajectory to be followed by the laser beam, said trajectory being stored and / or sent to a control unit of the selective additive manufacturing device.

[0151] Because the reference path T i is initially selected at the beginning of the method, or because the reference path T i is determined during the method, so the reference path T i is predetermined, and the reference path T i It is then used to determine new adjacent paths.

[0152] For each reference point, neighboring points are determined. The number of reference points determined within the reference path enables a relatively good or poor definition of the neighboring path. The greater the number of reference points selected, the better the neighboring path is defined. The number of reference points can be selected in particular depending on the expected length of the neighboring path.

[0153] For each reference point, the determination of the relevant neighboring points takes into account two simulated melting zones: the melting zone around the neighboring point T i+1j The simulation of adjacent melting zones and around the reference point T ijThis involves an estimation of the area of ​​the powder layer around adjacent points or reference points that would become liquid if the laser scanned along the determined trajectory.

[0154] More precisely, the method takes into account the overlap between two simulated melt zones such that the estimated overlap is between a predetermined minimum fraction (αmin) and a predetermined maximum fraction (αmax).

[0155] The degree of overlap between the simulated melt zones is equal to the ratio of the overlap to the lateral width of the melt zone associated with the adjacent path (here, the reference path) scanned first by the laser beam.

[0156] A preliminary estimate of the melt zone enables the arrangement of adjacent points relative to a reference point so as to obtain an overlap within the tolerance interval.

[0157] The overlap of the melt zones produced during the method is thus optimized, so that complete remelting of the regions that were already melted during the first laser scan or the presence of unmelted parts of the powder layer can be avoided.

[0158] Setting the maximum fraction αmax can limit the overheated area, while setting the minimum fraction αmin can limit the unmelted area. In this way, the control of the uniformity of the temperature field during the manufacturing process is improved.

[0159] The trajectory determination method can be used at multiple adjacent points T i+1j The determination may include determining for each adjacent point T i+1j , perform the following steps in sequence in one direction of the trajectory:

[0160] -For adjacent points T i+1j Related reference point T ij , estimate the lateral width L of the simulated reference melting zone ij ,

[0161] - Determine the adjacent points T i+1j Possible positions of adjacent points T i+1j The possible positions and reference point T ij The distance between the positions of the simulated reference melting zone and the predetermined target overlap αc is equal to the product of the lateral width of the simulated reference melting zone and the predetermined target overlap αc. i+1j Relative to the reference point T ij Arranged at reference point T ij T i The orthogonal direction (which is included in the plane of the powder layer and is from the reference path T i Pointing to the adjacent path T i+1 )superior,

[0162] - A loop that performs the following sub-steps:

[0163] -- Estimate the possible lateral width L of the simulated adjacent melting zone i+1j ,

[0164] -- estimate the possible overlap between the simulated reference melt zone and the simulated adjacent melt zones,

[0165] If the estimated possible overlap corresponds to a fraction of the simulated reference melt region that is less than a predetermined minimum fraction or greater than a predetermined maximum fraction, then modify the neighboring point T i+1j The loop of the secondary steps is executed again while the possible positions are being determined.

[0166] Step b) of the above determination method can first be defined as: for each adjacent point T i+1j The determination is performed continuously. Once a neighboring point is determined, the next neighboring point is determined, specifically the next neighboring point in the direction of travel of the laser scanning trajectory of the laser.

[0167] The determination includes estimating the lateral width L of the simulated reference melt zone ij The lateral width is the total lateral width of the reference melting zone in a direction orthogonal to the reference path. ij Depends on the reference point T ij A portion of the laser scanning trajectory upstream: it depends on the temperature before consolidation, which depends on the energy delivered to the powder layer by the laser along the trajectory upstream of the reference point until the reference point itself. No need to determine the adjacent points T i+1j The horizontal width L can be estimated by ij .

[0168] Adjacent point T i+1j The position of the adjacent point T is determined in an iterative manner. i+1j The initial possible position of is based on the simulated reference melting zone lateral width L ij Calculate the predetermined target overlap αc.

[0169] The predetermined target overlap is the ideal overlap that is desired to be achieved. As already mentioned above, the predetermined target overlap may be equal to 15% and may ensure the continuity of the melting of the powder layer of a path adjacent to the next adjacent path.

[0170] Horizontal width L ij Multiplying the target overlap αc gives the reference point T ij With adjacent points T i+1j The distance between the initial possible positions of adjacent points T i+1j Arranged at reference point T ij T i The orthogonal direction (which is included in the plane of the powder layer and is from the reference path Ti Pointing to the adjacent path T i+1 )superior.

[0171] Then, in the loop of the secondary step, the adjacent points T i+1j The possible positions of are refined in an iterative manner. More precisely, the reference point T is adjusted ij With possible adjacent points T i+1j The distance between adjacent points relative to the reference point T ij The possible positions are always arranged on the reference path T i The orthogonal direction (which is contained in the plane of the powder layer and is from the reference path T i Pointing to the adjacent path T i+1 )superior.

[0172] The first sub-step consists in estimating the simulated adjacent melting zone L i+1j possible lateral width of the adjacent points. Since the adjacent points are determined successively in the direction of the trajectory, the part of the trajectory located upstream of the adjacent point in the determination process has been set. This makes it possible to determine the temperature before consolidation, which depends on the energy transferred to the powder layer by the upstream trajectory of the adjacent point in the determination process by laser scanning and the energy transferred to the powder layer by the possible continuation of the trajectory through the possible position of the adjacent point by laser scanning. Since the transferred energy is known, the possible lateral width of the adjacent melting zone can be estimated. Specifically, the lateral width can be the possible total lateral width of the adjacent melting zone in a direction orthogonal to the adjacent path.

[0173] Since the lateral width L of the simulated reference melting zone ij , the possible lateral width of the simulated adjacent melt zone, the position of the reference point and the possible position of the adjacent point are known, so the possible overlap between the simulated reference melt zone and the simulated adjacent melt zone can be estimated.

[0174] Depending on the estimated possible overlap value obtained, the iterative sub-step is repeated or not repeated.

[0175] If the estimated possible overlap corresponds to a fraction of the simulated reference melt zone between a predetermined minimum fraction and a predetermined maximum fraction, then the possible position of the neighboring point is an acceptable position for the verified neighboring point. The method continues with determining the next neighboring point in the scanning direction of the trajectory.

[0176] Otherwise, the iterative secondary step is repeated using the new possible position of the neighboring point. The new position may specifically take into account the estimated possible overlap value obtained: if the overlap is too large, the new possible position of the neighboring point is further away from the reference point, and if the overlap is too small, the new possible position of the neighboring point is closer to the reference point.

[0177] The following notation can be introduced: i+1j In the kth iteration of the loop of the secondary step, the possible positions of the adjacent points are T i+1j (k), reference point T ij Possible positions of adjacent points T i+1j (k) The distance between them is d ij (k), simulating the possible lateral width of adjacent melt zones as L i+1j (k), the estimated possible overlap between the simulated reference melting zone and the simulated adjacent melting zone is L ij α ij (k), the associated overlap is α ij (k).

[0178] Figure 5 The method just introduced is shown.

[0179] First, it is necessary to provide the parameters of the manufacturing process (laser power, laser beam radius or the laser beam cross section at the junction of the laser beam and the powder layer, the speed of the laser beam moving along the laser scanning trajectory), the physical parameters of the material (thermal conductivity, heat capacity, density, melting point), the first reference path, the minimum score αmin and the maximum score αmax.

[0180] Then on path T 1 On the one hand, a certain number of reference points T are selected. 1j , on the other hand, a simulated reference melting zone is estimated for each of these points.

[0181] Specifically, the width L of each melting zone is estimated 1j .

[0182] Then determine the path T 2 The initial possible position T of the adjacent point that you want to determine 2j (1).

[0183] For the first adjacent point corresponding to j=1, that is, the path T scanned by the laser along the track direction 2 The first point of the simulation is used to estimate the possible lateral width L of the adjacent melt zone. 21 (1), which is around point T 21 (1) Object for thermal simulation.

[0184] From this we can extract an estimate of the overlap α 21 (1), and compare it with the minimum score αmin and the maximum score αmax.

[0185] If the estimated value α 21 If the value of (1) is between the two extreme values, the current possible position T of the adjacent point is verified. 21(1). Otherwise, change the possible position to a new position T 21 (2), and execute the adjacent point T again 21 The thermal simulation steps and the overlap estimation steps are as follows.

[0186] When the adjacent point T has been verified 21 When the position is reached, increase the value of j, that is, proceed to the next adjacent point in the laser scanning direction of the adjacent path. The steps are the same, and the reference point used this time is point T 12 , around point T 22 The thermal simulation step takes into account the pre-set neighboring points T 21 location.

[0187] Similarly, on the adjacent path T 2 Determine adjacent points in the scanning direction.

[0188] The number of neighboring points to be determined is given by the number of reference points initially selected (which corresponds to Figure 5 When all adjacent points are determined, the adjacent path T is determined. 2 .

[0189] The method continues by starting to determine a new neighbor path, whose reference path is the neighbor path just determined. When an "i final" number of paths have been determined, the method can be interrupted.

[0190] To determine the estimated overlap L ij α ij (k) whether it corresponds to a fraction of the simulated reference melting zone between a predetermined minimum fraction αmin and a predetermined maximum fraction αmax, the deviation between the estimated possible overlap and the target overlap can be calculated, wherein the target overlap is equal to the product of the lateral width Lij of the simulated reference melting zone and the target overlap degree αc mentioned above.

[0191] When the absolute value of the deviation is greater than the product of the lateral width of the simulated reference melt zone and a predetermined threshold overlap degree αs, the estimated possible overlap may correspond to a fraction of the simulated reference melt zone that is less than a predetermined minimum fraction αmin or greater than a predetermined maximum fraction αmax.

[0192] This is possible when, on the one hand, the maximum score αmax is equal to the sum of the target overlap αc and the threshold overlap αs, and, on the other hand, the minimum score αmin is equal to the difference between the target overlap αc and the threshold overlap αs.

[0193] In particular, when the maximum score is αmax=18% and the minimum score is αmin=12%: then the target overlap can be selected as αc=15% and the threshold overlap as αs=3%.

[0194] Applicable to the case of a trajectory formed by concentric circles

[0195] As described in the “Background Art” section, the determination method has been implemented in the case of a trajectory formed by concentric circles.

[0196] The first circle is used as the first reference path T 1 , and using this method to determine subsequent circular adjacent paths, each new adjacent path is outside the previously determined path.

[0197] The method was implemented using the following values: maximum score αmax=18%, minimum score αmin=12%, target overlap αc=15%, threshold overlap αs=3%.

[0198] The calculation results of the concentric trajectory from inside to outside are as follows Figure 6 shown.

[0199] The determination method can obtain an adaptive trajectory corresponding to an overlap degree that is always included in the allowable interval between the minimum score and the maximum score. Figure 7 The overlap 70 is shown according to the length of the trajectory formed by each concentric circle. The length of the trajectory corresponds to the curve position along the trajectory scanning direction on the trajectory formed by each circle. A trajectory length equal to zero is consistent with the first path T 1 corresponds to the beginning.

[0200] This situation corresponds to the ideal case where the best quality index is equal to 1. Therefore, the trajectory is adapted so that at every point along the trajectory, the same quality is obtained in terms of the overlap between the melt zones around adjacent paths.

[0201] Figure 8 Describes Figure 6 The variation of the scanning pitch of the track shown. Curve 80 shows the distance separating one circle from the next one outside according to the length of the track formed by the various concentric circles. The jump in curve 80 reflects the transition from one circle to the next one outside. The pitch at the beginning of the track is equal to 85 μm and then increases to 109 μm. Away from the center, the scanning pitch decreases overall to 95 μm, which corresponds to the decrease in the lateral width of the melt zone.

[0202] In this way, the overlap between the melt zones is kept within tolerances.

[0203] It should be noted that for certain circles of the trajectory, an increase in the scanning pitch can enable the overall length of the trajectory to be reduced and thus the production time to be reduced.

[0204] Table 1 presents a summary of trajectory lengths for various cases envisaged for the type of trajectory formed by concentric circles.

[0205]

[0206] The adaptive track can achieve a gain of about 29% in total track length relative to the initial recipe and a gain of 14% relative to the recipe with a fixed pitch of 95 μm.

[0207] Fig. 9 It shows that when the laser beam Figure 6 The maximum temperature field reached by the powder when the adaptive trajectory scans the powder layer.

[0208] The highest temperature recorded was equal to 3150K, the lowest value was equal to 1700K.

[0209] and Figure 3 The maximum value in the highest temperature field is shown to be lower than the maximum value of 3300 K obtained in the case of the recipe with a fixed pitch equal to 70 μm.

[0210] Application to spiral trajectories

[0211] Fig.10 Another type of laser scanning trajectory that may be selected to manufacture a component having a disc shape is schematically shown.The disc shape may be scanned using a continuous spiral trajectory. Fig.10 This corresponds to a scanning pitch of 70 μm. The laser scans the area from the inside to the outside.

[0212] The highest temperature field reached by the powder in the region can be established, and the maximum value of the highest temperature field is measured to be 3300K and the minimum value is 2350K.

[0213] exist Fig.10 And in the case of a scanning pitch of 70μm, Fig.10 The overlap of the traces shown is measured by Fig.11 The curve 110 in is given. The curve 110 varies from 100% at the start of the trajectory (the trajectory length is equal to zero), i.e. from the center of the spiral. The overlap decreases to 40% at the outer edge of the spiral. Therefore, the super quality index is equal to 100%.

[0214] In order to reduce the overlap, a larger set scanning spacing of 95 μm can be used. The maximum temperature field reached by the powder in the area can be established for this new spacing, and the maximum value of the maximum temperature field is measured to be 3200K and the minimum value is 1950K.

[0215] Fig.12The results of the measurement of the overlap for a spiral track with a constant pitch equal to 95 μm are schematically shown 120. Setting the scanning pitch to 95 μm reduces the overlap at the edges of the area (i.e. for longer track lengths). The best quality indicator is equal to 63.96%. The overlap at the start of the track (i.e. the center of the spiral) is still greater than the maximum acceptable value. The super quality indicator is equal to 36.04%.

[0216] The implementation of the trajectory determination method can be applied to the case of spiral trajectories. The reference path initially set at the beginning of the process corresponds to one turn of a spiral, which has been dimensioned so that the overlap lies between a maximum fraction αmax=18% and a minimum fraction αmin=12%.

[0217] Fig.13 shows the obtained adaptive trajectory, Fig.14 The scanning pitch as a function of the position on the adaptive trajectory is shown.

[0218] The pitch at the start of the track (ie at the centre of the spiral) is equal to 125 μm and the minimum value of the pitch is equal to 103 μm.

[0219] In the highest temperature field associated with this adaptive trajectory, the maximum value recorded is equal to 3100K and the minimum value is equal to 1800K.

[0220] Fig.15 The degree of overlap as a function of the position on the adaptation trajectory is shown 150. The entire curve 150 is contained within the best quality region, corresponding to an best quality rate of 100%.

[0221] The adaptive trajectory can also reduce the length of the trajectory. Table 2 lists the trajectory lengths in the case of two set pitch recipes and in the case of the adaptive trajectory.

[0222]

[0223] The adaptive trajectory is able to reduce by about 38% relative to the trajectory calculated using the initial recipe.

[0224] Application to four-pointed star-shaped components

[0225] Fig.16 A laser scanning trajectory that may be selected to produce a component having a four-pointed star shape is schematically shown. Fig.16 This corresponds to a scanning pitch of 70 μm.

[0226] The laser scans the trajectory from the center of the spiral in region A. Next, the laser scans the arm in the following region sequence: B, C, D, and E. The portion of the trajectory in each of regions B, C, D, and E consists of adjacent paths in the shape of a circular arc that scan from the inside of the part to the outside of the part.

[0227] For this trajectory, the highest temperature field reached by the powder in the region can be established, and it is measured that the maximum value of the highest temperature field is equal to 3500K and the minimum value is equal to 2500K.

[0228] The maximum temperature reached in the center of region A is higher than the outside of region A. In the arms of the star (i.e., in regions B, C, D, and E), the maximum temperature reached is higher than the center of region A. As the length of the arc-shaped adjacent paths gradually decreases in the arms, the maximum temperature reached increases, and an overheating area appears at the outer end of each arm.

[0229] As the overlap increases, the maximum temperature increases. Fig.17 The variation of the overlap along the trajectory is schematically shown.

[0230] The center of the star (i.e., at the start of the trajectory, which is Fig.17 =0) is 100% overlap and then decreases to 40%. There are thus four variation patterns in the curve. Each variation pattern consists of an increase in overlap toward 80% followed by a sharp drop below 50%. Each variation pattern corresponds to a scan of one arm. During the scan of the arm, the overlap increases until it reaches a maximum value at the end of the scan. The very beginning of the scan of the next arm corresponds to a sharp drop in overlap.

[0231] Super Quality Index I sq Equal to 100%.

[0232] Increasing the scan pitch to 95 μm can reduce the maximum temperature achieved and reduce the overlap.

[0233] For the star-shaped tracks with a pitch equal to 95 μm, the highest temperature field reached by the powder shows a maximum value equal to 3200 K and a minimum value equal to 2000 K.

[0234] Best Quality Index I op However, for most trajectories, the overlap is still greater than the maximum score, and the super quality index I sq It is 87.75%.

[0235] The implementation of the trajectory determination method can be applied to the case of a quadrangular star trajectory. The reference path initially set at the beginning of the process corresponds to one turn of a spiral, the dimensions of which have been set so that the overlap lies between a maximum fraction αmax=18% and a minimum fraction αmin=12%.

[0236] Fig.18 shows the adaptive trajectory obtained, Fig.19 The scanning pitch as a function of the position on the adaptive trajectory is shown.

[0237] The value of the spacing is at the very beginning of the trajectory (i.e., at Fig.18 The largest is at the center of helix A shown in FIG, which is 125 μm.

[0238] Then, as the laser scans the area A, the spacing decreases.

[0239] Next, there are four variation modes of the pitch curve, each of which increases to 120 μm and then decreases to less than 115 μm, and each variation mode corresponds to the scanning of one arm.

[0240] The minimum spacing value is recorded as 100 μm (curve length between 11 mm and 12 mm). This value corresponds to the first adjacent path of the last arm E. Given the time required to scan the first three arms B, C and D, the energy delivered by the laser has dissipated. Therefore, the temperature of the powder before consolidation along the first path of arm E is significantly lower than that of the first path of arm B. In order to ensure that the melting zone of a part of area A near arm E is connected to the area around the first path of arm E, it is necessary to reduce the scanning spacing.

[0241] In the relevant highest temperature field, the maximum value recorded is equal to 3150K and the minimum value is equal to 1800K.

[0242] The degree of overlap according to the position on the adaptation trajectory is always contained within the best quality region, corresponding to a best quality rate of 100%.

[0243] Likewise, the adaptive trajectory enables the length of the trajectory to be reduced. Table 3 lists the trajectory lengths in the case of two recipes for setting the pitch and in the case of the adaptive trajectory.

[0244]

[0245] The adaptive trajectory can reduce about 36% relative to the trajectory calculated using the initial recipe.

[0246] Example of estimating overlap

[0247] In order to estimate the possible overlap between the simulated reference melt zone and the simulated adjacent melt zones, the adjacent points (T i+1j ) possible locations and reference points (T ij ) minus half the sum of the lateral width of the simulated reference melt zone and the possible lateral widths of the simulated adjacent melt zones.

[0248] Fig. 20 and Fig.21The estimation is illustrated by schematic diagrams of simulated melt zones showing two different overlapping configurations between simulated reference melt zones 38 and 48 (which surround reference points of position vectors numbered 31 and 41) and simulated adjacent melt zones 39 and 49 (which surround possible positions of adjacent points of position vectors numbered 32 and 42).

[0249] Fig. 20 The melting zone 38 is centered around the reference point T of the position vector 31. ij The total lateral width 36 of the melt zone 38 corresponds to the term L ij .

[0250] In addition, Fig. 20 In the direction of the vector numbered 34, there are adjacent points T around the position vector numbered 32. i+1j The possible total width 37 of the melting zone 39 corresponds to the possible width L i+1j . Adjacent points (T i+1j ) and the possible positions of the reference point (T ij ) are separated by a distance of Fig. 20 It is marked as 33 and can be expressed as d ij .

[0251] Fig. 20 corresponds to the case where regions 38 and 39 intersect and have a common area. In this case, the overlap can be estimated, which is Fig. 20 The mark in the middle is 35, and its value is estimated to be:

[0252]

[0253] Fig.21 The melting zone 48 is centered around the reference point T of the position vector 41. ij The total width 46 of the melt zone 48 corresponds to the term L ij .

[0254] In addition, Fig.21 In the direction of the vector numbered 44, there are adjacent points T around the position vector numbered 42. i+1j The possible width 47 of the melting zone 49 corresponds to the possible width L i+1j . Adjacent points (T i+1j ) and the possible positions of the reference point (T ij ) are separated by a distance of Fig.21 It is marked as 43 and can be expressed as d ij .

[0255] Fig.21corresponds to the case where regions 38 and 39 do not intersect and have no common area. In this case, the overlap cannot be estimated, but an interval can be defined, which is Fig.21 The middle mark is 45,

[0256]

[0257] In the trajectory determination method described above, when the loop of the secondary step is executed again, the adjacent points (T i+1j ) possible positions, so that the adjacent point (T i+1j ) and the possible positions of the reference point (T ij ) is replaced by the difference between that distance and the deviation between the estimated possible overlap and the product of the lateral width of the simulated reference melt zone and the target overlap.

[0258] In this case, before repeating the iterative sub-step, the new possible positions of the neighboring points T i+1j (k+1) takes into account the value of the estimated overlap obtained: if the overlap is too large, the new possible position of the neighboring point is further away from the reference point; if the overlap is too small, the new possible position of the neighboring point is closer to the reference point.

[0259] More precisely, the deviation between the estimated overlap and the product of the lateral width of the simulated reference melt zone and the target overlap (L ij α ij (k)-L ij αc).

[0260] Possible positions of adjacent points T i+1j (k) and reference point T ij The distance d separating the positions i+1j (k) Replaced by the new possible position T of the adjacent point i+1j (k+1) and the reference point T ij The positions are separated by a new distance d i+1j (k+1). The relationship between these distances is given by:

[0261] d i+1j (k+1)=d i+1j (k)-(L ij α ij (k)-L ij αc).

[0262] This can provide new possible positions T of neighboring points. i+1j (k+1).

[0263] Estimate the lateral width of the simulated melt zone at points around the laser scan trajectory

[0264] Some previously described methods for determining the trajectory followed by a selective additive manufacturing laser beam may require estimating the lateral width of a simulated melt zone around a particular point of a particular path (e.g., a reference point of a reference path or a point located at a possible location of an adjacent point). The particular point may be referred to as an investigation point, and the lateral width of the simulated melt zone around the investigation point may be estimated by performing the following steps.

[0265] In a first step, a plurality of calculation points are determined among the points of the powder layer that are located in the neighborhood of the investigation point.

[0266] The extent of the neighborhood of the study point and the number of computational points within that neighborhood determine, on the one hand, the quality of the estimate obtained and, on the other hand, the computational time required to obtain the estimate.

[0267] As the size of the neighborhood increases or the number of calculation points increases, the quality of the estimate improves and the calculation time increases.

[0268] In a second step, the maximum temperature reached by the powder is estimated at each calculation point. This estimation can take into account the temperature variation of the powder layer at the investigation point due to the emission of the laser beam to consolidate the region of the powder layer surrounding an upstream point of the trajectory portion upstream of the laser beam passing through the investigation point. The investigation point can be a reference point or an adjacent point in the determination process, the trajectory portion upstream of the investigation point being known at the beginning of the method or having been determined by the method.

[0269] The estimation may also take into account temperature variations of the powder layer at the point of interest due to the emission of the laser beam to consolidate the region of the powder layer surrounding the point of interest. In the same way, the estimation may take into account temperature variations of the powder layer at the point of interest due to consolidation of a previous powder layer or due to preheating the powder layer using a heating device.

[0270] In a third step, the maximum temperature thus estimated is compared with the melting point of the powder.

[0271] In a fourth step, a calculated point is identified where the estimated maximum temperature is greater than or equal to the melting point of the powder. The calculated point may be denoted by the expression "melting point".

[0272] All these melting points are grouped around the studied point. All calculated points for which the estimated maximum temperature is strictly below the melting point of the powder are located at a distance from the studied point, outside the region occupied by the melting points.

[0273] Knowing the distribution of the melting points, the lateral width of the region where the melting points are located can be estimated. This region corresponds to the simulated melting zone. The accuracy of estimating this region increases with the size of the selected neighborhood and the number of calculation points.

[0274] Finally, in a fifth step, the lateral width of the melt zone around the investigated point is estimated in the direction pointing from the reference path to the adjacent path.

[0275] Estimate the maximum temperature reached at the calculation point

[0276] Some previously described methods for determining the trajectory followed by a selective additive manufacturing laser beam may require estimating the maximum temperature reached by the powder at a calculated point in the powder layer during scanning of the powder with the laser beam.

[0277] This estimation can be performed based on the implementation of the following steps, taking into account the spread of the energy transmitted by the laser to the powder layer to consolidate the area of ​​the powder layer located upstream of the laser scanning trajectory at the calculation point.

[0278] In a first step, a calculation is performed for each upstream point to estimate the temperature variation of the powder at the calculated point due to the emission of a laser beam to consolidate a region of the powder layer surrounding the upstream point. This calculation also enables an estimation of the temperature variation of the powder at the calculated point due to the emission of a laser beam to consolidate a region of the powder layer surrounding the point of interest.

[0279] The temperature change of the powder at the calculated point due to firing the laser beam to consolidate the area of ​​the powder layer around the upstream point or the investigation point is a series of dated values. The temperature change is estimated at different times within the estimation time interval, which includes the time when the laser beam passes the investigation point. The estimation time interval is the total duration of the estimated recipe from any preheating of the powder or the first consolidation of the area of ​​the powder layer to the final consolidation of the area of ​​the powder layer.

[0280] Assuming that at time u a laser beam is emitted to consolidate a region of the powder layer surrounding an upstream point or point of interest, the energy received by the layer during the emission of the laser beam to consolidate said region of the powder layer is denoted as Q.

[0281] An estimate of the temperature change ΔT of the powder at the calculation point at time t after time u can be expressed as follows:

[0282]

[0283] Where ε is the heat absorption coefficient of the powder layer, R is the radius of the laser beam, a is the thermal diffusivity of the powder layer, and t 0 is a predetermined time, r is the distance between the calculation point and a point which is an upstream point or a research point and belongs to the region of the powder layer consolidated at time u.

[0284] In the second step, an estimate of the powder temperature at the calculation point is calculated. Again, this estimate is a series of dated values. The powder temperature at the calculation point is estimated at different times within the estimation time interval.

[0285] The calculation takes into account the emission of the laser beam to scan the portion of the trajectory located upstream of the point of interest and to consolidate the area of ​​the powder layer around the point of interest. The estimated value of the temperature T of the powder at the time t at the calculation point can be expressed in the following way:

[0286]

[0287] Among them, T 0 is the initial temperature of the powder,

[0288]

[0289] corresponds to the sum of all said upstream points or investigation points surrounded by the area of ​​the powder layer consolidated by the laser at time t. It should be noted that the term "r" in the preceding expression varies as a function of time "u".

[0290] In a third step, the maximum value retained as the maximum temperature reached at the calculation point is extracted from the series of dated values ​​forming an estimate of the powder temperature at the calculation point.

[0291] Temporal and spatial neighborhoods

[0292] As the accuracy of the estimate increases (ie, as the number of upstream points increases), the time required to determine the maximum temperature at the calculation point increases.

[0293] In order to limit the calculation time without compromising the quality of the estimate, a spatial neighborhood Vl and a temporal neighborhood Vt can be defined, which restricts the number of upstream points to be considered in the calculation.

[0294] The time neighborhood Vt represents the duration of the thermal effect of a scan trajectory segment. Beyond this duration, the energy diffused into the environment of the scan segment and transferred during the scan can be considered to have a negligible effect on the powder temperature.

[0295] The spatial neighborhood V1 represents the maximum distance of the thermal effect of the scanning trajectory segment. Beyond this distance, the energy diffused into the environment of the scanning segment and provided during scanning can be considered to have a negligible effect on the powder temperature.

[0296] The negligible characteristic requires the definition of a temperature threshold difference D s The thermal effects of the scan corresponding to temperature changes below this difference are considered negligible.

[0297] The time neighborhood Vt and the space neighborhood Vl can be determined using the following method: Fig. 22 As shown:

[0298] In the first step, the following information is stored in the computer's memory:

[0299] - parameters of the laser scanning process (laser power and radius, laser scanning speed),

[0300] - Material parameters (thermal conductivity, heat capacity, density, melting point and initial temperature T of the powder 0 ),

[0301] - Coordinates of the trajectory of the straight line segment.

[0302] In a second step, the computer provides an estimate of the powder temperature in a predefined spatial domain containing the trajectory defined in the previous step.

[0303] The estimated value of the temperature provided by the computer corresponds to the temperature of the powder at a predefined time which is temporally located after the thermalization time of the powder at the end of the laser scanning of the entire trajectory.

[0304] The estimate may be calculated based on the elements defined above, for example the sum of the temperature changes of the powder layer due to emitting the laser beam to consolidate a region of the powder layer around the point of the trajectory.

[0305] At the end of the second step, a temperature map of the powder in a predefined spatial domain at a predefined time is obtained.

[0306] In the third step, the temperature map obtained in the second step is used to determine the temperature corresponding to the initial temperature T of the powder. 0 and the temperature threshold difference D S The sum of T 0 +D S The corresponding isotherm curve. The difference between the isotherm curve and the temperature threshold value D s corresponds to the temperature increase.

[0307] In a fourth step, the spatial neighborhood is determined as the maximum distance between two points of the isotherm curve determined in the previous step in a direction perpendicular to the trajectory of the straight section profile.

[0308] In a fifth step, the time neighborhood is determined as the ratio of the maximum distance between two points of the isothermal curve determined in the third step in the direction of the trajectory of the straight section type to the laser scanning speed.

[0309] Fig.23 The distances used to determine spatial and temporal neighbors are shown.

[0310] Fig.23 The X-axis shown represents the direction of the straight portion of the trajectory defined in the first step of the above method. The trajectory is scanned in the direction of increasing X values. The Y-axis represents the direction perpendicular to the straight portion of the trajectory.

[0311] The closed curve 100 represents the isotherm curve defined in the third step of the above method.

[0312] The spatial neighborhood corresponds to the length of line segment 101 .

[0313] The maximum distance between two points of the isothermal curve determined in the third step in the direction of the trajectory of the straight-line portion corresponds to the length of the line segment 102 .

[0314] The ratio of the length of line segment 102 to the scanning speed can define a temporal neighborhood.

[0315] Once the spatial neighborhood V1 and the temporal neighborhood Vt are determined, these data can be used to limit the computational time required to predetermine the temperature evolution, thus enabling the calculation of the maximum temperature reached by the powder during the selective additive manufacturing process.

[0316] More specifically, for each upstream point, calculating an estimate of a temperature change of the powder at the calculation point caused by emitting a laser beam to consolidate a region of the powder layer surrounding the upstream point may include the following steps:

[0317] - calculating for each upstream point the distance separating the study point from said upstream point,

[0318] - comparing said distance with a predetermined spatial neighborhood distance,

[0319] - For each upstream point spaced at a distance greater than the spatial neighborhood distance from the study point, the temperature change of the powder at the calculated point due to firing the laser beam to consolidate the region of the powder layer surrounding the upstream point is estimated to be zero.

[0320] Calculating, for each upstream point, an estimate of the temperature change of the powder at the calculation point due to emitting the laser beam to consolidate a region of the powder layer surrounding the upstream point may also include the following steps:

[0321] - for each upstream point, calculating the duration of firing the laser beam so as to consolidate the area of ​​the powder layer surrounding the upstream point until the laser beam passes through the investigated point,

[0322] - comparing said duration with a duration of a predetermined time neighbourhood,

[0323] - For each upstream point whose calculated duration is greater than the duration of a temporal neighbour, the temperature change of the powder at the calculated point due to firing the laser beam to consolidate the region of the powder layer surrounding the upstream point is estimated to be zero.

[0324] Selective Additive Manufacturing Process and Apparatus

[0325] A process for selective additive manufacturing of a three-dimensional object based on powder layers in an additive manufacturing device is provided, the process comprising the following steps:

[0326] Applying the additively manufactured powder layer to a carrier or a previously consolidated layer,

[0327] The laser beam is emitted onto the powder layer along a trajectory consisting of a plurality of adjacent paths, through which the laser beam causes the powder layer to melt,

[0328] The trajectory is determined by implementing, for example, one of the trajectory determination methods mentioned above, and the trajectory is stored and / or sent to a control unit of the selective additive manufacturing device.

[0329] The manufacturing process may be implemented specifically by a selective additive manufacturing device 121 of a three-dimensional object 122 based on a powder layer, the device comprising:

[0330] A powder tank 127, which is located above the horizontal plate 123,

[0331] Arrangement device 124, which is used to distribute the metal powder onto the plate and is configured to successively spread a plurality of powder layers,

[0332] A laser source 1212 and a control unit 129 configured to control the laser source to emit a laser beam onto the powder layer along a trajectory consisting of a plurality of adjacent paths.

[0333] Fig.24 Such a selective additive manufacturing apparatus 121 is shown, and shows:

[0334] - a carrier (e.g. a horizontal plate 123) on which different layers of additive manufacturing powder (metal powder, ceramic powder, etc.) are successively deposited, thereby enabling the manufacture of a three-dimensional object ( Fig.24 fir-tree-shaped object 122),

[0335] - a powder tank 127, which is located above the horizontal plate 123,

[0336] - a dispensing device 124 for distributing the metal powder on the plate, the dispensing device 124 comprising, for example, a scraper 125 and / or a layering roller to spread out each successive layer of powder (moving along the double arrow A),

[0337] an assembly 128 comprising at least one laser source 1212 for (completely or partially) melting the spread thin layer, the laser beam generated by the laser source 1212 coming into contact with the spread thin layer in the powder plane (i.e. in the plane in which the powder layer has been spread by the scraper 125),

[0338] - A control unit 129, which controls the various components of the selective additive manufacturing device 121. The control unit 129 is connected to a memory M that can store predetermined trajectories,

[0339] - A mechanism 1210 enabling the support of the horizontal plate 123 to be lowered (moved along the double arrow B) as the layer is deposited.

[0340] In reference Fig.24 In the example described, at least one galvanometer mirror 1214 enables the laser beam output by the laser source 1212 to be directed and moved relative to the object 122 according to information sent by the control unit 129. Any other deflection system may of course be envisaged.

[0341] The components of the selective additive manufacturing apparatus 121 are arranged in a sealed chamber 1217, which can be connected to an air or inert gas processing circuit. The air or inert gas processing circuit can be further configured to adjust the pressure in the sealed chamber 1217 to be lower or higher than atmospheric pressure.

[0342] like Fig.24 As shown, the selective additive manufacturing device 121 may also include a computer C to determine an estimate of the temperature variation after the start of the manufacturing process, or more generally, to implement one of the trajectory determination methods mentioned above.

[0343] The computer C is configured to process each point of the path quickly enough, specifically, the time required for the computer to process each point must be less than or at least equal to the time required for the laser beam to illuminate or scan these points at a scanning speed.

[0344] Such a computer C may cooperate with a memory M in order to store the estimated value of the temperature variation after it has been generated.

[0345] Finally, any steps of the above trajectory determination method can be implemented by instructions of a suitable computer program.

[0346] A computer program comprising one or more instructions of this type may be executed on a computer.

Claims

1. A method (P) for determining a trajectory followed by a laser beam for selective additive manufacturing of a three-dimensional object, the laser beam being intended to be emitted towards a powder layer and moving along a trajectory comprising a plurality of paths in order to melt the powder layer, characterized in that The path is determined by performing the following steps: a) The predetermined reference path (T i ) to determine multiple reference points (T ij ), the determining step includes for each reference point (T ij ) Perform the following steps in order: -For reference point (T ij ), estimate the lateral width of the simulated reference melting zone (L ij ), the simulated reference melting zone surrounds the reference point (T ij ), - Determine the reference point (T ij ) related adjacent points (T i+1j ) possible position, the adjacent point (T i+1j ) is located on the adjacent path of the trajectory (T i+1 ), the adjacent path (T i+1 ) is included in the trajectory, the adjacent path (T i+1 ) and the reference path (T i ) are adjacent, and adjacent points (T i+1j ) and the possible positions of the reference point (T ij ) are separated by a distance equal to the lateral width of the simulated reference melting zone (L ij ) and the product of the predetermined target overlap (αc), the adjacent point (T i+1j ) relative to the reference point (T ij ) is arranged at the reference point (T ij ) and the reference path (T i ) in a direction perpendicular to the reference point (T ij ) and the reference path (T i ) is included in the plane of the powder layer and is perpendicular to the reference path (T i ) points to the adjacent path (T i+1 ), - A loop that performs the following sub-steps: --For adjacent points (T i+1j ), estimate the possible lateral width of the simulated adjacent melt zone (L i+1j ), the simulated adjacent melting zone surrounds the adjacent point (T i+1j ), -- estimate the possible overlap between the simulated reference melt zone and the simulated adjacent melt zones, If the estimated possible overlap corresponds to a fraction of the simulated reference melt region that is less than a predetermined minimum fraction or greater than a predetermined maximum fraction, then modify the neighboring points (T i+1j ) and execute the secondary step loop again while looking for possible positions. b) Determine multiple adjacent points (T i+1j ), each adjacent point (T i+1j ) so that the simulated adjacent melt regions and the simulated reference melt region have a lateral width (L) of the simulated reference melt region between a predetermined minimum fraction (αmin) and a predetermined maximum fraction (αmax) ij ) corresponds to the overlap of the fractions, c) Determine the number of adjacent points (T i+1j )'s adjacent path (T i+1 ), d) When the adjacent path (T i+1 ) is defined as a new reference path, and steps a) to c) are iterated, all determined paths defining a trajectory to be followed by the laser beam, which trajectory is stored and / or sent to a control unit of the selective additive manufacturing device.

2. The method (P) for determining a trajectory followed by a laser beam for selective additive manufacturing of a three-dimensional object according to claim 1, further comprising: The deviation between the estimated possible overlap and a target overlap is determined, the target overlap being equal to the product of the lateral width of the simulated reference melt zone and a target overlap (αc).

3. Method (P) for determining a trajectory followed by a laser beam for selective additive manufacturing of a three-dimensional object according to claim 2, wherein: The target overlap (αc) is equal to 15%, the minimum fraction (αmin) is equal to 12%, and the maximum fraction (αmax) is equal to 18%.

4. Method (P) for determining a trajectory followed by a laser beam for selective additive manufacturing of three-dimensional objects according to any one of claims 2 to 3, wherein: In order to estimate the possible overlap between the simulated reference melt zone and the simulated adjacent melt zones, the adjacent points (T i+1j ) possible locations and reference points (T ij ) minus half the sum of the lateral width of the simulated reference melt zone and the possible lateral widths of the simulated adjacent melt zones.

5. Method (P) for determining a trajectory followed by a laser beam for selective additive manufacturing of a three-dimensional object according to claim 2, wherein: When the secondary step cycle is executed again, the adjacent points (T i+1j ) possible positions, so that the adjacent point (T i+1j ) and the possible positions of the reference point (T ij ) is replaced by the difference between that distance and a deviation between the estimated possible overlap and the product of the lateral width of the simulated reference melt zone and the target overlap.

6. Method (P) for determining a trajectory followed by a laser beam for selective additive manufacturing of a three-dimensional object according to claim 1, wherein: The step of estimating the lateral width of the simulated melt zone around the investigation point located on the powder layer comprises the following steps: - determining a plurality of calculation points, said calculation points being points of the powder layer situated in the neighborhood of the investigation point, - an estimation of the maximum temperature reached at each calculated point, the estimation being dependent on the temperature variation caused by emitting a laser beam to consolidate a region of the powder layer around a point upstream of a plurality of paths of the laser beam passing upstream of the point under investigation, and the estimation being dependent on the temperature variation of the powder at the calculated point caused by emitting a laser beam to consolidate a region of the powder layer around the point under investigation, - compare the maximum temperature thus estimated to be reached with the melting point of the powder, - identifying, among the calculated points, a melting point for which the estimated value of the maximum temperature reached is greater than or equal to the melting point of the powder, - Estimate the lateral width of the area occupied by the melt site.

7. Method (P) for determining a trajectory followed by a laser beam for selective additive manufacturing of a three-dimensional object according to claim 6, wherein: The procedure for estimating the maximum temperature at a calculation point includes the following steps: - for each upstream point, calculating an estimate of the temperature change of the powder at the calculation point resulting from the emission of the laser beam to consolidate the region of the powder layer surrounding the upstream point, - calculating an estimate of the temperature change of the powder at the calculation point resulting from firing the laser beam to consolidate a region of the powder layer surrounding the upstream point, - calculation of an estimate of the temperature variation of the powder at the point of investigation resulting from the emission of the laser beam to consolidate the region of the powder layer surrounding the point of investigation, - calculating an estimate of the temperature of the powder at the point of calculation, based on an estimate of the temperature variation caused by emitting a laser beam to consolidate a region of the powder layer surrounding the point of investigation or upstream of the point, - Calculates an estimate of the maximum temperature at the calculation point.

8. Method (P) for determining a trajectory followed by a laser beam for selective additive manufacturing of a three-dimensional object according to claim 6, wherein: The step of estimating, for each upstream point, an estimated value of a temperature change of the powder at the calculation point resulting from emitting a laser beam to consolidate a region of the powder layer surrounding the upstream point comprises the following steps: - calculating for each upstream point the distance separating the study point from said upstream point, - comparing said distance with a predetermined spatial neighborhood distance, - For each upstream point spaced at a distance greater than the spatial neighborhood distance from the study point, the temperature change of the powder at the calculated point due to firing the laser beam to consolidate the region of the powder layer surrounding the upstream point is estimated to be zero.

9. Method (P) for determining a trajectory followed by a laser beam for selective additive manufacturing of a three-dimensional object according to claim 6, wherein: The step of estimating, for each upstream point, an estimated value of a temperature change of the powder at the calculation point resulting from emitting a laser beam to consolidate a region of the powder layer surrounding the upstream point comprises the following steps: - for each upstream point, calculating the duration of firing the laser beam so as to consolidate the area of ​​the powder layer surrounding the upstream point until the laser beam passes through the investigated point, - comparing said duration with a duration of a predetermined time neighbourhood, - For each upstream point whose calculated duration is greater than the duration of a temporal neighbour, the temperature change of the powder at the calculated point due to firing the laser beam to consolidate the region of the powder layer surrounding the upstream point is estimated to be zero.

10. A process for selective additive manufacturing of a three-dimensional object based on powder layers, the process comprising performing the following steps in an additive manufacturing apparatus: - applying the additively manufactured powder layer to a carrier or a previously consolidated layer, - emitting a laser beam onto the powder layer along a trajectory consisting of a plurality of adjacent paths, the passage of the laser beam causing the powder layer to melt, The process is characterized in that the trajectory is determined by implementing the method according to any one of claims 1 to 9, and the trajectory is stored and / or sent to a control unit of the selective additive manufacturing device.

11. A selective additive manufacturing device (121) for selective additive manufacturing of a three-dimensional object (122) based on a powder layer, the device comprising: a powder tank (127) located above the horizontal plate (123), an arrangement device (124) for distributing the powder onto the plate and configured to successively spread a plurality of powder layers, A laser source (1212), a control unit (129) and a memory (M), wherein the control unit (129) is configured to control the laser source to emit a laser beam onto a powder layer along a trajectory consisting of a plurality of adjacent paths, the laser beam passing through the paths causing the powder layer to melt, and the memory (M) communicates with the control unit and stores a trajectory determined by implementing the method according to any one of claims 1 to 9.

12. The selective additive manufacturing apparatus according to claim 11, further comprising a computer (C), wherein the computer (C) is configured to implement the trajectory determination method according to any one of claims 1 to 9.

13. A computer program product comprising instructions suitable for implementing the steps of the method according to any one of claims 1 to 9 when said program product is executed on a computer.

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