Additive Pathways for Additive Manufacturing Using Laser Light Sources

Abstract

The present invention relates to a method (P) for determining the trajectory to be followed by a laser beam for the selective additive manufacturing of three-dimensional objects, wherein a laser beam is emitted towards a powder bed and is intended to move along a trajectory made up of a plurality of adjacent paths in order to melt the powder bed, characterized in that the path is determined by carrying out the following steps: a) A predetermined reference path (T i ) on multiple reference points (T ij ) and b) Multiple adjacent points (T i+1j ), determining the neighboring points (T i+1j ) is the reference point (T ij ) and the adjacent points (T i+1j ) and the simulated adjacent melt zone surrounding the reference point (T ij ) such that the simulated reference melt zone surrounding the reference melt zone has an overlap corresponding to a percentage of the lateral width of the simulated reference melt zone included between a predetermined minimum percentage (αmin) and a predetermined maximum percentage (αmax); c) Determine the adjacent path (T i+1 ) and d) repeating steps a) to c) using the defined adjacent path as a new reference path, determining a new adjacent path in each iteration, all the adjacent paths thus determined defining a trajectory that the laser beam is intended to follow, the trajectory being stored and / or transmitted to a control unit of the selective additive manufacturing apparatus; is determined by executing

Description

[Technical field]

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

[0002] Selective additive manufacturing creates three-dimensional objects by solidifying selected zones in successive layers of powder material (metal powder, ceramic powder, etc.). The solidified zones represent successive cross sections of the three-dimensional object. Solidification is performed layer-by-layer by, for example, total or partial selective melting using an energy source.

[0003] Conventionally, high-power laser sources or electron beam sources have been used as energy sources for melting the powder layer. In the case of a three-dimensional object manufacturing process using a high-power laser source, the laser scan trajectory can be defined as all the adjacent paths traveled by the laser beam in each layer of powder, along which the material is melted to define the outer shape and fill the interior of the part.

[0004] The laser scan trajectory plays a key role in influencing on the one hand the geometrical quality and the mechanical properties of the part, and on the other hand the efficiency of the process in terms of speed and productivity. The scan pitch is an important parameter defined in the laser scanning method. It is the distance separating two adjacent passes of the trajectory.

[0005] In general, while manufacturing parts with the selective laser melting (SLM) process, the use of trajectories consisting of adjacent paths separated by a set scan pitch can present certain problems. Depending on the shape of the track or the shape of the part, thermally isolated zones may exist, which can lead to heat buildup and the creation of overheated zones. Such temperature increases in localized zones cause large thermal gradients, which can lead to the development of residual stresses that adversely affect the mechanical properties of the component.

[0006] Also, in case of overheating, "keyhole" regions may appear. This phenomenon is the cause of porosity in the part. Specifically, in this case, the depth of the molten pool increases and the temperature reaches the vaporization temperature of the material. This leads to vaporization and gas generation at the bottom of the pool, which causes recoil pressure there. Due to the instability and rapid cooling of the molten pool, the generated gas cannot escape and is trapped in the material. Given the depth of the formed porosity, melting the next layer cannot melt the surrounding material and release the gas.

[0007] In addition, the recoil pressure in the molten pool can cause the Marangoni effect, which leads to splashing and the scattering and ejection of material from the molten pool. Such extracted beads of material can then re-attach to already solidified surfaces and interfere with the deposition of the next layer, and can also damage the powder deposition equipment and disrupt the manufacturing process.

[0008] Especially for materials with low thermal conductivity, a very large scan pitch can result in unmelted zones between adjacent passes, leading to porosity in the part, which directly affects the mechanical properties of the resulting part and its surface quality. For the laser powder melting process, the scan pitch (p) is generally calculated as a function of the laser beam diameter (D) by the formula p = (1-λ) x D, where λ is the overlap factor. The value of the overlap factor is between 0 and 1.

[0009] Explanation of two adjacent paths Figure 1 shows diagrammatically a laser scan trajectory 1 consisting of two adjacent paths 3, 5 for a constant scan pitch 2 with a laser beam of constant diameter 24. Figure 1 corresponds to an overlap factor λ equal to 30%. For a diameter of the laser beam 24 equal to 100 μm, the scan pitch 2 is equal to 70 μm. The laser beam is emitted towards the powder bed and moves along an adjacent path so that a point 9 of the adjacent path 5 is illuminated by a laser spot 11 at a certain moment. The laser spot is a laser spot that corresponds to a cross section of the laser beam located at the intersection of the laser beam with the powder bed.

[0010] The laser locally delivers sufficient energy to melt the powder bed. During scanning, powder is melted in melted regions 12 of the powder bed surrounding adjacent pass 3 and in melted regions 14 of the powder bed surrounding adjacent pass 5. The lateral width of the region 12 can be characterized by its overall width 13a in a direction perpendicular to the scanning direction of the laser beam. The lateral width of the region 12 allows the dimension of the region 12 to be evaluated in a direction perpendicular to the direction of the reference path, which is also the scanning direction of the laser. The lateral extent of region 14 is characterized by an overall width 15a.

[0011] Adjacent paths are separated by the scan pitch 2. At a point 20 of adjacent path 3, a tangent 19 to adjacent path 3 is shown. A vector 21 is perpendicular to tangent 19 and has a length equal to the scan pitch 2. Vector 21 makes it possible to pass from point 20 of adjacent path 3 to point 22 of adjacent path 5. Paths 3 and 5 are connected everywhere by such a local configuration, and the length of the vector makes it possible to pass from a point on path 3 to a point on path 5 while remaining constant and equal to the pitch 2.

[0012] Considering the pitch 2 separating the paths 3,5 and considering the widths 13b,15b of the regions 12,14, there is an overlap 23 between the regions 12,14. The overlap 23 is the lateral length of a portion of the melted area or zone. It is the lateral length of the portion of the powder bed that melted during the laser beam's passage on the first pass 3 and remelted during the laser beam's passage on the second pass 5. In other words, the overlap is the lateral length of the intersection between the melted areas surrounding two adjacent passes. The overlap is not a constant value anywhere along the adjacent passes and therefore needs to be evaluated locally.

[0013] In FIG. 1, overlap 23 is the lateral extent of the intersection of molten regions 12 and 14 . 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 neighboring path first scanned by the laser beam. In general, the neighboring paths are T indexed by i in the chronological order scanned by the laser beam. i It can be expressed in the form:

[0014] Route T i The jth point of T ij and can be identified by a position vector.

number

number

number

[0015] For a trajectory of a set pitch, the overlap value and non-uniformity depend on the material, process parameters, and trajectory geometry. For example, scanning an area of ​​a first material and another area of ​​a more conductive second material with the same trajectory parameters, in particular the same set pitch corresponding to the same overlap factor, will result in a different degree of overlap in each case. In the case of the second material, the overlap is greater since the melted region is larger.

[0016] With regard to non-uniformity of overlap, the presence of curvature leads to heat accumulation and consequently an increase in the lateral width of the melted region, which generates a greater overlap in this localized region of curvature.

[0017] In the case of a trajectory formed by concentric circles Figure 2 shows a schematic of the laser scanning trajectory selected to produce a disk-shaped part, which is composed of circular and concentric adjacent paths, regularly spaced apart with a constant pitch of 70 μm. Figure 3 shows a schematic of the maximum temperature field reached by the powder when the laser beam is scanned along the laser scan trajectory shown in Figure 2. The first adjacent path scanned by the laser beam is located at the center of the part. The scan speed and laser power remain constant during the scan.

[0018] Figure 3 was created by digitally simulating the temperatures during the manufacturing process. For each investigation point, a time series can be generated of the temperature reached by the powder at that point during the process. From this time series, the maximum value can be extracted, which corresponds to the highest temperature reached by the powder at the point investigated during the process.

[0019] The field of maximum temperatures at each point within the region shown in Figure 3 shows the effect of the trajectory on the thermal behavior during manufacturing. The map of the maximum temperature field shows a higher maximum temperature at the center of the part and a lower maximum temperature at the edge of the part. The highest recorded temperature corresponds to 3300K and the lowest temperature to 2000K. The overlap obtained by the laser scan trajectory can be determined, and in the case of FIG. 3, the overlap value varies between 100% at the center and 39% at the edges.

[0020] This observation can be explained by the effect of the trajectory on the temperature of the powder before solidification, which is an estimate of the temperature of the powder bed just before the laser pass, which characterizes the spread of energy imparted by the laser beam at a particular point in the powder bed just before the laser pass, during the scan of the portion of the laser scan trajectory located upstream of that point.

[0021] At the start of the laser scan of the powder bed in the center of the part, the length of the adjacent passes is small, so little time passes between the laser moving from one adjacent pass to the next, allowing the powder to heat up before solidifying. This leads to high maximum temperatures and causes the entire zone in the center of the part to re-melt with each adjacent pass.

[0022] Furthermore, moving away from the center along the laser scan trajectory, the length of adjacent passes increases, and therefore the time between laser passes from one adjacent pass to the next increases, resulting in lower powder temperatures before solidification. This leads to a lower maximum temperature and a more stable lateral width of the melt zone, i.e. less material splashing and ultimately a lower degree of overlap.

[0023] Duplicate Quality Indicators To characterize the overlap along the trajectory, metrics can be defined to determine and evaluate optimal overlap zones, overheated zones (i.e., excessive overlap zones), and zones where there is not enough melt between adjacent melt zones (i.e., insufficient overlap zones). Optimal quality index I qop The overlap is said to be optimal if the degree of overlap is contained in a tolerance interval defined between a predefined minimum percentage and a predefined maximum percentage.

[0024] It can be estimated that an overlapping degree equal to 15% is sufficient to ensure continuity of the melting of the powder bed of one adjacent pass to the next adjacent pass. It is possible to select a tolerance interval around a target overlapping degree equal to 15% with a predetermined minimum percentage equal to 12% and a predetermined maximum percentage equal to 18%.

[0025] Optimal quality index I qop is calculated by determining the ratio of the length of adjacent path segments whose overlap is within the tolerance interval to the total length of the trajectory. Excessive quality index I sq is calculated by determining the ratio of the length of adjacent path segments whose overlap exceeds the tolerance interval to the total length of the trajectory. Inadequate quality indicator I nq is calculated by determining the ratio of the length of adjacent path segments whose overlap is less than or equal to the tolerance interval to the total length of the trajectory.

[0026] For a given laser scan trajectory, the sum of these three metrics is always 100% (I qop +I sq +I nq =100%). Index I qop is 100% and other indicators I sq and I nq If is zero, then the laser scan trajectory is optimal with respect to overlap. For a constant pitch equal to 70 μm for the laser scan trajectory corresponding to Figure 3, the minimum measured overlap is equal to 39%. Thus, the over-quality index I sq is equal to 100% and the other indices are zero. In other words, there are overheated zones all over the trajectory.

[0027] To improve the quality of the trajectory, a first option consists in increasing the scan pitch: the shape of the trajectory formed by concentric circles is maintained, these circles being further apart than in the case of figure 2. A new value for the constant scan pitch can be calculated to obtain zones where the overlap is within the tolerance interval and to prevent zones where the overlap is outside the tolerance interval.

[0028] The new calculated scan pitch is 95 μm, which is larger than the laser scan trajectory in Figure 2. At this time, the maximum temperature recorded was equal to 3200K, and the minimum was equal to 1750K. By measuring the overlap, we can set the value of the index, I sq =50.91% and I qop =49.09%. There are only two types of zones: excessive quality zone and optimal quality zone. There is no insufficient quality zone. Increasing the scan pitch improved the overlap, but this was not enough.

[0029] It should be noted that at a constant pitch of 95 μm or more, areas of poor quality occur, which create unmelted zones in the powder bed. It should be noted that high overlap can result in overheated zones as well as sputtering and part defects, leading to long production times. Summary of the Invention [Problem to be solved by the invention]

[0030] Therefore, there is a need to optimize the overlap of adjacent passes to ensure a more uniform heat distribution within the powder bed while avoiding unmelted zones and reducing production time. [Means for solving the problem]

[0031] A general objective of the present invention is to overcome the shortcomings of prior art additive manufacturing processes. In particular, one object of the present invention is to provide a way to better control the temperature field during the process and to ensure a more uniform heat distribution within the powder bed.

[0032] It is another object of the present invention to provide a method for optimizing the overlap of adjacent paths of a laser scan trajectory while avoiding unmelted zones. Another object of the present invention is to provide a method for reducing production time.

[0033] This object is achieved within the context of the present invention by a method for determining a trajectory to be 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 bed and to move along a trajectory made up of a plurality of adjacent paths in order to melt the powder bed, the adjacent paths being: a) determining a number of reference points on a predetermined reference path; b) determining a number of adjacent points located on the same side of the reference path, each adjacent point being associated with a reference point such that the simulated adjacent melt zone surrounding the adjacent point and the simulated reference melt zone surrounding the reference point have an overlap corresponding to a percentage of the lateral width of the simulated reference melt zone that is comprised between a predetermined minimum percentage and a predetermined maximum percentage; c) determining an adjacent path that passes through the determined adjacent points; d) repeating steps a) to c) using the defined adjacent path as a new reference path, determining in each iteration a new adjacent path, all the adjacent paths thus determined defining a trajectory that the laser beam is intended to follow, the trajectory being stored and / or transmitted to a control unit of the selective additive manufacturing device; It is determined by executing

[0034] Such a method is advantageously supplemented by various of the following features, implemented alone or in combination: The step of determining a plurality of neighboring points includes, for each neighboring point in one moving direction of the trajectory: - estimating the lateral width of the simulated reference melt zone for a reference point relative to an adjacent point; - determining possible positions of adjacent points, the distance separating the possible positions of the adjacent points from the position of the reference point being equal to the product of the lateral width of the simulated reference melt zone and a predetermined target overlap, the adjacent points being orthogonal to the reference path at the reference point, contained in the plane of the powder bed, and positioned relative to the reference point in a direction directed from the reference path to the adjacent paths; - A step of performing a quadratic step in a loop; consecutively including The second step is - estimating the possible lateral width of the simulated adjacent molten zones; - estimating a possible overlap between a simulated reference melt zone and a simulated adjacent melt zone; - if the estimated possible overlap corresponds to a percentage of the simulated reference melt zone that is smaller than a predetermined minimum percentage or larger than a predetermined maximum percentage, restarting the loop of the secondary steps while modifying the possible positions of the adjacent points; Including, The method further includes determining a dissimilarity between the estimated possible overlap and a target overlap equal to a product of a lateral width of the simulated reference melt zone and the target overlap; The target overlap is equal to 15%, the minimum ratio is equal to 12%, and the maximum ratio is equal to 18%. To estimate the possible overlap between the simulated reference melt zone and the simulated adjacent melt zone, the distance separating the possible location of the adjacent point from the location of the reference point is subtracted from half the sum of the possible lateral width of the simulated reference melt zone and the possible lateral width of the simulated adjacent melt zone; When restarting the loop of the secondary step, the possible positions of the adjacent points are modified such that the distance separating the possible positions of the adjacent points from the position of the reference point is replaced by the difference between the distance and a dissimilarity value, the dissimilarity value being the dissimilarity value between the estimated possible overlap and the product of the lateral width of the simulated reference melt zone and the target overlap; estimating a lateral width of a simulated melt zone surrounding an investigation point located on the powder bed, comprising: - determining a number of calculation points, the calculation points being points of the powder bed located in the vicinity of the interrogation points; - estimating a maximum reached temperature at each of the calculation points, the estimation being dependent on temperature changes due to irradiation of the laser beam to solidify a zone of the powder bed surrounding an upstream point located on a plurality of paths upstream of the path of the laser beam to the interrogation point, and further the estimation being dependent on temperature changes of the powder at the calculation point due to irradiation of the laser beam to solidify a zone of the powder bed surrounding the interrogation point; comparing the maximum temperature thus estimated with the melting point of the powder. - identifying a melting point among the calculation points, the melting point having an estimated maximum temperature equal to or higher than the melting point of the powder; - estimating the lateral width of the zone occupied by the melting point; Including, The step of estimating a maximum temperature at a calculation point comprises: - calculating, for each upstream point, an estimate of the change in temperature of the powder at the calculation point due to the emission of the laser beam such that a zone of the powder bed surrounding the upstream point is solidified; - calculating an estimate of the change in temperature of the powder at the calculation point resulting from the emission of the laser beam to solidify a zone of the powder bed surrounding the upstream point; - calculating an estimate of the change in temperature of the powder at the calculation point due to the emission of the laser beam so as to solidify a zone of the powder bed surrounding the investigation point; - calculating an estimate of the temperature of the powder at a calculation point in response to an estimate of the temperature change resulting from the irradiation of the laser beam to solidify a zone of the powder bed surrounding the investigation point or an upstream point; - calculating an estimate of the maximum temperature at the calculation point; Including, estimating, for each upstream point, an estimate of a change in temperature of the powder at the calculation point due to emission of the laser beam to solidify a zone of the powder bed surrounding the upstream point, comprising: - calculating, for each upstream point, the distance separating the survey point from the upstream point; - comparing the distance to a predetermined spatial proximity distance; - for each upstream point that is at least a spatial proximity distance away from the survey point, estimating the change in temperature of the powder at the calculation point due to the emission of the laser beam to solidify the powder bed surrounding the upstream point as zero; Including, estimating, for an upstream point, a change in temperature of the powder at the calculation point due to irradiation of the laser beam to solidify a zone of the powder bed surrounding the upstream point, - calculating for each upstream point a duration separating the emission of the laser beam so as to solidify a zone of the powder bed surrounding the upstream point and the movement of the laser beam to the interrogation point; - comparing the duration with a predetermined temporal neighborhood duration; - for each upstream point whose calculated duration is greater than the temporal neighborhood duration, estimating the change in temperature of the powder at the calculated point due to the emission of the laser beam so as to solidify a zone of the powder bed surrounding the upstream point as zero; Includes.

[0035] The present invention also relates to a process for selectively additively manufacturing a three-dimensional object from a powder bed, the process comprising: - applying a powder layer for additive manufacturing to a carrier or to a previously solidified layer; - emitting a laser beam at the powder bed along a trajectory comprised of a plurality of adjacent paths, the movement of the laser beam on the path melting the powder bed; Including, The trajectory is determined by the trajectory determination method as described above, and the trajectory is stored and / or transmitted to a control unit of the selective additive manufacturing device.

[0036] The present invention also relates to a selective additive manufacturing apparatus for selectively additively manufacturing a three-dimensional object from a powder bed, the apparatus comprising: a powder reservoir located above the horizontal plate; a mechanism for distributing metal powder onto the plate, the mechanism being configured to spread multiple layers of powder in succession; a laser light source; and a control unit configured to control the laser light source to irradiate the powder bed with a laser beam along a trajectory comprising a plurality of adjacent paths, such that movement of the laser beam on the path melts the powder bed; a memory in communication with the control unit, in which a trajectory determined by executing the trajectory determination method as described above is stored; Equipped with.

[0037] Such an apparatus may advantageously be supplemented by a computer suitable for carrying out the trajectory determination method as presented above. Finally, the invention relates to a computer program comprising instructions suitable for carrying out, when executed on a computer, at least one step of the trajectory determination method as presented above.

[0038] Further characteristics and advantages of the invention will become more apparent from the following description, which is purely illustrative and non-limiting and which must be read in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0039] [Figure 1] A schematic diagram of a laser scanning trajectory containing two adjacent paths has already been presented. [Diagram 2] FIG. 1 is a schematic diagram of a laser scanning trajectory according to the prior art, already presented. [Diagram 3] Schematically, the field of maximum temperatures reached by the powder when scanning the powder bed with a laser beam according to the prior art has already been presented. [Figure 4] FIG. 2 is a schematic diagram of a method for determining a laser scan trajectory according to the present invention; [Diagram 5] FIG. 2 is a schematic diagram of a method for determining a laser scan trajectory according to the present invention; [Figure 6] 1 shows a schematic diagram of a laser scan trajectory. [Figure 7] 1 illustrates a schematic representation of the overlap associated with a laser scan trajectory. [Figure 8] 1 illustrates a schematic diagram of a scan pitch associated with a laser scan trajectory. [Figure 9] Schematic showing the maximum temperature field reached by the powder when the powder bed is scanned by a laser beam along the laser scan trajectory. [Figure 10] FIG. 1 is a schematic diagram of a laser scanning trajectory according to the prior art. [Figure 11] 1 illustrates a schematic of the overlap associated with a laser scan trajectory according to the prior art; [Figure 12] 1 illustrates a schematic of the overlap associated with a laser scan trajectory according to the prior art; [Figure 13] FIG. 2 is a schematic diagram of a laser scan trajectory. [Figure 14] 1 illustrates a schematic diagram of a scan pitch associated with a laser scan trajectory. [Figure 15] 1 illustrates a schematic representation of the overlap associated with a laser scan trajectory. [Figure 16] FIG. 1 is a schematic diagram of a laser scanning trajectory according to the prior art. [Figure 17] 1 illustrates a schematic of the overlap associated with a laser scan trajectory according to the prior art; [Figure 18] FIG. 2 is a schematic diagram of a laser scan trajectory. [Figure 19] 1 illustrates a schematic diagram of a scan pitch associated with a laser scan trajectory. [Figure 20] FIG. 13 is a schematic diagram of a simulated melt zone in an overlap configuration. [Figure 21] FIG. 13 is a schematic diagram of a simulated melt zone in another overlapping configuration. [Figure 22] 1 illustrates a schematic of a method for determining the spatial and temporal neighborhood of a point in a powder bed. [Diagram 23] 13A-13C show schematic diagrams of the spatial and temporal neighborhood of a point in a powder bed; [Figure 24] FIG. 1 is a schematic diagram of an additive manufacturing apparatus according to one possible embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Additional trajectories formed from adjacent paths A method is provided that can construct a trajectory formed from multiple adjacent paths that are recursively determined, for example as shown in FIG. The method can determine a trajectory to be followed by a laser beam for selective additive manufacturing of a three-dimensional object, where the laser beam is intended to be emitted towards a powder bed to melt the powder bed and move along a trajectory that is made up of a plurality of adjacent paths, the path being determined by performing the following steps: a) A given reference path T i Above, multiple reference points T ij determining b) Multiple adjacent points T located on the same side of the reference path i+1jdetermining, for each neighboring point T i+1j is the reference point T ij and the adjacent point T i+1j The simulated adjacent melt zone surrounding the reference point T ij a simulated reference melt zone surrounding the first melt zone has an overlap corresponding to a percentage of the lateral width of the simulated reference melt zone that is comprised between a predetermined minimum percentage α and a predetermined maximum percentage α; c) The adjacent path T passing through the determined adjacent points i+1 determining d) repeating steps a) to c) using the defined adjacent path as a new reference path, determining at each iteration a new adjacent path, all the adjacent paths thus determined defining a trajectory that the laser beam is intended to follow, this trajectory being stored and / or transmitted to a control unit of the selective additive manufacturing device; It is.

[0041] Reference path T i is predetermined, either because it is initially selected at the start of the method, or because it is determined during the method and then used to determine new neighboring routes. For each reference point, adjacent points are determined. The number of reference points determined in the reference path gives a relatively good or bad definition of the adjacent path. The more reference points selected, the better the adjacent path is defined. The number of reference points can be selected depending in particular on the expected length of the adjacent path.

[0042] For each reference point, the determination of the associated neighboring point takes into account two simulated melt zones, i.e., the neighboring point T i+1j The simulated adjacent melt zone surrounding the reference point T ijThis is an estimate of the area of ​​the powder bed surrounding the adjacent or reference point that would become liquid if the laser were to scan the determined trajectory.

[0043] More precisely, the method takes into account the overlap between two simulated melt zones, such that the estimated overlap is included between a predefined minimum percentage (αmin) and a predefined maximum percentage (αmax). 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 relative to the adjacent path first scanned by the laser beam (here the reference path).

[0044] With a priori estimates of the melt zone, adjacent points can be positioned relative to a reference point to obtain an overlap within an acceptable interval. Thus, the overlap of the melted regions created during the method is optimized, thus avoiding complete re-melting of zones already melted in the first laser scan or the presence of unmelted parts of the powder bed. By setting a maximum percentage αmax, the overheated zone can be limited, and by setting a minimum percentage αmin, the unmelted zone can be limited, thus improving the control of the uniformity of the temperature field during the manufacturing process.

[0045] The trajectory determination method is to use multiple adjacent points T i+1j The determination method can be defined as the determination of the adjacent point T i+1j For each unidirectional movement of the trajectory, the following steps may be included in sequence: - Adjacent point T i+1j Reference point T relative to ij With respect to the lateral width of the simulated reference fusion zone, L ij estimating - determining possible positions of the neighboring points Ti+1j, i+1j The possible positions of the reference point T ijThe distance separating the positions of adjacent points T is equal to the product of the lateral width of the simulated reference fusion zone and the predetermined target overlap αc. i+1j is the reference point T ij For the reference point T ij Reference path T in i and is included in the plane of the powder bed. i From adjacent route T i+1 The steps are arranged in a direction toward the performing the following secondary steps in a loop: -- the possible lateral width L of the simulated adjacent molten zones i+1j estimating - estimating a possible overlap between a simulated reference melt zone and a simulated adjacent melt zone; If the estimated possible overlap corresponds to a percentage of the simulated reference melt zone that is smaller than a predetermined minimum percentage or larger than a predetermined maximum percentage, the adjacent point T i+1j restarting the loop of the secondary step while modifying the possible positions of It is.

[0046] Step b) of the above decision method is to determine whether this decision is true for each neighboring point T i+1j Once an adjacent point has been determined, the next adjacent point is determined, in particular the next adjacent point in the direction of movement of the laser scanning trajectory of the laser.

[0047] This determination is based on the lateral width L of the simulated reference fusion zone. ij This lateral width is the total lateral width of the nominal fusion zone in a direction perpendicular to the nominal path. This lateral width L ij is the reference point T ijThe lateral width L depends on the part of the laser scanning trajectory that is located upstream of the reference point, which depends on the pre-solidification temperature, which depends on the energy imparted to the powder bed by the laser along the trajectory upstream of the reference point and up to the reference point itself. ij To estimate i+1j There is no need to determine the location of

[0048] Adjacent point T i+1j The location of the adjacent point T is determined iteratively. i+1j The initial possible positions of are determined by the lateral width L of the simulated reference fusion zone. ij and a predetermined target overlap degree αc. The predetermined target overlap is the ideal overlap that one wishes to achieve, which, as mentioned above, can be equal to 15% and makes it possible to guarantee the continuity of melting of the powder bed of an adjacent pass to the next adjacent pass.

[0049] Lateral width L ij The product of multiplying by the target overlap αc is the reference point T ij and adjacent point T i+1j gives the distance between the initial possible position of the adjacent point T i+1j is the reference point T ij Reference path T at i and is included in the plane of the powder bed, and the reference path T i From adjacent route T i+1 It is placed in the direction towards. Next, the adjacent point T i+1j The possible positions of are iteratively improved in a loop of quadratic steps. More precisely, the reference point T ij and possible adjacent points T i+1j The distance between the reference point T ij The positions of possible neighboring points for a reference path T i , and is included in the plane of the powder bed, and is aligned perpendicular to the reference path T i From adjacent route T i+1 is directed towards.

[0050] The first step of the secondary step is the simulation of the adjacent molten zone L i+1j The method includes a step of estimating the possible lateral width of the adjacent melt zone. Since the adjacent points are determined sequentially in the direction of the trajectory, the part of the trajectory located upstream of the adjacent point in the process of being determined is already set. This allows to determine a temperature before solidification, which temperature depends on the energy supplied to the powder bed by the laser scanning the trajectory upstream of the adjacent point in the process of being determined and on the energy supplied to the powder bed by the laser scanning the possible continuation of the trajectory passing through the possible positions of the adjacent point. Since this supplied energy is known, it is possible to estimate the possible lateral width of the adjacent melt zone. This lateral width may in particular be the total possible lateral width of the adjacent melt zone in the direction perpendicular to the adjacent path.

[0051] The lateral width of the simulated reference fusion zone, L ij Knowing the possible lateral width of the simulated adjacent melt zone, the location of the reference point, and the possible locations of the adjacent points, it is possible to estimate the possible overlap between the simulated reference melt zone and the simulated adjacent melt zone. Depending on the obtained value of the estimated possible overlap, a decision is made whether to repeat the secondary step or not.

[0052] If the estimated possible overlap corresponds to a percentage of the simulated reference melt zone that falls between a predetermined minimum percentage and a predetermined maximum percentage, the possible location of the neighboring point is an acceptable location of the neighboring point, which is valid, and the method continues with determining the next neighboring point in the scan direction of the trajectory. If not, the second step is repeated using new possible positions of the neighboring points, which may take into account in particular the obtained value of the estimated possible overlap: if the overlap is too large, the new possible positions of the neighboring points will be farther away from the reference point, if the overlap is too small, the new possible positions of the neighboring points will be closer to the reference point.

[0053] We can introduce the following notation: i+1j In the k-th iteration of the quadratic step loop to determine T i+1j (k) is the possible location of the adjacent point, d ij (k) is the reference point T ij and the possible positions of the adjacent points T i+1j Distance between (k), L i+1j (k) is the possible lateral width of the simulated adjacent molten zone, L ij α ij (k) is the estimated possible overlap between the simulated reference melt zone and the simulated adjacent melt zones, α ij (k) is the association multiplicity.

[0054] FIG. 5 illustrates the above method. Firstly, it is necessary to provide the parameters of the process (laser power, radius of the laser beam cross section located at the intersection point between the laser beam or the laser beam and the powder bed, movement speed of the laser beam along the laser scan trajectory), the physical parameters of the material (thermal conductivity, heat capacity, density, melting point), the first reference path, the minimum rate αmin and the maximum rate αmax.

[0055] Next, a thermal simulation is performed on the path T1. That is, on the one hand, a certain number of reference points T 1j is selected while a simulated reference melt zone is estimated for each of these points. Specifically, the width of the melting zone L 1j is estimated. Next, the first possible location T2 of the adjacent point on the path T2 to be determined 2j (1) is determined.

[0056] For the first adjacent point corresponding to j=1, i.e., the first point of the path T2 scanned by the laser in the trajectory direction, the possible lateral width L of the simulated adjacent melt zone 21 (1) is estimated, which is the point T 21The area around (1) is the subject of a thermal simulation. From here, the multiplicity α 21 (1) can be extracted and compared with the minimum value αmin and the maximum value αmax.

[0057] Estimated value α 21 If (1) has a value between its limits, the adjacent point T 21 (1) The current possible position of is valid. If not, this possible position is changed to a new position T 21 (2) is changed to adjacent point T 21 The thermal simulation and multiplicity estimation steps for .times. ...

[0058] Adjacent point T 21 If the position of j is valid, the value of j is incremented, i.e., move to the next adjacent point in the scanning direction of the laser on the adjacent path. This step is the same, and the reference point used this time is point T 12 and the predefined adjacent point T 21 Considering the position of point T 22 A thermal simulation is performed around the Additionally, adjacent points are determined in the scanning direction of the adjacent path T2.

[0059] The number of neighboring points determined is given by the number of initially selected reference points and corresponds to the value "j final" in Figure 5. Once all neighboring points have been determined, the resulting neighboring path T2 is determined. The method proceeds to start determining a new adjacent path, whose reference path is the previously determined adjacent path. The method can be interrupted when the number of paths "i final" has been determined.

[0060] Estimated overlap L ij α ijTo determine whether k corresponds to a fraction of the simulated reference fusion zone that is between a predetermined minimum fraction αmin and a predetermined maximum fraction αmax, the estimated possible overlap and the lateral width L of the simulated reference fusion zone are calculated. ij and the target overlap, α c , as described above, can be calculated.

[0061] If the dissimilarity value is greater in absolute value than the product of the lateral width of the simulated reference melt zone and a predetermined threshold overlap αs, the estimated possible overlap may correspond to a percentage of the simulated reference melt zone that is less than a predetermined minimum percentage αmin or greater than a predetermined maximum percentage αmax. This situation is possible if, on the one hand, the maximum proportion αmax is equal to the sum of the target multiplicity αc and the threshold multiplicity αs, and, on the other hand, the minimum proportion αmin is equal to the difference between the target multiplicity αc and the threshold multiplicity αs. This is especially true when the maximum percentage is equal to αmax=18% and the minimum percentage is equal to αmin=12%, and a target overlapping degree equal to αc=15% and a threshold overlapping degree equal to αs=3% can be selected.

[0062] Application to trajectories formed by concentric circles This determination method is carried out in the case of a trajectory formed from concentric circles, as presented in the "Background Art" section. The first circle is used as a first reference path T1, and the method is used to determine the following circular neighboring paths, each new neighboring path being located outside the previously determined path. The invention has been implemented with the following values: maximum percentage αmax=18%, minimum percentage αmin=12%, target overlap equal to αc=15%, and threshold overlap equal to αs=3%. FIG. 6 shows the calculation results of a concentric circular trajectory from the inside to the outside.

[0063] This determination method allows to obtain an adaptive trajectory corresponding to an overlapping degree that is always included in the tolerance interval between the minimum and maximum percentages. Figure 7 shows the overlapping degree 70 as a function of the length of the trajectory formed by the various concentric circles. The length of the trajectory corresponds to the curve position on the trajectory formed by the various circles in the scanning direction of the trajectory. A trajectory length equal to zero corresponds to the beginning of the first path T1. This situation corresponds to the ideal case where the optimal quality index is equal to 1. Thus, the adaptive trajectory results in equal quality in terms of overlap between the melt zones surrounding adjacent paths at all points along the trajectory.

[0064] FIG. 8 illustrates the variation of the scan pitch of the trajectory shown in FIG. 6. Curve 80 shows the distance separating one circle from the next outer circle as a function of the length of the trajectory formed from the various concentric circles. The abrupt changes in curve 80 reflect the transition from one circle to the next outer circle. At the start of the trajectory the pitch is equal to 85 μm and then increases to 109 μm. Moving away from the center, the scan pitch decreases overall to 95 μm, which corresponds to a decrease in the lateral width of the melt zone. In this way, the overlap between the molten zones is maintained within an acceptable interval. It should be noted that by increasing the scan pitch of a particular circle of the trajectory, the total length of the trajectory can be reduced, resulting in shorter manufacturing time.

[0065] Table 1 gives an overview of the trajectory lengths for the various cases assumed for the type of trajectory formed by concentric circles. [Table 1]

[0066] With the adaptive trajectory, the total trajectory length can be increased by about 29% over the initial recipe and 14% over the modified recipe with a pitch of 95 μm. FIG. 9 shows the maximum temperature field reached by the powder when the powder bed is scanned by the laser beam along the adaptive trajectory shown in FIG. The maximum temperature recorded is equal to 3150K, the minimum is equal to 1700K. The maximum value of the maximum temperature field is lower compared to the maximum temperature of 3300 K obtained for the recipe with a fixed pitch equal to 70 μm shown in FIG.

[0067] Application to helical trajectories Figure 10 shows diagrammatically another type of laser scanning trajectory that can be selected to manufacture a part with a disk shape. The disk shape can be scanned with a continuous spiral trajectory. Figure 10 corresponds to a scanning pitch equal to 70 μm. The laser scans the area from the inside to the outside. A field of maximum powder temperatures reached in this region is defined, in which a maximum value equal to 3300K and a minimum value equal to 2350K can be measured.

[0068] For a scan pitch of 70 μm in FIG. 10, the measure of the overlap of the trajectory shown in FIG. 10 is given by curve 110 in FIG. 11. It varies from 100% at the start of the trajectory (where the trajectory length is equal to zero), i.e. at the center of the spiral. The overlap decreases to 40% at the outer edge of the spiral. The over-quality index is therefore equal to 100%.

[0069] To reduce the overlap, a larger set of scanning pitches equal to 95 μm can be used. With this new pitch it is possible to define a field of the maximum powder temperature reached in that area and to measure in this field a maximum value equal to 3200 K and a minimum value equal to 1950 K.

[0070] Figure 12 shows diagrammatically the measured overlap 120 of a spiral trajectory with a constant pitch equal to 95 μm. By setting the scan pitch to 95 μm, it was possible to reduce the overlap at the edge of the region, i.e. for long trajectory lengths. The optimal quality index was 63.96%. The overlap at the start of the trajectory, i.e. at the center of the spiral, is still greater than the maximum allowed value. The excessive quality index is 36.04%.

[0071] The implementation of the trajectory determination method can be applied in the case of a spiral trajectory: the reference path set at the start of the process corresponds to a spiral turn whose size is set so that the overlapping degree is comprised between a maximum percentage αmax=18% and a minimum percentage αmin=12%.

[0072] FIG. 13 shows the resulting adaptive trajectory, and FIG. 14 shows the scan pitch as a function of position on the adaptive trajectory. The pitch at the start of the trajectory, i.e. at the centre of the spiral, is equal to 125 μm and the minimum value of the pitch is equal to 103 μm. In the maximum temperature field associated with this adaptation trajectory the maximum value recorded is equal to 3100 K and the minimum value is equal to 1800 K.

[0073] 15 shows the overlap as a function of position on the adaptation trajectory 150. The entire curve 150 is contained within the optimum quality zone, which corresponds to an optimum quality ratio of 100%.

[0074] The adaptive trajectory can also reduce the trajectory length. Table 2 lists the trajectory lengths for two cases: a set pitch recipe and an adaptive trajectory. [Table 2] The adaptive trajectory allows a reduction of about 38% with respect to the trajectory calculated with the initial recipe.

[0075] Application to four-pointed star shaped parts Figure 16 shows diagrammatically the laser scanning trajectories that can be selected to produce a four-pointed star shaped part, which corresponds to a scan pitch equal to 70 μm. The trajectory is scanned by the laser from the center of the spiral in Zone A. The laser then scans the arm through Zones B, C, D, and E in that order. The portion of the trajectory within each of Zones B, C, D, and E consists of adjacent arc-shaped paths scanned from the inside to the outside of the part.

[0076] For this trajectory, one defines a field of maximum powder temperatures reached in that region, in which a maximum value equal to 3500K and a minimum value equal to 2500K can be measured. The maximum temperature reached is higher in the center of Zone A than outside Zone A. Within the arms of the four-pointed star, i.e., Zones B, C, D, and E, the maximum temperature reached is higher than in the center of Zone A. As the length of the adjacent arcuate paths gradually decreases within an arm, the maximum temperature reached increases and an overheated zone appears at the outer end of each arm. As the length of the adjacent arcuate paths gradually decreases, the maximum temperature reached increases and an overheated zone appears at the outer end of each path.

[0077] As the degree of overlap increases, the maximum temperature increases. Figure 17 shows a schematic of the variation of the degree of overlap along the trajectory. At the center of the star, i.e. the beginning of the trajectory (in Fig. 17 the trajectory length is equal to 0), the overlap is 100% and then decreases to 40%. Then the curve has four variation patterns. Each variation pattern includes an increase to 80% followed by a steep drop to below 50%. Each variation pattern corresponds to the scan of one arm. The overlap increases during the scan of the arm and reaches a maximum value towards the end of the scan. The beginning of the scan of the next arm corresponds to a steep drop in the overlap. The oversaturation quality index Isq is equal to 100%.

[0078] By setting the scan pitch to 95 μm, both the maximum temperature and the overlapping degree can be reduced. The field of maximum powder temperature exhibits a maximum value equal to 3200 K and a minimum value equal to 2000 K for a star trajectory with a pitch of 95 μm; The optimal quality index Iop is equal to 12.25%. However, the overlap remains greater than the maximum percentage in the majority of the trajectories, and the excessive quality index Isq is 87.75%.

[0079] The implementation of the trajectory determination method can be applied in the case of a four-pointed star-shaped trajectory: the reference path set at the start of the process corresponds to a spiral turn whose size is set so that the overlapping degree is comprised between a maximum percentage αmax = 18% and a minimum percentage αmin = 12%.

[0080] FIG. 18 shows the resulting adaptive trajectory, and FIG. 19 shows the scan pitch as a function of position on the adaptive trajectory. The pitch value is maximum at 125 μm at the beginning of the trajectory, i.e. at the centre A of the spiral shown in FIG. Then, as the laser scans this zone A, the pitch decreases. The pitch curve then has four variation patterns, each of which includes an increase to 120 μm followed by a decrease to below 115 μm, with each variation pattern corresponding to the scan of one arm.

[0081] The minimum value of the pitch is recorded as 100 μm (curve length between 11 and 12 mm). This value corresponds to the first adjacent pass of the last arm E. As a result of the time taken to scan the three previous arms B, C, D, the energy delivered by the laser has been dissipated. The pre-solidification temperature of the powder along the first pass of arm E is therefore much lower than in the first pass of arm B. To ensure that the melted zones in the part of zone A close to arm E and the surrounding zones of the first pass of arm E are joined together, the scan pitch needs to be reduced.

[0082] In the associated maximum temperature field the maximum value mentioned is equal to 3150K and the minimum value is equal to 1800K. The overlap as a function of position on the adaptive trajectory is always contained in the optimal quality zone, which corresponds to an optimal quality ratio of 100%. The adaptive trajectory can also reduce the trajectory length in this case. Table 3 lists the trajectory lengths for two cases: the set pitch recipe and the adaptive trajectory. [Table 3] The adaptive trajectory allows a reduction of about 36% with respect to the trajectory calculated with the initial recipe.

[0083] Example of estimated duplication To estimate the possible overlap between the simulated reference melt zone and the simulated adjacent melt zones, the possible locations of the adjacent points (T i+1j ) and the reference point position (T ij ) is subtracted from half (1 / 2) the sum of the simulated lateral width of the reference molten zone and the possible lateral width of the simulated adjacent molten zones. Figures 20 and 21 illustrate this estimation, which is explained based on schematic representations of simulated melt zones for two different configurations of overlap between simulated reference melt zones 38, 48 surrounding the reference points of position vectors no. 31, 41 and simulated adjacent melt zones 39, 49 surrounding the possible positions of the adjacent points of position vectors no. 32, 42.

[0084] The melting zone 38 in FIG. 20 is located at the reference point T ij The total lateral width 36 of the melt zone 38 is expressed as L ij Corresponds to. Furthermore, in the direction of vector number 34 in FIG. 20, there is an adjacent point T i+1j A melt zone 39 is found that surrounds the possible locations of the melt zone 39. The total possible width 37 of the melt zone 39 is the possible width L i+1j The possible positions of the adjacent points (T i+1j ) and the reference point position (T ij ) is referenced 33 in FIG. 20, and d ij It can be expressed as:

[0085] Figure 20 corresponds to the situation where regions 38 and 39 intersect and have a common area. In this situation, it is possible to estimate the overlap, shown as 35 in Figure 20, and its value is estimated as follows:

number

[0086] The melt zone 48 in FIG. 21 is located at the reference point T ij The overall width 46 of the melt zone 48 is expressed as L ij Corresponds to. Furthermore, in the direction of vector number 44 in FIG. 21, there is an adjacent point T i+1j A melt zone 49 is found that surrounds the possible location of the melt zone 49. The possible width 47 of the melt zone 49 is the possible width L i+1j The possible positions of the adjacent points (T i+1j ) and the reference point position (T ij ) is referred to as 43 in FIG. 21, and d ij It can be expressed as:

[0087] Figure 21 corresponds to the situation where faces 38 and 39 do not intersect and have no common area. In this situation, no overlap can be inferred, but it is possible to define an interval, indicated at 45 in Figure 21.

number

[0088] Through the above trajectory determination method, when restarting the quadratic step loop, the adjacent points (T i+1j ) and possible positions of the reference point (T ij The possible positions of adjacent points are modified such that the distance separating the position of the adjacent point from the position of the adjacent point is replaced by the difference between this distance and a dissimilarity value, where the dissimilarity value is the dissimilarity value between the estimated possible overlap and the product of the lateral width of the simulated reference melt zone and the target overlap. In this case, the new possible positions T of the neighboring points before the quadratic step are i+1j(k+1) takes into account the estimated overlap value obtained: if the overlap is too large, the new possible positions of the neighboring points are far from the reference point, if the overlap is too small, the new possible positions of the neighboring points are close to the reference point.

[0089] More precisely, the dissimilarity value 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) is used. Possible positions of adjacent points T i+1j (k) and reference point T ij The distance d separating the positions i+1j (k) is the new possible position T of the neighboring point. i+1j (k+1) and reference point T ij The new distance d separating the positions of i+1j (k+1). The relationship between these distances is given by the following equation: d i+1j (k+1)=d i+1j (k)-(L ij α ij (k)-L ij αc) is given by: This gives us new possible positions T i+1j (k+1) can be provided.

[0090] Estimation of the lateral width of the simulated melt zone surrounding the points of the laser scanned trajectory Some of the above-mentioned methods for determining the trajectory followed by a selective additive manufacturing laser beam may require an estimation of the lateral width of the simulated melt zone surrounding a particular point of a particular path, such as a point at the possible location of a reference point or an adjacent point of a reference path. This particular point may be referred to as an investigation point, and the lateral width of the simulated melt zone surrounding the investigation point may be estimated by performing the steps described below.

[0091] In the first step, a number of calculation points are determined, which are points in the powder bed located in the vicinity of the interrogation point. The extent of the neighborhood of the survey point and the number of calculation points within this neighborhood determine, on the one hand, the quality of the estimate obtained and, on the other hand, the calculation time necessary to obtain the estimate. The quality of the estimate and the computation time each increase with increasing extent of the neighborhood region or with a larger number of computation points.

[0092] In a second step, the maximum temperature reached by the powder at each calculation point is estimated. This estimation can take into account the temperature change of the powder bed at the investigation point due to the emission of the laser beam to solidify a zone of the powder bed surrounding the point upstream of the part of the trajectory located upstream of the path of the laser beam to the investigation point. The investigation point can be either a reference point or an adjacent point in the process of being determined, the part of the trajectory located upstream from the investigation point being known from the start of the method or already determined by the method. The estimation may also take into account temperature changes in the powder bed at the interrogation point due to the irradiation of the laser beam to solidify a zone of the powder bed surrounding the interrogation point. Similarly, the estimation may take into account temperature changes in the powder bed at the interrogation point due to a previous powder bed being solidified or due to pre-heating the powder bed with a heating means.

[0093] The third step is to compare the maximum temperature thus estimated with the melting point of the powder.

[0094] In the fourth step, the calculated points whose estimated maximum temperature is equal to or greater than the melting point of the powder are identified. These can be denoted by the expression "melting point". All these melting points are grouped and placed around the investigation point, and all calculated points whose estimated maximum temperature is strictly lower than the melting point of the powder are located outside the region occupied by the melting point and further away from the investigation point. Knowing the distribution of the melting points, it is possible to estimate the lateral width of the zone within which the melting points are located. This zone corresponds to the simulated melting region, the estimation accuracy of which increases with the size of the selected neighborhood and with the number of calculation points.

[0095] Finally, in a fifth step, the lateral width of the melt zone surrounding the interrogation point is estimated in the direction from the reference path towards the adjacent paths.

[0096] Estimation of maximum temperature reached at calculation point Some of the above mentioned methods for determining the trajectory to be followed by a selective additive manufacturing laser beam may require an estimation of the maximum temperature that the powder will reach at a calculated point in the powder bed during the process of scanning the powder with the laser beam. This estimation can be performed based on the execution of the steps described below, taking into account the diffusion of energy imparted by the laser to the powder bed at the calculation points to solidify a zone of the powder bed located upstream of the laser scan trajectory.

[0097] In a first step, for each upstream point, a calculation is performed to estimate the change in temperature of the powder at the calculation point due to the irradiation of the laser beam to solidify a zone of the powder bed surrounding the upstream point. The calculation can also estimate the temperature change of the powder at the calculation point due to the irradiation of the laser beam to solidify a zone of the powder bed surrounding the interrogation point. The temperature change of the powder at the calculation point due to the irradiation of the laser beam to solidify a zone of the powder bed surrounding the upstream point or interrogation point is a series of date values. The temperature change is estimated at various times located in an estimated time interval that includes the time of the passage of the laser beam to the interrogation point. The estimated time interval is the total duration of the estimated recipe from any pre-heating of the powder or initial solidification of the zone of the powder bed to the final solidification of the zone of the powder bed.

[0098] Assuming that the laser beam is emitted at time u to solidify a zone of the powder bed surrounding either the upstream point or the interrogation point, the energy received by the powder bed during the emission of the laser beam to solidify the zone of the powder bed is denoted by Q. The estimation of the temperature change ΔT of the powder at a calculation point at time t following time u can be written as:

number

[0099] In a second step, an estimate of the temperature of the powder at the calculation point is calculated. Again, this estimate is a series of date values. The temperature of the powder at the calculation point is estimated at various times that fall within an estimation time interval. The calculation takes into account the emission of a laser beam that scans the part of the trajectory located upstream of the investigation point and solidifies the zone of the powder bed surrounding the investigation point. The estimation of the powder temperature T at the calculation point at time t can be written as:

number

number

[0100] In a third step, from the series of date values ​​yielding an estimate of the powder temperature at the calculation point, the maximum value is extracted which is retained as the maximum temperature reached at the calculation point.

[0101] Temporal and spatial neighborhoods The time it takes to find the maximum temperature of a calculation point increases as the estimation becomes more accurate, i.e., the number of upstream points increases. To limit the computation time without compromising the estimation quality, a spatial neighborhood Vl and a temporal neighborhood Vt can be defined that limit the number of upstream points considered in the computation.

[0102] The temporal neighborhood Vt represents the duration of the thermal effect of the scanning of a trajectory segment, beyond which the energy delivered during that scan, diffused in the environment of the scanned segment, can be considered to have negligible effect on the powder temperature. The spatial neighborhood Vl represents the maximum distance of the thermal influence of the scanning of a trajectory segment, beyond which the energy diffused in the environment of the scanned segment and delivered during that scan can be considered to have negligible effect on the powder temperature.

[0103] The negligible characteristic is the temperature threshold difference D S It is necessary to define the thermal effect of the scan corresponding to a temperature change below this difference. The temporal neighborhood Vt and the spatial neighborhood Vl can be determined using the following method shown in FIG.

[0104] In a first step, the following information is stored in a computer memory: -Laser scanning process parameters (laser power and beam, laser scanning speed), -Material parameters (thermal conductivity, heat capacity, density, melting point, initial temperature T0 of the powder), - coordinates of the trajectory of the straight line segment type, It is.

[0105] In a second step, the computer provides an estimate of the temperature of the powder in a predefined spatial region that contains the trajectory defined in the previous step. The temperature estimate provided by the computer corresponds to the temperature of the powder at a given time after the powder thermalization time at the end of the laser scan of the entire trajectory. This estimate can be calculated based on the factors defined above, e.g., the sum of the temperature changes in the powder bed due to the irradiation of the laser beam to solidify a zone of the powder bed surrounding a point of the trajectory. At the end of the second step, a temperature map of the powder in a given spatial region at a given time is obtained.

[0106] In the third step, the difference D between the initial powder temperature T0 and the temperature threshold is calculated in the temperature map obtained in the second step. S Sum of T0+D S The isothermal curve is determined according to the temperature threshold difference D S corresponds to a temperature rise of

[0107] In a fourth step, the spatial neighborhood is determined as the maximum distance in the direction perpendicular to a straight line segment type locus between two points of the isothermal curves determined in the previous step.

[0108] In the fifth step, the temporal neighborhood is determined as the ratio of the maximum distance in the direction of a straight line segment type trajectory between two points of the isothermal curve determined in the third step to the scanning speed of the laser.

[0109] FIG. 23 shows the distances used to determine spatial and temporal neighborhood. The X-axis shown in Fig. 23 represents the direction of the straight line segments of the trajectory defined in the first step of the method above. The trajectory is scanned in the direction of increasing values ​​of X. The Y-axis represents the direction perpendicular to the straight line segment type trajectory. The closed curve 100 represents the isothermal curve defined in the third step of the method above. The spatial neighborhood corresponds to the length of the segment 101 . In the direction of the straight line segment type trajectory, the maximum distance between two points of the isothermal curve determined in the third step corresponds to the length of the segment 102 . The ratio of the length of the segment 102 to the scan speed can define a temporal neighborhood.

[0110] Once the spatial neighborhood V1 and the temporal neighborhood Vt are determined, these data can be used to limit the calculation time it takes to pre-determine the temperature change, which allows for calculating the maximum temperature the powder will reach during the selective additive manufacturing process. More precisely, the calculation of an estimate of the change in temperature of the powder at the calculation point due to the emission of the laser beam so as to solidify a zone of the powder bed surrounding the upstream point may comprise the following steps: - calculating for each upstream point the distance separating the survey point from this upstream point; - comparing this distance with a predetermined spatial proximity distance; - for each upstream point that is at least a spatial proximity distance away from the survey point, estimating the change in temperature of the powder at the calculation point due to the application of the laser beam to solidify a region of the powder bed surrounding the upstream point as zero; It is.

[0111] Also, for each upstream point, the calculation of an estimate of the change in temperature of the powder at the calculation point due to the emission of the laser beam to solidify a zone of the powder bed surrounding the upstream point may include the steps of: - calculating for each upstream point a duration separating the emission of the laser beam so as to solidify a zone of the powder bed surrounding the upstream point and the movement of the laser beam to the investigation point; - comparing this duration with a predetermined temporal neighborhood duration; - for each upstream point whose calculated duration is greater than the time-neighborhood duration, estimating as zero the change in temperature of the powder at the calculated point due to the emission of the laser beam so as to solidify a zone of the powder bed surrounding the upstream point; It is.

[0112] SELECTIVE ADDITIVE MANUFACTURING PROCESSES AND APPARATUS A process is provided for selectively additively manufacturing a three dimensional object from a powder bed, the process comprising: - applying a powder layer for additive manufacturing to a carrier or to a previously solidified layer; - emitting a laser beam at the powder bed along a trajectory comprised of a plurality of adjacent paths, the movement of the laser beam on these paths melting the powder bed; wherein the trajectory is determined by implementing one of the trajectory determination methods described above, and the trajectory is stored and / or transmitted to a control unit of the selective additive manufacturing device.

[0113] The manufacturing process can in particular be performed by an apparatus 121 for selectively additively manufacturing a three-dimensional object 122 from a powder bed, the apparatus comprising: a powder reservoir 127 located above the horizontal plate 123; a mechanism 124 for distributing metal powder onto the plate, the mechanism 124 being configured to spread multiple layers of powder successively; - a laser source 1212 and a control unit 129 configured to control the laser source to emit a laser beam onto the powder bed following a trajectory composed of a plurality of adjacent paths; Equipped with.

[0114] FIG. 24 shows such a selective additive manufacturing apparatus 121, which shows: - a carrier such as a horizontal plate 123, on which various layers of additive manufacturing powders (metal powders, ceramic powders, etc.) can be successively deposited to produce a three-dimensional object (in Fig. 24 a fir-tree shaped object 122). A powder reservoir 127 located above the plate 123. a mechanism 124 for distributing the metal powder onto the plate, said mechanism 124 comprising, for example, a doctor blade 125 and / or layer forming rollers (moving along the double-headed arrow A) for spreading various successive layers of powder. - an assembly 128 comprising at least one laser source 1212 for melting (fully or partially) the spread thin layer. The laser beam generated by the laser source 1212 contacts the spread thin layer at the powder plane, i.e. the plane where the powder layer was spread by the doctor blade 125. A control unit 129 which controls each of the components of the device 121. The control unit 129 is connected to a memory M in which predefined trajectories can be stored. a mechanism 1210 (moving along the double-headed arrow B) capable of lowering the carrier of the plate 123 once a layer has been deposited.

[0115] 24, at least one galvanometer mirror 1214 is capable of directing and moving the laser beam output by the laser source 1212 relative to the object 122 in response to information sent from the control unit 129. Of course, any other deflection system can be envisaged. The components of the device 121 are disposed inside a sealed chamber 1217 that can be connected to an air or inert gas treatment circuit. Furthermore, the air or inert gas treatment circuit can be configured to regulate the pressure within the sealed chamber 1217 to subatmospheric or superatmospheric pressure.

[0116] The selective additive manufacturing apparatus 121 may include a computer C, as shown in FIG. 24, for determining an estimate of the temperature change once the manufacturing process is initiated, or more generally for implementing one of the trajectory determination methods as shown above. the computer C is arranged to rapidly process the various points of the path, in particular the time it takes for the computer to process the various points must be less than or at least equal to the time it takes the laser beam to illuminate or scan these same points at the scanning speed; Such a computer C may cooperate with a memory M in order to store the estimate of the temperature change once this value is generated.

[0117] Finally, any steps of the above-mentioned trajectory determination method may be performed by suitable instructions of a computer program. A computer program containing one or more instructions of this type is capable of being executed on a computer.

Claims

1. A method (P) for determining a trajectory to be followed by a laser beam for the selective additive manufacturing of a three-dimensional object, said laser beam being emitted towards a layer of powder and intended to move along a trajectory comprising a plurality of paths in order to melt said layer of powder, said path being determined by carrying out the following steps (a) to (d), said steps (a) to (d) being: a) a predetermined reference path (T i ) on multiple reference points (T ij ), wherein the determining step determines the distance between each reference point (T ij ) comprising, in succession, the following steps: - the reference point (T ij ) for the lateral width (L ij ) - determining a possible position of an adjacent point (T i+1j) relative to said reference point (T ij ), said adjacent point (T i+1j ) being located on an adjacent path (T i+1 ) of said trajectory, said adjacent path (T i+1 ) being included in said trajectory, said adjacent path (T i+1 ) being adjacent to said reference path (T i ), said adjacent point (T i+1 ) being located on an adjacent path (T i+1 ) of said trajectory, said adjacent path (T i+1 ) being adjacent to said reference path (T i ), i+1j ) and the possible positions of the reference point (T ij ) is equal to the product of the lateral width (L ij ) of the simulated reference fusion zone and a predetermined target overlap (αc), and the distance separating the adjacent points (T i+1j ) is the reference point (T ij ) on the reference path (T i ) and is included in the plane of the powder layer, i ) to the adjacent path (T i+1 ) in a direction directed toward the reference point (T ij ) with respect to the - executing the secondary steps in a loop, The secondary step comprises: - estimating, for said adjacent point (T i+1j ), the possible lateral width (L i+1j ) of a simulated adjacent molten zone surrounding said adjacent point (T i+1j ); - estimating a possible overlap between the simulated reference melt zone and the simulated adjacent melt zones; If the estimated possible overlap corresponds to a percentage of the simulated reference fusion zone that is smaller than a predetermined minimum percentage or larger than a predetermined maximum percentage, the adjacent points (T i+1j and resuming the loop of said secondary steps while modifying the possible positions of b) Multiple adjacent points (T i+1j ), determining the adjacent points (T i+1j ) is a lateral width (L) of the simulated reference fusion zone where the adjacent fusion zone and the simulated reference fusion zone are contained between a predetermined minimum percentage (αmin) and a predetermined maximum percentage (αmax). ij ) ) ) ) ) ) ) ) ) c) determining an adjacent path (T i+1j ) passing through the determined adjacent points (T i+1j ); i+1 ) d) repeating steps a) to c) while defining said adjacent path (T i+1 ) as a new reference path, all said paths determined defining a trajectory that the laser beam is intended to follow, said trajectory being stored and / or transmitted to a control unit of the selective additive manufacturing device. That is, A method for determining a trajectory followed by a selective additive manufacturing laser beam (P),

2. determining a difference between the estimated possible overlap and a target overlap equal to the product of the lateral width of the simulated reference melt zone and a target overlap (αc); 2. A method (P) for determining a trajectory followed by a selective additive manufacturing laser beam according to claim 1.

3. the target overlap (α) is equal to 15%, the minimum percentage (α) is equal to 12%, and the maximum percentage (α) is equal to 18%; 2. A method (P) for determining a trajectory followed by a selective additive manufacturing laser beam according to claim 1.

4. To estimate the possible overlap between the simulated reference melt zone and the simulated adjacent melt zone, the possible positions of the adjacent points (T i+1j ) and the position of the reference point (T ij ) is subtracted from half the sum of the lateral width of the simulated reference fusion zone and the possible lateral width of the simulated adjacent fusion zones; 4. A method (P) for determining a trajectory followed by a selective additive manufacturing laser beam according to claim 2 or 3.

5. When restarting the loop of the secondary step, the adjacent point (T i+1j ) and the possible positions of the reference point (T ij the possible locations of the adjacent points are modified such that a distance separating the adjacent points from the location of the adjacent points is replaced by the difference between the distance and the product of the estimated possible overlap and the lateral width of the simulated reference melt zone and the target overlap; A method (P) for determining a trajectory followed by a selective additive manufacturing laser beam according to any one of claims 2 to 4.

6. estimating a lateral width of a simulated melt zone surrounding an interrogation point located on the bed of powder, comprising: - determining a number of calculation points, which are points of the powder layer located in the vicinity of said investigation points; - estimating a maximum reached temperature at each of said calculation points, said estimation depending on the temperature change caused by irradiation of the laser beam to solidify a zone of the powder layer surrounding an upstream point located on a plurality of paths upstream of the path of the laser beam to said investigation point, and further said estimation depending on the temperature change of the powder at said calculation point due to irradiation of the laser beam to solidify a zone of the powder layer surrounding said investigation point; - comparing the maximum temperature thus estimated with the melting point of the powder; - identifying, among said calculation points, a melting point where said estimated value of said maximum temperature reached is equal to or greater than the melting point of said powder; - estimating the lateral width of the zone occupied by said melting point; Including, A method (P) for determining a trajectory followed by a selective additive manufacturing laser beam according to any one of claims 1 to 5.

7. The step of estimating a maximum temperature at the calculation point comprises: - calculating, for each of said upstream points, an estimate of the change in temperature of the powder at said calculation point due to the emission of a laser beam so as to solidify a zone of the layer of powder surrounding said upstream point; of - calculating an estimate of the change in temperature of the powder at the calculation point due to the emission of a laser beam so as to solidify a zone of the layer of powder surrounding the investigation point; - calculating an estimate of the temperature of the powder at the calculation point depending on the estimate of the temperature change due to the emission of a laser beam so as to solidify a zone of the layer of powder surrounding the investigation point or the upstream point; - calculating an estimate of the maximum temperature at said calculation points; Including, A method (P) for determining a trajectory followed by a selective additive manufacturing laser beam according to claim 6.

8. estimating, for the upstream point, a change in temperature of the powder at the calculation point due to irradiation of the laser beam to solidify a zone of the layer of powder surrounding the upstream point, comprising: - calculating, for each of said upstream points, the distance separating said survey point and said upstream point; - comparing said distance with a predefined spatial proximity distance; - for each of the upstream points that are at least the spatial proximity distance away from the interrogation point, estimating as zero the change in temperature of the powder at the calculation point due to the emission of a laser beam so as to solidify the layer of powder surrounding the upstream point; Including, 8. A method (P) for determining a trajectory followed by a selective additive manufacturing laser beam according to claim 6 or 7.

9. estimating, for the upstream point, a change in temperature of the powder at the calculation point due to irradiation of the laser beam to solidify a zone of the layer of powder surrounding the upstream point, comprising: - calculating for each of said upstream points a duration separating the emission of a laser beam so as to solidify a zone of said layer of powder surrounding said upstream point and the movement of the laser beam to said investigation point; - comparing said duration with a predetermined temporal neighbourhood duration; for each of the upstream points whose calculated duration is greater than the temporal neighborhood duration, estimating as zero the change in temperature of the powder at the calculation point due to the emission of a laser beam so as to solidify a zone of the layer of powder surrounding the upstream point, 9. A method (P) for determining a trajectory followed by a selective additive manufacturing laser beam according to any one of claims 6 to 8.

10. 1. A process for selectively additively manufacturing a three-dimensional object from a bed of powder, comprising: - applying a layer of additive manufacturing powder onto a carrier or onto a previously solidified layer; - emitting a laser beam on a layer of powder along a trajectory composed of a plurality of adjacent paths, the movement of the laser beam on said paths melting said layer; Including, 10. A process for selectively additively manufacturing a three-dimensional object from a bed of powder, characterized in that the trajectory is determined by performing a process according to any one of claims 1 to 9, and the trajectory is stored and / or transmitted to a control unit of the selective additive manufacturing apparatus.

11. A selective additive manufacturing apparatus (121) for selectively additively manufacturing a three-dimensional object (122) from a bed of powder, comprising: a powder reservoir (127) located above the horizontal plate (123); a mechanism (124) for distributing the powder onto the plate, the mechanism (124) being configured to successively spread multiple layers of powder; a laser light source (1212) and a control unit (129) configured to control the laser light source to irradiate the layer of powder with the laser beam following a trajectory comprised of a plurality of adjacent paths, such that movement of the laser beam on the path melts the layer of powder; a memory (M) in communication with the control unit and in which a trajectory determined by executing the method according to any one of claims 1 to 9 is stored, A selective additive manufacturing apparatus comprising:

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

13. A computer program comprising instructions suitable for carrying out at least one step of the method according to any one of claims 1 to 9, when said computer program is executed on a computer.

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