METHOD AND DEVICE FOR TEMPERATURE INSPECTION DURING AN ADDITIVE MANUFACTURING PROCESS

Abstract

The present invention relates to a method for inspecting the temperature during additive manufacturing of a part by powder bed fusion in an additive manufacturing system, the fusion being obtained by scanning an activation source on the powder bed, the method comprising the steps of: - manufacturing at least one ultrasonic waveguide layer by layer simultaneously with the manufacturing of at least one part in the powder bed; - for a layer 'n': - measuring a time of flight for an ultrasonic beam emitted in combined transmitter-receiver mode in said at least one waveguide; - obtaining by simulation a value of the propagation of an ultrasonic beam in a temperature field, the simulation being based on a model representative of the additive manufacturing system for said layer 'n'; - comparing the measured time of flight in said at least one waveguide to the propagation value obtained by simulation;- update the simulation model according to the result of the comparison; - repeat the previous steps; and - generate an estimate of the temperature field prevailing in said at least one waveguide from the result of the comparisons.

Description

METHOD AND DEVICE FOR TEMPERATURE INSPECTION DURING OF AN ADDITIVE MANUFACTURING PROCESS Scope of the invention The invention lies in the field of additive manufacturing and concerns a method and a device for inspecting the temperature during an additive manufacturing process, and more particularly of an additive manufacturing process by bed fusion powder. The term additive manufacturing (AM) designates, according to the NF E standard 67-001 _ Set of processes for manufacturing layer by layer by adding material to a physical object from an object digital”. This term encompasses dozens of names for manufacturing technologies, classified into seven process categories according to standard NF ISO 17296-2 June 2015, among which is the powder bed fusion category abbreviated as (PBF) from English "Powder Bed Fusion". PBF processes share the common feature of proceeding to a partial or total melting of static powder, the powder generally derived from metallic, ceramic or plastic materials. PBF processes differ depending on the nature of the energy source. used to produce the fusion, which can be a laser (a process known as LMF) for — Laser Metal Fusion"), an electron beam or even a infrared lamp, to name just one example. Long dedicated to rapid prototyping, the use of Additive manufacturing for the production of functional parts is constantly evolving. to grow. Its strengths are numerous, notably its capacity to produce pieces of high geometric complexity unattainable by others State of the Art means, such as architecturally designed structures, commonly called structure — lattice — according to Fanglicism. Most of the time, these pigces constructed layer by layer, they are built on supporting structures temporary supports to stabilize and secure the parts to the platform manufacturing. These supports are also designed to prevent The collapse of molten metal, particularly when a wall of the pigce has a significant angle or overhang, to limit the thermal deformations and to dissipate the heat generated by 'radiation / powder interaction. They are not very massive in order to, on the one hand, limit the consumption of powder needed to make them and other part of facilitating their post-manufacturing separation. These supports can take various forms: alveolar structure, multiple pyldones, spider web, so-called raft structure, etc. However, several technological hurdles are delaying a more widespread adoption of PBF processes, particularly for the production of high-criticality parts. One of the main challenges concerns the development of quality control and assurance methodologies ensuring the reliability of the produced gauges. In particular the knowledge of the thermal history of a manufactured part Additive manufacturing is fundamental to the quality of the parts. Like all... thermal shaping processes (molding, etc.), cooling is fundamental. In particular, it defines the microstructure of the material, which conditions its macroscopic properties, including the properties mechanical. Furthermore, thermal history conditions the presence of Residual stresses. Residual stresses (field magnitude) (constraints, location within the room, etc.) are responsible for the appearance of cracks, deformations, etc. To ensure within a bed of powder, and the To ensure reproducibility from one machine to another, it is necessary to monitor the temperature at different points, ideally of the entire system (manufacturing room, room under construction). This is all the more It is important that additive manufacturing is particularly timely for small series or even single issues, especially the issues customized. But unlike production lines In traditional methods, the manufacturing temperature varies for each piece. It is therefore imperative to monitor the temperature at each manufacturing, with precise control at the heart of the material. However, the temperature at the core of a pig is difficult to predict by not knowing that the manufacturing cycle, because many parameters have an influence on thermal performance, such as the geometry of the gauge, of the one or more supports, the scanning strategy, to name just a few parameters. II There then exists a need for an instrumentation device that takes into account the influencing parameters. Several solutions exist for inspecting / controlling the temperature during the manufacturing processes of gauges. Some are limited to measures on the periphery and do not allow access to the heart of the matter. Other approaches, such as that of Ikuo Ihara et al. "Ultrasonic Thermometry for Temperature Profiling of Heated Materials. _in Advancement in Sensing Technology, SSMI 1 pp. 211–36, are based on the use of ultrasound to control temperature gradients during the heating of materials. However, the known solutions Although producing relevant information, they remain limited to Control of directly accessible and unburied traps. Furthermore, The methods are operational on part geometries that are fixed and not evolving layer by layer. Finally, the known approaches They generally assume a steady-state heat input, unlike additive manufacturing on powder bed or EFapport of Heat is extremely rapid, for example by laser. Thus, the known temperature control methods apply has superficial or very localized control and they do not allow access at the cost of the material produced. This is all the more important because several layers are generally remelted with each pass of the energy beam, and that the buried layers undergo significant structural modifications under the effect of strong gradients thermal processes, such as solid-state transformations, the creation of significant constraints. This lack of health control— The material is due to the difficulty of accessing a room buried in a bed of powder of the same material. There is therefore a need for an appropriate solution that addresses the disadvantages of known approaches to inspecting the temperature of parts during manufacturing in a process of Powder bed additive manufacturing. The present invention addresses this need. One object of the present invention relates to a method and a temperature inspection device during a process of additive manufacturing, and more specifically additive manufacturing by powder bed fusion. The present invention aims to overcome the limitations of techniques known for offering volumetric measurement by ultrasound of the temperature in a powder bed and / or in parts being manufactured. The invention will find advantageous applications in numerous technical fields such as the aeronautical industries, space or automotive, to name just a few examples. The general principle of the invention is based on the analysis of the round-trip propagation speed (or time of flight) of ultrasonic waves in waveguides that are manufactured simultaneously with the manufacturing additive of one or more parts, comparison with values obtained through simulation in order to estimate the prevailing temperature field in the powder bed and / or in the piece(s) being made. The process described is iterative; it proceeds through comparisons. successive values ​​of flight time between, on the one hand, values Summary of 'invention' experimental measurements taken during the propagation of ultrasonic waves in waveguides under construction, and on the other hand values ​​obtained from simulations with an ultrasonic propagation model in a material subjected to a temperature field. At each iteration, An update is performed on the model's temperature field. A model, preferably digital, is a simplified representation of the real physical system, in the form of a simulated system. It comprises an ultrasonic propagation model, a behavioral model thermal of the simulated system within a geometry similar to that of the a real system that evolves at each layer of its construction, and a elastodynamic model of the behavior of elastic waves within the inspected area. Advantageously, the method of the invention allows for a measurement adaptive which takes into account the heat input from the source activation, as well as the change in geometry of a part as and when measurement of its manufacturing layer by layer. To obtain the desired results, a process is proposed. to inspect the temperature during additive manufacturing of pigce by powder bed fusion in an additive manufacturing system, the fusion being achieved by scanning an activation source onto the bed of powder, the process comprising the steps of to manufacture at least one ultrasonic waveguide layer by layer simultaneously with the manufacture of at least one piece in the powder bed; for a layer 'n' to measure the time of flight for an ultrasonic beam emitted in transmitter-receiver mode combined in said at least one guide waves to obtain, through simulation, a value for the propagation of a beam ultrasonic simulation in a temperature field based on a representative model of the manufacturing system additive for said layer 'n' compare the measurement of flight time in said guide at least wave has the propagation value obtained by simulation; update the simulation model according to the result of the comparison repeat the previous steps and generate an estimate of the prevailing temperature field in said at least one waveguide from the result of the comparisons. In a preferred implementation the simulation model is a numerical model comprising at least a geometric description of the inspected area has layer 'n' one thermal behavior model and an elastodynamic model of the behavior of elastic waves within the inspected area. According to embodiments The geometric description of the inspected area includes a description of EF: set of elements traversed by the beam ultrasonic device, including at least one description of said device and at least one guide of waves and of the said at least one pig in the process of being manufactured. The elastodynamic model includes equations whose solution is done in a semi-analytical manner before repeating the steps for a given layer 'n' the process includes a step to determine if there has been a scan by the activation source on layer 'n' in the area of ​​said at least one guide waves if there has been a scan by the activation source on layer 'n' in the area of ​​said at least one waveguide, the process includes a step to update the geometry of the area in the simulation model inspected with the addition of a new 'n+1' layer if there has been a scan by the activation source on layer 'n' in the area of ​​said at least one waveguide, the process includes a step to update the parameters in the thermal model surface temperature of said at least one waveguide The simulation model update takes temperature into account on the surface of said at least one waveguide, said temperature being obtained by non-contact temperature measurement means; The simulation model update takes temperature into account of the manufacturing system's construction platform, said temperature being obtained by means of temperature measurement not ultrasound before the steps of measuring the flight time for a layer 'n' the The process includes a step to determine that the signals produced by The ultrasonic beams can be used at the aforementioned 'n' layer to perform a flight time measurement The process includes a step of initializing the simulation model. consisting of initializing the model at layer 'n' Initializing the model at layer 'n' consists of initializing the geometry of the inspected area and the temperature field parameters. The invention also covers a device for inspecting the temperature during additive manufacturing of a pin by powder bed fusion in an additive manufacturing system, the fusion is achieved by scanning an activation source on the powder bed, the device including means for implementing the steps of the process claimed. Depending on implementation variants said at least one waveguide is a waveguide isolated from said at minus one part currently being manufactured said at least one waveguide is a waveguide integral with said at least one pin in the process of being manufactured non-contact means for measuring the surface temperature of said at least one waveguide is of the pyrometer or thermal camera type non-ultrasonic methods for measuring the temperature of the plateau construction of the thermocouple-type manufacturing system the ultrasonic beam is emitted into said at least one waveguide by at least one piezoelectric translator, said at least one translator being connected to an electronic acquisition system capable of sending pulses of excitement towards said at least one translator The electronic acquisition system is capable of digitizing signals analog regus of said at least one translator to generate a value flight time, compare the flight time value with a value of propagation of an ultrasonic beam in a temperature field obtained through simulation, the simulation being based on a model representative of the additive manufacturing system, update the model simulation and generate an estimate of the temperature field reigning in said at least one waveguide from the result of the comparisons. Description of the figures Various aspects and advantages of the invention will become apparent in support for the description of a preferred method of implementing the invention but not exhaustive, with reference to the figures below Figure 1 is a simplified representation of a manufacturing system additive enabling the implementation and operation of the device of the invention; Figure 2 illustrates, in cross-section, a first embodiment of the device of the invention; Figures 3a to 3a illustrate, in cross-sectional view, at different stages. of the additive manufacturing of a pin, the implementation of the process of invention Figure 4 illustrates a sequence of the general steps in the process of temperature control according to an embodiment of the invention; Figure 5 illustrates a detailed sequence of steps in Figure 4. Detailed description of the invention Figure 1 shows a known additive manufacturing system (100) enabling the operation of the process of the invention. The system comprises a construction board (102) on which one or more pieces (104) are manufactured using an additive manufacturing process by melting on a powder bed (106), process family in its broadest sense including sintering. The system includes a powder reservoir (108) and a powder spreading system (110) which allows a powder layer from the reservoir to the powder bed (106) or under the effect from a heat source (112), the local melting of the powder operates to produce a layer of the part(s) to be manufactured. The process is Repeat layer by layer until the final piece(s) are obtained. The complete process is not described in more detail, and a 'man of the trade' can refer to the extensive literature on the processes of Additive manufacturing and related manufacturing variants principle. Figure 2 shows, in a cross-sectional view, a system of Additive manufacturing according to a first embodiment of the invention. II It should be noted that the identical elements between the figures bear the Same references. For the sake of simplifying the description but not being in any way limiting, the figure shows only one instance of arrival at end of its manufacture according to an additive manufacturing process by fusion on a powder bed by laser. The person skilled in the art will extend the principles described in the cases of additive manufacturing of a plurality of parts that can to be of identical or variable size and shape, having geometries simple or complex. In the chosen example, the gauge (202) is manufactured on a temporary support structure (204) allowing in particular the stabilize on a build platform (206). Waveguides (208–1 a 4) are inserted into the support structure and built simultaneously. The general principle of the process of the invention consists, starting from dune mesure de la temps de vols d’ultrasonne en un (or several) waveguides which are manufactured simultaneously with the manufacturing of a piece, and iterative comparative analyses with results obtained by a numerical simulation model, to determine the field of temperature in the waveguide(s), and more broadly in the room and / or powder bed. The waveguide(s), which may be designated in the description by the acronym GO, are manufactured by melting powder, as well as temporary supports and clips. They are anchored to the upper face of the construction platform (206). Preferably, the manufacturing of GOs is carried out with a strategy of a scanning pattern similar or identical to that of the adjacent samples, particularly in terms of laser power, laser speed and trajectories. Manufactured directly on the build platform, the GOs can optionally present a slight reduction in section at the level of their anchoring with the plate and, where applicable, with the pin, in order to facilitate their separation at the end of the cycle. The expert in the field understands that the reduction in section must be limited so as not to induce artifacts on emitted and reflected ultrasonic beams. The GOs preferentially have a simple, full geometry and axial, without bifurcation throughout the control zone. Their section is predefined to allow the passage of a beam ultrasonic, while minimizing powder and time consumption of a process to achieve it. In a preferred embodiment, Waveguides are constructed as upright cylinders. simultaneously with the gauge (or set of gauges) and its support structure, layer by layer. In different embodiments, the GO can exhibit other section geometries such as bases oval, square, triangular, rectangular, etc. The minimum cross-section of a GO is chosen according to the material controlled and ultrasonic wave used for control, in particular Its type and frequency. Also, the diameter of a longwave antenna is always chosen greater than the c / f ratio”, and preferably greater than 3*co / f », or c_ denotes the propagation speed of the ultrasonic wave in the controlled material and f the principal wave frequency ultrasound. For example, for temperature control for a bed of steel powder with a 10 MHz transverse wave, the speed of Since the propagation speed of transverse waves in steel is 3230 m / s, then the diameter of a cylindrical GO must exceed _ c / f=323 µm », and of The preferred method must exceed _ 3*c / f=969 um”. The dimension The minimum preferred value of a GO is on the order of millimeters. Returning to Figure 2, ultrasonic translators (212—1 to 212— 4, 213) attached to the construction platform are arranged under the platform so that each can emit an acoustic beam in a GO created in his view. Thus, for example, a translator (212-1 to 212-4, 213) is positioned respectively under the plateau a Location of the manufacture of each GO (208-1 to 208-4, 210). In a preferred embodiment, the translator is a translator — piezoelectric used in transmit-receive mode combined, called pulse-echo — according to recognized anglicism. Each The waveguide allows an ultrasonic signal to be delivered to the heart of the bed. powder. The beam propagates in the GO parallel to the GO axis. A preferred implementation is one where the waveguides are orthogonal to the construction platform, that is to say, vertical in the bed of powder, in order to allow the majority of the signal to reflecting off the upper surface, it travels as an echo towards the receiver. The translator, which is attached to the back face of the platform, The construction is mounted in such a way as to ensure acoustic connection between the translator and the set. This can be obtained, for example, by employment of a layer of coupling agent (grease, oil, cellulose glue, gels) special) which can have a thickness of one to several tenths of a millimeter. The translator and the coupler are selected to withstand the maximum temperature of the platform (which is a function of the fused material and manufacturing strategy, typically from Ford (of a few tens of °C). The diameter of a GO is preferably defined as being equal to or slightly greater (e.g., +10%) than the dimension of the piezoelectric chip of the translator. Common translators as of the date of filing of the patent application with dimensions of a few millimeters, usually a fraction of an inch, the GOs have for example a diameter of approximately 1.6 mm for a 1 / 16 aperture sensor inch, 3.4 mm diameter for a 1 / 8 inch aperture sensor, or even around 6.4 mm for an aperture sensor % of inch. In order to minimize both the time and powder required for their manufacturing, preferably the diameter of the GO for common additive manufacturing devices do not exceed a few centimeters. A person skilled in the art can deduce the sizing of the GO exhibiting different section geometries according to the same principles, by replacing the diameter with the smallest dimension of the section, such as the shortest axis of an ellipse or the shortest side of a rectangle for example. Advantageously, for temperature measurement according to the principle According to the invention, two types of waveguides can be manufactured Simultaneously with the manufacture of parts, each type of GO having a Different location and functionality. Thus, it can be manufactured: GOs—witnesses and GO—supports. In the example chosen from Figure 2, five waveguides ultrasonic devices are illustrated, including one LW-control (210) and four LW- supports (208-1 to 208-4) without limitation, the number of GB— witnesses and GO—supports may vary. The GOs—witnesses have no contact with the pigeons in manufacturing, they are isolated from the pieces and inserted into free spaces for samples, as compliance indicators. In an advantageous implementation, a GO—witness is located in the vicinity of a key, or each critical key. A GO—witness can be placed in close proximity to a piece ranging from a millimeter to a few centimeters to increase the representativeness of the control. In other implementations, particularly in the case of large pigs dimensions and / or high criticality, a plurality of GO—witnesses may be placed in the vicinity of a piece, for example all around its perimeter. A control group can be used to assess the homogeneity of the manufacturing takes place within the powder bed. Indeed, the powder beds exhibit temperature heterogeneities. The comparison of ultrasonic signals from the various LWs—witnesses, in particular the comparison of estimated values ​​of temperature fields allows to qualify IE homogeneity on the plateau. In an implementation advantageous, a plurality of GO—witnesses is distributed within the bed of powder, interspersed between the different pieces to be manufactured. The The number of GOs—witnesses can vary and range from at least one to several dozens. A GO—witness differs from a simple control sample in this sense that its positioning is suitable, even optimized, for control at proximity of a room or of the entire surface of the tray. Anchoring on the GO-witness plateau does not bring back a drawback in the sense that the GO—witnesses can be sacrificial, unlike witness pieces. The GO—supports are integrated into the temporary supports of the pieces in manufacturing. A GO—support is attached to a pin, and according to its location on the pin, it can be fixed to the pin or from the completion of the first layers of the pigce, either later than during manufacturing. The waveguides are integral to a part made of using an ultrasonic beam to inspect the temperature at heart of the puzzle. They differ from temporary supports in that they have larger sections than those of the usual elements. The section of GO—supports is chosen to be of sufficient size to allow the passage of the ultrasonic beam, while being minimized on the one hand avoid excessive consumption of powder to make them and other part of avoiding an excessive concentration of constraints. Advantageously, GO-supports will be arranged in such a way as to To deliver an ultrasonic beam to critical areas of the chamber. II This could include regions with a strong temperature gradient. A GO— integrated support structure advantageously presents a symmetry or periodicity to limit the asymmetry of deformations Scale of the gauge. In one embodiment, GO—support may be present across the entire support area of ​​the piece, separated by n _ usual supports, n _ being constant between each GO—support. Returning to Figure 2, the translator(s) are linked to a electronic acquisition system (214) which allows the digitization of Analog signals from the translators. The acquisition system electronics send excitation pulses at fixed time intervals towards the translators and receives any signal reflected by a GO in a time interval less than F interval between pulses. The signal regulated is processed and cross-referenced with the simulation results according to the described procedure with reference to figures 4 and 5 to allow the determination of the field of temperature in the volume of the GO corresponding to the analyzed signal. The additive manufacturing system of the invention further comprises at least one thermocouple (216) for measuring the temperature of the construction platform (206). In one embodiment, the system may also include a pyrometer (218) or a thermal camera to measure the temperature at the top of a waveguide. Figures 3a to 3c show, in a cross-sectional view, different stages in the manufacture of a pin (202), the simultaneous manufacture of four ultrasonic waveguides (208-1 to 208-4) allowing operation the process of the invention. Figure 3a illustrates an early stage of In manufacturing, a single waveguide (208-2) reaches the pigce, and three guides of waves (208-1, 208-3, 208-4) which are also manufactured simultaneously They don't reach it. At this stage of manufacturing, a temperature measurement according to the process of the invention, the waveguide attached to the piece (208—2) to estimate the temperature field for the volume already manufactured from the pigce and by the isolated waveguides of the pigce (208—1 208-3, 208-4) to estimate the temperature field in the powder bed. Figure 3b shows an intermediate step in the manufacturing of the piece or at this stage, two waveguides (208-2, 208-3) reach the piece and can be used as GO—support to inform about the Temperature field at the level of the probe. The other two guides of waves (208-1, 208-4) not yet reaching the point, they can always &be used to provide information on the temperature field in the bed of powder. Figure 3c illustrates the final stage where the pig is entirely manufactured and / or the four waveguides (208-1 to 208-4) reach the piece, allowing them to be used to provide information on the field of temperature at the center of the room. The example in Figure 3 is simplified, but does not limit the possible embodiment variants or GO-type waveguides— witnesses (not illustrated), isolated and independent of any piece, may also be manufactured simultaneously (like the GO—witness 210 on the figure 2). Thus, advantageously, during the same manufacturing cycle additive powder bed fusion, the process of the invention makes it possible to combine a temperature control of the powder bed concomitantly with a temperature control at the core of one or more parts during manufacturing. Figure 4 illustrates a sequence (400) of general steps of the temperature inspection process according to an embodiment of invention. The process begins simultaneously with the start of the Manufacturing a part. Temperature measurements in the tray manufacturing processes are initiated (401) by means of the thermocouple, as well as ultrasonic measurements (402) during a preliminary waiting phase as long as the signal is not usable (or the echoes mix and do not are not temporally separable). Thermocouple measurements continue continuously throughout the entire manufacturing process, and the values The measured values ​​are taken into account for updating the thermal model. (412). Ultrasonic measurements (402) consist of sending a signal in pulse-echo mode (transmitter-receiver combined) in the guides of waves and to determine when the measurement of a time of flight becomes possible, that is to say, as soon as it is possible to dissociate the background echo (or rebound) corresponding to the reflection of the ultrasonic beam on the top of the waveguide into which the signal is sent. Thus, it is It is possible that the additive manufacturing process has operated several layers before obtaining measurements that become usable for the inspection procedure. As soon as flight time measurements can be used, the The process initializes the numerical simulation model (404). The model is a simplified representation of the real physical system, in the form of a simulated system. The simulated system is composed, at a minimum, of the following elements non-granular solids traversed by the ultrasonic wave (the waveguide, the plateau region located between the waveguide and the sound translator (look), or even, where applicable, of the part (for the case of GO—support). Preferably, the simplified representation includes (1) The geometry of the region of interest (ROI) or inspected area has a layer 'n' which is extracted from so-called sliced ​​CAD files — and already communicated to the machine for the needs of layer manufacturing a layer. Preferably, the geometric description of the The inspected area includes a description of all the elements traversed by the ultrasonic beam, of which at least one description said at least one waveguide and said at least one part in manufacturing process. (2) The thermal behavior of the system, that is to say the distribution and the propagation of heat over time within the The geometry considered / simulated. The behavioral model Thermal analysis can be analytical or numerical. An analytical thermal behavior model is based on Heat equation (or well-known diffusion equation of man) of the trade), applied to geometry, generally by means of series and mathematical functions (Fourier, Green, Kirchhoff...). This type of Analytical models are generally reserved for simple geometries, by example for the GO—witnesses. A numerical thermal behavior model, 2D or 3D, This involves decomposing the system into several thousand units. virtual, the heat equation then being applied to each of them They. The systems of equations are then solved using a method Numerical mathematics (finite element method, finite difference method) FDM or by boundary elements BEM) which allows us to have the temperature distribution within the structure. This type of model meshed numerical data, even if their computation times are longer than Analytical models are preferred when one wishes to obtain Temperature maps on complex structures. A person skilled in the art will consider that for these two models, the The choice of boundary conditions applied to the thermal model is Important. Boundary conditions describe the behavior of the system concerning heat exchange with the surrounding environment system. Different possibilities exist, a temperature fixed at the edge of the model, a fixed heat flux, a heat flux as a function of Fécart of temperature, or mixed conditions. (3) The behavior of elastic waves within the ROI. The model Elastodynamics describes the effect of a mechanical perturbation during of time, depending on the temperature field prevailing in the environment. The behavior of matter allows waves to propagate elastics whose speed depends on the local temperature has the geometry. The elastodynamic model is based on several equations that must be verified jointly and that change over time. The method of solving the The equations of the elastodynamic model can be semi-analytical, that is to say, based on a known approach to ray casting,” a Finstar, the CIVA commercial software of the applicant, or to be by elements finished, relying on a discretization of the propagation medium under the form of a grid, not necessarily regular, of the geometry. Returning to Figure 4, the initialization of the numerical model (404) takes into account thermal data that characterize the flux of heat in the material from which the pin is made, as well as the boundary conditions (on the edge of the model). Furthermore, the model of The simulation is initialized using the elastic properties of matter. solid produced by the manufacturing process as well as by the knowledge of its dependence on temperature, specifically the propagation speed in this material at different temperatures. After initialization, the process allows determining (406) if the The laser has just scanned the considered waveguide in order to take in account in the digital model for an additional heat input at the top of the waveguide. The process continues at the next step (408) to obtain real and simulated values. It allows, on the one hand, for a measurement ultrasonic time-of-flight analysis on the real system and, on the other hand, simulation ultrasonic propagation with a numerical simulation model. Then, the process allows us to compare (410) the differences between the values obtained through actual measurements and simulation. The result of the Comparison allows updating the simulation model (412) and to estimate the temperature field when the differences between simulated and measured values ​​fall below a predefined threshold. Advantageously, the process of the invention makes it possible to do evolve the simulation model during a manufacturing sequence of a pigeon. The simulation model described using geometry, the temperature field in the waveguide at a given moment. The The geometry of a piece is determined based on the last layer completed with the waveguide. Advantageously, the model update takes into account the passage of the laser. If the laser is passed over a waveguide, the process considers that the layer addition is almost instantaneous (of order) (a few seconds), and the geometry update then takes place with an additional layer. During the update, the temperature in the waveguide at the instant before the update is known, the The process uses the same temperature field, which is assumed to be invariant. between the two moments of time that frame the passage of the laser. One once the additional layer is added to the model's geometry, the value the temperature field from the previous model is copied to the new geometry for all existing layers in the the previous model. An average temperature value in the new layer is then determined using Fdeviation of measurement data of flight time observed at the comparison stage (410) and by the knowledge of the properties of matter. If there was no laser passage, the geometry of the pigce will not Don't change. For the simulation model update in from a heat input by the laser, the model considers that the heat flows through the support of the manufacturing machine. Thus, the knowledge of the temperature at the support level (401) allows to estimate the heat flow using the thermal properties and therefore estimate the evolution over time of the temperature throughout the geometry. The temperature value is updated with Fdeviation of flight time observed in the experimental measurement. If Fdeviation is zero, the The correction made at this stage is zero. The assumption taken is that only The top of the waveguide cools down as a result of this temperature difference. This allows you to change the temperature value at the end of the guide waves so that the model gives after correction exactly the same flight time as that measured experimentally. After the model update (412), the process loops back to the step of determining the laser passage (406) to iterate on new measurements (real and simulated) of flight time. Thus, at each iteration of The model update process allows for the provision of (414) in time actual, an estimate of the temperature field of either the powder bed via a a control waveguide, either at the heart of the device via a waveguide support. Figure 5 illustrates a detailed sequence of steps in the figure 4. During the initial F step (402) simultaneously with the launch of a In the manufacturing sequence of the pieces, a measurement is taken of the Reference temperature of the support (502). Ultrasonic waves are sent in pulse-echo mode (504) in the waveguides manufacturing process continues until the measurements are usable. When ultrasonic signals are separable (506), the process continues to the next step (404) to initialize the model and the field of temperature. According to some embodiments, the initialization (508) of the field thermal (T_omega_c) can be chosen based on one of the following criteria following let T_ omega_c be a constant, that is to say that the temperature in The entire waveguide is taken to be constant, by example equals the temperature of the support Tc which is measured by the thermocouple. either T_omega_c — estimated, that is to say that the temperature of the waveguide is that given by a thermal simulation model alone. either T_omega_c — T_s, that is to say that the temperature of the guide donde is the surface temperature, measured using a pyrometer or by any other method of measuring surface temperature. An additional hypothesis can be taken into account for the temperature field profile by adding a function from a semi-analytical model (linear function, exponential, ...), which allows, based solely on surface area measurements, the prediction of the field's shape of temperature throughout the waveguide. The initialization (510) of the model geometry is taken at the geometry of the waveguide at the layer 'n' in which the process is located at this stage. So for example, if the laser has made 5 passes and melted 5 layers, the waveguide height has an initialization step F is taken equal to 5 layers. The next step in the process is to determine if the laser (or any other heat source) has just passed (512), that is to say, has just passed scan the waveguide in question. This information is available and provided by the manufacturing control system, known as CAM (computer-aided manufacturing). If so, the process allows for updating the surface layer temperature (514), by adding to the model thermal, a heat input at the top of the waveguide (516), creating a new layer on the surface. Then the process moves to the next step (408). An alternative way of taking this heat input into account is to measure the temperature at the top of the waveguide considered by an additional device provided for this purpose (such as a pyrometer) and to introduce the result of this measurement in the thermal model. If it is determined that the laser has not just passed, the process proceeds directly to the next step (408) without adding a new one layer in the thermal model. The next step in flight time measurement (408) consists of a part in a measure (518) of the time of flight of the ultrasonic beam in the real system, and on the other hand in a simulation (520) of the propagation ultrasonic in the system as simulated. The value (520) produced by the simulation model takes into account the geometry of the system at the last layer with the corresponding temperature field. In the next step (410), the process allows comparison (522) of the two flight time values, actual value and simulated value, and of calculate (524) F gap existing between the values. Advantageously, the The process allows for taking into account the calculated deviation, by adjusting the simulated thermal profile (526), ​​in order to get closer to the flight time which is measured. For example, if the time of flight measured in the waveguide is less than the simulated flight time and the propagation speed decreases with temperature, which is the case for Facier, the process considers that the actual average temperature is higher than the average temperature of the model. A corrective action is then applied to the average temperature of the model by an increase in temperature in proportion to the measured difference. In practice, and preferably, the process allows for choose in which region of the model, the correction linked to Fdeviation of The temperature measured by the model must be applied. Given that the The only source of heat is the laser; the correction is applied to the model a place close to the surface, for example on the first layer of the model or on average over several layers near the laser. Through this step of comparing and updating the model, the profile The temperature proposed by the model is improved, refined, and tends to be approaching the actual temperature field prevailing in the chamber manufacturing considering that the thermal conditions of the process are well modeled. The temperature field then constitutes the estimation of the temperature of the waveguide (528). The process can iterate over steps 512 to 526 with the profile of Simulated temperature updated. Advantageously, filtration allows one to to get as close as possible to the actual temperature profile, which evolves in function of time. The iteration can be continued continuously until the end of the manufacturing sequence, or even beyond if a phase of Cooling is monitored during the manufacturing process. Furthermore, advantageously after the simultaneous manufacture of a batch of chips and waveguides, the latter can be taken for further analyses, such as characterizations metallurgical or mechanical tests (after machining or not), their proximity to the traps in the bed of powder making them strong representative of these. The present description illustrates a preferred implementation. of invention, but is not exhaustive. An example was chosen for to allow a good understanding of the principles of invention, and a concrete application, but it is by no means exhaustive and must allow a 'A skilled professional to make modifications and variations' implementation while maintaining the same principles. Thus, although the The method described for measuring temperature can be used to estimate the heat / calories transferred by the laser to material with the aim of ensuring that the laser always delivers the same power during manufacturing, or between two places on the bed of powder. A skilled craftsman can, following the same principles, use the measurements to control the process, and implement a feedback loop on the manufacturing of the part. Furthermore, although the present invention relates preferentially to materials Metallic materials, it can be applied to other sufficiently ultrasonic wave propagators at frequencies of interest, such as certain ceramics. Finally, the invention has been described for a process of Additive manufacturing by laser powder fusion, however it can to be implemented with other sources of fusion activation, by for example an electron beam, or a combination of sources activation (e.g., two lasers of different power or wavelengths) different).

Claims

Demands 1. A method for inspecting the temperature during additive manufacturing of a part by powder bed fusion in an additive manufacturing system, the fusion being achieved by scanning an activation source over the powder bed, the method comprising the steps of: - manufacture at least one ultrasonic waveguide layer by layer simultaneously with the manufacture on a build platform of at least one part in the powder bed, said at least one waveguide being integral with the build platform and having a minimum value of the smallest dimension of the section greater than the ratio "c / f", "c" denoting the propagation speed of ultrasonic Fonde in the controlled material and "f" the principal frequency of ultrasonic Fonde; - for a layer 'n': - measure a time of flight for an ultrasonic beam emitted in transmitter-receiver mode combined in said at least one waveguide; - to obtain by simulation a value of the propagation of an ultrasonic beam in a temperature field, the simulation being based on a model representative of the additive manufacturing system for said layer 'n'; - compare the time of flight measurement in said at least one waveguide to the propagation value obtained by simulation; - update the simulation model according to the result of the comparison; - repeat the previous steps; and - generate an estimate of the temperature field prevailing in said at least one waveguide from the result of the comparisons.

2. The method according to claim 1, wherein the simulation model is a numerical model comprising at least a geometric description of the inspected area at layer n', a thermal behavior model, and a model elastodynamics of the behavior of elastic waves within the inspected area.

3. The method according to claim 2 wherein the geometric description of the inspected area includes a description of all the elements traversed by the ultrasonic beam, including at least a description of said at least one waveguide and of said at least one part being manufactured.

4. The method according to claims 2 or 3 in which the elastodynamic model comprises equations whose solution is done in a semi-analytical manner.

5. The method according to any one of claims 1 to 4 comprising, before repeating the steps for a given layer 'n', a step to determine whether there has been a scan by the activation source on the layer 'n' in the area of ​​said at least one waveguide.

6. The method according to claim 5 comprises, if there has been a scan by the activation source on the 'n' layer in the area of ​​said at least one waveguide, a step of updating in the simulation model the geometry of the inspected area with the addition of a new 'n+1' layer 7. The method according to claim 5 or 6 comprising, if there has been a scan by the activation source on the 'n' layer, in the area of ​​said at least one waveguide, a step of updating in the thermal model the surface temperature parameters of said at least one waveguide.

8. The method according to any one of claims 1 to 7 wherein the updating of the simulation model takes into account the surface temperature of said at least one waveguide, said temperature being obtained by non-contact temperature measurement means.

9. The method according to any one of claims 1 to 8, wherein the update of the simulation model takes into account the temperature of the plateau of construction of the manufacturing system, said temperature being obtained by non-ultrasonic temperature measurement means.

10. The method according to any one of claims 1 to 9 comprising, before the steps of measuring the time of flight for a layer 'n', a step of determining that the signals produced by the ultrasonic beam are usable at said layer 'n' to perform a time of flight measurement.

11. The method according to claim 10 comprising a simulation model initialization step consisting of initializing the model at layer 'n'.

12. The method according to claim 11 wherein the initialization of the model at layer 'n' consists of initializing the geometry of the inspected area and the parameters of the temperature field.

13. A powder bed fusion additive manufacturing system for parts, fusion being achieved by scanning an activation source over the powder bed, the system comprising a device for inspecting the temperature during the manufacturing of a part, said device comprising means adapted to implement the steps of the process according to any one of claims 1 to 12.

14. The system according to claim 13 in which said device comprises at least one waveguide isolated from said at least one part during manufacture.

15. The system according to claim 13 in which said device comprises at least one waveguide integral with said at least one part during manufacture.

16. The system according to any one of claims 13 to 15 in which said device comprises non-contact means of the pyrometer or thermal camera type for measuring the surface temperature of said at least one waveguide. 4 7. The system according to any one of claims 13 to 16 in which said device comprises non-ultrasonic thermocouple-type means for measuring the temperature of the build platform of the manufacturing system. 5 18. The system according to any one of claims 13 to 17 wherein an ultrasonic beam is emitted into said at least one waveguide by at least one piezoelectric transducer, said at least one transducer being connected to an electronic acquisition system capable of sending excitation pulses to said at least one transducer. 10 19. The system according to claim 18 wherein the electronic acquisition system is capable of digitizing the analog signals received from said at least one translator to generate a time-of-flight value, comparing the time-of-flight value with a propagation value of an ultrasonic beam in a temperature field obtained by simulation, the simulation being based on a model representative of the additive manufacturing system, updating the simulation model and generating an estimate of the temperature field prevailing in said at least one waveguide from the result of the comparisons.

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