Device for detecting a defect during the manufacturing of a part

Abstract

Device for detecting a defect during the manufacturing of a part. This device for detecting a defect during the manufacturing of a part by an additive manufacturing process comprises: - a support including an optical fiber (56) extending from a proximal end (82) to a distal end (80) passing through measurement points (P1 to P24), this optical fiber having, at each of these measurement points, a Bragg grating, and - a processing unit (50) connected to the proximal end (82) of the optical fiber and configured to obtain a measurement of a temperature or an acoustic signal at each of the measurement points from a measurement of an optical signal that has interacted with the Bragg grating located at that measurement point. Fig. 5

Description

Title of the invention: Device for detecting a defect during the manufacturing of a part

[0001] The invention relates to a device for detecting a defect during the manufacturing of a part by an additive manufacturing process. The invention also relates to a method for detecting, using this detection device, a defect during the manufacturing of a part by an additive manufacturing process. Finally, the invention relates to an additive manufacturing system for a part incorporating this defect detection device.

[0002] Such a known detection device is disclosed in US patent application 2020290121A1. This device is advantageous because it allows the detection of any manufacturing defect that results in a change in the heat flow between the part being manufactured and the substrate on which it is being produced. In particular, this method makes it possible to detect the detachment of the part being manufactured from the substrate on which it is being produced. Thus, if a defect is detected, it is possible to interrupt the manufacturing process before its completion to avoid unnecessary material waste. This detection device is also easy to integrate into an additive manufacturing machine because the temperature sensors are integrated into the substrate on which the part is being produced.

[0003] However, the spatial resolution of this fault detection device is limited by the number of temperature sensors integrated into the support. Indeed, it must be possible, if necessary, to measure a high temperature with each of the temperature sensors. A high temperature here is a temperature above 300°C or 500°C. This is why, in the fault detection device of application US2020290121A1, the temperature sensors are thermocouples. Thermocouples are rather bulky. Furthermore, each temperature sensor is connected to an electronic processing unit via a respective wired connection. Thus, the support includes not only the temperature sensors but also, for each of them, a groove for the wires that connect it to the processing unit.The space occupied by the grooves used for the wires substantially limits the number of locations in the substrate where a temperature sensor can be housed. Therefore, with the detection device described in US2020290121A1, it is very difficult to achieve a high density of measurement points and thus high spatial resolution. Because of this, defects located between two temperature sensors are difficult to detect and / or are detected very late, that is, generally, at a time when the defect has grown to a certain size. a stage where at least part of this defect extends above one of the temperature sensors.

[0004] The invention aims to remedy this drawback by proposing a device for detecting a defect during the manufacture of a part by an additive manufacturing process which makes it possible to obtain a higher spatial resolution without complicating the manufacture of the device.

[0005] The invention therefore relates to a device for detecting a defect during the manufacture of a part by an additive manufacturing process, this device comprising:

[0006] - a support comprising:

[0007] - a top surface on which the part is manufactured when the process of Additive manufacturing is implemented.

[0008] - temperature measurement points or points of an acoustic signal, these points of measurements being contained within a measurement plane located under the upper face and distributed within this measurement plane in such a way that at least one of these measurement points is located under the part when the additive manufacturing process is implemented,

[0009] - a processing unit configured to obtain temperature or of the acoustic signal at each of the measurement points when the additive manufacturing process is implemented and to detect, from these measurements, a defect in the part during its manufacture by the additive manufacturing process,

[0010] wherein:

[0011] - the support comprises an optical fiber extending from a proximal end up to a distal end, passing through each of the measurement points, this optical fiber comprising, at each of these measurement points, a Bragg grating, and

[0012] - the processing unit is connected to the proximal end of the optical fiber and configured to obtain the measurement of the temperature or acoustic signal at each of the measurement points from a measurement of an optical signal that has interacted with the Bragg grating located at that measurement point.

[0013] Embodiments of this device may include one or more of the following features:

[0014] 1) The support comprises:

[0015] - a base comprising a top face,

[0016] - a lid comprising an upper face and, on the opposite side, a lower face, the upper face of the support being formed by the upper face of the lid,

[0017] - means for fixing the cover to the base, these fixing means being reversibly movable between:

[0018] - an assembled state in which the cover is fixed without any degree of freedom on the base and the lower face of the cover is pressed against the upper face of the base, and

[0019] - a disassembled state in which the cover can be detached from the base,

[0020] - a groove cut into the upper face of the base or into the lower face of the lid, and

[0021] - the optical fiber is received inside this groove in a removable manner.

[0022] 2)

[0023] - on the side opposite its upper face, the support comprises a lower face, and

[0024] - the support has a groove cut into its lower face, this groove being able to receive optical fiber in a removable manner.

[0025] 3) The processing unit is configured:

[0026] - to obtain temperature measurements using a first part of the Bragg gratings when the additive manufacturing process is implemented and to detect, from these temperature measurements, a defect in the part during its manufacture by the additive manufacturing process, and

[0027] - to obtain measurements of the acoustic signal at the level of a second part of the Bragg networks when the additive manufacturing process is implemented and to detect, from these measurements of the acoustic signal, a defect in the part during its manufacture by the additive manufacturing process.

[0028] 3) The processing unit is configured to measure both the temperature and the acoustic signal using the same Bragg grating.

[0029] 4) The number of Bragg gratings is greater than ten or twenty.

[0030] 5) Each Bragg grating of the optical fiber is characterized by a length of the interrogated wavelength at which it reflects the incident optical signal and, for each Bragg grating of the optical fiber, this interrogated wavelength of this Bragg grating is separated from the interrogated wavelengths of the other Bragg gratings of the optical fiber by at least 1 nm.

[0031] 6) The processing unit is capable of acquiring an optical signal that has interacted with one Bragg gratings at an acquisition frequency greater than 1 kHz.

[0032] 7) The processing unit is capable of obtaining a temperature measurement, at the level from one of the measurement points, which exceeds 500°C.

[0033] The invention also relates to a method for detecting, using the above-mentioned detection device, a defect during the manufacture of a part by an additive manufacturing process, this detection method comprising:

[0034] - for each measurement point of a first group of measurement points and at regular time interval, the calculation of a standard deviation Oi>p representative of the amplitude of temperature variations measured during a sliding time window predetermined at this measurement point, the measurement points of this first group being located under the part being manufactured, then

[0035] - the detection of a fault at a measurement point of the first group from of the different successive values ​​of the standard deviation Oi>p calculated for each regular time interval.

[0036] Embodiments of this process may include one or more of the following features:

[0037] 1) The process comprises:

[0038] - for each measurement point of a second group of measurement points and at regular time interval, the calculation of a standard deviation π2,P representative of the amplitude of the temperature variations measured during a predetermined sliding time window at this measurement point, each measurement point in this second group not being located under any metal part being manufactured, then

[0039] - the calculation of an average of the standard deviations o2,P to obtain a standard deviation o2ref of reference, then

[0040] - the detection of a fault at a measurement point of the first group from of the ratio 0ijP / 02jref calculated for this measurement point.

[0041] The invention also relates to an additive manufacturing system for a part, this system comprising:

[0042] - an apparatus for forming successive layers stacked one on top of the other to form, by stacking these layers, the part to be manufactured,

[0043] - the above device for detecting a defect during the manufacturing of the part by the device, this device comprising:

[0044] - a support comprising:

[0045] - a top surface on which the part is manufactured when the process of Additive manufacturing is implemented.

[0046] - temperature measurement points or points of an acoustic signal, these points of measurements being contained within a measurement plane located under the upper face and distributed within this measurement plane in such a way that at least one of these measurement points is located under the part when the additive manufacturing process is implemented,

[0047] - a configured processing unit:

[0048] - to obtain temperature or acoustic signal measurements at the level of each of the measurement points when the additive manufacturing process is implemented,

[0049] - to detect, from these measurements, a defect in the part during its manufacturing using the additive manufacturing process, and

[0050] - to, in response to the detection of a fault, control a human- machine or forming device in such a way as to stop the manufacturing of the part or to change parameters of the forming device.

[0051] Embodiments of this system may include the following characteristic: the successive layer formation apparatus is capable of forming successive layers of metal stacked one on top of the other to form, by stacking these layers, all the metal parts to be manufactured.

[0052] The invention will be better understood upon reading the following description, given solely by way of non-limiting example and made with reference to the drawings in which:

[0053] - Fig. 1 is a schematic illustration of the architecture of a system of additive manufacturing incorporating a defect detection device

[0054] - [Fig.2] is a perspective view of a support for the system of [Fig.1],

[0055] - [Fig.3] is a perspective view of a base of the support of [Fig.2],

[0056] - [Fig.4] is a top view of the base of [Fig.3],

[0057] - [Fig. 5] is a schematic illustration of the architecture of the detection device of the system of [Fig.1],

[0058] - [Fig. 6] is a flowchart of a method for detecting a defect using the device of the [Fig.5],

[0059] - Figures 7 and 8 are graphs illustrating the temporal evolutions, respectively, of temperatures and standard deviations measured during the implementation of the process of [Fig.6],

[0060] - [Fig. 9] is a flowchart of another method for detecting a defect using of the device in [Fig. 5],

[0061] - [Fig. 10] is a schematic illustration, in vertical section, of another mode of construction of the support for [Fig.2].

[0062] In this description, the terminology, conventions, and definitions of the terms used in this text are introduced in Chapter I. Detailed examples of embodiments are then described in Chapter II with reference to the figures. Variants of these embodiments are presented in Chapter III. Finally, the advantages of the different embodiments are specified in Chapter IV.

[0063] Chapter I: Definitions, terminology and conventions:

[0064] In the figures, the same references are used to designate the same elements.

[0065] In the remainder of this description, the well-known characteristics and functions of a person skilled in the art are not described in detail.

[0066] Figures 1 to 4 and 9 are oriented with respect to an orthogonal XYZ coordinate system, where the X and Y directions are horizontal and the Z direction is vertical. Terms such as "above", "below", "top", "bottom", "superior", "inferior" are defined with respect to the Z direction.

[0067] The term “high temperature” refers to a temperature above 300°C or 500°C.

[0068] The term “low frequency” refers to a frequency below 20 Hz and, typically, below 10 Hz or 5 Hz.

[0069] The term “high frequency” refers to a frequency greater than 1 kHz or 5 kHz.

[0070] The effective propagation index of an optical fiber is also known as The "phase constant of the mode" is defined by the following relationship: ng = ne - Xdne / dX, where ng is the group index and X is the wavelength of the optical signal guided by the optical fiber. The effective propagation index of an optical fiber depends on the dimensions of the fiber's core and the materials forming both the core and the cladding. It can be determined experimentally or by numerical simulation.

[0071] Additive manufacturing devices are also known as "3D printers".

[0072] Chapter II: Examples of embodiments

[0073] Figure 1 represents an additive manufacturing system 2 for a metal part 4. The system 2 comprises:

[0074] - an apparatus 10 for forming successive layers stacked one on top of the other to form, by stacking these layers, a set of 4 pieces, and

[0075] - a device 12 for detecting a defect during the manufacture of assembly 4 of parts.

[0076] In this embodiment, by way of illustration, the apparatus 10 implements the additive manufacturing process known as "Selective Laser Powder Bed Fusion" and designated by the acronym L-PBF ("Laser Powder Bed Fusion or SLM, Selective Laser Melting"). Such an apparatus is well known. Thus, only its main components are presented. The apparatus 10 comprises:

[0077] - a support 20,

[0078] - an actuator 22 which moves the support 20 downwards in successive steps,

[0079] - a laser source 24 that emits a laser beam 26 that scans the surface of a bed 28 of powder following a predetermined path

[0080] - a powder reservoir 30 equipped with a movable bottom 32,

[0081] - a scraper 34 capable of scraping the surface of the reservoir 30 to deposit on the set of 4 parts, in the process of being manufactured, a new layer of powder, and

[0082] - an actuator 38 which moves, by successive steps, the movable bottom 32 upwards.

[0083] The support 20 has an upper face 40 and, on the opposite side, a lower face 42. The set 4 of parts is manufactured on the upper face 40. The upper face 40 is horizontal.

[0084] Here, the powder used in the apparatus 10 is a metallic powder such as 316L stainless steel powder.

[0085] The fault detection device 12 comprises the support 20 and an electronic processing unit 50. Here, the support 20 is therefore part of both the device 10 and the fault detection device 12.

[0086] The support 20 is now described in more detail with reference to figures 2 to 4.

[0087] The support 20 is instrumented, that is to say, it has N points Pp ([Fig.4]) of Temperature or acoustic signal measurements, where the index p is a sequence number that identifies a particular measurement point. The measurement points Pp are all contained within a horizontal measurement plane Pm ([Fig. 3] and 4) located below the top face 40. The distance between the plane Pm and the face 40 is preferably less than 5 mm or 3 mm.

[0088] Points Pp are distributed in this plane Pm such that a first group Gi ([Fig. 4]) of several measurement points is located under the assembly 4 of parts during its manufacture. The number NGi of measurement points in group Gi is chosen so that the density of measurement points under the assembly 4 of parts is less than 3 cm² or 2 cm². The density of measurement points is equal to the surface area of ​​the face of the assembly 4 of parts in contact with the face 40 divided by the number of measurement points located under the assembly 4 of parts. In general, the number Ngi is greater than four or eight.

[0089] In this embodiment, the set of parts 4 comprises two identical parts manufactured simultaneously in parallel on the face 40 of the support 20. Each part is mechanically distinct from the other and each directly bears against a respective area of ​​the face 40. Here, each of the parts in the set 4 is a parallelepiped. In [Fig. 4], the bearing areas of these parts on the face 40 are represented by rectangles Bi and B2. Here, the dimensions of rectangles Bi and B2 are identical and equal to 45 mm by 12 mm. The measurement points Pu to Pi5 are located inside rectangle Bi, and the measurement points P15 to P22 are located inside rectangle B2. Thus, in this example, group Gi comprises the measurement points Pu to P15 and Pi8 to P22.

[0090] Here, measurement points Pp are also distributed in the plane Pm so that a second group G2 ([Fig. 4]) of NG2 measurement points is not located under the set 4 of parts but around each of the support areas Bi and B2. For this purpose, preferably, the number NG2 is greater than two, four, or eight. Here, the number NG2 of measurement points in group G2 is chosen so that the density of measurement points located outside the support zones is also less than 3 cm2 or 2 cm2. Group G2 includes all measurement points that do not belong to group Gp. Thus, in the example of [Fig.4], group G2 includes measurement points Pi to P10, Pi6, Pn, P23 and P24.

[0091] In the case where the support 20 has several measurement points in each of the Giet G2 groups, the total number N of measurement points is generally greater than ten, twenty, or thirty. Here, the total number N of measurement points is equal to twenty-four.

[0092] In this embodiment, the measurement points Pp are located along a spiral-shaped trajectory 54 ([Fig.4]). Here, the spiral winds several times around a vertical axis that passes through the center of the upper face 40.

[0093] A temperature or acoustic signal sensor is located at each of the points Pp. Each of these sensors must be able to withstand, without degradation, a high temperature of up to 900 °C or 1000 °C. To obtain sensors resistant to such temperatures while still allowing the desired density of measurement points and without complicating the fabrication of the device 12, the support 20 contains a single optical fiber 56 ([Fig. 5]) which includes a Bragg grating at each of the measurement points. Hereafter, the Bragg grating located at the measurement point Pp is designated by the same symbol "Pp". The optical fiber 56 extends along the path 54 to pass through each of the measurement points Pp.

[0094] Each Bragg grating Pp is characterized by a wavelength XB>P. The wavelength XB>P is the wavelength of the fundamental resonant frequency fB>p of that Bragg grating. An optical signal incident on the Bragg grating Pp is reflected by that Bragg grating Pp only if its wavelength is equal to the wavelength XB>P or to the wavelength XB>p,k of one of its harmonics, where k is the order number of the harmonic. Typically, the order number k of the harmonics used is less than five.

[0095] Each Bragg grating Pp is formed by a succession, along the optical axis of the fiber 56, of patterns spaced from each other at a regular spacing Ap. Under these conditions, the wavelength XB>P is defined by the following relation (1): XB>P = 2*ne *AP, where:

[0096] - ne is the effective index of optical fiber 56,

[0097] - Ap is the step of the Bragg grating, and

[0098] - the symbol “*” denotes the scalar multiplication operation in this text.

[0099] The wavelength XB p,k of the kth order harmonic is then defined by the relation (2) following: XB>p,k = 2*ne*Ap / k.

[0100] Each pattern of a Bragg grating is for example formed using a pulse from a femtosecond laser.

[0101] The wavelengths XB>P and XB>p,k vary as a function of temperature and deformation, which induces a change in the refractive index ne and the pitch Ap. In particular, these wavelengths XB>P and XB>p,k vary as a function of an applied mechanical deformation, at least one non-zero component of which is parallel to the optical axis of the Bragg grating. Thus, a Bragg grating makes it possible to measure the temperature and / or an acoustic signal that propagates parallel to the optical axis of the Bragg grating.

[0102] In this text, the wavelength of the Bragg grating used to measure the temperature and / or the acoustic signal is called the "interrogated wavelength." The interrogated wavelength is therefore either the fundamental wavelength XB>P or the wavelength XB>p,k of one of the harmonics of this Bragg grating. The following description is given in the particular case where the interrogated wavelength of each Bragg grating is its fundamental wavelength XB>P. However, everything described in this particular case applies to the case where the interrogated wavelength of each Bragg grating is the wavelength XB>p,k of one of the harmonics of this Bragg grating.

[0103] In this embodiment, to identify the response of each Bragg grating, each of the Bragg gratings Pp is sized to exhibit, under normal temperature and pressure conditions, a wavelength XB>P different from those of the other Bragg gratings inscribed in the fiber 56. Here, the XB>P wavelengths are uniformly distributed within the interrogation range of the fiber 56 such that the difference between two successive wavelengths XB>P and XB>p+i is greater than 1 nm and, preferably, greater than 3 nm, or even greater than 10 nm. Here, the interrogation range extends from 1460 nm to 1620 nm and the XB>P wavelengths are spaced at least 6 nm apart.

[0104] Here, the length of each Bragg grating Pp is optimized to be able to measure both a temperature and an acoustic signal. For example, for this purpose, the length of each Bragg grating is between 1 mm and 20 mm.

[0105] The fiber 56 may include a coating made of a material such as a polymer, metal, ceramic, adapted to the operational operating temperature range of the measurement points Pp.

[0106] The fiber 56 is integrated into the support 20 in a removable manner to allow its replacement with another optical fiber without requiring a change to the entire support 20. To this end, in this first embodiment, the support 20 comprises a top cover 60, a base 62 and means 64 for fixing, without any degree of freedom, the cover 60 to the base 62.

[0107] The cover 60 is here a metal disc with a thickness e60 of less than 5 mm and, preferably, less than 3 mm. Here, the thickness e60 is 2.5 mm. The upper face of the cover 60 forms the upper face 40 of the support 20. The cover 60 also has a flat lower face on the side opposite the face 40.

[0108] The base 62 is a metal cylinder with a cross-section identical or substantially identical to that of the cover 60. The base 62 has an upper face 66 which extends mainly in a horizontal plane.

[0109] The base 62 also includes a groove 68 cut into its face 66. This groove is dimensioned to receive the fiber 56. For this purpose, the groove 68 follows the trajectory 54.

[0110] The fastening means 64 are reversibly movable between:

[0111] - an assembled state, visible in [Fig.2], in which the cover 60 is fixed without any degrees of freedom on basis 62, and

[0112] - a disassembled state in which the cover 60 can be removed from the base 62.

[0113] For example, here, the means 64 include screws 70 which pass through the cover 60 and are screwed into respective holes 72 made in the face 66 of the base 62.

[0114] In the assembled state, the lower face of the cover is pressed against the face 66 of the base 62 so that the fiber 56 is trapped inside the groove 68. Optionally, a thermally conductive paste is interposed between the fiber 56 and the walls of the groove 68 to improve heat conduction between the cover 60 and the fiber 56.

[0115] Fig. 5 represents in more detail the fiber 56 and a possible embodiment of the processing unit 50.

[0116] The fiber 56 extends between a distal end 80 and a proximal end 82 connected to the unit 50. The end 80 is located at the end of the groove 68 closest to the center of the axis of symmetry of the base 62. For example, the fiber 56 is a single-mode optical fiber also known by the acronym SMF (“Single Mode Fiber”).

[0117] Unit 50 is configured to obtain temperature or acoustic signal measurements at each of the measurement points Pp when the additive manufacturing process is implemented and to detect, from these measurements, a defect in the assembly 4 of parts during its manufacture. In particular, in this first embodiment, unit 50 makes it possible to detect the occurrence of a delamination between one of the parts of assembly 4 and the face 40 of the support 20. To this end, it comprises:

[0118] - a 90 laser source,

[0119] - an optical sensor 92,

[0120] - a programmable microprocessor 94, and

[0121] - a memory 96.

[0122] The laser source 90 is optically connected to the end 82 of the fiber 56. It emits an optical signal that propagates in the core of the fiber 56 in a direction D pointing towards the end 80. The wavelength of the optical signal emitted by the source 90 is in the optical range. For example, here, the source 90 is a scanning laser source that emits a single-frequency optical signal at a wavelength Xs that varies over time to scan a predefined range of wavelengths of interest, referred to here as the "interrogation range." Here, the interrogation range is the range extending from 1460 nm to 1620 nm.

[0123] The sensor 92 is also optically connected to the end 82 of the optical fiber 56. The sensor 92 measures the optical signal backscattered by the optical fiber 56. The backscattered optical signal propagates in the optical fiber 56 in the opposite direction to direction D. The sensor 92 has an observation spectral range located in the optical domain and which encompasses the interrogation range.

[0124] The microprocessor 94 executes the instructions stored in memory 96. Memory 96 contains the data and instructions necessary for the execution of the process of [Fig.6] or 9.

[0125] The unit 50 is also connected to a human-machine interface 98 in order to signal the presence of a fault to a human. For example, the human-machine interface 98 includes a screen or an indicator light.

[0126] Unit 50 is also connected to device 10 to control this device and, in particular, to control its shutdown.

[0127] The operation of manufacturing system 2 is now described with reference to the process of [Fig.6] in the particular case where Bragg gratings are only used to measure temperatures.

[0128] The additive manufacturing process of the set 4 of parts using the system 2 includes a phase 150 of manufacturing the set 4 of parts and, in parallel, a phase 152 of detecting, using the device 12, a defect during the manufacturing of the set 4 of parts.

[0129] Phase 150 of manufacturing the set 4 of parts proceeds mainly as follows.

[0130] During a step 160, the actuator 22 is commanded to lower the support 20 by a predetermined step downwards and the actuator 38 is commanded to raise the bottom 32 by a predetermined step upwards.

[0131] Then, in a step 162, the scraper 34 is commanded to move a thin layer of metal powder from the surface of the reservoir 30 to the surface of the bed 28. This thin metal layer then covers the upper face of the assembly 4 of parts being manufactured.

[0132] In step 164, the laser source 24 is controlled so that the laser beam 26 scans the surface of the bed 28 along a predetermined path. The laser beam 26 is focused onto the surface of the bed and melts the metal powder along its path. By melting and then resolidifying, the layer of metal powder bonds with the upper surface of the assembly 4 of metal parts being manufactured. Thus, a new layer of metal is deposited on the upper surface of the assembly 4 of parts.

[0133] Once the beam 26 has traveled the entire predetermined path, the process returns to step 160 to deposit a new layer of metal on the set 4 of parts.

[0134] Steps 160 to 164 are repeated until the set 4 of parts is fully manufactured or manufacturing phase 150 is interrupted beforehand.

[0135] During phase 152 of fault detection, the following steps are repeated at regular intervals. Here, the following steps are repeated at an acquisition frequency fa. In the embodiment described here, where Bragg gratings are used only to measure temperature, the frequency fa can be chosen to be less than 1 kHz. For example, in this case, the frequency fa is chosen to be between 1 Hz and 500 Hz and, preferably, between 10 Hz and 500 Hz or between 100 Hz and 500 Hz. Here, the frequency fa is equal to 10 Hz.

[0136] Phase 152 begins with a step 168 of querying the Bragg gratings Pp. For example, step 168 comprises the following two operations:

[0137] - during an operation 170, the laser source 90 emits, in the optical fiber 56, a signal optics that scan the entire interrogation range, and

[0138] - in parallel, during an operation 172, the sensor 92 measures the retro- optical signal distributed by each of the Bragg Pp networks.

[0139] Next, in a step 174, the microprocessor 94 determines a current value of the wavelength XB>P for each of the N Bragg gratings Pp. Preferably, in this step, the unit 50 filters the acquired values ​​of the wavelength XB>P in order to eliminate the high-frequency components of this measured signal. Indeed, the temperature Tp at a measurement point Pp varies slowly. To this end, the unit 50 implements a low-pass filter whose cutoff frequency at -3 dB is less than fa / 2 and 500 Hz. If the frequency fa / 2 is greater than 100 Hz, preferably, the cutoff frequency is also chosen to be greater than 100 Hz. Subsequently, the current value of the wavelength / .Hp used to measure the temperature Tp is denoted "7.BîP t".

[0140] During a step 176, the microprocessor 94 establishes a temperature measurement Tp at each of the measurement points Pp. For example, for this purpose, the memory Unit 96 contains a pre-recorded reference value XBjP>ref for the wavelength XB,p of each of the Bragg gratings Pp. The reference value was measured under reference conditions. For example, the reference value was measured at a temperature of 25°C. Memory 94 also contains a pre-recorded table that converts the difference between the values ​​XB>P>T and XBjPjref into a temperature value Tp. Here, unit 50 therefore establishes the temperature Tp from the reference value XBjP>ref and the current value XB>P>T of the wavelength XB>P determined in step 174.

[0141] Then, in step 180, unit 50 calculates, for each measurement point Pp, an average value Tm>p of the temperature Tp over a sliding time window. The sliding time window ends at the instant when the last measurement of the temperature Tp has been established. The duration AF of the sliding time window is equal to the time required to deposit Nc metallic layers, where Nc is a rational number generally between 0.1 and 5 or between 0.1 and 10 and, preferably, between 1 and 3 or between 1 and 2. For example, here, Nc is equal to three. Thus, during the sliding time window, steps 160 to 164 are executed Nc times.

[0142] During step 182, for each measurement point Pp, unit 50 also calculates the standard deviation op of the temperatures Tp established during the same sliding time window. Thus, during step 182, unit 50 calculates:

[0143] - the standard deviations Oi>p of the temperatures measured at the measurement points of the GB group and

[0144] - the standard deviations o2,P of the temperatures measured at the measurement points of the group G2.

[0145] During a step 184, unit 50 calculates an arithmetic mean of the standard deviations o2>p calculated during step 182 to obtain a reference standard deviation o2ref.

[0146] Then, in a step 186, for each measurement point Pp of the group Gi, the microprocessor 94 detects a defect at that measurement point from the ratio Ol,p / O2îre5 OU.

[0147] - OijP is the standard deviation calculated at point Pp during the last execution of step 182, and

[0148] - o2ref is the reference standard deviation calculated during the last execution of the step 184.

[0149] For example, in step 186, unit 50 compares the ratio 0ijP / 02jref to a predetermined threshold Sref and triggers a defect report if the ratio 0ijP / 02jref falls below this threshold Sref. For example, the threshold Sref is chosen to be half the lowest value of the ratio 0ijP / 02jref observed when no manufacturing defects occur during the manufacture of assembly 4 of parts.

[0150] If a defect is detected during step 186, the process continues with a step 190 of controlling the device 10 and / or the human-machine interface 98. For example, during step 190, unit 50 controls device 10 to immediately stop the manufacturing of the assembly 4 of parts or to modify a manufacturing parameter of the assembly 4 of parts in order to mitigate the detected defect. During step 186, unit 50 also typically controls the human-machine interface 98 to inform the user of device 10 that a defect has been detected.

[0151] If no defect is detected, the process returns directly to step 168.

[0152] Figures 7 and 8 represent the evolution over time, respectively, of the temperatures Tm>i0 to Tm>i6 and the ratios O10 / O2jref to Oie / c^ref. These temporal evolutions were measured in the case where delamination of set 4 of parts occurs at points Pu and Pi2. This delamination occurs approximately 25 minutes after the start of the manufacturing of set 4 of parts. In this particular case, the manufacturing of set 4 of parts was continued to completion despite the existence of this delamination in order to trace the temporal evolution of the temperatures Tm>p and the corresponding ratios op / o2,ref from the beginning to the end of the manufacturing of set 4 of parts. As can be seen in [Fig. 8], the occurrence of delamination at points Pu and Pn results in a significant decrease in the ratios O10 / o2.ief and O10 / c^ref. lAh.rd which does not occur for the other ratios. On the other hand, as illustrated in the [Fig.[7], the appearance of this defect is much more difficult to discern solely from the temporal evolution of average temperatures Tm>p. .

[0153] Figure 9 represents a detection method that can be implemented with The same equipment as that described with reference to [Fig. 1] is used, except that acoustic signals are also measured and used. In this case, the acquisition frequency fa is greater than 300 Hz and, preferably, greater than 1 kHz and, even more advantageously, greater than 5 kHz or 10 kHz. Here, the frequency fa is 10 kHz. Indeed, since the acquisition frequency fa is greater than 1 kHz, each Bragg grating Pp can also be used to measure an acoustic signal Sap that propagates parallel to the axis of the optical fiber 56 at point Pp. Now, certain defects that appear during the manufacture of the assembly 4 of parts produce a characteristic acoustic signal. Examples of such defects include the appearance of a fracture, a porosity defect, or the propagation of a crack.

[0154] The process implemented by unit 50 is then the same as that of [Fig.6] except that, in addition to phase 152, it includes a phase 202 of detecting a fault from the measured acoustic signals Sap.

[0155] Phase 202 begins with a step 208 of interrogating the Bragg gratings Pp. Step 208 can be carried out like step 168 or, preferably, by implementing a technique that allows for the precise extraction of high-frequency variations of each wavelength XB>P. For example, this technique is that described in the following article: Arnaud Recoquillay et al.: “Guided wave imaging of composite plates using passive acquisitions by fiber Bragg gratings”, J. Acoustic, Soc. Am. 147(5), May 2020. Here, step 208 is common to the detection phases 152 and 202. Step 208 replaces step 168 and is executed only once at the frequency fa. Thus, each Bragg grating Pp is used both to measure the temperature Tp and an acoustic signal Sap at the measurement point Pp.This is made possible by the fact that the temperature information Tp is encoded by the low-frequency components of the measured signal, while the acoustic signal information Sap is encoded by the high-frequency components of the same measured signal.

[0156] Next, in step 214, the microprocessor 94 determines a current value of the wavelength XB>P for each of N Bragg gratings Pp. In this step, unit 50 filters the acquired values ​​of the wavelength XB>P to eliminate the low-frequency components of this measured signal. To do this, unit 50 implements a bandpass filter that selects only the high-frequency components of the signal measured by each of the Bragg gratings. Typically, the -3 dB cutoff frequency of this filter is higher than that of the low-pass filter implemented in step 174 and also higher than 20 Hz, 100 Hz, or 300 Hz. The -3 dB cutoff frequency of this filter is less than or equal to fa / 2. The signal thus filtered is the acoustic signal Sap measured at point Pp.

[0157] Then, in step 216, unit 50 processes each of the measured acoustic signals Sap as described, for example, in application WO2017216059A1, to detect a fault from such an acoustic signal. More specifically, in step 216, a classifier is used to classify the acoustic signal Sap either into the category of signals representative of a fault or, conversely, into the category of signals not representative of a fault.

[0158] The process then proceeds to step 190 only if the acoustic signal Sap has been classified in the category of acoustic signals representative of a defect.

[0159] Figure 10 shows a support 220 that can be used in place of the support 20. The support 220 is identical to the support 20 except that the cover 60 is omitted and the base 62 is replaced by a base 222. The base 222 has a groove 228 identical to the groove 68 except that it is cut into the lower face 224 of the base 222. In this embodiment, the depth of the groove 228 is sufficient so that the bottom of the groove is located less than 5 mm or less than 3 mm from the upper face 40 of the base 222. The optical fiber 56 is then inserted into this groove 228 from the lower face of the base 222 and then pushed into the groove 228 until it is pressed against the bottom of this groove 228. The optical fiber 56 is then held pressed against the bottom of the groove 228, for example, by means of an adhesive paste.

[0160] Chapter III: Variants:

[0161] The set 4 of parts may comprise a single part or, on the contrary, more than three or five parts mechanically independent of each other.

[0162] The number NG2 of measurement points located under any part to be manufactured may be zero or equal to one or two.

[0163] In alternative configurations, the wavelengths XB>P are all equal. In this case, each Bragg grating is configured to be weakly reflective at the wavelength XB>P, meaning that it reflects less than 5% of the incident optical signal at this wavelength. Generally, each Bragg grating reflects at least 0.5% or 1% of the incident optical signal at the wavelength XB>P. In this alternative configuration, for example, the time it takes for the optical signal reflected by a Bragg grating to be received allows the response of that Bragg grating to be distinguished from the responses of the other Bragg gratings inscribed in the optical fiber. However, this alternative configuration does not allow the measurement of acoustic signals.

[0164] Other trajectories than a spiral-shaped trajectory are possible for groove 68. For example, groove 68 can also follow a zigzag trajectory.

[0165] Alternatively, the groove 68 is cut into the lower face of the cover 60 and not into the upper face 66 of the base 62. In another alternative, the groove 68 is cut into both the upper face of the base 62 and the lower face of the cover 60.

[0166] In the case where each of the Bragg gratings is used only to measure a respective acoustic signal Sap, then the optical fiber 56 can extend in a plane Pm located more than 5 mm from the upper face 40.

[0167] In the case where a Bragg grating is used solely to measure a temperature variation, preferably its length is less than or equal to 2 mm or 1 mm. This helps to mitigate the effect of thermal gradients. Conversely, if a Bragg grating is used solely to measure an acoustic signal Sap, then its length can be specifically optimized for measuring this acoustic signal Sap without taking into account that it must also be capable of measuring a temperature.

[0168] Alternatively, a first part of the Bragg gratings is used to measure the temperature and a second part of the Bragg gratings of optical fiber 56, different from the first part, is used to measure the acoustic signals Sap In one particular variant, a Bragg grating of optical fiber 56 belongs only to the first or second part. In the latter case, the same Bragg grating of optical fiber 56 is either used only to measure the temperature Tp or only to measure the acoustic signal Sap. Typically, the lengths of the Bragg gratings in the first part are optimized solely for temperature measurements, and the lengths of the Bragg gratings in the second part are optimized solely for acoustic signal measurements.

[0169] The medium may comprise more than one optical fiber. For example, alternatively, the medium comprises only a first and a second optical fiber. These two optical fibers are connected to the processing unit 50, and each of these optical fibers is used as described in the specific case of fiber 56. In this case, these two fibers can be received in two separate channels which, preferably, do not intersect. Preferably, the first optical fiber comprises only Bragg gratings whose lengths are optimized solely for temperature measurement, and the second optical fiber comprises only Bragg gratings whose lengths are optimized solely for acoustic signal measurement.

[0170] Other embodiments of the fastening means 64 are possible. For example, alternatively, the cover has a threaded portion and the base has a tapped hole into which the threaded portion of the cover can be screwed to move from the disassembled to the assembled state. For example, the face 66 forms the bottom of this tapped hole. In this alternative, the threaded portion of the fastening means forms a single piece of material with the cover.

[0171] In a particularly simplified embodiment, the fiber 56 is not replaceable. For example, the cover 60 is welded to the face 66 of the base 62. In this case, the removable fastening means 64 are omitted.

[0172] When unit 50 automatically controls device 10 in response to fault detection, the human-machine interface 98 can be omitted. Conversely, unit 50 may not control device 10 in response to fault detection and may simply report the existence of the fault via the human-machine interface 98. In this latter case, it is the responsibility of the device 10 operator to implement the necessary actions to address the fault reported by unit 50.

[0173] The detection device 12 can also be implemented in other additive manufacturing devices for an assembly of metal parts. For example, it can be implemented with a device implementing the additive manufacturing process known as Selective Laser Sintering or SLS, or Directed Energy Deposition, also known as DED. It can also be implemented in an additive manufacturing device for an assembly of metal parts that does not use a laser. to melt the metal powder. For example, it can be implemented in a device implementing the WAAM ("Wire Arc Additive Manufacturing") additive manufacturing process.

[0174] What has been described here in the particular case of the additive manufacturing of a set of metal parts also applies to the additive manufacturing of a set of parts made of other materials and, in particular, to the additive manufacturing of a set of polymer parts.

[0175] Instead of using the wavelength XB>P of each Bragg grating, it is possible to use instead the wavelength XB>p,k of a harmonic of this Bragg grating.

[0176] Alternatively, a defect at a measurement point is detected simply using the standard deviations Oi>p and without using the standard deviation o2,ref or the standard deviations o2>p. For example, a defect is detected when the slope of the time variation of one of the standard deviations Oi>p falls below a predetermined threshold or deviates from the standard deviations calculated for the other measurement points in group Gi by a value greater than another predetermined threshold. In this case, the number NG2 of measurement points can be zero.

[0177] In a simplified variant, steps 182 and 184 are omitted and a fault is detected solely from temperature measurements without using standard deviations.

[0178] Each standard deviation op can also be calculated directly from the XB>P wavelength measurements before they are converted into a temperature measurement expressed in degrees. For this purpose, for example, at each regular interval and for each measurement point Pp, unit 50 calculates the average of the XB>P wavelengths measured during the sliding time window. Then, the standard deviation op of the variations in the XB>P wavelength measured during this sliding time window is calculated. The standard deviation op thus obtained is representative of the standard deviation of the temperature Tp during this sliding time window.

[0179] In a simplified embodiment, group G2 comprises only one measurement point. In this case, the standard deviation o2>ref is equal to the standard deviation o2>p calculated for the single measurement point of group G2. In such an embodiment, there may exist measurement points in group G2 that are therefore not used to detect a manufacturing defect.

[0180] Step 180, which calculates the average temperature Tm>p, can be omitted. In this case, the calculation of the average temperature Tm>p is performed only during step 182 to calculate the standard deviations op.

[0181] During step 184, the reference standard deviation o2ref can be calculated from a weighted average of the standard deviations o2>p.

[0182] Several of the variants described above can be combined in the same embodiment.

[0183] Chapter IV: Advantages of the embodiments described:

[0184] The fact that the support 20 is used both to make the apparatus 10 and the detection device 12 simplifies the making of the detection device because it is not necessary to integrate additional parts into the apparatus 10 to serve as support for the measurement points.

[0185] Using an optical fiber with a Bragg grating at each measurement point makes it possible to substantially increase the number of measurement points that can be placed in the support. This is because the number of measurement points can be increased without increasing the size of the groove that receives the optical fiber, simply by adding Bragg gratings to the optical fiber. Thus, the number of measurement points can be increased while maintaining the same overall size. This allows for a much higher density of measurement points and therefore a spatial resolution superior to that which can be obtained when thermocouples are used.

[0186] Moreover, similarly to a thermocouple, a Bragg network allows for the measurement of high temperatures.

[0187] Finally, the acquisition frequency fa of the wavelength reflected by a Bragg grating can be very high. Thanks to this, a Bragg grating can also be used to measure an acoustic signal. Thus, the same optical fiber can be used to measure, simultaneously or alternately, temperatures and acoustic signals. This capability can then be exploited to detect a greater number of defects during manufacturing. It is emphasized here that Rayleigh scattering of an optical fiber does not allow the measurement of acoustic signals.

[0188] Moreover, because of the fact that optical fiber has Bragg gratings, the constraints on the groove trajectory are less than when Rayleigh scattering is used.

[0189] Placing the optical fiber in a groove between the base and the cover allows for easy replacement of the optical fiber with another optical fiber containing, for example, more Bragg gratings. This is made possible by the fact that a Bragg grating allows for the measurement of temperature and / or an acoustic signal without requiring permanent anchoring of the optical fiber in the support 20.

[0190] Placing the optical fiber in the groove 228 cut into the underside of the support 220 also makes it easy to replace the optical fiber with another optical fiber.

[0191] Using Bragg gratings inscribed in the same optical fiber 56 to measure both temperatures at different measurement points and acoustic signals at different measurement points increases the device 12's ability to detect a defect. Furthermore, this improvement is achieved without complicating the design of the support 20.

[0192] Using the same Bragg grating to measure, at the same measurement point, both the temperature and the acoustic signal simplifies the realization of the support 20.

[0193] The fact that the XB>P wavelengths of each Bragg grating are different makes it easier to demultiplex the backscattered signals and thus increase the number of measurement points located along the optical fiber axis. This also makes it possible to associate a backscattered signal more precisely with a particular Bragg grating and therefore to know with high accuracy the location, along the fiber axis, where the measurement is performed.

[0194] An acquisition frequency fa greater than 1 kHz allows an acoustic signal to be measured using this Bragg network.

[0195] The ability of the detection device to measure temperatures above 500°C allows this detection device to be used with virtually all additive manufacturing processes and, in particular, additive manufacturing processes of metal parts where the temperature of the support can be very high.

[0196] Detecting a defect from the standard deviation Oi p improves the sensitivity of the detection process.

[0197] Detecting a defect from the ratio 0i>p / 02,ref makes it possible to increase the sensitivity of the detection process even further.

Claims

1. Demands A device for detecting defects during the manufacturing of a part using an additive manufacturing process; this device comprises: - a support (20; 220) comprising: - a top surface (40) on which the part is manufactured when the additive manufacturing process is implemented, - measurement points (Pi to P24) for temperature or an acoustic signal, these measurement points being contained within a measurement plane (Pm) located under the top face and distributed within this measurement plane in such a way that at least one of these measurement points is located under the part when the additive manufacturing process is implemented, - an optical fiber (56) which extends from a proximal end (82) to a distal end (80) passing through each of the measurement points (Pi to P24), - a processing unit (50) connected to the proximal end (82) of the optical fiber and configured to obtain temperature or acoustic signal measurements at each of the measurement points when the additive manufacturing process is implemented and to detect, from these measurements, a defect in the part during its manufacture by the additive manufacturing process, characterized in that: - the optical fiber includes, at each of these measurement points, a Bragg grating, and - The processing unit (50) is configured: - to obtain the measurement of the temperature or the acoustic signal at each of the measurement points from a measurement of an optical signal that has interacted with the Bragg grating located at that measurement point, and - to perform the following steps: - for each measurement point in a first group of measurement points and at regular time intervals, the calculation of a standard deviation Oi>p representative of the amplitude of the variations in the temperature measured during a predetermined sliding time window at the level of this measurement point, the measurement points of this first group being located under the part being manufactured, then - the detection of a defect at a measurement point of the first group from the different successive values ​​of the standard deviation Oi>p calculated for each regular time interval.

2. Device according to claim 1, wherein the support comprises: - a base (62) having an upper face (66), - a cover (60) having an upper face (40) and, on the opposite side, an lower face, the upper face of the support being constituted by the upper face of the cover, - means (64) for fixing the cover on the base, these fixing means being reversibly movable between: - an assembled state in which the cover is fixed without any degree of freedom on the base and the lower face of the cover is pressed against the upper face of the base, and - a disassembled state in which the cover can be detached from the base, - a groove (68) cut into the upper face of the base or in the lower face of the cover, and - the optical fiber (56) is received inside this groove in a removable manner.

3. Device according to claim 1, wherein: - on the side opposite its upper face, the support (220) has a lower face (224), and - the support has a groove (228) cut into this lower face of the support, this groove being able to receive the optical fiber in a removable manner.

4. Device according to any one of the preceding claims, wherein the processing unit (50) is configured: - to obtain temperature measurements using a first part of the Bragg gratings when the additive manufacturing process is implemented and to detect, from these temperature measurements, a defect in the part during its manufacture by the additive manufacturing process, and - to obtain acoustic signal measurements at the level of a second part of the Bragg gratings when the additive manufacturing process is implemented and to detect, from these acoustic signal measurements, a defect in the part during its manufacture by the additive manufacturing process.

5. Device according to claim 4, wherein the processing unit (50) is configured to measure both temperature and acoustic signal using the same Bragg grating.

6. Device according to any one of the preceding claims, wherein the number of Bragg gratings is greater than ten or twenty.

7. A device according to any one of the preceding claims, wherein each Bragg grating of the optical fiber is characterized by an interrogated wavelength at which it reflects the incident optical signal and, for each Bragg grating of the optical fiber, this interrogated wavelength of that Bragg grating is separated from the interrogated wavelengths of the other Bragg gratings of the optical fiber by at least 1 nm.

8. Device according to any one of the preceding claims, wherein the processing unit (50) is capable of acquiring an optical signal having interacted with one of the Bragg gratings at an acquisition frequency greater than 1 kHz.

9. Device according to any one of the preceding claims, wherein the processing unit is capable of obtaining a temperature measurement, at one of the measurement points, which exceeds 500°C.

10. A method for detecting, using a detection device according to any one of the preceding claims, a defect during the manufacture of a part by an additive manufacturing process, this detection method comprising: - for each measurement point of a first group of measurement points and at regular time intervals, the calculation (182) of a standard deviation OijP representative of the amplitude of the temperature variations measured during a predetermined sliding time window at the level of this measurement point, the measurement points of this first group being located under the part being manufactured, then - the detection (186) of a defect at the level of a measurement point of the first group from the different successive values ​​of the standard deviation OijP calculated for each regular time interval.

11. A method according to claim 10, wherein the method comprises: - for each measurement point of a second group of measurement points and at regular time intervals, the calculation (182) of a standard deviation σ2,P representative of the amplitude of the temperature variations

12. measured during a predetermined sliding time window at this measurement point, each measurement point in this second group not being located under any metal part being manufactured, then - the calculation (184) of an average of the standard deviations o2>p to obtain a reference standard deviation 02>ref, then - the detection (186) of a fault at a measurement point of the first group from the ratio 0ijP / 02jref calculated for that measurement point. Additive manufacturing system for a part, this system comprising: - a device (10) for forming successive layers stacked one on top of the other to form, by stacking these layers, the part to be manufactured, - a device (12) for detecting a defect during the manufacturing of the part by the apparatus (10), this device comprising: - a support (20; 220) comprising: - a top surface (40) on which the part is manufactured when the additive manufacturing process is implemented, - measurement points (Pi to P24) for temperature or an acoustic signal, these measurement points being contained within a measurement plane (Pm) located under the top face and distributed within this measurement plane in such a way that at least one of these measurement points is located under the part when the additive manufacturing process is implemented, - a configured processing unit (50): - to obtain temperature or acoustic signal measurements at each measurement point when the additive manufacturing process is implemented, - to detect, from these measurements, a defect in the part during its manufacture by the additive manufacturing process, and - to, in response to the detection of a defect, control a human-machine interface or the forming device so as to stop the manufacture of the part or to modify parameters of the forming device, characterized in that the detection device conforms to any one of claims 1 to 9. 25

13. System according to claim 12, wherein the successive layer formation apparatus (10) is capable of forming successive layers of metal stacked one on top of the other to form, by stacking these layers, the set of metal parts to be manufactured.