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 manufacture of a part

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

[0002] Such a known detection device is disclosed in application US2020290121A1. This device is advantageous in that it makes it possible to detect any manufacturing defect that results in a modification of the heat flow between the part being manufactured and the support on which it is manufactured. In particular, this method makes it possible to detect the detachment of the part being manufactured from the support on which it is manufactured. Thus, if a defect is detected, in response, it is possible to interrupt the manufacturing process before its end to avoid wasting material unnecessarily. This detection device is also simple to integrate into an additive manufacturing device because the temperature sensors are integrated into the support on which the part is manufactured.

[0003] On the other hand, the spatial resolution of this fault detection device is limited by the number of temperature sensors integrated in 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 the reason why in the detection device of application US2020290121A1, the temperature sensors are thermocouples. However, thermocouples are quite bulky. In addition, each temperature sensor is connected to an electronic processing unit via a respective wire connection. Thus, the support includes not only the temperature sensors but also, for each of them, a groove for the passage of the wires which connects it to the processing unit.The space occupied by the grooves used for the passage of the wires substantially limits the number of locations, in the support, where it is possible to accommodate a temperature sensor. Thus, with the detection device described in application US2020290121A1, it is very difficult to obtain a high density of measurement points and therefore a high spatial resolution. Because of this, defects located between two temperature sensors are difficult to detect and / or are detected very late, that is to say, generally, at a time when the defect has grown to 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] - an upper face on which the part is manufactured when the fa process additive building is implemented,

[0008] - temperature or acoustic signal measurement points, these points of measurement being contained in a measurement plane located under the upper face and distributed in 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 the measurements of the temperature or the acoustic signal at each of the measuring 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] in which:

[0011] - the support comprises an optical fiber which extends from a proximal end 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 the acoustic signal at each of the measurement points from a measurement of an optical signal having interacted with the Bragg grating located at this 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 an upper face,

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

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

[0018] - a mounted 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 furrow dug in the upper face of the base or in the lower face of the cover, 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 has a lower face, and

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

[0025] 3) The processing unit is configured:

[0026] - to obtain the 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 a second part of the Bragg gratings 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 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 having 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 of one of the measuring points, which exceeds 500°C.

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

[0034] - for each measuring point of a first group of measuring points and at in regular time interval, 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 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 measuring 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 method may include one or more of the following features:

[0037] 1) The method comprises:

[0038] - for each measurement point of a second group of measurement points and at intervals of regular time, the calculation of a standard deviation o2,P representative of the amplitude of the variations of the temperature measured during a predetermined sliding time window at this measurement point, each measurement point of 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 measuring point of the first group from of the 0ijP / 02jref ratio calculated for this measurement point.

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

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

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

[0044] - a support comprising:

[0045] - an upper face on which the part is manufactured when the fa process additive building is implemented,

[0046] - temperature or acoustic signal measurement points, these points of measurement being contained in a measurement plane located under the upper face and distributed in 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 processing unit configured:

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

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

[0050] - to, in response to the detection of a fault, control a human-interface machine or forming device so as to stop the manufacture of the part or to modify parameters of the forming device.

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

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

[0053] - [Fig.l] is a schematic illustration of the architecture of a fa system additive manufacturing comprising a defect detection device

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

[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.l],

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

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

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

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

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

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

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

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

[0066] Figures 1 to 4 and 9 are oriented relative 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", "upper", "lower" are defined relative to the Z direction.

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

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

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

[0070] The effective propagation index ne of an optical fiber is also known as the "mode phase constant". It is defined by the following relationship: ng = ne - Xdne / dk, 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 core of this optical fiber and the materials forming this core and the optical cladding of this optical fiber. 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] [Fig.l] represents a system 2 for additive manufacturing of a metal part 4. The system 2 comprises:

[0074] - an apparatus 10 for forming successive layers stacked on top of each 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 the assembly 4 of parts.

[0076] In this embodiment, by way of illustration, the apparatus 10 implements the additive manufacturing process known as the “Selective Laser Powder Bed Fusion process” 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, in successive steps, the support 20 downwards,

[0079] - a laser source 24 which emits a laser beam 26 which 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 tank 30 to deposit on the 4-piece set, in production, a new powder coat, and

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

[0083] The support 20 comprises an upper face 40 and, on the opposite side, an in face lower 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 metal powder such as a 316L stainless steel powder.

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

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

[0087] The support 20 is instrumented, that is to say that it comprises N points Pp ([Fig.4]) of measurements of temperature or an acoustic signal, where the index p is a serial number that identifies a particular measurement point. The measurement points Pp are all contained in a horizontal measurement plane Pm ([Fig. 3] and 4) located under the upper 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 so that a first group Gi ( [Fig.4]) of several measurement points is located under the set 4 of parts during its manufacture. The number NGi of measurement points of the group Gi is chosen so that the density of the measurement points under the set 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 set 4 of parts in contact with the face 40 divided by the number of measurement points located under the set 4 of parts. In general, the number NGi is greater than four or eight.

[0089] In this exemplary embodiment, the set 4 of parts comprises two identical parts simultaneously manufactured in parallel on the face 40 of the support 20. Each part is mechanically distinct from the other and each directly rests on a respective area of ​​the face 40. Here, each of the parts of the set 4 is a parallelepiped. In [Fig. 4], the areas of support of these parts on the face 40 are represented by rectangles Bi and B2. Here, the dimensions of the rectangles Bi and B2 are identical and equal to 45 mm by 12 mm. The measurement points Pu to Pi5 are located inside the rectangle Bi and the measurement points Pi8 to P22 are located inside the rectangle B2. Thus, in this example, the group Gi comprises the measurement points Pu to P15 and P18 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 zones Bi and B2. For this purpose, preferably, the number NG2 is greater than two or four or eight. Here, the number NG2 of measurement points of the 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. The group G2 includes all the measurement points which do not belong to the group Gb. Thus, in the example of [Fig.4], the group G2 includes the measurement points Pi to P10, Pi6, Pn, P23 and P24.

[0091] In the case where the support 20 comprises several measurement points in each of the Giet G2 groups, the total number N of measurement points is generally greater than ten or 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 which passes through the center of the upper face 40.

[0093] A temperature sensor or an acoustic signal is located at each of the points Pp. Each of these sensors must be capable of withstanding, without degrading, a high temperature of up to 900°C or 1000°C. To obtain sensors resistant to such temperatures while making it possible to obtain the desired density of measurement points and without complicating the manufacture of the device 12, the support 20 contains a single optical fiber 56 ([Fig. 5]) which comprises a Bragg grating at each of the measurement points. Subsequently, 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 at each of the measurement points Pp.

[0094] Each Pp Bragg grating is characterized by a wavelength XB>P. The wavelength XB>P is the wavelength of the fundamental frequency fB>p of resonance of this Bragg grating. An optical signal incident on the Pp Bragg grating is reflected by this Pp Bragg grating 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 by a regular pitch 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 the optical fiber 56,

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

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

[0099] The wavelength XB p,k of the harmonic of order k 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 wavelength XB>P and the wavelengths XB>p,k vary as a function of the temperature and of a deformation which induces a change in the index ne and of the pitch Ap. In particular, these wavelengths XB>P and XB>p,k vary as a function of an applied mechanical deformation of which at least one non-zero component 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 which 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. Subsequently, the description is made 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 Pp Bragg gratings is sized to have, 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 wavelengths XB>P are uniformly distributed within the interrogation range of the fiber 56 so 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 wavelengths XB>P are spaced from each other by at least 6 nm.

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

[0105] The fiber 56 may comprise 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 in order to allow its replacement by another optical fiber without this requiring changing the entire support 20. For this purpose, in this first embodiment, the support 20 comprises an upper cover 60, a base 62 and means 64 for fixing, without any degree of freedom, the cover 60 on the base 62.

[0107] The cover 60 is here a metal disc whose thickness e60 is less than 5 mm and, preferably, less than 3 mm. Here, the thickness e60 is equal to 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 has a groove 68 dug in its face 66. This groove is di- mentioned to receive the fiber 56. For this purpose, the groove 68 follows the trajectory 54.

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

[0111] - a mounted state, visible in [Fig.2], in which the cover 60 is fixed without any degree of freedom on the basis of 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 comprise 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 mounted 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 the conduction of heat between the cover 60 and the fiber 56.

[0115] [Fig.5] shows 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] The unit 50 is configured to obtain measurements of the temperature or the acoustic signal at each of the measurement points Pp when the additive manufacturing process is implemented and to detect, from these measurements, a defect in the set 4 of parts during its manufacture. In particular, in this first embodiment, the unit 50 makes it possible in particular to detect the appearance of a detachment between one of the parts of the set 4 and the face 40 of the support 20. For this purpose, it comprises:

[0118] - a laser source 90,

[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 which propagates in the core of the fiber 56 in a direction D which points towards the end 80. The wavelength of the optical signal emitted by the source 90 is in the optical domain. For example, here, the source 90 is a scanning laser source which emits a single-frequency optical signal at a wavelength Xs which varies over time to scan a predefined range of wavelengths of interest called here “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 the direction D. The sensor 92 has a spectral observation range located in the optical domain and which encompasses the interrogation range.

[0124] The microprocessor 94 executes the instructions stored in the memory 96. The memory 96 contains the data and instructions necessary for executing the method 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 being. For example, the human-machine interface 98 comprises a screen or an indicator light.

[0126] The unit 50 is also connected to the device 10 to control this device and, in particular, to control its stopping.

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

[0128] The method of additive manufacturing of the set 4 of parts using the system 2 comprises 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 takes place mainly as follows.

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

[0131] Then, during a step 162, the scraper 34 is controlled 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 set 4 of parts being manufactured.

[0132] During a 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 on the surface of the bed and melts the metal powder along its path. By melting and then resolidifying, the layer of metal powder therefore consolidates with the upper face of the set 4 of metal parts being manufactured. Thus, a new layer of metal is deposited on the upper face of the set 4 of parts.

[0133] Once the beam 26 has traveled the entire predetermined path, the method 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 completely manufactured or the manufacturing phase 150 is interrupted before.

[0135] During the phase 152 of detecting a defect, 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 the Bragg gratings are only used to measure a temperature, the frequency fa can be chosen to be less than 1 kHz. For example, in this case, the frequency fa is chosen 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 interrogating 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 broadcast by each of the Bragg Pp networks.

[0139] Then, during a step 174, the microprocessor 94 determines a current value of the wavelength XB>P for each of the N Bragg gratings Pp. Preferably, during 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. For this purpose, the unit 50 here implements a low-pass filter whose cutoff frequency at -3 dB is lower 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 XB>P used to measure the temperature Tp is noted “XB,p,T

[0140] During a step 176, the microprocessor 94 establishes a measurement of the temperature Tp at each of the measurement points Pp. For example, for this, the memory 96 includes a pre-recorded reference value XBjPref 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 for a temperature of 25°C. The memory 94 also includes a pre-recorded table which makes it possible to convert the difference between the values ​​XB>p T and XBjPref into a value of the temperature Tp. Here, the unit 50 therefore establishes the temperature Tp from the reference value XBjPref and the current value XB>pT of the wavelength XB>P determined during step 174.

[0141] Then, during a step 180, the 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 was established. The duration AF of the sliding time window is equal to the time required to deposit Nc metal 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 a step 182, for each measurement point Pp, the unit 50 also calculates the standard deviation op of the temperatures Tp established during the same sliding time window. Thus, during step 182, the unit 50 calculates:

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

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

[0145] During a step 184, the unit 50 calculates an arithmetic mean of the standard deviations o 2>p calculated during step 182 to obtain a reference standard deviation o2ref.

[0146] Then, during a step 186, for each measurement point Pp of the group Gi, the microprocessor 94 detects a fault at this measurement point from the ratio Oi>p 1^1,ref, WHERE I

[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, during step 186, the unit 50 compares the ratio 0ijP / 02jref to a predetermined threshold Sref and triggers the reporting of a defect if the ratio 0ijP / 02jref falls below this threshold Sref. For example, the threshold Sref is chosen to be two times lower than the smallest value of the ratio 0ijP / 02jref observed when no manufacturing defect occurs during the manufacturing of the set 4 of parts.

[0150] If during step 186, a defect is detected, then the method continues with a step 190 of controlling the apparatus 10 and / or the human-machine interface 98. For example, during step 190, the unit 50 controls the apparatus 10 to immediately interrupt the manufacturing of the set 4 of parts or to modify a manufacturing parameter of the set 4 of parts in order to limit the detected defect. During step 186, generally, the unit 50 also controls the human-machine interface 98 to indicate to the user of the apparatus 10 that a defect has been detected.

[0151] If no fault is detected, the method 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 of the ratios 0io / o2,ref to 016 / 02,ref- These temporal evolutions were measured in the case where a detachment of the set 4 of parts occurs at the points Pu and P[2. This detachment occurs approximately 25 min after the start of the manufacture of the set 4 of parts. In this particular case, the manufacture of set 4 of parts was continued until the end despite the existence of this detachment to trace the temporal evolution of the temperatures Tm>p and the ratios 0p / 02,ref corresponding from the beginning to the end of the manufacturing of set 4 of parts. As visible in [Fig.8], the appearance of the detachment at points Pu and P 12 results in a significant drop in the ratios 0ii / 02,ref and 0n / 02,ref which does not occur for the other ratios. On the other hand, as illustrated in [Fig.7], the appearance of this defect is much more difficult to discern solely from the temporal evolution of the average temperatures Tm>p.

[0153] [Fig. 9] represents a detection method capable of being implemented with the same equipment as that described with reference to [Fig. 1] except that, in addition, acoustic signals are measured and used. In this case, the acquisition frequency fa used 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 equal to 10 kHz. Indeed, from the moment when the acquisition frequency fa is greater than 1 kHz, each Bragg grating Pp can also be used to measure an acoustic signal Sap which propagates parallel to the axis of the optical fiber 56 at the point Pp. However, certain defects which appear during the manufacture of the set 4 of parts produce a characteristic acoustic signal. Examples of such defects include the appearance of a fracture or a porosity defect, or even the propagation of a crack.

[0154] The method implemented by the 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 Pp Bragg gratings. Step 208 can be carried out like step 168 or, preferably, by implementing a technique making it possible to precisely extract the 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 detection phases 152 and 202. Step 208 replaces step 168 and is executed only once at frequency fa. Thus, each Bragg grating Pp is used to measure both the temperature Tp and an acoustic signal Sap at the measurement point Pp.This is made possible by the fact that the information on the temperature Tp is coded by the low frequency components of the measured signal while the information on the acoustic signal Sap is coded by the high frequency components of the same measured signal.

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

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

[0158] The method then continues with step 190 only if the acoustic signal Sap has been classified in the category of acoustic signals representative of a fault.

[0159] The [Fig. 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 hollowed out in 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, using 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 can be zero or equal to one or two.

[0163] In variants, the wavelengths XB>P are all equal. In this case, each of the Bragg gratings is configured to be weakly reflective at the wavelength XB>P, i.e. 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 variant, it is for example the time at which the optical signal reflected by a Bragg grating is received which makes it possible to distinguish the response of this Bragg grating from the responses of other Bragg gratings inscribed in the optical fiber. However, this variant does not allow acoustic signals to be measured.

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

[0165] As a variant, the groove 68 is hollowed out in the lower face of the cover 60 and not in the upper face 66 of the base 62. In another variant, the groove 68 is hollowed out both in the upper face of the base 62 and in the lower face of the cover 60.

[0166] In the case where each of the Bragg gratings is only used 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 only used to measure a temperature variation, preferably, its length is less than or equal to 2 mm or 1 mm. Indeed, this makes it possible to mitigate the effect of thermal gradients. Conversely, if a Bragg grating is only used to measure an acoustic signal Sap, then its length can be specifically optimized for the measurement of this acoustic signal Sap without taking into account the fact 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 the optical fiber 56, different from the first part, is used to measure the acoustic signals Sap. In a particular variant, a Bragg grating of the optical fiber 56 belongs only to the first or to the second part. In the latter case, the same Bragg grating of the optical fiber 56 is either only used to measure the temperature Tp or only used to measure the acoustic signal Sap. Typically, the lengths of the Bragg gratings of the first part are only optimized for temperature measurements and the lengths of the Bragg gratings of the second part are only optimized for acoustic signal measurements.

[0169] The support may comprise more than one optical fiber. For example, as a variant, the support 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 particular case of the fiber 56. In this case, these two fibers may be received in two separate grooves which, preferably, do not cross. Preferably, the first optical fiber comprises only Bragg gratings whose lengths are optimized only for the measurement of temperatures and the second optical fiber comprises only Bragg gratings whose lengths are optimized only for the measurement of acoustic signals.

[0170] Other embodiments of the fixing means 64 are possible. For example, alternatively, the cover comprises a threaded portion and the base comprises a tapped hole into which the threaded portion of the cover can be screwed to move from the disassembled state to the assembled state. For example, the face 66 forms the bottom of this tapped hole. In this variant, the threaded portion of the fixing means forms only a single block 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 fixing means 64 are omitted.

[0172] When the unit 50 automatically controls the apparatus 10 in response to the detection of a fault, the human-machine interface 98 may be omitted. Conversely, the unit 50 may not control the apparatus 10 in response to the detection of a fault and simply signal the existence of this fault via the human-machine interface 98. In the latter case, it is up to the operator of the apparatus 10 to implement the actions necessary to take into account the fault signaled by the unit 50.

[0173] The detection device 12 can also be implemented in other additive manufacturing devices for a set of metal parts. For example, it can be implemented with an apparatus implementing the additive manufacturing process known as Selective Laser Sintering on powder bed or SLS, or directed energy deposition also known by the acronym DED. It can also be implemented in an additive manufacturing device for a set of metal parts not using a laser to melt the metal powder. For example, it can be implemented in an apparatus implementing the additive manufacturing process WAAM (Wire Arc Additive Manufacturing).

[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 from another material 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 fault at a measurement point is simply detected using the standard deviations Oi>p and without using the standard deviation o2,ref or the standard deviations o2,P- For example, a fault 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 of the group Gi by a value greater than another predetermined threshold. In this case, the number NG2 of measurement points may be zero.

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

[0178] Each standard deviation op can also be calculated directly from the measurements of the wavelengths XB>P before they are converted into a temperature measurement expressed in degrees. For this, for example, at each regular interval and for each measurement point Pp, the unit 50 calculates the average of the wavelengths XB>P measured during the sliding time window. Then, the standard deviation op of the variations of the wavelength XB>P 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 variant, group G2 has 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 a variant, there may be measurement points of group G2 which are therefore not used to detect a manufacturing defect.

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

[0181] In step 184, the reference standard deviation o2>ref 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 described embodiments:

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

[0185] Using an optical fiber comprising a Bragg grating at each measuring point makes it possible to substantially increase the number of measuring points that can be placed in the support. Indeed, the increase in the number of measuring points can be achieved without increasing the size of the groove that receives the optical fiber, simply by adding Bragg gratings in the optical fiber. Thus, the increase in the number of measuring points can be achieved with constant size. Thanks to this, it is possible to obtain a much higher density of measuring points and therefore a spatial resolution higher than that which can be obtained when thermocouples are used.

[0186] In addition, similar to a thermocouple, a Bragg grating allows high temperatures to be measured.

[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 for measure, simultaneously or alternately, temperatures and acoustic signals. This possibility can then be used to detect a greater number of defects during manufacturing. It is emphasized here that the Rayleigh scattering of an optical fiber does not allow the measurement of acoustic signals.

[0188] Furthermore, because the optical fiber includes Bragg gratings, the constraints on the path of the groove are less than when Rayleigh scattering is used.

[0189] Placing the optical fiber in a groove between the base and the cover makes it easy to replace the optical fiber with another optical fiber comprising, for example, more Bragg gratings. This is made possible by the fact that a Bragg grating makes it possible to measure a temperature and / or an acoustic signal without requiring definitive anchoring of the optical fiber in the support 20.

[0190] Placing the optical fiber in the groove 228 dug in the lower face 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 the temperatures at different measurement points and the acoustic signals at different measurement points increases the ability of the device 12 to detect a defect. Moreover, this improvement is achieved without complicating the production 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 production 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 therefore to increase the number of measurement points located along the axis of the optical fiber. This also makes it possible to more precisely associate a backscattered signal with a particular Bragg grating and therefore to know with great precision the location, along the axis of the fiber, where the measurement is carried out.

[0194] An acquisition frequency fa greater than 1 kHz makes it possible to measure an acoustic signal using this Bragg grating.

[0195] The ability of the detection device to measure temperatures above 500°C allows this detection device to be used with practically 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 GijP makes it possible to improve the sensitivity of the detection method.

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

Claims

Claims

1. Device for detecting a defect during the manufacture of a part by an additive manufacturing process, this device comprising: - a support (20; 220) comprising: - an upper face (40) on which the part is manufactured when the additive manufacturing process is implemented, - measurement points (Pi to P24) of the temperature or of an acoustic signal, these measurement points being contained in a measurement plane (Pm) located under the upper face and distributed in this measurement plane so that at least one of these measurement points is located under the part when the additive manufacturing process is implemented, - a processing unit (50) configured to obtain measurements of the temperature or 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, characterized in that: - the support (20; 220) comprises 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), this optical fiber comprising, at each of these measurement points, a Bragg grating, and - the processing unit (50) is connected to the proximal end (82) of the optical fiber and 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 having interacted with the Bragg grating located at this measurement point.

2. Device according to claim 1, in which the support comprises: - a base (62) comprising an upper face (66), - a cover (60) comprising an upper face (40) and, on the opposite side, a lower face, the upper face of the support being constituted by the upper face of the cover, - means (64) for fixing the cover to the base, these fixing means being reversibly movable between: - a mounted 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) dug in 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, in which: - on the side opposite its upper face, the support (220) comprises a lower face (224), and - the support comprises a groove (228) hollowed out in this lower face of the support, this groove being capable of receiving the optical fiber in a removable manner.

4. Device according to any one of the preceding claims, in which the processing unit (50) is configured: - to obtain the 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 the acoustic signal measurements at 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 the temperature and the acoustic signal using the same Bragg grating.

6. A device according to any preceding claim, wherein the number of Bragg gratings is greater than ten or twenty.

7. A device according to any preceding claim, 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 this Bragg grating is separated from the interrogated wavelengths of the other Bragg gratings of the optical fiber by at least 1 nm.

8. A device according to any preceding claim, in in which 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, in which the processing unit is capable of obtaining a measurement of the temperature, at one of the measurement points, which exceeds 500°C.

10. 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 Oi>p representative of the amplitude of the variations in the temperature measured during a predetermined sliding time window at 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 a measurement point of the first group from the different successive values ​​of the standard deviation OijP calculated for each regular time interval.

11. Method according to claim 10, in which 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 o2>p representative of the amplitude of the variations in the temperature measured during a predetermined sliding time window at this measurement point, each measurement point of 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 o2ref, then - the detection (186) of a defect at a measurement point of the first group from the ratio 0ijP / 02jref calculated for this measurement point.

12. Additive manufacturing system for a part, this system comprising: - an apparatus (10) for forming successive layers stacked on top of each other to form, by stacking these layers, the part to be manufactured, - a device (12) for detecting a defect during the manufacture of the part by the apparatus (10), this device comprising: - a support (20; 220) comprising: - an upper face (40) on which the part is manufactured when the additive manufacturing process is implemented, - measurement points (Pi to P24) of the temperature or of an acoustic signal, these measurement points being contained in a measurement plane (Pm) located under the upper face and distributed in this measurement plane so that at least one of these measurement points is located under the part when the additive manufacturing process is implemented, - a processing unit (50) configured: - to obtain temperature or acoustic signal measurements at each of the measurement points 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 apparatus so as to stop the manufacture of the part or to modify parameters of the forming apparatus, characterized in that the detection device conforms to any one of claims 1 to 9.

13. System according to claim 12, in which the apparatus (10) for forming successive layers is capable of forming successive layers of metal stacked on top of each other to form, by stacking these layers, all of the metal parts to be manufactured.

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