Method for calibrating a sensor for monitoring a melt pool in an additive manufacturing machine

Abstract

The invention relates to a method for calibrating a sensor for monitoring a molten bath, the sensor belonging to a system for monitoring a molten bath of an additive manufacturing machine, the method comprising at least the following steps: - measuring and recording the signal value sent by the monitoring sensor when not exposed to a reference radiation, - exposing the monitoring sensor to a reference radiation, - measuring and recording the signal value sent by the monitoring sensor when exposed to the reference radiation, - calculating a correction coefficient for the monitoring sensor as a function of a reference value related to the reference radiation and of the signal values sent by the monitoring sensor when not subjected to the reference radiation and when subjected to the reference radiation, - recording in a correction table the specific correction coefficient of the monitoring sensor and the signal value sent by the monitoring sensor when not exposed to the reference radiation.

Description

Technical Field

[0001] This invention relates to the calibration of sensors for monitoring the molten pool in additive manufacturing machines, particularly in machines that perform additive manufacturing through powder bed deposition and selective melting. Background Technology

[0002] Additive manufacturing via powder bed deposition and selective melting is an additive manufacturing method that manufactures one or more parts by selectively melting various stacked additive manufacturing powder layers. A first powder layer is deposited on a support such as a platform, and then selectively melted along a first horizontal cross-section of the one or more parts to be manufactured using one or more energy or heat sources. A second powder layer is then deposited on the newly cured first powder layer, and then the second powder layer itself is selectively cured, and so on, until the last powder layer is used to manufacture the last horizontal cross-section of the part to be manufactured.

[0003] To ensure the quality of manufactured parts and to predict any malfunctions in the manufacturing equipment, additive manufacturing machines can be equipped with systems for monitoring the molten pool generated in each powder layer by one or more energy or heat sources used for selective melting. For example, systems for monitoring the molten pool include sensors for measuring the heat emission level of the molten pool.

[0004] In order to achieve accurate monitoring of the molten pool in additive manufacturing machines, or to compare the monitoring results of the molten pool in the first machine with the monitoring results of the molten pool in the second machine, it is necessary to calibrate the sensors of the system used to monitor the molten pool of each machine.

[0005] US Patent Application 2019323951 discloses a method and apparatus for calibrating a melt pool monitoring system for additive manufacturing machines.

[0006] In application US2019323951, the calibration apparatus includes a calibration platform 232 that supports a light source 240 for calibration.

[0007] For the calibration method to be performed correctly, the calibration light source must be positioned very accurately within the machine and relative to the sensor of the molten pool monitoring device. For this purpose, the calibration light source is positioned very accurately on the calibration platform, and the calibration platform is positioned very accurately within the machine, specifically by utilizing positioning devices 234 and 236.

[0008] The necessary precise positioning of the light source relative to the sensor of the molten pool monitoring device is the first drawback of the calibration method and apparatus described in application US2019323951.

[0009] This is because all machines to be calibrated must be able to be positioned with the same precision relative to the sensors of the machine’s own molten pool monitoring system.

[0010] Therefore, only the same machine that enables the platform and its positioning device to be placed in the correct position can be calibrated using the calibration method and apparatus described in application US2019323951.

[0011] After accurately positioning the calibrated light source within the machine, the calibration method described in application US2019323951 specifies that the sensors of the monitoring system are exposed to reference radiation emitted by the calibrated light source. The monitoring system measures this reference radiation, compares the measured value with the measured reference value, and adjusts the monitoring system to transmit the same measured value as the reference value. This adjustment step requires specific modifications to the physical gain, optical focus, filter position, or electronic gain, or even replacement of the sensor.

[0012] This final adjustment step is another drawback of the method described in application US2019323951, and may also prevent its use in any type of machine. This is because if the monitoring system is not designed for such adjustments, or if the means providing these adjustment options do not offer adjustments with sufficient resolution, then the operation for adjusting the monitoring system may be difficult to implement, or even impossible to perform. Summary of the Invention

[0013] The purpose of this invention is to provide a method for calibrating sensors used to monitor the molten pool in an additive manufacturing machine that does not exhibit the aforementioned drawbacks.

[0014] Therefore, the present invention proposes a method for calibrating a sensor used for monitoring a molten pool, the sensor belonging to a system for monitoring the molten pool of an additive manufacturing machine, the method comprising at least the following steps:

[0015] - Measure and record the signal values ​​transmitted by the monitoring sensor when it is not exposed to reference radiation.

[0016] - Expose the monitoring sensor to reference radiation.

[0017] - Measure and record the signal values ​​transmitted by the monitoring sensor when exposed to reference radiation.

[0018] -Calculate the correction coefficients for the monitoring sensor based on the reference value associated with the reference radiation and the signal values ​​transmitted by the monitoring sensor when it is not exposed to the reference radiation and when it is exposed to the reference radiation.

[0019] Record the calibration coefficients used for the monitoring sensor and the signal values ​​transmitted by the monitoring sensor when it is not exposed to reference radiation in the calibration table.

[0020] Advantageously, but not necessarily, the present invention can also provide:

[0021] - Calibration tables associated with the monitoring sensors are recorded in the system used to monitor the molten pool (the monitoring sensors are part of this system).

[0022] - If the electronic gain of the monitoring sensor is adjustable, adjust the electronic gain to a predefined value before measuring and recording the signal value sent by the sensor.

[0023] - Before measuring and recording the signal values ​​transmitted by the sensor, set the electronic gain of the monitoring sensor to maximum.

[0024] - The reference radiation exposed to each monitoring sensor comes from a light source calibrated with respect to light intensity and wavelength, which includes an incandescent lamp equipped with a device such as a card for adjusting its light output power.

[0025] Ideally, the method according to the invention utilizes at least two different monitoring sensors, and the method includes at least the following steps:

[0026] - Measure and record the signal values ​​transmitted by each monitoring sensor when not exposed to reference radiation.

[0027] - Expose each monitoring sensor to reference radiation.

[0028] - Measure and record the signal values ​​transmitted by each monitoring sensor when exposed to reference radiation.

[0029] -Calculate the correction factor for each monitoring sensor based on the reference value associated with the reference radiation and the signal values ​​transmitted by the monitoring sensor when it is not exposed to the reference radiation and when it is exposed to the reference radiation.

[0030] Record the correction factor for each monitoring sensor and the signal value transmitted by each monitoring sensor when it is not exposed to reference radiation in the calibration table.

[0031] If the method according to the invention is implemented using at least two different monitoring sensors, the invention may also provide:

[0032] The method utilizes at least two monitoring sensors belonging to the same additive manufacturing machine.

[0033] The method utilizes at least two monitoring sensors belonging to different additive manufacturing machines.

[0034] For example, the method according to the invention is applied to one or more sensors for monitoring the melt pool in one or more machines used for additive manufacturing by powder bed deposition and selective melting. Attached Figure Description

[0035] Further features and advantages of the invention will become apparent from the following description. This description, given by way of non-limiting example, refers to the accompanying drawings, in which:

[0036] - Figure 1 This is a schematic diagram of an additive manufacturing machine in which the calibration method according to the present invention can be implemented.

[0037] - Figure 2 This is a schematic diagram of a system used to monitor the molten pool in an additive manufacturing machine.

[0038] - Figure 3 The positioning of a calibrated light source in an additive manufacturing machine conforming to the calibration method according to the present invention is shown.

[0039] - Figure 4 This is a detailed schematic diagram of the positioning of a calibrated light source in an additive manufacturing machine conforming to the calibration method according to the present invention.

[0040] - Figure 5 This is a schematic diagram of a component of a light source that can be used for calibration according to the calibration method of the present invention. Detailed Implementation

[0041] The present invention relates to a method for calibrating sensors used to monitor the molten pool belonging to an additive manufacturing machine (e.g., a machine that performs additive manufacturing by powder bed deposition and selective melting).

[0042] Figure 1 An example of a machine for additive manufacturing via powder bed deposition and selective melting is shown.

[0043] The additive manufacturing machine 10 may include a manufacturing chamber 12 and two laser sources 141, 142, each emitting a laser beam 161, 162 to selectively melt the additive manufacturing powder layer deposited within the manufacturing chamber 12. The laser sources are mounted outside the manufacturing chamber, and windows 151, 152 allow the laser beams to pass through the top wall of the manufacturing chamber.

[0044] In order to enable selective melting of each powder layer, each laser source 141, 142 is equipped with a scanning head 171, 172, which includes mechanical and optical devices (e.g., various optical lenses and at least one mirror) to move the laser beam and control its focusing within the manufacturing chamber.

[0045] Manufacturing chamber 12 is a closed chamber that may be filled with an inert gas, such as nitrogen. Advantageously, the inert gas can be circulated within the manufacturing chamber to expel fumes generated by the melting of the powder and to cool the gas circulating within the manufacturing chamber.

[0046] Within the manufacturing chamber 12, the additive manufacturing machine 10 includes at least one working area 18 defined by a manufacturing platform 20 and a manufacturing outer sheath 22, the platform 20 being moved within the outer sheath 22 by an actuator 24 such as a lifter.

[0047] The manufacturing chamber 12 includes a working surface 26, an outer sheath 22 extending vertically below the working surface 26 and opening to the working surface 26 through an opening formed in the working surface 26.

[0048] To produce various powder layers for additive manufacturing of a part P to be manufactured, the machine includes apparatus for depositing powder layers.

[0049] In passing Figure 1 In the machine illustrated in the example, these devices for depositing powder layers include two powder dispensers 281, 282, two powder receiving sliders 301, 302, and a powder spreading device 32. The two powder dispensers 281, 282 are connected to at least one powder reservoir (not shown). The two powder receiving sliders 301, 302 are located on both sides of the working area 18. The powder spreading device 32 can be in the form of a roller or a scraper. Advantageously, the sleeves 341, 342 that house the sliders can also be used to recover excess powder deposits.

[0050] To create a powder layer in working area 18, a distributor delivers a row of powder to a slider, and then a spreading device spreads the powder onto working area 18. For the deposition of a row of powder, the slider moves translationally below its associated distributor.

[0051] In order to monitor the molten pool generated by the beams 161, 162 of the two laser sources 141, 142, the machine 10 may include systems 361, 362 for monitoring the molten pool associated with each laser source.

[0052] like Figure 2 As shown, the systems 361 and 362 for monitoring the molten pool include at least one molten pool monitoring sensor 38.

[0053] Systems 361 and 362 for monitoring the molten pool are positioned between laser sources 141 and 142 and their scanning heads 171 and 172. Therefore, laser beams 161 and 162 emitted by the laser sources pass through the monitoring systems before entering the scanning heads 171 and 172 associated with those sources.

[0054] After entering the scanning head, laser beams 161 and 162 selectively melt the powder layer present on the manufacturing platform 20.

[0055] When a molten pool is generated by the laser beam, the powder emits radiation. The emitted radiation portion 40 is transmitted back to the laser sources 141 and 142 via the optical devices of the scanning head. This emitted radiation portion 40 is measured by the molten pool monitoring sensor 38. For this purpose, a first semi-transparent mirror 42 is positioned along the laser beam path between the laser sources 141 and 142 and the scanning heads 171 and 172, so that the laser beam can be transmitted from the laser sources toward the scanning heads, and the emitted radiation portion 40 of the molten powder is redirected back to the laser source and toward the monitoring sensor 38. For example, the first semi-transparent mirror 42 is positioned at 45° to the transmission axis of the laser beam between the laser source and the scanning head.

[0056] For example, the molten pool monitoring sensor 38 is a thermal sensor. For example, the molten pool monitoring sensor 38 is a photodiode-type thermal sensor. In variations, the molten pool monitoring sensor 38 may take the form of a pyrometer, or an optical, hyperspectral, or infrared camera.

[0057] For example, when exposed to radiation, the monitoring sensor 38 transmits a signal related to the color temperature of the radiation via a linear function. Furthermore, when exposed to radiation with a given color temperature, the monitoring sensor 38 also transmits a signal related to the optical power of the radiation via a linear function.

[0058] For example, the monitoring sensor 38 transmits voltage signals.

[0059] To improve the measurements performed by the monitoring sensor 38, an optical filter 44 and a converging lens 46 can be positioned between the semi-transparent mirror 42 and the monitoring sensor along the optical path followed by the radiating portion 40 of the powder emission.

[0060] Advantageously, the systems 361, 362 for monitoring the molten pool may further include a sensor 48 for sensing the power of the laser beam. When the laser beam emitted by the laser source passes through the first semi-transparent mirror 42, the power sensor 48 utilizes the beam 50 reflected by the mirror. A beam absorber 52 and a second semi-transparent mirror 54 may be placed between the first semi-transparent mirror 42 and the power sensor 48 to absorb a portion of the reflected beam 50 and reduce the load on the power sensor 48. An optical filter 56 and a diffuser 57 may also be installed between the second semi-transparent mirror 54 and the power sensor 48.

[0061] The power sensor 48 can be in the form of a photodiode or a thermopile.

[0062] In summary, this invention provides a method for calibrating a melt pool monitoring sensor in an additive manufacturing machine.

[0063] For example, the calibration method according to the invention can be applied to machine 10 for additive manufacturing by powder bed deposition and selective melting, systems 361 and 362 for monitoring the molten pool, and monitoring sensor 38, as described above.

[0064] For its implementation, the calibration method specifically includes the step of exposing the monitoring sensor 38 to reference radiation from the calibrated light source 58.

[0065] In order to ensure that the monitoring sensor 38 is exposed to the reference radiation from the calibrated light source 58 as optimally as possible, the calibrated light source must be accurately positioned within the machine's manufacturing chamber 12.

[0066] Instead of providing accurate positioning of a calibrated light source relative to the manufacturing platform and machine frame through high-precision mechanical assembly, this invention provides positioning of a calibrated light source within an additive manufacturing machine through a laser aiming beam (which is different from the laser beam used to generate the molten pool).

[0067] In other words, the calibrated light source 58 is independent of the additive manufacturing machine. The calibrated light source is a device independent of the additive manufacturing machine and can be freely moved within the manufacturing chamber of the machine by the operator responsible for calibration.

[0068] like Figure 3 As shown, and as provided by the present invention, the calibrated light source 58 is placed on the manufacturing platform 20 and positioned on the platform using a laser aiming beam 163, which is different from the laser beams 161 and 162 used to generate the molten pool.

[0069] More specifically, the laser aiming beam 163 is visible to the operator and poses no danger to the operator. The laser aiming beam 163 has a wavelength between 400 nm and 700 nm, for example, equal to 633 nm, to form a red dot on the surface or material it is pointing at. The positioning of the calibrated light source 58 in the manufacturing chamber 12 is performed by the operator using this red dot.

[0070] The laser aiming beam 163 is completely coaxial with the laser beams 161 and 162 used to generate the molten pool. For this purpose, the laser sources 181 and 182 that generate the laser aiming beam 163 are integrated into the laser sources 141 and 142 that generate the laser beams 161 and 162 (which are used to generate the molten pool), or integrated into the scanning heads 171 and 172 associated with the laser sources 141 and 142 that generate the laser beams 161 and 162 (which are used to generate the molten pool).

[0071] Ideally, to eliminate any errors that may be caused by the scanning head, when the calibrated light source 58 is located in the manufacturing chamber 12, the laser aiming beam 163 is oriented through the scanning head toward the origin of the reference system associated with the scanning head. For example, during the positioning of the calibrated light source 58 in the manufacturing chamber 12, the laser aiming beam 163 is vertically oriented below the scanning head and toward the working area 18.

[0072] To assist the operator in positioning the calibrated light source 58 within the manufacturing chamber 12, the calibrated light source 58 may be equipped with a movable aiming target 60. This aiming target 60 is positioned on an optical output element 62 through which reference radiation is emitted from the calibrated light source.

[0073] Once the calibrated light source 58 has been positioned, in order not to interfere with the emission of reference radiation, the aiming target 60 is removed during the step of exposing the monitoring sensor 38 to the reference radiation emitted from the calibrated light source.

[0074] The aiming target 60 is mostly opaque across its entire surface and has a perforation at the aiming point 64 located at its center. For example, the aiming target is made of frosted glass. More specifically, the aiming point is a circular hole with a diameter between 0.5 mm and 1 mm.

[0075] During the positioning of the calibrated light source 58 within the manufacturing chamber 12, the operator moves the light source so that the spot of the laser aiming beam (e.g., in the form of a red dot) coincides with the aiming point. More specifically, when the light source is correctly positioned within the manufacturing chamber 12, the spot of the laser aiming beam disappears within the aperture forming the aiming point, as... Figure 4 As shown.

[0076] The light source 58 that can be used for calibration according to the calibration method of the present invention is as follows: Figure 5 As shown.

[0077] The calibrated light source 58 is a light source that has been calibrated regarding its light intensity and wavelength. More specifically, the calibrated light source 58 may include an incandescent lamp 66 equipped with a device 68 (e.g., a carte) for adjusting its light output power.

[0078] Advantageously, incandescent lamps are less dangerous to handle than blackbody emitters, which have significantly higher temperatures, and offer a larger emission surface area than LED laser sources, which require more complex beam shaping.

[0079] For example, Incandescent Lamp 66 is a tungsten filament lamp.

[0080] The calibrated light source 58 emits radiation via an incandescent lamp 66, the color temperature of which is preferably 2796K with a variation of ±15K, and is therefore essentially equal to the color temperature of blackbody radiation.

[0081] For example, the light output power of the calibrated light source 58 is adjusted around a nominal value (which has a variation of less than 0.05% of that nominal value).

[0082] The calibrated light source 58 emits reference radiation via an incandescent lamp 66, the wavelength of which is between 360 nm and 2500 nm, and the radiation peak essentially corresponds to the emission spectrum of the radiation emitted by the molten pool (which is to be measured by the monitoring sensor 38 during the manufacturing cycle), for example, between 1200 nm and 1700 nm.

[0083] To improve the uniformity of the reference radiation, the calibrated light source 58 may be equipped with at least one optical diffuser 70.

[0084] exist Figure 5 In the example shown, reference radiation 72 emitted by incandescent lamp 66 passes through a first diffuser 70, is then reflected at 90° by a mirror 74 positioned at 45°, and finally passes through a second diffuser 70, which is also an optical output element 62 through which the reference radiation 72 is emitted from the calibrated light source. The two diffusers 70 and the mirror 74 constitute part of the calibrated light source 58.

[0085] Similarly, to improve the uniformity of the reference radiation, a collimator (not shown) can be placed between the incandescent lamp 66 and the first diffuser 70.

[0086] The calibrated light source 58 used in this invention is an inexpensive and highly compact solution. Furthermore, the calibrated light source 58 is a portable (e.g., to a customer's business premises) and easy-to-use tool.

[0087] Since the calibration light source 58 is independent of the machine, and since it is positioned within the machine by means of a laser aiming beam, the calibration method according to the invention can be used with any type of additive manufacturing machine that uses a laser beam to generate a molten pool and has a laser aiming beam.

[0088] According to another advantage, the calibration method according to the invention does not require adjusting the molten pool monitoring sensor so that it transmits the same measured value as the reference value when the sensor in the monitoring system is exposed to reference radiation.

[0089] According to the present invention, in order to calibrate the molten pool monitoring sensor 38 belonging to the molten pool monitoring system of the additive manufacturing machine 10, the method includes at least the following steps:

[0090] - Measure and record the signal values ​​transmitted by monitoring sensor 38 when not exposed to reference radiation 72.

[0091] - Expose the monitoring sensor to reference radiation 72.

[0092] - Measure and record the signal values ​​transmitted by the monitoring sensor when exposed to reference radiation.

[0093] - The correction coefficient of the monitoring sensor is calculated based on the reference value associated with the reference radiation and the signal values ​​transmitted by the monitoring sensor when it is not exposed to the reference radiation and when it is exposed to the reference radiation.

[0094] Record the calibration coefficient of the monitoring sensor and the signal value sent by the monitoring sensor 38 when it is not exposed to the reference radiation 72 in the calibration table.

[0095] For example, the reference values ​​associated with reference radiation 72 are dimensionless values ​​representing the optical power and color temperature of the reference radiation.

[0096] To calculate the correction coefficient, it is assumed that the monitoring sensor 38 sends a signal related to the color temperature of the radiation it is exposed to via a linear function, and it is also assumed that when the monitoring sensor 38 is exposed to radiation with a given color temperature, the monitoring sensor 38 also transmits a signal related to the optical power of that radiation via a linear function.

[0097] In addition, the calculation of the correlation coefficient also takes into account the background noise that can be measured by the monitoring sensor when it is not exposed to the reference radiation.

[0098] Therefore, when exposed to reference radiation, the signal value Y sent by the monitoring sensor is related to the reference value X with respect to the reference radiation by the following relationship: Y = a.X + b, where a is a correction coefficient associated with the sensor, and b is the measurement deviation caused by the background noise measured by the sensor when it is not exposed to reference radiation.

[0099] The calibration method according to the invention aims to determine the correction coefficient 'a' and measurement deviation 'b' for each monitoring sensor. These two values, 'a' and 'b', are stored in a calibration table for each monitoring sensor calibrated according to the method, and are used via linear interpolation during monitoring of the molten pool to correct the signal values ​​transmitted by each sensor, and to match them with dimensionless correction values ​​representing the optical power of the radiation from the monitored molten pool and the color temperature of the radiation from the monitored molten pool.

[0100] To determine the measurement deviation b, the signal transmitted by the monitoring sensor when not exposed to reference radiation is measured, preferably wherein the manufacturing chamber 12 of the machine is closed and the calibrated light source is turned off or placed outside the manufacturing chamber.

[0101] To determine the correction factor a, the monitoring sensor is exposed to reference radiation associated with the reference value X, and the measurement deviation b of the monitoring sensor has been pre-measured using the value Y transmitted by the monitoring sensor when exposed to the reference radiation. The correction factor a is given by the following relationship: a = (Yb) / X.

[0102] Since the calibration light source 58 is selected to substantially match the emission spectrum of the radiation emitted by the molten pool to be monitored, a unitless reference value X can be freely chosen. However, it must be selected in a manner that facilitates reading and displaying the values ​​sent by the monitoring sensor or the sensor itself (e.g., via software and a monitoring screen).

[0103] For example, calibration tables related to monitoring sensors are recorded in a molten pool monitoring system (which includes the monitoring sensors as part of the system). The molten pool monitoring system includes data acquisition cards 191 and 192, on which the monitoring sensors or their calibration tables are stored, for example,.

[0104] Advantageously, the correction coefficients associated with the monitoring sensor are calculated by the data acquisition card of the monitoring system (of which the monitoring sensor is part).

[0105] Advantageously, the calibration method according to the invention can be implemented using a molten pool monitoring system, particularly using a molten pool monitoring sensor that does not have, for example, the ability to adjust with respect to sensor gain.

[0106] If the electronic gain of the monitoring sensor is adjustable, the calibration method according to the invention specifies that the electronic gain is adjusted to a predefined value before the step of measuring and recording the signal value transmitted by the sensor. For example, the electronic gain of the monitoring sensor 38 is adjusted to its maximum before the step of measuring and recording the signal value transmitted by the sensor. However, if the monitoring sensor provides a sufficient signal level when adjusted to its minimum gain, the electronic gain of the sensor can be kept at its minimum to maximize the measurement bandwidth of the sensor.

[0107] The calibration method according to the invention is more specifically designed to be implemented using a variety of monitoring sensors.

[0108] According to the first example, the calibration method can be implemented using at least two monitoring sensors belonging to the same additive manufacturing machine.

[0109] According to the second example, the calibration method can be implemented using at least two monitoring sensors belonging to different additive manufacturing machines.

[0110] According to the third example, the calibration method can be implemented in multiple additive manufacturing machines, each of which includes multiple melt pool monitoring sensors.

[0111] In these different situations, to calibrate at least two molten pool monitoring sensors 38, the method includes the following steps:

[0112] - Measure and record the signal values ​​transmitted by each monitoring sensor 38 when not exposed to reference radiation 72.

[0113] - Expose each monitoring sensor to reference radiation 72.

[0114] - Measure and record the signal values ​​transmitted by each monitoring sensor when exposed to reference radiation.

[0115] -Calculate the correction factor for each monitoring sensor based on the reference value associated with the reference radiation and the signal values ​​transmitted by the monitoring sensor when it is not exposed to the reference radiation and when it is exposed to the reference radiation.

[0116] - Record the correction factor for each monitoring sensor and the signal value transmitted by each monitoring sensor 38 when not exposed to reference radiation 72 in the calibration table.

[0117] Finally, as stated at the beginning of the specification, the calibration method according to the invention is particularly applicable to one or more sensors used for monitoring the molten pool in one or more machines used for additive manufacturing by powder bed deposition and selective melting.

Claims

1. A method for calibrating a molten pool monitoring sensor (38), said molten pool monitoring sensor (38) being part of a molten pool monitoring system (361, 362) of an additive manufacturing machine (10), said method comprising at least the following steps: - Measure and record the signal values ​​transmitted by the monitoring sensor (38) when not exposed to reference radiation (72), - Expose the monitoring sensor to reference radiation (72). - Measure and record the signal values ​​transmitted by the monitoring sensor when exposed to reference radiation. - Calculate the correction coefficients for the monitoring sensor based on the reference value associated with the reference radiation and the signal values ​​transmitted by the monitoring sensor when it is not exposed to the reference radiation and when it is exposed to the reference radiation. - Record the calibration coefficients used for the monitoring sensor and the signal values ​​transmitted by the monitoring sensor (38) when it is not exposed to the reference radiation (72) in the calibration table. The reference radiation (72) is emitted by a calibrated light source (58) independent of the additive manufacturing machine (10). The calibrated light source (58) is positioned inside the manufacturing chamber (12) of the additive manufacturing machine (10) via a visible aiming laser beam (163) coaxial with the laser beams (161, 162) used to generate the molten pool. In this context, with the manufacturing room (12) closed and the calibrated light source (58) either off or located outside the manufacturing room, measurements are performed and the signal values ​​transmitted by the monitoring sensor (38) when not exposed to reference radiation (72) are recorded to determine the measurement deviation b caused by background noise. The correction coefficient is calculated according to the relationship a = (Y - b) / X, where Y is the signal value emitted by the monitoring sensor when exposed to reference radiation, X is the reference value related to the reference radiation, and b is the measurement deviation caused by background noise. The correction coefficient a and the measurement deviation b are recorded in a correction table and are used to correct the signal sent by the monitoring sensor by the software during the molten pool monitoring process without adjusting the molten pool monitoring sensor.

2. The method for calibrating a molten pool monitoring sensor according to claim 1, wherein, Calibration tables associated with the monitoring sensors are recorded in the molten pool monitoring system, which is part of the monitoring system.

3. The method for calibrating a molten pool monitoring sensor according to any one of the preceding claims, wherein, The electronic gain of the monitoring sensor is adjustable, and it is adjusted to a predefined value before the step of measuring and recording the signal value sent by the monitoring sensor.

4. The method for calibrating a molten pool monitoring sensor according to claim 3, wherein, Before measuring and recording the signal values ​​sent by the monitoring sensor, the electronic gain of the monitoring sensor is set to maximum.

5. The method for calibrating a molten pool monitoring sensor according to claim 1, wherein, The reference radiation exposed to each monitoring sensor comes from a light source calibrated with respect to light intensity and wavelength, which includes an incandescent lamp equipped with a device for adjusting its light output power.

6. The method for calibrating a molten pool monitoring sensor according to claim 1, wherein, The method utilizes at least two different monitoring sensors and includes at least the following steps: - Measure and record the signal values ​​transmitted by each monitoring sensor (38) when not exposed to reference radiation (72), - Expose each monitoring sensor to reference radiation (72). - Measure and record the signal values ​​transmitted by each monitoring sensor when exposed to reference radiation. - Calculate correction factors for each monitoring sensor based on reference values ​​associated with reference radiation and the signal values ​​transmitted by the monitoring sensor under and without reference radiation. - Record the calibration coefficients for each monitoring sensor and the signal values ​​transmitted by each monitoring sensor (38) when not exposed to reference radiation (72) in the calibration table.

7. The method for calibrating a molten pool monitoring sensor according to claim 6, wherein, The method utilizes at least two monitoring sensors belonging to the same additive manufacturing machine.

8. The method for calibrating a molten pool monitoring sensor according to claim 6, wherein, The method utilizes at least two monitoring sensors belonging to different additive manufacturing machines.

9. The method for calibrating a molten pool monitoring sensor according to claim 1, wherein, The method is applied to one or more monitoring sensors used to monitor the molten pool in one or more machines used for additive manufacturing via powder bed deposition and selective melting.

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