A method for online monitoring of laser power

Abstract

The present invention discloses a method for online monitoring of laser power, belonging to the technical field of additive manufacturing. The present invention uses a system including a laser, a collimating mirror, a beam expander, a dichroic mirror, a galvanometer scanner, a field lens, a filter, a beam splitter, a focusing lens, a photodetector, a lens, and a high-speed camera to realize laser power monitoring, specifically including the following steps: S1 Offline power test; S2 Online intensity monitoring and power calibration; S3 Real-time power monitoring. By reducing the optical path of the power monitoring module, the present invention effectively solves the problem of narrow space in multi-laser devices due to many optical components on the top. In multi-laser devices, it can monitor each laser beam, make full use of the device space, avoid the situation where multiple monitoring modules cannot be placed simultaneously due to space limitations, and make the optical path layout of multi-laser devices more reasonable and efficient.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and particularly relates to a method for online monitoring of laser power. Background Art

[0002] Additive manufacturing is an advanced manufacturing technology. For example, selective laser melting (SLM) technology can manufacture fully dense metal parts with complex shapes and has properties comparable to those of traditional processes. Its manufacturing process includes steps such as converting a 3D model into slice data, preheating the powder, and scanning and melting the powder layer by layer. However, there are many influencing parameters in the SLM process chain, and continuous monitoring of forming parameters, powder layer quality, and properties is crucial. Existing technologies use sensors to collect various signals to monitor the forming process, but there are defects in the optical path design.

[0003] In existing SLM monitoring technologies, the laser is divided into two paths by a dichroic mirror after shaping. One path is reflected to a power monitoring module to monitor the laser power, and the other path is transmitted to a galvanometer scanner and focused by a field lens for printing. The radiation light from the molten pool is reflected by the field lens, galvanometer scanner, and dichroic mirror to a molten pool monitoring module. The powder bed monitoring is an independent module. This optical path is feasible for single-laser additive manufacturing equipment. However, for multi-laser equipment, due to the need for multiple optical paths and a large number of top optical components, the space is narrow, making it difficult to place three monitoring modules simultaneously and unable to achieve simultaneous monitoring of laser intensity, morphology, and power. Therefore, a method for online monitoring of laser power is needed to solve the above problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for online monitoring of laser power to solve the problems raised in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A method for online monitoring of laser power is realized by a system including a laser, a collimator, a beam expander, a dichroic mirror, a galvanometer scanner, a field lens, a filter, a beam splitter, a focusing lens, a photodetector, a lens, and a high-speed camera. Specifically, it includes the following steps:

[0006] S1: Before the device starts printing, use a power meter to test the output optical power of the laser offline. The specific operation is as follows:

[0007] S11: Start the laser and open the printing software of the device;

[0008] S12: Control the output optical power range of the laser to be 50W - 450W, with a step size of 50W for measurement and record the data;

[0009] S13: Organize the output power data and record the test result as ;

[0010] S2: When the printer starts printing, use the molten pool intensity online monitoring system to monitor the molten pool intensity signal. The specific operations are as follows:

[0011] S21: Start the laser, and open the printing software and intensity monitoring software of the device;

[0012] S22: Print the entire area of the device substrate, control the laser power range emitted by the laser to be 50W - 450W, measure and record data with a step size of 50W, and use the intensity software to collect the molten pool intensity data of the entire large area under different power conditions;

[0013] S23: Organize and output the test data, and record the test result as ;

[0014] S24: Obtain the laser power value measured by the power meter corresponding to the intensity of the molten pool from the recorded data, and obtain the expression between the two through curve fitting , and the output optical power of the laser corresponding to different intensities can be obtained through the expression. In the formula: P is the output optical power of the laser; U is the amplitude of the molten pool intensity;

[0015] S25: When changing materials, repeat steps S21 - S24 to achieve the calibration of the power of different materials. Different materials correspond to different expressions. When using this system to characterize the laser power, the expression corresponding to the material should be selected;

[0016] S3: During the printing process, monitor the stability of the laser power by outputting the molten pool intensity signal through a photodetector, and at the same time achieve the real-time output of the laser power value. Among them, the photodetector converts the received laser power into an electric current signal through photoelectric conversion, and the electric current signal is converted into a voltage signal through a transimpedance amplifier circuit and output. The stability of the laser power is characterized by the output voltage signal. If the voltage signal detected by the detector remains stable, it indicates that the optical power received by the detector is stable, and further indicates that the output optical power of the laser is stable.

[0017] As a preferred implementation manner, the collimating mirror shapes the Gaussian beam output by the laser, shaping the divergent beam into a parallel beam to reduce the aberration of the laser passing through the field lens.

[0018] As a preferred implementation manner, the beam expander expands the spot diameter of the parallel beam emerging from the collimating mirror without changing the spot shape.

[0019] As a preferred implementation manner, the dichroic mirror has high transmittance for 1070nm laser and high reflectance for light with wavelengths of 750nm - 950nm, providing a path for the signal source of the monitoring module without affecting the printing laser.

[0020] As a preferred embodiment, the galvanometer controls the mirror through a drive board and a high-speed swing motor to achieve changes in position and direction, thereby changing the position where the reflected light hits the target.

[0021] As a preferred embodiment, the filter is an absorption filter, which absorbs some specific wavelengths and has little or no effect on light of other wavelengths.

[0022] As a preferred embodiment, the beam splitter divides the laser into two paths, and the beam splitting ratio is , where T is the transmittance and R is the reflectance.

[0023] As a preferred embodiment, the focusing lens focuses the radiation light of the molten pool onto the photodetector.

[0024] As a preferred embodiment, the lens images the morphology of the molten pool on a high-speed camera, and the high-speed camera is used to collect the morphology image of the molten pool.

[0025] The present invention discloses a system for on-line monitoring of laser power, including a laser, a collimating mirror, a beam expander, a dichroic mirror, a galvanometer, a field lens, a filter, a beam splitter, a focusing lens, a photodetector, a lens, and a high-speed camera used in the method for on-line monitoring of laser power described above. The laser emitted by the laser sequentially passes through the collimating mirror, the beam expander, the dichroic mirror, the galvanometer, and the field lens and then acts on the metal powder on the substrate. After the radiation light of the molten pool sequentially passes through the field lens, the galvanometer, the dichroic mirror, the filter, and the beam splitter, a part is focused onto the photodetector by the focusing lens, and the other part is imaged on the high-speed camera by the lens.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. Traditional multi-laser devices require multiple optical paths and need to be equipped with 3 or more monitoring modules for optical path monitoring. However, the present invention effectively solves the problem of narrow space in multi-laser devices due to many optical components on the top by reducing the optical paths of the power monitoring module. In multi-laser devices, it can monitor each path of laser, make full use of the device space, avoid the situation where multiple monitoring modules cannot be placed simultaneously due to space limitations, and make the optical path layout of multi-laser devices more reasonable and efficient.

[0028] 2. The present invention can use one optical signal to simultaneously monitor the laser optical power and the intensity of the molten pool, and complete the monitoring of both through a signal processing system. Compared with multiple independent monitoring modules and optical paths in the prior art, it simplifies the complexity of the monitoring system, improves the integration degree of monitoring, and reduces the system coordination and maintenance costs brought by multiple optical paths and multiple modules.

[0029] 3. With one less light path, the number of optical components used is directly reduced. This not only lowers the manufacturing cost of the device, but also, due to the reduced number of optical components, correspondingly reduces the risk of monitoring damage caused by component failures, improving the overall stability and reliability of the monitoring system.

[0030] 4. Based on a unique monitoring process testing method, it is able to analyze in real time the reasons for the instability of the molten pool intensity signal. During the printing process, once an abnormal intensity signal appears, the problem can be promptly detected and processed, avoiding part defects caused by factors such as unstable laser power, thereby improving the printing efficiency, increasing the success rate of the final parts, and enhancing the product quality.

[0031] 5. By characterizing the laser power through the molten pool intensity signal, the magnitude of the laser power can be quantitatively output while monitoring the molten pool intensity signal. This method realizes real-time and accurate monitoring of the laser power, providing a reliable basis for the precise control of the laser power during the printing process, helping to further optimize the printing process parameters, and improving the consistency and stability of the printing quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a flowchart of the method for online monitoring of laser power according to the present invention;

[0033] Figure 2 It is a schematic diagram of the offline power test steps of the present invention;

[0034] Figure 3 It is a schematic diagram of the online intensity monitoring and power calibration steps of the present invention;

[0035] Figure 4 It is a schematic diagram of the system monitoring optical path of the present invention;

[0036] Figure 5 It is a flowchart of the online monitoring of laser power of the present invention;

[0037] Figure 6 It is a schematic diagram of the measurement method of the system laser power of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention will be further described below in conjunction with the embodiments.

[0039] The following embodiments are used to illustrate the present invention, but cannot be used to limit the protection scope of the present invention. The conditions in the embodiments can be further adjusted according to specific conditions. Any simple improvement of the method of the present invention under the premise of the concept of the present invention belongs to the scope required to be protected by the present invention. Specific Embodiment 1

[0041] Please refer to Figure 1-6, the present invention provides a method for online monitoring of laser power, which realizes laser power monitoring by using a system including a laser, a collimating mirror, a beam expander, a dichroic mirror, a galvanometer scanner, a field lens, a filter, a beam splitter, a focusing lens, a photodetector, a lens, and a high-speed camera. The specific steps are as follows:

[0042] S1: Before the device starts printing, use a power meter to test the output optical power of the laser offline. The specific operations are as follows:

[0043] S11: Start the laser and open the printing software of the device;

[0044] S12: Control the output optical power range of the laser to be 50W - 450W, with a step size of 50W for measurement and record the data;

[0045] S13: Organize the output power data and record the test result as ;

[0046] S2: When the printer starts printing, use the molten pool intensity online monitoring system to monitor the molten pool intensity signal. The specific operations are as follows:

[0047] S21: Start the laser and open the printing software and the intensity monitoring software of the device;

[0048] S22: Print the entire area of the device substrate, control the output laser power range of the laser to be 50W - 450W, with a step size of 50W for measurement and record the data. Use the intensity software to collect the molten pool intensity data of the entire large area under different power conditions;

[0049] S23: Organize and output the test data and record the test result as ;

[0050] S24: Obtain the laser power value corresponding to the molten pool intensity measured by the power meter from the recorded data, and obtain the expression between the two through curve fitting , and the output optical power of the laser corresponding to different intensities can be obtained through the expression. In the formula: P is the output optical power of the laser; U is the amplitude of the molten pool intensity;

[0051] S25: Replace the material and use the above steps to calibrate the power of different materials. Different materials correspond to different expressions. When using this system to characterize the laser power, the expression corresponding to the material should be selected;

[0052] S3: During the printing process, the stability of the laser power is monitored by outputting the molten pool intensity signal through a photodetector, and at the same time, the real-time output of the laser power value is realized. Among them, the photodetector converts the received laser power into an electric current signal through photoelectric conversion, and the electric current signal is converted into a voltage signal through a transimpedance amplifier circuit and output. The stability of the laser power is characterized by the output voltage signal. If the voltage signal detected by the detector remains stable, it indicates that the optical power received by the detector is stable, and further indicates that the output optical power of the laser is stable.

[0053] The collimating mirror shapes the Gaussian beam output by the laser, shaping the divergent beam into a parallel beam to reduce the aberration of the laser passing through the field lens.

[0054] The beam expander expands the spot diameter of the parallel beam emerging from the collimating mirror without changing the spot shape.

[0055] The dichroic mirror has high transmittance for 1070nm laser and high reflectance for light with wavelengths from 750nm to 950nm, providing a path for the signal source of the monitoring module without affecting the printing laser.

[0056] The galvanometer controls the position and direction changes of the reflecting mirror through the driving board and the high-speed swing motor, thereby changing the position where the reflected light hits the target.

[0057] The filter is an absorption type filter, which absorbs some specific wavelengths and has little or no effect on light of other wavelengths.

[0058] The beam splitter divides the laser into two paths, and the beam splitting ratio is , where T is the transmittance and R is the reflectance.

[0059] The focusing mirror focuses the radiation light of the molten pool onto the photodetector.

[0060] The lens images the morphology of the molten pool on the high-speed camera, and the high-speed camera is used to collect the morphology image of the molten pool.

[0061] The present invention discloses a system for on-line monitoring of laser power, including a laser, a collimating mirror, a beam expander, a dichroic mirror, a galvanometer, a field lens, a filter, a beam splitter, a focusing mirror, a photodetector, a lens, and a high-speed camera used in the method for on-line monitoring of laser power. The laser emitted by the laser passes through the collimating mirror, the beam expander, the dichroic mirror, the galvanometer, and the field lens in sequence and acts on the metal powder on the substrate. The radiation light of the molten pool passes through the field lens, the galvanometer, the dichroic mirror, the filter, and the beam splitter in sequence, and a part is focused onto the photodetector through the focusing mirror, and the other part is imaged on the high-speed camera through the lens.

[0062] Working principle and usage process of the present invention: First, in the equipment preparation stage, before starting the additive manufacturing equipment for printing tasks, perform step S1. The operator starts the laser and opens the printing software of the equipment, and then controls the output optical power of the laser to be between 50W and 450W, and measures it successively in steps of 50W. For example, starting from 50W, record the power data P1 collected by the power meter at this time. Then adjust the output optical power of the laser to 100W and record the power data P2 again, and so on. Complete the measurement of the entire power range and organize the data. When the printer starts printing work, enter step S2. The operator first starts the laser, and at the same time opens the printing software and a dedicated intensity monitoring software of the equipment. Subsequently, perform the printing operation on the entire area of the equipment substrate. During this process, control the output laser power of the laser to start from 50W and gradually adjust it in steps of 50W. At each power value, not only use the intensity software to collect the melt pool intensity data of the entire large area, such as recording the melt pool intensity data U1 at 50W power and U2 at 100W power, etc., but also measure and record the laser power itself. After completing all data collection, organize and output these test data. By analyzing and processing the melt pool intensity data and the laser power value measured by the power meter, for example, using the mathematical fitting method, obtain the expression between the two , where: P is the output optical power of the laser; U is the amplitude of the melt pool intensity;

[0063] Moreover, when different printing materials are replaced, repeat the above steps from S21 to S24, so as to achieve the calibration of the power of different materials, ensure that the accurate expression corresponding to the material can be selected when using this system to characterize the laser power. During the entire printing process, always perform step S3. The photodetector continuously receives the laser, converts the laser power into an electrical current signal through internal photoelectric conversion, and then converts this electrical current signal into a voltage signal through a transimpedance amplifier circuit for output. The system analyzes the output voltage signal. If the voltage signal remains stable, it can be determined that the optical power received by the detector is stable, which further indicates that the output optical power of the laser is in a stable state. At the same time, according to the expression obtained from the previous calibration , it is possible to calculate and output the current laser power size in real time based on the monitored melt pool intensity signal, realizing the on-line monitoring of the laser power. During this process, each optical element in the system works together. The collimating mirror shapes the Gaussian beam output by the laser into a parallel beam to reduce the aberration influence of the subsequent field lens; the beam expander expands the spot diameter; the dichroic mirror provides a reasonable path for the optical path and the monitoring signal according to the wavelength characteristics; the galvanometer accurately controls the position of the reflected light; the filter selects light of a specific wavelength; the beam splitter splits the beam in proportion; the focusing mirror focuses the melt pool radiation light onto the photodetector; the lens images the melt pool morphology on the high-speed camera, and the high-speed camera collects the melt pool morphology image, jointly ensuring the effective implementation of the entire method for on-line monitoring of the laser power. Specific Embodiment 2

[0065] As Figure 5 shown, in combination with Specific Embodiment 1, the present invention proposes an on-line monitoring method for laser power, which includes the following steps:

[0066] S1 System initialization;

[0067] S2 Collect melt pool intensity data;

[0068] S3 Determine whether the intensity data is stable. If it is stable, it is determined that the laser power is stable; if it is not stable, proceed to the next step;

[0069] S3 Obtain printing process parameter data;

[0070] S4 Compare the melt pool intensity data obtained in S3 with the printing process parameter data to determine consistency. If they are consistent, it is determined that the laser power is stable; if they are not consistent, proceed to the next step;

[0071] S5 Perform powder bed monitoring to judge the powder spreading uniformity. If the powder spreading is uniform, it is determined that the unstable melt pool intensity data is caused by unstable laser power, and perform a dimming operation, return to system initialization to re-obtain the intensity data; if the powder spreading is not uniform, proceed to the next step;

[0072] S6 Obtain image data and compare the obtained image data with the melt pool intensity data. If they are consistent, it is determined that the laser power is stable; if they are not consistent, it is determined that the laser power is unstable, and perform a dimming operation, return to system initialization to re-obtain the intensity data;

[0073] S7 Process the melt pool intensity data determined to be stable in laser power in steps S3 - S6 using an algorithm, and calculate the power value to end the process.

[0074] Based on the unique monitoring process test method of the present invention, it can analyze in real time the reasons for the instability of the melt pool intensity signal. During the printing process, once an abnormal intensity signal appears, the problem can be discovered and processed in time, avoiding part defects caused by factors such as unstable laser power, thereby improving the printing efficiency, increasing the success rate of the final part, and enhancing the product quality.

[0075] Characterize the laser power through the melt pool intensity signal, and be able to quantitatively output the magnitude of the laser power while monitoring the melt pool intensity signal. This method realizes real-time and accurate monitoring of the laser power, provides a reliable basis for the precise control of the laser power during the printing process, helps to further optimize the printing process parameters, and improves the consistency and stability of the printing quality.

[0076] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for online monitoring of laser power, characterized in that, A system including a laser, a collimating mirror, a beam expander, a dichroic mirror, a galvanometer scanner, a field lens, a filter, a beam splitter, a focusing lens, a photodetector, a lens, and a high-speed camera is used to monitor the laser power. The specific steps are as follows: S1: Before the device starts printing, use a power meter to test the output optical power of the laser offline. The specific operations are as follows: S11: Start the laser and open the printing software of the device; S12: Control the output optical power range of the laser to be 50W - 450W, with a step size of 50W for measurement and data recording; S13: Organize the output power data and record the test results as ; S2: When the printer starts printing, use a molten pool intensity online monitoring system to monitor the molten pool intensity signal. The specific operations are as follows: S21: Start the laser and open the printing software and the intensity monitoring software of the device; S22: Print the entire area of the device substrate, control the output laser power range of the laser to be 50W - 450W, with a step size of 50W for measurement and data recording, and use the intensity software to collect the molten pool intensity data of the entire large area under different power conditions; S23: Organize and output the test data, and record the test result as ; S24: Obtain the intensity of the molten pool corresponding to the laser power value measured by the power meter from the recorded data, and obtain the expression between the two through curve fitting , where: P is the output optical power of the laser; U is the amplitude of the molten pool intensity; The output optical power of the laser corresponding to different intensities can be obtained through the expression; S25: Replace the material and repeat steps S21 - S24 to achieve the calibration of different material powers. Different materials correspond to different expressions. When using this system to characterize the laser power, the expression corresponding to the material should be selected; S3: During the printing process, monitor the stability of the laser power by the molten pool intensity signal output by the photodetector, and at the same time achieve the real-time output of the laser power value. Among them, the photodetector converts the received laser power into an electric current signal through photoelectric conversion, and the electric current signal is converted into a voltage signal by a transimpedance amplifier circuit and output. The stability of the laser power is characterized by the output voltage signal. If the voltage signal detected by the detector remains stable, it indicates that the optical power received by the detector is stable, and further indicates that the output optical power of the laser is stable.

2. The method for online monitoring of laser power according to claim 1, wherein: The collimating mirror shapes the Gaussian beam output by the laser, shaping the divergent beam into a parallel beam to reduce the aberration of the laser passing through the field lens.

3. The method for online monitoring of laser power according to claim 1, characterized in that: The beam expander expands the spot diameter of the parallel beam emerging from the collimating mirror without changing the spot shape.

4. The method for online monitoring of laser power according to claim 1, characterized in that: The dichroic mirror has high transmittance for 1070nm laser and high reflectance for light with wavelengths of 750nm - 950nm, providing a path for the signal source of the monitoring module without affecting the printing laser.

5. The method for online monitoring of laser power according to claim 1, wherein: The galvanometer scanner controls the mirror to change its position and direction through a drive board and a high-speed swing motor, thereby changing the position where the reflected light hits the target.

6. The method for online monitoring of laser power according to claim 1, characterized in that: The filter is an absorption type filter, which absorbs some specific wavelengths and has little or no effect on light of other wavelengths.

7. The method for online monitoring of laser power according to claim 1, characterized in that: The beam splitter divides the laser into two paths, and the beam splitting ratio is , where T is the transmittance and R is the reflectance.

8. The method for online monitoring of laser power according to claim 1, characterized in that: The focusing lens focuses the radiation light of the molten pool onto the photodetector.

9. The method for online monitoring of laser power according to claim 1, characterized in that: The lens images the morphology of the molten pool on the high-speed camera, and the high-speed camera is used to collect the morphology image of the molten pool.

10. An online laser power monitoring system, characterized in that: Including the laser, collimating mirror, beam expander, dichroic mirror, galvanometer, field lens, filter, beam splitter, focusing lens, photodetector, lens, and high-speed camera used in the method for online monitoring of laser power according to any one of claims 1-9, the laser emitted by the laser sequentially passes through the collimating mirror, beam expander, dichroic mirror, galvanometer, and field lens and acts on the metal powder on the substrate, and the molten pool radiation light sequentially passes through the field lens, galvanometer, dichroic mirror, filter, and beam splitter, and a part of it is focused on the photodetector through the focusing lens, and the other part is imaged on the high-speed camera through the lens.

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