Method for monitoring laser power on line

Abstract

The invention discloses a method for monitoring laser power online, and belongs to the technical field of additive manufacturing, laser power monitoring is realized by adopting a system comprising a laser, a collimating mirror, a beam expander, a dichroscope, a galvanometer, a field lens, an optical filter, a beam splitter, a focus lens, a photoelectric detector, a lens and a high-speed camera, and the method specifically comprises the following steps: S1, offline power testing; s2, on-line intensity monitoring and power calibration; and S3, real-time power monitoring. By reducing the light paths of the power monitoring module, the problem that the space of the multi-laser equipment is narrow due to many top optical components is effectively solved, in the multi-laser equipment, monitoring of each path of laser can be achieved, the equipment space is fully utilized, the situation that multiple monitoring modules cannot be placed at the same time due to space limitation is avoided, and the working efficiency of the multi-laser equipment is improved. And the light path layout of the multi-laser equipment is more reasonable and efficient.

Description

Technical Field

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

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

[0003] In the existing SLM monitoring technology, the laser is divided into two paths after shaping through a dichroic mirror. One path is reflected to the power monitoring module to monitor the laser power, and the other path is transmitted to the galvanometer and focused by the field lens before printing. The molten pool radiation light is reflected to the molten pool monitoring module through the field lens, galvanometer, and dichroic mirror. The powder bed monitoring is an independent module. This optical path is feasible on a single laser additive manufacturing device, but multi-laser devices require multiple optical paths and have a narrow space due to the large number of optical components on the top. It is difficult to place three monitoring modules at the same time, and it is impossible to monitor the laser intensity, morphology, and power simultaneously. Therefore, a method for online monitoring of laser power is needed to solve the above problems. Summary of the invention

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

[0005] To achieve the above object, the present invention provides the following technical solution: a method for online monitoring of laser power, using a system including a laser, a collimator, 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 to realize laser power monitoring, specifically comprising the following steps: S1: Before the device starts printing, use a power meter to test the output optical power of the laser when it is offline. The specific operation is as follows: S11: Start the laser and open the printing software of the device; S12: Control the laser output light power range to be 50W-450W with a step size of 50W to measure and record data; S13: Arrange the output power data and record the test results as ; S2: When the printer starts printing, the melt pool strength online monitoring system is used to monitor the melt pool strength signal. The specific operations are as follows: S21: Start the laser, open the printing software and intensity monitoring software of the device; S22: Print the entire format of the equipment substrate, control the laser output power range to be 50W-450W, and measure and record the data with a step length of 50W. Use the intensity software to collect the molten pool intensity data of the entire large format under different power conditions; S23: Organize and output the test data, and record the test results as ; S24: The intensity of the molten pool is obtained from the recorded data, corresponding to the laser power value tested by the power meter, and the expression between the two is obtained by curve fitting , the laser output optical power corresponding to different intensities can be obtained through the expression, where: P is the laser output optical power; U is the amplitude of the molten pool intensity; S25: When changing the material, repeat steps S21-S24 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; S3: During the printing process, the stability of the laser power is monitored by outputting the melt pool intensity signal through the photoelectric detector, and the real-time output of the laser power value is realized at the same time. The photoelectric detector converts the received laser power into a current signal through photoelectric conversion, and the current signal is converted into a voltage signal output through a transimpedance amplifier circuit. The output voltage signal represents the stability of the laser power. If the voltage signal detected by the detector is stable and unchanged, it means that the optical power received by the detector is stable, and then the output optical power of the laser is stable.

[0006] As a preferred implementation, the collimator shapes the Gaussian beam output by the laser, and shapes the divergent beam into a parallel beam, so as to reduce the aberration of the laser passing through the field lens.

[0007] As a preferred implementation, the beam expander enlarges the spot diameter of the parallel light beam emitted from the collimator but does not change the spot shape.

[0008] As a preferred embodiment, the dichroic mirror has high transmittance to 1070nm laser and high reflectivity to 750nm-950nm light, thus providing a path for the signal source of the monitoring module without affecting the printing laser.

[0009] As a preferred implementation, the galvanometer controls the reflector through a drive plate and a high-speed swing motor to achieve changes in position and direction, thereby changing the position where the reflected light hits the target.

[0010] As a preferred implementation, the filter is an absorption filter, which absorbs certain specific wavelengths and has little or no effect on light of other wavelengths.

[0011] As a preferred embodiment, the beam splitter splits the laser into two paths, and the beam splitting ratio is , where T is the transmittance and R is the reflectivity.

[0012] As a preferred embodiment, the focusing mirror focuses the radiation light of the molten pool onto the photodetector.

[0013] As a preferred implementation, 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.

[0014] The present invention discloses a system for online monitoring of laser power, comprising a laser, a collimator, a beam expander, a dichroic mirror, a galvanometer, a field mirror, a filter, a beam splitter, a focusing mirror, a photoelectric detector, a lens, and a high-speed camera used in the above-mentioned method for online monitoring of laser power. The laser emitted by the laser sequentially passes through the collimator, the beam expander, the dichroic mirror, the galvanometer, and the field mirror and then acts on metal powder on a substrate. The radiation light from the molten pool sequentially passes through the field mirror, the galvanometer, the dichroic mirror, the filter, and the beam splitter, and then a part of the light is focused on the photoelectric detector through the focusing mirror, and the other part of the light is imaged on the high-speed camera through the lens.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. Traditional multi-laser equipment requires multiple optical paths and needs to be equipped with 3 or more monitoring modules for optical path monitoring. The present invention effectively solves the problem of narrow space due to many top optical components in multi-laser equipment by reducing the optical path of the power monitoring module. In the multi-laser equipment, each laser can be monitored, and the equipment space can be fully utilized to avoid the situation where multiple monitoring modules cannot be placed at the same time due to space limitations, making the optical path layout of the multi-laser equipment more reasonable and efficient.

[0016] 2. The present invention can utilize one optical signal to simultaneously realize the joint monitoring of the laser optical power and the molten pool intensity, 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 of monitoring, and reduces the system coordination and maintenance costs caused by multiple optical paths and multiple modules.

[0017] 3. One less optical path directly reduces the number of optical components used, which not only reduces the manufacturing cost of the equipment, but also reduces the risk of monitoring damage due to component failure due to the reduction in the number of optical components, thereby improving the overall stability and reliability of the monitoring system.

[0018] 4. Based on the unique monitoring process testing method, it can analyze in real time the reasons for the unstable strength signal of the molten pool. During the printing process, once the strength signal is abnormal, the problem can be discovered and handled in time to avoid part defects caused by factors such as unstable laser power, thereby improving printing efficiency, increasing the success rate of the final parts, and improving product quality.

[0019] 5. The laser power is characterized by the molten pool intensity signal. 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, provides a reliable basis for the precise control of the laser power during the printing process, and helps to further optimize the printing process parameters and improve the consistency and stability of the printing quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the process of the method for online monitoring of laser power of the present invention; Figure 2 A schematic diagram of the offline power test steps of the present invention; Figure 3 It is a schematic diagram of the online intensity monitoring and power calibration steps of the present invention; Figure 4 A schematic diagram of the monitoring optical path of the system of the present invention; Figure 5 This is a flow chart of online monitoring of laser power of the present invention; Figure 6 Schematic diagram of the laser power measurement method of the system of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the embodiments.

[0022] The following examples are used to illustrate the present invention, but they cannot be used to limit the scope of protection of the present invention. The conditions in the examples can be further adjusted according to specific conditions. Simple improvements to the method of the present invention under the premise of the concept of the present invention belong to the scope of protection claimed in the present invention. Specific embodiment 1 See also Figure 1-6 The present invention provides a method for online monitoring of laser power, which uses a system including a laser, a collimator, 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 to realize laser power monitoring, and specifically includes the following steps: S1: Before the device starts printing, use a power meter to test the output optical power of the laser when it is offline. The specific operation is as follows: S11: Start the laser and open the printing software of the device; S12: Control the laser output light power range to be 50W-450W with a step size of 50W to measure and record data; S13: Arrange the output power data and record the test results as ; S2: When the printer starts printing, the melt pool strength online monitoring system is used to monitor the melt pool strength signal. The specific operations are as follows: S21: Start the laser, open the printing software and intensity monitoring software of the device; S22: Print the entire format of the equipment substrate, control the laser output power range to be 50W-450W, and measure and record the data with a step length of 50W. Use the intensity software to collect the molten pool intensity data of the entire large format under different power conditions; S23: Organize and output the test data, and record the test results as ; S24: The intensity of the molten pool is obtained from the recorded data, corresponding to the laser power value tested by the power meter, and the expression between the two is obtained by curve fitting , the laser output optical power corresponding to different intensities can be obtained through the expression, where: P is the laser output optical power; U is the amplitude of the molten pool intensity; S25: Change the material. 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. S3: During the printing process, the stability of the laser power is monitored by outputting the melt pool intensity signal through the photoelectric detector, and the real-time output of the laser power value is realized at the same time. The photoelectric detector converts the received laser power into a current signal through photoelectric conversion, and the current signal is converted into a voltage signal output through a transimpedance amplifier circuit. The output voltage signal represents the stability of the laser power. If the voltage signal detected by the detector is stable and unchanged, it means that the optical power received by the detector is stable, and then the output optical power of the laser is stable.

[0024] The collimator shapes the Gaussian beam output by the laser and shapes the divergent beam into a parallel beam to reduce the aberration of the laser passing through the field lens.

[0025] The beam expander enlarges the spot diameter of the parallel light beam emitted from the collimator without changing the spot shape.

[0026] The dichroic mirror is highly transparent to 1070nm laser and highly reflective to 750nm-950nm light, providing a path for the signal source of the monitoring module without affecting the printing laser.

[0027] The galvanometer controls the reflector 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.

[0028] The filter is an absorption filter that absorbs some specific wavelengths and has little or no effect on light of other wavelengths.

[0029] The beam splitter divides the laser into two paths, and the beam splitting ratio is , where T is the transmittance and R is the reflectivity.

[0030] The focusing mirror focuses the radiation light from the molten pool onto the photodetector.

[0031] 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.

[0032] The invention discloses a system for online monitoring of laser power, comprising a laser, a collimator, a beam expander, a dichroic mirror, a galvanometer, a field mirror, a filter, a beam splitter, a focusing mirror, a photoelectric detector, a lens, and a high-speed camera used in a method for online monitoring of laser power. The laser emitted by the laser sequentially passes through the collimator, the beam expander, the dichroic mirror, the galvanometer, and the field mirror, and then acts on metal powder on a substrate. The radiation light from the molten pool sequentially passes through the field mirror, the galvanometer, the dichroic mirror, the filter, and the beam splitter, and then a part of the radiation light is focused on the photoelectric detector through a focusing mirror, and the other part of the radiation light is imaged on the high-speed camera through a lens.

[0033] The working principle and use process of the present invention are as follows: First, in the equipment preparation stage, such as before starting the additive manufacturing equipment to perform a printing task, step S1 is executed, the operator starts the laser and opens the printing software of the equipment, and then controls the laser output light power between 50W and 450W, and performs measurements in steps of 50W. For example, starting from 50W, the power data P1 collected by the power meter is recorded at this time, and then the laser output light power is adjusted to 100W, and the power data P2 is recorded again, and so on, the measurement of the entire power range is completed and the data is sorted. When the printer starts printing, step S2 is entered, and the operator first starts the laser and opens the printer software. The equipment's printing software and special intensity monitoring software are used, and then the entire format of the equipment substrate is printed. In this process, the laser output power is controlled to start from 50W and gradually adjusted in 50W steps. At each power value, not only the intensity software is used to collect the molten pool intensity data of the entire large format, such as recording the molten pool intensity data U1 at 50W power and U2 at 100W power, but also the laser power itself is measured and recorded. After all data collection is completed, these test data are sorted and output. By analyzing and processing the molten pool intensity data and the laser power value measured by the power meter, for example, a mathematical fitting method is used to obtain the expression between the two. , where: P is the laser output power; U is the amplitude of the molten pool intensity; Furthermore, when different printing materials are replaced, the above steps from S21 to S24 are repeated to achieve the calibration of the power of different materials, ensuring that the accurate expression of the corresponding material can be selected when the system is used to characterize the laser power. During the entire printing process, step S3 is always executed, the photoelectric detector continuously receives the laser, and the laser power is converted into a current signal through internal photoelectric conversion, and the current signal is then converted into a voltage signal output through a transimpedance amplifier circuit. The system analyzes the output voltage signal. If the voltage signal is stable, it can be determined that the optical power received by the detector is stable, which indicates that the output optical power of the laser is in a stable state. At the same time, according to the expression obtained by the previous calibration , can calculate and output the current laser power in real time according to the monitored molten pool intensity signal, and realize online monitoring of laser power. In this process, the various optical components in the system work together. The collimator 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 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 proportionally; the focusing mirror focuses the molten pool radiation light onto the photodetector; the lens images the molten pool morphology on the high-speed camera, and the high-speed camera collects the molten pool morphology image, which together ensure the effective implementation of the entire online monitoring laser power method. Specific embodiment 2 like Figure 5 As shown, in combination with specific embodiment 1, the present invention proposes a laser power online monitoring method, comprising the following steps: S1 system initialization; S2 collects melt pool strength data; S3 determines whether the intensity data is stable. If it is stable, the laser power is determined to be stable. If it is not stable, proceed to the next step. S3 obtains printing process parameter data; S4 compares the molten pool intensity data obtained in S3 with the printing process parameter data to determine the consistency. If they are consistent, it is determined that the laser power is stable; if they are inconsistent, proceed to the next step; S5 monitors the powder bed and determines the uniformity of the powder. If the powder is evenly spread, it is determined that the unstable laser power leads to unstable molten pool intensity data, and dimming operation is performed, and the system returns to initialization to re-acquire intensity data; if the powder is uneven, proceed to the next step; S6 acquires image data, and compares the acquired image data with the molten pool intensity data. If they are consistent, it is determined that the laser power is stable; if they are inconsistent, it is determined that the laser power is unstable, and a dimming operation is performed, and the system returns to initialization to re-acquire intensity data; S7 Steps S3-S6 process the molten pool intensity data determined to be stable by the laser power using an algorithm, calculate the power value, and end the process.

[0035] The present invention is based on a unique monitoring process testing method, which can analyze in real time the reasons leading to the instability of the molten pool intensity signal. During the printing process, once an abnormal intensity signal occurs, the problem can be discovered and dealt with in time to avoid part defects caused by factors such as unstable laser power, thereby improving printing efficiency, increasing the success rate of the final parts, and improving product quality.

[0036] The laser power is characterized by the molten pool intensity signal. 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, provides a reliable basis for the precise control of the laser power during the printing process, and helps to further optimize the printing process parameters and improve the consistency and stability of printing quality.

[0037] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that 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: Laser power monitoring is achieved by using a system including a laser, a collimator, 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. Specifically, the following steps are included: S1: Before the device starts printing, use a power meter to test the output optical power of the laser when it is offline. The specific operation is as follows: S11: Start the laser and open the printing software of the device; S12: Control the laser output light power range to be 50W-450W with a step size of 50W to measure and record data; S13: Arrange the output power data and record the test results as ; S2: When the printer starts printing, the melt pool strength online monitoring system is used to monitor the melt pool strength signal. The specific operations are as follows: S21: Start the laser, open the printing software and intensity monitoring software of the device; S22: Print the entire format of the equipment substrate, control the laser output power range to be 50W-450W, and measure and record the data with a step length of 50W. Use the intensity software to collect the molten pool intensity data of the entire large format under different power conditions; S23: Organize and output the test data, and record the test results as ; S24: The intensity of the molten pool is obtained from the recorded data, corresponding to the laser power value tested by the power meter, and the expression between the two is obtained by curve fitting , where: P is the laser output power; U is the amplitude of the molten pool strength; The laser output optical power corresponding to different intensities can be obtained through the expression; S25: Change the material and repeat steps S21-S24 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; S3: During the printing process, the stability of the laser power is monitored by outputting the melt pool intensity signal through the photoelectric detector, and the real-time output of the laser power value is realized at the same time. The photoelectric detector converts the received laser power into a current signal through photoelectric conversion, and the current signal is converted into a voltage signal output through a transimpedance amplifier circuit. The output voltage signal represents the stability of the laser power. If the voltage signal detected by the detector is stable and unchanged, it means that the optical power received by the detector is stable, and then the output optical power of the laser is stable.

2. The method for online monitoring of laser power according to claim 1, characterized in that: The collimator shapes the Gaussian beam output by the laser, and shapes the divergent beam into a parallel beam, so as 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 light beam emitted from the collimator but does not change 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 to 1070nm laser and high reflectivity to 750nm-950nm light, 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, characterized in that: The galvanometer controls the reflector through a driving plate and a high-speed swing motor to achieve changes in position and direction, 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 optical filter is an absorption 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 splits the laser into two paths, and the beam splitting ratio is , where T is the transmittance and R is the reflectivity.

8. The method for online monitoring of laser power according to claim 1, characterized in that: The focusing mirror 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. A system for online monitoring of laser power, characterized in that: The method comprises a laser, a collimator, a beam expander, a dichroic mirror, a galvanometer, a field mirror, a filter, a beam splitter, a focusing mirror, a photoelectric detector, a lens, and a high-speed camera used in the method for online monitoring of laser power as described in any one of claims 1 to 9, wherein the laser emitted by the laser sequentially passes through the collimator, the beam expander, the dichroic mirror, the galvanometer, and the field mirror and then acts on the metal powder on the substrate; the radiated light from the molten pool sequentially passes through the field mirror, the galvanometer, the dichroic mirror, the filter, and the beam splitter, and then a part of it is focused on the photoelectric detector through the focusing mirror, and the other part is imaged on the high-speed camera through the lens.

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