A laser processing absorptivity measurement system and method

Abstract

The application belongs to the technical field of laser processing, and discloses a kind of laser processing absorption rate measuring system and method, comprising: the laser emitted by continuous fiber laser is gathered by laser gathering device, and laser beam is shot into substrate by coaxial powder feeding head;Step motor is opened, and step motor drives laser gathering device to move, to realize processing to substrate;When processing ends, collector continues to collect temperature change data with time, until substrate cools to near room temperature;And the temperature data collected is sent to computer, and computer processes substrate temperature signal, calculates the convection heat transfer coefficient in laser processing process and the average temperature curve of substrate in laser processing process by lumped parameter method, and obtains the absorption rate corrected by heat convection according to temperature curve and convection heat transfer coefficient.The application realizes the measurement of absorption rate in industrial processing process, uses surface heat dissipation correction, and improves the precision of absorption rate measurement.

Description

Technical Field

[0001] The invention belongs to the technical field of laser processing and relates to a laser processing absorptivity measurement system and method. Background Art

[0002] Laser processing plays an important role in metal joining, manufacturing, repair, and welding. Evaluating the absorptivity of metals with different laser wavelengths is a hot topic. Ideal absorptivity can be calculated using Drude theory. However, during laser processing, oxides increase the material's absorptivity. Therefore, spectroscopic methods are widely used to measure the absorptivity of metal powders used in processing. However, due to the significant temperature fluctuations surrounding the metal when the laser is applied, spectrometers can only measure absorptivity at room temperature. For transient absorptivity measurement, some researchers have applied integrating sphere equipment to keyhole-mode melt pool laser processing. This equipment can be embedded in in-situ X-ray monitoring systems, combining keyhole morphology and transient absorptivity. However, to maximize the capture of reflected light, the substrate must be tilted at a certain angle, which results in discrepancies with actual production processes, and the integrating sphere equipment is relatively expensive. Calorimetry is a traditional absorptivity calculation method based on the physical relationship between heat conduction conditions, material properties, temperature, and absorptivity. This method is suitable for situations with minimal dimensional variation in the melt pool, such as thermally conductive melt pools, and the calculated absorptivity value is not an average value over the sampling process. However, when calculating the absorptivity using the calorimetric method, the absorptivity measurement value is low due to the long processing time and the loss caused by the heat exchange between the substrate and the surrounding environment during the processing. Summary of the Invention

[0003] The purpose of the present invention is to solve the problem in the prior art that the absorptivity measurement value is low due to the long time taken by the calorimetric method to calculate the absorptivity and the loss caused by the heat exchange between the substrate and the surrounding environment during the processing, and to provide a laser processing absorptivity measurement system and method.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A laser processing absorptivity measurement system includes: a laser processing device and a laser absorptivity measurement device; the laser absorptivity measurement device includes: a substrate, a thermocouple, an insulation plate, a collector and a computer; the laser processing device includes a continuous fiber laser, a laser focusing device and a powder feeding device;

[0006] The laser emitted by the continuous fiber laser is focused by a laser focusing device, the powder feeding device is connected to the coaxial powder feeding head, the coaxial powder feeding head is connected to the laser focusing device, and the substrate is set directly below the coaxial powder feeding head; the laser beam focused by the laser focusing device is shot into the substrate through the coaxial powder feeding head; a thermocouple is set on the substrate, and an insulation plate is set at the bottom of the substrate to prevent and reduce the thermal conduction loss from the substrate to the processing platform, so that most of the heat loss of the substrate during the laser processing process is through convection between the substrate and the air rather than heat conduction to the processing platform; the collector is connected to the thermocouple, collects the substrate temperature signal and transmits the collected temperature signal to the computer; the computer processes the substrate temperature signal to obtain the laser absorption rate value and the average temperature curve of the substrate.

[0007] A further improvement of the present invention is:

[0008] Furthermore, the laser focusing device and the continuous laser generator are externally connected to a water cooler to prevent the laser focusing device and the continuous laser generator from overheating.

[0009] Furthermore, the continuous laser generator and the laser focusing device are integrated into one design; the continuous laser generator is externally connected to a stepper motor, and the stepper motor drives the continuous laser generator to move to scan the substrate.

[0010] Furthermore, the powder feeding device includes a powder cylinder and a connecting pipe; the powder cylinder evenly feeds the metal powder to the substrate through a coaxial powder feeding head via the connecting pipe; the coaxial powder feeding head is located at one end of the laser focusing device.

[0011] Furthermore, there are several thermocouples, which are arranged on the drilled holes on the substrate, and the thermocouples and the substrate are connected with thermal conductive glue; an air pump is provided on the coaxial powder feeding head; the air pump includes a protective gas port and a powder feeding gas port; when the laser beam scans the substrate and the substrate is cooled, the protective gas is not closed; when the laser beam scans the substrate, when the powder cylinder needs to transport metal powder to the substrate, the powder feeding gas port is opened for gas delivery; when the substrate is cooled, the protective gas and the powder feeding gas are not closed.

[0012] A method for measuring laser processing absorptivity comprises: a collector recording the initial temperature of a substrate before an experiment begins; a continuous fiber laser is turned on, the laser light emitted by the continuous fiber laser is focused by a laser focusing device, and the laser beam focused by the laser focusing device is emitted onto the substrate through a coaxial powder feeding head; a stepper motor is turned on, and the stepper motor drives the laser focusing device to move, thereby processing the substrate; when processing is completed, the collector continues to collect data on temperature changes over time until the substrate cools to near room temperature; and the collected temperature data is sent to a computer, which processes the substrate temperature signal to obtain a laser absorptivity value and an average substrate temperature curve.

[0013] Furthermore, processing the substrate includes: if during the processing, the powder cylinder does not transport metal powder to the substrate through the coaxial powder feeding head, the scanning path of the laser beam is to scan back and forth along the laser scanning direction; and during the cooling process, the protective gas is not closed; if during the processing, the powder cylinder transports metal powder to the substrate through the coaxial powder feeding head, the scanning path of the laser beam is to keep moving along a path perpendicular to the laser scanning path when no powder is added; and during the cooling process, the protective gas and the powder feeding gas are not closed.

[0014] Furthermore, processing the substrate includes: processing the substrate temperature signal by a computer to obtain the convective heat transfer coefficient and the laser absorption rate value, specifically:

[0015] Denoise the collected temperature data, and obtain the convective heat transfer coefficient based on the denoised and smoothed temperature data and the lumped parameter method;

[0016] Based on the substrate temperature at the end of processing determined by the lumped parameter method, the temperature of each sampling point in the temperature data is corrected, and the corrected temperatures are averaged to obtain the average temperature curve during the substrate heating process;

[0017] The laser absorptivity value is obtained based on the average temperature curve of the substrate during heating, the convection heat transfer coefficient between the substrate and air during processing, the start time of laser processing, and the end time of laser processing.

[0018] Furthermore, based on the denoised and smoothed temperature data and the lumped parameter method, the convective heat transfer coefficient is obtained, specifically:

[0019]

[0020] After mathematical transformation, it is expressed as a regression equation:

[0021]

[0022] Where θ is the temperature difference between the substrate and the atmosphere, θ cs The cooling phase starts at t cs The temperature difference between the substrate and the air. The start time of the cooling phase is defined as 10 seconds after the end of processing to ensure that the substrate temperature is uniform during the cooling phase. T is the temperature measured by the thermocouple, T f is the air temperature, T cs t cs The substrate temperature at the time of laser processing is 0.040°; c is the substrate specific heat capacity, h is the surface heat transfer coefficient, m is the substrate mass, t is the experimental time, including the laser processing and the cooling time after processing; S is the substrate surface area;

[0023] The substrate temperature at the end of the processing determined according to the lumped parameter method is used to correct the temperature of each sampling point in the temperature data, and the corrected temperature is averaged to obtain the average temperature curve during the substrate heating process, specifically:

[0024] The average temperature curve of the substrate during the heating process is determined by averaging the rescaled sampling point temperature curves. The sampling point temperature curve is linearly rescaled, with the temperature at the start of the processing as the temperature before substrate heating and the temperature at the end of the processing as the temperature at the end of substrate heating:

[0025]

[0026] where T n is the linearly rescaled temperature of the sampling point, T end is the substrate temperature at the end of heating, T start is the substrate temperature at the start of heating, T 20 is the thermocouple measurement temperature at the end of heating, T 10 is the thermocouple measurement temperature at the start of heating, and T s is the thermocouple measurement temperature; T is the average temperature of the substrate during heating.

[0027] Further, based on the average temperature curve during the substrate heating process, the convective heat transfer coefficient between the substrate and the air during the processing, the start time of the laser processing, and the end time of the laser processing, the laser absorption rate value is obtained, specifically:

[0028]

[0029] where η is the calculated absorption rate, S is the surface area of the substrate, Δt is the interval between adjacent sampling times, P is the laser beam power; T is the average temperature of the substrate during heating, which varies with experimental time t, and ΔT is the difference in average temperature of the substrate between adjacent sampling time intervals; t end is the end of heating, t start is the start of heating; c(T) is the specific heat capacity of the substrate material, which is a function of the average temperature of the substrate; m(t) is the mass of the substrate, which is a function of the experimental time t. For experiments without powder feeding, the mass of the substrate is considered not to change, and for powder feeding experiments, the mass of the substrate increases after powder feeding, and the mass of the substrate is considered to increase linearly during laser processing:

[0030]

[0031] where m0 represents the mass of the substrate before processing, m1 represents the mass of the substrate after processing, t start is the start of laser processing, and t end is the end of laser processing.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention applies laser light generated by a laser to a substrate. The substrate temperature signal is connected to a collector via thermocouple wires. The collector collects the temperature signal and transmits it to a computer for storage. The computer then calculates an energy correction value for surface heat dissipation during the heating process based on the collected substrate heating and cooling curves, and also calculates the corrected absorptivity value. This method enables absorptivity measurement during long-term laser processing. Using surface heat dissipation correction, the accuracy of absorptivity measurement is improved, making it widely applicable to processes such as laser additive manufacturing and laser welding at any wavelength. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 Schematic diagram of the structure of the laser processing absorptivity measurement system of the present invention;

[0036] Figure 2 This is a schematic diagram of the thermocouple points on the substrate;

[0037] Figure 3 Schematic diagram of the process for obtaining the convective heat transfer coefficient and laser absorptivity values.

[0038] Among them, 1- substrate; 2- thermocouple; 3- insulation board; 4- collector; 5- computer; 6- powder cylinder; 7- connecting pipe; 8- laser focusing device; 9- coaxial powder feeding head. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0040] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0041] It should be noted that like reference numerals and letters refer to like items throughout the accompanying drawings, and once an item is defined in one drawing, it is not necessary to further define and explain it in subsequent drawings.

[0042] In the description of the embodiments of the present application, it should be noted that if the terms "upper", "lower", "horizontal", "inner" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the present application is usually placed, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0043] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly inclined. For example, "horizontal" only means that its direction is relatively more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0044] In the description of the embodiments of the present application, it should also be noted that unless otherwise explicitly specified and limited, if the terms "arrangement", "installation", "connection", "connection" appear, they should be understood in a broad sense, for example, they can be fixedly connected, or can be detachably connected, or integrally connected; can be mechanically connected, or can be electrically connected; can be directly connected, or can be indirectly connected through an intermediate medium; can be the communication between two elements inside. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0045] The present application will be described in further detail below with reference to the accompanying drawings:

[0046] Referring to Figure 1 The present application discloses a kind of laser processing absorption rate measurement system, comprising: laser processing device and laser absorption rate measurement device;Laser absorption rate measurement device includes: substrate 1, thermocouple 2, heat insulation plate 3, collector 4 and computer 5;Laser processing device includes continuous fiber laser, laser gathering device 8 and powder feeding device;

[0047] The laser emitted by the continuous fiber laser is focused by a laser focusing device 8, the powder feeding device is connected to a coaxial powder feeding head 9, the coaxial powder feeding head 9 is connected to the laser focusing device 8, and the substrate 1 is arranged directly below the coaxial powder feeding head 9; the laser beam focused by the laser focusing device 8 is emitted onto the substrate 1 through the coaxial powder feeding head 9; a thermocouple 2 is arranged on the substrate 1, and an insulation plate 3 is arranged at the bottom of the substrate 1 to prevent and reduce the thermal conduction loss from the substrate 1 to the processing platform, so that most of the heat loss of the substrate during the laser processing process is through convection between the substrate and the air rather than heat conduction to the processing platform; the collector 4 is connected to the thermocouple 2, collects the temperature signal of the substrate 1 and transmits the collected temperature signal to the computer 5; the computer 5 processes the temperature signal of the substrate 1 to obtain the laser absorption rate value and the average temperature curve of the substrate.

[0048] The laser focusing device 8 and the continuous laser generator are externally connected to a water cooler to prevent the laser focusing device 8 and the continuous laser generator from overheating.

[0049] The continuous laser generator and the laser focusing device 8 are integrated into one design; the continuous laser generator is externally connected to a stepping motor, and the stepping motor drives the continuous laser generator to move to scan the substrate 1.

[0050] The powder feeding device includes a powder cylinder 6 and a connecting pipe 7 ; the powder cylinder 6 evenly feeds the metal powder to the substrate 1 through the coaxial powder feeding head 9 via the connecting pipe 7 ; the coaxial powder feeding head 9 is located at one end of the laser focusing device 8 .

[0051] There are several thermocouples 2, which are set on the drilled holes on the substrate 1, and their point distribution is as follows: Figure 2 As shown, the thermocouple 2 and substrate 1 are connected with thermally conductive adhesive. The thermocouple 2 extends 5 mm into the substrate, which measures 100 mm × 100 mm × 15 mm. An air pump is provided on the coaxial powder feeder 9. The air pump includes a shielding gas port and a powder feed port. The shielding gas is not shut off when the laser beam is scanning the substrate 1 and the substrate is cooling. When the laser beam is scanning the substrate 1 and the powder cylinder 6 needs to deliver metal powder to the substrate 1, the powder feed port is opened to deliver air. When the substrate is cooling, the shielding gas and powder feed ports are not shut off.

[0052] A method for measuring laser processing absorptivity includes: a collector 4 records the initial temperature of a substrate 1 before the experiment begins, a continuous fiber laser is turned on, the laser light emitted by the continuous fiber laser is focused by a laser focusing device 8, and the laser beam focused by the laser focusing device 8 is emitted onto the substrate 1 through a coaxial powder feeding head 9; a stepper motor is turned on, and the stepper motor drives the laser focusing device 8 to move, thereby processing the substrate 1; when the processing is completed, the collector 4 continues to collect temperature change data over time until the substrate 1 cools to near room temperature; and the collected temperature data is sent to a computer 5, which processes the temperature signal of the substrate 1 to obtain a laser absorptivity value and an average substrate temperature curve.

[0053] Processing the substrate includes: if during the processing, the powder cylinder 6 does not transport metal powder to the substrate 1 through the coaxial powder feeding head 9, the scanning path of the laser beam is to scan back and forth along the laser scanning direction; and during the cooling process, the shielding gas is not closed; if during the processing, the powder cylinder 6 transports metal powder to the substrate 1 through the coaxial powder feeding head 9, the scanning path of the laser beam is to keep moving along a path perpendicular to the laser scanning path when no powder is added; and during the cooling process, the shielding gas and the powder feeding gas are not closed.

[0054] During the measurement of absorptivity without powder feeding, the laser scanning path is along Figure 2 The AB segment is scanned cyclically. The substrate temperature should be between 150°C and 250°C after scanning to minimize the impact of temperature measurement errors on the calculated absorptivity. The substrate temperature should be below 40°C before the experiment begins. The scanning speed is set at 1000 mm / min, with a single pass length of 60 mm. During the powder feeding absorptivity measurement, the laser scanning path precesses perpendicularly to the AB direction, in addition to the AB direction, to avoid uneven heat dissipation in the deposition area due to excessively high deposited layers.

[0055] See also Figure 3 , processing the substrate includes: computer processing the substrate temperature signal to obtain the convection heat transfer coefficient and laser absorption rate value, specifically:

[0056] S101, performing noise reduction and smoothing processing on the collected temperature data, and obtaining the convective heat transfer coefficient based on the noise-reduced temperature data and the lumped parameter method;

[0057] The collected temperature data was denoised using a Hample filter to remove outliers. The window width was set to 11, and the removal threshold was set to 20 times the median absolute deviation. The window width for curve smoothing was set to 360, and the smoothed data point value was the average of the data within the window.

[0058] The moment the laser starts or ends is determined by the collection point closest to the laser processing point. The start time of laser processing is determined using the double linear regression intersection method. First, select the temperature-time curve of the collection point closest to the laser starting point, select 4 points before and after the start of heating, and define the curve into two stages: a constant stage and a linear growth stage. The selection principle is to ensure that the temperature changes linearly with time. Before the start moment of the constant stage, the temperature should fluctuate around a constant, while the linear growth stage occurs after the laser is turned on. Then, the linear regression equation is calculated based on the points in these two stages. The time coordinate of the intersection of the two linear equations is the start time of laser processing. The method for determining the end time of laser processing is to obtain the maximum temperature point in the last thermal cycle of the collection point closest to the laser end point as the end time.

[0059] Based on the denoised temperature data and the lumped parameter method, the convective heat transfer coefficient is obtained, specifically:

[0060]

[0061] After mathematical transformation, it is expressed as a regression equation:

[0062]

[0063] Where θ is the temperature difference between the substrate and the atmosphere, θ cs The cooling phase starts at t cs The temperature difference between the substrate and the air. The start time of the cooling phase is defined as 10 seconds after the end of processing to ensure that the substrate temperature is uniform during the cooling phase. T is the temperature measured by the thermocouple, T f is the air temperature, T cs t cs The substrate temperature at the time of laser processing is 0.040°; c is the substrate specific heat capacity, h is the surface heat transfer coefficient, m is the substrate mass, t is the experimental time, including the laser processing and the cooling time after processing; S is the substrate surface area;

[0064] S102, correcting the temperature of each sampling point in the temperature data according to the substrate temperature at the end of processing determined by the lumped parameter method, and averaging the corrected temperatures to obtain an average temperature curve during the substrate heating process;

[0065] According to the conditions of the lumped parameter method, the substrate has good internal heat conduction and the temperature is approximately the same everywhere. In this case, the temperature of each sampling point is corrected, and the temperature at the start and end of heating is set as a fixed value, and the temperature at each intermediate moment is corrected accordingly.

[0066]

[0067] The average temperature rise curve of the substrate during the heating process is determined by scaling the temperature curves of each sampling point and averaging them. The sampling point temperature curve adopts linear scaling. The constraint point is that the temperature at the start of the process is the temperature before the substrate is heated, and the temperature at the end of the process is the temperature at the end of the substrate heating:

[0068]

[0069] Among them, T n is the temperature of the sampling point after linear scaling, T end is the substrate temperature at the end of heating, T start is the substrate temperature at the start of heating, T 20 is the temperature measured by the thermocouple at the end of heating, T 10 is the temperature measured by the thermocouple at the start of heating, T sis the temperature measured by the thermocouple; T is the average temperature of the substrate during the heating process.

[0070] S103 , obtaining a laser absorptivity value based on an average temperature curve during the substrate heating process, a convection heat transfer coefficient between the substrate and air during the processing, a start time of the laser processing, and an end time of the laser processing.

[0071]

[0072] Where η is the calculated value of the absorption rate, S is the surface area of ​​the substrate, Δt is the time interval between two adjacent samplings, and P is the laser beam power; T is the average temperature of the substrate during the heating process, which changes with the experimental time t, and ΔT is the difference in the average temperature of the substrate between two adjacent sampling times; t end is the heating end time, t start is the starting time of heating; c(T) is the specific heat capacity of the substrate material, which is a function of the average temperature of the substrate; m(t) is the substrate mass, which is a function of the experimental time t. For experiments without powder feeding, it is assumed that the substrate mass does not change. For experiments with powder feeding, the substrate mass increases after powder feeding. During laser processing, it is assumed that the substrate mass increases linearly:

[0073]

[0074] Among them, m0 represents the mass of the substrate before processing, m1 represents the mass of the substrate after processing, and t start is the starting time of laser processing, t end This is the time when laser processing ends.

[0075] Here t start The starting time of laser processing is the same as the above t start The heating start time, expressed in different ways, has the same meaning. end The laser processing end time is the same as the above t end The heating end time is expressed differently but has the same meaning.

[0076] m is the mass of the substrate. In the cooling section, the value of m is the same as m1. For experiments without powder feeding, m = m0 = m1.

[0077] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for measuring laser processing absorptivity, characterized in that: include: Laser processing devices and laser absorptivity measuring devices; The laser absorption rate measuring device comprises: a substrate (1), a thermocouple (2), an insulating plate (3), a collector (4) and a computer (5); the laser processing device comprises a continuous fiber laser, a laser focusing device (8) and a powder feeding device; The laser emitted by the continuous fiber laser is focused by a laser focusing device (8), the powder feeding device is connected to a coaxial powder feeding head (9), the coaxial powder feeding head (9) is connected to the laser focusing device (8), and the substrate (1) is arranged directly below the coaxial powder feeding head (9); the laser beam focused by the laser focusing device (8) is injected into the substrate (1) through the coaxial powder feeding head (9); the thermocouple (2) is arranged on the substrate (1), and the thermal insulation plate (3) is arranged at the bottom of the substrate (1) to prevent and reduce the heat loss from the substrate (1) to the processing platform, so that most of the heat loss of the substrate during the laser processing process is through convection between the substrate and the air rather than heat conduction to the processing platform; the collector (4) is connected to the thermocouple (2), collects the temperature signal of the substrate (1) and transmits the collected temperature signal to the computer (5); the computer (5) processes the temperature signal of the substrate (1) to obtain the laser absorption rate value and the average temperature curve of the substrate; The powder feeding device comprises a powder cylinder (6) and a connecting pipe (7); the powder cylinder (6) uniformly feeds the metal powder onto the substrate (1) through a coaxial powder feeding head (9) via the connecting pipe (7); the coaxial powder feeding head (9) is located at one end of the laser focusing device (8); There are a plurality of thermocouples (2), which are arranged on the drilled holes on the substrate (1), and the thermocouples (2) and the substrate (1) are connected with a heat-conducting adhesive; an air pump is provided on the coaxial powder feeding head (9); the air pump includes a protective air port and a powder feeding air port; when the laser beam scans the substrate (1) and the substrate (1) is cooled, the protective air is not closed; when the laser beam scans the substrate (1), the powder cylinder (6) needs to feed metal powder to the substrate (1), and the powder feeding air port is opened to feed air; when the substrate (1) is cooled, the protective air and the powder feeding air are not closed; The measuring method comprises: the collector (4) records the initial temperature of the substrate (1) before the experiment begins, the continuous fiber laser is turned on, the laser emitted by the continuous fiber laser is focused by the laser focusing device (8), and the laser beam focused by the laser focusing device (8) is injected into the substrate (1) through the coaxial powder feeding head (9); the stepper motor is turned on, and the stepper motor drives the laser focusing device (8) to move, thereby processing the substrate (1); when the processing is completed, the collector (4) continues to collect temperature change data over time until the substrate (1) is cooled to near room temperature; and the collected temperature data is sent to the computer (5), and the computer (5) processes the temperature signal of the substrate (1) to obtain the laser absorption rate value and the average temperature curve of the substrate.

2. The laser processing absorptivity measurement method according to claim 1, wherein: The laser focusing device (8) and the continuous laser generator are externally connected to a water cooler to prevent the laser focusing device (8) and the continuous laser generator from overheating.

3. The laser processing absorptivity measurement method according to claim 2, wherein: The continuous laser generator and the laser focusing device (8) are of an integrated design; the continuous laser generator is externally connected to a stepping motor, and the stepping motor drives the continuous laser generator to move to scan the substrate (1).

4. The laser processing absorptivity measurement method according to claim 1, wherein: The processing of the substrate includes: if during the processing, the powder cylinder (6) does not transport metal powder to the substrate (1) through the coaxial powder feeding head (9), the scanning path of the laser beam is a reciprocating scanning along the laser scanning direction; and during the cooling process, the protective gas is not closed; if during the processing, the powder cylinder (6) transports metal powder to the substrate (1) through the coaxial powder feeding head (9), the scanning path of the laser beam is a movement perpendicular to the laser scanning path when no powder is added; and during the cooling process, the protective gas and the powder feeding gas are not closed.

5. The laser processing absorptivity measurement method according to claim 4, characterized in that: The processing of the substrate includes: processing the substrate temperature signal by a computer to obtain the convective heat transfer coefficient and the laser absorption rate value, specifically: Denoise the collected temperature data, and obtain the convective heat transfer coefficient based on the denoised and smoothed temperature data and the lumped parameter method; Based on the substrate temperature at the end of processing determined by the lumped parameter method, the temperature of each sampling point in the temperature data is corrected, and the corrected temperatures are averaged to obtain the average temperature curve during the substrate heating process; The laser absorptivity value is obtained based on the average temperature curve during the substrate heating process, the convection heat transfer coefficient between the substrate and air during the processing, the start time of the laser processing, and the end time of the laser processing.

6. The laser processing absorptivity measurement method according to claim 5, characterized in that: The convective heat transfer coefficient is obtained based on the temperature data after noise reduction and smoothing and the lumped parameter method, specifically: ; After mathematical transformation, it is expressed as a regression equation: ; in, θ is the temperature difference between the substrate and the atmosphere, θ cs The cooling phase starts t cs The temperature difference between the substrate and the air. The start time of the cooling phase is defined as 10 s after the end time of processing to ensure that the substrate temperature is uniform during the cooling phase. T is the temperature measured by the thermocouple, T f is the air temperature, T cs for t cs The base temperature at ; c is the specific heat capacity of the substrate, h is the surface heat transfer coefficient, m is the substrate quality, t is the experimental time, including the laser processing and the cooling time after processing; S is the substrate surface area; The substrate temperature at the end of processing is determined according to the lumped parameter method. The temperature of each sampling point in the temperature data is corrected, and the corrected temperature is averaged to obtain the average temperature curve during the substrate heating process, specifically: The average temperature rise curve of the substrate during the heating process is determined by scaling the temperature curves of each sampling point and averaging them. The sampling point temperature curve adopts linear scaling. The constraint point is that the temperature at the start of the process is the temperature before the substrate is heated, and the temperature at the end of the process is the temperature at the end of the substrate heating: ; in, T n is the temperature of the sampling point after linear scaling, T end is the substrate temperature at the end of heating, T start is the substrate temperature at the start of heating, T 20 The temperature measured by the thermocouple at the end of heating is T 10 The temperature measured by the thermocouple at the start of heating is T s Measure temperature for thermocouples; is the average temperature of the substrate during the heating process.

7. The laser processing absorptivity measurement method according to claim 6, characterized in that: The laser absorption rate value is obtained based on the average temperature curve of the substrate during the heating process, the convection heat transfer coefficient between the substrate and the air during the processing, the start time and the end time of the laser processing, and is specifically: ； in, η is the calculated value of absorbance, S is the substrate surface area, Δ t is the time interval between two adjacent samplings, P is the laser beam power; is the average temperature of the substrate during the heating process, which changes with the experimental time t change, is the difference in the average temperature of the substrate between two adjacent sampling time intervals; t end The heating end time, t start is the heating start time; is the specific heat capacity of the substrate material, which is a function of the average temperature of the substrate; m ( t ) is the substrate mass, is the experimental time t For the experiment without powder feeding, the substrate mass is considered to be unchanged. For the experiment with powder feeding, the substrate mass increases after powder feeding. During the laser processing, the substrate mass is considered to increase linearly: ； in, m 0 means the quality of substrate before processing, m 1 indicates the quality of the substrate after processing, t start is the starting time of laser processing, t end This is the time when laser processing ends.

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