CN119666926A - Laser processing absorptivity measurement system and method - Google Patents
Laser processing absorptivity measurement system and method Download PDFInfo
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- CN119666926A CN119666926A CN202411836233.5A CN202411836233A CN119666926A CN 119666926 A CN119666926 A CN 119666926A CN 202411836233 A CN202411836233 A CN 202411836233A CN 119666926 A CN119666926 A CN 119666926A
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Abstract
The invention belongs to the technical field of laser processing, and discloses a system and a method for measuring the absorptivity of laser processing, wherein laser emitted by a continuous fiber laser is gathered by a laser gathering device, and the laser beam is injected onto a substrate by a coaxial powder feeding head; the method comprises the steps of starting a stepping motor, driving a laser gathering device to move to process a substrate, continuously collecting temperature change data along with time by a collector when the processing is finished until the substrate is cooled to be close to room temperature, sending the collected temperature data to a computer, processing a substrate temperature signal by the computer, calculating a convection heat exchange coefficient in the laser processing process and an average temperature curve of the substrate in the laser processing process by a lumped parameter method, and obtaining the absorption rate of thermal convection correction according to the temperature curve and the convection heat exchange coefficient. The invention realizes the measurement of the absorption rate in the industrial processing process, uses the surface heat dissipation correction, and improves the accuracy of the absorption rate measurement.
Description
Technical Field
The invention belongs to the technical field of laser processing, and relates to a laser processing absorptivity measuring system and method.
Background
Laser processing is important in the fields of metal joining, manufacturing, repair and welding. How to evaluate the absorption of different wavelength lasers to metals is also a current hot topic, and the ideal absorption can be calculated by the Drude theory. However, oxides increase the absorptivity of the material during laser processing. Thus, spectroscopic methods are widely used by researchers for absorbance measurements of metal powders for processing. However, since the temperature change around the metal is significant when the laser light acts on the metal, the spectrometer can only obtain the absorption rate at room temperature. For measuring the transient absorptivity, researchers apply the integrating sphere device to keyhole mode molten pool laser processing, and can be embedded in an in-situ X-ray monitoring system, and the small hole form and the transient absorptivity are combined. However, in order to capture the reflected light as much as possible, the substrate needs to be inclined at an angle, which results in a difference from the actual production process, and the integrating sphere device is costly. Calorimetric measurement is a conventional method of calculating absorption rate based on the physical relationship between heat conduction conditions, material properties, temperature and absorption rate. The method is suitable for the situation that the size change of the molten pool is small, such as a thermal conduction type molten pool, and the calculated value of the absorption rate is not the average value of the sampling process. However, the absorption measurement is low due to the long time of the calorimetric method in counting the absorption, and the loss caused by the exchange of heat of the substrate and the surrounding environment during the processing.
Disclosure of Invention
The invention aims to solve the problem that in the prior art, the absorption rate measurement value is low due to the fact that the time is long when the absorption rate is counted by a calorimeter, and the loss caused by the exchange of heat of a substrate and surrounding environment in the processing process, and provides a laser processing absorption rate measurement system and a laser processing absorption rate measurement method.
In order to achieve the purpose, the invention is realized by adopting the following technical scheme:
The laser processing absorptivity measuring system comprises a laser processing device and a laser absorptivity measuring device, wherein the laser absorptivity measuring device comprises a substrate, a thermocouple, an insulating plate, a collector and a computer, and the laser processing device comprises a continuous fiber laser, a laser gathering device and a powder feeding device;
The laser emitted by the continuous fiber laser is gathered through the laser gathering device, the powder feeding device is connected with the coaxial powder feeding head, the coaxial powder feeding head is connected with the laser gathering device, the substrate is arranged right below the coaxial powder feeding head, the laser beams gathered by the laser gathering device are injected onto the substrate through the coaxial powder feeding head, the thermocouple is arranged on the substrate, the heat insulation board is arranged at the bottom of the substrate, so that heat conduction loss from the substrate to the processing platform is prevented, most of heat loss of the substrate in the laser processing process is conducted to the processing platform through convection of the substrate and air instead of heat conduction, the collector is connected with the thermocouple, the temperature signals of the substrate are collected and transmitted into the computer, and the computer processes the temperature signals of the substrate to obtain the laser absorption rate value and the average temperature curve of the substrate.
The invention further improves that:
Further, the laser gathering device and the continuous laser generator are externally connected with a water cooler, so that overheating of the laser gathering device and the continuous laser generator is prevented.
Furthermore, the continuous laser generator and the laser gathering device are integrally designed, the continuous laser generator is externally connected with a stepping motor, and the stepping motor drives the continuous laser generator to move so as to realize scanning of the substrate.
The powder feeding device comprises a powder cylinder and a connecting pipe, wherein the powder cylinder uniformly feeds metal powder to the substrate through the connecting pipe through a coaxial powder feeding head, and the coaxial powder feeding head is positioned at one end of the laser gathering device.
The device comprises a base plate, a plurality of thermocouples, a coaxial powder feeding head, a gas pump, a protection gas port, a powder feeding port and a powder feeding port, wherein the thermocouples are arranged on a drill hole on the base plate and connected with the base plate through heat conducting glue, the gas pump comprises the protection gas port and the powder feeding port, the protection gas is not closed when a laser beam scans the base plate and cools the base plate, the powder feeding port is opened to feed gas when the laser beam scans the base plate and the powder cylinder is required to convey metal powder to the base plate, and the protection gas and the powder feeding gas are not closed when the base plate is cooled.
A measuring method for laser processing absorptivity includes recording initial temperature of substrate by collector before experiment is started, starting continuous fiber laser, collecting laser emitted by continuous fiber laser by laser collecting device, injecting laser beam collected by laser collecting device onto substrate by coaxial powder feeding head, starting step motor, driving laser collecting device to move for processing substrate, collecting temperature change data with time by collector until substrate is cooled to near room temperature when processing is finished, sending collected temperature data to computer, and processing substrate temperature signal by computer to obtain laser absorptivity value and average substrate temperature curve.
Further, the processing of the substrate comprises the steps that if the powder cylinder does not convey metal powder to the substrate through the coaxial powder conveying head in the processing process, the scanning path of the laser beam is scanned back and forth along the scanning direction of the laser, and the shielding gas is not closed in the cooling process, if the powder cylinder conveys metal powder to the substrate through the coaxial powder conveying head in the processing process, the scanning path of the laser beam keeps moving along the path perpendicular to the scanning path of the laser in the condition of no powder adding, and the shielding gas and the powder conveying gas are not closed in the cooling process.
Further, processing the substrate comprises processing the substrate temperature signal by a computer to obtain a convective heat transfer coefficient and a laser absorption rate value, specifically:
Noise reduction is carried out on the acquired temperature data, and a convection heat exchange coefficient is acquired based on the temperature data after noise reduction and smoothing treatment and a total parameter method;
Correcting the temperature of each sampling point in the temperature data according to the substrate temperature at the processing end time determined by the lumped parameter method, and carrying out average treatment on the corrected temperature to obtain an average temperature curve in the substrate temperature rising process;
the laser absorption rate value is obtained based on an average temperature curve in the substrate heating process and the convective heat transfer coefficient of the substrate and air in the processing process, and the starting time and the ending time of laser processing.
Further, based on the temperature data after noise reduction and smoothing treatment and a total parameter method, the convective heat transfer coefficient is obtained, specifically:
the mathematical transformation is expressed as a regression equation:
Wherein θ is the temperature difference between the substrate and the atmosphere, θ cs is the temperature difference between the substrate and the air at the start time T cs of the cooling stage, which is defined as 10S after the end time of the processing to ensure the uniformity of the substrate temperature in the cooling stage, T is the temperature measured by the thermocouple, T f is the air temperature, T cs is the base temperature at T cs, c is the substrate specific heat capacity, h is the surface heat exchange coefficient, m is the substrate mass, T is the experimental time including the cooling time after the laser processing and the processing is finished;
The substrate temperature at the processing end time determined according to the lumped parameter method corrects the temperature of each sampling point in the temperature data, and carries out average treatment on the corrected temperature to obtain an average temperature curve in the substrate temperature rising process, specifically:
The average temperature rise curve of the substrate in the heating process is determined by averaging after the temperature curves of all sampling points are scaled, the temperature curves of the sampling points are linearly scaled, the temperature at the processing starting moment is the temperature before the substrate is heated, and the temperature at the processing ending moment is the temperature at the substrate heating ending moment:
Wherein T n is the temperature after the temperature of the sampling point is linearly scaled, T end is the temperature of the substrate at the heating end time, T start is the temperature of the substrate at the heating start time, T 20 is the temperature measured by a thermocouple at the heating end time, T 10 is the temperature measured by the thermocouple at the heating start time, T s is the temperature measured by the thermocouple, and T is the average temperature of the substrate in the heating process.
Further, based on an average temperature curve in the substrate heating process and a convective heat transfer coefficient of the substrate and air in the processing process, a laser processing starting time and a laser processing ending time, a laser absorption rate value is obtained, specifically:
Wherein eta is an absorptivity calculation value, S is a substrate surface area, deltat is an adjacent two sampling time interval, P is laser beam power, T is an average substrate temperature in a heating process, and is changed along with an experiment time T, deltat is a difference value of the average substrate temperature in the adjacent two sampling time intervals, T end is a heating end time, T start is a heating start time, c (T) is a specific heat capacity value of a substrate material and is a function of the average substrate temperature, m (T) is a substrate mass and is a function of the experiment time T, the substrate mass is considered not changed for experiments without powder feeding, the substrate mass is increased after powder feeding for the powder feeding experiments, and the substrate mass is considered to be linearly increased in the laser processing process:
Wherein m 0 represents the substrate mass before processing, m 1 represents the substrate mass after processing, t start represents the laser processing start time, and t end represents the laser processing end time.
Compared with the prior art, the invention has the following beneficial effects:
The invention applies the laser generated by the laser to the substrate, the temperature signal of the substrate is connected to the collector through the thermocouple wire, the temperature signal collected by the collector is transmitted to the computer for storage, the computer calculates the energy correction value of surface heat dissipation in the heating process according to the collected substrate heating and cooling curves, and calculates the corrected absorption rate value. The invention realizes the measurement of the absorptivity in the long-time laser processing process, improves the accuracy of the absorptivity measurement by using the surface heat dissipation correction, and can be widely applied to the processes of laser additive manufacturing, laser welding and the like of any wavelength.
Drawings
For a clearer description of the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present invention and should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a laser processing absorptivity measurement system according to the present invention;
FIG. 2 is a schematic diagram of a thermocouple point location on a substrate;
FIG. 3 is a schematic flow chart for obtaining a convective heat transfer coefficient and a laser absorption rate value.
Wherein, the device comprises a 1-substrate, a 2-thermocouple, a 3-heat insulation plate, a 4-collector, a 5-computer, a 6-powder cylinder, a 7-connecting pipe, an 8-laser gathering device and a 9-coaxial powder feeding head.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be noted that like reference numerals and letters refer to like items in the following figures, and thus once an item is defined in one figure, no further definition or explanation thereof is necessary in the following figures.
In the description of the embodiments of the present invention, it should be noted that, if the terms "upper," "lower," "horizontal," "inner," and the like indicate an azimuth or a positional relationship based on the azimuth or the positional relationship shown in the drawings, or the azimuth or the positional relationship in which the inventive product is conventionally put in use, it is merely for convenience of describing the present invention and simplifying the description, and does not indicate or imply that the apparatus or element to be referred to must have a specific azimuth, be configured and operated in a specific azimuth, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used merely to distinguish between descriptions and should not be construed as indicating or implying relative importance.
Furthermore, the term "horizontal" if present does not mean that the component is required to be absolutely horizontal, but may be slightly inclined. As "horizontal" merely means that its direction is more horizontal than "vertical", and does not mean that the structure must be perfectly horizontal, but may be slightly inclined.
In the description of the embodiments of the present invention, it should also be noted that, unless explicitly stated or limited otherwise, the terms "disposed," "mounted," "connected," and "connected" should be interpreted broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected, mechanically connected, electrically connected, directly connected, indirectly connected through an intermediate medium, or communicating between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.
The invention is described in further detail below with reference to the attached drawing figures:
Referring to fig. 1, the invention discloses a laser processing absorptivity measuring system, which comprises a laser processing device and a laser absorptivity measuring device, wherein the laser absorptivity measuring device comprises a base plate 1, a thermocouple 2, an insulating plate 3, a collector 4 and a computer 5, and the laser processing device comprises a continuous fiber laser, a laser gathering device 8 and a powder feeding device;
The laser emitted by the continuous fiber laser is gathered through a laser gathering device 8, a powder feeding device is connected with a coaxial powder feeding head 9, the coaxial powder feeding head 9 is connected with the laser gathering device 8, a substrate 1 is arranged right below the coaxial powder feeding head 9, a laser beam gathered by the laser gathering device 8 is emitted onto the substrate 1 through the coaxial powder feeding head 9, a thermocouple 2 is arranged on the substrate 1, an insulating plate 3 is arranged at the bottom of the substrate 1 to prevent the heat conduction loss from the substrate 1 to a processing platform, so that most of the heat loss of the substrate in the laser processing process is conducted to the processing platform through convection of the substrate and air instead of heat conduction, a collector 4 is connected with the thermocouple 2 to collect a temperature signal of the substrate 1 and transmit the collected temperature signal into a computer 5, and the computer 5 processes the temperature signal of the substrate 1 to obtain a laser absorption value and a substrate average temperature curve.
The laser focusing device 8 and the continuous laser generator are externally connected with a water cooler, so that the laser focusing device 8 and the continuous laser generator are prevented from being overheated.
The continuous laser generator and the laser gathering device 8 are designed integrally, the continuous laser generator is externally connected with a stepping motor, and the stepping motor drives the continuous laser generator to move so as to realize scanning of the substrate 1.
The powder feeding device comprises a powder cylinder 6 and a connecting pipe 7, wherein the powder cylinder 6 uniformly feeds metal powder to the substrate 1 through the connecting pipe 7 by virtue of a coaxial powder feeding head 9, and the coaxial powder feeding head 9 is positioned at one end of the laser gathering device 8.
The number of the thermocouples 2 is several, the thermocouples 2 are arranged on the drilling holes on the base plate 1, the point positions of the thermocouples 2 are distributed as shown in figure 2, the thermocouples 2 are connected with the base plate 1 through heat conducting glue, the thermocouples 2 penetrate into the base plate 5mm, and the size of the base plate is 100mm multiplied by 15mm. The coaxial powder feeding head 9 is provided with an air pump, the air pump comprises a protection air port and a powder feeding air port, when the laser beam scans the substrate 1 and the substrate 1 is cooled, the protection air is not closed, when the laser beam scans the substrate 1, the powder cylinder 6 is required to convey metal powder to the substrate 1, the powder feeding air port is opened for feeding air, and when the substrate 1 is cooled, the protection air and the powder feeding air are not closed.
A measuring method of laser processing absorptivity comprises the steps of recording initial temperature of a substrate 1 by a collector 4 before an experiment starts, starting a continuous fiber laser, collecting laser emitted by the continuous fiber laser through a laser collecting device 8, enabling the laser beam collected by the laser collecting device 8 to be injected onto the substrate 1 through a coaxial powder feeding head 9, starting a stepping motor, driving the laser collecting device 8 to move to achieve processing of the substrate 1, continuously collecting temperature change data with time by the collector 4 until the substrate 1 is cooled to near room temperature when the processing is finished, sending the collected temperature data to a computer 5, and processing temperature signals of the substrate 1 by the computer 5 to obtain a laser absorptivity value and a substrate average temperature curve.
The processing of the substrate comprises that if the powder cylinder 6 does not convey metal powder to the substrate 1 through the coaxial powder feeding head 9 in the processing process, the scanning path of the laser beam is to scan back and forth along the scanning direction of the laser, and the shielding gas is not closed in the cooling process, if the powder cylinder 6 conveys metal powder to the substrate 1 through the coaxial powder feeding head 9 in the processing process, the scanning path of the laser beam keeps moving along the path perpendicular to the scanning path of the laser in the condition of no powder feeding, and the shielding gas and the powder feeding gas are not closed in the cooling process.
In the process of measuring the absorption rate without powder feeding, the laser scanning path circularly scans along the AB line segment shown in fig. 2, and the temperature of the substrate after scanning is between 150 and 250 ℃ so as to reduce the influence of temperature measurement errors on the calculated absorption rate. The substrate temperature should be below 40 ℃ before the experiment starts. The scanning speed is set to 1000mm/min, the single-channel length is 60mm, and in the powder feeding absorption rate measuring process, the laser scanning path precesses in the direction vertical to the AB direction on the basis of the AB direction so as to avoid uneven heat dissipation of a deposition area caused by overhigh deposition layer.
Referring to fig. 3, processing the substrate includes processing a substrate temperature signal by a computer to obtain a convective heat transfer coefficient and a laser absorption rate value, specifically:
S101, noise reduction and smoothing are carried out on the acquired temperature data, and a convection heat transfer coefficient is acquired based on the noise-reduced temperature data and a total parameter method;
The collected temperature data is subjected to noise reduction and outlier noise point removal through a Hample filter, the window width is set to be 11, and the median absolute deviation of which the threshold value is 20 times is removed. The window width for curve smoothing is set to 360 and the smoothed data point value is the average of the data in the window.
The moment of starting or ending the laser is determined from the acquisition point closest to the laser processing point. The laser processing start time is determined by a bilinear regression intersection method. Firstly, a temperature-time curve of a closest acquisition point from a laser starting point is selected, 4 points are selected before and after the temperature rise starts, and the curve is defined as two stages, namely a constant stage and a linear growth stage. The selection principle is to ensure that the temperature varies linearly with time. The constant phase is before the start time, the temperature should fluctuate around a constant, while the linearly increasing phase is after the laser start time. Then, a linear regression equation is calculated from the points of the two stages. The time coordinate of the intersection point of the two linear equations is the starting time of laser processing. The method for determining the laser processing end time is to acquire the maximum temperature point in the last thermal cycle of the acquisition point closest to the laser end point as the end time.
Based on the temperature data after noise reduction and a total parameter method, the convective heat transfer coefficient is obtained, and the method specifically comprises the following steps:
the mathematical transformation is expressed as a regression equation:
Wherein θ is the temperature difference between the substrate and the atmosphere, θ cs is the temperature difference between the substrate and the air at the start time T cs of the cooling stage, which is defined as 10S after the end time of the processing to ensure the uniformity of the substrate temperature in the cooling stage, T is the temperature measured by the thermocouple, T f is the air temperature, T cs is the base temperature at T cs, c is the substrate specific heat capacity, h is the surface heat exchange coefficient, m is the substrate mass, T is the experimental time including the cooling time after the laser processing and the processing is finished;
s102, correcting the temperature of each sampling point in temperature data according to the substrate temperature at the processing end time determined by a lumped parameter method, and carrying out average treatment on the corrected temperature to obtain an average temperature curve in the substrate temperature rising process;
according to the use condition of the lumped parameter method, the internal heat conduction of the substrate is good, and the temperature is approximately the same everywhere. In this case, the temperature at each sampling point is corrected by defining the temperature at the start and end of heating to a fixed value, and correcting the temperature at each intermediate point
The average temperature rise curve of the substrate in the heating process is determined by averaging after the temperature curves of all sampling points are scaled, the temperature curves of the sampling points are linearly scaled, the temperature at the processing starting moment is the temperature before the substrate is heated, and the temperature at the processing ending moment is the temperature at the substrate heating ending moment:
Wherein T n is the temperature after the temperature of the sampling point is linearly scaled, T end is the temperature of the substrate at the heating end time, T start is the temperature of the substrate at the heating start time, T 20 is the temperature measured by a thermocouple at the heating end time, T 10 is the temperature measured by the thermocouple at the heating start time, T s is the temperature measured by the thermocouple, and T is the average temperature of the substrate in the heating process.
S103, obtaining a laser absorption rate value based on an average temperature curve in the substrate heating process and the convective heat transfer coefficient of the substrate and air in the processing process, and the starting time and the ending time of laser processing.
Wherein eta is an absorptivity calculation value, S is a substrate surface area, deltat is an adjacent two sampling time interval, P is laser beam power, T is an average substrate temperature in a heating process, and is changed along with an experiment time T, deltat is a difference value of the average substrate temperature in the adjacent two sampling time intervals, T end is a heating end time, T start is a heating start time, c (T) is a specific heat capacity value of a substrate material and is a function of the average substrate temperature, m (T) is a substrate mass and is a function of the experiment time T, the substrate mass is considered not changed for experiments without powder feeding, the substrate mass is increased after powder feeding for the powder feeding experiments, and the substrate mass is considered to be linearly increased in the laser processing process:
Wherein m 0 represents the substrate mass before processing, m 1 represents the substrate mass after processing, t start represents the laser processing start time, and t end represents the laser processing end time.
Here, the laser processing start time of t start is different from the heating start time of t start, and the expressions are the same. The laser processing end time at t end is different from the above description of the heating end time at t end, but the meanings are the same.
M is the substrate mass, and in the cooling section, the value of m is the same as m 1, and m=m 0＝m1 in the experiment without powder feeding.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The laser processing absorptivity measuring system is characterized by comprising a laser processing device and a laser absorptivity measuring device, wherein the laser absorptivity measuring device comprises a substrate (1), a thermocouple (2), an insulating plate (3), a collector (4) and a computer (5), and the laser processing device comprises a continuous fiber laser, a laser gathering device (8) and a powder feeding device;
The laser emitted by the continuous fiber laser is concentrated through a laser concentration device (8), the powder feeding device is connected with a coaxial powder feeding head (9), the coaxial powder feeding head (9) is connected with the laser concentration device (8), the substrate (1) is arranged right below the coaxial powder feeding head (9), laser beams concentrated by the laser concentration device (8) are injected onto the substrate (1) through the coaxial powder feeding head (9), the thermocouple (2) is arranged on the substrate (1), the heat insulation plate (3) is arranged at the bottom of the substrate (1) and is used for preventing reduction of heat conduction loss from the substrate (1) to a processing platform, so that most of heat loss of the substrate in the laser processing process is conducted to the processing platform through convection of the substrate and air instead of heat conduction, the collector (4) is connected with the thermocouple (2), temperature signals of the substrate (1) are collected and the collected temperature signals are transmitted into a computer (5), and the computer (5) processes the temperature signals of the substrate (1) to obtain laser absorption values and a substrate average temperature curve.
2. The laser machining absorptivity measurement system according to claim 1, characterized in that the laser focusing device (8) and the continuous laser generator are externally connected with a water cooler, and overheating of the laser focusing device (8) and the continuous laser generator is prevented.
3. The laser processing absorptivity measuring system according to claim 2, wherein the continuous laser generator and the laser focusing device (8) are integrally designed, the continuous laser generator is externally connected with a stepping motor, and the stepping motor drives the continuous laser generator to move so as to scan the substrate (1).
4. The laser processing absorptivity measurement system according to claim 3, wherein the powder feeding device comprises a powder cylinder (6) and a connecting pipe (7), the powder cylinder (6) uniformly feeds metal powder onto the substrate (1) through the connecting pipe (7) through a coaxial powder feeding head (9), and the coaxial powder feeding head (9) is positioned at one end of the laser focusing device (8).
5. The laser processing absorptivity measurement system according to claim 4, wherein the number of thermocouples (2) is several, the thermocouples (2) are arranged on the drill holes on the substrate (1), the thermocouples (2) are connected with the substrate (1) by using heat conducting glue, the coaxial powder feeding head (9) is provided with an air pump, the air pump comprises a protection air port and a powder feeding air port, the protection air port is not closed when the laser beam scans the substrate (1) and cools the substrate (1), the powder feeding air port is opened when the laser beam scans the substrate (1) and the powder cylinder (6) needs to convey metal powder to the substrate (1) for feeding air, and the protection air port and the powder feeding air port are not closed when the substrate (1) is cooled.
6. A laser processing absorptivity measurement method is characterized by comprising the steps of recording the initial temperature of a substrate (1) before an experiment starts by a collector (4), starting a continuous fiber laser, collecting laser emitted by the continuous fiber laser through a laser collecting device (8), enabling the laser beam collected by the laser collecting device (8) to be injected onto the substrate (1) through a coaxial powder feeding head (9), starting a stepping motor, driving the laser collecting device (8) to move, achieving processing of the substrate (1), continuously collecting temperature change data with time by the collector (4) until the substrate (1) is cooled to be close to room temperature when the processing is finished, and sending the collected temperature data to a computer (5), wherein the computer (5) processes temperature signals of the substrate (1) to obtain a laser absorption rate value and an average temperature curve of the substrate.
7. The method according to claim 6, wherein the processing the substrate comprises the steps that if the powder cylinder (6) does not convey the metal powder to the substrate (1) through the coaxial powder feeding head (9) during the processing, the scanning path of the laser beam is scanned back and forth along the scanning direction of the laser, and the shielding gas is not closed during the cooling process, and if the powder cylinder (6) conveys the metal powder to the substrate (1) through the coaxial powder feeding head (9) during the processing, the scanning path of the laser beam is kept moving along the path perpendicular to the scanning path of the laser when the powder is not added, and the shielding gas and the powder feeding gas are not closed during the cooling process.
8. The method for measuring the absorptivity of the laser processing according to claim 7, wherein the processing the substrate comprises the steps of processing a substrate temperature signal by a computer to obtain a heat convection coefficient and a laser absorptivity value, specifically:
Noise reduction is carried out on the acquired temperature data, and a convection heat exchange coefficient is acquired based on the temperature data after noise reduction and smoothing treatment and a total parameter method;
Correcting the temperature of each sampling point in the temperature data according to the substrate temperature at the processing end time determined by the lumped parameter method, and carrying out average treatment on the corrected temperature to obtain an average temperature curve in the substrate temperature rising process;
the laser absorption rate value is obtained based on an average temperature curve in the substrate heating process and the convective heat transfer coefficient of the substrate and air in the processing process, and the starting time and the ending time of laser processing.
9. The method for measuring absorptivity of laser processing according to claim 8, wherein the obtaining a convective heat transfer coefficient based on the temperature data after noise reduction and smoothing and the integrated parameter method specifically includes:
the mathematical transformation is expressed as a regression equation:
Wherein θ is the temperature difference between the substrate and the atmosphere, θ cs is the temperature difference between the substrate and the air at the start time T cs of the cooling stage, which is defined as 10S after the end time of the processing to ensure the uniformity of the substrate temperature in the cooling stage, T is the temperature measured by the thermocouple, T f is the air temperature, T cs is the base temperature at T cs, c is the substrate specific heat capacity, h is the surface heat exchange coefficient, m is the substrate mass, T is the experimental time including the cooling time after the laser processing and the processing is finished;
The substrate temperature at the processing end time determined according to the lumped parameter method corrects the temperature of each sampling point in the temperature data, and carries out average treatment on the corrected temperature to obtain an average temperature curve in the substrate temperature rising process, specifically:
The average temperature rise curve of the substrate in the heating process is determined by averaging after the temperature curves of all sampling points are scaled, the temperature curves of the sampling points are linearly scaled, the temperature at the processing starting moment is the temperature before the substrate is heated, and the temperature at the processing ending moment is the temperature at the substrate heating ending moment:
wherein, T n is the temperature after the temperature of the sampling point is linearly scaled, T end is the temperature of the substrate at the heating end time, T start is the temperature of the substrate at the heating start time, T 20 is the temperature measured by a thermocouple at the heating end time, T 10 is the temperature measured by a thermocouple at the heating start time, and T s is the temperature measured by a thermocouple; is the average temperature of the substrate during heating.
10. The method for measuring the absorptivity of the laser processing according to claim 9, wherein the laser absorptivity value is obtained based on an average temperature curve during the substrate heating process, a heat convection coefficient between the substrate and air during the processing process, a laser processing start time and a laser processing end time, specifically:
Wherein eta is an absorption rate calculated value, S is a substrate surface area, delta t is an adjacent two sampling time interval, and P is laser beam power; for the average temperature of the substrate during heating, as the experimental time t varies, The difference value of the average temperature of the substrate in the time interval of two adjacent sampling times is t end which is the heating end time and t start which is the heating start time; The specific heat capacity value of the substrate material is a function of the average temperature of the substrate, m (t) is the substrate mass and is a function of the experiment time t, the substrate mass is considered not to be changed for experiments without powder feeding, the substrate mass is considered to be increased after powder feeding for powder feeding experiments, and the substrate mass is considered to be linearly increased in the laser processing process:
Wherein m 0 represents the substrate mass before processing, m 1 represents the substrate mass after processing, t start represents the laser processing start time, and t end represents the laser processing end time.
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