Measurement and calibration method for laser in-situ auxiliary heating temperature field

Abstract

The invention relates to a method for measuring and calibrating a laser in-situ auxiliary heating temperature field, and belongs to the technical field of precision measurement. Comprising the following steps: firstly, measuring physical characteristics such as absorptivity, radiance and heat conductivity coefficient of a sample; thirdly, establishing a temperature field model for laser in-situ auxiliary heating in simulation software, and defining boundary conditions of the model according to actual working conditions; further, the temperatures at positions 2mm, 3mm and 4mm away from the center of the light spot are measured through three thermocouple experiments, and the relation that the temperatures change along with laser heating time is recorded; and finally, the diameter of the light spot is calibrated by approaching a simulation value and a measured value through a trial-and-error method, measurement and calibration of a temperature field are completed, and time-varying characteristics of temperatures at the center of the light spot and each point can be extracted. The method solves the problems of difficulty in temperature measurement and low calibration accuracy in the field of laser in-situ auxiliary processing / testing, quantitatively reveals the influence of the temperature on the characteristics of a material removal mechanism and the like as a technical basis, and promotes the progress and development of the field.

Description

Technical Field

[0001] The present invention relates to the field of precision measurement technology, and in particular to a method for measuring and calibrating a temperature field of laser in-situ assisted heating. The method will serve as a technical basis in the field of laser in-situ assisted processing / testing, and will be used to quantitatively study the influence of temperature on characteristics such as material removal mechanism, and has important scientific value for the development of this field. Background Art

[0002] Laser-assisted processing, as an energy field-assisted processing technology, uses the thermal effect of a high-energy laser beam to thermally soften the workpiece, thereby achieving the effect of improving processing efficiency, improving processing quality, and reducing tool wear. In laser-assisted processing, according to the relative position relationship between the laser beam and the tool, it can be divided into laser ex-situ heating and in-situ heating. Among them, ex-situ heating refers to preheating the workpiece in front of the tool's travel trajectory. In-situ heating refers to arranging the laser beam and the tool coaxially, so as to achieve simultaneous heating and processing. It can not only effectively improve energy utilization, but also complete ductile processing of hard and brittle materials in a smaller heat-affected zone.

[0003] Temperature, as a key parameter in this energy field assisted processing technology, will directly affect the softening degree of the workpiece and the wear state of the tool. However, due to the small spot size, high temperature gradient and spatial interference of the tool, the temperature field of laser in-situ assisted heating cannot be directly measured by infrared thermometer. How to obtain an accurate and reliable temperature field has always been a difficult problem in the industry. Existing research often only establishes a numerical model of the temperature field through simulation or theoretical analysis, and then predicts the temperature at each point. However, due to the lack of effective temperature measurement methods, the accuracy of the temperature field model cannot be verified. To this end, the present invention proposes a temperature field measurement and calibration method that combines experiments with simulations, which can accurately obtain the time-varying characteristics of the laser in-situ assisted heating temperature field, thereby realizing the controllable adjustment of the temperature field and the heat-affected zone range, and providing a technical basis for quantitatively revealing the influence of temperature on characteristics such as material removal mechanism in the field of laser in-situ assisted processing / testing. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method for measuring and calibrating the temperature field of laser in-situ assisted heating. The present invention realizes the measurement and calibration of the temperature field in laser in-situ assisted heating by combining experiments with simulations, solves the technical problems of difficult temperature field calibration and low accuracy caused by small laser spot, large temperature gradient and tool space interference in laser in-situ assisted heating, helps to realize the controllable adjustment of the temperature field and the range of the heat-affected zone, and provides a technical basis for the calibration of the temperature field in the field of laser in-situ assisted processing / testing, which is of great significance to the development and progress of this field.

[0005] The technical solution adopted by the present invention to achieve the above-mentioned purpose is as follows:

[0006] A method for measuring and calibrating a temperature field of laser in-situ assisted heating, characterized in that it comprises the following steps:

[0007] (1) Determination of physical parameters of samples: The samples were ground and polished until they were mirror-smooth with a surface roughness of no more than 10 nm. The reflectivity and emissivity of the samples were measured using a near-infrared spectrophotometer and a radiometer, respectively. The thermal conductivity, specific heat capacity and other thermodynamic parameters of the samples were measured using a thermal conductivity meter.

[0008] (2) Establishment of temperature field model: A physical model of the sample is established in the simulation software according to the actual size of the sample and the physical parameters measured in step (1). The boundary conditions of the laser in-situ assisted heating of the sample are defined according to the actual working conditions. The laser is applied to the upper surface of the sample in the form of a surface heat source, and the laser power should take into account the transmittance of the light-transmitting tool head.

[0009] (3) Experimental measurement of temperature field: The position of the light-transmitting tool head was adjusted to ensure that the laser was coaxially transmitted through the light-transmitting tool head and irradiated on the sample surface in situ. The light-transmitting tool head was placed close to the sample surface. A patch-type K-type thermocouple array with a spacing of 1 mm was used to measure the temperature at 2 mm, 3 mm, and 4 mm from the center of the laser spot. The time-varying curves of the temperature measured by the three thermocouples at different laser powers versus the laser heating time were recorded.

[0010] (4) Calibration of the spot diameter and the temperature field: The laser spot diameter is preliminarily preset and substituted into the temperature field model established in step (2), and the time-varying curves of the temperature at 2 mm, 3 mm, and 4 mm from the center of the laser spot are extracted. The simulated value of the temperature at each point is approached to the measured value of the temperature at the corresponding position obtained in step (3), and the laser spot diameter is continuously adjusted to narrow the gap between the simulated value and the measured value until the error between the two is minimized, thus completing the calibration of the spot diameter and the temperature field;

[0011] (6) Extract the real-time temperature at each point in the calibrated temperature field model, where the temperature at the center of the light spot is the temperature of the active area of ​​the light-transmitting tool head at that moment.

[0012] Furthermore, the absorption rate of the sample to the laser should be much higher than the absorption rate of the light-transmitting tool head to the laser.

[0013] Furthermore, the power of the laser in step (3) should not exceed the ablation threshold of the sample.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The present invention proposes a temperature field measurement and calibration method that combines experiments with simulations. By calibrating the laser spot diameter, the real temperature distribution characteristics can be effectively restored. Existing studies only obtain temperature field models through simulation or theoretical analysis, which requires a series of assumptions and simplifications and cannot objectively reflect the real situation. In contrast, the temperature field obtained by this method has been corrected by experimental results, and the errors caused by the assumed conditions can be ignored. It has the advantages of high accuracy and high authenticity, and provides a technical basis for the calibration of temperature fields in the field of laser in-situ assisted processing / testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings described herein are used to provide further understanding of the present invention and constitute a part of this application. The illustrative examples of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0017] Figure 1 Schematic diagram of energy distribution and temperature measurement point arrangement of laser in-situ assisted heating according to Embodiment 1 of the present invention;

[0018] Figure 2 is a comparison diagram of the measurement and simulation results of the temperature at each point under different laser powers involved in Example 1 of the present invention;

[0019] Figure 3 is a comparison diagram of the measured values ​​and simulation values ​​of the stable temperature at each point involved in Example 1 of the present invention; DETAILED DESCRIPTION

[0020] The details of the present invention and its specific implementation methods are further described below in conjunction with the accompanying drawings and examples.

[0021] Embodiment 1:

[0022] The method proposed in the present invention is applied to the field of laser in-situ assisted scratch testing. The light-transmitting tool head is a sapphire indenter, the sample is a zirconium-based amorphous alloy, the wavelength of the continuous laser is 1080nm, and the laser presents a Gaussian intensity distribution. Figure 1 The figure shows the energy distribution and temperature measurement point arrangement of the laser in-situ assisted heating involved in this embodiment. The three thermocouples are arranged at 2 mm, 3 mm and 4 mm from the center of the light spot. eff = Laser output energy E out × The transmittance β of sapphire = the radiation energy E1 of the zirconium-based amorphous alloy + the absorption energy E2 of the zirconium-based amorphous alloy.

[0023] (1) Determination of physical parameters of samples: The samples were ground and polished until they were mirror-smooth with a surface roughness of no more than 10 nm. The reflectivity and emissivity of the samples were measured using a near-infrared spectrophotometer and a radiometer, respectively. The thermal conductivity, specific heat capacity and other thermodynamic parameters of the samples were measured using a thermal conductivity meter.

[0024] (2) Establishment of temperature field model: A physical model of the sample is established in the simulation software according to the actual size of the sample and the physical parameters measured in step (1). The boundary conditions of the laser in-situ assisted heating of the sample are defined according to the actual working conditions. The bottom is in contact with the cold end, so it is set to be constant at room temperature. The other surfaces are set to have thermal convection with the air. The laser is applied to the upper surface of the sample in the form of a surface heat source. The laser power should take into account the transmittance of the light-transmitting tool head.

[0025] (3) Experimental measurement of temperature field: The position of the light-transmitting tool head was adjusted to ensure that the laser was coaxially transmitted through the light-transmitting tool head and irradiated on the sample surface in situ. The light-transmitting tool head was placed close to the sample surface. A patch-type K-type thermocouple array with a spacing of 1 mm was used to measure the temperature at 2 mm, 3 mm, and 4 mm from the center of the laser spot. The time-varying curves of the temperature measured by the three thermocouples at different laser powers versus the laser heating time were recorded.

[0026] (4) Calibration of the spot diameter and the temperature field: The laser spot diameter is preliminarily preset and substituted into the temperature field model established in step (2), and the time-varying curves of the temperature at 2 mm, 3 mm, and 4 mm from the center of the laser spot are extracted. The simulated value of the temperature at each point is approached to the measured value of the temperature at the corresponding position obtained in step (3), and the laser spot diameter is continuously adjusted to narrow the gap between the simulated value and the measured value until the error between the two is minimized, thus completing the calibration of the spot diameter and the temperature field;

[0027] (6) Extract the real-time temperature at each point in the calibrated temperature field model, where the temperature at the center of the light spot is the temperature of the active area of ​​the light-transmitting tool head at that moment.

[0028] Figure 2 The comparison between the calibrated temperature and the experimentally measured temperature in this embodiment is given. It can be seen that under the conditions of laser power of 1.5W, 4.5W, 7.5W and 10.5W, the temperature first experienced a rising stage within 0-50s, and reached a stable stage after 50s. The simulation and measured temperature trends at the three points of 2mm, 3mm and 4mm from the center of the laser spot are the same, and the stable temperature error is small.

[0029] Figure 3The comparison results between the simulated stable temperature values ​​and the measured values ​​at three points, 2mm, 3mm and 4mm away from the center of the laser spot, under the above-mentioned laser power conditions are given. It can be seen that the temperature field calibrated by the method proposed in the present invention can accurately restore the temporal and spatial distribution of temperature under actual working conditions, which is specifically manifested in that the error between the stable temperature values ​​at each position of the obtained temperature field and the experimental measurement results is extremely small.

[0030] The above content does not impose any formal limitation on the structure and shape of the present invention. Any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for measuring and calibrating the temperature field of laser in-situ assisted heating, characterized in that: The following steps are involved: (1) Determination of physical parameters of samples: The samples were ground and polished until they were mirror-smooth with a surface roughness of no more than 10 nm. The reflectivity and emissivity of the samples were measured using a near-infrared spectrophotometer and a radiometer, respectively. The thermal conductivity, specific heat capacity and other thermodynamic parameters of the samples were measured using a thermal conductivity meter. (2) Establishment of temperature field model: A physical model of the sample is established in the simulation software according to the actual size of the sample and the physical parameters measured in step (1). The boundary conditions of the laser in-situ assisted heating of the sample are defined according to the actual working conditions. The laser is applied to the upper surface of the sample in the form of a surface heat source, and the laser power should take into account the transmittance of the light-transmitting tool head. (3) Experimental measurement of temperature field: The position of the light-transmitting tool head was adjusted to ensure that the laser was coaxially transmitted through the light-transmitting tool head and irradiated on the sample surface in situ. The light-transmitting tool head was placed close to the sample surface. A patch-type K-type thermocouple array with a spacing of 1 mm was used to measure the temperature at 2 mm, 3 mm, and 4 mm from the center of the laser spot. The time-varying curves of the temperature measured by the three thermocouples at different laser powers versus the laser heating time were recorded. (4) Calibration of the spot diameter and the temperature field: The laser spot diameter is preliminarily preset and substituted into the temperature field model established in step (2), and the time-varying curves of the temperature at 2 mm, 3 mm, and 4 mm from the center of the laser spot are extracted. The simulated value of the temperature at each point is approached to the measured value of the temperature at the corresponding position obtained in step (3), and the laser spot diameter is continuously adjusted to narrow the gap between the simulated value and the measured value until the error between the two is minimized, thus completing the calibration of the spot diameter and the temperature field; (6) Extract the real-time temperature at each point in the calibrated temperature field model, where the temperature at the center of the light spot is the temperature of the active area of ​​the light-transmitting tool head at that moment.

2. The method for measuring and calibrating the temperature field of laser in-situ assisted heating according to claim 1, characterized in that: The absorption rate of the laser by the sample should be much higher than the absorption rate of the laser by the light-transmitting tool head.

3. The method for measuring and calibrating the temperature field of laser in-situ assisted heating according to claim 1, characterized in that: The power of the laser in step (3) should not exceed the ablation threshold of the sample.

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