A method for measuring the absorption rate of incident laser by materials in laser welding

Abstract

The present invention discloses a method for measuring the absorptivity of a material to an incident laser during laser welding, which is applied to the field of laser material processing technology. A non-penetrating laser welding method is adopted, and the fusion line profile, weld cross-sectional area and melt volume in the weld cross section, and the mass loss of the plate before and after welding are measured; by comparing the melting point isotherm in the temperature field with the fusion line in the weld cross section, when the two match, the absorptivity set in the temperature field simulation is the absorptivity A1 of the incident laser required for thermal conduction of the material; the absorptivity A2 required to overcome the latent heat of melting of the molten pool is calculated; the evaporation and ablation mass of the material is characterized by the mass loss of the plate before and after welding, and then the absorptivity A3 required to overcome the latent heat of evaporation is obtained. The absorptivity of the material to the incident laser is A=A1+A2+A3. The present invention can simply, quickly and accurately obtain the actual absorptivity of the material to the incident laser.

Description

Technical Field

[0001] The present invention relates to the technical field of laser material processing, and more particularly to a method for measuring the absorptivity of a material to incident laser light during laser welding. Background Art

[0002] For experimental research on the laser absorption rate of materials, such as the method for testing the laser absorption rate of materials after coating as described in invention patent CN106353361A, the finite element temperature field and the experimentally measured temperature distribution on the surface of the plate are combined to analyze and compare to obtain the absorption rate of the coated material to the laser. Similarly, the calibration method for the absorption rate of a metal material to laser as described in patent CN107462597A also uses a thermocouple to measure the temperature change over time of the test point of the workpiece under laser irradiation, and then compares and analyzes the value with the numerical simulation temperature field, and then obtains the absorption rate of the material to the laser based on the absorption rate set in the simulation. In the experimental temperature measurement of the above two methods, the non-contact temperature measuring device mainly measures the temperature of the surface or back of the material, while the contact temperature measuring device measures the temperature of the non-laser action area. However, these two methods based on temperature measurement and numerical simulation to obtain the actual absorption rate of the material during the processing process have the following limitations:

[0003] First, neither of the above methods can effectively measure the temperature inside the molten pool; they only measure the surface temperature of the sheet. During laser processing, the molten pool is the area where the laser interacts with the material, and it is full of flow and oscillation. The flow and surface oscillation of the molten pool inevitably disturb the temperature distribution on the sheet surface.

[0004] Second, devices such as infrared thermal imagers or thermistors are affected by factors such as test conditions, measurement methods, component accuracy and response time, and they themselves may have obvious measurement errors.

[0005] Third, both methods measure the sheet's surface temperature, and the results obtained are based on the laser energy required for the sheet's heat conduction—that is, the absorption rate relative to the laser power required for heat conduction. However, they fail to capture the sheet's melt zone mass and evaporation loss mass. This means they fail to consider the impact of the latent heat of melting and evaporation required to overcome the material's solid-liquid-gas phase transition, and instead simply compare and analyze changes in the temperature field. However, in the actual laser processing energy coupling process, absorbed energy, in addition to being converted into a thermal conductivity temperature field, also needs to overcome the latent heat of melting and evaporation.

[0006] Therefore, it is an urgent problem for those skilled in the art to propose a method for measuring the absorptivity of incident laser light during laser welding to solve the difficulties existing in the prior art. Summary of the Invention

[0007] In view of this, the present invention provides a method for measuring the absorptivity of materials to incident laser light during laser welding. This method is simple and easy to operate, is not restricted by experimental conditions, requires little calculation, and has high accuracy. It is suitable for measuring the actual absorptivity of various materials, especially metal materials, to laser light under different processing conditions.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] A method for measuring the absorptivity of a material to an incident laser during laser welding comprises the following steps:

[0010] S1. Pre-treat the material using the same surface treatment process to obtain a sample;

[0011] S2. Place the sample in a splash-proof storage box for laser processing;

[0012] S3, cutting, grinding, polishing, and etching the sample after laser processing to obtain the cross-sectional morphology of the processed area;

[0013] S4. Compare and analyze the cross-sectional morphology of the processed area with the results of the simulated temperature field analysis. When the melting point isotherm in the obtained temperature field matches the fusion line in the cross section, the absorptivity set in the numerical simulation is the absorptivity A1 of the incident laser required by the heat transfer part of the material.

[0014] S5. Measure the weld cross section and melt volume of the welded sample, and derive the melt mass based on the material density, and then calculate the absorptivity A2 required to overcome the latent heat of molten pool.

[0015] S6. Measure the mass of the storage box before and after welding to obtain the mass loss of the sample, and then calculate the absorption rate A3 required to overcome the latent heat of evaporation of the sample;

[0016] S7. Based on the obtained A1, A2 and A3, the absorption rate A of the sample to the incident laser is obtained.

[0017] Optionally, the laser used is in a focused state, and the spot energy thereof is Gaussian distributed; the welding mode of the laser on the sample is a thermal conduction mode or a deep penetration mode.

[0018] Optionally, when simulating the laser heating temperature field of a sample, the laser heat source model in the thermal conductivity mode is a Gaussian surface heat source model as follows:

[0019]

[0020] Where r0 is the spot radius; A1 is the absorptivity set in the simulation; P is the laser power; and the material density is ρ.

[0021] Optionally, the laser heat source model in deep melting mode is a Gaussian rotating body heat source model as follows:

[0022]

[0023] Where r0 is the spot radius; A1 is the absorptivity set in the simulation; P is the laser power; and H is the height of the heat source.

[0024] Optionally, the sample in S1 is in plate shape.

[0025] Optionally, the absorption rate A2 to overcome the latent heat of fusion can be calculated using the following formula:

[0026]

[0027] Where M m is the melting mass, L m is the latent heat of melting; P is the laser power, and t is the laser action time.

[0028] Optionally, the absorption rate A3 required to overcome the latent heat of evaporation of the material can be calculated using the following formula:

[0029]

[0030] Where M v is the ablation evaporation mass, L v is the latent heat of vaporization; P is the laser power, and t is the laser action time.

[0031] Optionally, the sample's absorption rate A of the incident laser can be calculated by the following formula:

[0032] A=A1+A2+A3.

[0033] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a method for measuring the absorptivity of a material to an incident laser during laser welding, which has the following beneficial effects:

[0034] This method uses the solidification morphology of the molten pool to determine the melting state of the laser-affected area. The measured actual weld fusion line is then compared with the melting point isotherms in the finite element temperature field. The method also comprehensively considers the latent heat of melting and latent heat of vaporization that the material must overcome during laser processing to determine the material's actual absorptivity of the incident laser light. This simple, computationally efficient, and highly accurate method is suitable for measuring the actual laser absorptivity of various materials, particularly metals, under different processing conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0036] Figure 1 A flow chart of a method for measuring the absorptivity of a material to an incident laser during laser welding provided by the present invention;

[0037] Figure 2 This is a comparison diagram of the actual weld cross section and the simulated temperature of the present invention;

[0038] Among them, 1-melting point isotherms in the simulated temperature field, 2-actual fusion line, 3-weld reinforcement. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0040] Reference Figure 1 As shown, the present invention discloses a method for measuring the absorptivity of a material to an incident laser during laser welding, comprising the following steps:

[0041] S1. First, pre-treat the material with the same surface treatment process to maintain the consistency of the material surface state, thereby ensuring the consistency of the material surface's laser absorption rate;

[0042] S2. Place the sample in a splash-proof storage box for laser processing, and perform multiple tests with the same parameters to ensure the accuracy of the test results;

[0043] S3, cutting, grinding, polishing, and etching the sample after laser processing to obtain the cross-sectional morphology of the processed area;

[0044] S4. Compare and analyze the cross-sectional morphology of the processing area with the results of the simulated temperature field analysis, and continuously adjust the absorptivity in the numerical simulation. When the melting point isotherm in the obtained temperature field matches the fusion line in the cross section, the absorptivity set in the numerical simulation is the absorptivity A1 of the incident laser required by the heat transfer part of the material.

[0045] S5. Measure the weld cross section and melt volume of the plate after welding, and derive the melt mass based on the material density, etc., and then calculate the absorption rate A2 required to overcome the latent heat of molten pool;

[0046] S6. Measure the mass of the storage box before and after welding to obtain the mass loss of the plate, which is used to characterize the evaporation and ablation mass of the material, and then calculate the absorption rate A3 required to overcome the latent heat of evaporation of the material;

[0047] S7. Based on the obtained A1, A2, and A3, the absorption rate A of the material to the incident laser is obtained.

[0048] Furthermore, the laser used is in a focused state, and the spot energy thereof is Gaussian distributed; the welding mode of the laser on the plate is a thermal conduction mode or a deep penetration mode.

[0049] Furthermore, when simulating the temperature field of laser heating of materials, the laser heat source model in the thermal conductivity mode is a Gaussian surface heat source model as follows:

[0050]

[0051] Furthermore, the laser heat source model in deep melting mode is a Gaussian rotating body heat source model as follows:

[0052]

[0053] Where r0 is the spot radius; A1 is the absorptivity set in the simulation; P is the laser power; and H is the height of the heat source.

[0054] Furthermore, the material to be tested is in plate shape.

[0055] Furthermore, the absorption rate A2 of the part that overcomes the latent heat of melting is calculated using the following formula:

[0056]

[0057] Where M m is the melting mass, L m is the latent heat of melting; P is the laser power, and t is the laser action time.

[0058] Furthermore, the absorption rate A3 required to overcome the latent heat of evaporation of the material is calculated using the following formula:

[0059]

[0060] Where M v is the ablation evaporation mass, L v is the latent heat of vaporization; P is the laser power, and t is the laser action time.

[0061] Furthermore, the absorption rate A of the material to the incident laser can be calculated by the following formula:

[0062] A=A1+A2+A3.

[0063] Reference Figure 2 As shown, this embodiment uses 10mm thick Q235 low-carbon steel as the material, the equipment is an IPGYSL-6000 fiber laser, the optical power is 3000W, multi-mode continuous output, the emitted laser wavelength is 1070nm, the defocus distance is 50mm, the spot diameter is 4.2mm, and the light output time is set to 30ms, and thermal conductivity mode processing is performed. The specific steps of this embodiment are as follows:

[0064] First, the material surface is treated by grinding, and the oil and impurities on the sample surface are wiped clean with acetone solution. The laser beam and the plate are kept relatively stationary, and the laser emits light for 30ms, ablating the surface of the plate, melting the material surface to form a molten pool;

[0065] After the molten pool solidifies, the cross-sectional morphology of the processed area is obtained by wire cutting, grinding, polishing, and etching. The etching solution is 5% nitric acid alcohol solution;

[0066] According to formula 1: The temperature field under these conditions was obtained using simulation software. The cross-sectional morphology of the processed area was compared with the results of the simulated temperature field analysis, and the absorptivity in the numerical simulation was continuously adjusted. When the melting point isotherms in the obtained temperature field matched the fusion line in the cross section well, the absorptivity set in the numerical simulation was the absorptivity A1 of the incident laser beam in the heat transfer portion of the Q235 low-carbon steel plate under the above processing conditions, which was 39.6%.

[0067] According to formula 3: The calculation shows that the absorption rate A2 required for Q235 low carbon steel plate to overcome the latent heat of melting in the molten pool under the above processing conditions is 1.36%;

[0068] According to formula 4: The calculation shows that the absorption rate A3 required to overcome the latent heat of evaporation of Q235 low carbon steel plate under the above processing conditions is 1.78%;

[0069] According to Formula 5: A=A1+A2+A3, the actual absorption rate A of the incident laser of the Q235 low carbon steel plate under the above processing conditions is 42.74%.

[0070] The method of the present invention uses a high-power laser to act on the surface of the material to be tested, causing the surface of the material to melt and produce a molten pool. After the molten pool solidifies, it is subjected to wire cutting, grinding, and etching to obtain the cross-sectional morphology of the weld, and the weld penetration and melting area are measured. Then, numerical simulation is used to obtain the temperature field of the molten pool, and the melting point isotherms in the temperature field are compared with the fusion line in the weld cross section. When the melting point isotherms in the simulated temperature field match the fusion line in the weld cross section well, the absorptivity set in the numerical simulation is the absorptivity A1 of the incident laser required for thermal conduction of the material; and through measurement and calculation, the absorptivity A2 required for the material to overcome the latent heat of melting of the molten pool and the absorptivity A3 required to overcome the latent heat of evaporation during laser processing are comprehensively considered; finally, the absorptivity A of the material to the incident laser is obtained. The present invention has the characteristics of being able to simply, quickly, and accurately obtain the actual absorptivity of the material to the incident laser.

[0071] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0072] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for measuring the absorptivity of a material to an incident laser during laser welding, characterized in that: The following steps are involved: S1. Pre-treat the material using the same surface treatment process to obtain a sample; S2. Place the sample in a splash-proof storage box for laser processing; S3, cutting, grinding, polishing, and etching the sample after laser processing to obtain the cross-sectional morphology of the processed area; S4. Compare and analyze the cross-sectional morphology of the processed area with the results of the simulated temperature field analysis. When the melting point isotherm in the obtained temperature field matches the fusion line in the cross section, the absorptivity set in the numerical simulation is the absorptivity A1 of the incident laser required by the heat transfer part of the material. S5. Measure the weld cross section and melt volume of the welded sample, and derive the melt mass based on the material density, and then calculate the absorptivity A2 required to overcome the latent heat of molten pool. S6. Measure the mass of the storage box before and after welding to obtain the mass loss of the sample, and then calculate the absorption rate A3 required to overcome the latent heat of evaporation of the sample; S7. Calculate the absorption rate A of the sample to the incident laser based on the obtained A1, A2 and A3; The laser used is in a focused state, and its spot energy is Gaussian distribution; the laser welding mode on the sample is thermal conduction mode or deep penetration mode; When simulating the laser heating temperature field of a sample, the laser heat source model in the thermal conductivity mode is a Gaussian surface heat source model, as shown below: （1） Where, is the spot radius; is the absorption rate set in the simulation; P is the laser power; The absorption rate A2 of the part that overcomes the latent heat of melting is calculated using the following formula: （3） Where, is the melting mass, is the latent heat of melting; P is the laser power, and t is the laser action time; The laser heat source model in deep melting mode is a Gaussian rotating body heat source model, as shown below: （2） Where, is the spot radius; A1 is the absorption rate set in the simulation; P is the laser power; H is the height of the heat source; Use the following formula to calculate the absorption rate A required to overcome the latent heat of evaporation of the sample 3： （4） Where, is the ablation evaporation mass, is the latent heat of vaporization; P is the laser power, and t is the laser action time; The sample's absorption rate A of the incident laser can be calculated by the following formula: 。 2. The method for measuring the absorptivity of a material to an incident laser during laser welding according to claim 1, wherein: The sample in S1 is in plate shape.

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