Method for actively regulating laser-induced liquid-vapor interface delayed evaporation and application

Abstract

The present application relates to the technical field of laser material processing, and especially relates to a method for actively regulating and controlling laser-induced liquid-vapor interface delayed evaporation and application. The method comprises the following steps: establishing a closed mixed protective atmosphere in a laser processing area; collecting liquid-vapor interface evaporation data during laser irradiation in real time in the process of forming a molten pool by laser irradiation welding plate; comparing the liquid-vapor interface evaporation data with target liquid-vapor interface evaporation data; and actively regulating and controlling the content of reactive gas in the protective atmosphere according to the comparison result through an atmosphere supply device. The above method is suitable for energy coupling optimization and evaporation behavior regulation in the process of laser welding, laser melting and laser additive manufacturing. By actively setting and adjusting the content of the reactive gas in the closed mixed protective atmosphere, the present application realizes controllable adjustment of the evaporation start time and delay amplitude. The evaporation inhibition and energy coupling requirements are considered under different process windows.

Description

Technical Field

[0001] This invention relates to the field of laser material processing technology, and in particular to a method and application of actively controlling laser-induced delayed evaporation at the vapor-liquid interface. Background Technology

[0002] Laser material processing technologies such as laser welding, laser melting, and laser additive manufacturing are widely used for joining and forming metal materials such as iron-based alloys, nickel-based alloys, aluminum alloys, and titanium alloys due to their advantages of high energy density, small heat-affected zone, and high processing efficiency. However, during the process of laser irradiation of metal to form a molten pool and the generation of a keyhole, the vapor-liquid interface of the molten pool usually undergoes violent evaporation and jetting, which induces a series of coupled instabilities such as metal vapor / feathering, spatter, keyhole disturbance, and molten pool fluctuations. These instabilities not only lead to energy coupling fluctuations and poor weld uniformity, but may also cause alloy element burn-off, intensified interface reactions, and an increased tendency for defects such as porosity, lack of fusion, and cracks, becoming one of the important factors restricting high-quality laser processing.

[0003] In existing technologies, the suppression of molten pool evaporation and process stability typically employs inert gas protection via side-blowing / coaxial blowing to reduce air entrainment, weaken the absorption and scattering of laser plume, and improve process stability. Simultaneously, research has also explored optimizing laser power and welding speed, altering defocusing and spot morphology, using oscillating welding or multi-beam composites, and introducing external fields (such as magnetic fields or ultrasound) to improve keyhole stability and molten pool flow. However, these methods primarily aim to reduce evaporation intensity or suppress plume interference, relying mainly on airflow scouring and energy input redistribution. This makes it difficult to actively and predictably control the evaporation initiation time on a millisecond-scale timescale. Furthermore, under certain process windows, excessive suppression of evaporation / plume may lead to decreased keyhole maintenance, limited deep penetration, or abnormal molten pool backfilling, resulting in new forming and defect risks. Summary of the Invention

[0004] The purpose of this invention is to provide a method and application for actively controlling laser-induced delayed evaporation at the vapor-liquid interface, thereby solving the aforementioned technical problems.

[0005] To achieve the above objectives, the present invention provides a method for actively controlling laser-induced delayed evaporation at the vapor-liquid interface, the specific steps of which are as follows: Step S1: Before or in the early stage of molten pool formation, a closed mixed protective atmosphere is established in the laser processing area through an atmosphere supply device, and the initial reactive gas content in the closed mixed protective atmosphere is adjusted through the atmosphere supply device. Step S2: During the process of forming a molten pool by laser irradiation welding of the plate, the vapor-liquid interface evaporation data during the laser action is collected in real time, and the vapor-liquid interface evaporation data is compared with the target vapor-liquid interface evaporation data. Step S3: Based on the comparison results of step S2, the content of reactive gas in the protective atmosphere is actively adjusted by the atmosphere supply device to control the timing and extent of the interface state change, thereby achieving active adjustment of the evaporation start time and evaporation delay of the molten pool vapor-liquid interface.

[0006] Preferably, the enclosed mixed protective atmosphere includes an inert gas and a reactive gas.

[0007] Preferably, the inert gas includes any one or both of argon and helium; The reacting gases include oxygen-containing gases or nitrogen-containing gases.

[0008] Preferably, the inert gas includes any one or more of argon, helium, or nitrogen; The reacting gases include oxygen-containing gases.

[0009] Preferably, the atmosphere supply device includes an inert gas source, a reactive gas source, a gas mixing unit, and a gas supply pipeline. Both the inert gas source and the reactive gas source are connected to the gas inlet of the gas mixing unit, and the gas outlet of the gas mixing unit is connected to the gas supply pipeline.

[0010] Preferably, the initial reactive gas content is a set value or continuously adjusted according to a preset function curve. The active control of the reactive gas content in the protective atmosphere includes adjusting the volume fraction of the reactive gas, adjusting the partial pressure of the reactive gas, and adjusting the total flow rate of the closed-loop mixed protective atmosphere. The closed protection adopts a fiberglass cavity to isolate external air disturbances, and the gas supply pipeline is connected to the fiberglass cavity.

[0011] Preferably, the vapor-liquid interface evaporation data includes evaporation start time and evaporation delay amplitude; the evaporation start time and evaporation delay amplitude are determined and calculated by at least one of the following: plume appearance time, vapor emission spectrum characteristics, molten pool surface radiation temperature, keyhole opening fluctuation characteristics, and splash event characteristics.

[0012] Preferably, the material of the welding plate is any one or more of iron-based alloys, nickel-based alloys, aluminum alloys, or titanium alloys.

[0013] Preferably, the laser used for laser irradiation is any one of fiber laser, Nd:YAG laser, disk laser, blue laser, green laser, semiconductor laser or CO2 laser; The output power of the laser is 0.5kW-100kW.

[0014] The method of actively controlling laser-induced delayed evaporation at the vapor-liquid interface is described above and its application in laser welding, laser melting manufacturing, or laser additive manufacturing processes is provided.

[0015] Therefore, the present invention employs the above-mentioned method and application for actively controlling laser-induced delayed evaporation at the vapor-liquid interface, and has the following beneficial effects: (1) Using the content of reactant gas in a closed mixed protective atmosphere as an active and controllable variable, the vapor-liquid interface can be induced to undergo controllable interface state changes in the millisecond stage after the formation of the molten pool, thereby achieving a controllable delay in the evaporation start-up time (the time when the feather appears) and enabling timed regulation of the evaporation start-up time.

[0016] (2) By collecting vapor-liquid interface evaporation data during the formation of the molten pool, the evaporation start-up is determined in situ. Combined with the dynamic setting and adjustment of the reactive gas content, the process parameters are adaptively controlled, thereby improving repeatability and stability under different process windows and reducing the forming differences caused by working condition fluctuations.

[0017] (3) By actively regulating the content of reactive gas to balance the requirements of evaporation suppression and laser energy coupling, the evaporation start-up conditions and evaporation intensity evolution characteristics of the vapor-liquid interface can be changed, which can reduce the fluctuation of evaporation intensity and the loss of alloy elements, weaken the process disturbance induced by plume and splash, and thus reduce the tendency of defects such as porosity and cracks.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 This is a flowchart of a method for actively controlling laser-induced delayed evaporation at the vapor-liquid interface according to the present invention. Figure 2 This is a schematic diagram of an experimental system for a method of actively controlling laser-induced delayed evaporation at the vapor-liquid interface according to the present invention; Figure 3 A comparative diagram showing the timing of feather appearance under different oxygen content conditions; Figure 4 This is a graph showing the relationship between oxygen content and the timing of feather appearance.

[0020] Figure Labels 1. Molten pool; 2. Fiberglass cavity; 3. Processing laser beam; 4. Feather; 5. Gas mixing unit; 6. Oxygen source; 7. Argon source; 8. Processing terminal; 9. High-speed camera; 10. Welding plate. Detailed Implementation

[0021] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0023] like Figures 1-2 As shown, a method for actively controlling laser-induced delayed evaporation at the vapor-liquid interface includes the following specific steps: Step S1: Before or in the early stage of the formation of the molten pool 1, a closed mixed protective atmosphere is established in the laser processing area through an atmosphere supply device. The initial reactive gas content in the closed mixed protective atmosphere is adjusted by the atmosphere supply device. The initial reactive gas content is a set value or is continuously adjusted according to a preset function curve.

[0024] A closed-loop protective atmosphere includes inert gases and reactive gases.

[0025] The appropriate inert gas and reactant gas are selected according to the material of the welding plate. In this embodiment, the welding plate is an iron-based alloy (e.g., stainless steel). The inert gas includes any one or more of argon, helium, or nitrogen. In this embodiment, argon is used as the inert gas, and the reactant gas is an oxygen-containing gas. In this embodiment, oxygen with a purity of 99% is used, but other oxygen-containing gases can also be used.

[0026] For titanium alloys, nitrogen reacts with the alloy to form nitrides. Nitrogen can be used as a reactant gas, as can oxygen. Inert gases include any one or both of argon and helium.

[0027] The atmosphere supply device includes an inert gas source (argon source 7 in this embodiment), a reaction gas source (oxygen source 6), a gas mixing unit 5, and a gas supply pipeline. Both the inert gas source and the reaction gas source are connected to the gas inlet of the gas mixing unit 5. The gas outlet of the gas mixing unit 5 is connected to the gas supply pipeline. The gas supply pipeline is connected to the fiberglass cavity 2 to supply the mixed gas.

[0028] The chemical reaction between the interface and the reacting gases causes controllable changes in the interface state of the molten pool vapor-liquid interface on a millisecond timescale. By controlling the timing and extent of these interface state changes, the evaporation initiation time and evaporation delay of the molten pool vapor-liquid interface can be effectively adjusted.

[0029] Step S2: The laser used for laser irradiation is any one of fiber laser, Nd:YAG laser, disk laser, blue laser, green laser, semiconductor laser or CO2 laser; the output power of the laser is 0.5kW-100kW.

[0030] During the process of forming a molten pool 1 by irradiating the welding plate 10 with a laser beam 3, the vapor-liquid interface evaporation data during the laser irradiation period is collected in real time and compared with the target vapor-liquid interface evaporation data. Data acquisition is performed using a high-speed camera 9, and the acquired images are transmitted to a processing terminal 8 for analysis. The vapor-liquid interface evaporation data includes the evaporation start time and evaporation delay amplitude; the evaporation start time and evaporation delay amplitude are determined and calculated using at least one of the following data: the appearance time of plume 4, vapor emission spectrum characteristics, surface radiation temperature of the molten pool 1, keyhole opening fluctuation characteristics, and spatter event characteristics.

[0031] Step S3: Based on the comparison results of step S2, the content of reactive gas in the protective atmosphere is actively adjusted by the atmosphere supply device to control the timing and extent of the interface state change, thereby achieving active adjustment of the evaporation start time and evaporation delay of the molten pool vapor-liquid interface.

[0032] The content of reactive gas (oxygen) has a significant impact on the vapor-liquid interface state of molten pool 1. The participation of oxygen alters the surface reaction process and interface morphology of molten pool 1, affecting surface tension and its temperature coefficient, thereby changing the flow pattern of molten pool 1. Simultaneously, changes in the interface state impede or modulate the evaporation flux and interfacial heat and mass transfer processes. Inducing controllable state changes at the vapor-liquid interface in the millisecond stage after molten pool 1 formation, maintaining or adjusting the reactive gas content to balance evaporation suppression and laser energy coupling requirements, can alter the evaporation initiation conditions and evaporation intensity evolution characteristics of the vapor-liquid interface. This reduces evaporation intensity fluctuations and minimizes alloy element burn-off and process variability, improving the energy coupling stability and defect suppression capabilities of laser welding, laser melting, and additive manufacturing processes. Active control of the reactive gas content in the protective atmosphere includes adjusting the reactive gas volume fraction, adjusting the reactive gas partial pressure, and adjusting the total flow rate of the closed-loop mixed protective atmosphere.

[0033] Therefore, the method in this embodiment can controllably adjust the evaporation start-up time (the time when feather 4 appears) and the delay range, thereby balancing the needs of evaporation suppression and energy coupling under different process windows, reducing evaporation-induced process fluctuations and alloy element burn-off, and suppressing defects such as porosity and cracks. Compared with traditional methods that rely solely on inert protection or empirical adjustment of process parameters, the technical solution in this embodiment has the advantages of controllable environmental variables, timed evaporation start-up, and quantifiable effects.

[0034] A method for actively controlling laser-induced delayed evaporation at the vapor-liquid interface is applied in laser welding, laser melting manufacturing, or laser additive manufacturing processes to improve energy coupling stability and reduce the tendency for at least one defect, such as porosity, lack of fusion, or cracks.

[0035] To verify the effect of oxygen content on the appearance time of Featherbloom 4, tests were conducted using different oxygen contents, such as... Figures 3-4 As shown, the correlation between oxygen content and the time of appearance of Feather 4 is obtained. The evaporation time first increases and then decreases with the increase of oxygen content, thus quantifying the delayed evaporation effect. Combined with the dynamic setting and adjustment of the reactive gas content, the process parameters are adaptively optimized, thereby improving the repeatability and stability under different process windows and reducing the forming differences caused by the fluctuation of working conditions.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for actively controlling laser-induced delayed evaporation at the vapor-liquid interface, characterized in that, The specific steps are as follows: Step S1: Before or in the early stage of molten pool formation, a closed mixed protective atmosphere is established in the laser processing area through an atmosphere supply device. The initial reactive gas content in the closed mixed protective atmosphere is regulated by the atmosphere supply device. The closed mixed protective atmosphere includes inert gas and reactive gas. The atmosphere supply device includes an inert gas source, a reactive gas source, a gas mixing unit, and a gas supply pipeline. Both the inert gas source and the reactive gas source are connected to the gas inlet of the gas mixing unit. The gas outlet of the gas mixing unit is connected to the gas supply pipeline. The closed protection adopts a fiberglass cavity to isolate external air disturbances. The gas supply pipeline is connected to the fiberglass cavity. Step S2: During the process of forming a molten pool by laser irradiation welding of the plate, the vapor-liquid interface evaporation data during the laser action is collected in real time, and the vapor-liquid interface evaporation data is compared with the target vapor-liquid interface evaporation data. Step S3: Based on the comparison results of step S2, the content of reactive gas in the protective atmosphere is actively adjusted by the atmosphere supply device to control the timing and extent of the interface state change, thereby achieving active adjustment of the evaporation start time and evaporation delay of the molten pool vapor-liquid interface.

2. The method for actively controlling laser-induced delayed evaporation at the vapor-liquid interface according to claim 1, characterized in that: Inert gases include any one or both of argon and helium; The reacting gases include oxygen-containing gases or nitrogen-containing gases.

3. The method for actively controlling laser-induced delayed evaporation at the vapor-liquid interface according to claim 1, characterized in that: Inert gases include any one or more of argon, helium, or nitrogen; The reacting gases include oxygen-containing gases.

4. A method for actively controlling laser-induced delayed evaporation at the vapor-liquid interface according to claim 2 or 3, characterized in that: The initial reactive gas content is either a set value or continuously adjusted according to a preset function curve. The methods for actively controlling the reactive gas content in the protective atmosphere include adjusting the volume fraction of reactive gases, adjusting the partial pressure of reactive gases, and adjusting the total flow rate of the closed-loop mixed protective atmosphere.

5. The method for actively controlling laser-induced delayed evaporation at the vapor-liquid interface according to claim 1, characterized in that: The vapor-liquid interface evaporation data includes the evaporation start time and the evaporation delay amplitude; the evaporation start time and the evaporation delay amplitude are determined and calculated by at least one of the following: plume appearance time, vapor emission spectrum characteristics, molten pool surface radiation temperature, keyhole opening fluctuation characteristics, and splash event characteristics.

6. The method for actively controlling laser-induced delayed evaporation at the vapor-liquid interface according to claim 1, characterized in that: The welding plate material is any one or more of iron-based alloys, nickel-based alloys, aluminum alloys, or titanium alloys.

7. The method for actively controlling laser-induced delayed evaporation at the vapor-liquid interface according to claim 1, characterized in that: The laser used for laser irradiation can be any one of the following: fiber laser, Nd:YAG laser, disk laser, blue laser, green laser, semiconductor laser, or CO2 laser. The output power of the laser is 0.5kW-100kW.

8. The application of the method for actively controlling laser-induced delayed evaporation at the vapor-liquid interface as described in claim 1 in laser welding, laser melting manufacturing, or laser additive manufacturing processes.

Images