Welding process with laser-induced plasma enhancement

Abstract

The laser-induced plasma enhanced welding process comprises the following steps that firstly, active gas and protective gas are synchronously conveyed through a coaxial gas path composite gas supply system, secondly, a pulse laser beam is adopted to act on the surface of a workpiece, and controlled plasma is induced to be generated, and thirdly, laser-induced plasma enhanced welding is conducted. A plasma emission spectrum is collected in real time through a spectrum diagnosis unit, and the characteristic spectral line intensity and broadening characteristics are detected; and 4, the laser power, the pulse frequency and the gas component proportion are dynamically adjusted based on the spectral analysis result. By adopting a coaxial gas path composite gas supply system and arranging an inner-layer active gas channel and an outer-layer protective gas channel, an axial velocity gradient composite gas curtain is formed, plasma expansion is dynamically restrained, and the form of plasma is accurately controlled, so that the problem that the form of the plasma is difficult to accurately control is solved; the energy loss caused by the plasma shielding effect is reduced, and the utilization rate of laser energy is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of welding processes, and particularly to a welding process enhanced by laser-induced plasma. Background Art

[0002] In modern manufacturing, welding, as a key material joining technology, is widely used in many fields such as aerospace, automotive manufacturing, and electronic devices. With the continuous development of industrial technology, higher requirements are put forward for aspects such as welding quality, efficiency, and material adaptability. Laser welding, as a high-energy beam welding technology, has advantages such as high energy density, fast welding speed, and small heat-affected zone, and overcomes some deficiencies of traditional welding processes to a certain extent.

[0003] Currently, existing welding processes have problems such as low welding quality and low welding efficiency when facing some special materials or high-precision welding requirements. Plasma is generated during the laser welding process, and the plasma has an absorption and scattering effect on laser energy, forming a plasma shielding effect, resulting in laser energy loss and restricting the further improvement of welding penetration and welding speed. Summary of the Invention

[0004] The object of the present invention is to address the deficiencies of the prior art and propose a welding process enhanced by laser-induced plasma to solve the technical problem of difficult precise control of plasma morphology mentioned in the background art.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A welding process enhanced by laser-induced plasma includes the following steps:

[0007] Step 1, synchronously supply active gas and shielding gas through a coaxial gas path composite gas supply system, where the volume fraction of the active gas is 0.5%-5%, the shielding gas is helium or argon, the coaxial gas path includes an inner-layer active gas channel and an outer-layer shielding gas channel, and the exit angles of the two differ by 15°-45° to form an axial velocity gradient composite gas curtain to dynamically confine plasma expansion;

[0008] Step 2, use a pulsed laser beam to act on the surface of the workpiece, the laser peak power density is 106-107W / cm 2 , the pulse width is 10-100ns, the pulse train interval is adjustable, and a 50-200kHz high-frequency jitter modulation is applied to enhance the stability of the molten pool;

[0009] Step 3: Use the time-resolved spectroscopy diagnostic unit to collect the plasma emission spectrum within the time window of 10 - 100 μs after the laser pulse ends, and detect the intensity of any two characteristic spectral lines and the Stark broadening characteristics among FeI 358.1 nm, AlI 396.1 nm, and TiII 334.9 nm;

[0010] Step 4: Based on the spectral analysis, obtain the plasma electron density and temperature parameters, and dynamically adjust the laser power, pulse frequency, and gas component ratio through the fuzzy PID control algorithm. The adjustment response time ≤ 50 ms, and the control objectives include maintaining the plasma electron density and suppressing the characteristic spectral lines to achieve an even distribution of the thermal input at the interface of dissimilar materials.

[0011] Working principle:

[0012] First, with the help of the coaxial gas path composite gas supply system, the reactive gas and the protective gas are synchronously transported at a specific ratio from the inner-layer reactive gas channels and the outer-layer protective gas channels with different emission angles. At a certain volume fraction, the reactive gas can undergo specific physical and chemical reactions with the plasma induced by the laser, while the protective gas forms an isolation layer to reduce external interference. The axial velocity gradient composite gas curtain formed by the two can affect the flow field around the plasma by changing the gas flow rate and pressure distribution, thereby dynamically constraining the expansion direction and range of the plasma;

[0013] Subsequently, a pulsed laser beam with a specific peak power density, pulse width, and pulse train interval and applied with high-frequency jitter modulation acts on the workpiece surface. The laser energy instantaneously vaporizes and ionizes the surface material of the workpiece to form a plasma. The high-frequency jitter modulation makes the laser energy distribution more uniform, promotes the mixing and flow of substances in the molten pool, and enhances the stability of the molten pool;

[0014] Within a specific time window after the laser pulse ends, the time-resolved spectroscopy diagnostic unit collects the plasma emission spectrum. Atoms or ions of different elements will emit spectral lines with specific wavelengths in the plasma. By detecting the intensity of the characteristic spectral lines of FeI 358.1 nm, AlI 396.1 nm, and TiII 334.9 nm and the Stark broadening characteristics, the internal physical state of the plasma can be inferred. The spectral line intensity is related to the element content, and the Stark broadening is closely related to the plasma electron density. After obtaining the plasma electron density and temperature parameters based on the spectral analysis, the fuzzy PID control algorithm compares these parameters with the preset ideal values, calculates according to the deviation, and dynamically adjusts the laser power, pulse frequency, and gas component ratio to achieve precise control of the thermal input at the interface of dissimilar materials and achieve the purpose of evenly distributing the thermal input.

[0015] The beneficial effects of the present invention are:

[0016] In the present invention, by adopting a coaxial gas path composite gas supply system, an inner layer active gas channel and an outer layer protective gas channel are set, and their emission angles differ by 15°-45°, forming an axial velocity gradient composite gas curtain, enabling dynamic constraint of plasma expansion, precisely controlling the morphology of the plasma, thereby solving the problem that the plasma morphology is difficult to precisely control, reducing the energy loss caused by the plasma shielding effect, and improving the utilization rate of laser energy.

[0017] By using a pulsed laser beam with a peak power density of 106-107W / cm 2 , a pulse width of 10-100ns, an adjustable pulse train interval, and a 50-200kHz high-frequency jitter modulation applied to act on the surface of the workpiece, making the laser energy distribution more uniform, enhancing the mixing and flow of substances in the molten pool, thereby solving the problem of poor stability of the molten pool during the welding process and improving the weld forming quality.

[0018] By using a time-resolved spectroscopic diagnostic unit, collecting the plasma emission spectrum within a 10-100μs time window after the laser pulse ends, detecting the intensity of specific characteristic spectral lines and the Stark broadening characteristics, and obtaining the plasma electron density and temperature parameters based on spectral analysis, and then using a fuzzy PID control algorithm to dynamically adjust the laser power, pulse frequency, and gas component ratio, enabling real-time and precise adjustment of welding parameters according to the plasma state, thereby solving the problem of metallurgical defects caused by the mismatch of thermophysical parameters during the welding of dissimilar materials, realizing the balanced distribution of heat input at the interface of dissimilar materials, improving the quality and performance of the welded joints of dissimilar materials. At the same time, the adjustment response time ≤50ms, enabling timely response to changes in the plasma state, ensuring the stability and reliability of the welding process.

[0019] Further, in the first step, the inner layer active gas channel of the coaxial gas path composite gas supply system has a diameter of 1.2-2.5mm, the annular gap width of the outer layer protective gas channel is 0.3-0.8mm, and the total gas flow rate is 10-30L / min.

[0020] Further, in the third step, a high-speed spectrometer is used for spectroscopic detection. The incident slit width of the spectrometer is 5-20μm, the grating line density is 2400lines / mm, and the spectral resolution reaches 0.05-0.1nm.

[0021] Further, in the fourth step, when it is detected that the plasma electron temperature exceeds 1.8eV, the protective gas flow rate is increased by 20%-40%, the laser peak power density is reduced by 10%-15% within the subsequent 3-5 pulse cycles, and the piezoelectric ceramic vibrator is activated to remove the nozzle attachments at a frequency of 5kHz.

[0022] Further, in the second step, the spatial trajectory of the high-frequency jitter modulation adopts Lissajous figure mode, spiral scanning mode, and random perturbation mode;

[0023] In the Lissajous figure mode, the vibration frequency ratio of the X / Y axis is 3:2;

[0024] In the spiral scanning mode, the radial step is 0.1 - 0.3 times the spot diameter;

[0025] In the random perturbation mode, the perturbation amplitude follows a normal distribution N(0, 0.1d 2 ), where d is the spot diameter.

[0026] Further, in the first step, the mixing gradient control of the active gas and the shielding gas includes the following steps:

[0027] Within 3 ms before the start of welding, linearly increase the active gas concentration from 0% to the set value;

[0028] In the interface region of dissimilar materials, increase the O2 ratio to the upper limit value of 5%;

[0029] When detecting the generation of spatter, instantaneously switch to pure Ar gas protection.

[0030] Further, in the fourth step, the interface heat distribution control for dissimilar material welding is through the following steps:

[0031] High melting point material side: Maintain the laser power density ≥ 8×10 6 W / cm 2 , and the plasma electron temperature is 1.5 - 1.8 eV;

[0032] Low melting point material side: Control the plasma electron density ≤ 3×10 18 cm -3 , and shorten the laser dwell time by 20% - 40%.

[0033] Further, in the fourth step, in the fuzzy PID control algorithm, when the rising rate of the electron density > 10 17 cm -3 / ms, trigger the instruction of the step - down of the laser power. When the spectral line intensity exceeds the limit for 2 consecutive pulse periods, start the gas ratio reset protocol. When the number of system oscillations > 5 times, automatically switch to the open - loop control mode.

[0034] Further, when welding dissimilar materials with a copper - steel dissimilar joint in the fourth step, a nickel - based transition layer with a thickness of 0.1 - 0.3 mm is pre - placed on the copper side, and a shielding gas with a helium ratio ≥ 70% is used on the steel side to control the Fe / Ni atomic diffusion ratio in the interface region to be 1:1.2 - 1:1.5.

[0035] Further, the selection criteria for the characteristic spectral lines are as follows:

[0036] For iron-based materials, the ratio of the double spectral lines of FeI 358.1 nm and FeII 275.5 nm is preferentially monitored;

[0037] For aluminum-based materials, the intensity correlation between AlI 396.1 nm and AlIII 451.2 nm is monitored;

[0038] The fluctuation threshold of the spectral line intensity ratio is set at ±15%. Brief Description of the Drawings

[0039] Figure 1 It is a schematic flow chart of the process steps of the embodiment of the present invention. Detailed Embodiments

[0040] The technical solutions in the present invention will be further described below with reference to the drawings and embodiments.

[0041] As Figure 1 shown, a laser-induced plasma-enhanced welding process includes the following steps:

[0042] Step 1: Synchronously supply the active gas and the shielding gas through a coaxial gas path composite gas supply system, where the volume fraction of the active gas is 0.5%-5%, the shielding gas is helium or argon, the coaxial gas path includes an inner active gas channel and an outer shielding gas channel, and the exit angles of the two differ by 15°-45° to form an axial velocity gradient composite gas curtain to dynamically confine the plasma expansion. The diameter of the inner active gas channel of the coaxial gas path composite gas supply system is 1.2-2.5 mm, the annular gap width of the outer shielding gas channel is 0.3-0.8 mm, and the total gas flow rate is 10-30 L / min;

[0043] The mixing gradient control of the active gas and the shielding gas includes the following steps: linearly increasing the concentration of the active gas from 0% to the set value within 3 ms before the start of welding; increasing the proportion of O2 to the upper limit value of 5% in the interface area of dissimilar materials; instantaneously switching to pure Ar gas shielding when spatter is detected;

[0044] It can accurately control the expansion direction and range of the plasma, reduce the shielding effect of the plasma on the laser energy, enable more laser energy to act on the workpiece surface, improve the energy utilization rate, thereby providing a more stable and efficient energy environment for the subsequent welding process, and helping to improve the welding quality and efficiency;

[0045] From a fluid mechanics perspective, different exit angles of the inner active gas channel and the outer protective gas channel will cause a velocity difference when the gas flows out, thereby generating an axial velocity gradient. This velocity gradient will form a specific flow field structure around the plasma, exerting a constraint on the plasma. The active gas participates in the physical and chemical reactions in the plasma, changing the properties of the plasma;

[0046] The protective gas plays a role in isolating external impurities and maintaining the purity of the plasma environment. The specific channel diameter, annulus width, and total gas flow rate can precisely control the gas flow velocity and pressure distribution, further optimizing the constraint effect on the plasma. The mixing gradient control dynamically adjusts the concentration of the active gas according to different stages and conditions of the welding process to meet different welding requirements;

[0047] Dynamically constraining the plasma expansion can effectively avoid energy loss caused by excessive plasma diffusion and adverse effects on the welding area, ensuring the stability of the welding process. Gradually increasing the active gas concentration at the beginning of welding can make the formation of the plasma more stable and reduce unstable factors at the initial stage. Increasing the proportion of O2 in the interface area of dissimilar materials helps to enhance the chemical reaction in this area and improve the bonding performance between dissimilar materials. Switching to pure Ar gas protection when spatter is detected can prevent spatter from having a negative impact on the welding quality and ensure the smooth progress of the welding process;

[0048] Step 2: Apply a pulsed laser beam to the surface of the workpiece. The peak power density of the laser is 106 - 107 W / cm 2 , the pulse width is 10 - 100 ns, the pulse train interval is adjustable, and a high-frequency jitter modulation of 50 - 200 kHz is applied to enhance the stability of the molten pool. The spatial trajectory of the high-frequency jitter modulation adopts Lissajous pattern mode, spiral scanning mode, and random perturbation mode;

[0049] For the Lissajous pattern mode, the vibration frequency ratio in the X / Y axis is 3:2; for the spiral scanning mode, the radial step size is 0.1 - 0.3 times the spot diameter; for the random perturbation mode, the perturbation amplitude follows a normal distribution N(0,0.1d 2 ), where d is the spot diameter;

[0050] Through the pulsed laser setting and high-frequency jitter modulation, the stability of the molten pool is significantly enhanced, making the weld formation more regular and uniform, reducing the generation of welding defects such as pores and cracks, improving the quality and mechanical properties of the welded joint, and meeting the requirements of high-precision welding;

[0051] A high-energy density pulsed laser beam acts instantaneously on the surface of the workpiece, causing the material to rapidly absorb energy and undergo vaporization and ionization, forming a plasma. The peak power density, pulse width, and pulse train interval of the laser jointly determine the amount of energy input to the workpiece and its temporal distribution, playing a crucial role in the melting of the material and the formation process of the plasma. High-frequency jitter modulation changes the action position and energy distribution of the laser beam on the workpiece surface, causing different forms of movement of the substances in the molten pool. The Lissajous pattern mode uses a specific X / Y axial vibration frequency ratio to make the laser energy distribute in a specific trajectory within the plane, promoting two-dimensional mixing of the substances in the molten pool;

[0052] The spiral scanning mode makes the laser energy distribute in a spiral shape within the molten pool through radial stepping, enhancing the mixing of substances from the center to the edge of the molten pool; The random perturbation mode, based on the perturbation amplitude of the normal distribution, makes the distribution of the laser energy have a certain randomness, avoiding the formation of a fixed flow pattern of the substances in the molten pool and further enhancing the mixing effect. These modes can all make the temperature and composition in the molten pool more uniform, thereby enhancing the stability of the molten pool;

[0053] Enhancing the stability of the molten pool is crucial for ensuring the welding quality. A stable molten pool can enable the weld metal to form a uniform organizational structure during solidification, reducing defects caused by compositional segregation and temperature non-uniformity. Different high-frequency jitter modulation modes can be selected according to the welding materials and process requirements, providing flexible process control means to meet diverse welding needs;

[0054] Step 3: Use the time-resolved spectroscopy diagnostic unit to collect the plasma emission spectrum within a 10 - 100 μs time window after the laser pulse ends, detect the intensity of any two characteristic spectral lines and the Stark broadening characteristics among FeI 358.1 nm, AlI 396.1 nm, and TiII 334.9 nm, and perform spectroscopic detection using a high-speed spectrometer. The incident slit width of the spectrometer is 5 - 20 μm, the grating ruling density is 2400 lines / mm, and the spectral resolution reaches 0.05 - 0.1 nm;

[0055] It can accurately obtain the key information of the plasma, provide reliable data support for the subsequent precise control of the welding process, help detect abnormal situations in the welding process in a timely manner, ensure the stability and consistency of the welding quality, and achieve refined control of the welding process;

[0056] The spectrum is collected within a specific time window after the laser pulse ends because the spectral characteristics of the plasma during this time period can accurately reflect its internal physical and chemical states. Atoms or ions of different elements will emit spectral lines with specific wavelengths in the plasma. By detecting the intensities and Stark broadening characteristics of these characteristic spectral lines, important parameters such as the electron density and temperature of the plasma can be obtained. The specific parameters of the high-speed spectrometer, the incident slit width, the grating line density, and the spectral resolution, determine its spectral resolution ability and detection accuracy. A narrower incident slit width and a higher grating line density can improve the spectrometer's resolution ability for light of different wavelengths, thus accurately detecting the subtle changes in the characteristic spectral lines; a high spectral resolution ensures that the intensities and broadening degrees of the spectral lines can be accurately measured, providing a guarantee for accurately analyzing the plasma state;

[0057] Accurately detecting the characteristic spectral lines of the plasma is crucial for real-time understanding of the state changes of the plasma during the welding process. By monitoring these characteristic spectral lines, the electron density and temperature parameters of the plasma can be grasped in real time. When these parameters are abnormal, the welding process parameters can be adjusted in a timely manner to avoid welding defects caused by unstable plasma states, achieve closed-loop control of the welding process, and improve the controllability of the welding quality;

[0058] Step 4: Based on spectral analysis, obtain the plasma electron density and temperature parameters, and dynamically adjust the laser power, pulse frequency, and gas component ratio through the fuzzy PID control algorithm. The adjustment response time ≤ 50 ms. The control objectives include maintaining the plasma electron density and suppressing the characteristic spectral lines to achieve an even distribution of the heat input at the interface of dissimilar materials. When it is detected that the plasma electron temperature exceeds 1.8 eV, increase the protective gas flow rate by 20% - 40%, and reduce the laser peak power density by 10% - 15% within the subsequent 3 - 5 pulse periods. Activate the piezoelectric ceramic vibrator to remove the nozzle attachments at a frequency of 5 kHz;

[0059] For the control of the interface heat distribution during the welding of dissimilar materials, the following steps are taken: On the side of the high-melting-point material: Maintain the laser power density ≥ 8×10 6 W / cm 2 , and the plasma electron temperature is 1.5 - 1.8 eV; On the side of the low-melting-point material: Control the plasma electron density ≤ 3×10 18 cm -3 , shorten the laser residence time by 20% - 40%. In the fuzzy PID control algorithm, when the rising rate of the electron density > 10 17 cm -3 / ms, trigger the instruction for a step-down of the laser power. If the spectral line intensity exceeds the limit for two consecutive pulse periods, start the gas ratio reset protocol. When the number of system oscillations > 5 times, automatically switch to the open-loop control mode;

[0060] When welding dissimilar materials to a copper-steel dissimilar joint, a nickel-based transition layer with a thickness of 0.1 - 0.3 mm is pre-placed on the copper side, and a shielding gas with a helium content of ≥ 70% is used on the steel side to control the Fe / Ni atomic diffusion ratio in the interface area to be 1:1.2 - 1:1.5. The selection criteria for characteristic spectral lines are as follows: for ferrous materials, the ratio of the double spectral lines FeI358.1 nm and FeII275.5 nm is preferentially monitored; for aluminum-based materials, the intensity correlation between AlI396.1 nm and AlIII451.2 nm is monitored; the fluctuation threshold of the spectral line intensity ratio is set at ±15%.

[0061] The comprehensive and precise control of the welding process is achieved, effectively solving the problem of uneven heat input during the welding of dissimilar materials, significantly improving the quality and performance of the dissimilar material welded joints, enhancing the stability and reliability of the welding process, meeting the welding requirements of different material combinations, and expanding the application scope of the welding process;

[0062] Based on the plasma electron density and temperature parameters obtained from spectral analysis, the fuzzy PID control algorithm dynamically adjusts the laser power, pulse frequency, and gas component ratio according to the deviation between these parameters and the preset target values through a specific algorithm logic. This algorithm can handle complex systems that are difficult to accurately model and adapt to various uncertain factor changes during the welding process. When the plasma electron temperature exceeds 1.8 eV, increasing the shielding gas flow rate can carry away more heat and reduce the plasma temperature; reducing the laser peak power density reduces the energy input, and the combined effect of the two restores the plasma temperature to a reasonable range;

[0063] Activating the piezoelectric ceramic vibrator to remove the attachments on the nozzle can ensure the stability of gas supply and avoid affecting the welding process due to nozzle blockage. For the welding of dissimilar materials, according to the melting point difference of the materials, a higher laser power density and a specific plasma electron temperature are maintained on the side of the high-melting-point material to ensure sufficient melting of the material; on the side of the low-melting-point material, the plasma electron density is controlled and the laser residence time is shortened to prevent the material from overheating and melting. In the fuzzy PID control algorithm, different triggering conditions are set to cope with the rapid changes in the plasma state, ensuring the timeliness and accuracy of control. For the welding of a copper-steel dissimilar joint, a nickel-based transition layer is pre-placed on the copper side, and the good metallurgical compatibility of nickel with copper and steel is utilized to improve the interface bonding; on the steel side, a shielding gas with a high helium ratio is used to change the plasma properties, control the Fe / Ni atomic diffusion ratio in the interface area, and optimize the interface microstructure. Selecting specific characteristic spectral lines and setting the fluctuation threshold for different materials are based on the spectral characteristics of different elements in the plasma, and the changes in the plasma state are accurately reflected by monitoring these characteristic spectral lines;

[0064] Ensured the stability and reliability of the welding process, improved the welding quality, solved the problem of uneven heat input in dissimilar material welding, avoided welding defects caused by improper heat input, enhanced the strength and toughness of the dissimilar material welded joints. Different control strategies and parameter adjustments are targeted at different welding situations and material characteristics, providing an effective solution for diverse welding requirements in actual production, and enhancing the practicability and adaptability of this welding process.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A laser-induced plasma enhanced welding process, characterized in that: The following steps are involved: Step 1: synchronously deliver active gas and shielding gas through a coaxial gas path composite gas supply system, wherein the volume fraction of active gas is 0.5%-5%, and shielding gas is helium or argon. The coaxial gas path includes an inner layer active gas channel and an outer layer shielding gas channel, and the exit angles of the two differ by 15°-45°, forming an axial velocity gradient composite gas curtain to dynamically constrain plasma expansion; Step 2: Use a pulsed laser beam to act on the workpiece surface, with a laser peak power density of 106-107W / cm 2 , pulse width 10-100ns, pulse train interval adjustable, and 50-200kHz high frequency jitter modulation is applied to enhance the stability of the molten pool; Step 3: The plasma emission spectrum is collected in a 10-100 μs time window after the laser pulse ends by a time-resolved spectral diagnostic unit to detect the intensity and Stark broadening characteristics of any two characteristic spectral lines of FeI358.1 nm, AlI396.1 nm, and TiII334.9 nm; Step 4: Obtain plasma electron density and temperature parameters based on spectral analysis, dynamically adjust laser power, pulse frequency and gas component ratio through fuzzy PID control algorithm, and adjust the response time to ≤50ms. The control objectives include maintaining plasma electron density and suppressing characteristic spectral lines to achieve balanced distribution of heat input at the interface of heterogeneous materials.

2. The laser-induced plasma enhanced welding process according to claim 1, characterized in that: In the step 1, the diameter of the inner active gas channel of the coaxial gas path composite gas supply system is 1.2-2.5 mm, the annular gap width of the outer protective gas channel is 0.3-0.8 mm, and the total gas flow rate is 10-30 L / min.

3. The laser-induced plasma enhanced welding process according to claim 1, characterized in that: In the step three, a high-speed spectrometer is used for spectroscopic detection, the incident slit width of the spectrometer is 5-20 μm, the grating line density is 2400 lines / mm, and the spectral resolution reaches 0.05-0.1 nm.

4. The laser-induced plasma enhanced welding process according to claim 1, characterized in that: In step 4, when it is detected that the plasma electron temperature exceeds 1.8 eV, the protective gas flow rate is increased by 20%-40%, the laser peak power density is reduced by 10%-15% in the subsequent 3-5 pulse cycles, and the piezoelectric ceramic vibrator is activated at a frequency of 5 kHz to remove nozzle attachments.

5. The laser-induced plasma enhanced welding process according to claim 1, characterized in that: In the step 2, the spatial trajectory of the high-frequency jitter modulation adopts a Lissajous pattern mode, a spiral scanning mode and a random disturbance mode; In the Lissajous pattern, the X / Y axial vibration frequency ratio is 3:2; In the spiral scanning mode, the radial stepping amount is 0.1-0.3 times the spot diameter; The random disturbance mode and the disturbance amplitude follow the normal distribution N(0,0.1d 2 ), where d is the spot diameter.

6. The laser-induced plasma enhanced welding process according to claim 1, characterized in that: In the step 1, the mixed gradient control of the active gas and the protective gas includes the following steps: The active gas concentration is linearly increased from 0% to the set value within 3ms before the start of welding; Increase the O2 ratio to an upper limit of 5% in the interface area of ​​dissimilar materials; When splash generation is detected, it is instantly switched to pure Ar gas protection.

7. The laser-induced plasma enhanced welding process according to claim 1, characterized in that: In step 4, the interface heat distribution control for the welding of dissimilar materials is carried out through the following steps: High melting point material side: maintain laser power density ≥ 8×10 6 W / cm 2 , plasma electron temperature 1.5-1.8eV; Low melting point material side: control plasma electron density ≤3×10 18 cm -3 , laser dwell time is shortened by 20%-40%.

8. The laser-induced plasma enhanced welding process according to claim 1, characterized in that: In the step 4, in the fuzzy PID control algorithm, when the electron density rise rate is greater than 10 17 cm -3 / ms, the laser power step-down command is triggered. If the spectral line intensity exceeds the limit for two consecutive pulse cycles, the gas ratio reset protocol is started. When the system oscillates more than 5 times, it automatically switches to the open-loop control mode.

9. The laser-induced plasma enhanced welding process according to claim 1, characterized in that: In the step 4, when welding dissimilar materials and copper-steel dissimilar joints, a 0.1-0.3 mm thick nickel-based transition layer is preset on the copper side, and a protective gas with a helium ratio of ≥ 70% is used on the steel side to control the Fe / Ni atomic diffusion ratio in the interface area to 1:1.2-1:1.

5.

10. The laser-induced plasma enhanced welding process according to claim 3, characterized in that: The selection criteria of the characteristic spectral lines are: For iron-based materials, the dual-line ratio of FeI358.1nm and FeII275.5nm should be monitored first; For aluminum-based materials, the intensity correlation between AlI396.1nm and AlIII451.2nm is monitored; The fluctuation threshold of the spectral line intensity ratio was set to ±15%.

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