Electronic component precision machining spot welding control system

Abstract

The application discloses an electronic component precision machining spot welding control system and relates to the technical field of laser processing.The system comprises an adjustable annular light spot laser, a coaxial multi-spectrum sensing module, an FPGA controller, an ARM processor and a motion platform.The sensing module synchronously collects reflected light signals and plasma radiation light signals, the FPGA controller judges the moment of material absorption rate mutation according to the signals, controls the laser to switch the output mode from center light beam to annular light beam, suppresses metal spatter and crater collapse in a single pulse, and the ARM processor calculates the cumulative temperature of a to-be-welded spot according to the heat input and the space-time relationship of a welded spot, feeds forward compensates the initial power and pulse width of the to-be-welded spot, and eliminates the fusion depth drift of continuous spot welding.The application is suitable for precision spot welding of electronic components such as connector terminals, IGBT module pins and gold-plated copper terminals.

Description

Technical Field

[0001] This invention relates to the field of laser processing technology, specifically to a precision spot welding control system for electronic components. Background Technology

[0002] As the electronic components industry develops towards refinement, thinness, miniaturization, and high-density arrays, precision components such as connector terminals, insulated gate bipolar transistor module pins, and gold-plated copper terminals commonly use laser spot welding technology to achieve electrical and mechanical connections. These components often use high-reflectivity and high-thermal-conductivity metal materials such as copper, gold, and aluminum. The basic principle of laser spot welding is to use a high-power-density laser beam to irradiate the surface of the workpiece, causing the surface material to melt rapidly and locally, and forming a weld nugget after cooling, thereby achieving the connection of two or more metal components. A traditional laser spot welding system typically includes a laser, a focusing optical path, a workpiece clamping and moving platform, and a controller. The controller drives the laser to output laser pulses according to preset process parameters such as power, pulse width, and frequency, completing the welding point by point. This type of spot welding technology has been widely used in the field of intelligent manufacturing precision machining equipment and the electronic components manufacturing industry.

[0003] The laser spot welding control scheme that is currently closest to this invention generally includes a pulsed fiber laser or a yttrium aluminum garnet laser, a power sensor for monitoring the actual output power of the laser and feeding it back to the laser power supply, a focusing galvanometer or focusing lens, a workpiece motion platform, and a host process controller. The working process of this type of scheme is as follows: the process personnel pre-set a single combination of power, pulse width, and frequency parameters through the host computer according to the material type and thickness.

[0004] The controller drives the laser power supply according to the preset parameters, so that the laser outputs laser pulses at a constant power or according to a preset power-time curve;

[0005] After the laser beam passes through the focusing system, it is vertically irradiated to the workpiece to be welded. After one spot weld is completed, the motion platform moves to the next weld position according to the preset coordinate sequence. The above process is repeated until all welds are completed. Some solutions also introduce a post-weld visual inspection module to perform offline quality judgment on the appearance of the welds, or introduce the laser's own output power closed loop to ensure the stability of the laser output power. However, this power closed loop only applies to the power of the laser output end itself and does not involve the perception of the change in the absorptivity of the workpiece surface material, nor does it involve the dynamic adjustment of the beam energy distribution method.

[0006] The existing solutions described above have the following technical defects:

[0007] Firstly, because the control logic does not perceive the physical state changes of the workpiece surface material during the duration of a single welding pulse, when the high reflectivity material changes from solid to molten state and the surface absorptivity jumps from a low value to a high value during the pulse duration, the laser continues to output power according to the power set for the low absorptivity stage, causing the molten pool to absorb far more energy than it needs in a very short time, which in turn causes keyhole collapse and metal spatter, resulting in quality defects such as inconsistent weld penetration, incomplete welding, and over-melting.

[0008] Secondly, the existing intelligent welding equipment focuses on weld trajectory tracking and post-weld visual quality inspection, lacking a prediction and feedforward compensation mechanism for the point-to-point heat accumulation effect during continuous spot welding. The heat conducted from the preceding weld point to the workpiece will continuously accumulate to the subsequent weld points, causing the subsequent weld points to be in a higher initial temperature state before welding. If the same excitation power and pulse width parameters are still used, the actual penetration depth and heat input of the subsequent weld points will be much greater than that of the first weld point, forming a penetration depth drift that gradually increases along the processing sequence, affecting the electrical conductivity consistency and mechanical reliability of the electronic component weld points. Summary of the Invention

[0009] The technical problem to be solved by this invention is: how to sense the sudden change in surface absorptivity of a high reflectivity and high thermal conductivity metal material when it transitions from a solid state to a molten state in real time during the duration of a single laser welding pulse, and dynamically adjust the beam energy distribution accordingly, so as to suppress metal spatter and inconsistent melting depth caused by instantaneous energy excess.

[0010] Furthermore, in the context of high-density array continuous spot welding, this paper explores how to pre-quantify and predict the residual heat transferred and accumulated from previous weld points to subsequent weld points, and how to perform feedforward adaptive compensation on the excitation parameters of the weld points to be welded, thereby solving the problem of inconsistent weld point formation caused by heat accumulation drift in continuous spot welding.

[0011] To address the aforementioned technical problems, this invention provides a precision spot welding control system for electronic components, comprising an adjustable ring-shaped laser, a coaxial multispectral high-frequency sensing module, an FPGA controller, an ARM processor, a precision motion platform, and a process parameter database. The adjustable ring-shaped laser has a center beam output port and a ring beam output port capable of independent power modulation.

[0012] The coaxial multispectral high-frequency sensing module is coaxially set with the processing optical path of the adjustable ring spot laser, and is used to synchronously acquire the first band reflected light signal reflecting the material state of the workpiece surface and the second band radiated light signal reflecting the plasma state of the molten pool.

[0013] The FPGA controller is connected to the signal output terminal of the coaxial multispectral high-frequency sensing module and is used to calculate the inflection point criterion signal based on the first band reflected light signal and the second band radiated light signal. When the inflection point criterion signal exceeds a preset threshold, the controller controls the adjustable ring spot laser to switch the output mode from center beam as the main component to ring beam as the main component.

[0014] The ARM processor is connected to the FPGA controller via a bus. It is used to calculate the cumulative temperature of the solder joint before welding based on the spatial distance and time interval between the solder joint and the solder joint to be welded, as well as the heat input of the solder joint. Based on the deviation between the cumulative temperature and the reference temperature, it calculates the compensated initial power and compensated pulse width of the solder joint to be welded and sends them to the FPGA controller.

[0015] The present invention also provides a precision machining spot welding control method for electronic components corresponding to the above system. By judging the moment of sudden change in the absorptivity of the workpiece surface material in real time during the duration of a single welding pulse, and dynamically switching the power ratio of the central beam and the ring beam after detecting the sudden change, energy reshaping in the single pulse dimension is achieved.

[0016] Simultaneously, by comprehensively calculating the heat input, spatial distance, and time interval of the welded joints, the cumulative temperature of the joint to be welded before welding is obtained. Based on this, the initial excitation power and pulse width of the joint to be welded are feedforwarded to achieve cross-pulse dimension heat accumulation compensation. The above-mentioned single-pulse micro-closed-loop control and cross-pulse macro-feedforward control are implemented collaboratively by the FPGA controller and the ARM processor, respectively, forming a two-level collaborative control architecture. The two interact with the actual heat input statistics and compensation parameters through a bus, which can simultaneously take into account the single-pulse forming quality and the consistency of continuous spot welding in the same control system.

[0017] Compared with the prior art, the beneficial effects of the present invention by adopting the above technical solution are as follows:

[0018] 1. This invention, by synchronously monitoring and jointly judging the reflected light signal and the plasma radiation light signal during the duration of a single welding pulse, can dynamically switch the beam energy ratio within a microsecond timescale when the absorptivity of the workpiece surface material changes abruptly. This suppresses keyhole collapse and metal spatter caused by excess energy from a physical mechanism, thereby improving the forming quality of a single weld point.

[0019] 2. This invention pre-quantifies and predicts the residual heat generated and conducted and accumulated point by point during continuous spot welding, and performs feedforward compensation on the initial excitation power and pulse width of the weld point to be welded. This eliminates the drift phenomenon of the weld penetration depth gradually increasing along the processing sequence due to heat superposition, improves the consistency of weld penetration depth and contact resistance in high-density array spot welding scenarios, and thus improves the electrical and mechanical reliability of electronic component products.

[0020] 3. This invention employs a two-level collaborative control architecture that combines single-pulse micro-closed-loop and cross-pulse macro-feedforward, enabling the system to simultaneously address both single-point forming quality and batch processing consistency requirements. It is suitable for automated spot welding production of high-density arrayed electronic components in the field of intelligent manufacturing precision machining equipment. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall system architecture in an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of the single-pulse dynamic energy reshaping control process in an embodiment of the present invention;

[0023] Figure 3 This is a schematic diagram of the continuous spot welding cross-pulse thermal compensation process in an embodiment of the present invention. Detailed Implementation

[0024] The following is in conjunction with the appendix Figure 1-3 The specific embodiments of the present invention will be further described below. It should be noted that the description of these embodiments is for the purpose of helping to understand the present invention, but does not constitute a limitation of the present invention.

[0025] The technical solution of the present invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the following embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0026] Example 1

[0027] The precision machining spot welding control system for electronic components provided in this embodiment includes an adjustable ring spot laser, a coaxial multispectral high-frequency sensing module, an FPGA controller, an ARM processor, a precision motion platform, and a process parameter database, which is used to perform point-by-point laser welding on workpieces mounted on the precision motion platform.

[0028] The tunable ring beam laser has a central beam output port and a ring beam output port. The beam output from the central beam output port is a Gaussian or quasi-Gaussian concentrated beam, while the beam output from the ring beam output port is a ring-shaped beam distributed around the central beam. The output power of the two can be independently modulated, with a power response time in the range of 10 microseconds to 50 microseconds. The central beam and the ring beam output from the tunable ring beam laser are combined by a beam splitter and a focusing assembly, and then vertically illuminate the workpiece at the point to be welded.

[0029] The coaxial multispectral high-frequency sensing module is coaxially arranged with the processing optical path of the tunable ring spot laser, including a beam splitter, a narrowband interference filter, and a high-frequency photodiode. The beam splitter is used to separate the light signal returning along the processing optical path into a reflected light detection branch and a plasma radiation light detection branch. The narrowband interference filter is set in the two detection branches respectively to perform narrowband filtering on the light signal of the corresponding wavelength band. The high-frequency photodiode is used to convert the filtered light signal into an electrical signal and output it to the FPGA controller. The reflected light detection branch is used to collect the first band reflected light signal in the nanometer band. This signal reflects the surface reflection state of the workpiece surface material before the transition from solid to molten state.

[0030] The plasma radiation light detection branch is used to collect the second-band radiation light signal in the nanometer to nanometer wavelength range. This signal reflects the plasma radiation state of the keyhole and the molten pool during the welding process. The sampling frequency of the coaxial multispectral high-frequency sensing module is not less than kilohertz to ensure that the rapid change process of the material state on the workpiece surface can be captured during the duration of a single welding pulse.

[0031] The FPGA controller is connected to the signal output terminal of the coaxial multispectral high-frequency sensing module, and also to the power modulation interface of the center beam output port and the ring beam output port of the adjustable ring spot laser, forming a low-level real-time closed-loop control loop during the single pulse duration. The FPGA controller performs analog-to-digital conversion and filtering on the first band reflected light signal and the second band radiated light signal, and calculates the inflection point criterion signal based on the processed signal to determine whether the absorptivity of the workpiece surface material has changed abruptly.

[0032] The ARM processor and the FPGA controller can interact via a bus to run a cross-pulse thermal accumulation feedforward adaptive compensation algorithm. The ARM processor calculates the cumulative temperature of the weld point before welding based on the weld point coordinate sequence, workpiece material thermal property parameters and historical welding heat input records stored in the process parameter database. Based on this, the ARM processor performs feedforward correction on the initial excitation power and pulse width of the weld point and sends the corrected parameters to the FPGA controller as the initial parameters for the next weld point single-pulse energy reshaping control method.

[0033] Meanwhile, after completing the soldering of each solder joint, the FPGA controller feeds back the actual output power of the solder joint and the actual heat input statistics obtained by integrating the pulse width to the ARM processor, which then uses this data to calculate the cumulative temperature of subsequent solder joints.

[0034] The process parameter database is connected to the ARM processor to store the solder joint coordinate sequence corresponding to the processing task, the thermal properties parameters of the workpiece such as the thermal conductivity and thermal diffusivity of the material, as well as the actual heat input records of previously soldered solder joints, which are called by the ARM processor during the calculation process.

[0035] The precision motion platform is used to carry the workpiece. It can be a precision servo worktable with grating ruler position feedback. According to the weld point coordinate sequence stored in the process parameter database, it moves each weld point of the workpiece to the focal position of the adjustable ring spot laser in sequence, and completes the point-by-point welding in conjunction with the adjustable ring spot laser.

[0036] During the duration of a single welding pulse, this embodiment employs the following dynamic energy reshaping control method within a single pulse: the adjustable ring spot laser first starts the output of this welding pulse in the mode of the central beam as the main mode, according to the initial power, and utilizes the energy concentration of the central beam to quickly break through the reflective barrier of the workpiece surface material;

[0037] At the same time, the coaxial multispectral high-frequency sensing module simultaneously acquires the first band reflected light signal and the second band radiated light signal, and outputs them to the FPGA controller.

[0038] The FPGA controller performs analog-to-digital conversion and filtering on the acquired signals to obtain the intensity of the first band reflected light signal and the intensity of the second band radiated light signal at the current sampling time, and calculates the inflection point criterion signal at the current sampling time according to the following formula:

[0039] ;

[0040] In the formula, Indicates the first Inflection point criterion signal at each sampling time;

[0041] , They represent the first The sampling time and the first sampling time The intensity of the first band reflected light signal acquired by the coaxial multispectral high-frequency sensing module at each sampling time;

[0042] This represents the time interval between two consecutive samples, and its value is the reciprocal of the sampling frequency.

[0043] Indicates the first The intensity of the second-band radiated light signal collected at each sampling time;

[0044] , The weighting coefficients representing the rate of change component of reflected light and the plasma radiation component are determined through process pre-calibration experiments.

[0045] Preset threshold Similarly, through process pre-calibration experiments, specific workpiece materials and welding process parameters are pre-determined and stored in the process parameter database.

[0046] The FPGA controller will calculate the inflection point criterion signal. With preset threshold Comparison:

[0047] when Not exceeding the preset threshold At that time, the adjustable ring spot laser continues to output in the mode of the central beam as the main mode, and the coaxial multispectral high-frequency sensing module continues to collect signals at the next sampling moment;

[0048] when Exceeding the preset threshold At that moment, the FPGA controller determines that the workpiece surface material has changed from a solid state to a molten state, i.e., a sudden change in absorptivity has occurred. Within 10 to 50 microseconds after detecting this inflection point, the tunable ring laser dynamically switches the output mode from center beam-dominant to ring beam-dominant according to the pre-calibrated switching curve. That is, the center beam power decreases from the initial power to the switched power, while the ring beam power increases from the initial power to the switched power, and the switched ring beam power is greater than the switched center beam power. This avoids the molten pool from continuing to receive excessive energy after the absorptivity jump, suppressing keyhole collapse and metal spatter. After completing the beam mode switching, the tunable ring laser maintains the ring beam-dominant power ratio mode for the remaining pulse time until the total duration of the single pulse ends, completing the welding of this joint.

[0049] After completing the soldering of the current solder joint, the ARM processor executes the cross-pulse thermal accumulation feedforward adaptive compensation method to correct the initial excitation parameters of the next solder joint to be soldered. The solder joint is the first The contribution of residual temperature rise generated by each weld joint to be welded is calculated according to the following point heat source transient conduction model:

[0050] ;

[0051] In the formula, Indicates the first The solder joint is the first The contribution of residual temperature rise generated by each weld point to be welded;

[0052] Indicates the first The actual heat input of each solder joint is obtained by integrating the actual output laser power and pulse width of that solder joint.

[0053] Indicates the thermal conductivity of the workpiece material;

[0054] Indicates the first The solder joint and the first Spatial distance between each weld point to be welded;

[0055] Indicates the thermal diffusivity of the workpiece material;

[0056] Indicates from the first The welding of each weld point was completed by the time of the [number]th weld point. The time interval between the expected welding times of each weld point to be welded;

[0057] Represents the complementary error function, for any independent variable Its definition is This function is used to describe the attenuation of temperature rise along spatial distance during transient conduction of a point heat source in the workpiece material. The value of this function decreases as the independent variable increases.

[0058] No. The cumulative temperature of each weld point before welding, compared to all previously welded welds... The residual temperature rise is obtained by summing the contributions of each solder joint to the residual temperature rise, and the calculation method is as follows:

[0059] ;

[0060] In the formula, Indicates the first The cumulative temperature of each weld point before welding;

[0061] Indicates the initial ambient reference temperature of the workpiece;

[0062] The summation term represents all previously welded items. The solder joint is the first The sum of the residual temperature rise contributions from each weld point to be welded.

[0063] ARM processors based on cumulative temperature Compared with reference temperature The deviation between them, for the first The initial excitation power and pulse width of each solder joint are feedforward compensated, and the calculation method is as follows:

[0064] ;

[0065] ;

[0066] In the formula, , They represent the number of compensations after the first compensation. The initial center beam excitation power and total pulse width used in the single-pulse energy reshaping control method for each solder joint;

[0067] , These represent the uncompensated process preset reference power and reference pulse width, respectively;

[0068] , These represent the power compensation coefficient and the pulse width compensation coefficient, respectively, which are determined through process pre-calibration experiments.

[0069] This indicates the reference temperature used to determine whether compensation is needed; it is taken as the initial ambient reference temperature of the workpiece. .

[0070] The ARM processor will calculate the compensated initial excitation power. and compensated pulse width The data is sent to the FPGA controller via the bus, and the FPGA controller executes the first... The initial center beam power and total duration of the single pulse are set in the single-pulse dynamic energy reshaping control method for each solder joint. The FPGA controller and ARM processor, in accordance with the above method, sequentially and collaboratively execute the single-pulse dynamic energy reshaping control and cross-pulse thermal accumulation feedforward compensation control for all solder joint coordinate sequences stored in the process parameter database until the welding of all solder joints is completed, thereby achieving consistent control of the weld depth dimensions of each solder joint in continuous high-density spot welding scenarios.

[0071] Example 2

[0072] Taking the continuous array spot welding of gold-plated copper terminals as an example, the implementation of the present invention will be further explained. The workpiece is set as a gold-plated copper terminal, the points to be welded are arranged in a rectangular array, the total duration of a single welding pulse is set to a preset value in milliseconds, the initial power of the center beam of the adjustable ring spot laser is set to the preset reference power of the process, the initial power of the ring beam is set to zero, the sampling frequency of the coaxial multispectral high-frequency sensing module is set to a value higher than kilohertz, that is, the time interval between two adjacent samplings is a value in microseconds. When welding the first weld point, the cumulative temperature is taken as the initial ambient reference temperature of the workpiece, and the ARM processor does not correct the initial excitation power and pulse width of the weld point.

[0073] The FPGA controller switches the beam mode within a single pulse of the solder joint based on the aforementioned inflection point criterion signal, obtains the actual heat input of the solder joint, and records the welding completion time. Before welding subsequent solder joints, the ARM processor calculates the cumulative temperature of the solder joint to be welded based on the heat input of all previously welded solder joints, the spatial distance between each solder joint and the solder joint to be welded, and the corresponding time interval. Based on this, the initial excitation power and pulse width of the solder joint are feedforward corrected and then sent to the FPGA controller for welding. After welding all solder joints point by point in the above manner, the consistency of the weld depth and contact resistance of each solder joint in the array is improved. The workpiece described in this embodiment can also be replaced with the pin of an insulated gate bipolar transistor module or other electronic component connection parts made of high reflectivity and high thermal conductivity metal materials, and the control principle is the same.

[0074] As an alternative embodiment of the present invention, the adjustable ring spot laser can also be replaced by two independently set lasers. One laser is used to output a concentrated spot to form a central beam, and the other laser outputs a ring spot to form a ring beam after optical shaping. The beams output by the two lasers are coaxially coupled by a beam splitter and beam combiner and output to the same focusing optical path. The power supply of the two lasers is independently modulated, which can also realize the dynamic switching of the power ratio of the central beam and the ring beam during the single pulse duration.

[0075] As another alternative implementation of the present invention, the calculation of cumulative temperature and compensation parameters in the cross-pulse thermal accumulation feedforward compensation method can also be replaced by a regression model trained based on historical measured data: a training sample set is constructed in advance for typical weld point layout and workpiece material type by measuring the actual penetration depth and temperature rise data of each weld point, and a regression model is trained with the weld point coordinate sequence and historical thermal input sequence as input and the power compensation amount and pulse width compensation amount as output. The ARM processor calls the trained regression model in the actual processing process and outputs the compensation parameters of the weld point to be welded in real time, which can also achieve the feedforward control effect of penetration depth consistency in continuous spot welding scenarios.

[0076] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope defined by the claims of the present invention.

Claims

1. A precision machining and spot welding control system for electronic components, characterized in that, include: An adjustable ring beam laser has a center beam output port and a ring beam output port that can independently modulate power. The coaxial multispectral high-frequency sensing module is coaxially set with the processing optical path of the adjustable ring spot laser, and is used to synchronously acquire the first band reflected light signal reflecting the material state of the workpiece surface and the second band radiated light signal reflecting the plasma state of the molten pool. An FPGA controller is connected to the signal output terminal of the coaxial multispectral high-frequency sensing module. It is used to calculate the inflection point criterion signal based on the first band reflected light signal and the second band radiated light signal. When the inflection point criterion signal exceeds a preset threshold, it controls the adjustable ring spot laser to switch the output mode from center beam to ring beam. An ARM processor, connected to the FPGA controller via a bus, is used to calculate the cumulative temperature of the solder joint before soldering based on the spatial distance between the soldered solder joint and the solder joint to be soldered, the time interval between the soldered solder joint and the solder joint to be soldered, and the heat input of the soldered solder joint. Based on the deviation between the cumulative temperature and the reference temperature, the processor calculates the compensated initial power and compensated pulse width of the solder joint to be soldered, and sends the compensated initial power and the compensated pulse width to the FPGA controller. A precision motion platform is used to carry the workpiece and move the workpiece to the welding position according to the weld point coordinate sequence; A process parameter database, connected to the ARM processor, is used to store weld point coordinate sequences, workpiece material thermal property parameters, and historical welding heat input records.

2. The system according to claim 1, characterized in that, The first band reflected light signal is a 1064 nm band reflected light signal, and the second band radiated light signal is a 400 nm to 600 nm band plasma radiated light signal; The coaxial multispectral high-frequency sensing module includes a beam splitter, a narrowband interference filter, and a high-frequency photodiode. The sampling frequency of the coaxial multispectral high-frequency sensing module is not less than 100 kHz.

3. The system according to claim 1, characterized in that, After detecting that the inflection point criterion signal exceeds a preset threshold, the FPGA controller reduces the center beam power of the adjustable ring spot laser from the initial power to the switched power within a time period of 10 microseconds to 50 microseconds, and increases the ring beam power of the adjustable ring spot laser from the initial power to the switched power. The switched ring beam power is greater than the switched center beam power.

4. The system according to claim 1, characterized in that, The FPGA controller performs a weighted summation based on the ratio of the difference in intensity of the first band reflected light signal between the current sampling time and the previous sampling time to the sampling time interval, and the intensity of the second band radiated light signal at the current sampling time, to obtain the inflection point criterion signal.

5. The system according to claim 1, characterized in that, The ARM processor calculates the contribution of the welded solder joints to the residual temperature rise of the solder joint to the solder joint to be welded based on the heat input of the welded solder joints, the spatial distance between the welded solder joints and the solder joint to be welded, the thermal conductivity of the workpiece material, the thermal diffusivity of the workpiece material, and the time interval between the completion time of the welded solder joints and the expected welding time of the solder joint to be welded. The processor then sums up the contributions of all the welded solder joints to the residual temperature rise of the solder joint to be welded to obtain the cumulative temperature of the solder joint to be welded before welding.

6. A method for controlling spot welding in precision machining of electronic components, applied to the system described in claim 1, characterized in that, include: During the duration of a single welding pulse, the adjustable ring spot laser is controlled to output laser in the mode of center beam as the main mode, and the first band reflected light signal and the second band radiated light signal are synchronously acquired by the coaxial multispectral high-frequency sensing module. The inflection point criterion signal is calculated based on the reflected light signal of the first band and the radiated light signal of the second band; When the inflection point criterion signal exceeds the preset threshold, it is determined that the absorptivity of the workpiece surface material has changed from solid to molten state. The adjustable ring spot laser is then controlled to switch the output mode from being dominated by the central beam to being dominated by the ring beam until the current welding pulse ends. After completing the welding of the current weld point, the cumulative temperature of the next weld point before welding is calculated based on the spatial distance between the next weld point to be welded and the welded weld point, the time interval between the next weld point to be welded and the welded weld point, and the heat input of the welded weld point. Based on the deviation between the accumulated temperature and the reference temperature, the initial excitation power and pulse width of the next weld point are compensated to obtain the compensated initial excitation power and compensated pulse width. Based on the compensated initial excitation power and the compensated pulse width, the aforementioned steps of outputting laser in the mode of the central beam to the inflection point judgment criterion signal are repeated for the next weld point until the welding of all weld points is completed.

7. The method according to claim 6, characterized in that, The step of calculating the inflection point criterion signal based on the first band reflected light signal and the second band radiated light signal includes: weighting and summing the ratio of the difference in intensity of the first band reflected light signal between the current sampling time and the previous sampling time to the sampling time interval, and the intensity of the second band radiated light signal at the current sampling time, to obtain the inflection point criterion signal.

8. The method according to claim 6, characterized in that, The calculation of the cumulative temperature before welding the next weld point includes: calculating the residual temperature rise contribution of the welded weld points to the next weld point based on the heat input of the welded weld points, the spatial distance between the welded weld points and the next weld point, the thermal conductivity of the workpiece material, the thermal diffusivity of the workpiece material, and the time interval between the completion time of the welded weld points and the expected welding time of the next weld point; and summing up the residual temperature rise contributions of all welded weld points to the next weld point to obtain the cumulative temperature before welding the next weld point. The compensation of the initial excitation power and pulse width of the next solder joint includes: subtracting the product of the power compensation coefficient and the deviation from the process preset reference power of the next solder joint to obtain the compensated initial excitation power; The compensated pulse width is obtained by subtracting the product of the pulse width compensation coefficient and the deviation from the preset reference pulse width of the next welding point.

9. The method according to claim 6, characterized in that, During the process of controlling the adjustable ring spot laser to switch the output mode from center beam-dominant to ring beam-dominant, the transition time between the center beam power decreasing from the initial power to the switched power and the ring beam power increasing from the initial power to the switched power is 10 microseconds to 50 microseconds, and the switched ring beam power is greater than the switched center beam power.

10. The system according to claim 1, characterized in that, The process parameter database stores the workpiece material thermal properties parameters, including the workpiece material's thermal conductivity and thermal diffusivity.

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