A sheet low-splashing high-frequency spot welding device and process

Abstract

This invention discloses a low-spatter high-frequency spot welding device and process for thin plates, relating to the field of resistance spot welding technology. The device includes a high-frequency inverter DC spot welding power supply, a precision servo pressurizing mechanism, an integrated control unit, and upper and lower electrodes. The upper and lower electrodes are electrically connected to the high-frequency inverter DC spot welding power supply via a welding machine. The integrated control unit is electrically connected to the high-frequency inverter DC spot welding power supply and the precision servo pressurizing mechanism. This invention utilizes the extremely high response speed of the high-frequency inverter power supply to achieve precise reproduction and control of the current waveform based on a continuous smooth function model, thereby achieving truly "flexible" heating with no step jumps and infinite slope changes in heat input. Combined with precisely coordinated dynamic pressure control, the conditions for spatter generation are eliminated at the source.

Description

Technical Field

[0001] This invention belongs to the field of resistance spot welding technology, and particularly relates to a low-spatter, high-frequency spot welding equipment and process for thin plates. Background Technology

[0002] In the manufacturing of precision electromagnetic components such as relays and contactors, the quality of spot welding of internal conductive parts directly determines the product's electrical performance, mechanical lifespan, and long-term reliability. Currently, the mainstream and mature process for welding such thin sheet metal parts in the industry is energy storage welding (capacitor discharge welding). Energy storage welding utilizes capacitor banks to store electrical energy and release it instantaneously, generating a pulse current with an extremely high peak value and a very short duration (typically 3-10 milliseconds) for welding. Its advantages include relatively low equipment cost, high instantaneous power, and the ability to quickly break through the oxide layer on the workpiece surface.

[0003] However, when energy storage welding is applied to the welding of precision thin plates such as relays, its inherent defects are extremely prominent: welding spatter is exceptionally severe. This is because the instantaneous energy density is too high, causing the metal to melt and vaporize rapidly. The metal vapor pressure inside the molten core instantly breaks through the plastic ring constraint of the plate being welded, thus ejecting liquid metal particles at high speed. Severe spatter brings many problems:

[0004] 1. Pollution and safety hazards: Metal particles can contaminate the internal insulation frame, coil, and narrow air gap of the relay, which may cause insulation degradation or momentary short circuits, posing serious quality hazards.

[0005] 2. Deterioration of solder joint quality: Spatter carries away some molten metal, resulting in a reduction in the effective connection area of ​​the solder joint, forming incomplete solder joints, shrinkage cavities, or overheating, which seriously affects the conductivity and mechanical strength of the solder joint.

[0006] 3. Poor process stability: The degree of spatter is greatly affected by power grid fluctuations, capacitor aging, and workpiece surface condition, making it difficult to guarantee the consistency of solder joint quality and increasing quality control costs.

[0007] 4. High subsequent costs: To remove internal splashes, complex cleaning processes are often required, reducing production efficiency.

[0008] To overcome the spatter problem, medium-frequency inverter DC spot welding technology was introduced as an improvement solution. Medium-frequency inverter spot welding machines typically convert industrial frequency AC power into 400-1200Hz medium-frequency AC power, which is then rectified to output DC welding current. Compared to energy storage welding, medium-frequency inverter technology has a certain degree of current control capability, enabling multi-pulse welding and improving the stability and controllability of the welding process to some extent. However, medium-frequency inverter spot welding still has the following limitations when applied to extremely thin, high-precision workpieces:

[0009] 1. Insufficient response speed: The medium-frequency inverter has a low frequency and a relatively long current regulation response time, making it difficult to achieve precise control at the microsecond level, and the dynamic process control at the beginning and end of the welding process is not delicate enough.

[0010] 2. Larger current ripple: The ripple coefficient of the medium-frequency DC output is higher than that of the high-frequency system, and there are still some periodic fluctuations in the heat input, which is not conducive to the uniform growth of the melt nugget;

[0011] 3. Limited spatter suppression capability: Although superior to energy storage welding, local spatter may still occur in the welding of highly conductive materials or ultra-thin laminates due to uneven heat input or lag in dynamic response.

[0012] To further improve welding quality and process control precision, high-frequency inverter DC spot welding technology has emerged as a more advanced alternative. Its working principle involves converting industrial frequency AC power into a continuous, smooth, and extremely fast-responding DC welding current through high-frequency inversion (typically 1-4kHz, or even higher) and rectification. Compared to medium-frequency inverters, high-frequency inverter technology is significantly superior in the following aspects:

[0013] 1. Extremely fast response speed: The inverter frequency is high, and the current regulation response can reach the microsecond level, which can realize more precise slow rise, slow fall and multi-segment waveform control;

[0014] 2. Smoother output: Minimal DC ripple and continuous, stable heat input, which is beneficial for uniform melt nugget formation;

[0015] 3. Finer control granularity: Supports more complex timing logic and real-time dynamic adjustment, and is easy to coordinate with parameters such as pressure and displacement for control.

[0016] However, simply applying high-frequency inverter technology directly to thin-plate welding of relays cannot automatically achieve the desired low-splash effect. If parameters are not properly matched, splashing may still occur due to excessive heat input or pressure mismatch. More importantly, to balance efficiency and splash suppression, a highly matched and refined process control strategy is needed, particularly how to leverage the programmable current waveform and coordinate it with a dynamically adjustable pressure system – something lacking in existing technologies. Summary of the Invention

[0017] To address the problems of severe spatter in existing energy storage welding and insufficient precision in medium-frequency inverter welding control, this invention aims to provide a low-spatter, high-frequency spot welding device and process for thin plates. Its core lies in utilizing the extremely high response speed of the high-frequency inverter power supply to achieve precise reproduction and control of the current waveform based on a continuous smooth function model. This enables truly "flexible" heating with no step jumps and infinite slope changes in heat input. Combined with precisely coordinated dynamic pressure control, the conditions for spatter generation are eliminated at the source.

[0018] To achieve the above objectives, the present invention provides the following technical solution:

[0019] A thin plate low-spatter high-frequency spot welding equipment includes a high-frequency inverter DC spot welding power supply, a precision servo pressurization mechanism, an integrated control unit, and upper and lower electrodes;

[0020] The high-frequency inverter DC spot welding power supply has an inverter frequency range of 10kHz to 40kHz, outputs DC welding current with a ripple rate of less than 5%, and has the ability to generate real-time waveforms based on a continuous function model. It can output welding current waveforms with continuous and smooth amplitude changes over time and continuous first derivative.

[0021] The precision servo pressurization mechanism is driven by a servo motor or linear motor, with a response time of less than 10ms. It can realize dynamic and stepless adjustment of electrode pressure during welding, and the pressure control accuracy is better than ±2%.

[0022] The integrated control unit has a built-in high-speed processor and function waveform library. It can calculate and issue the set values ​​of current and pressure in real time according to the welding process model, and synchronously coordinate the output of the high-frequency inverter DC spot welding power supply and the action of the precision servo pressurization mechanism, forming a collaborative closed-loop control system based on the combination of function model feedforward and real-time electrical signal feedback.

[0023] The upper and lower electrodes are electrically connected to the high-frequency inverter DC spot welding power supply via a welding machine, and the integrated control unit is electrically connected to the high-frequency inverter DC spot welding power supply and the precision servo pressurization mechanism.

[0024] As a preferred embodiment of the present invention, the function waveform library includes at least three types of continuous and smooth reference current waveform functions: "S-shaped rise-exponential fall" waveform, "multi-peak resonant decay" waveform, and "flat-top cosine modulation" waveform.

[0025] As a preferred embodiment of the present invention, the high-frequency inverter DC spot welding power supply includes an AC power input, a main controller, a rectifier bridge, an IGBT inverter module, a fast recovery diode rectifier bridge, a transformer, and a filter circuit. A capacitor bank is connected to the AC power input terminal, and a rectifier bridge is connected between the capacitor bank and the AC power input terminal. The phase detection circuit of the main controller samples in parallel from the AC power input terminal. The input terminal of the IGBT inverter module is connected across the capacitor bank, and a filter circuit is connected between its output terminal and the fast recovery diode rectifier bridge. The output terminal of the IGBT inverter module is connected in series with the primary winding of the transformer. The diodes inside the fast recovery diode rectifier bridge are connected in a bridge configuration, with the diodes in the upper and lower bridge arms connected in series and the bridge arms connected in parallel, used to rectify the high-frequency high-voltage AC signal into a high-voltage DC signal.

[0026] Furthermore, a voltage sensor is connected in parallel to the rectified DC high-voltage output terminal through a voltage divider resistor network to collect the output voltage signal; a current sensor is connected in the load circuit to collect the output current signal. The output terminals of both the voltage sensor and the current sensor are connected to the analog input terminal of the main controller to realize closed-loop control and protection.

[0027] This invention also provides a low-spatter, high-frequency spot welding process for thin plates, based on the aforementioned equipment, characterized by the following steps:

[0028] S1. Pre-pressure and contact resistance optimization stage: Control the precision servo pressurization mechanism to drive the electrodes at a first preset pressure. Press the workpiece to be welded firmly. The workpiece is a thin plate, with a thickness of 0.1mm to 0.5mm, made of copper, copper alloy, or plated steel. Hold for [duration missing]. At the end of the holding phase, the high-frequency inverter DC spot welding power supply outputs a low-amplitude "contact optimization pulse," whose pulse current waveform is a continuous, smooth bell-shaped curve with a peak value of... Pulse width T_s = 3~8ms;

[0029] S2. Main Welding Stage: After the S1 stage ends, the main welding current waveform is output without interruption. This waveform is a continuous and smooth time-varying function curve I(t). Its function form, time constant and amplitude are determined according to the workpiece material, thickness and target weld nugget size. The total energy input makes the workpiece contact surface reach the melting state.

[0030] S3. Dynamic forging and post-heat control stage: When the S2 main welding current waveform function value drops to (40%~60%) of its peak value I_w, the precision servo pressurizing mechanism starts the pressure boosting program, increasing the electrode pressure from... Smoothly increase to the second preset pressure Meanwhile, the high-frequency inverter DC spot welding power supply outputs a continuously decaying "post-heat control waveform". This waveform starts at I_w (20%~40%) and decays to zero within 15~40ms according to an exponential or polynomial law.

[0031] S4. Holding and Return Phase: Maintain forging pressure After the thermal control waveform ends, hold for another 20-50ms before the electrode returns to its original position.

[0032] Furthermore, in the S2 main welding stage, for copper or copper alloys with a total thickness of 0.3mm~0.5mm, an "S-shaped rise-exponential fall" waveform is adopted. The current function I(t) follows an S-shaped logical growth curve in the rising segment, and then decreases exponentially after reaching its peak value I_w. The specific expression is as follows:

[0033] Ascending segment ,in is the rise rate constant, with a value that ensures that 10%-90% of the peak rise time is within 2~5ms; t_rise is the total rise time, 3~6ms.

[0034] Descent , where τ is the decay time constant, taking a value of 1~3ms;

[0035] The peak current I_w is determined based on material and thickness tests, and ranges from 1.8 to 4.0 kA.

[0036] Furthermore, in the S2 main welding stage, for materials with ultra-high thermal conductivity or prone to thermal stress cracking, a "multi-peak resonant attenuation" waveform is adopted. Its current function I(t) is a damped oscillation containing 2 to 3 consecutive attenuating resonant peaks, mathematically consisting of an exponentially attenuating envelope modulating an attenuating sine wave.

[0037] ,in The initial amplitude is τ_envelope, which is the envelope decay constant (2~5ms). The oscillation frequency is (500~1500Hz). With I_base as the DC bias (0.1~0.3kA), this waveform achieves heat oscillation penetration and homogenization through periodic, decaying energy input.

[0038] Furthermore, in the S2 main welding stage, for coated steel or copper alloys requiring a wide and uniform weld nugget, a "flat-top cosine modulation" waveform is adopted, where the current function I(t) is a flat-top waveform whose amplitude is modulated by a cosine function:

[0039] Where I_w is the average current amplitude, m is the modulation depth (0.1~0.3), and f_mod is the modulation frequency (200~600Hz), this waveform maintains the main heat input while promoting the homogenization of the composition by stirring the melting nucleus through low-frequency modulation.

[0040] Furthermore, the dynamic forging start time and pressure rise curve of the S3 stage are triggered and planned by the integrated control unit based on the real-time calculated value of the current function I(t) of the S2 stage or the real-time monitored differential conductance between electrodes (dI / dU).

[0041] In summary, the beneficial technical effects of the present invention are as follows:

[0042] 1. Achieved "impact-free" heat input: The continuous and smooth current waveform eliminates any abrupt changes in the heat accumulation and release process, fundamentally avoiding the explosive generation of metal vapor caused by sudden current changes, and achieving a new level of splash suppression capability.

[0043] 2. Superior solder joint structure and performance: Smooth thermal cycling facilitates the formation of weld nuclei with finer grains and more uniform structure, reduces internal stress and micro-defects, and significantly improves fatigue life and electrical conductivity stability.

[0044] 3. Enhanced control precision and consistency: The function-based waveform description is accurate and unaffected by piecewise approximation errors, resulting in an unprecedented level of consistency in solder joint quality.

[0045] 4. Distinctly different from existing technologies: The current waveform of this invention appears as a perfectly smooth curve on an oscilloscope, forming a direct and strong technical contrast with the burr peaks of energy storage welding and even the segmented broken lines of traditional medium and high frequency welding, highlighting the absolute advantage of high frequency inverters in the ability to accurately reproduce waveforms.

[0046] 5. Powerful process modeling and expansion capabilities: Functional waveforms are easily combined with physical models (heat conduction, phase change), laying a solid foundation for realizing model-based intelligent process optimization and adaptive control. Attached Figure Description

[0047] The accompanying drawings are provided to further illustrate the invention and form part of the specification, but do not constitute a limitation thereof. In the drawings:

[0048] Figure 1 This is a flowchart illustrating a low-splash, high-frequency spot welding process for thin plates.

[0049] Figure 2 This is a circuit diagram of a high-frequency inverter DC spot welding power supply for a thin-plate low-spatter high-frequency spot welding equipment.

[0050] Figure 3 The "S-shaped rise-exponential fall" continuous smooth current waveform used in Embodiment 1 of the present invention;

[0051] Figure 4 This is a schematic diagram of the "multi-peak resonance attenuation" continuous smooth current waveform used in Embodiment 2 of the present invention. Detailed Implementation

[0052] The present invention will be further described in detail below with reference to the accompanying drawings.

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] Please see Figure 1-4The present invention provides a technical solution: a thin plate low-spatter high-frequency spot welding equipment includes a high-frequency inverter DC spot welding power supply, a precision servo pressurization mechanism, an integrated control unit, and upper and lower electrodes;

[0055] The high-frequency inverter DC spot welding power supply has an inverter frequency range of 10kHz to 40kHz and outputs DC welding current with a ripple rate of less than 5%. It has the ability to generate real-time waveforms based on a continuous function model and can output welding current waveforms with continuous and smooth amplitude changes over time and continuous first derivative.

[0056] The precision servo pressurization mechanism, driven by a servo motor or linear motor, has a response time of less than 10ms and can achieve dynamic and stepless adjustment of electrode pressure during welding, with a pressure control accuracy better than ±2%.

[0057] The integrated control unit, with a built-in high-speed processor and function waveform library, can calculate and issue the set values ​​of current and pressure in real time according to the welding process model, and synchronously coordinate the output of the high-frequency inverter DC spot welding power supply and the action of the precision servo pressurization mechanism, forming a collaborative closed-loop control system based on the combination of function model feedforward and real-time electrical signal feedback.

[0058] The upper and lower electrodes are electrically connected to the high-frequency inverter DC spot welding power supply via the welding machine, and the integrated control unit is electrically connected to the high-frequency inverter DC spot welding power supply and the precision servo pressurization mechanism.

[0059] The function waveform library includes an "S-shaped rise-exponential fall" waveform for general connections, a "multi-peak resonant decay" waveform for suppressing splashing of high thermal conductivity materials, and a "flat-top cosine modulation" waveform for optimizing thermal cycling.

[0060] The high-frequency inverter DC spot welding power supply includes an AC power input, a main controller, a rectifier bridge, an IGBT inverter module, a fast recovery diode rectifier bridge, a transformer, and a filter circuit. A capacitor bank is connected to the AC power input, and a rectifier bridge connects the capacitor bank to the AC power input. The phase detection circuit of the main controller samples in parallel from the AC power input. The input of the IGBT inverter module is connected across the capacitor bank, and a filter circuit connects its output to the fast recovery diode rectifier bridge. The output of the IGBT inverter module is connected in series with the primary winding of the transformer. The diodes inside the fast recovery diode rectifier bridge are connected in a bridge configuration, with the diodes in the upper and lower bridge arms connected in series and the bridge arms connected in parallel, used to rectify the high-frequency high-voltage AC signal into a high-voltage DC signal.

[0061] The rectified DC high voltage output terminal is connected in parallel with a voltage divider resistor network to a voltage sensor for acquiring the output voltage signal; a current sensor is connected in the load circuit to acquire the output current signal. The output terminals of both the voltage sensor and the current sensor are connected to the analog input terminal of the main controller to realize closed-loop control and protection.

[0062] Specifically, the main controller includes:

[0063] Analog input / output (8 channels):

[0064] Analog input: It can accept continuously changing physical quantities such as voltage signals (e.g., mains voltage, capacitor bank voltage), current signals (e.g., load current, charging current), temperature signals (IGBT or transformer temperature rise), and power factor, for real-time monitoring of system status.

[0065] Analog output: It can output controllable voltage or current signals to adjust the thyristor firing angle, control the IGBT drive waveform, or adjust the parameters of the regulated power supply.

[0066] Digital input / output:

[0067] 16-channel digital input: used to monitor equipment status, such as circuit breaker opening and closing signals, relay contact status, emergency stop button signals, cooling fan fault alarms, access control switches and other discrete signals.

[0068] 8-channel switch output: used to control external devices, such as contactor engagement / disengagement, indicator light activation / deactivation, alarm triggering, solenoid valve on / off, etc.

[0069] Local area network (such as Ethernet): Enables high-speed data transmission, supports remote monitoring, data interaction with host computer, and collaborative control of multiple devices.

[0070] RS232: Short-range point-to-point communication, often used for debugging, parameter configuration or connection to local industrial control equipment.

[0071] RS485: Strong anti-interference capability, supports long-distance multi-point communication.

[0072] The operation of this circuit is clearly divided into a capacitor charging stage and a DC inverter output stage. The workflow of each stage is as follows:

[0073] 1. Capacitor Bank Charging Stage

[0074] 1.1 Mains Input and Phase Detection

[0075] After the 220V AC mains power is input, it is processed by a voltage transformer or zero-crossing detection circuit to convert the sinusoidal voltage into a square wave signal of the same frequency; the main controller accurately calculates the real-time phase of the grid voltage by capturing the rising or falling edge of the square wave signal, i.e., the voltage zero-crossing point.

[0076] 1.2 Thyristor Triggering and Controlled Rectification

[0077] Thyristors are connected in series at the front or rear of the rectifier bridge as phase control switches. The main controller calculates the thyristor conduction angle based on the set target charging voltage and the actual voltage value fed back by the capacitor bank. At the corresponding conduction angle phase point of each half-wave of the grid voltage, the main controller outputs a trigger pulse to the gate of the thyristor. The thyristor conducts from that phase point until the current half-wave voltage naturally crosses zero and then turns off, realizing controllable power supply to the subsequent circuits.

[0078] 1.3 Closed-loop feedback control of charging voltage

[0079] The voltage across the capacitor bank is sampled in real time by a DC voltage sensor, converted into a low-voltage analog signal, and fed back to the analog input port of the main controller, forming a closed-loop control circuit. The main controller compares the feedback voltage with the set target voltage: when the feedback voltage is lower than the target value, the thyristor conduction angle is reduced to trigger the thyristor earlier and increase the charging current to accelerate charging; when the feedback voltage approaches or reaches the target value, the conduction angle is increased and the triggering is delayed until the triggering stops and the voltage maintenance state is entered; when the feedback voltage is abnormally high, the main controller immediately blocks all trigger pulses to achieve overvoltage protection and ensure the safe and stable charging of the capacitor bank.

[0080] 2. DC Inverter Output Stage

[0081] 2.1 PWM Signal Generation and IGBT Driving

[0082] The main controller generates a high-frequency PWM pulse width modulation signal based on the load's output power requirements and sends the signal to the IGBT drive module. The drive module processes the signal: it achieves electrical isolation between the controller's weak current and the IGBT's high-voltage power through optocouplers or transformers; it amplifies the weak PWM signal into a high-current drive signal required for the IGBT gate switch; it applies a negative voltage to the IGBT gate in the off state to prevent the device from being mis-turned on; and it monitors the IGBT's operating status in real time. When overcurrent or short circuit is detected, it softly turns off the IGBT within microseconds and sends a fault signal back to the main controller.

[0083] 2.2 IGBT Inverter and Transformer Voltage Transformation

[0084] After receiving the drive signal, the IGBT module converts the DC output from the capacitor bank into a high-frequency AC square wave of 10kHz-40kHz according to the PWM signal timing. The high-frequency AC square wave is input to the power transformer, which achieves electrical isolation and voltage boost or buck conversion to match the output voltage to the load's operating requirements.

[0085] 2.3 Voltage and Current Signal Acquisition and Feedback

[0086] A voltage sensor is connected in parallel across the capacitor bank and at the transformer output terminal to measure the high voltage. A Hall voltage sensor is used to convert the measured voltage into a proportional analog voltage signal, which is then sent to the main controller for output voltage regulation control and overvoltage and undervoltage protection.

[0087] The current sensor is connected in the inverter input circuit and the transformer output circuit. The Hall current sensor converts the measured current into a proportional analog voltage signal and sends it to the main controller for overcurrent, short circuit protection, power calculation and current closed-loop control in constant current mode.

[0088] 2.4 Secondary Rectification and Load Output

[0089] The high-frequency AC output from the transformer is processed by a fast recovery diode rectifier bridge and an LC filter circuit to convert it into smooth DC; this DC is then... After two-stage transformation, both voltage and current can be precisely controlled and ultimately delivered to the upper and lower electrode loads to complete processes such as heating, welding, and melting.

[0090] Based on the above equipment and the corresponding DC power output circuit, the following process is used for soldering, specifically including the following steps:

[0091] S1. Pre-pressure and contact resistance optimization stage: Control the precision servo pressurization mechanism to drive the electrodes at a first preset pressure. Press the workpiece to be welded firmly. The workpiece is a thin plate, with a thickness of 0.1mm to 0.5mm, made of copper, copper alloy, or plated steel. Hold for [duration missing]. At the end of the holding phase, the high-frequency inverter DC spot welding power supply outputs a low-amplitude "contact optimization pulse," whose pulse current waveform is a continuous, smooth bell-shaped curve with a peak value of... Pulse width T_s = 3~8ms;

[0092] S2. Main Welding Stage: After the S1 stage ends, the main welding current waveform is output without interruption. This waveform is a continuous and smooth time-varying function curve I(t). Its function form, time constant and amplitude are determined according to the workpiece material, thickness and target weld nugget size. The total energy input makes the workpiece contact surface reach the melting state.

[0093] S3. Dynamic forging and post-heat control stage: When the S2 main welding current waveform function value drops to (40%~60%) of its peak value I_w, the precision servo pressurizing mechanism starts the pressure boosting program, increasing the electrode pressure from... Smoothly increase to the second preset pressure Meanwhile, the high-frequency inverter DC spot welding power supply outputs a continuously decaying "post-heat control waveform". This waveform starts at I_w (20%~40%) and decays to zero within 15~40ms according to an exponential or polynomial law.

[0094] S4. Holding and Return Phase: Maintain forging pressure After the thermal control waveform ends, the electrode returns to its original position after holding for another 20-50ms.

[0095] The following are examples 1-2. The difference between examples 1 and 2 lies in the welding materials. Example 1 uses 0.15mm tin-plated phosphor bronze welded to 0.3mm nickel-plated steel, while Example 2 uses 0.3mm pure copper welded together with 0.3mm pure copper. The specific processes are as follows:

[0096] Example 1

[0097] Welding object: The connection between the internal signal terminals of the relay and the steel bracket, the materials are 0.15mm thick tin-plated phosphor bronze sheet and 0.3mm thick nickel-plated steel sheet (total thickness 0.45mm).

[0098] Technical challenges: The two materials have large differences in thermal conductivity and resistivity, the coating is prone to volatilization or uneven alloying at high temperatures, and traditional energy storage welding is prone to spatter and brittle compounds at the interface.

[0099] Waveform selection: A continuous smooth waveform of "S-shaped rise-exponential fall" is adopted. This waveform ensures stable and shock-free heat input, which is conducive to the formation of a uniform melt nugget at the interface of dissimilar materials and avoids violent vaporization and splashing of the coating due to thermal shock.

[0100] Process parameters and function settings:

[0101] 1. Pre-pressure and contact optimization: Setting electrode pressure Pre-compression time At the end of the preload phase, a bell-shaped (Gaussian function approximation) "contact optimization pulse" is superimposed, with a peak current... The pulse width T_s = 4ms is used to stabilize the contact resistance and clean the micro-contact points.

[0102] 2. Main welding stage:

[0103] The target peak current I_w is set to 1.8kA (determined through process testing and optimization), and the start time of the main welding stage is set as time zero (t=0).

[0104] Rise stage (0 ≤ t < t_rise): An S-shaped logical growth function is adopted, and the rise rate constant is set , so that the time for the current to rise from 10% of the peak value (0.18 kA) to 90% of the peak value (1.62 kA) is 2 ms, and the total rise time t_rise = 3 ms.

[0105] Current function:

[0106] Fall stage (t ≥ t_rise): An exponential decay function is adopted, and the decay time constant τ = 1.5 ms.

[0107] Current function:

[0108] Energy integral estimation: Integrate the function waveform within 0 - 10 ms, and its area (energy input) is approximately 17.1 kA·ms. This energy is slightly higher than the curve in the attached figure (about 12 kA·ms), mainly to overcome the higher heat capacity and heat dissipation of nickel-plated steel and ensure the effective formation of the fusion core. However, through the smooth and slow rise and fall curves, the energy input rate is controlled, which is essentially different from the peak impact of energy storage welding.

[0109] 3. Dynamic forging and post-heat control (S3 stage): When the value of the current function calculated in real time drops to 60% of the peak value I_w (i.e., 1.08 kA), the integrated control unit synchronously triggers the following actions:

[0110] Dynamic forging: Control the precision servo pressurizing mechanism to increase the electrode pressure from along a preset S-shaped curve and smoothly and shocklessly increase it to the forging pressure within 3 ms .

[0111] Post-heat control: The high-frequency inverter power supply outputs an exponential decay post-heat waveform starting from 0.72 kA (40% I_w), and the function is , which decays to zero in about 40 ms to slow down the solidification speed of the fusion core and improve the microstructure.

[0112] 4. Pressure holding and return stroke (S4 stage): Maintain the forging pressure of 360 N until the end of the post-heat waveform, and then hold the pressure for 30 ms before the electrode returns.

[0113] Implementation effect: The current and pressure curves during the entire welding process are continuous and smooth function curves with continuous first derivatives, achieving true "shockless" flexible thermal-mechanical coupling. There are no visible spatter and explosion sounds during the welding process, the weld bead is beautifully formed, the interface alloy layer is uniform and dense, and the tensile shear strength is high and stable.

[0114] Example 2

[0115] Welding target: Welding of double-layer pure copper current conductors in high-current relays (total thickness 0.6mm).

[0116] Technical challenges: Pure copper has extremely low resistivity and extremely high thermal conductivity, requiring a very large instantaneous heat input to initiate melting. However, if the heat input is too fast or too concentrated, it can easily cause violent spatter or even burn-through.

[0117] Waveform selection: A "multi-peak resonant attenuation" continuous smooth waveform is adopted. This waveform uses multiple continuously attenuating current peaks for oscillating heating, which can achieve the accumulation and penetration of heat into the depth of the workpiece interface without excessively increasing the individual current peak, making it particularly suitable for ultra-high thermal conductivity materials.

[0118] Process parameters and function settings:

[0119] 1. Pre-pressure and contact optimization (S1 stage): Setting electrode pressure Pre-compression time The contact optimization pulse is a bell-shaped pulse with a peak value of I_s = 0.4kA and a base width of T_s = 5ms.

[0120] 2. Main welding stage (S2 stage):

[0121] Using the damped oscillating current function:

[0122] Setting parameters: Initial amplitude Envelope decay constant τ_envelope = 3ms, oscillation frequency phase =0, DC bias I_base=0.15kA, and the start time of the main welding stage is set as time zero (t=0).

[0123] This function describes a sinusoidal oscillating current with an initial amplitude of 1.2kA, which decays exponentially with a time constant of 3ms and a frequency of 1kHz, superimposed on a 0.15kA DC base. The overall waveform is continuous, smooth, and without inflection points.

[0124] Energy integration estimation: Integrating the oscillation waveform over 0-15ms, the effective average current is approximately 0.8kA, and the total input energy area is approximately 12kA·ms, which is highly comparable to the energy input of the reference waveform shown in the attached figure. However, through high-frequency oscillation at 1kHz, heat is input in a periodic "stirring" manner, which greatly promotes the uniform distribution of heat in the thickness direction of the copper sheet and avoids surface overheating.

[0125] 3. Dynamic forging and post-heat control (S3 stage): When the envelope amplitude of the oscillation current... Triggered when decaying to 0.3kA (approximately t≈4.5ms):

[0126] Dynamic forging: The pressure smoothly increases from 200N to 400N within 3ms according to an S-shaped curve.

[0127] Post-thermal control: Outputs an exponentially decaying thermal waveform starting at 0.3kA. It lasts for about 25ms.

[0128] 4. Pressure holding and return (S4 stage): Maintain 400N pressure until the end of post-heating, hold pressure for 40ms and then return.

[0129] Implementation Results: The output current exhibits a smooth, high-frequency oscillation curve with decreasing amplitude. At peak currents of only... Under ideal conditions, reliable welding of double-layer pure copper was successfully achieved without any spatter. Metallographic examination revealed a uniformly elliptical weld nugget penetrating both copper layers with a narrow heat-affected zone, effectively overcoming the challenges of pure copper welding. This fully demonstrates the powerful ability of high-frequency inverter power supplies to reproduce complex continuous function waveforms to meet special process requirements. Compared to single-peak or stepped waveforms, effective welding was achieved at a lower peak current, completely avoiding burn-through or cracking of thin parts. This waveform vividly illustrates the unique ability of high-frequency inverter power supplies to reproduce complex continuous functions, something that energy storage welding and even traditional waveform control methods cannot achieve.

[0130] This invention maximizes the technological advantages of high-frequency inverter spot welding by introducing continuously smooth, functionalized current waveform control. The waveform generated by this invention is mathematically continuous and differentiable, and physically impact-free. This is fundamentally different from the uncontrollable impact discharge in energy storage welding, and represents a clear technological leap compared to ordinary control methods that can only produce piecewise linear waveforms (such as stepped waves).

[0131] This precise control capability transforms the welding process from "energy release" to "energy form programming," providing a completely new solution for achieving near-ideal spatter-free welding and consistently high solder joint quality, which is revolutionary in the field of high-end precision electronic component manufacturing.

[0132] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0133] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sheet low-fly high-frequency spot welding process, characterized by, Includes the following steps: S1. Pre-pressure and contact resistance optimization stage: Control the precision servo pressurization mechanism to drive the electrodes at a first preset pressure. Press the workpiece to be welded and hold for a certain period of time. At the end of the holding phase, the high-frequency inverter DC spot welding power supply outputs a low-amplitude "contact optimization pulse." This pulse current waveform is a continuous, smooth bell-shaped curve with a peak value of... Pulse width T_s = 3~8ms; S2. Main Welding Stage: After the S1 stage ends, the main welding current waveform is output without interruption. This waveform is a continuous and smooth time-varying function curve I(t). Its function form, time constant and amplitude are determined according to the workpiece material, thickness and target weld nugget size. The total energy input makes the workpiece contact surface reach the melting state. The S2 main welding stage is for copper or copper alloys with a total thickness of 0.3mm to 0.5mm, or for materials with ultra-high thermal conductivity or prone to thermal stress cracking, or for coated steel or copper alloys that require a wide and uniform weld nugget. For copper or copper alloys with a total thickness of 0.3mm to 0.5mm, an "S-shaped rise-exponential fall" waveform is adopted. The current function I(t) follows an S-shaped logical growth curve during the rising segment, and then decreases exponentially after reaching its peak value I_w. The specific expression is as follows: Rise time wherein is the rise rate constant, chosen to give a 10%-90% peak rise time of 2-5 ms; t_rise is the total rise time, 3-6 ms; falling segment where τ is a decay time constant, having a value of 1-3 ms; The peak current I_w is determined based on material and thickness tests, and ranges from 1.8 to 4.0 kA. For materials with ultra-high thermal conductivity or prone to thermal stress cracking, a "multi-peak resonant decay" waveform is adopted. Its current function I(t) is a damped oscillation containing 2 to 3 consecutive decaying resonant peaks, mathematically consisting of an exponentially decaying envelope modulating a decaying sine wave. wherein is the initial amplitude, is the envelope decay constant, is the oscillation frequency, is the phase, and I_base is the DC bias, the waveform achieving oscillatory penetration and homogenization of heat through periodic, decaying energy input; For coated steel or copper alloys requiring a wide and uniform melt nugget, a "flat-top cosine modulation" waveform is used, where the current function I(t) is a flat-top waveform whose amplitude is modulated by a cosine function: where I_w is the average current amplitude, m is the modulation depth, and f mod is the modulation frequency. This waveform, while maintaining the bulk heat input, promotes composition homogenization by low frequency modulation stirring the nugget. S3. Dynamic forging and post-heat control stage: When the S2 main welding current waveform function value drops to 40%~60% of its peak value I_w, the precision servo pressurizing mechanism starts the pressure boosting program, increasing the electrode pressure from... Smoothly increase to the second preset pressure Meanwhile, the high-frequency inverter DC spot welding power supply outputs a continuously decaying "post-heat control waveform". This waveform starts at 20%~40% of I_w and decays to zero within 15~40ms according to an exponential or polynomial law. S4. Pressure maintaining and backstroke phase: maintaining the forging pressure After the end of the post-heating control waveform, the electrode is kept for 20-50 ms and then retracted.

2. The process according to claim 1, characterized in that, Based on a thin plate low-spatter high-frequency spot welding equipment, the equipment includes a high-frequency inverter DC spot welding power supply, a precision servo pressurization mechanism, an integrated control unit, and upper and lower electrodes; The high-frequency inverter DC spot welding power supply has an inverter frequency range of 10kHz to 40kHz, outputs DC welding current with a ripple rate of less than 5%, and has the ability to generate real-time waveforms based on a continuous function model. It can output welding current waveforms with continuous and smooth amplitude changes over time and continuous first derivative. The precision servo pressurization mechanism is driven by a servo motor or linear motor, with a response time of less than 10ms. It can realize dynamic and stepless adjustment of electrode pressure during welding, and the pressure control accuracy is better than ±2%. The integrated control unit has a built-in high-speed processor and function waveform library. It can calculate and issue the set values ​​of current and pressure in real time according to the welding process model, and synchronously coordinate the output of the high-frequency inverter DC spot welding power supply and the action of the precision servo pressurization mechanism, forming a collaborative closed-loop control system based on the combination of function model feedforward and real-time electrical signal feedback. The upper and lower electrodes are electrically connected to the high-frequency inverter DC spot welding power supply via a welding machine, and the integrated control unit is electrically connected to the high-frequency inverter DC spot welding power supply and the precision servo pressurization mechanism.

3. The process of claim 2, wherein, The function waveform library contains at least three types of continuous and smooth reference current waveform functions: "S-shaped rise-exponential fall" waveform, "multi-peak resonant decay" waveform, and "flat-top cosine modulation" waveform.

4. The process of claim 2, wherein, The high-frequency inverter DC spot welding power supply includes an AC power input, a main controller, a rectifier bridge, an IGBT inverter module, a fast recovery diode rectifier bridge, a transformer, and a filter circuit. A capacitor bank is connected to the AC power input, and a rectifier bridge connects the capacitor bank to the AC power input. The phase detection circuit of the main controller samples in parallel from the AC power input. The input of the IGBT inverter module is connected across the capacitor bank, and a filter circuit connects its output to the fast recovery diode rectifier bridge. The output of the IGBT inverter module is connected in series with the primary winding of the transformer. The diodes inside the fast recovery diode rectifier bridge are connected in a bridge configuration, with the diodes in the upper and lower bridge arms connected in series and the bridge arms connected in parallel, used to rectify the high-frequency high-voltage AC signal into a high-voltage DC signal.

5. The process of claim 4, wherein, The rectified DC high voltage output terminal is connected in parallel with a voltage sensor through a voltage divider resistor network to collect the output voltage signal; a current sensor is connected in the load circuit to collect the output current signal. The output terminals of the voltage sensor and the current sensor are both connected to the analog input terminal of the main controller to realize closed-loop control and protection.

6. The process of claim 1, wherein, The dynamic forging start time and pressure rise curve in stage S3 are triggered and planned by the integrated control unit based on the real-time calculated value of the current function I(t) in stage S2 or the real-time monitored differential conductance between electrodes.

Images