CN-121972785-A - Thin plate low-splashing high-frequency spot welding equipment and process

CN121972785ACN 121972785 ACN121972785 ACN 121972785ACN-121972785-A

Abstract

The invention discloses a sheet low-splash high-frequency spot welding device and a process, which relate to the technical field of resistance spot welding, and the device comprises a high-frequency inversion direct-current spot welding power supply, a precise servo pressurizing mechanism, an integrated control unit, an upper electrode and a lower electrode, wherein the upper electrode and the lower electrode are electrically connected with the high-frequency inversion direct-current spot welding power supply through a welding machine, and the integrated control unit is electrically connected with the high-frequency inversion direct-current spot welding power supply and the precise servo pressurizing mechanism.

Inventors

LI YI
LI XIANG
GAO YUZENG
Rong Zichang
DENG BOXIN
LI YUANQI
YIN LI

Assignees

湘潭大学

Dates

Publication Date: 20260505
Application Date: 20260409

Claims (9)

1. A low-splash high-frequency spot welding device for thin plates is characterized by comprising a high-frequency inversion direct-current spot welding power supply, a precise servo pressurizing mechanism, an integrated control unit, an upper electrode and a lower electrode; The high-frequency inversion direct-current spot welding power supply has the inversion frequency range of 10kHz to 40kHz, outputs direct-current welding current with ripple rate lower than 5%, has the real-time waveform generating capacity based on a continuous function model, and can output welding current waveforms with continuous and smooth amplitude change along with time and continuous first derivative; The precise servo pressurizing mechanism is driven by a servo motor or a linear motor, the response time is less than 10ms, the dynamic and stepless regulation of the electrode pressure in the welding process can be realized, and the pressure control precision is better than +/-2%; The integrated control unit is internally provided with a high-speed processor and a function waveform library, can calculate and send set values of current and pressure in real time according to a welding process model, and synchronously coordinates and controls the output of the high-frequency inversion direct-current spot welding power supply and the action of the precise servo pressurizing mechanism to form a cooperative closed-loop control system based on the combination of feedforward of the function model and real-time electric signal feedback; The upper electrode and the lower electrode are electrically connected with the high-frequency inversion direct-current spot welding power supply through a welding machine, and the integrated control unit is electrically connected with the high-frequency inversion direct-current spot welding power supply and the precise servo pressurizing mechanism.
2. The apparatus of claim 1, wherein the library of function waveforms comprises at least three consecutive smooth reference current waveform functions of an "S-shaped rise-exponential fall" waveform, a "multi-peak resonance decay" waveform, and a "flat-top cosine modulation" waveform.
3. The device of claim 1, wherein the high-frequency inversion direct-current spot-welding power supply comprises an alternating-current power supply input, a main controller, a rectifier bridge, an IGBT inversion module, a fast recovery diode rectifier bridge, a transformer and a filter circuit, wherein the alternating-current power supply input end is connected with a capacitor bank, the rectifier bridge is connected between the capacitor bank and the alternating-current power supply input end, a phase detection circuit of the main controller is connected with the alternating-current power supply input end in parallel and samples, the input end of the IGBT inversion module is connected with two ends of the capacitor bank, the output end of the IGBT inversion module is connected with the fast recovery diode rectifier bridge in a filter circuit, the output end of the IGBT inversion module is connected with a primary winding of the transformer in series, diodes in the fast recovery diode rectifier bridge are connected in a bridge type, the diodes of an upper bridge arm and a lower bridge arm are connected in series, and the bridge arms are connected in parallel and are used for rectifying high-frequency high-voltage alternating-current signals into direct-current high voltages.
4. The device according to claim 3, wherein the rectified DC high voltage output end is connected with a voltage sensor in parallel through a voltage dividing resistor network for collecting output voltage signals, a current sensor is connected in a load loop for collecting output current signals, and the output ends of the voltage sensor and the current sensor are connected with an analog input end of a main controller for realizing closed-loop control and protection.
5. A process for low splash high frequency spot welding of thin sheets, based on the apparatus of claim 1, characterized in that it comprises the following steps: s1, controlling a driving electrode of a precise servo pressurizing mechanism to have a first preset pressure in a prepressing and contact resistance optimizing stage Compacting the workpiece to be welded, wherein the workpiece to be welded is a thin plate, and the thickness of copper, copper alloy and plating steel is 0.1mm to 0.5mm, and the holding time is prolonged The high-frequency inversion direct-current spot welding power supply outputs a low-amplitude contact optimizing pulse which has a continuous smooth bell-shaped curve and a peak value Pulse bottom width ts=3 to 8ms; S2, outputting a main welding current waveform at intervals after the step S1 is finished, wherein the waveform is a continuous and smooth time-varying function curve I (t), the function form, the time constant and the amplitude of the waveform are determined according to the material and the thickness of a workpiece and the size of a target nugget, and the total energy input enables the contact surface of the workpiece to reach a molten state; s3, in the stage of dynamic forging and post-heat control, when the waveform function value of the main welding current of S2 is reduced to (40% -60%) of the peak value I_w, the precise servo pressurizing mechanism starts a pressure lifting program to drive the electrode pressure to be equal to the electrode pressure Smoothly lifting to a second preset pressure Meanwhile, the high-frequency inversion direct-current spot welding power supply outputs a section of continuously attenuated post-heat control waveform which starts from (20% -40%) of I_w and attenuates to zero within 15-40 ms according to an exponential or polynomial rule; s4, maintaining pressure and returning stage, namely maintaining forging pressure And after the post-heat control waveform is finished and is kept for 20-50 ms, the electrode returns.
6. The process according to claim 5, wherein the S2 main welding stage employs an "S-shaped rise-exponential fall" waveform for copper or copper alloy with a total thickness of 0.3mm to 0.5mm, wherein the current function I (t) follows an S-shaped logical growth curve in the rising section, and after reaching the peak value i_w, the current function I (t) falls exponentially by the following expression: Ascending section Wherein Taking a value to enable the 10% -90% peak rising time to be within 2-5 ms for rising rate constant, wherein t_rise is the total rising time and is 3-6 ms; Descending section Wherein τ is a decay time constant, and the value is 1-3 ms; the peak current I_w is determined according to material and thickness tests and ranges from 1.8 to 4.0kA.
7. The process according to claim 5, characterized in that said S2 main welding phase uses a "multimodal resonance decay" waveform, with current function I (t) in the form of damped oscillations comprising 2 to 3 successive decaying resonance peaks, mathematically consisting of an exponential decay envelope modulation of a decaying sine wave, for materials of ultra high thermal conductivity or susceptible to thermal stress cracking: wherein For the initial amplitude, τ_envelope is the envelope decay constant (2-5 ms), The oscillation frequency is 500-1500 Hz, For the phase, I_base is a direct current bias (0.1-0.3 kA), and the waveform realizes oscillation permeation and homogenization of heat through periodic and attenuated energy input.
8. The process according to claim 5, wherein the S2 main welding stage uses a "flat-top cosine modulated" waveform for a coated steel or copper alloy requiring a wide and uniform nugget, and the current function I (t) is a flat-top waveform with amplitude modulated by a cosine function: Wherein I_w is the average current amplitude, m is the modulation depth (0.1-0.3), f_mod is the modulation frequency (200-600 Hz), and the waveform is used for stirring the nugget through low-frequency modulation while maintaining the main body heat input, so that component homogenization is promoted.
9. The process according to claim 7, wherein the dynamic forging start time and pressure rise profile of step S3 are triggered and programmed by the integrated control unit based on real-time calculated values of the S2 stage current function I (t) or real-time monitored differential conductance between electrodes (dI/dU).

Description

Thin plate low-splashing high-frequency spot welding equipment and process Technical Field The invention belongs to the technical field of resistance spot welding, and particularly relates to a sheet low-splash high-frequency spot welding device and a sheet low-splash high-frequency spot welding process. Background In the manufacture of precision electromagnetic components such as relays, contactors, etc., the quality of the spot-welded connection of the internal conductive components directly determines the electrical performance, mechanical life and long-term reliability of the product. Currently, the mainstream and mature process for welding such sheet metal parts in the industry is energy storage welding (capacitive discharge welding). Energy storage welding uses a capacitor bank to store and instantaneously discharge electrical energy, producing a very high peak, very short duration (typically 3-10 milliseconds) pulse current for welding. The method has the advantages of relatively low equipment cost, high instantaneous power and capability of rapidly breaking through the oxide layer on the surface of the workpiece. However, when the energy storage welding is applied to welding of precise thin plates such as relays, the inherent defects are extremely remarkable, and welding spatter is extremely serious. The method is characterized in that the metal is melted and vaporized rapidly due to the excessively high instantaneous energy density, and the pressure of metal vapor in the molten core instantaneously breaks through the plastic ring constraint of the welded plate, so that liquid metal particles are sprayed out at a high speed. Serious splashing presents a number of problems: 1. Pollution and potential safety hazards, namely that metal particles pollute an insulating framework, a coil and a narrow air gap in the relay, insulation drop or instant short circuit can be caused, and serious quality hazards exist. 2. And the quality of the welding spot is degraded, namely part of molten metal is taken away by splashing, so that the effective connection area of the welding spot is reduced, and the virtual welding, shrinkage cavity or overburning are formed, thereby seriously affecting the conductivity and mechanical strength of the welding spot. 3. The process stability is poor, the splashing degree is greatly influenced by power grid fluctuation, capacitor aging and workpiece surface state, the consistency of welding spot quality is difficult to ensure, and the quality control cost is increased. 4. The subsequent cost is high, and in order to remove internal splashes, complex cleaning procedures are often required to be added, so that the production efficiency is reduced. To overcome the problem of spattering, intermediate frequency inversion direct current spot welding technology has been introduced as an improvement. The medium frequency inversion spot welder generally converts the power frequency alternating current into 400-1200Hz medium frequency alternating current, and then outputs direct current welding current through rectification. Compared with energy storage welding, the medium-frequency inversion technology has certain current control capability, can realize multi-pulse welding, and improves the stability and controllability of the welding process to a certain extent. However, intermediate frequency inversion spot welding has the following limitations when applied to extremely thin, high precision workpieces: 1. The response speed is still insufficient, the intermediate frequency inversion frequency is lower, the current regulation response time is relatively longer, microsecond-level accurate control is difficult to realize, and the dynamic process control at the initial stage and the final stage of welding is not fine enough; 2. the current ripple is larger, namely the ripple coefficient of the medium-frequency direct current output is higher than that of a high-frequency system, and certain periodic fluctuation still exists in the heat input, so that the even growth of nuggets is not facilitated; 3. The spatter suppression capability is limited, although superior to energy storage welding, in highly conductive materials or ultra-thin laminate welding, localized spatter due to non-uniform heat input or delayed dynamic response may still occur. In order to further improve welding quality and process control accuracy, high frequency inversion direct current spot welding technology is used as a more advanced alternative to enter the field of view. The working principle is that after the power frequency alternating current is subjected to high-frequency inversion (usually 1-4kHz and even higher) and rectification, continuous, smooth and extremely fast-response direct current is output. Compared to mid-frequency inversion, the high-frequency inversion technique performs significantly better in: 1. The response speed is extremely high, the inversion frequency is high, the current regulation response