GMAW welding arc initiation device

Abstract

The GMAW arc striking device is composed of arc striking auxiliary circuit and protection circuit. The device can realize the rapid lifting of current in the arc striking process, so that the arc is stable and established, and the wire breakage at the conducting nozzle is inhibited. The basic working principle is that the state detection circuit detects the welding state, when the voltage between the conducting nozzle and the base material is higher than the reference voltage, the state switching switch tube is turned on to charge the inductor in the loop in advance, when the voltage between the conducting nozzle and the base material is lower than the reference voltage, the switch tube is turned off to realize the direct energy output. Compared with the conventional GMAW arc striking process, the arc striking device can realize the accurate energy given in the arc striking process and the steep rise of the arc striking current, which can effectively improve the stability in the arc striking process.

Description

Technical Field

[0001] This invention relates to an arc-starting device applicable to GMAW welding power supplies, and is situated within the field of power electronic devices and welding power supply technology. Background Technology

[0002] Gas metal arc welding (GMAW) is a welding method that uses an externally supplied gas as the arc medium. The arc between the welding wire and the workpiece melts the continuously fed welding wire and base metal to form a molten pool and weld. GMAW has advantages such as high efficiency, high quality, and low consumption, and is therefore widely used in various industries. With the development of modern industry, new requirements have been placed on welding quality and the stability of the welding process.

[0003] Currently, GMAW welding machines on the market use a high-current wire breakage method for arc initiation. However, due to the inductance in the welding power supply, the current rise rate at the wire end during arc initiation is insufficient, leading to problems such as the wire short-circuiting the base material, inability to stably establish an arc, and wire breakage at the contact tip causing excessive spatter. To improve the current rise rate, existing arc initiation auxiliary circuits add a switching transistor to bypass the inductance of the main welding power supply circuit during arc initiation, increasing the arc current rise rate. However, due to parasitic inductance in the cable, this inductance also hinders the current rise rate, and the circuit cannot solve the problem of rapid charging of parasitic inductance in the circuit. To solve the aforementioned arc initiation problems, a switching transistor can be connected in series between the positive and negative terminals of the welding power supply, and a detection circuit can be added between the contact tip and the base material. The detection circuit judges the wire state and controls the switching transistor to turn on and off, achieving accurate and rapid energy input during arc initiation. This circuit can achieve a sharp increase in wire end current while reducing wire breakage at the contact tip during arc initiation, allowing for stable arc establishment. Summary of the Invention

[0004] The purpose of this invention is to provide a gas metal arc welding (GMAW) arc ignition device with state detection to ensure stable arc ignition during GMAW welding. The specific implementation method is as follows:

[0005] This invention includes

[0006] The state-switching switch Q1 allows energy transfer between different branches to control whether current flows between the welding wire and the base material. The state detection circuit determines the welding state by detecting the voltage between the contact tip and the base material, thereby determining the operating state of the switch Q1. In the arc-starting auxiliary circuit, the collector of Q1 is connected to terminal 2 of the welding power supply inductor L1, the anode of diode D1, and the anode of diode D3. The emitter of Q1 is connected to the negative terminal of the constant current power supply and the base material. In the state detection circuit, the detection power supply VDC is connected to the anode of diode D2, the cathode of diode D3 is connected to the collector of switch Q3, the emitter of switch Q3 is connected to terminal 1 of resistor R1, and terminal 2 of resistor R1 is connected to the contact tip. In the protection circuit, the cathode of diode D3 is connected to terminal 1 of resistor R2 and terminal 1 of capacitor C1, terminal 2 of resistor R2 is connected to the collector of switch Q2, the emitter of switch Q2 is connected to terminal 2 of capacitor C1, and the charging rectifier bridge is connected in parallel across capacitor C1. When the switching transistor Q1 is turned on, the power supply output current flows back to the power supply through the inductor L1 and the switching transistor Q1; when the switching transistor Q1 is turned off, the welding power supply output current flows back to the welding power supply through the inductor L1, the diode D1, the contact tip, the welding wire, and the base material.

[0007] When arc ignition begins, switch Q3 in the detection circuit is turned on to detect the voltage between the contact tip and the base material. When this voltage is higher than the set value (90% VDC), the welding wire is relatively far from the base material, and the arc ignition auxiliary circuit operates in the inductor charging state, i.e., switch Q1 is turned on. When the voltage is lower than the set value (90% VDC), the welding wire is relatively close to the base material, and the state switching circuit operates in the arc ignition state, i.e., Q1 is turned off to release energy, and at the same time, Q2 in the detection circuit is turned off to complete arc ignition. When the voltage across capacitor C1 exceeds the set safety threshold, switch Q2 is turned on to discharge the energy of the capacitor through R2.

[0008] Compared with the prior art, the present invention has the following advantages:

[0009] The welding status is detected by a detection circuit, and the switching transistor Q1 of the state switching circuit is turned on and off according to the welding status, realizing the sharp increase of current and precise energy supply at the welding wire end during arc ignition. Compared with the existing GMAW arc ignition method, this invention can pre-store energy in the inductor and capacitor according to the actual welding status, and then rapidly deliver energy just before the welding wire short circuits, suppressing the problem of welding wire breakage at the contact tip during arc ignition and achieving stable arc establishment. At the same time, the charging voltage across the capacitor is clamped to a high voltage, which can charge the stray inductor L2 in the circuit when entering the arc ignition state. Attached Figure Description

[0010] Figure 1 Main circuit schematic

[0011] Figure 2 System overall block diagram

[0012] Figure 3 Inductor energy storage state

[0013] Figure 4 Given the current at the welding wire end

[0014] Figure 5 Charging the capacitor for the protection circuit

[0015] Figure 6 To protect the circuit capacitor discharge

[0016] Figure 7 Schematic diagram of the arc-starting circuit's operating waveform

[0017] Figure 8 Schematic diagram of the protection circuit's operating waveform

[0018] Figure 1 Q1, Q2, and Q3 are switching transistors, L1 is the internal inductance of the welding power supply, L2 is the parasitic inductance in the circuit, and the area within the dashed line is a schematic diagram of the arc-starting auxiliary circuit.

[0019] Figure 2 (1) Arc ignition auxiliary circuit, (2) Voltage sampling circuit, (3) Voltage sampling circuit, (4) Comparator, (5) Discharge switch driving circuit, (6) Current sampling and filtering, (7) Switch driving circuit, (8) Detection switch driving circuit, (9) Digital signal processing control system, (10) Comparator, (11) Human-machine interface. Detailed Implementation

[0020] The specific implementation method of this circuit is as follows:

[0021] This equipment detects the welding status through a status detection circuit and switches the current path accordingly, thereby preventing a sharp increase in current during arc ignition and suppressing the problem of welding wire breakage at the contact tip. Compared with other arc ignition equipment, this equipment can achieve precise control of the energy input timing and address the issue of stray inductance charging in the circuit, making the arc ignition process more stable.

[0022] Reference Figure 1 , Figure 2As shown, when the arc is not ignited, the welding status is detected by the detection circuit. The switching of the energy transmission circuit is controlled by the alternating on and off of the switch Q1 in the welding status switching circuit. At the start of arc ignition, the welding wire is fed into the switching circuit, where switch Q3 is turned on. The voltage sampling circuit samples the voltage between the contact tip and the base material. When the sampled voltage is higher than the set value (90% VDC), the welding wire is relatively far from the base material. Switch Q1 in the status switching circuit is turned on, and current flows from the positive terminal of the welding power supply, through the welding power supply inductor L1 and switch Q1, back to the negative terminal of the welding power supply. At this time, there is no large current flowing between the welding wire and the base material. When the welding wire is about to short-circuit with the base material, the sampling circuit in the detection circuit detects a voltage lower than the set value. Switch Q1 in the switching circuit is turned off, and switch Q3 in the detection circuit is turned off. The large arc ignition current flows back to the negative terminal of the welding power supply through inductor L1, diode D1, the welding wire, and the base material. At this time, the arc is ignited by the arc ignition current. When powered on, the rectifier bridge charges the capacitor, bringing the voltage across the capacitor to the set value Vlow. This voltage value can be set according to the current rise rate. At the same time, the switch Q1 turns on and off, and the peak energy is absorbed through the capacitor C1. When the voltage across C1 is higher than the safety threshold Vhigh, the switch Q2 turns on and discharges the energy in the capacitor through the resistor R2.

[0023] Figure 3 When the voltage between the contact tip and the base material is higher than the set value, the circuit operates in the inductor energy storage state. Switches Q1 and Q3 are turned on, and the welding power supply output current flows through its own inductance L1 and the switch Q1 and finally flows back to the negative terminal of the welding power supply. At this time, no current flows between the contact tip and the welding wire, and the inductor L1 stores energy.

[0024] Figure 4 When the voltage between the conductive tip and the base material is lower than the set value, the circuit operates in the current given state at the welding wire end, the switching transistors Q1 and Q2 are turned off, and the current is output to the welding wire end to ignite the arc.

[0025] Figure 5 During the initial stage of arc ignition, capacitor C1 is charging. At this time, switch Q2 is turned off. In order to quickly charge the parasitic inductance L2 in the arc ignition circuit and increase the current rise rate during the arc ignition process, the capacitor is pre-charged through the rectifier circuit to clamp the potential at the anode of diode D1 to above the set value Vhigh.

[0026] Figure 6 When the switch Q2 is turned on, the capacitor C1 is discharging. At this time, the voltage on the capacitor C1 exceeds the preset safe voltage value Vhigh. If the voltage continues to rise, the inductor current will rise faster when arcing occurs. If it rises too fast, it will cause the circuit components to break down. Therefore, the energy on the capacitor is released through the resistor R1 and the switch Q2.

[0027] Figure 7The diagram shows the waveform of the arc ignition circuit. As can be seen, in the initial stage after power-on, the welding wire is far from the base material, so switching transistors Q1 and Q3 are on, and switching transistor Q2 is off. The current at the contact tip is zero to prevent the welding wire from breaking due to current rise during wire feeding. The welding power supply output current charges the inductor in the circuit, and simultaneously, capacitor C1 in the protection circuit charges, clamping the voltage across inductor L1 to a set value. When the arc ignition time base is reached, the switching circuit changes the current flow. Because the inductor has been pre-charged, and the voltage across the capacitor clamps the anode of diode D2 to a high voltage state, the current at the welding wire tip increases sharply to the arc ignition current, allowing the arc to be established stably.

[0028] Figure 8 The diagram illustrates the operating waveforms of the protection circuit. V1 represents the DC output voltage of the rectifier bridge, Vlow is the set voltage across the capacitor in the protection circuit (this value can be set according to the required current rise rate), and Vhigh is the circuit's safe operating threshold (1.2 times the set value). When the voltage across the capacitor exceeds the safe threshold, switch Q2 turns on, discharging the voltage across the capacitor. When the voltage falls below the set value, switch Q2 turns off, and the rectifier bridge charges the capacitor, causing its voltage to rise. The protection circuit, on the one hand, ensures that the voltage across the capacitor remains above the set value Vlow, guaranteeing reliable arc ignition; on the other hand, it absorbs the voltage spikes caused by the switching transistor's on / off states.

[0029] Figure 2This is the overall system block diagram of the present invention. The current sensor in the diagram mainly works with the current sampling and filtering circuit (6) to measure the output current in the main circuit. The collected current signal will be transmitted to the digital signal processing control system (9) and compared, analyzed and calculated with the value set through the human-machine interface (11). The calculated signal is then fed back to the welding power source to control the current output. The digital signal processing control system (9) generally includes some analog-to-digital and digital-to-analog conversion circuits, microcontroller chips and control circuits, etc. In order to meet the requirements of convenient control system, the digital signal processing control system (9) is also connected to the human-machine interface (11). The working status of the entire system can be intuitively monitored through the human-machine interface, and various parameters in the welding process, such as the arc ignition current value, can be easily adjusted. As described above, to achieve successful arc ignition, the state detection circuit and the state switching switch Q1 need to work together. Specifically, the voltage signal between the conductive nozzle and the base material collected by the sampling circuit (2) is compared with the set reference value of 60V by the comparator (10). The result is transmitted to the digital signal processing system (9) to determine whether the arc has reached the ignition time base. If it has not reached the time base, the digital signal processing system (9) sends a high-level signal, which controls the switching transistors Q1 and Q3 to continue conducting through the switching transistor drive circuit (7) and the detection switching transistor drive circuit (8), charging the inductor L1. If the arc reaches the ignition time base, the digital signal processing system (9) sends a low-level signal to the switching transistor drive circuit. After being amplified by the switching transistor drive circuit (7) and the detection switching transistor drive circuit (8), Q1 and Q3 are turned off, and the arc current is applied to the welding wire end, completing the circuit working state switching. The switching of Q2 is controlled by sampling circuit (3) to collect the voltage on capacitor C1. This voltage is compared with the voltage reference value preset by comparator (4) (this value is set according to the loop gain of sampling circuit (3). If the maximum voltage on capacitor C1 is to be 1000V, the loop gain of sampling circuit is 500:1, that is, the sampling voltage is 1V, which represents the actual voltage of 500V. Then the reference value of comparator (4) needs to be set to 2V). When the voltage value obtained by sampling circuit (3) is greater than the reference value of comparator (9), switch Q2 is turned on; when it is less, switch Q2 is turned off. If there is no switch Q2 and resistor R2 in this invention, when switch Q1 changes from on to off, diode D3 will turn on, and the energy in inductor L1 will charge capacitor C1 in arc-starting auxiliary circuit, and the voltage across C1 will rise. If this working mode is continued, the voltage across capacitor C1 will continue to rise until it reaches the capacitor's maximum withstand voltage and eventually breaks down. Therefore, to prevent this from happening, resistor R2 and switching transistor Q2 are needed to release the excess energy in the capacitor.

[0030] In the detection circuit, the reference voltage VDC is generally selected between 70V and 100V, and the state switching threshold voltage can be set to 90% VDC. Resistor R1 is a pull-up resistor. Due to the large resistance when the welding wire and the base material are close, a 10K-class resistor is selected for R1. Diode D1 carries a large arc-starting current during the arc-starting process, so a 100A-class power diode should be selected. In the protection circuit, the capacitor setting value Vlow is 300-1000V, which can be set according to the current rise rate requirement. The safety voltage value Vhigh is 1.2 times the setting value. AC is calculated based on the voltage setting value across the capacitor. The switching transistors Q1 and Q2 introduced in this invention take IGBT as an example. In actual applications, the type of switching transistor can be selected according to the actual situation.

Claims

1. A GMAW welding arc ignition device, comprising an arc ignition and current switching circuit; the arc ignition and current switching circuit includes: Switching transistors Q1 and Q3, diodes D1 and D2, resistor R1, and arc-starting auxiliary power supply VDC; the collector of Q1 is connected to terminal 2 of the welding power supply inductor L1 and the anode of diode D1; the emitter of Q1 is connected to the negative terminal of the constant current power supply, the base material, and the reference ground; the collector of Q3 is connected to the cathode of diode D2; the emitter of Q3 is connected to terminal 1 of resistor R1; the arc-starting auxiliary power supply VDC is connected to the anode of diode D2; terminal 2 of resistor R1 is connected to the cathode of diode D1 and the contact tip; circuit parasitics. One end of inductor L2 is connected to the cathode of diode D1 and the two ends of resistor R1, and the two ends of L2 are connected to a conductive nozzle; the feature is that it also includes an active protection circuit; the active protection circuit includes: a switching transistor Q2, a diode D3, a capacitor C1, a resistor R2 and a charging rectifier bridge; the cathode of diode D3 is connected to one end of resistor R2 and one end of capacitor C1, the two ends of resistor R2 are connected to the collector of switching transistor Q2, the emitter of switching transistor Q2 is connected to the two ends of capacitor C1, and the charging rectifier bridge is connected in parallel across capacitor C1.

2. The GMAW welding arc striking device according to claim 1, characterized in that: When the state switching transistor Q1 is turned on, the current output by the welding power supply flows directly back to the welding power supply through inductor L1 and switching transistor Q1 to charge inductor L1; when the switching transistor Q1 is turned off, the current output by the welding power supply flows back to the welding power supply through inductor L1, diode D1, contact tip, welding wire, and base material.

3. The GMAW welding arc striking device according to claim 1, characterized in that: When welding begins, the welding wire is fed in. When the welding wire is not short-circuited with the base material, the voltage between the contact tip and the base material is higher than the set voltage. At this time, the switching circuit is in the charging state, i.e., Q1 is turned on. When the welding wire contacts the base material, the voltage between the contact tip and the base material is lower than the set voltage. At this time, the switching circuit is in the arc ignition state, i.e., Q1 is turned off.

4. The GMAW welding arc striking device according to claim 1, characterized in that: By using a detection circuit in conjunction with a switching transistor Q1, the power supply inductor and stray inductance in the circuit are pre-charged.

5. The GMAW welding arc ignition device according to claim 1, the capacitor is charged by the rectifier circuit to raise its voltage to a set value Vlow, the set value voltage range is 300-1000V, and the collector voltage of the switch Q1 is clamped to the set value; at the same time, the capacitor C1 absorbs the peak energy of Q1 turning on and off, protecting the switch Q1, and the voltage across the capacitor is sampled. When the set safety threshold Vhigh is reached, Vhigh is 1.2 times the set value, the energy on the capacitor C1 will be released through the resistor R2 and the switch Q2.

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