An integrated multimodal current waveform and wire feed drive coordinated control method

Abstract

This invention provides an integrated multimodal current waveform and wire feed drive coordinated control method, implemented based on an integrated multimodal current waveform and wire feed drive coordinated control system. The method includes the following steps: setting the mode and current characteristic values ​​of the welding current waveform, inputting the current waveform-wire feed speed matching model, calculating the average current, and then calculating the set wire feed speed; controlling the actual output welding current waveform and wire feed speed; then acquiring the actual output welding current waveform and inputting it into the current waveform-wire feed speed matching model to calculate the average current, and then calculating the set wire feed speed. This method aims to coordinate the welding current output and wire feed drive of an inverter welding machine, flexibly adjusting the wire feed speed through the current waveform-wire feed speed matching model to adapt to different current waveforms, achieving a dynamic balance between wire feed speed and welding current, and improving the stability of the welding process and the weld quality.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically, to an integrated multimodal current waveform and wire feed drive coordinated control method. Background Technology

[0002] Composite pulsed MIG welding technology uses pulsed current to control droplet transfer to obtain an ideal droplet transfer form. It not only has the characteristics of wide current adjustment range, easy to realize all-position welding, effective control of heat input, and easy automation, but also the arc force generated by the change of average current has a stirring effect on the molten pool, thereby reducing the porosity and refining the grains. It is widely used in high-efficiency automated welding industrial applications.

[0003] The wire feed motor is used to replenish the welding wire consumed during MIG welding. Currently, the wire feed speed is not coordinated with the welding current. However, the welding current determines the wire consumption rate, and an imbalance between the wire consumption rate and the wire feed speed directly leads to fluctuations in the arc length, which in turn affects the arc voltage and molten pool flow, thus damaging the weld quality. Therefore, there is an urgent need to design a method that coordinates the welding current output with the wire feed drive. Furthermore, with the application of SiC power devices and the rapid development of digital control technology, inverter welding machines can output complex composite current waveforms, requiring the wire feed speed to be flexibly adjusted to match multi-modal current waveforms. Summary of the Invention

[0004] To overcome the shortcomings and deficiencies of the existing technology, the purpose of this invention is to provide an integrated multimodal current waveform and wire feeding drive coordinated control method. This method aims to coordinate the welding current output and wire feeding drive of an inverter welding machine, and flexibly adjust the wire feeding speed to adapt to different current waveforms through a current waveform-wire feeding speed matching model, thereby achieving a dynamic balance between wire feeding speed and welding current, and improving the stability of the welding process and the quality of the weld.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: an integrated multimodal current waveform and wire feed drive coordinated control method, based on an integrated multimodal current waveform and wire feed drive coordinated control system; the welding current waveform of the integrated multimodal current waveform and wire feed drive coordinated control system has multiple modes; the modes of the welding current waveform include: a low-frequency pulse mode that only includes a low-frequency pulse current waveform, a fast-frequency pulse mode that includes a fast-frequency pulse current waveform, and a fast-frequency single-pulse mode obtained by superimposing a low-frequency pulse current waveform and a fast-frequency pulse current waveform;

[0006] An integrated multimodal current waveform and wire feed drive coordinated control method includes the following steps:

[0007] Step S1: Initialize the welding current waveform and wire feed setting speed, including: setting the mode and current characteristic value of the welding current waveform; inputting the set welding current waveform current characteristic value into the current waveform-wire feed speed matching model; the current waveform-wire feed speed matching model calculates the average current, and then calculates the wire feed setting speed according to the average current and the linear fitting formula.

[0008] Step S2: Based on the set welding current waveform and wire feeding speed, control the actual output welding current waveform and wire feeding speed respectively.

[0009] Step S3: Collect the actual output welding current waveform; input the current characteristic value of the actual output welding current waveform into the current waveform-wire feed speed matching model to calculate the average current, and then calculate the wire feed set speed according to the average current and the linear fitting formula; repeat steps S2 and S3 until welding is completed.

[0010] Preferably, in steps S1 and S3, the current characteristic value of the welding current waveform refers to: when the welding current waveform includes a low-frequency pulse current waveform, the current characteristic value includes the peak current I of the low-frequency pulse current waveform. Bp Current base value I Bb Frequency f B and duty cycle D B When the welding current waveform includes a fast-frequency pulse current, the current characteristic value includes the peak current I of the fast-frequency pulse current waveform. D and frequency f D ;

[0011] The average current I is calculated using a current waveform-wire feed speed matching model. avgi and wire feeding speed v i This means that i = 1, 2, 3 correspond to low-frequency pulse mode, fast-frequency pulse mode, and fast-frequency single-pulse mode, respectively.

[0012] When the welding current waveform is in a low-frequency pulse mode, the average current I avg1 for:

[0013] I avg1 =I Bp ·D B +I Bb ·(1-D B )

[0014] When the welding current waveform is in the fast pulse mode, the average current I avg2 for:

[0015]

[0016] When the welding current waveform is in the fast-frequency single-pulse mode, the average current Iavg3 for:

[0017] I avg3 =I avg1 +I avg2

[0018] Wire feed setting speed v corresponding to various welding current waveforms i ,for:

[0019] v i =K i ·I avgi +b i

[0020] Among them, K i b represents the response coefficient; i This represents the bias value.

[0021] Preferably, the response coefficient K i In the given information, K2 > K1; K3 = K2.

[0022] Preferably, in step S2, the actual output welding current waveform and wire feed speed are controlled by a DSC controller; wherein, the peak current I Bp Current base value I Bb and peak current I D The output duty cycle of the PWM drive module is controlled via a DSC controller; frequency f B Duty cycle D B and frequency f D They are controlled by the TIM3 built into the DSC controller.

[0023] Preferably, in step S2, two independent ADCs are used to acquire the actual output welding current waveform and wire feed speed respectively; the two independent ADCs are triggered by TIM1 and TIM2 respectively; and an incremental PID algorithm is used to control the actual output welding current waveform and wire feed speed.

[0024] Preferably, using an incremental PID algorithm to control the actual output welding current waveform means:

[0025] The actual output low-frequency pulse current waveform and the actual output high-frequency pulse current waveform are collected separately; the data are smoothed using an extreme value removal and mean filtering algorithm to obtain the peak current I of the actual output low-frequency pulse current waveform. Bp Current base value I Bb and the peak current I of the fast-frequency pulse current waveform DThe current difference value is obtained by comparing it with the current characteristic value corresponding to the set welding current waveform. The current difference value is adjusted by the incremental PID algorithm to adjust the output duty cycle of the PWM drive module, thereby controlling the actual output welding current waveform.

[0026] Preferably, using a PID algorithm to control the wire feeding speed means: collecting the actual wire feeding speed, comparing it with the set wire feeding speed to obtain the wire feeding difference value, and then adjusting the actual wire feeding speed by adjusting the wire feeding difference value through an incremental PID algorithm;

[0027] Set fine-tuning settings in the human-computer interaction interface; fine-tune the wire feeding speed calculated in step S3 according to the fine-tuning settings.

[0028] Preferably, the integrated multimodal current waveform and wire feeding drive coordinated control system includes a human-machine interface, an integrated control circuit, a welding robot, an integrated high-frequency MIG inverter welding machine, and a wire feeding motor.

[0029] Preferably, the integrated high-frequency MIG inverter welding machine includes a three-phase rectifier input terminal, a motor drive circuit, a high-frequency pulse modulation circuit, a low-frequency pulse modulation circuit, and a current parallel terminal; wherein, the three-phase rectifier input terminal receives three-phase power from the industrial environment and supplies it to the motor drive circuit, the high-frequency pulse modulation circuit, and the low-frequency pulse modulation circuit respectively; the output terminal of the motor drive circuit is connected to the wire feeding motor; the currents output by the high-frequency pulse modulation circuit and the low-frequency pulse modulation circuit are combined and output at the current parallel terminal; the positive terminal of the current parallel terminal is connected to the welding wire, and the negative terminal is connected to the workpiece.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0031] 1. This invention aims to coordinate the welding current output and wire feeding drive of an inverter welding machine, match different wire feeding speeds for welding current waveforms of various modes, and establish a "current waveform-wire feeding speed" matching model with high fitting degree, so that the wire feeding speed can flexibly adapt to a variety of complex composite current waveforms, greatly reducing the operator's debugging work, and adjusting the wire feeding speed in real time according to the actual welding current during the welding process to achieve dynamic balance between wire feeding speed and welding current, thereby improving the stability of the welding process and the quality of the weld.

[0032] 2. Currently, the welding machine used for outputting current and the motor used for driving the wire feed are usually controlled by two separate circuit boards, which can transmit signals to each other wirelessly or via wired communication. However, the high-order harmonics generated by the fast-frequency (≥20kHz) pulse current used in current inverter welding machines based on SiC power devices may cause serious interference to communication. This invention integrates the current output control and wire feed drive control circuits to avoid the problem of communication interference by fast-frequency pulse current, reduce the space occupied by the circuit board and external wiring, and make the system easier to install and maintain.

[0033] 3. This invention utilizes two independent ADCs for parallel acquisition, achieving a higher acquisition efficiency than a single ADC acquisition, and can better isolate each input channel, reduce crosstalk between signals, and improve the system's anti-interference capability.

[0034] 4. The two independent ADCs used in this invention employ different TIM triggers, which can achieve different sampling frequencies for specific needs. Using a higher sampling frequency to acquire fast-frequency pulse current can more accurately capture rapid changes in the signal, while using a lower sampling frequency to acquire the armature voltage of the wire feeding motor can reduce the amount of data and computational cost, and improve computational efficiency.

[0035] 5. The present invention provides a fine-tuning setting for the wire feeding speed in the human-machine interface, giving users some operational space, enabling the system to flexibly cope with complex working conditions and improve the user experience. Attached Figure Description

[0036] Figure 1 This is a flowchart of the main control functions of the integrated multimodal current waveform and wire feed drive coordinated control method of the present invention.

[0037] Figure 2 This is the overall block diagram of the integrated multimodal current waveform and wire feed drive coordinated control system used in this invention;

[0038] Figure 3 This is a block diagram of the control circuit module of the integrated multimodal current waveform and wire feed drive coordinated control system used in this invention.

[0039] Figure 4 This is a block diagram of the main circuit structure of the integrated multimodal current waveform and wire feeding drive coordinated control system used in this invention.

[0040] Figure 5 These are the current waveform diagrams of each mode of the integrated multimodal current waveform and wire feeding drive coordinated control system used in this invention. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0042] Example

[0043] This embodiment presents an integrated multimodal current waveform and wire feed drive coordinated control method, such as... Figure 1 As shown. This is achieved based on an integrated multi-modal current waveform and wire feed drive coordinated control system; as... Figure 2 As shown, the integrated multimodal current waveform and wire feed drive coordinated control system includes a human-machine interface, an integrated control circuit, a welding robot, an integrated high-frequency MIG inverter welding machine, and a wire feed motor. The human-machine interface receives user-set parameters and sends them to the integrated control circuit. The integrated control circuit controls the welding robot, the integrated high-frequency MIG inverter welding machine, and the wire feed motor, and also receives their feedback signals. The integrated high-frequency MIG inverter welding machine can also provide sufficient drive power to the wire feed motor.

[0044] Specifically, if Figure 3 As shown, the integrated high-frequency MIG inverter welding machine includes a three-phase rectifier input terminal, a motor drive circuit, a high-frequency pulse modulation circuit, a low-frequency pulse modulation circuit, and a current parallel terminal. The three-phase rectifier input terminal receives three-phase power from the industrial environment and supplies it to the motor drive circuit, the high-frequency pulse modulation circuit, and the low-frequency pulse modulation circuit, respectively. The output terminal of the motor drive circuit is connected to a wire feed motor to drive the welding wire feed. The currents output from the high-frequency pulse modulation circuit and the low-frequency pulse modulation circuit are combined and output from the current parallel terminal. The positive terminal of the current parallel terminal is connected to the welding wire, and the negative terminal is connected to the workpiece, thereby generating an arc-starting voltage between the two terminals. After arc ignition, a current is output for welding operations. The welding wire is loaded inside the welding torch, which is mounted on the end effector of a welding robot. During welding, the welding robot moves its robotic arm, driving the welding torch to move and complete the preset welding operation path.

[0045] like Figure 4As shown, the integrated control circuit of this invention includes a DSC controller, a power supply module, a sampling module, a PWM drive module, a relay module, and a communication module. The DSC controller preferably uses an STM32F405RGT6 chip with an embedded lightweight real-time operating system (FreeRTOS) and an integrated hardware floating-point unit (FPU). The power supply module supplies power to the entire control circuit. The sampling module uses two independent ADCs to acquire the armature voltage and output current of the wire feed motor, respectively. The PWM drive module includes a wire feed drive module, a fast-frequency current drive module, and a low-frequency current drive module; the wire feed drive module is connected to the motor drive circuit in the integrated fast-frequency MIG inverter welder, the fast-frequency current drive module is connected to the fast-frequency pulse modulation circuit in the integrated fast-frequency MIG inverter welder, and the low-frequency current drive module is connected to the low-frequency pulse modulation circuit in the integrated fast-frequency MIG inverter welder. The welding robot is connected to the DSC controller via the relay module, receiving a start signal to begin movement and sending a welding termination signal to stop current output. The human-machine interface is connected to the DSC controller via the communication module, responsible for transmitting welding parameter signals and displaying fault signals sent by the DSC controller.

[0046] like Figure 5 As shown, the integrated multi-modal current waveform and wire feed drive coordinated control system of this invention can output current waveforms in multiple modes. Here, we take the three most commonly modulated current waveforms as examples. The modes of the welding current waveform include: low-frequency pulse mode, which only includes low-frequency pulse current waveforms, such as... Figure 5 The current waveform is shown in Figure 1; it includes the fast-frequency pulse mode of the fast-frequency pulse current waveform, such as... Figure 5 The current waveform is shown in Figure 2; and the fast-frequency single-pulse waveform mode obtained by superimposing the low-frequency pulse current waveform and the fast-frequency current waveform is shown in Figure 2. Figure 5 The current waveform is shown in Figure 3. Furthermore, waveforms with more specific modes can be modulated as needed.

[0047] When the welding current waveform includes a low-frequency pulse current waveform, the current characteristic value includes the peak current I of the low-frequency pulse current waveform. Bp Current base value I Bb Frequency f B and duty cycle D B When the welding current waveform includes a fast-frequency pulse current waveform, the current characteristic value includes the peak current I of the fast-frequency pulse current waveform. D and frequency f D The duty cycle is constant at 50%. Bp >I Bb ;f D >f B .

[0048] Among them, the peak current I Bp Current base value I Bband peak current I D The output duty cycle of the PWM drive module is controlled via a DSC controller; frequency f B Duty cycle D B and frequency f D They are controlled by the TIM3 built into the DSC controller.

[0049] An integrated multimodal current waveform and wire feed drive coordinated control method includes the following steps:

[0050] Step S1: Initialize the welding current waveform and wire feed setting speed, including: setting the mode and current characteristic value of the welding current waveform; after setting, send it to the integrated control circuit through the human-machine interface;

[0051] The set welding current waveform current characteristic value is input into the current waveform-wire feed speed matching model; the current waveform-wire feed speed matching model calculates the average current, and then calculates the set wire feed speed based on the average current and the linear fitting formula;

[0052] Step S2: Based on the set welding current waveform and wire feeding speed, control the actual output welding current waveform and wire feeding speed respectively.

[0053] Step S3: Collect the actual output welding current waveform; input the current characteristic value of the actual output welding current waveform into the current waveform-wire feed speed matching model to calculate the average current, and then calculate the wire feed set speed according to the average current and the linear fitting formula; repeat steps S2 and S3 until welding is completed.

[0054] The average current I is calculated using a current waveform-wire feed speed matching model. avgi And calculate the wire feeding set speed v based on the average current and linear fitting formula. i , which means: i = 1, 2, 3 correspond to low-frequency pulse mode, fast-frequency pulse mode, and fast-frequency single-pulse mode, respectively; the preferred linear fitting formula is a univariate linear regression equation based on the least squares method.

[0055] When the welding current waveform is in a low-frequency pulse mode, the average current I avg1 for:

[0056] I avg1 =I Bp ·D B +I Bb ·(1-D B )

[0057] When the welding current waveform is in the fast pulse mode, the average current I avg2 for:

[0058]

[0059] When the welding current waveform is in the fast-frequency single-pulse mode, the average current I avg3 for:

[0060] I avg3 =I avg1 +I avg2

[0061] Wire feed setting speed v corresponding to various welding current waveforms i ,for:

[0062] v i =K i ·I avgi +b

[0063] Among them, K i b represents the response coefficient; i This represents the bias value.

[0064] Using high-frequency pulsed current increases the arc core temperature and improves the wire melting rate, thus requiring a faster wire feed speed. Its linear slope is significantly higher than that of low-frequency pulsed current, i.e., K2 > K1. Since the high-frequency single-pulse mode includes the high-frequency pulsed current waveform, K3 = K2 can be used.

[0065] Closed-loop control functions are designed for both current modulation and wire feed drive. In step S2, two independent ADCs are used to acquire the actual output welding current waveform and wire feed speed, respectively; the two independent ADCs are triggered by TIM1 and TIM2, respectively. For example, in the closed-loop control process of current modulation, TIM1 triggers ADC1 for acquisition, and in the closed-loop control process of wire feed drive, TIM2 triggers ADC2 for acquisition; wherein TIM2 and TIM1 have different trigger frequencies, and ADC1 and ADC2 are independent of each other.

[0066] An incremental PID algorithm is used to control the actual output welding current waveform and wire feeding speed.

[0067] Among them, using an incremental PID algorithm to control the actual output welding current waveform means:

[0068] The actual output low-frequency pulse current waveform and the actual output high-frequency pulse current waveform are collected separately; the data are smoothed using an extreme value removal and mean filtering algorithm to obtain the peak current I of the actual output low-frequency pulse current waveform. Bp Current base value I Bb and the peak current I of the fast-frequency pulse current waveform DThe current difference value is obtained by comparing it with the current characteristic value corresponding to the set welding current waveform. The current difference value is adjusted by the incremental PID algorithm to adjust the output duty cycle of the PWM drive module, thereby controlling the actual output welding current waveform.

[0069] Using a PID algorithm to control the wire feeding speed means: collecting the actual wire feeding speed, comparing it with the set wire feeding speed to obtain the wire feeding difference value, and then adjusting the actual wire feeding speed by adjusting the incremental PID algorithm based on the wire feeding difference value.

[0070] To improve the user's operating space, fine-tuning settings are set in the human-machine interface, such as fine-tuning knobs. Based on the fine-tuning settings, the wire feeding speed calculated in step S3 is finely adjusted; that is, the wire feeding speed calculated in step S3 is slightly increased or decreased to cope with complex working conditions.

[0071] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. An integrated multi-mode current waveform and wire feed drive coordinated control method, characterized in that: It is implemented based on an integrated multimodal current waveform and wire feed drive coordinated control system; The welding current waveform of the integrated multimodal current waveform and wire feed drive coordinated control system has multiple modes; The modes of welding current waveform include: low-frequency pulse mode which only includes low-frequency pulse current waveform, fast-frequency pulse mode which includes fast-frequency pulse current waveform, and fast-frequency single-pulse mode which is obtained by superimposing low-frequency pulse current waveform and fast-frequency pulse current waveform. An integrated multimodal current waveform and wire feed drive coordinated control method includes the following steps: Step S1: Initialize the welding current waveform and wire feed setting speed, including: setting the mode and current characteristic value of the welding current waveform; inputting the set welding current waveform current characteristic value into the current waveform-wire feed speed matching model; the current waveform-wire feed speed matching model calculates the average current, and then calculates the wire feed setting speed according to the average current and the linear fitting formula. Step S2: Based on the set welding current waveform and wire feeding speed, control the actual output welding current waveform and wire feeding speed respectively. Step S3: Acquire the actual output welding current waveform; input the current characteristic value of the actual output welding current waveform into the current waveform-wire feed speed matching model to calculate the average current, and then calculate the wire feed set speed according to the average current and the linear fitting formula; repeat steps S2 and S3 until welding is completed. In steps S1 and S3, the current characteristic value of the welding current waveform refers to: when the welding current waveform includes a low-frequency pulse current waveform, the current characteristic value includes the peak current I of the low-frequency pulse current waveform. Bp Current base value I Bb Frequency f B and duty cycle D B When the welding current waveform includes a fast-frequency pulse current waveform, the current characteristic value includes the peak current I of the fast-frequency pulse current waveform. D and frequency f D ; The average current I is calculated using a current waveform-wire feed speed matching model. avgi and wire feeding speed v i This means that i = 1, 2, 3 correspond to low-frequency pulse mode, fast-frequency pulse mode, and fast-frequency single-pulse mode, respectively. When the welding current waveform is in a low-frequency pulse mode, the average current I avg1 for: I avg1 =I Bp ·D B +I Bb ·(1-D B ) When the welding current waveform is in the fast pulse mode, the average current I avg2 for: When the welding current waveform is in the fast-frequency single-pulse mode, the average current I avg3 for: I avg3 =I avg1 +I avg2 Wire feed setting speed v corresponding to various welding current waveforms i ,for: v i =K i ·I avgi +b i Among them, K i b represents the response coefficient; i Indicates the bias value; The response coefficient K i In the given information, K2 > K1; K3 = K2.

2. The integrated multi-mode current waveform and wire feed drive coordinated control method according to claim 1, characterized in that: In step S2, the actual output welding current waveform and wire feed speed are controlled by the DSC controller; wherein, the peak current I Bp Current base value I Bb and peak current I D The output duty cycle of the PWM drive module is controlled via a DSC controller; frequency f B Duty cycle D B and frequency f D They are controlled by the TIM3 built into the DSC controller.

3. The integrated multi-mode current waveform and wire feed drive coordinated control method according to claim 2, characterized in that: In step S2, two independent ADCs are used to collect the actual output welding current waveform and wire feeding speed respectively; the two independent ADCs are triggered by TIM1 and TIM2 respectively; and an incremental PID algorithm is used to control the actual output welding current waveform and wire feeding speed.

4. The integrated multi-mode current waveform and wire feed drive coordinated control method according to claim 3, characterized in that: Using an incremental PID algorithm to control the actual output welding current waveform means: The low-frequency pulse current waveform and the high-frequency pulse current waveform of the actual output are collected respectively. The data is smoothed using an extremum removal and mean filtering algorithm, thereby obtaining the actual output low-frequency pulse current waveform and its peak current I. Bp Current base value I Bb and the peak current I of the fast-frequency pulse current waveform D The current difference value is obtained by comparing it with the current characteristic value corresponding to the set welding current waveform. The current difference value is adjusted by the incremental PID algorithm to adjust the output duty cycle of the PWM drive module, thereby controlling the actual output welding current waveform.

5. The integrated multi-mode current waveform and wire feed drive coordinated control method according to claim 3, characterized in that: Using a PID algorithm to control the wire feeding speed means: collecting the actual wire feeding speed, comparing it with the set wire feeding speed to obtain the wire feeding difference value, and then adjusting the actual wire feeding speed by adjusting the wire feeding difference value through an incremental PID algorithm. Set fine-tuning settings in the human-computer interaction interface; fine-tune the wire feeding speed calculated in step S3 according to the fine-tuning settings.

6. The integrated multi-mode current waveform and wire feed drive coordinated control method according to claim 1, characterized in that: The integrated multimodal current waveform and wire feeding drive coordinated control system includes a human-machine interface, an integrated control circuit, a welding robot, an integrated high-frequency MIG inverter welding machine, and a wire feeding motor.

7. The integrated multi-mode current waveform and wire feed drive coordinated control method according to claim 6, characterized in that: The integrated high-frequency MIG inverter welding machine includes a three-phase rectifier input terminal, a motor drive circuit, a high-frequency pulse modulation circuit, a low-frequency pulse modulation circuit, and a current parallel terminal. The three-phase rectifier input terminal receives three-phase power from the industrial environment and supplies it to the motor drive circuit, the high-frequency pulse modulation circuit, and the low-frequency pulse modulation circuit, respectively. The output terminal of the motor drive circuit is connected to a wire feed motor. The currents output from the high-frequency pulse modulation circuit and the low-frequency modulation circuit are combined and output from the current parallel terminal. The positive terminal of the current parallel terminal is connected to the welding wire, and the negative terminal is connected to the workpiece.

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