With the development of the times and the demand for lightweight products, thin plates, especially aluminum alloy sheets, are widely used in manufacturing processes, often requiring arc welding of thin plates. The most common quality issue when welding thin plates is sagging of the weld pool. Therefore, it is necessary to research welding processes that are fast and shallow, ensuring stable welding quality while improving welding efficiency.

While Tungsten Inert Gas (TIG) welding can be used for thin plates, it is characterized by low welding speed and significant deformation. Alternating Current Pulse Melted Pole Arc Welding (AC PMIG) arc consists of EP polarity and EN polarity, which can be seen as alternating between DCEP PMIG arc and DCEN MIG arc. The arc force and arc heat of AC PMIG are between DCEP PMIG and DCEN MIG, with the weld penetration depth being between the two, and the maximum weld penetration depth is that of DCEP PMIG. Additionally, when welding thin plates, the welding current is small, the arc stiffness is weak, and the arc is easily affected by arc blow. AC PMIG arc can overcome the arc blow of DC arc, which is beneficial for stabilizing the welding process.

I. Composition of AC PMIG Arc Welding Power Source: The arc welding power source is composed using a full-bridge full-wave method. The composition of the arc welding power source is as shown in the figure below:

The inverter arc welding power source utilizes IGBT power devices to convert 50/60Hz mains frequency to high frequency (above 20KHz), followed by voltage reduction rectification. Through pulse width modulation (PWM) technology, a high-power DC source is outputted. EP polarity and EN polarity are switched using high-power IGBT modules, ensuring fast response and precise control.

II. Performance Indicators:

  1. Intelligent Control Technology: Utilizes MCU to achieve a hybrid or alternate combination of voltage outer loop control electronic reactance and constant current (CC) / constant voltage (CV) characteristics, as well as the conversion between EP polarity and EN polarity. During low-current welding, the output of the welding equipment is controlled by software to achieve energy transfer and reduce heat input.
  2. Software Control Technology: Establishes a welding expert system for different wire materials and diameters. Utilizes unified, no individual adjustment technology. Undertakes all control and operational functions related to the power source characteristics: current PI required for melting pole arc power characteristics, voltage PI, inertial link between voltage PI and current PI (algorithm limiting short-circuit current rise rate at welding power source output), and various processing during welding.
  3. Accurate Wire Feeding Speed Control: Uses DC42V/24M speed motors to monitor the wire feeding speed in real-time, ensuring precise and smooth wire feeding. Utilizes CPU-controlled speed motors to ensure rapid response.

III. Output of AC PMIG Arc Welding Power Source: To address the issues of weak and poorly directed arc during EN polarity, pulse current is added to the output of the arc welding power source. The output waveforms are as shown in the figures below:

  1. Power Output: Current 100A, Arc Voltage 11.5V. Output waveform as shown below:
  1. Power Output: Current 200A, Arc Voltage 23V. Output waveform as shown below:

IV. Conclusion:

  1. The circuit of the AC PMIG arc welding power source adopts a dual inverter structure, and the control system adopts a dual closed-loop control structure, meeting the requirements of welding process control.
  2. Based on the deviation signal of the AC PMIG arc voltage and the arc state, corresponding control rules and control parameter calculation methods are designed. Frequency control of AC pulse frequency is performed during normal welding states, with corresponding control rules in interference states. Welding experiments show that the welding process has strong stability and anti-interference ability.

The above discussion is on the AC PMIG arc welding power source. Any differences or corrections are welcomed. Thank you!

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