IGBT Dual-Inverter Square Wave AC TIG Welding Machine

Literature Overview

The research by Liu Guiqiu, Hang Zhengxiang, and Wang Hui from Shenyang University of Technology and Liaoyang Petrochemical Specialized School (1997) presents the design and development of an IGBT-based dual-inverter square wave AC TIG welding machine. This work addresses a critical need in aluminum and magnesium alloy welding—processes that are fundamental to the fabrication of lightweight pressure vessels, heat exchangers, and bimetal products involving non-ferrous materials.

Core Technical Principles

Conventional AC TIG welding machines used sine wave alternating current, which presents several limitations for aluminum welding applications:

• The sinusoidal waveform provides insufficient arc cleaning action on the oxide film during the negative half-cycle
• Current zero-crossings cause frequent arc restrikes, leading to unstable arc behavior
• The peak-to-average current ratio is fixed, limiting process flexibility

The IGBT dual-inverter topology with square wave output addresses these limitations by:

1. Providing a controllable negative-to-positive time ratio for optimizing oxide cleaning versus penetration
2. Enabling independent adjustment of peak current amplitude and duration in each half-cycle
3. Eliminating the current zero-crossing problem through the square wave waveform shape
4. Allowing dynamic adjustment of parameters during the welding process

Technical Architecture and Key Parameters

The dual-inverter configuration employs two separate inverter bridges operating in complementary phases, with IGBT (Insulated Gate Bipolar Transistor) modules as the switching elements. This architecture provides superior control authority compared to conventional thyristor-based inverters, enabling faster response times and more precise waveform shaping.

Engineering Significance for Bimetal and Cladding Applications

The square wave AC TIG welding machine developed in this research has direct applications in several areas of bimetal manufacturing:

Copper-Steel Cladding: AC TIG welding with controlled negative half-cycle parameters enables effective oxide removal on both copper and steel surfaces, facilitating strong metallurgical bonds in copper/steel bimetal products used in marine heat exchangers and electrical equipment.

Titanium Welding: The precise control of arc energy and cleaning action provided by square wave AC is essential for titanium and titanium alloy welding, where oxide contamination must be rigorously controlled to maintain material integrity in titanium/steel clad structures.

Zirconium Component Fabrication: In nuclear industry applications, zirconium components require welding under extremely strict contamination control. The stable arc characteristics of square wave AC TIG welding reduce the risk of arc wandering and incomplete oxide removal.

Process Optimization for Overlay Applications

For overlay welding applications, the square wave AC TIG power source offers several advantages:

• Dilution control: By adjusting the positive half-cycle parameters, the heat input to the base metal can be reduced, minimizing dilution of the overlay material and preserving its alloy composition
• Bead profile control: The negative half-cycle duration and amplitude directly influence bead width and reinforcement, enabling precise control of overlay layer geometry
• Cracking resistance: Reduced heat input per pass decreases the thermal gradient at the overlay-base metal interface, lowering the risk of hot cracking in nickel-based alloy overlays
• Arc cleaning enhancement: The intensified negative half-cycle provides superior oxide film removal, which is critical for maintaining clean weld beads in multi-pass overlay sequences

Quality Control Implications

The implementation of IGBT-based square wave AC TIG welding in production environments requires careful attention to:

1. Parameter stability verification: The switching frequency and dead time settings must be validated to ensure consistent waveform output throughout the welding cycle
2. Thermal management: High-frequency switching generates significant heat in the power electronics, requiring robust cooling systems to maintain reliable operation during extended production runs
3. Electromagnetic compatibility: The high-frequency switching can interfere with nearby sensitive instrumentation, requiring proper shielding and grounding
4. Component reliability: IGBT modules have finite switching cycles and must be monitored for degradation, particularly in high-duty-cycle production environments

Study Insights

The 1997 publication of this work coincided with the rapid advancement of power electronics technology, where IGBT devices were transitioning from high-voltage power transmission applications to industrial welding power sources. The dual-inverter topology represents a significant architectural innovation that decouples the waveform generation process from the main power conversion, enabling unprecedented control flexibility.

For engineers working in pressure vessel fabrication, the availability of programmable AC TIG power sources has expanded the range of materials and configurations that can be reliably welded. The ability to independently control oxide cleaning and penetration parameters is particularly valuable when fabricating clad vessels containing aluminum or magnesium alloy components, or when performing repair welding on non-ferrous alloy overlays.

The principles established in this research—precise waveform control, dynamic parameter adjustment, and efficient power conversion—remain foundational to modern welding power source design and continue to influence the development of advanced automated welding systems for demanding industrial applications.