STM32-Based Integrated Dual-Wire Pulsed MIG Welding Power Supply System Design

Literature Overview

This paper by Wu Kaiyuan, Zhang Tao, He Zuowei, and Li Huajia from the School of Mechanical and Automotive Engineering at South China University of Technology presents the design and implementation of an integrated dual-wire pulsed MIG welding power supply system based on STM32 microcontroller architecture. Published in 2015 in the Welding Journal (焊接学报), this work represents a significant advancement in welding power source technology, particularly for high-productivity applications requiring dual-wire processes such as tandem GMAW and spray transfer welding configurations.

The research was supported by multiple funding sources including the National Natural Science Foundation of China (51205136), the Ministry of Education Doctoral Program (20100172120003), and the Guangdong Provincial Science and Technology Department collaborative project (2013B091500082), reflecting its importance in advancing Chinese welding technology capabilities.

Technical Background and Motivation

Dual-wire MIG welding (also known as tandem GMAW or dual-wire spray transfer) has gained increasing attention in heavy industrial applications including shipbuilding, pressure vessel fabrication, and structural steel construction. The key advantages include:

• Deposition rates of 15-25 kg/h compared to 5-8 kg/h for single-wire processes
• Improved weld bead geometry with reduced dilution
• Enhanced arc stability through dual-arc interaction
• Better control of heat input and penetration profile

However, dual-wire welding demands sophisticated power supply control to maintain independent arc stability for each wire while coordinating the interaction between the two arcs. Conventional welding power supplies with analog control circuits struggle to provide the dynamic response and precise current waveform control required for optimal dual-wire operation.

System Architecture

Hardware Design

The system employs a modular architecture centered around the STM32F4 series microcontroller (ARM Cortex-M4 core, 168 MHz). The hardware consists of:

The dual-channel design allows independent control of each wire's current waveform while maintaining synchronization through the central microcontroller. Each channel includes a dedicated buck converter for welding current regulation, with switching frequencies in the range of 20-40 kHz for the main power stage and 1-10 kHz for the pulse modulation.

Software Architecture

The firmware implements a layered control architecture:

1. Real-time control layer (10 μs cycle): Current loop regulation, pulse timing, arc voltage regulation
2. Process control layer (100 μs cycle): Pulse parameter adjustment, wire feed speed control, transfer mode optimization
3. Monitoring layer (1 ms cycle): Signal acquisition, data logging, fault detection
4. User interface layer (10 ms cycle): Parameter display, alarm management, communication

The pulsed current waveform is generated using a combination of carrier modulation and pulse envelope control. The STM32's hardware timers provide precise timing for pulse-on and pulse-off periods, while the ADC sampling at 1 MHz enables rapid feedback correction.

Pulsed Current Waveform Design

The core innovation lies in the pulsed current waveform design for dual-wire operation. Unlike single-wire pulsed MIG where one arc must be maintained throughout the pulse cycle, dual-wire operation allows one wire to be in its pulse-off period while the other maintains the arc, effectively providing continuous arc energy with periodic high-current pulses.

This phase-shifted arrangement ensures that at least one wire is always in its high-current pulse phase, maintaining stable arc energy input while the other wire transitions smoothly between base and pulse currents. The result is a more stable arc with reduced spatter and improved droplet transfer characteristics.

Performance Characteristics

Dynamic Response

The STM32-based system achieves current regulation response times of less than 50 μs, compared to 200-500 μs for conventional analog controllers. This rapid response is critical for maintaining arc stability during the rapid transitions between base and pulse currents in pulsed operation.

Efficiency and Power Factor

The system achieves:

• Power conversion efficiency: 88-92% at rated output
• Input power factor: >0.95 with PFC circuit
• Short-circuit current limit: Adjustable from 50-200 A
• Current ripple: <5% of set value

Welding Performance

For carbon steel S355JR with ER50-6 wire at 1.2 mm diameter:

Applications in Bimetal and Cladding Fabrication

While this power supply was designed for general dual-wire MIG applications, the technology has direct relevance to cladding and overlay welding operations:

• Multi-pass overlay welding: The high deposition rate reduces the number of passes required for thick overlay layers, minimizing heat input to the base metal and reducing dilution
• Dissimilar metal overlay: The precise current control enables better control of dilution when welding nickel-based alloys onto carbon steel substrates
• Hot-wire TIG hybrid: The pulsed current capability can be adapted for hot-wire TIG processes used in cladding applications
• Repair welding: Rapid deposition with controlled dilution is valuable for repairing corroded or worn overlay surfaces

Quality Control Integration

The integrated system includes built-in monitoring capabilities that support welding quality assurance:

1. Arc voltage monitoring: Detects arc interruptions and unstable transfer conditions
2. Current waveform analysis: Identifies abnormal transfer modes (globular instead of spray)
3. Wire feed speed verification: Ensures consistency between set and actual feed rates
4. Power supply health monitoring: Tracks component degradation over time

These monitoring capabilities align with the requirements of welding procedure qualification standards (NB/T 47014, ASME IX) by providing documented evidence of process parameter control throughout the welding operation.

Key Questions and Reflections

Several technical questions arise from this work. First, the long-term reliability of the IGBT modules under the high-duty-cycle conditions of dual-wire welding requires extended testing. Second, the electromagnetic interference between the two power channels, particularly at high pulse frequencies, needs careful evaluation. Third, the scalability of this architecture to higher power levels (above 600 A per channel) for heavy plate applications is an open question.

From a practical engineering perspective, the integration of digital control with welding power supplies represents a paradigm shift from the analog era. The advantages are clear in terms of flexibility, programmability, and diagnostic capability. However, the complexity of the software introduces new failure modes that must be addressed through rigorous testing and validation protocols.

Study Insights and Implications

This research demonstrates that modern microcontroller technology can be effectively applied to welding power supply design, enabling capabilities that were previously unavailable with analog controllers. For the cladding and bimetal fabrication industry, the implications are significant: precise control of dilution ratios through optimized pulse parameters, improved deposition rates reducing production costs, and built-in quality monitoring supporting compliance with fabrication standards.

The work also highlights the importance of system integration. The welding power supply is not an isolated component but must be considered as part of a complete welding system including wire feeders, torch systems, and process monitoring. The STM32-based architecture provides a platform for future integration with robotic systems, automated monitoring, and digital manufacturing workflows.