DC Pulse MIG Welding Machine Control System and Program Control

Literature Overview

The paper by Hang Zhengxiang, Wang Qijun, and Zhang Jingquan (2013, Welder, Vol. 43, No. 10, pp. 10-13), published from Shenyang University of Technology, presents the design and implementation of a DC pulse MIG welding machine control system. The system employs IGBT inverter power technology with a microcontroller-based control architecture. This work is particularly relevant to engineers involved in aluminum welding, where pulse MIG is the dominant process for achieving stable metal transfer, low heat input, and high-quality joints in thin-to-medium thickness sections.

System Architecture and Control Design

The control system comprises four main subsystems: a microcontroller control system, a wire feed control system, an IGBT driver circuit, and a protection circuit. The microcontroller handles welding parameter control and welding program sequencing. The power circuit uses IGBT inverter technology to generate the pulse current waveform required for controlled metal transfer.

The paper describes two control strategies: a two-step control mode and a four-step control mode. The two-step mode is simpler, providing basic pulse-on and pulse-off control suitable for straightforward welding applications. The four-step mode offers more refined control, likely incorporating a pre-pulse, main pulse, background current, and short-circuit phase, which allows for more stable metal transfer and reduced spatter.

The wire feed system employs a semi-closed-loop speed control with a switch circuit, featuring a rapid braking function specifically designed to meet arc-out (crater filling) requirements. This is a critical design consideration: during arc-out, the wire feed must stop quickly to avoid wire protrusion, and the current must be reduced to fill the crater before the arc is extinguished. Poor arc-out control leads to crater cracks and poor restart characteristics, both of which are significant quality concerns in production welding.

Arc-Start, Welding, Crater Filling, and Arc-Out Processes

The paper provides detailed descriptions of four sequential welding processes:

1. Arc-start (ignition): Reliable arc initiation is essential for consistent weld quality. The control system likely employs a high-voltage pulse or increased current to ionize the arc gap and establish stable arc burning. For aluminum welding, arc-start reliability is particularly challenging due to the oxide film (Al2O3) that forms on the aluminum surface, which has a much higher melting point than the base metal.
2. Welding (steady-state): During steady welding, the pulse current parameters (pulse current, background current, pulse frequency, pulse on-time) are controlled to maintain stable short-circuit or spray metal transfer. The wire feed speed is synchronized with the current to maintain constant arc length.
3. Crater filling: Before arc extinction, the current is reduced to a background level to allow the molten pool to solidify in a controlled manner, preventing crater formation. The wire feed speed is also adjusted to ensure proper filler metal deposition in the final section of the weld.
4. Arc-out (extinction): The current is rapidly reduced to zero to extinguish the arc. The wire feed is stopped simultaneously to prevent wire protrusion. The paper emphasizes that good arc-out performance directly determines the reliability of the next arc-start, creating a quality loop where each weld segment's end conditions affect the next segment's beginning.

This quality loop concept is particularly important in multi-pass welding of thick sections, where restart quality at the beginning of each pass influences the overall joint integrity. Engineers should pay close attention to arc-start and arc-out parameters when developing welding procedures for multi-pass applications.

Engineering Practice and Quality Implications

From a quality control perspective, the control system design directly impacts weld quality through several mechanisms. Stable pulse parameters ensure consistent metal transfer, which reduces spatter and porosity. Rapid wire feed braking during arc-out prevents wire protrusion and crater defects. Reliable arc-start ensures proper fusion at weld beginnings, which is a common location for lack-of-fusion defects.

For aluminum welding applications, the pulse MIG process is preferred over continuous current MIG because it allows for lower heat input while maintaining adequate penetration through the pulse energy. The pulse current heats the wire end to a temperature where surface tension forces can expel the droplet, achieving spray transfer without the high currents needed for continuous spray transfer. This results in a narrower weld bead, reduced distortion, and minimal HAZ, all of which are critical for aluminum structures where dimensional stability and corrosion resistance are important.

The IGBT inverter technology described in this paper represents a significant advancement over older thyristor-based power sources. IGBTs offer faster switching speeds, enabling precise pulse waveform control, and higher power density, resulting in more compact and energy-efficient equipment. For production welding cells, these advantages translate to reduced floor space, lower energy consumption, and improved weld quality consistency.

Key Questions and Reflections

One area for further investigation is the adaptability of the two-step and four-step control modes to different welding positions (flat, horizontal, vertical, overhead). The paper focuses on parameter control and program sequencing but does not address position-specific challenges such as gravity effects on the molten pool in vertical or overhead welding. Engineers applying this system to multi-position welding should expect to develop position-specific parameter sets and possibly modified control algorithms.

Another consideration is the integration of this control system with modern digital welding interfaces. Contemporary welding power sources often feature CAN bus or Ethernet connectivity, enabling remote monitoring, data logging, and integration with manufacturing execution systems. The microcontroller-based architecture described here could be upgraded to support such connectivity, providing traceability and quality documentation capabilities that are increasingly required in regulated industries.

Study Insights and Outlook

This paper presents a well-structured approach to pulse MIG welding machine design, emphasizing the importance of coordinated control between the power source, wire feed, and program sequencing. The focus on arc-start and arc-out quality as determinants of overall weld quality reflects a practical engineering philosophy that prioritizes process reliability over peak performance. For engineers developing or upgrading welding equipment, the key takeaways are: invest in robust arc-start and arc-out control, ensure wire feed braking capability for clean arc extinction, and provide flexible program control modes to accommodate different welding applications. As welding technology continues to evolve toward higher levels of automation and digital integration, the fundamental principles of pulse MIG control described in this study remain relevant and form the technical foundation upon which more advanced systems are built.