Microcomputer-Controlled Pulsed MIG Arc Starting and Arc Ending Study

Literature Overview

The paper published in Hansolder (Welding) in 1992 by Gang Tie, Yin Shuyan, Wang Kehong, and Huang Zanzhi investigates the arc starting and arc ending mechanisms in microcomputer-controlled pulsed MIG welding (MC-PMIG) systems. The authors, affiliated with Harbin Institute of Technology, Huazhong Institute of Technology, and Mudanjiang Radio No. 6 Factory, systematically compared the arc starting behavior of MC-PMIG welders against conventional CO₂ gas-shielded arc welding machines. The study is particularly significant because it addresses a practical bottleneck in automated pulsed MIG welding—the reliability of arc initiation and termination—which directly affects production efficiency and weld quality in high-volume manufacturing environments.

Core Technical Analysis

Arc Starting Mechanism

The authors identified that the arc starting success rate in MC-PMIG welding depends on two critical factors: (1) the appropriateness of the breakout point after contact short-circuit, and (2) the regulation process from arc ignition to steady-state operation. This is a fundamentally different challenge from conventional CO₂ welding, where the arc starting is relatively straightforward due to the simpler current waveform and less demanding process control requirements.

In conventional CO₂ welding, the arc starting process relies primarily on the contact resistance heating and subsequent short-circuit breakout. The arc stabilizes quickly because the current waveform is relatively simple—typically a constant current or constant voltage output. However, in MC-PMIG welding, the pulsed current waveform introduces additional complexity. The transition from the initial short-circuit breakout to the first pulse cycle must be managed precisely to avoid arc blowout or unstable transfer during the critical first few milliseconds of arc establishment.

The microcomputer control system plays a pivotal role here. Unlike analog control circuits, the microcomputer can dynamically adjust the pulse parameters—including pulse current magnitude, base current level, pulse frequency, and pulse duration—during the transient arc starting phase. This adaptability allows the system to compensate for variations in contact resistance, wire feed speed, and shielding gas conditions that would otherwise cause arc failure.

Two Methods for Improving Arc Starting Success Rate

The authors proposed two methods to achieve an arc starting success rate exceeding 94%:

1. Optimized breakout point control: By carefully managing the contact resistance heating phase and the timing of wire retraction after short-circuit, the system ensures that the breakout occurs at an optimal moment when sufficient arc energy is available to sustain the arc.
2. Transient regulation process optimization: The microcomputer implements a tailored current regulation strategy during the transition from arc ignition to steady-state pulsed operation. This involves gradually ramping up the pulse parameters rather than abruptly switching to full pulse amplitude, thereby preventing arc instability during the critical first cycle.

Arc Ending Method

A novel arc ending method was proposed specifically tailored to the characteristics of MC-PMIG welding. The key finding from the experiments was that the post-weld wire end exhibited a sharp, pointed shape characteristic of spray transfer (spray droplet transfer). This indicates that the arc ending method successfully maintained the spray transfer regime throughout the entire welding process, including the termination phase. The sharp wire end is a positive indicator because it suggests that the last few pulses were delivered with sufficient energy to maintain proper droplet transfer, avoiding the globular transfer that would leave a rounded, oversized wire end and potentially cause crater defects.

Engineering Practice Implications

For engineers working with automated pulsed MIG welding systems, several practical lessons emerge from this study. First, the arc starting and ending phases—often considered minor details in welding process design—can significantly impact overall process reliability. In high-production environments where thousands of welds are produced daily, even a 1-2% reduction in arc starting success rate translates to hundreds of defective joints requiring rework. Second, the microcomputer control approach demonstrates that real-time adaptive control is essential for maintaining stable pulsed transfer throughout the entire weld cycle, including the transient phases.

The study also highlights an important principle: the arc ending method should be designed to maintain the desired transfer mode until the very end of the weld. If the pulse parameters are abruptly changed during arc termination, the transfer mode may shift to globular or short-circuit transfer, leading to crater porosity, undercut, or other terminal defects. The proposed method avoids this by maintaining spray transfer characteristics throughout, as evidenced by the sharp wire end morphology.

Key Reflections

The 1992 publication predates modern welding power sources by more than three decades, yet its fundamental insights remain highly relevant. Contemporary pulsed MIG welding systems—whether for aluminum, stainless steel, or carbon steel—still rely on microcomputer-based (or microprocessor-based) control for managing arc starting and ending transients. The 94% success rate achieved in this study would be considered a baseline requirement in modern automated welding, where expectations are typically 98-99% or higher.

One area where this study could be further extended is the investigation of arc starting behavior under varying environmental conditions—such as wind, ambient temperature, and humidity. In outdoor or poorly controlled workshop environments, arc starting reliability can degrade significantly. The microcomputer control strategy could potentially incorporate sensor feedback (e.g., arc voltage monitoring) to adaptively adjust the starting parameters in real time.

Another reflection concerns the applicability of these findings to other pulsed welding processes, such as pulsed GMAW with different shielding gases (Ar/He mixtures for aluminum, Ar/CO₂ mixtures for steel). The fundamental principles of transient control during arc starting and ending should transfer across process variants, though the specific parameter windows would differ based on the gas composition and material being welded.

Summary

This 1992 study by Gang Tie and colleagues represents a foundational contribution to the understanding of arc starting and ending dynamics in microcomputer-controlled pulsed MIG welding. The identification of two critical factors—breakout point appropriateness and transient regulation process—provides a clear framework for optimizing arc initiation reliability. The proposed methods achieving over 94% arc starting success rate and the novel arc ending technique that maintains spray transfer throughout the weld cycle offer practical solutions that remain relevant to modern automated welding applications. For engineers designing or troubleshooting pulsed MIG welding systems, this paper reinforces the importance of treating arc transients as first-class process variables rather than afterthoughts, and demonstrates that microcomputer-based adaptive control is the key to achieving high-reliability automated welding.