CLADDING TECHNOLOGY SHANXI CO., LTDMicrocomputer-Controlled Pulse MIG Arc Starting and Arc Ending Research
Literature Overview
The paper by Gang Tie, Yin Shuyan, Wang Kehong, and Huang Zanzhi (1992), from Harbin Institute of Technology, Huazhong Institute of Technology, and Mudanjiang Radio Factory No. 6, addresses a fundamental but often neglected aspect of pulse MIG welding: the arc starting and arc ending sequences. The study develops a microcomputer-controlled system for precisely managing the transient phases at the beginning and end of each welding cycle, ensuring stable arc ignition, consistent weld initiation, and defect-free weld termination. This work represents an early contribution to the automation and digital control of welding processes, laying groundwork for modern CNC welding systems.
Core Technical Content
The arc starting sequence in pulse MIG welding involves establishing a stable arc from a non-ignited state, which requires careful management of the current ramp-up, wire feed initiation, and gas flow activation. The arc ending sequence must ensure complete solidification of the weld pool without crater cracking, undercut, or porosity. The study proposes the following control sequence:
| Phase | Control Action | Duration | Purpose |
|---|---|---|---|
| Pre-gas Flow | Activate shielding gas | 1–3 seconds before arc strike | Protect electrode and weld pool |
| Current Ramp-Up | Gradually increase current from zero | 0.5–2 seconds | Prevent arc blow and spatter |
| Wire Feed Initiation | Start wire feed at welding speed | Simultaneous with current ramp | Maintain constant electrode extension |
| Pulse Cycle Establishment | Transition to normal pulse waveform | After arc stabilization | Achieve stable droplet transfer |
| Pulse Termination | Cease pulsing, maintain background current | 0.5–2 seconds | Allow final droplet transfer |
| Current Ramp-Down | Gradually reduce current to zero | 1–3 seconds | Prevent crater cracking |
| Post-gas Flow | Continue shielding gas | 2–5 seconds after arc extinction | Protect solidifying weld pool |
The microcomputer system coordinates these actions with millisecond-level precision, ensuring that the timing relationships between current, wire feed, and gas flow are maintained consistently throughout the welding cycle.
Interpretation of Technical Points
The study highlights several critical aspects of arc starting and ending that are often overlooked in process development. During arc starting, the initial current must be sufficient to ionize the shielding gas and establish a stable arc, but not so high as to cause excessive spatter or electrode burning. The current ramp-up rate must be controlled to prevent arc instability and ensure smooth transition to the pulse waveform. Similarly, during arc ending, the current must be reduced gradually to allow the weld pool to solidify uniformly, preventing the formation of shrinkage craters that can act as crack initiation sites.
The paper also discusses the importance of wire feed speed synchronization during the transient phases. During arc starting, the wire feed speed must be adjusted to match the increased electrode extension caused by the initial arc heating, preventing short-circuiting. During arc ending, the wire feed must be stopped at the appropriate time to prevent excess filler metal deposition at the weld terminus, which can result in a raised, uneven weld toe.
Integration with Engineering Practice
In modern welding automation systems, the arc starting and ending sequences are critical for ensuring consistent weld quality, particularly in multi-pass welding operations where each pass begins and ends at different locations. For pressure vessel fabrication, the quality of the weld initiation and termination is especially important, as these regions are prone to defects that can compromise the structural integrity of the weld. The microcomputer-controlled approach described in this study is the precursor to modern welding controllers that integrate arc sensing, wire feed control, and gas flow management into a unified control system.
In cladding applications, where multiple overlay layers are deposited sequentially, the arc starting and ending quality of each layer directly affects the bond strength and surface quality of the overlay. Poor arc termination can result in surface irregularities that affect the subsequent layer's deposition quality, while inadequate arc starting can lead to incomplete fusion at the layer interface. The study's emphasis on precise control of these transient phases is therefore directly relevant to cladding process optimization.
Key Questions and Reflections
A key question is how the arc starting and ending sequences should be adapted for different material systems. For example, welding thin-section austenitic stainless steel requires a more gradual current ramp-up and longer post-gas flow to minimize thermal distortion and prevent sensitization. Similarly, welding high-alloy materials such as Inconel 625 or Hastelloy C276 may require modified sequences due to their different arc characteristics and solidification behavior. The study's framework provides a starting point for developing material-specific arc control sequences, but further investigation is needed for each material system.
Another reflection concerns the evolution from microcomputer-controlled systems to modern PLC-based and real-time control systems. The principles established in this 1992 study — precise timing, coordinated control of current, wire feed, and gas flow — remain fundamental to modern welding automation, but the implementation technology has advanced significantly. Modern systems offer faster response times, more sophisticated algorithms, and greater flexibility in adapting to varying welding conditions.
Study Insights and Implications
This paper makes an important contribution to the understanding of welding process control, particularly in the area of transient phase management. The microcomputer-controlled approach demonstrated in the study represents a significant advancement over manual or semi-automated control methods, enabling consistent and repeatable weld initiation and termination. For engineers working in cladding, bimetal fabrication, and pressure vessel manufacturing, the study's findings underscore the importance of attention to detail in all phases of the welding cycle, not just the steady-state welding phase. The principles of precise timing, coordinated parameter control, and systematic sequence design are directly transferable to modern welding automation systems and should be incorporated into process development and quality assurance procedures.