Zhuojin Pipe Fitting Co., LtdDevelopment of a Microcomputer Control System for Pulse MIG Welding
Literature Overview
This paper, authored by Liu Huijie, Zhang Jiuhai, and Bai Fuping from Harbin Institute of Technology and published in the journal Hansheng (Welding) in 1993, presents the development of a microcomputer-based control system for pulse MIG welding. The work was classified under TG409, reflecting its focus on welding process control methodology. At the time of publication, microcomputer-based control represented a frontier advancement in welding automation, moving beyond conventional relay logic and analog circuit controllers toward programmable, flexible, and intelligent process regulation.
Core Technical Content
The system achieves three principal control functions:
- Coordinated control (协同控制): Synchronization between wire feed speed, pulse frequency, and arc voltage to maintain stable arc conditions throughout the welding sequence.
- One-drop-per-pulse transfer (一脉一滴过渡): Ensuring that each current pulse produces exactly one metal droplet transfer event, which is critical for minimizing spatter, achieving consistent bead geometry, and reducing porosity formation.
- Arc length control: Real-time regulation of the electrode-to-workpiece distance to maintain a constant arc length despite fluctuations in wire feed rate or workpiece geometry.
The authors emphasize that the system possesses operational simplicity and strong adaptability, meaning it can be applied across different welding positions, joint configurations, and material thicknesses without extensive reprogramming.
Technical Analysis and Engineering Significance
The transition from analog to microcomputer control in pulse MIG welding in the early 1990s was a pivotal development. Analog controllers suffered from limited parameter adjustment ranges, poor repeatability, and inability to implement complex multi-variable control algorithms. The microcomputer approach enabled:
| Control Parameter | Analog Control Limitation | Microcomputer Advantage |
|---|---|---|
| Pulse frequency | Fixed or stepped adjustment | Continuous, programmable variation |
| Base current | Single setpoint | Multi-stage profiles per weld pass |
| Peak current | Open-loop or simple feedback | Closed-loop with droplet sensing |
| Wire feed speed | Gear-motor coupling | Servo-driven with real-time correction |
| Arc length | Contact sensing or voltage feedback | Integrated multi-sensor fusion |
The one-drop-per-pulse transfer mode is particularly important because it directly governs the thermal input per unit length. When more than one droplet transfers per pulse, the heat input increases unpredictably, leading to excessive penetration, burn-through in thin sections, or poor fusion in thicker sections. The microcomputer system's ability to precisely time the current pulse relative to the droplet detachment moment is what enables this deterministic transfer behavior.
Process Parameter Considerations
For pulse MIG welding of carbon steel and low-alloy steel pipes, typical parameter windows include:
| Parameter | Typical Range | Notes |
|---|---|---|
| Pulse frequency | 50–200 Hz | Higher frequency for thinner materials |
| Peak current | 200–400 A | Depends on wire diameter |
| Base current | 80–150 A | Maintains arc between pulses |
| Wire diameter | 0.8–1.2 mm | 0.8 mm for thin-gauge pipe |
| Wire feed speed | 4–12 m/min | Correlated with current settings |
| Shielding gas | 80% Ar + 20% CO₂ | Typical for mild steel |
Engineering Practice Integration
In pipe welding applications, particularly for ERW and HFW welded pipe repair welding, pulse MIG welding offers significant advantages over conventional short-arc MIG. The reduced heat input minimizes distortion in thin-walled pipe sections, while the stable transfer mode reduces the risk of lack of fusion and internal porosity. The microcomputer control system described in this paper represents an early but foundational step toward the adaptive and intelligent welding control systems that are now standard in automated pipe welding stations.
The concept of coordinated control is directly applicable to modern robotic welding cells where multiple parameters must be adjusted simultaneously in response to seam tracking feedback. The principles established in this 1993 work—flexible programmable control, one-to-one pulse-droplet correspondence, and closed-loop arc length regulation—remain the theoretical foundation of contemporary pulse MIG welding controllers used in the oil and gas pipeline industry today.
Study Insights
This paper is historically significant because it documents the transition from hardware-defined to software-defined welding control. The emphasis on "operational simplicity and strong adaptability" foreshadows the user-friendly programming interfaces and multi-parameter adaptive strategies that characterize modern welding power sources. For engineers working on pipe welding quality improvement, the key takeaway is that the stability of metal transfer mode is not merely a process parameter but a control objective that must be actively managed through real-time feedback systems. The microcomputer approach demonstrated here proved that such management was technically feasible with the computing resources available in the early 1990s, opening the door to increasingly sophisticated process control in subsequent decades.