CLADDING TECHNOLOGY SHANXI CO., LTDComparison of Pulsed MIG Welding Process for Different Median Current
Literature Overview
The paper published in China Welding (2009) by Wen Yuanmei, Xue Jiaxiang, Yao Ping, and Huang Shisheng from Guangdong University of Technology and South China University of Technology investigates the influence of median current settings on the pulsed metal inert gas (MIG) welding process. The research was supported by the National Natural Science Foundation of China (Grant Nos. 50575074 and 50875088) and the Guangdong Science Foundation (Grant No. 07006479). The study addresses a fundamental parameter selection problem in pulsed MIG welding — how the choice of median current affects welding stability, metal transfer mode, weld geometry, and ultimately joint quality.
Core Technical Content
In pulsed MIG welding, the current waveform consists of a peak current pulse and a background (median) current that flows between pulses. The median current serves a dual purpose: it maintains the arc stability between pulses and contributes to the overall heat input into the weld pool. The authors systematically compared welding results obtained at different median current levels while keeping other parameters (welding speed, wire diameter, shielding gas composition, and pulse frequency) relatively constant.
The key findings revolve around several interdependent phenomena:
- Arc stability: Lower median currents may cause arc interruption between pulses, leading to spatter and irregular bead profiles. Higher median currents stabilize the arc but increase heat input, potentially causing excessive penetration or burn-through on thin sections.
- Metal transfer mode: The median current determines whether the process operates in the stable pulse transfer regime or transitions toward short-circuiting or globular transfer. The critical threshold depends on the wire diameter, gas composition, and electrical characteristics of the power source.
- Weld pool dynamics: Higher median currents increase the weld pool volume and fluidity, which affects solidification pattern, grain orientation, and susceptibility to solidification cracking.
- Deposition efficiency: The ratio of pulse current contribution to total heat input changes with median current level, directly impacting deposition rate and dilution — a critical parameter in cladding and weld overlay applications.
Technical Parameters and Process Windows
| Parameter | Typical Range | Effect of Variation |
|---|---|---|
| Median current | 80–200 A (for 1.0 mm wire) | Arc stability, heat input, transfer mode |
| Peak current | 180–400 A | Single droplet transfer, penetration depth |
| Pulse frequency | 80–300 Hz | Transfer stability, spatter level |
| Wire feed speed | 4–12 m/min | Deposition rate, bead width |
| Welding speed | 200–800 mm/min | Travel speed vs. heat input balance |
| Shielding gas | Ar/CO₂ mixtures | Arc force, wetting, transfer characteristics |
Interpretation of Technical Points
The study highlights that the median current is not merely a "filler" between pulses but a process variable that fundamentally alters the welding physics. From an engineering perspective, this has direct implications for weld overlay applications where dilution control is paramount. In cladding operations — such as depositing stainless steel or nickel-based alloy layers on carbon steel substrates — excessive dilution from high median currents can compromise the corrosion resistance of the overlay layer. Conversely, too low a median current may result in poor bond strength and incomplete fusion at the overlay-substrate interface.
The authors also discuss the interaction between median current and the electrical characteristics of the welding power source. Different power source types (conventional transformer, inverter-based, and digital control) exhibit varying inductance values, which affect the current rise and decay rates during each pulse cycle. This means that the optimal median current setting is not universal but depends on the specific power source configuration.
Integration with Engineering Practice
In my experience with weld overlay cladding for pressure vessels and heat exchangers, the median current parameter is often underappreciated by welders and quality engineers. The standard practice in many fabrication shops is to focus on peak current and pulse frequency while treating the median current as a secondary adjustment. However, the literature demonstrates that median current directly influences:
- Dilution control in multi-layer cladding: For a typical 316L stainless steel overlay on SA-516 Gr.70 carbon steel, the dilution in the first layer can range from 15% to 40% depending on heat input. The median current is a primary lever for managing this dilution without compromising arc stability.
- Crack sensitivity management: In overlay deposits of Inconel 625 or Hastelloy C-276, solidification cracking is a persistent concern. Lower median currents reduce the weld pool volume and cooling rate asymmetry, potentially reducing crack susceptibility.
- Bond strength assurance: The fusion zone microstructure, which governs bond strength between the overlay and base metal, is significantly affected by the thermal cycle — and thus by the median current level.
For engineers involved in NB/T 47014 welding procedure qualification, the median current should be explicitly documented and controlled within the qualified WPS. The procedure qualification test should include verification of dilution levels at the qualified median current setting to ensure that the overlay composition meets the required corrosion resistance specifications.
Key Questions and Reflections
A critical question arising from this work is whether the optimal median current can be predicted analytically or whether empirical testing remains the only reliable approach. The complex interactions between arc physics, metal transfer, and weld pool behavior suggest that empirical optimization — guided by the principles outlined in this literature — remains the most practical approach for production environments.
Another reflection is the relationship between median current and the emerging technology of hot-wire TIG (HWT) overlay, where the hot wire acts as an additional heat source. In HWT, the concept of a "median current" is replaced by the wire preheating temperature, but the underlying principle — controlling heat input between primary energy events to optimize dilution and bond strength — remains analogous.
Study Insights and Implications
This literature provides a foundational understanding of how the median current parameter shapes the pulsed MIG welding process. For engineers in the cladding and bimetal fabrication industry, the key takeaway is that median current must be treated as a primary process variable rather than a secondary adjustment. The systematic approach advocated by the authors — varying one parameter while controlling others — should be adopted in welding procedure development and qualification testing.
The implications extend beyond conventional welding to advanced overlay processes. As the industry moves toward higher-performance cladding applications — such as hydrogenation reactor liners and high-purity nickel overlay for nuclear applications — the precise control of dilution and bond quality becomes increasingly critical. The median current parameter, as demonstrated in this study, is one of the most effective levers available for achieving the required metallurgical control. Engineers should incorporate median current optimization into their standard procedure development protocols and ensure that production welders receive adequate training on its significance.