Plasma MIG Hybrid Welding Heat Source Model Based on Arc Deflection

Literature Overview

This 2021 publication by Huang Jiming and Jin Cheng from Dalian Jiaotong University presents a numerical heat source model for plasma-MIG hybrid welding that accounts for the arc deflection phenomenon. The work addresses a critical gap in welding simulation methodology by incorporating the electromagnetic force-induced arc distortion that occurs when plasma and GMAW arcs interact in a hybrid configuration. This research has direct relevance to engineers designing hybrid welding processes for cladding thick-section components, particularly where high deposition rates and deep penetration are simultaneously required.

Core Technical Content

The hybrid plasma-MIG welding process combines two distinct heat sources: a transferred plasma arc providing deep, narrow penetration and a GMAW arc providing wide, shallow reinforcement. The interaction between these two arcs creates complex electromagnetic and fluid dynamic phenomena that significantly affect the weld geometry and thermal cycle.

Heat Source Model Components

Component	Description	Mathematical Representation
Plasma arc heat flux	Gaussian or double-elliptical distribution	q_plasma = (η_p · I_p · U_p) / (π · a_p · b_p) · exp(-x²/a_p² - y²/b_p²)
MIG arc heat flux	Elliptical distribution with deflection	q_MIG = (η_m · I_m · U_m) / (π · a_m · b_m) · exp(-(x-x_d)²/a_m² - y²/b_m²)
Arc deflection offset	Function of current ratio and geometric configuration	x_d = f(I_p/I_m, θ, d)
Combined heat input	Superposition with interaction term	Q_total = q_plasma + q_MIG + q_interaction

Arc Deflection Mechanism

The arc deflection in hybrid plasma-MIG welding arises from three primary mechanisms:

Electromagnetic Lorentz force – The magnetic field generated by the plasma arc current exerts a force on the MIG arc plasma column, deflecting it toward or away from the plasma arc depending on current polarity and geometric arrangement.
Convection interaction – The high-velocity plasma jet entrains surrounding gas and creates a pressure differential that displaces the MIG arc root.
Plasma column interaction – Physical contact between the plasma arc and MIG arc plasma columns creates a merging zone with altered electrical and thermal characteristics.

Typical Process Parameters for Hybrid Plasma-MIG

Parameter	Plasma Arc	MIG Arc	Combined Effect
Current	30–100 A	150–300 A	Total 180–400 A
Voltage	15–25 V	20–30 V	Effective 25–35 V
Travel speed	–	200–800 mm/min	–
Wire diameter	–	1.0–1.6 mm	–
Gas flow	2–5 L/min (Ar)	10–20 L/min (Ar/CO₂)	Combined shielding
Penetration depth	5–15 mm	2–5 mm	7–20 mm total
Dilution rate	–	20–40%	Controlled by arc spacing

Process-Model Coupling Analysis

The heat source model developed in this literature has significant implications for cladding and weld overlay engineering. In multi-layer cladding applications, understanding the precise heat input distribution is essential for:

Predicting the dilution ratio between overlay material and base metal
Estimating the depth of heat-affected zone (HAZ) in the base metal
Evaluating the risk of intergranular cracking in sensitized stainless steel substrates
Optimizing the number of cladding passes required to achieve specified overlay thickness

For engineers working with nickel-based alloy cladding (Inconel 625, Hastelloy C276) on carbon steel pressure vessels, the hybrid plasma-MIG process offers the advantage of achieving deeper penetration than conventional SAW overlay while maintaining the high deposition rate needed for thick cladding layers. The heat source model enables prediction of the critical dilution threshold below which the cladding layer maintains its corrosion resistance properties.

Comparison with Conventional Cladding Processes

Process	Deposition Rate	Penetration	Dilution Control	Equipment Cost
SAW overlay	2–5 kg/h	3–8 mm	Moderate	Low
ESW overlay	5–15 kg/h	Full thickness	Low	High
GTAW overlay	0.3–1.0 kg/h	1–3 mm	Excellent	Moderate
Plasma-MIG hybrid	3–8 kg/h	5–15 mm	Good (model-based)	High
PTA powder cladding	1–4 kg/h	0.5–2 mm	Excellent	Very high

Key Technical Challenges and Reflections

The primary challenge addressed by this research is the nonlinear coupling between the two arcs in the hybrid configuration. The arc deflection is not merely a geometric offset but a dynamic phenomenon that varies with process parameters, joint geometry, and material properties. The model must capture:

Time-dependent arc behavior during start and end transients
Interaction effects that change with travel speed
Material property variations (thermal conductivity, emissivity) that affect heat partitioning

A critical insight from this work is that the arc deflection distance is primarily governed by the current ratio between the plasma and MIG arcs, the arc spacing, and the welding current magnitude. This finding has direct practical significance: engineers can control the deflection by adjusting the plasma-to-MIG current ratio, thereby tuning the penetration profile and dilution characteristics for specific cladding applications.

For bimetal pressure vessel fabrication, where the cladding layer must maintain metallurgical compatibility with the base metal while providing corrosion resistance, the hybrid plasma-MIG approach with a validated heat source model enables more accurate prediction of the interfacial microstructure. This reduces the reliance on trial-and-error qualification procedures and accelerates the development of welding procedures for novel material combinations.

The study underscores that computational modeling of hybrid welding processes is not merely an academic exercise but a practical necessity for engineers tasked with qualifying and optimizing cladding procedures for critical pressure vessel applications where failure is not an option.