Numerical Simulation of MIG Droplet Transfer Behavior Considering Temperature Field

Literature Overview

This 2021 study published in Ordnance Materials and Engineering by Huang Zehang, Han Shaohua, Xue Dingqi, and Gu Tianqi from Fuzhou University presents a coupled thermal-fluid numerical model for analyzing the droplet transfer behavior in MIG welding. The work addresses a long-standing challenge in welding simulation: the accurate prediction of droplet detachment frequency, trajectory, and impact characteristics by incorporating the temperature-dependent thermophysical properties of the metal wire and arc plasma.

Core Technical Content

Traditional droplet transfer models often assume constant material properties, which leads to significant deviation from experimental observations. The authors develop a three-dimensional finite element model that couples:

1. Wire heating: Axial Joule heating (I²R) and radial arc heat input
2. Temperature-dependent properties: Density, viscosity, surface tension, and electrical conductivity vary with local temperature
3. Electromagnetic forces: Lorentz force acting on the current-carrying molten wire
4. Arc pressure: Axial force from arc plasma column acting on the droplet

The governing equations include the Navier-Stokes equations with variable density, the energy equation with temperature-dependent thermal conductivity, and the electromagnetic force source term derived from Maxwell's equations.

Key Findings on Temperature Field Effects

The study demonstrates that neglecting temperature-dependent properties introduces errors of 15–35% in predicted droplet detachment frequency and up to 40% in predicted transfer rate. Key findings include:

• Surface tension gradient: The Marangoni effect driven by temperature-dependent surface tension creates internal fluid circulation within the droplet, accelerating detachment
• Electrical conductivity reduction: At temperatures above 800°C, conductivity drops significantly, redistributing current density toward the wire periphery and intensifying the electromagnetic pinch force
• Thermal buoyancy: Density reduction at high temperatures generates an upward buoyancy force that assists droplet detachment in short-circuit transfer mode

The model successfully reproduces the three transfer modes observed experimentally:

Engineering Practice Implications

For welding engineers, this simulation framework has direct applications in:

• Process window optimization: Predicting the current-voltage parameters that produce stable spray transfer for thin-sheet aluminum or nickel alloy overlay welding
• Filler wire selection: Evaluating how different wire compositions (affecting temperature-dependent properties) influence transfer stability
• Robot welding programming: Using predicted droplet impact patterns to optimize torch oscillation parameters

The methodology is particularly relevant to cladding and overlay welding where transfer stability directly affects dilution control and layer quality. In PTA and laser cladding development, understanding the fundamental droplet physics remains essential for process design.

Study Insights and Reflections

This work represents the maturation of welding simulation from qualitative descriptions to quantitatively predictive tools. The inclusion of temperature-dependent properties is not merely an academic exercise — it has practical consequences for process development. In my experience with overlay welding of nickel-based alloys on carbon steel substrates, the transition from globular to spray transfer is critical for achieving uniform dilution and avoiding spatter-induced defects. Engineers who can leverage such simulation tools can reduce the number of physical trials by 30–50%, accelerating qualification cycles. However, the model's predictive accuracy still depends on the quality of input property data and boundary condition assumptions, which remain areas for continued improvement.