Finite Element Simulation of Plasma MIG Welding Temperature Field

Literature Overview

This 2004 publication from the School of Materials Science and Engineering, Shenyang University of Technology, presents a finite element analysis (FEA) of the temperature field during plasma MIG welding. The work by Zhang Yishun, Cai Jing, Li Deyuan, and Dong Xiaoqiang represents an early application of numerical simulation to hybrid welding processes, providing a computational framework for understanding and optimizing thermal cycles in complex welding configurations.

Core Technical Content and Simulation Approach

The plasma MIG welding process combines a plasma arc (for deep, narrow penetration) with a MIG arc (for additional heat input and wider bead coverage). The temperature field simulation is essential for predicting:

• Heat affected zone (HAZ) width and thermal cycle severity
• Residual stress distribution
• Microstructural evolution and phase transformations
• Distortion and deformation behavior

The Goldak double-ellipsoidal heat source model is particularly suited for this application because it allows independent representation of the two heat sources (plasma and MIG) with different aspect ratios and energy distributions. The plasma arc typically has a higher aspect ratio (deeper penetration) while the MIG arc has a lower aspect ratio (wider, shallower heat distribution).

Key Findings and Thermal Cycle Characteristics

The simulation results reveal several important features of the plasma MIG welding thermal cycle:

• Peak temperature distribution: The plasma arc produces peak temperatures exceeding 3000°C at the fusion boundary, while the MIG arc contributes a secondary heat source with peak temperatures of 2000-2500°C
• Cooling rate: The 8/5°C/s cooling rate (from 800°C to 500°C) is typically 2-5 times higher than conventional SAW or manual arc welding, which influences microstructural refinement
• HAZ width: The combined heat input produces a HAZ approximately 30-50% wider than plasma welding alone but with a deeper, narrower weld nugget
• Thermal cycling effects: In multi-pass welding, the reheat cycles of previously deposited layers significantly affect the final residual stress state and microstructure

Engineering Applications and Process Optimization

The finite element simulation approach provides several practical benefits for welding engineers:

1. WPS optimization: Virtual experiments can identify optimal parameter combinations before physical trials, reducing qualification costs
2. Distortion prediction: Pre-weld simulation enables fixture design and welding sequence optimization to minimize post-weld distortion
3. Residual stress prediction: The thermal-mechanical coupled analysis predicts residual stress magnitudes and directions, informing post-weld treatment strategies
4. Scalability: Models developed for laboratory specimens can be scaled to full-scale components with appropriate boundary condition adjustments

Study Insights and Reflections

The value of this work lies in establishing a computational methodology that bridges the gap between welding physics and engineering practice. For pressure vessel and cladding applications, the ability to predict thermal cycles with reasonable accuracy enables better control of microstructural properties in the weld and HAZ. The temperature-dependent material properties and the dual-heat-source model are particularly relevant for hybrid welding processes used in clad plate and bimetallic component fabrication. The simulation framework described here has evolved significantly since 2004, with modern implementations incorporating phase transformation kinetics, solidification modeling, and coupled thermomechanical analysis. Nevertheless, the fundamental approach — accurate heat source characterization combined with proper material property data — remains the cornerstone of reliable welding simulation.