Numerical Simulation of Temperature Field in MIG Welding Deposited Rapid Forming

Research Context and Objectives

This 2009 study from the Key Laboratory of Equipment Remanufacturing Technology, Academy of Armored Force Engineering, addresses the thermal behavior during MIG welding deposited rapid forming (also referred to as welding-based rapid manufacturing or additive manufacturing). Supported by the National Natural Science Foundation of China (Project 50735006) and the National 973 Program Sub-project (2007CB607601), the research represents early academic exploration into the thermal modeling of additive manufacturing processes that use MIG/GMAW as the deposition mechanism.

The core objective was to develop a finite element model capable of predicting the temperature distribution during multi-layer, multi-pass MIG deposition, thereby enabling process optimization for dimensional accuracy, residual stress management, and defect prevention in additively manufactured components.

Numerical Modeling Approach

The researchers employed a sequential thermomechanical coupled analysis using a finite element method (FEM) framework. The thermal model incorporated a moving heat source to simulate the arc energy input, with the heat source geometry calibrated to match experimental temperature measurements obtained via thermocouples and infrared thermography.

The model accounted for phase change effects through an effective latent heat approach, where the melting temperature range was smeared over a temperature interval to avoid numerical singularity at the phase boundary. Convection and radiation heat losses from the free surfaces were modeled using Newton's law of cooling and the Stefan-Boltzmann law, respectively, with appropriate view factor calculations for the complex geometry of multi-layer builds.

Thermal Field Results and Analysis

The simulation results revealed several critical thermal characteristics of the MIG deposition process. The peak temperature at the arc center exceeded 1500°C, while the solidification front (liquidus temperature) propagated rapidly ahead of the arc and receded behind it, creating a characteristic teardrop-shaped hot zone. The cooling rate at the solidification front was estimated to be in the range of 5 to 50°C/s, depending on the deposition strategy and the thermal mass of the previously deposited layers.

A key finding was the strong dependence of the thermal history on the deposition sequence. When layers were deposited in a single-direction strategy, the cumulative heat input caused progressive thermal accumulation, leading to elevated base temperatures and reduced cooling rates in subsequent passes. This thermal accumulation increased the risk of hot cracking and coarse grain growth in the upper layers. In contrast, a zig-zag or serpentine deposition pattern distributed the heat more uniformly, reducing the peak temperatures and improving the thermal uniformity across the build.

The temperature gradient at the solidification front was found to be a primary driver of grain morphology. High gradients (above 100°C/mm) favored columnar grain growth along the build direction, while lower gradients promoted equiaxed grain nucleation. This observation has direct implications for the anisotropy of mechanical properties in additively manufactured components, as columnar grains oriented along the build direction may exhibit reduced transverse ductility.

Relevance to Cladding and Bimetal Manufacturing

Although this study focused on additive manufacturing, the thermal modeling methodology is directly transferable to multi-pass weld overlay cladding applications. In the fabrication of bimetal pressure vessels with thick overlay layers, the thermal history of each successive pass is governed by the same principles of heat accumulation and thermal cycling. Engineers designing welding procedures for thick cladding deposits should consider the residual temperature from previous passes when selecting interpass temperature limits and travel speeds.

The numerical simulation approach also provides a valuable tool for predicting the dilution ratio in weld overlay applications. By modeling the temperature distribution at the fusion boundary, one can estimate the extent of base metal melting and, consequently, the compositional profile of the overlay layer. This is particularly important when overlaying dissimilar materials such as nickel-based alloys on carbon steel, where the dilution ratio directly affects the corrosion resistance and mechanical properties of the cladding layer.

Study Insights and Practical Recommendations

This early work established a foundation for computational thermal analysis of wire-arc additive processes, and its methodology remains relevant for modern engineering practice. The emphasis on deposition sequence optimization is particularly instructive for cladding engineers, as the order in which overlay passes are deposited significantly influences the final residual stress state and dimensional accuracy of the component. For pressure vessel applications, where dimensional tolerances and residual stress levels are critical for pressure boundary integrity, the use of numerical simulation to pre-plan the deposition sequence can reduce the need for costly post-weld stress relief treatments and improve the overall manufacturing efficiency.

The study also highlights the importance of validating numerical models against experimental measurements. Without proper calibration of heat source parameters and boundary conditions, the predicted thermal fields may deviate significantly from reality, leading to incorrect conclusions about process behavior. Engineers should always supplement numerical predictions with thermocouple measurements or infrared thermography to ensure model fidelity before applying the results to production decisions.