Zhuojin Pipe Fitting Co., LtdTemperature Field Simulation of MIG-Based Arc Additive Manufacturing with Interlayer Dwell Time
Literature Overview
The paper by Zhang Tianlei and colleagues from Shanghai University of Engineering Science and Beijing Haiji Technology Development Co., Ltd., published in Light Industry Machinery (2020, Vol. 38, No. 3, pp. 37–42), presents a three-dimensional transient thermal simulation of MIG-based arc additive manufacturing (AM) using ABAQUS finite element software. Funded by the Shanghai University of Engineering Science Graduate Research Innovation Project (18KY0514), the study investigates the temperature field characteristics during multi-layer deposition and the effect of interlayer dwell time on the thermal state of the workpiece. The simulation results are validated against infrared thermometry measurements of the thermal cycle curves.
Technical Methodology
Simulation Model
The ABAQUS-based simulation employs a three-dimensional transient heat transfer model that accounts for the moving heat source of the welding arc, the sequential deposition of layers, and the thermal interaction between deposited layers. The model parameters include:
| Parameter | Description | Typical Value/Range |
|---|---|---|
| Heat source model | Moving Gaussian or double-elliptical | Based on MIG arc characteristics |
| Material properties | Temperature-dependent thermal conductivity, specific heat, density | Aluminum alloy properties |
| Deposition rate | Layer deposition speed and rate | Process-specific |
| Interlayer dwell time | Time between successive layer depositions | Variable parameter |
| Boundary conditions | Convective and radiative heat loss | Environment-dependent |
Validation Approach
The validation methodology is robust: infrared thermometry was used to measure the thermal cycle curves during actual MIG-based AM deposition, and these experimental data were compared with the simulation predictions. The good agreement between simulated and measured thermal cycles validates the model's accuracy and provides confidence in the simulation results for conditions that are difficult to measure experimentally.
Key Findings
Temperature Field Evolution with Layer Number
The simulation reveals that as the number of deposited layers increases, the high-temperature region of the workpiece progressively expands. This is a direct consequence of the cumulative thermal load: each new layer adds heat to the system, and the previously deposited layers act as thermal mass that retains and redistributes this heat. The expanding high-temperature zone has several implications:
- Grain coarsening: The increased thermal exposure promotes grain growth in previously deposited layers, potentially degrading mechanical properties.
- Phase transformation: In precipitation-hardening alloys, the elevated temperatures may cause over-aging of precipitates, reducing strength.
- Residual stress: The expanding thermal gradient contributes to residual stress development, which may lead to distortion or cracking.
- Process window narrowing: As the workpiece heats up, the effective process window for subsequent layers may shift, requiring parameter adjustments.
Effect of Interlayer Dwell Time
The most practically significant finding is the effect of interlayer dwell time on the high-temperature region. With all other parameters held constant, increasing the interlayer dwell time reduces the size of the high-temperature region. This is intuitive: a longer dwell time allows more heat to dissipate from the workpiece before the next layer is deposited, resulting in a lower starting temperature for the subsequent layer.
The quantitative relationship between dwell time and high-temperature region size is not linear. Initially, increasing dwell time from zero produces a significant reduction in the high-temperature zone. However, beyond a certain dwell time, the marginal benefit diminishes as the workpiece approaches its ambient temperature. This suggests an optimal dwell time range that balances thermal management with deposition efficiency.
Metallurgical Bonding
The study confirms that MIG-based arc additive manufacturing achieves good metallurgical bonding between layers. This is a critical requirement for any AM process, as the mechanical integrity of the deposited structure depends on the quality of the interlayer bonds. In MIG-based AM, the bonding is achieved through the melting of the top surface of the previous layer by the arc and wire feed of the subsequent layer, creating a fusion bond.
Engineering Practice Implications
Thermal Management Strategies
The findings of this study directly inform thermal management strategies for MIG-based AM production:
- Active cooling: For applications where the expanding high-temperature zone is unacceptable, active cooling (water cooling, forced air) can be employed to accelerate heat dissipation between layers.
- Dwell time optimization: The simulation results provide a basis for determining the optimal dwell time for specific component geometries and material specifications.
- Layer thickness control: Thinner layers reduce the heat input per layer but increase the total number of layers and deposition time. The optimal layer thickness must balance thermal management with deposition efficiency.
- Deposition sequence planning: The order in which layers are deposited can be optimized to minimize thermal accumulation in critical regions of the component.
Process Parameter Selection
For MIG-based AM, the following process parameters interact with the thermal state:
| Parameter | Thermal Effect | Optimization Consideration |
|---|---|---|
| Welding current | Higher current = more heat input | Balance penetration with thermal load |
| Travel speed | Higher speed = less heat per unit length | Balance productivity with bond quality |
| Wire feed rate | Higher rate = more material per unit time | Balance deposition rate with dilution |
| Shielding gas | Gas composition affects arc energy | Ar/CO₂ mixtures can modulate heat input |
| Dwell time | Longer = more cooling | Balance thermal management with cycle time |
Quality Control Considerations
The thermal history of MIG-based AM deposits is complex and varies with layer position, deposition sequence, and process parameters. This thermal variability has implications for:
- Mechanical property uniformity: Properties may vary between layers due to different thermal histories.
- Residual stress distribution: The thermal gradients create a complex residual stress state that may require post-deposition stress relief.
- Defect susceptibility: Regions with higher thermal exposure may be more susceptible to solidification cracking, hot cracking, or porosity.
Reflections and Critical Analysis
The use of finite element simulation for AM process development is now well-established, and the ABAQUS-based approach described here follows standard methodology. The validation against infrared thermometry measurements is essential and provides credibility to the simulation results. I note that infrared thermometry measures surface temperatures, while the simulation provides internal temperature distributions. The agreement between surface measurements and simulation predictions is a strong indicator of model accuracy.
The finding regarding the progressive expansion of the high-temperature zone with increasing layer number is a critical consideration for large component fabrication. In my experience with welding of thick sections, thermal accumulation is a well-known challenge that can lead to distortion, residual stress, and property degradation. The AM context amplifies this challenge because the thermal cycles are closely spaced and the workpiece is continuously heated over extended periods.
The interlayer dwell time as a thermal management tool is a practical and cost-effective strategy. Unlike active cooling, which requires additional equipment and infrastructure, dwell time is simply a matter of process scheduling. However, the productivity penalty of extended dwell times must be weighed against the quality benefits. For large components with many layers, the cumulative dwell time can significantly increase the total production time.
One limitation of the study is that it focuses exclusively on thermal analysis. While the thermal field is a primary driver of microstructure and properties, other factors such as fluid flow in the molten pool, solidification dynamics, and residual stress development are not addressed. A complete process model would require coupling thermal, mechanical, and fluid dynamics analyses, which is computationally intensive but increasingly feasible with modern simulation capabilities.
The confirmation of good metallurgical bonding between layers is reassuring but should be qualified. Bond quality depends not only on the thermal conditions but also on the cleanliness of the layer interface, the wire feed consistency, and the arc stability. In production environments, contamination and process variability can degrade bond quality, and the simulation does not account for these real-world factors.
Study Insights and Implications
The work by Zhang Tianlei and colleagues provides valuable thermal simulation insights for MIG-based arc additive manufacturing. The identification of interlayer dwell time as an effective thermal management parameter offers a practical tool for process optimization. For the engineering community, the key takeaways are: (1) thermal accumulation is a significant concern in multi-layer AM that must be actively managed; (2) interlayer dwell time is a simple yet effective means of controlling the thermal state; and (3) simulation validated against experimental data is a powerful tool for process development and optimization. The work demonstrates the value of computational methods in understanding and controlling the complex thermal behavior of AM processes, and it provides a foundation for more comprehensive multi-physics simulations that can address microstructural evolution and mechanical property prediction in future studies.