Toward Stabilizing the Keyhole in Laser Spot Welding of Aluminum: Numerical Analysis
Abstract
:1. Introduction
2. Materials and Methods
2.1. Model Geometrics, Material, and Laser Heat Source
2.2. Heat and Fluid Flow Model
- The movement of molten material in the fusion zone was simulated assuming Newtonian behaviour, incompressibility, and laminar flow characteristics.
- Temperature-dependent changes in aluminum’s thermophysical properties were disregarded. Instead, the modified mixture theory was applied to calculate thermophysical properties, such as thermal conductivity, specific heat, and density, for each element by utilizing fixed values for the solid, liquid, and gas phases of aluminum. These properties were then averaged according to the phase proportions within each element, yielding an effective constant thermophysical property for the simulation [34].
- The mushy zone was treated as a porous medium permeated by molten metal [35].
- Plasma effects and the Knudsen layer were excluded from the model.
- Multiple reflections of the laser beam within the keyhole were disregarded in this study. This assumption is justified for scenarios with low penetration depths, as multiple reflections become significant primarily in cases of deeper weld penetration (greater than 600 μm) [7]. Moreover, the laser beam coefficient of absorption was assumed constant at keyhole walls.
- The vaporized material was modelled as an ideal gas that is transparent to the incoming laser beam.
- Energy equation and its concerning parameters
- Modified mass conservation equation and recoil pressure
- Momentum equation:
- Modified transport equations of the LS method
- Boundary and initial conditions
2.3. Numerical Considerations
2.3.1. Numerical Setup
2.3.2. Model Validation
2.3.3. Instability Analysis Procedure
3. Results and Discussion
3.1. Keyhole Geometry Analysis
3.2. Instability-Inducing Forces: Quantitative Analysis
3.3. Fluid Behavior
3.4. Understanding the Instability Nature of Selected Cases
4. Conclusions and Future Avenues
- The combination of the curvature effect, Darcy’s damping force, and more intense fluid flow behaviour contribute to the instability of the keyhole and the laser welding process.
- Using short pulse periods with higher laser energy density enhances instability and the possibility of keyhole collapse due to the increased curvature effect, Darcy’s damping force, and more intense fluid flow behaviour.
- The instability of the keyhole and process can be controlled using variant rectangular pulse shapes with gradual laser power ramp-up and -down pulse shapes due to smoother variations in velocity, smoother flow behaviour, and fewer curvature effects.
- The instability of the keyhole and forces can be controlled using combinations of triangular and rectangular pulse shapes.
- To minimize instability, the laser power should be high enough to induce evaporation and recoil pressure for keyhole propagation but balanced to avoid the excessive curvature effect, Darcy’s damping force, and fluid velocity that accompanies higher power and leads to increased instability.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Case No. | Laser Power | Pulse Width | Total Laser Energy | Number of Pulses | Pulse Shape | Total on Time |
---|---|---|---|---|---|---|
1 | 2 kW | 10 ms | 20 J | 1 | Continuous | 10 ms |
2 | 4 kW | 5 ms | 20 J | 1 | Rectangular constant | 5 ms |
3 | 1–3 kW | 2.5 ms | 20 J | 1 | Rectangular: ramp up–ramp down | 10 ms |
4 | 0.5–4 kW | 2.5 ms | 20 J | 1 | Rectangular: ramp down | 10 ms |
5 | 1–3 kW | 2 ms | 20 J | 1 | Rectangular: ramp down | 10 ms |
6 | 1–3 kW | 2 ms | 20 J | 1 | Rectangular: ramp up | 10 ms |
7 | 1.5–3 kW | 2 ms | 20 J | 1 | Rectangular: ramp down-up-down | 10 ms |
8 | 0–4 kW | 10 ms | 20 J | 1 | Triangular: single peaks | 10 ms |
9 | 0–4 kW | 5 ms | 20 J | 2 | Triangular: double peaks | 10 ms |
10 | 0–4 kW | 2.5 ms | 20 J | 4 | Triangular: quadruple peaks | 10 ms |
11 | 0–4 kW | 1.25 ms | 20 J | 8 | Triangular: octuple peaks | 10 ms |
12 | 0–6 kW | 1 ms | 18 J | 3 | Rectangular | 3 ms |
13 | 0–6 kW | 2 ms | 18 J | 3 | Triangular | 6 ms |
14 | 0–6 kW | 1–2 ms | 18 J | 3 | Rectangular–triangular | 4 ms |
15 | 0–6 kW | 2 ms | 18 J | 3 | Triangular–rectangular | 6 ms |
Property | Symbol | Magnitude |
---|---|---|
Solidus temperature | 847 (K) | |
Liquidus temperature | 905 (K) | |
Vaporization temperature | 2743 (K) | |
Thermal conductivity of solid | 238 (W/m/K) | |
Thermal conductivity of liquid | 100 (W/m/K) | |
Density of solid | 2700 (kg/m3) | |
Density of liquid | 2385 (kg/m3) | |
Latent heat of melting | 3.896 × 105 (J/kg) | |
Latent heat of vaporization | 9.462 × 106 (J/kg) | |
Specific heat capacity of solid | 917 (J/kg/K) | |
Specific heat capacity of liquid | 1080 (J/kg/K) | |
Convective heat transfer coefficient | h | 20 (W/m2/K) |
Coefficient of linear thermal expansion | 2.36 × 10−5 (1/K) | |
Dynamic viscosity | 1.6 × 10−3 (Pa.s) | |
Coefficient of surface tension | 0.95 × (1 + 0.13 × (1 − T/Tm))1.67 (N/m) | |
Temperature-dependent surface tension coefficient | −0.3 × 10−3 (N/m/K) | |
Radiation emissivity | 0.2 |
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SaediArdahaei, S.; Pham, X.-T. Toward Stabilizing the Keyhole in Laser Spot Welding of Aluminum: Numerical Analysis. Materials 2024, 17, 4741. https://doi.org/10.3390/ma17194741
SaediArdahaei S, Pham X-T. Toward Stabilizing the Keyhole in Laser Spot Welding of Aluminum: Numerical Analysis. Materials. 2024; 17(19):4741. https://doi.org/10.3390/ma17194741
Chicago/Turabian StyleSaediArdahaei, Saeid, and Xuan-Tan Pham. 2024. "Toward Stabilizing the Keyhole in Laser Spot Welding of Aluminum: Numerical Analysis" Materials 17, no. 19: 4741. https://doi.org/10.3390/ma17194741