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ABSTRACT
The melt pool is the general process of the laser additive manufacturing process. An in-depth understanding of the evolution of the melt pool will facilitate obtaining an optimum mechanical performance. In this paper, a novel 2D transient model is presented, which considers most physical phenomena taking place in the laser melt process and incorporates a coupled multiphase capture method. This model is validated by comparing it to Han’s research. Then an investigation on the transient thermal dynamic in the melt pool including quenching time is carried out, and the effects of evaporation and alternative material properties on the evolution of the melt pool are discussed. The results show that the deformation of the free surface and the temperature in the workpiece both increase with energy input. After quenching, the temperature in the workpiece decreases sharply and the melt pool also shrinks. The evaporation effect is vigorous in the center of the melt pool and negligible in the periphery. The material properties have significant influence on the evolution process because the convection and diffusion in the melt pool are directly dominated by them.
Nomenclature
| C | = | volume fraction function |
| Cp | = | specific heat, J/(kg · K) |
| d | = | distance from the grid to the interface, m |
| g | = | gravity, m/s2 |
| gl | = | liquid fraction in the melt pool |
| H | = | enthalpy, J/kg |
| ΔH | = | latent heat of melting, J/kg |
| κ0 | = | permeability coefficient |
| Lv | = | latent heat of evaporation, J/kg |
| pr | = | vapor recoil force, N |
| P | = | pressure, Pa |
| Plaser | = | laser power, W |
| ΔPe | = | Peclet number |
| QA | = | radiation energy of point A at 100 ms, W |
| Qct | = | radiation energy at current time, W |
| t | = | time, s |
| T | = | temperature, K |
| Tm | = | melting temperature, K |
| T0 | = | ambient temperature, K |
| Ts | = | solidification temperature, K |
| Tsurf | = | surface temperature of melt pool, K |
| U | = | heat of evaporation per Avogadro’s number atoms |
| = | velocity, m/s | |
| Vdv | = | rate of the free surface deformation, m/s |
| V0 | = | sound velocity in the workpiece, m/s |
| x, y | = | coordinate directions, m |
| δx | = | distance between the adjacent grid points |
| Greek symbols | = | |
| β | = | coefficient of volume expansion |
| γ | = | surface tension coefficient, N/m |
| ε | = | emissivity |
| ε0 | = | transition region thickness |
| ζ | = | small number |
| η | = | absorptivity coefficient |
| κ | = | interface curvature |
| λ | = | thermal conductivity, W/(m•K) |
| μ | = | dynamic viscosity coefficient, Pa•s |
| ρ | = | density, kg/m3 |
| σ | = | Stefan Boltzmann constant, 5.67 × 10−8 W/(m2 · K4) |
| τ | = | radiation ratio |
| ϕ | = | level set function |
| Subscripts | = | |
| 1 | = | liquid phase |
| 2 | = | gas phase |
| i, j | = | index of point |
| surf | = | surface |
| Abbreviations | = | |
| BFC | = | body-fitted coordinates |
| CSF | = | continuum surface force |
| LBAM | = | laser-based additive manufacture |
| LS | = | level set |
| SLM | = | selective laser melting |
| VOF | = | volume of fluid |
Nomenclature
| C | = | volume fraction function |
| Cp | = | specific heat, J/(kg · K) |
| d | = | distance from the grid to the interface, m |
| g | = | gravity, m/s2 |
| gl | = | liquid fraction in the melt pool |
| H | = | enthalpy, J/kg |
| ΔH | = | latent heat of melting, J/kg |
| κ0 | = | permeability coefficient |
| Lv | = | latent heat of evaporation, J/kg |
| pr | = | vapor recoil force, N |
| P | = | pressure, Pa |
| Plaser | = | laser power, W |
| ΔPe | = | Peclet number |
| QA | = | radiation energy of point A at 100 ms, W |
| Qct | = | radiation energy at current time, W |
| t | = | time, s |
| T | = | temperature, K |
| Tm | = | melting temperature, K |
| T0 | = | ambient temperature, K |
| Ts | = | solidification temperature, K |
| Tsurf | = | surface temperature of melt pool, K |
| U | = | heat of evaporation per Avogadro’s number atoms |
| = | velocity, m/s | |
| Vdv | = | rate of the free surface deformation, m/s |
| V0 | = | sound velocity in the workpiece, m/s |
| x, y | = | coordinate directions, m |
| δx | = | distance between the adjacent grid points |
| Greek symbols | = | |
| β | = | coefficient of volume expansion |
| γ | = | surface tension coefficient, N/m |
| ε | = | emissivity |
| ε0 | = | transition region thickness |
| ζ | = | small number |
| η | = | absorptivity coefficient |
| κ | = | interface curvature |
| λ | = | thermal conductivity, W/(m•K) |
| μ | = | dynamic viscosity coefficient, Pa•s |
| ρ | = | density, kg/m3 |
| σ | = | Stefan Boltzmann constant, 5.67 × 10−8 W/(m2 · K4) |
| τ | = | radiation ratio |
| ϕ | = | level set function |
| Subscripts | = | |
| 1 | = | liquid phase |
| 2 | = | gas phase |
| i, j | = | index of point |
| surf | = | surface |
| Abbreviations | = | |
| BFC | = | body-fitted coordinates |
| CSF | = | continuum surface force |
| LBAM | = | laser-based additive manufacture |
| LS | = | level set |
| SLM | = | selective laser melting |
| VOF | = | volume of fluid |