# Roles of Modeling and Artificial Intelligence in LPBF Metal Print Defect Detection: Critical Review
## 3 Advances in Numerical Modeling Techniques for LPBF Defect Detection
### Melt Pool Defect Modeling
#### 3.1.2 Thermo-Mechanical Simulations of LPBF Defects Using FVM
\begin{table}
\begin{tabular}{c c c c} \hline
**Powder** & **Defect(s)** & **Laser Energy Rate (W),** & \\
**Material** & **Observed** & **Daimeter (mm)** & **Code(s)** \\ \hline \multirow{4}{*}{SS316L [26]} & Thermal distortions, large residual stresses, & \multirow{4}{*}{45–275, 120–1500, 50–150} & \multirow{4}{*}{ANSYS, ALE3D, \multirow{4}{*}{Deal-II}} \\  & non-homogenous permanent strains, gas & & \\ \cline{1-1}  & bubbles, melt elongation, depression collapse, & & \\ \cline{1-1}  & material spatter, open pores, overhanging, & & \\ \cline{1-1}  & depression collapse, keyhole pores, LOF, track & & \\ \cline{1-1}  & discontinuity (unstable melt pool) & & \\ \hline \multirow{4}{*}{Ti6 Al4V} & Large residual stresses, sharper thermal & \multirow{4}{*}{40–400, 200–4500, 50–250} & MSC Marc, ABAQUS, \multirow{4}{*}{ANSYS, COMET, \multirow{4}{*}{Deal-II}} \\  & gradients, large recoil pressure, LOF pores, gas & & \\ \cline{1-1}  & pores, keyhole pores, capillary digging, hot spot & & \\ \cline{1-1}  & formation, balling, incompletely melted powder, & & \\ \cline{1-1}  & spatter formation, surface roughness, decreased & & \\ \cline{1-1}  & density, entrapped gas pores & & \\ \hline \multirow{4}{*}{718 [35,46]} & Large residual stresses, large recoil pressure, & \multirow{4}{*}{250–370, 1000–1300, 84–100} & \multirow{4}{*}{Netfabb, In-house FEM} \\  & LOF, keyholes, capillary digging & & \\ \cline{1-1} \cline{2-3}  & IN625 [44, 45, 46] & Increased porosity, large residual stresses, & \multirow{4}{*}{50–370, 130–1300, \multirow{4}{*}{Neftabbb}} & MATLAB, \multirow{4}{*}{Neftabb} \\  & undesired columnar grain growth direction & & \\ \cline{1-1} \cline{2-3}  & & Keyhole formation, thermal distortion, warping, & \\ \cline{1-1}  & melt pool distortion, large residual stresses & & \\ \hline \multirow{4}{*}{IN718 [47, 48, 50]} & Denudation, depressions, spatters, keyhole & \multirow{4}{*}{180–360, 685–1100, 100} & \multirow{4}{*}{JMatPro} \\  & pores, spheroidization & & \\ \cline{1-1} \cline{2-3}  & Hastelloy X [51] & Undesired temperature gradients & 150–250, 800–1300, 100 & COMSOL \\ \hline \multirow{4}{*}{AlSi10 Mg [52]} & \multirow{4}{*}{Large melt pool hydrodynamics} & \multirow{4}{*}{70–10, 20–10,000} & \multirow{4}{*}{COMSOL} \\  & & & \\ \cline{1-1}  & SS17-4 PH [53] & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \hline \multirow{4}{*}{AlSi10 Mg [50]} & \multirow{4}{*}{Large residual stresses} & \multirow{4}{*}{253–370, 1000–1300, Not listed} & \multirow{4}{*}{Netfabb} \\ \cline{1-1}  & & & \\ \cline{1-1} \cline{2-3}  & & & \\ \hline \end{tabular}
\end{table} 
Table 1: Compiled list of thermo-mechanical FEM analyses of the melt pool behavior and defect generation. The absence of the wetting effect primarily caused balling. Spatter particle trajectories during the LPBF process for SS316L and AlSi10 Mg were investigated using ANSYS Fluent [56]. Spatter particles directly contribute to defect formation. The effects of inert gas distribution around the sprinkled powder particles were analyzed, and the predicted eventual deposition on the powder bed was quantified. An investigation modeled the multi-track LPBF process for SS316L using FLOW3D [57]. For the multi-track melting process, the previously melted layer serves as the heating source for preheating the next layer, increasing the temperature and size of the printed molten pool. A high level of laser beam energy, low velocity, and spacing lead to large heat-affected angles and molten pool depths. Reducing the laser beam energy level and increasing its velocity and hatch spacing reduces the heat-affected angle. When the operating parameters are close to the extreme point, the thickness of the multitrack molten layer is thin, and interlayer defects such as non-melting and pores can occur easily [57]. A computational method to investigate the fluid flow regimes during the printing of Ti6 Al4V using OpenFOAM was developed [58].