**5. Conclusions**

An experimental setup was proposed to study the laser welding and melting of powder bed processes. The first aim of this setup was to analyze and understand these two processes better. The second aim was to build an experimental database (experimental benchmark) to validate the different types of numerical simulations of laser welding. The study involved instrumenting a laser welding machine to measure different quantities (molten pool morphology, temperature field, residual stresses, and distortions). Different instrumentation tools (high-speed camera, infrared camera, pyrometer, etc.) were used to achieve this.

In the first step, tests of laser welding were carried out on 316L samples. The effect of the welding speed on the molten pool morphology, temperature field, residual stresses, and distortions was studied. The measured quantities were very sensitive to this speed. For example, the weld pool was longer and shallower for high velocities. The longitudinal residual stresses and distortions decreased when the speed increased. The results of these different quantities will enable researchers to validate their numerical simulations of this process.

In the second step, tests of the melting of a powder bed were carried out using a laser welding machine. The idea was to fill a hollow substrate with a powder layer and then melt it using a laser. The aim of these tests was to understand this process better. As a result, the bead dimensions of two types of powder (spherical and irregular powders) were measured. These results, and especially the height of the bead, depicted that the shrinkage of the powder layer after melting cannot always be visible. Indeed, the height of the bead of the spherical powder exceeded the initial thickness of the powder layer for low velocities. This can be explained by the high-speed camera videos. They indicated that the molten pool absorbed the powder around it. This absorption facilitates the increase in the bead volume and creating a denuded zone between the bead and the unfused powder. The shrinkage of the powder layer was easily visualized with the irregular powder even for low scanning velocities. This can be explained by its low flowability, which delays its absorption by the molten pool (less material addition). The results also indicated that the bead morphology is sensitive to scanning velocities.

Finally, this study enabled us to understand the physics during laser welding and especially during the melting of a powder bed process better. It also enabled us to build a database of experimental results (experimental benchmark) of laser welding. This can assist in improving and validating the numerical simulation of these processes.

**Author Contributions:** Conceptualization, Y.S., J.S. and J.-M.B.; methodology, Y.S., M.D., E.F. and J.-M.B.; software, Y.S. and J.S.; validation, Y.S., M.D., E.F. and J.-M.B.; formal analysis, Y.S., J.S. and J.-M.B.; investigation, Y.S.; resources, P.B., E.F. and J.-M.B.; data curation, Y.S. and J.S.; writing–original draft preparation, Y.S.; writing–review and editing, J.S., M.D., P.B. and J.-M.B.; visualization, Y.S., P.B. and J.-M.B.; supervision, J.S., M.D. and J.-M.B.; project administration, J.-M.B.; funding acquisition, P.B., E.F. and J.-M.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors would like to thank ESI-GROUP and MELTED project for funding this study.

**Conflicts of Interest:** The authors declare no conflict of interest.
