In this work, a transient three-dimensional finite element model (FEM) of the laser micro spot welding (LMSW) process was established considering three heat source approaches: static heat source model (SHSM), dynamic heat source model (DHSM), and double dynamic heat source model (DDHSM). Each mode was computed according to the aspect ratio of spot width to depth and the absorptance of the material. The numerical simulation can compute the conduction-to-keyhole transition using an AISI 302 stainless steel (SS) alloy. Our results showed that the DDHSM results concord with the experiments reported in the literature. The conduction-to-keyhole transition for the SHSM and DHSM was observed to depend on laser power, having a constant keyhole aperture at 75 ms exposure time and 220 W laser power. On the other hand, the DDHSM configuration gives a conduction-to-keyhole transition with a similar constant aperture at 75 and 50 ms of exposure time for 200 and 220 W laser power, respectively. The percentage errors for the DDHSM were 8%, 15%, 17%, and 20% for the penetration depth, top, middle, and bottom width, respectively. The validation experiments confirmed that the proposed FEM simulation is reliable and accurate to predict the final micro spot weld shape enabling the fabrication of metallic porous structures for bone implant applications.