CNC toolpath-driven thermal modeling of WAAM: thermal assessment and microstructural interpretation

Wire Arc Additive Manufacturing (WAAM) involves highly transient thermal cycles, repeated reheating, and strong spatial temperature gradients, all of which govern the final microstructure of the deposited material. In this work, a three-dimensional transient thermal model for WAAM of ER70S-6 carbon steel was developed directly from the same processed CNC G-code used to operate the experimental system. This approach allowed the simulation to preserve the real deposition trajectory, torch motion, arc on/off sequence, and fan-assisted interpass cooling intervals. The computational workflow combined G-code parsing, geometric reconstruction of the deposited wall and substrate, structured voxelization, progressive material activation, and explicit transient heat-transfer solution. The thermal problem was formulated considering conduction, convection, radiation, and a moving volumetric Gaussian heat source following the deposition path. As a representative case study, the framework was applied to an eight-bead thin-wall deposition produced under a single controlled GMAW condition and compared with thermographic measurements acquired during processing. The simulated temperature fields showed good qualitative agreement with infrared observations during both active deposition and interpass cooling. Quantitative comparisons of maximum surface temperature and local temperature histories also showed that the model reproduced the main thermal evolution of the process, despite the saturation and spatial-resolution limitations of the thermal camera. The simulated thermal histories were interpreted alongside spatially corresponding metallographic observations along the build height. Faster cooling near the substrate was associated with finer acicular ferrite, repeated reheating in the intermediate region promoted more homogeneous equiaxed polygonal ferrite, and slower cooling in the upper region preserved a coarser as-deposited ferritic morphology.