Thermal history and microstructural evolution in MIG-Wire Arc Additive Manufacturing of low carbon steel: influence of key process parameters

Abstract This study investigates the influence of wire feed rate (WFR) and travel speed (TS) on Wire Arc Additive Manufacturing (WAAM) through a comprehensive experimental approach. Using an instrumented CNC machine with integrated voltage and current sensors, along with thermal IR imaging, we monitored process parameters and temperature evolution during multi-layer depositions. The experimental results revealed significant correlations between processing parameters and deposited bead geometry, microstructure, and mechanical properties. At lower travel speeds (250 mm/min), cooling rates remained relatively constant (~ 27 °C/s) across subsequent depositions, while higher travel speeds (1000 mm/min) produced significantly higher cooling rates (up to 115 °C/s) that varied with distance from the base plate. These variations in cooling rates directly influenced microstructural development, with higher travel speeds producing finer grain structures and increased microhardness (up to 283 HV compared to 237 HV at lower speeds). The study establishes predictive models for bead geometry based on mass conservation principles and identifies critical factors affecting microstructural evolution throughout the build height. These findings provide valuable insights for optimizing WAAM processing parameters to achieve desired geometrical accuracy and mechanical properties in additively manufactured components.