Influence of the process parameters involved in WAAM on the quality of single-bead deposited layers of low-carbon steel

Abstract Wire Arc Additive Manufacturing (WAAM) based on Gas Metal Arc Welding (GMAW) offers high deposition rates and scalability for large structural components. However, systematic understanding of how key process parameters influence single-bead deposit quality remains limited for low-carbon steels. This study investigates the effects of three input process parameters — arc power ( P = 2.9, 3.3, 3.5 kW), travel speed (v = 300, 450, 600, 750 mm/min), and stand-off distance (SOD = 8, 12 mm) — on the quality of single-bead deposits of low-carbon steel (AWS ER70S-6 wire, Ø 1.0 mm) at constant wire feed rate (Sw = 171.4 mm/s). A full factorial design comprising 24 conditions was applied to low-carbon steel substrates. The output responses — bead height, bead width, cross-sectional area, contact length, dilution ratio, peak temperature, microstructure morphology, and Vickers microhardness (HV1) — were systematically characterized through cross-sectional image analysis, infrared thermography, optical microscopy, and microindentation testing. Results showed that travel speed was the dominant parameter: increasing v from 300 to 750 mm/min reduced bead cross-sectional area, steepened thermal gradients, refined columnar grain morphology from coarse equiaxed to finer vertically-aligned structures, and raised microhardness (from 200 to 215 HV1 to 220–245 HV1 at P = 2.9 kW). Arc power primarily governed bead width and dilution; increasing P from 2.9 to 3.5 kW enlarged the bead–substrate contact length by 15–20% and enhanced conductive heat extraction into the substrate, paradoxically reducing peak bead temperature despite higher energy input. Stand-off distance significantly affected dilution ratio and penetration depth but showed minimal influence on bead width, height, and microhardness, enabling independent control of interlayer bonding without altering component cross-section. A stable process window was identified for v = 450–750 mm/min at P = 2.9–3.5 kW, while v = 300 mm/min produced kissing bonds ( P = 2.9 kW) or excessive penetration ( P ≥ 3.3 kW). The ferritic–pearlitic microstructure was preserved across all conditions, confirming that hardness variations arose from grain-size and dislocation-density effects rather than phase transformation. These parametric relationships provide a quantitative foundation for multi-layer WAAM process design of low-carbon steel components.