In-situ dynamic laser area heating during diode point melting for thermal gradient reduction in laser powder bed fusion

Additive Manufacturing (AM) via Laser Powder Bed Fusion (LPBF) generates steep thermal gradients and rapid solidification rates (105–10⁶ K/s) during processing. This can result in the formation of residual stresses and process defects such as cracking and warpage. Conventional thermal gradient mitigation techniques like substrate pre-heating or powder bed heating are energy-intensive, lack spatial precision, and compromise powder recyclability. This study introduces a novel in-situ Dynamic Laser Area Heating (DLAH) method, enabling spatially controlled surface heating up to 400 °C. The system uses a defocused 140 W, 915 nm diode laser with beam-homogenising optics, dynamically aligned to follow the melt pool. DLAH is integrated into a custom Diode Point Melting (DPM) platform that uses a 44 W, 450 nm laser for precision processing of Ti6Al4V powder. The addition of DLAH broadens the processing window by stabilising melt pools over wider scan speeds and energy densities. This enhanced thermal control suppresses stress-driven defects, achieving near-full density (99.99 %) and improved surface finish (Ra = 2.84 µm). Static heating rates reached ∼30.6 °C/s, but during actual scanning, effective cooling rates varied with scan speed and DLAH overlap, allowing spatial modulation of solidification kinetics. Microstructural analysis revealed that DLAH induced coarser α′ martensite (average width ∼ 3.0 µm vs < 2.6 µm) and reduced aspect ratios (2.4–2.5 vs > 2.8), with little change in lath length. These findings show that dynamic, localised thermal management enables control over microstructural features and mechanical properties, offering a scalable solution for improved process reliability and performance in metal AM.