Yazar "Mumtaz, K" seçeneğine göre listele

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    Öğe
    In-situ Dynamic laser area heating during diode point melting for thermal gradient reduction in laser powder bed fusion
    (ELSEVIER SCI LTD, 2025) Aydın, A; Çetin, E; Mumtaz, K
    Additive Manufacturing (AM) via Laser Powder Bed Fusion (LPBF) generates steep thermal gradients and rapid solidification rates (10(5)-10(6) 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 degrees 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 mu m). Static heating rates reached similar to 30.6 degrees 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 alpha ' martensite (average width similar to 3.0 mu m vs <2.6 mu m) 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.
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    Öğe
    Laser powder bed fusion of Ti6Al4V using low-cost high efficiency 450 nm diode point melting
    (ELSEVIER, 2025) Aydın, A; Çetin, E; Erman, SC; Mumtaz, K
    Laser Powder Bed Fusion (LPBF) is a commonly used Additive Manufacturing (AM) method for the production of geometrically complex metal components that are used in high-value sectors. It uses high power fibre lasers directed by a galvanometric scanner to rapidly melt powdered feedstock. LPBF systems are expensive, making them inaccessible to many sectors and have challenges related to in-process thermal control, production of large components and scalability limitations. As an alternative to traditional LPBF, this study introduces Diode Point Melting (DPM), combining multiple low-power, energy efficient blue (450 nm) diode lasers into a single focal point. DPM's laser source is fixed to a scanning gantry axis that traverses across the powder bed, creating a low-cost alternative to traditional LPBF (similar to x10 lower laser hardware cost). DPM processes slower than LPBF, generating reduced thermal gradients with improved material laser energy absorption due to use of a shorter laser wavelength. DPM processing of Ti6Al4V was undertaken using 38W creating samples that were 99.41% dense. DPM's slower melt pool solidification rate enabled the formation of a stable alpha + beta phase creating harder samples. The grain size of Ti6Al4V samples fabricated using DPM were significantly larger compared to those produced by LPBF (grain size area similar to x30 larger). Young's modulus of the samples produced via DPM was found to be higher than LPBF manufactured Ti6Al4V, indicating increased stiffness. DPM is a promising low-cost alternative to LPBF, offering the opportunity to make net-shape metal AM more widely accessible in both academic and industrial sectors.