ORALS

<p>This article addresses modeling of the solidifying material structure during 3D welding/printing of fully dense Mg alloy products by fused deposition of molten droplets from a uniform droplet spray source on a motorized X-Y table substrate [1]. The resulting crystallite size distribution is simulated by a solidification model consisting of nucleation/fragmentation and constrained growth description, calibrated via structural data from a single droplet splat [2]. This is enabled by a semi-analytical thermal modeling framework, based on superposition of moving Green's and Rosenthal functions for the temperature field from a Gaussian source distribution [3], in which the deposit solid geometry and heat transfer boundary conditions are accounted for by mirror source images of modulated efficiency [4]. The simulation model is implemented for layered ellipsoidal deposit sections on planar substrates by multi-pass spraying, and its predictions are validated against measured crystal size by image analysis of experimental micrographs of a Mg97ZnY2 alloy, to an error margin of +15%. The computationally efficient simulation provides insight to the deposit microstructure, and is intended as a process observer in a closed-loop, adaptive control scheme based on infrared temperature measurements.</p>

References:
<p>[1] Fukuda H, "Droplet-Based Processing of Magnesium Alloys for the Production of High-Performance Bulk Materials", PhD Thesis, MIE Dept, Northeastern University, Boston, MA (2009). [2] Ioannou Y, Fukuda H, Rebholz C, Liao Y, Ando T. Doumanidis C.C, "Constrained crystal growth during solidification of particles and splats in uniform droplet sprays", Int J Adv Manuf Technol 107, 1205&ndash;1221 (2020). [3] Rosenthal, D., "Mathematical Theory of Heat Distribution During Welding and Cutting", Welding Journal 20 (5), (1941), pp. 220s - 234s [4] Carslaw, H.S., Jaeger, J.C., Conduction of Heat in Solids, 2nd Ed, Oxford Science Publ. (1951)</p>