Virtual Prototyping and Experimental Assessment of Gating-System Optimization for Rapid Investment Casting of Miniaturized Cu–Al–Mn Shape Memory Alloy Helical Springs

Abstract This study investigates the optimization of a gating system for the rapid investment casting of miniaturized Cu-7.90Al-5.40Mn (wt.%) shape memory alloy helical springs by combining virtual prototyping through numerical simulation with representative casting trials. Sixteen simulation cases were examined as a function of primary runner-end geometry, injection direction, spring orientation, number of 0.70 mm vents, rotational speed (350–450 rpm), and pouring temperature (1039–1053 °C). The numerical analysis focused on recirculation, backflow-related mass loss, filling completeness, predicted void formation, misrun sensitivity, and shrinkage porosity. The results showed that the original spherical runner end promoted excessive recirculation and incomplete filling, whereas progressive redesign of the runner end substantially improved flow stabilization. Complete simulated filling without predicted void formation was obtained for the optimized runner-end design at 400 rpm/1043 °C and 450 rpm/1043 °C. Experimental castings using the optimized design showed markedly improved external integrity and filling quality relative to the baseline configuration, with the best overall experimental result obtained at 350 rpm/1053 °C. The cast-processed springs demonstrated successful thermomechanical actuation, where shape recovery is triggered by heating above 110 °C following initial deformation in the martensitic state at room temperature. Overall, the study demonstrates that modeling-based virtual prototyping is an effective tool for guiding gating-system redesign in the rapid investment casting of miniature Cu–Al–Mn SMA components, especially in geometries that are highly sensitive to backflow, gas evacuation, and local filling instability.