To achieve the desired mechanical properties from additively manufactured (AM) parts, post-processing is often required to modify the unconventional microstructure in the as-built configuration. However, this can undermine the benefits of AM as a limited-supply-chain and time-critical manufacturing method. To alleviate this situation, in situ grain modification methods, such as scanning strategy and field assist, are investigated as alternatives to post-processing. Among other field assist methods, ultrasonic treatment (UT) offers a low-cost, highly transferable, and effective solution. However, for extended builds, it suffers from limited understanding of ultrasonic wave attenuation and its interaction with the material subgrain structure. In this study, grain structure evolution induced by low-intensity UT across the build direction is investigated using high-magnification imaging and microhardness analysis. It is found that while low-energy UT, below previously reported levels, can cause beneficial modification of the microstructure. The attenuation of wave propagation is transient along the build direction and depends on spatial orientation, such as upstream and downstream locations relative to the shielding gas flow. However, it depends on the wave attenuation, and the effect becomes negligible after 25% of the total build height. It was found that UT reduced the area fraction of the Laves phase by 7% in the bottom region. Despite this limitation, it was found that low-power UT, at 2.1% of the industry-standard (persistently used) value, can be used to achieve favorable grain-structure modification in the PBF-LB/M process.
Lightweight cast automotive components are essential for reducing CO₂ emissions while ensuring sufficient structural performance. Sand casting of nodular cast iron remains a cost-efficient method for producing complex geometries; however, thin-walled sections are still challenging due to risks of incomplete filling, core-removal constraints, and defects associated with rapid solidification. This study introduces an integrated workflow that links topology optimization, casting-aware redesign, and shape optimization to develop a thin-walled demonstrator for a trailer component. Beginning with a simplified design space, topology optimization was used to establish an efficient load-carrying design. The geometry was then reworked to fulfill key casting constraints, including minimum wall thickness and core removability. A subsequent shape optimization step refined the hole regions to reduce local stress concentrations, while casting simulations were employed to assess manufacturability and identify potential defect-prone zones. The proposed workflow provides a manufacturing-oriented approach for converting topology-optimized designs into castable thin-walled components under realistic process constraints. By combining structural optimization with process-driven design adaptations, it delivers a lightweight and mechanically robust design that was experimentally validated through successful sand casting of the demonstrator.
