Shape optimisation of metal additive manufacturing connections in lightweight steel structures

The application of metal additive manufacturing (AM) to connections in lightweight side framing structure is explored. Two connection concepts are considered, namely key-wheel (KW) and gear-wheel (GW) connections. To identify the optimal wheel geometries for the proposed KW and GW connections, a genetic algorithm with multiple-objectives optimisation framework was employed. The optimised parameters included wheel radius R, tooth number n, along with other geometrical wheel parameters. The optimisation objectives were to maximise the initial rotational stiffness, yield strength and peak strength directly for the connections with Laser Metal Deposition (LMD) process, while an additional constraint of normalising these objectives with respect to material use was introduced for the connection with Wire Arc Additive Manufacturing (WAAM) process. The optimisation results suggest a wheel shape with 12 elongated teeth for the KW connection, and a shallow-tooth wheel shape for the GW connection. The maximum joist deflections of the frame-level analysis are reduced by 14%–20% when employing the optimised connections, while the normalised initial stiffness, yield strength and peak strength are increased by 69.6%–101.2%, 58.7%–212.6%, 48.8%–164.7%, respectively. In general, GW connection exhibits greater level of mechanical properties compared to the KW connection, while both connections offer viable alternatives since each of them showed trade-offs depending on performance requirements and practicality.