Path planning for the development of quarter iso-grid structure using wire arc additive manufacturing–cold metal transfer (WAAM–CMT): A streamlined and novel manufacturing approach

Self-stiffened structures, such as iso-grid and quarter iso-grid lattices, have emerged as a critical design solution in modern aerospace, launch vehicles, and advanced transportation systems due to their ability to achieve superior stiffness-to-weight ratios, exceptional compressive stability, and damage-tolerant behaviour. Moreover, wire arc additive manufacturing–cold metal transfer (WAAM–CMT) can deliver benefits such as lower heat input, reduced sputtering, improved dimensional stability, higher cladding, and greater energy efficiency. Hence, in the present work, the complex quarter iso-grid structure was manufactured using the WAAM–CMT technique. Initially, an optimised set of parameters, including wire feed speed (10.5 m/min) and welding speed (25 cm/min), was selected based on WAAM–CMT straight-bead trials of SS308L to achieve a stable, optimal bead geometry with acceptable hardness. Moreover, hardness increased, and grains were refined with increased welding speed and decreased wire feed speed. Pertaining to the criticality of nodes in a complex structure, a comparative route evaluation based on actual images and visual characteristics of critical sections, namely angular section, angular T-section, and angular crossing section, was conducted, and specific routes with designations AS7, ATS5, and ACS1, respectively, were identified as the optimal routes and integrated into a three-stage fabrication protocol. By utilising the designed three-step protocol, a quarter iso-grid lattice was successfully developed using WAAM–CMT without any signs of surface or dimensional irregularities. The microhardness was found to be higher for the WAAM–CMT-developed structure compared to its wrought variant, SS308L, which may be owing to the presence of finer dendritic arms with γ -austenite as the dominant phase. Further, the intra-layer bead and bead-surface interface were found to be flawless, with straight beads having higher hardness than nodes, which may be owing to the higher cooling rate and minimal heat accumulation, as the welding speed is steady in straight beads.