Accelerating large-format metal additive manufacturing: How controls R&D is driving speed, scale, and efficiency

This article highlights work at Oak Ridge NationalLaboratory's Manufacturing Demonstration Facility to developclosed-loop, feedback control for laser-wire based DirectedEnergy Deposition, a form of metal Big Area AdditiveManufacturing (m-BAAM), a process being developed inpartnership with GKN Aerospace specifically for the productionof Ti-6Al-4V pre-forms for aerospace components. A large-scalestructural demonstrator component is presented as a case-studyin which not just control, but the entire 3D printing workflow form-BAAM is discussed in detail, including design principles forlarge-format metal AM, toolpath generation, parameterdevelopment, process control, and system operation, as well aspost-print net-shape geometric analysis and finish machining. Interms of control, a multi-sensor approach has been utilized tomeasure both layer height and melt pool size, and multiple modesof closed-loop control have been developed to manipulateprocess parameters (laser power, print speed, deposition rate) tocontrol these variables. Layer height control and melt pool sizecontrol have yielded excellent local (intralayer) and global(component-level) geometry control, and the impact of melt poolsize control in particular on thermal gradients and materialproperties is the subject of continuing research. Further, thesemodes of control have allowed the process to advance to higherdeposition rates (exceeding 7.5 lb/hr), larger parts (1-meterscale), shorter build times, and higher overall efficiency. Thecontrol modes are examined individually, highlighting their development, demonstration, and lessons learned, and it isshown how they operate concurrently to enable the printing of alarge-scale, near net shape Ti-6Al-4V component.