The research objective for Phase I is to demonstrate feasibility to: (1) Incorporate sensor data feedback and utilize software tools and computation resources to demonstrate feasibility of a real-time closed-loop solution for WAM; (2) Evaluate the potential impact of the detected build defects on WAM part performance; (3) Detect, identify, and correct build defects for the WAM fabrication of a square coupon of alloy 316 stainless; and (4) Develop a Phase II plan. There are five deliverables: (1) Demonstrate sensors capable of operating in the build environment and software tools that can be integrated in the WAM printing workflow; (2) Generate safe processing window and a process map for WAM; (3) Demonstrate the timeliness of defect detection, its impact on part performance, methods for defect correction; (4) Validate the ability to detect, identify, and correct build defects; (5) Develop Phase II plan to apply the WAM real-time, closed-loop solution to full scale production for a large, complex part of current interest to NASA.
The significance of proposed work to WAM is due to five innovations: (1) An intra-layer controller will be used to maintain smooth metal transfer; (2) Lack-of-fusion and porosity defects will be detected and identified on the basis of anomalies in the in-situ sensing data and melt pool objective metrics, which are dimensionless ratios of melt pool dimensions, overlap between tracks, remelt depth, etc. These objective metrics will be generated using WAM process simulation results and its calibration data; (3) Impact of defects will be calculated as reduction in dynamic properties; (4) Modification of print parameters to correct defects will be obtained using WAM melt pool objective metrics; (5) Local or spot melting will be used to correct lack of fusion and porosity. The purpose these innovations is to allow physics-based knowledge gained via real-time process control for one part to be reused to produce another part.
The proposed work on physics-based, closed-loop control of WAM has direct applications in NASA for the production of low-cost liquid rocket engines and large rockets. In addition, the ability to correct defects has next generation applications under the Space Technology Mission Directorate efforts for Lunar and Mars missions for in-space repair, on-orbit assembly, and space-based AM structures due to limitations on the ability for post-deposition inspection and rework to correct defects.
The proposed work on physics-based, closed-loop control of WAM has direct non-NASA applications such as the sustainment and repair of commercial jet engine components, airframe rib-web structural parts, and complex structures with internal channels. New applications are for functionally-graded, multi-material components, and for WAM with advanced materials (e.g., high entropy alloys).