Hybrid directed energy deposition for fabricating metal structures with embedded sensors

Hybrid additive manufacturing combines additive manufacturing (AM) and traditional subtractive processing with synergistic layerwise access. The integration of both manufacturing methods simultaneously enables the benefits of AM (complex geometries and mass customization) with the benefits of traditional processes (superior surface finish and improved dimensional accuracies). By leveraging access to the structure at intermediate layers during fabrication with a suite of additional processes (e.g. component placement and micro-dispensing of functional inks, machining, etc.), the next generation of metal structural elements with printed internal sensors can be fabricated without the need for specific tooling (i.e. optical masks). A multi-axis motion platform allows the printing of sensors in arbitrary planes and on curved surfaces that can be subsequently embedded within the structure using additional laser cladding. Embedded printed sensors in metal have been demonstrated for decades in additive manufacturing, but have required tooling and disparate processing steps unsuitable for integration within AM directly. In this report, an Ambit™ system was used to fabricate a proof-of-concept tensile bar with an embedded thick-film printed strain sensor, and consequently, the potential for digital fabrication of multi-functional metal structures within a single manufacturing system without tooling was demonstrated. Careful process planning and thermal shielding are required to ensure the survival of printed sensors during the final high-temperature consolidation. A study was conducted to investigate the required thickness of protective plates, and for the thickness of 2.25 mm, sensors were functional. Both in situ and post-manufacturing data were captured. Failure analysis was performed on the non-operational sensors to understand the challenges of the proposed approach.