Laser Ultrasonic Testing for Defect Correction during In-Space Additive Manufacturing

Additive manufacturing (AM) has unrivaled capability for rapid, low-cost production of parts directly from a CAD file, but is limited by microstructural defects, which could significantly degrade the structural integrity of the product. Parts for NASA safety-critical applications require 100% inspection to certify uncompromised mechanical performance. There is thus a key opportunity for in-line, in-situ, identification and correction of defects during the AM build to produce finished parts that are already fully qualified, and eliminate the need for scrapping finished defective parts. Laser ultrasonic testing (LUT) is the only currently viable method for in-line defect detection during the AM build. The IOS LUT receiver's automatic compensation for optical distortion enables it to work on rough as-built surface finishes. Its noncontact nature allows it to operate on hot, moving, vibrating surfaces, while quickly moving along the surface of complex geometries. This gives close access to defects for sensitive detection, so that corrective measures can be taken, often during the following build layer, before they are covered over by further deposition. LUT thus has great potential to make AM parts more reliable and cost-efficient. Our previous work has addressed the application of LUT to detect defects in parts during AM conducted on Earth. This proposed project extends that work to AM in space, in reduced gravity. In Phase I we will produce interrupted-build samples with simulated defects on an AM machine designed for use in space, run LUT scans on them, and further develop algorithms and software to enhance defect detection and identification from the scans. We will also make preliminary assessments to show the feasibility of integrating LUT into this AM machine, of greatly reducing LUT system size, weight, power, and cost (SWaP-C), and of in-line correction of detected defects during a build. In Phase II we will develop and test a prototype in-line inspection system.

An in-line LUT inspection system will enable the production of fully qualified AM parts on the surfaces of the Moon and Mars, to support sustainable exploration there, as well as on the International Space Station.

An LUT system miniaturized for in-space use will also find utility in industrial applications where space and power are limited, or where greater portability is desirable. Equipment cost is also expected to be greatly reduced for such a system. The introduction of in-line, real-time laser ultrasonic testing for AM supports Executive Order 13329, "Encouraging Innovation in Manufacturing."

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