Real-Time Geometric Analysis of Additive Manufacturing

Current selective laser melting additive manufacturing (AM) systems do not have adequate process control features for wide-spread adoption across NASA. In this project Mound Laser & Photonics Center (MLPC) will work with Wright State University (WSU) to implement a novel system for layer-by-layer in-process monitoring for AM. The key innovation in this work will be the use of a line-laser profilometer (LLP) for 3-dimensional, in situ, sub-micron profilometry on every layer during an AM process, both before and after the layer has been melted. Several advantages will be gained from this approach: (1) Measurements on the spread powder layers will determine powder distribution and quality, enabling correlation between powder distribution and finished part material properties such as microstructure and density; (2) Measurements on the melted layer profile will determine the geometric accuracy of the melted layer (both in depth and lateral dimensions), compared to the CAD file, and allow correlations between geometric accuracy to powder distribution, laser parameters, and material properties; and (3) simple layer defects will be easily identified before the next layer is spread. This technology could enable real-time process qualification, and eventually automatic powder re-spreading or layer re-melting to fix defects in the layer. In this project, the SBC (MLPC) will build test coupons in their custom-built, fully tunable, research-grade AM testbed and monitor the build process with the LLP. The RI (WSU), who has tremendous expertise in AM sample characterization, will then perform in-depth material analysis on the test coupons to determine material properties. At the time of this proprosal, MLPC has already determined that the LLP can measure the AM testbed with micron-scale accuracy. Therefore, achieving success with this approach is very likely, the primary needs for implementation are the development of experimental methods and process control correlations.

(1) Improving SLM additive manufacturing processes: The in-process profilometry data collected in this STTR will be fully quantitative and useful for controlling AM processes. This will be possible through direct experimentation on the user's machine, experimentation across machines, or by supplying quantitative data to validate process modelling. (2) Non-Destructive evaluation (NDE) and part qualification: This project will provide verification and qualification of the build consistency, identify build errors layer-by-layer, and possibly enable inspectable 3D models of the built part constructed from the LLP measurements. (3) Materials Genome Initiative: The correlation of process parameters and sensor data to resultant material properties and microstructures would directly support NASA's role in this multi-agency initiative by providing better empirical methods to validate computational modeling of additive manufacturing processes. (4) Final inspection of part geometry: The LLP can measure the dimensions of finished parts. For dimensionally critical systems this is an important step, and using the same sensor for both in-process monitoring and post-process geometric verification will streamline the production process. (5) Closed-loop processing: Closed-loop process control could be realized by measuring each layer both before and after melting, and making automatic adjustments based on LLP feedback.

(1) Commercial aerospace applications have a high overlap with NASA applications, including strong interest in fabrication of rocket engine components and a variety of other lightweighted structures. (2) The US Army Armament Research and Development Engineering Center (ARDEC) has expressed an interest in AM process control technology. They seek to use AM manufacturing to enhance munitions and weapon systems under development at Picatinny Arsenal. ARDEC hopes to implement a process monitoring solution on commercial AM machines (made by EOS and SLM Solutions GmbH) (3) Sensorized Process Development Cell (PDC) for general research: There is a general frustration in the market with the limitations of commercial AM machines. End users are typically constrained to given material types and build protocols. Several institutions have expressed interest in obtaining a PDC similar to the one MLPC has developed for its own research. Examples are Rolls-Royce North America, and Lawrence Livermore National Laboratory. Integration of the PDC with the LLP-based process monitoring system developed under this project will create a comprehensive, low cost tool for AM research. (4) Miniature AM processes: MLPC also has a direct interest in using the STTR sensor technology, integrated with its PDC, to develop miniature additive manufacturing techniques to make components for the medical device industry.

This is early/mid-stage (TRL 4) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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