Additive Manufacturing (AM) Thrust

The importance and impact of Additive Manufacturing (AM), spanning almost all national and global industrial manufacturing processes cannot be overestimated. The ability to rapidly and reliably manufacture parts and components has transformed the way we currently look at manufacturing enterprise. Additive manufacturing however desirable, brings with itself significant inspection challenges of manufactured parts that take a plethora of shapes, geometries, sizes and properties (e.g., metals, ceramics, polymer-matrix composites, etc.).

In this respect, the following excerpts from a recent report entitled – Rapid Reliability Assessment of Safety-Critical and Emerging Technologies: Next Generation Nondestructive Evaluation¹, succinctly describes the challenges facing AM and four identified key areas in which focused research is needed to overcome these challenges.

“In-Process Additive Manufacturing – Quality and performance evaluation during AM processes is critical for both anomaly detection and prevention. A key barrier to the broad realization of AM, especially for safety-critical parts, is a poor understanding of the anomalies present in an additively manufactured part and their effect on lifetime part performance. This understanding must evolve within the context of the part’s functional requirements, so that manufacturers can determine when an anomaly becomes an unallowable defect. Detecting defects in-situ during the AM process could provide a host of benefits, including:

Early detection of unallowable defects so that building parts can be canceled early, reducing waste;

Real-time feedback and control of the AM process to produce higher quality parts with fewer anomalies;

In-situ repair of defects during manufacturing;

Better correlation of in-process data with final part condition;

Better understanding of the microstructure of the part, especially of internal portions that are difficult to assess; and

Enabling the creation of certifiable parts by AM processes.

AM uses many processes, materials, and raw material forms, which leads to a variety of NDE challenges that are specific to the material and/or process. With polymers, for example, the assessment of shrinkage is complicated. Post-processing, such as hot isostatic pressing, can create defects that must be better understood. Composites, including both polymer-matrix composites and ceramic-matrix composites, are a nascent AM area that is going to be particularly challenging to inspect. Manufacturers have expressed a very strong interest in advancing NDE for metal AM. Better NDE is needed throughout the process—from feedstock evaluation to assessment of powder beds to melt pool monitoring—and for the finished part.

Research into these critical areas is already under way, including with ASTM, which is working with the fabricators industry to develop E07.10 WK62181,^e “New Guide for Standard Guide for In-Situ Monitoring of Metal Additively Manufactured Aerospace Parts.” Federal agencies including the United States Air Force, National Institute for Standards and Technology (NIST), Federal Aviation Administration (FAA), and National Aeronautics and Space Administration (NASA),⁸ as well as the International Organization for Standardization(ISO), ASTM International, American National Standards Institute, and the America Makes Manufacturing USA Center, have held workshops and formed working groups to address the challenges of NDE for AM and have helped to inform critical research directions. The NDE and manufacturing community identified four key areas requiring a research focus:

Advancement of AM anomaly characterization, including characterization of geometric and microstructural anomalies, relation of anomalies to material and part performance, and definition of allowable ranges for anomaly detectability and acceptability.

Integration of NDE with feedback, control, and calibration, including real-time in-situ NDE inspection and analysis, control methods that leverage NDE data, AM machine calibration, and correlation of in-process data with final part condition.

Tools for assessing ceramic-and polymer-matrix composites during AM, addressing the challenges of NDE for multi-material and non-conductive materials.

Development of NDE technologies for metal powder bed AM that enable assessment and characterization of porous material and high-temperature melt pools.”

Center for Nondestructive Evaluation (CNDE), in cooperation with faculty from various academic departments at Iowa State University (ISU) and scientists at Ames National Laboratory (US Department of Energy) are working together, under an initiative to form a Thrust within CNDE to address a multitude of challenges pertinent to AM processes and in-situ and post-manufacture NDE of parts. This collaboration brings together scientists and engineers contributing to this Thrust through incorporating their unique and diverse NDE modalities (singularly or as a team) and know-how to address these challenges. Some of the specific AM NDE Capabilities and Processing Infrastructure are provided here.

AM-NDE National Testbed Initiative

Processing

The Rapid Manufacturing and Prototyping Laboratory, where work is performed on traditional Additive but also Hybrid Manufacturing. Hybrid manufacturing is the combination of Additive and Subtractive manufacturing. A rapid machining technology called CNC-RP has been developed, which enables push-button process planning for CNC machining and a rapid tooling technology that can create pattern and mold geometries for casting.

Research in process planning also includes planning AM build processes to enable post-process machining, including setup and orientation planning along with support structure use. Work is ongoing in the combination of hybrid in both serial (print then machine) and iterative (print, machine, repeat). A significant machine capability in the laboratory is a 5-axis HAAS CNC milling center with both Directed Energy Deposition and Screw-extrusion polymer printing.

The AM system is an AMBIT retrofit with a 1kw fiber laser, 1 mm and 3 mm metal deposition heads with dual metal powder feeders, along with a 1-5 mm screw extrusion system for polymers. PoC: M. Frank

Rapid Manufacturing and Prototyping Laboratory

A rapid machining technology called CNC-RP has been developed, which enables push-button process planning for CNC machining and a rapid tooling technology that can create pattern and mold geometries for casting. Research in process planning also includes planning AM build processes to enable post-process machining, including setup and orientation planning along with support structure use.

Work is ongoing in the combination of hybrid in both serial (print then machine) and iterative (print, machine, repeat). A significant machine capability in the laboratory is a 5-axis HAAS CNC milling center with both Directed Energy Deposition and Screw-extrusion polymer printing. The AM system is an AMBIT retrofit with a 1kw fiber laser, 1 mm and 3 mm metal deposition heads with dual metal powder feeders, along with a 1-5 mm screw extrusion system for polymers. PoC: M. Frank

Rapid manufacturing — Hybrid Additive/Subtractive manufactured Titanium components from the RMPL laboratory

Powders for AM

Ames National Laboratory has two high-pressure gas atomization units capable of making powder metal feedstock for AM. Capacity varies from 2 to 25 Kg. Plans are in place to construct a third unit, which will allow greater capacity of ~100 Kg, more in line with the needs for many commercial powder bed systems.
PoC: I. Anderson

Advanced Characterization for AM

The Sensitive Instrument Facility (SIF, website: sif.ameslab.gov) at Ames National Laboratory was completed in May 2016. It is the home of several state-of-the-art electron beam microanalysis instruments. The SIF has an FEI Titan Themis 300 Cubed probe aberration corrected (scanning) transmission electron microscope with monochromator, Super-X EDX detector, GIF quantum ER system, a biprism, and a Lorentz lens, which is specially designed for magnetic domain imaging. An FEI Tecnai F20 (S)TEM with Nanomegas PED system enables quick phase and orientation mapping of materials with nanometer resolution. An FEI Teneo field emission SEM with Oxford EDS/EBSD for combined elemental and phase mapping as well as texture determination; an FEI Helios Gallium Focus Ion Beam (dual beam) system with easy lift-out capabilities for TEM and 3D atom probe sample preparation, as well as auto-slice capability for 3D reconstruction. All these capabilities enable rapid, precise navigation from mesoscopic to atomic scale, as well as study of intrinsic magnetic and electric fields.
PoC: L. Zhou

Novel Alloys

Materials Preparation Center (MPC) was established in 1981, the MPC is a one-of-a-kind facility that is acutely sensitive to the needs of researchers. Providing research and developmental quantities of high-purity materials and unique characterization services to scientists at university, industry, and government facilities on a cost-recovery basis, the MPC allows access to novel materials and new technologies as they are developed. Most notably, the MPC is regarded as the premier source of high-purity rare earth metals, alloys, and compounds and continues to synthesize and prepare rare earth metals according to processes and protocols originally developed by Ames National Laboratory scientists. High-purity materials have led directly to scientific and technological advances by avoiding the confusion that often results when impurity effects blur the true intrinsic properties of materials. Meeting the requirements for high-quality materials and synthesis is even more essential today as vital materials of scientific and technological importance grow ever more complex.
PoC: M. Besser

Micro/nano Scale AM & Hybrid Manufacturing

The Flexible Electronics and Additive Printing (FEAP) Laboratory is led by Dr. Hantang Qin. The research areas include micro/nano scale fabrication, novel additive manufacturing processes (direct energy deposition), rapid prototyping methods and tools, and manufacturing systems based on inkjet printing and laser ablation for flexible electronics and optoelectronics. Ongoing projects include a feasibility study for 3D printing of concrete, in-situ NDE for direct energy deposition (DED), CT-scanning for pipeline inspection, development of in-space micro gravity 3D printing technique, 3D bioprinting for oral immunology, metrology and NDE for micro/nano manufacturing and additive manufacturing systems, 3D printing of solid state batteries, and laser ablation for flexible electronics.

The major laboratory infrastructure and resources that are available for these purposes are:

Electrohydrodynamic inkjet printer based on Aerotech 3-axis ANT130L Linear Nanopositioning Stages: the accuracy for X&Y&Z-Axis are +/- 0.3 microns, the repeatability for X&Y&Z-Axis is +/- 0.075 microns.

Zoom Lens and Machine Vision System: Navitar 12X zoom offers 12X (0.58-7X) magnification, and CMOS camera from ImagingSource offers 4.8 µm pixel sizes.

Hirox RH-2000E Focus Variation Microscope

ML869A He-Ne Laser Modulated 2.0 mW: Class IIIa laser

WPI PUL-1000 Micro Pipette Puller

Coherent LPX Pro 220 F ArF excimer laser: Class IV laser

Direct energy deposition machine (DED) in IMSE department

PoC: H. Qin