Lanigan, Erin

English

NASA Technical Reports Server

Erin Lanigan
NASA Marshall Space Flight Center
Nondestructive Evaluation Team
Manufacturing Problem 
Prevention Program (MP3)
The Aerospace Corporation
El Segundo, California
November 5th, 2019
A NASA Perspective on the Growing Role of In-Situ 
Process Monitoring in Managing Risk of AM Hardware
https://ntrs.nasa.gov/search.jsp?R=20200000032 2020-03-11T13:43:28+00:00Z
2NASA’s 
investment
Use of the 
technology
Qualification 
considerations
This presentation focuses on NASA’s interest in developing 
in-situ process monitoring as a tool for managing risk.
3NASA is most interested in in-situ monitoring for high criticality, 
complex parts that cannot be inspected using traditional NDE.
RS-25 Pogo Accumulator Z-Baffle
• Over 100 Welds Eliminated
• Nearly 35% Cost Reduction
28-Element Inconel® 625 Fuel Injector
Built using laser powder bed fusion (L-PBF)
• Using traditional manufacturing methods:
• 1 year, 163 parts
• Using L-PBF AM:
• 4 months, only 2 parts
• 70% cost reduction
Injector Assembly
MSFC Independent Research and Development (IRAD) 
project with Army Air and Missile Defense (AMD)
Cryogenic Heat Exchanger-Injector-Condenser Demo
4NASA has investigated in-situ process monitoring through 
various mechanisms.
Small Business Innovation Research Grants
OEM Commercial Systems
ASTM Working Group WK62181
“Standard Guide for In-Situ Monitoring of 
Metal Additive Manufactured Parts”
ASTM AM Center of Excellence
Kicked off a study to survey the landscape of 
in-situ monitoring technologies.
5There are many different in-situ process monitoring 
technologies which observe different physical phenomena.
Ultrasonic Frequency SpectrumElectromagnetic Frequency Spectrum
(No external excitation)
Monitor During Build Process Inspection Between Build Layers
Passive
(Added excitation)
Active
Infrared/near-IR 
melt pool monitoring
-
Visual
Laser profilometry
Laser ultrasonic
X-ray
6There are also different additive manufacturing 
technologies that can be monitored.
Powder Bed Systems
Process:
Feedstock:
Freeform Fabrication
Laser Powder Bed Fusion (L-PBF)
Electron Beam Melting (EBM)
Selective Laser Sintering (SLS)
Metals: Nickel alloys, copper 
alloys, titanium alloys, etc.
Polymers: nylon, polyamide
Laser Directed Energy Deposition (DED)
Electron Beam Free Form Fabrication (EBF3)
Rapid Plasma Deposition
Additive Friction Stir Weld
Fused Filament Fabrication (FFF)
Metal powder/wire/chips
Filament: polymer, carbon fiber, 
biological, etc.
7There are two main functions of in-situ process monitoring:
Process Control Function
• Quantitative analysis of part quality
• Requires a known correlation between 
indications, physics of the process, and 
actual defects in the finished part
• Need to know probability of detection
• Extra step – verify actual size, 
location of created defects
• Need to treat it like NDE – believe and 
investigate every indication
• Can’t dismiss anything as a false 
positive unless proven
vs.
Part Quality Function
• Real-time warning of build problems
• Use to check for process drift
• Monitor effects of parameter 
changes, spatter, etc. 
• Not counting on it for quantitative 
part quality metrics or defect 
detection
• May help tell you where to look 
for a problem, but would 
require verification with NDE
8When considering the use of in-situ process monitoring for part 
qualification, there are a few aspects that challenge the current paradigm.
Closed-loop process control
• Often, defect observations are indirect
• Directly observing process variation, inferring final defect
• Must understand physical basis for measured phenomena
• Need to prove a causal correlation from measured indications to defect state
• Probability of detection study must include secondary verification of created defects
• Current qualification logic based on a locked process
• For real-time parameter changes, a new approach is needed
In-process vs. post-process NDE
no longer 
nondestructive
9The current logic of additive manufactured part certification is 
outlined in NASA-STD-6016A, MSFC-STD-3716, and MSFC-SPEC-3717.
MSFC-SPEC-3717MSFC-STD-3716
Policy Procedure
NASA-STD-6016A
Requirements for traditional 
manufacturing – also apply to AM
NASA-STD-6030 NASA-SPEC-6033
Standard for Additively 
Manufactured Spaceflight 
Hardware by Laser Powder 
Bed Fusion in Metals
MSFC Technical Standard MSFC Technical Standard
Specification for Control and 
Qualification of Laser 
Powder Bed Fusion 
Metallurgical Processes 
NASA Technical Standard NASA Technical Standard
Additive Manufacturing 
Requirements for Crewed 
Spaceflight Systems
Additive Manufacturing 
Requirements for Equipment 
and Facility Control
10
The new NASA standards require comprehensive NDE for surface 
and volumetric defects, unless otherwise substantiated.
Language:
“All AM parts shall receive comprehensive nondestructive evaluation (NDE) for 
surface and volumetric defects within the limitations of technique and part 
geometry unless otherwise substantiated as part of the Integrated Structural 
Integrity Rationale of PPP [Part Production Plan] per section 7.3”
Rationale:
• “NDE provides a necessary degree of quality assurance for AM parts in addition 
to the process controls of this NASA Technical Standard.” 
• “There is currently no methodology to preclude all AM process failure modes 
through the available process controls.”
(emphasis added)
11
However, passive in-situ process monitoring may be used as a 
quantitative indicator of part quality, if qualified by the CEO.
Language:
“Prior to use as a quantitative indicator of part quality, passive in-situ process monitoring technologies shall 
be qualified by the CEO to the satisfaction of NASA in a manner analogous to other NDE technologies.”
Rationale:
• “All processes that are used to establish quantifiable quality assurance metrics are qualified to verify 
detection reliability, calibration, and implementation against established criteria. If in-situ monitoring 
techniques are employed for such purposes… the need for such qualification is unchanged.”
• “Certification of a passive in-situ monitoring technology relies upon:
• A thorough understanding of the physical basis for the measured phenomena
• A proven causal correlation of the measured phenomena to a well-defined defective process 
state, and a proven level of reliability for detection of the defective process state.”
(emphasis added)
12
In-situ monitoring can factor into several aspects of part certification.
• Qualification of Material Process (QMP)
• Use in sync with process 
development
• Part Classification
• Improve inspectability for better 
risk posture 
• Inspection process must be 
qualified by CEO
• Part Production Plan
• Integrated Structural Integrity 
Rationale (ISIR):
• Can be specified as a defect 
screening action
• Must be qualified by CEO
• Production Controls
• Could develop certain metrics to 
track over time
• Design
• Part Classification
• Part Production Plan
• Pre-Production Article Evaluation
• Additive Manufacturing Readiness Review
• Qualified Part Process
• Production Engineering Controls
• Production Controls
• Acceptance testing / Statistical Process Control
• Digital Thread
• Definition of Material Process
• Qualification of Material Process
• Equipment Control
• Personnel Training
• Material Property Suite
• Material property data
• Design values
• Process Control Reference Distribution
• Statistical Process Control Criteria
See NASA-SPEC-6033 for 
procedural implementation{
13
Risk-based part classifications for AM parts consider the risk of 
AM manufacturability and inspectability.
Catastrophic Failure?
Heavily Loaded?
Does the build have 
challenging aspects or areas 
that cannot be inspected?
14
The current certification approach does not accommodate the 
use of adaptive systems.
Two issues for verification:
• Monitor the process using sensors (e.g. meltpool thermal signature) and change a 
machine/process parameter (e.g. laser power) to optimize the response
• Currently available in many directed energy deposition (DED) systems
1. Verify the sensor performance, algorithm and machine response
2. Verify the physics – does controlling this parameter result in a good part?
Adaptive (Closed-Loop) Systems
(control system)
(materials)
“Active in-situ monitoring technologies that alter the defined AM process in response to monitored 
phenomena are not currently acceptable per this NASA Technical Standard.”
15
For certifying closed-loop control systems, NASA can leverage the 
expertise of the spacecraft control systems community.
Black box issue:
1. Verify the accuracy of the sensor data
2. Verify the software/algorithm processing and response
3. Verify that the changed parameter responds correctly
• For commercial systems, machine parameters may not be known, 
algorithms may not be accessible
• Ideal approach: collaborate with machine manufacturers
• Can also develop transfer function by studying inputs/outputs
Verification of a control system:
16
Verifying that the adaptive system results in good material is a 
challenge that will require further study.
What parameter will you change?
Assume you’re monitoring the meltpool thermal emissions
Are you looking to keep it constant, or vary it based on part geometry?
More complex if monitoring multiple signals and/or changing multiple parameters
Qualify process for each different system, alloy, part?
What is being monitored, and to what end?
What does it really tell you about the process and the material?
Is this a good indicator of material quality?
Is the resulting microstructure/morphology consistent and repeatable?
17
In summary, NASA encourages and wants to help enable the use of 
in-situ process monitoring for AM certification.
Use for process monitoring is highly encouraged.
→ Will help inform, develop, and prepare for part quality function
To use for quantitative part quality function, monitoring system must be qualified.
→ Main challenge: developing correlation of indication to verified defect
Qualifying closed-loop, adaptive systems will require a new approach to the QMP.
Thank you for your time!
Questions?


A NASA Perspective on the Growing Role of In-Situ Process Monitoring in Managing Risk of AM Hardware

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