NOVEL SIGNAL ANALYSIS TECHNIQUES

• Determine key signatures from complex signals

• Use to design optimal filtering and signal

processing

Time - [ms] Frequency - [kHz]

500 1000 1500 2000 2500

0

10

20

30

40

50 Pre-contour

First Stripe 

(Towards Camera) Post-contour

Second Stripe

(Away from Camera)

Third Stripe

(Towards Camera)

Fourth Stripe

(Away from Camera) JTFA of 

Photodetector

SWIR Camera 

Frames

SYNCHRONOUS ACQUISITION of HIGH FIDELITY

and LOW FIDELITY SENSOR SIGNALS

• High speed imaging/thermography provides

physical context for single-point sensors

• Use to relate observed phenomena (spatter,

keyholing, melt pool dynamics, plume dynamics) to

detector signal features

AMMT Metrology Systems, Tools, and Capabilities 

Laser Powder Bed Fusion (LPBF) Additive Manufacturing Process

FULL HIGH SPEED CONTROL OF LASER SPOT

• Position, power, speed, spot size control at 100 kHz

• Programmability with “AM G-code”

• Intra-vector and inter-vector power speed and position control

WHAT IS IT?

• Powder bed fusion: process in which thermal energy selectively

fuses regions of a powder bed (ISO/ASTM 52900:2015)

• LPBF is also known as Selective Laser Melting (SLM), or Direct

Metal Laser Sintering (DMLS).

• Common materials:

• Nickel alloy

• Aluminum alloys

MAJOR U.S. INDUSTRY INVESTMENT

• Aerospace, Biomedical, Automotive, Rapid

Prototyping, ...

1. Create 3D 

geometry 

model using 

CAD software

2. Apply layer 

of metal 

powder on 

substrate

3. Solidify powder 

by melting with 

controlled laser 

spot

4. Lower 

substrate by 

one layer 

thickness

5. Spread 

new powder 

layer

6. Repeat 

process for 

1000s of 

layers

7. Remove 

non-sintered 

powder

8. Post process to 

create final part 

(heat treatment, 

machining, etc.)

Repeat process for 1000s of layers 

Laser

Additive Manufacturing Metrology Testbed (AMMT) Research Goals for Advancing LPBF

Research Methods

Measurement Science for Additive Manufacturing at NIST

FUNDAMENTAL PROCESS PHYSICS RESEARCH

• Process parameter development

• Laser scan strategy development and optimization

• Defect formation mechanisms (pores, cracks, residual stress)

• Measurement of process physics (melting, wetting,

vaporization, radiant emission, plasma emission)

PROCESS MONITORING RESEARCH

• Develop “certify as you build” methodologies

• Calibration/characterization of monitoring instruments

• Probability of detection (PED) analysis of defects

• Develop correlations between input parameters, in-situ

process signatures, and final part qualities

CONTROLS RESEARCH

• Open architecture process control (G-code)

• Image/sensor signal processing

• Real-time power/velocity feedforward or feedback control

• Process-intermittent control (once-per-layer)

Bottom Line:

Optimized LPBF Process, High Quality Repeatable 

Parts, Methods for Rapid Certification

Rapid material and process development

• Improved fundamental understanding. 

• Known required parameters for each new material.

Targeted Sensing: 

• Know the physical source of sensor signatures to 

further guide sensor development, signal 

processing, and measurement uncertainty

Exemplar reference data: 

• Development and validation of models/simulations

• Inter-comparison with outside developers, 

sensor/controls developers, and OEMs

Monitoring Methods for “Certify as You Build”

• Quality-correlated metrics from sensor signals 

mapped to x,y,z,t during the build process

Reduced stochastic variability

• High speed feedback control of noisy process

Figure from EOS GmbH

CHALLENGES

• Inconsistent build quality, part-to-part variability

• Multiple part deficiencies:

Forward-Looking Research 

Possibilities

Rapid Growth of Metals AM in Industry

Uncertainties in powder characteristics

coupled with uncertainties in the AM

process and equipment lead to

uncertainties in the final product

Above: Example LPBF-built complex 

geometric structures and parts 

TYPICAL LPBF PROCESSING 

PARAMETERS

• Laser power: 50 W to 500 W

• Laser spot size: 30 to 200 mm

• Scan speed: 1 to 4 m/s

• Powder size: 5 to 60 mm

• Layer thickness: 20 mm to 50 mm

Left: Image of LPBF 

laser interacting 

with the metal 

powder

MARKET NUMBERS (Wohlers 2016)

• AM products and services: estimated

$2.365B in 2015, +18% from 2014

• Metal AM machine sales: 808 machines

sold in 2015, +46.9 % from 2014

• Nearly 5x growth of the AM market

since 2010.

• General Electric to invest $1.4B in metal

AM OEM acquisitions, announced 2016.

• NIST Laboratories (EL, PML, MML, ITL, 

CNST, NCNR)

• Industrial stakeholders (R&D, America 

Makes Members, AMC Members) 

• Other federal agencies (DOD, NASA, 

FAA, FDA)

• Academia and International 

collaborators

ADDITIVE MANUFACTURING

Process of joining materials to

make parts from 3D model data,

usually layer upon layer, as

opposed to subtractive

manufacturing and formative

manufacturing methodologies.

(ISO/ASTM 52900:2015)

• Volumetrically Controlled 

Microstructure

• High Temperature Melt Flow 

Dynamics

• Plasma/Plume Dynamics and 

Spectroscopy

• Ceramics, Composites, and New 

Alloy Development

FOCUS ON NON-CONTACT, RADIOMETRIC and IMAGING SENSORS

• Laser co-axial melt pool monitoring and build surface imaging

• Stationary global melt pool monitoring and build surface imaging

Fully controllable XY 

galvanometer 

positioning

Variable Focus Lens 

• Enable optimized 

imaging performance 

and laser focus control

• Reduced chromatic 

aberration

External port for offline 

observation

Controlled positioning of carriage provides access for coaxial instruments onto standards module

Low-res in-situ 

layerwise monitoring 

camera

Open platform for process 

monitoring cameras:

• Optimized for NIR spectrum

• Moderate mag (1x)

• High speed (>50 kHz), buffered 

• Low speed (<10 kHz), FPGA 

connected for feedback control

SUPPORT for OTHER NIST RESEARCH

• PML and TEMPS Support: provide functional 

platform for stable, continuous melt pool 

control for radiometric measurements.

• MML Support: Highly controlled and 

characterized sample or alloy construction 

KEY SYSTEM DEVELOPMENT 

BENCHMARKS

• Co-axially imaged melt pool at high frame 

rates (>50 kHz)

• 100 kHz laser position, speed, and power 

control

• Characterization of laser spot intensity 

distribution, position/speed control errors.

• Multi-layered, continuously monitored AM 

build

• Power-speed feedback control based on coaxial sensors

Key Beneficiaries

Instrumented Recoater Platform

• Multiple recoater type options 

(flexible, solid, roller, ...)

• Platform for variety of sensors and 

instruments

• Microscopic imagers

• Illumination sources

• AE, UT, or Accelerometer

LPBF RESEARCH AREAS ENABLED BY THE AMMT RESEARCH OUTPUT/GOALS

Defects: Pores, cracks, lackof-fusion

High surface roughness, 

surface cracks

Top view

15 mm

In-plane stress

1.3 mm from top MPa

High residual stress, distortion

316L

Multi-materials 

(courtesy I. Yadroitsev)

Controlled microstructure 

(courtesy ORNL)

Plasma plume spectroscopy 

(Gao et al., Appl. Surf. Sci. 2015)

METROLOGY SYSTEMS FOR LPBF MONITORING & CONTROLS RESEARCH

• Stainless steels

• Titanium alloys

• CoCrMo

• Maraging steels

500 μm

Inhomogeneous, anisotropic 

microstructure

500 

m

m

Designing & 

planning

Material 

Characterization

Process Monitoring 

and Control

Qualification of 

Part

Removable 

Splitter/ Reflector

Standards Module

(Light source and 

reflectance reference)

Powder 

Feed Bed

Low (<100 °C) or High 

(>400 °C) temperature 

heated build bed

Custom 

Imaging Lens

TEMPS Beampath

High purity Ar purged 

environment

Open platform for high-mag melt 

pool monitoring

• VIS to MIR (minus laser band)

• High magnification (3x)

• Optional illuminated build bed

500 W Yb fiber laser

High intensity LED 

illumination sources

Open platform for FPGAconnected optical sensors

• VIS-NIR spectrum

Metal matrix nanocomposite 

(Wu et al. JMPT 2011)

Melt flow simulation 

(courtesy LLNL)

Plasma/plume dynamics

(NIST)

CORRELATION BETWEEN PROCESS 

PARAMETERS, PROCESS SIGNATURES, 

and PRODUCT QUALITIES

• Utilize NIST-wide capabilities and ongoing

cross-laboratory collaborations for powder

characterization, destructive and nondestructive final part materials testing.

X-ray CT

Surface 

Roughness

Microstructure 

characterization

Mechanical 

Testing

Residual Stress 

Measurement

Powder materials characterization 

(physical, chemical, thermal)

Controlled scan 

strategies

MATERIAL & PROCESS PARAMETERS

FINAL PRODUCT QUALITY METRICS

IN-SITU PROCESS SIGNATURES

FOUR THRUST AREAS

• Characterization of AM 

Materials

• Qualification for AM Materials, 

Processes, and Parts

• Real-Time Monitoring and 

Control of AM Processes

• Systems Integration for AM

1

2 3 4 5

6 7 8

001 101

111

Example layer-wise 

image of part surface, 

feature recognition, 

and corrective action 

taken by controller

Example lasercoaxial melt pool 

image. Melt pool 

appears stationary 

in frame.

SOLUTIONS USING CUSTOM TESTBED

• Enables full control and flexibility to produce well

characterized research results

• Integrated through digital thread, results can

facilitate rapid part qualification and widespread

adoption