Molecules to Manufacturing:

Expanding the Polymeric Materials Toolbox

In-Situ Processing Measurements

Christopher B. Williams

Electromechanical Corporation Senior Faculty Fellow

Associate Professor, Mechanical Engineering

Director, DREAMS Lab

Associate Director, Macromolecules & 

Interfaces Institute

cbwill@vt.edu

http://www.me.vt.edu/dreams
2015 College of Engineering Team Hire 

Hang Yu (MSE)

Michael Bortner (ChemE)

Carolina Tallon (MSE)

James Kong (ISE)

Ran Jin (ISE)

Chris Williams (ME)

Rayne Zheng (ME)

Blake Johnson (ISE)

Tim Long (Chem)

AM Processes Advanced Materials Intelligent 

Manufacturing

VT Additive Manufacturing Faculty

Process Modeling

David Dillard (BEAM)

Scott Case (BEAM)

Steve McKnight (NCR)

Donald Baird (ChemE)

Shashank Priya (ME)
DREAMS Lab: Facilities

Extrusion Metal/Ceramic/Sand Binder Jetting Multi-Material Jetting

Polymer Powder Bed Fusion Mask Projection Vat 

Photopolymerization

6 DoF Extrusion
Additive Manufacturing Research Facilities

Mask Projection Vat 

Photopolymerization (R. Zheng)

Multi-Material Precision Extrusion (B. Johnson)
Research Across the AM Process

AM 

Processes

Advanced 

Materials for AM

Quality 

Assurance

Cyber-Physical 

Security

Application

Workforce 

Development

In-Situ 

Monitoring

Design for AM

Decision 

Support

Metamaterial 

Design Design

Optimization
James Kong (ISE)

Chris Williams (ME) Tim Long (Chem)

AM Processes Advanced Materials Intelligent 

Manufacturing

VT Additive Manufacturing Faculty

Process Modeling

David Dillard (BEAM)

Moore & Williams, Rapid Prototyping Journal, 2014
James Kong (ISE)

Chris Williams (ME) Tim Long (Chem)

AM Processes Advanced Materials Intelligent 

Manufacturing

VT Additive Manufacturing Faculty

Process Modeling

David Dillard (BEAM)

Schultz, Lambert, Chartrain, ..., Williams & Long, ACS Macro Lett., 2014
James Kong (ISE)

Chris Williams (ME) Tim Long (Chem)

AM Processes Advanced Materials Intelligent 

Manufacturing

VT Additive Manufacturing Faculty

Process Modeling

David Dillard (BEAM)

Vu, Bass, Meisel, Orler, Williams & Dillard, SFF, 2014
James Kong (ISE)

Chris Williams (ME) Tim Long (Chem)

AM Processes Advanced Materials Intelligent 

Manufacturing

VT Additive Manufacturing Faculty

Process Modeling

David Dillard (BEAM)

Rao, Liu, Roberson, Kong & Williams, ASME Trans Journal 

of Manufacturing Science and Engineering , 2015
From Molecules to Manufacturing

Opportunity to realize breakthrough products via 

concurrent design of polymer chemistry, 

part geometry, and manufacturing process.
To achieve this goal, we need ...

 Pre-process measurements

 Materials screening methodologies

What makes a material printable?

 Map characterization of raw material to process parameters

 In-situ process measurements

Process-structure-property relationships

How do process parameters affect the printed material?

What is the quality of the printing part’s shape & composition?

 Post-process measurements

Validate quality of final part shape and material

What are the properties of the printed part?
Projection Stereolithography

Image: https://nanocemms.illinois.edu/materials/3d_printing_full

• Selective UV light 

exposure via DMD

– White areas are exposed to 

UV light and cured

– Black areas remain uncured 

liquid resin
Relating Material Properties to 

Process Parameters

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

1 10 100

Cure Depth (microns)

Exposure (energy/area)

Working Curve for Photopolymers

Ec

Dp

Film Thickness

Jacobs, F. (1992). Rapid Prototyping & Manufacturing: Fundamentals of StereoLithography (First ed.), Society of 

Manufacturing Engineers.

Cd = Dpln(Emax / Ec) 
A photocuring accessory offers rheological 

characterization of UV-curable polymers 

TA Instruments-Discovery Hybrid Accessories 

http://www.tainstruments.com

UV Curing Accessory

 High-pressure mercury light source for UV radiation

 UV wavelengths in the range of 320 to 500 nm

 UV-curing accessory with light guide, reflecting mirror 

assembly, and collimator
Photorheology demonstrates decreasing 

photocured plateau modulus with increasing 

PDMS molecular weight

0.1

1

10

100

1000

10000

100000

1000000

10000000

0 50 100 150 200 250 300

Storage Modulus (Pa)

Time (sec)

PDMS2.5K-AA

PDMS5K-AA

PDMS12K-AA

PDMS27K-AA

Gel fraction via soxhlet extract., THF, reflux, 6 h

TA DHR-2 with UV Curing Accessory, 20mm parallel plate, 500 μm gap, 1 Hz, 0.3 % strain, N2

2 wt % DMPA, 7.0 mW/cm2, 30 s delay

Sample G’/G” xover (s)

Plateau 

Modulus (kPa)

Shrinkage

(%)

Gel fraction 

(%)

PDMS3.2K-AA 2.0 1208 0.90 96.0

PDMS5.5K-AA 2.0 667 0.71 95.0

PDMS11.7K-AA 4.0 257 0.36 94.0

PDMS30.6K-AA 2.5 136 0.00 91.5

PDMS-AA
A photocuring accessory offers calorimetric 

characterization of UV-curable polymers
Critical Exposure & Intensity

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20

Storage Modulus, G' (PA) x 100000

Exposure (mJ/cm^2)

Storage Modulus at 0.1 mW/cm2

0

20

40

60

80

100

120

140

160

180

0 200 400 600 800 1000 1200

Storage Modulus, G' (PA) x 100000

Exposure (mJ/cm^2)

Storage Modulus at 20 mW/cm2

• Photorheometry was used to compare critical exposures of 

polymer (with 2wt% QDs) cured at different intensities. 

• Less total energy is needed for lower intensities
Relevant Process Variables

 Exposure

 Wavelength

 Intensity

 Oxygen

 Temperature

 Humidity

 Material 

composition

 Photo initiator

 Photo absorber

 Fillers

 Age
In-situ Measurements for 

Photopolymerization

UV Intensity Correction via CCD

Zheng et al., Review of 

Scientific Instrument, 2012
In-situ Measurements for 

Photopolymerization

In-situ Interferometry

Jarawala, Schwerzel, Rosen, SFF, 2011

Jones, Kwatra, Jariwala, Rosen, SFF, 2013
In-situ Measurements for 

Photopolymerization

In-situ Interferometry + Closed Loop Control

Old World Labs; US 2015/0183168
Complexity of Polymer AM

 Material

 Rheology (shear & temp)

 Stiffness

 Degradation (recycling)

 Environment

 Temperature

 Humidity

 Heat transfer

 Print

 Melt temperature

 Shear

 Toolpath

 Part

 Heat transfer from shape & 

toolpath

 Location
Rheology can be affected by 

thermal history, humidity, time 

0

500

1000

1500

2000

2500

3000

3500

0 1000 2000 3000 4000

Viscosity (Pa.s)

Time (s)

poly(PEG8k-co-NaSIP)

poly(PEG8k-co-CaSIP)

Ares G2 rheometer, 1 % strain, 1 rad/s, Na: 77 °C, Ca: 120 °C
Process & Materials

Big Area Additive Manufacturing

ABS 20% CF-ABS 20% GF-ABS 40% GF-PPS

Printability

Material

Development

Structural 

Integrity

Analyze

Model

Talagain et al., SAMPE Journal, 2015
Heterogeneous Sensing + Data Fusion

13 sensors are installed on the machine.

Which are useful? Can we use all of them? Or should we use a few of them? 

Z. Kong (Virginia Tech) Rao, Liu, Roberson, Kong & Williams, ASME Trans Journal 

of Manufacturing Science & Engineering, 2015
Monitoring Extruder Temperature

Z. Kong (Virginia Tech)
Monitoring Video

Digital Microscope based Machine Vision System

Time

Z. Kong (Virginia Tech)
Monitoring Video

Digital Microscope based Machine Vision System

Time

Data Transformation

Z. Kong (Virginia Tech)
Looking ahead...
http://upload.wikimedia.org/wikipedia/commons/6/68/Fotothek_df_n-20_0000140_Zerspannungsfacharbeiter.jpg

vs.

AM enables a designer to specify material location 

and material properties on a voxel-by-voxel basis.
General AM Embedding Process

1. Design channels

2. Pause build 

(& remove support)

3. Embed component

4. Anchor component

5. Resume build

Stiltner, Elliott & Williams, 2011, Int’l 

Solid Freeform Fabrication Symposium

Meisel, Elliott, Williams, 2014, Journal 

of Intelligent Systems & Structures
Embedded Thermocouples

32

CAD models - channels for thermocouples

Thermocouples embedded during build process
Embedded Fiber Sensor
Material as a Sensor:

Jettable Quantum Dot Photoplymer

a b

Images of jetted QD Nanoink

in (a) visible and (b) UV light

Fluorescent microscope 

images of QD nanoparticles 

in 3D Printed part. Ivanova et al., Add Mfg, 2014; Elliot et al., Adv Eng Mat, 2013

Each polymer card is 

5.0cm x 9.0cm x 1.8mm 
AM Cyber-Physical Security

Design 

& PLM

Quality 

Control

File 

Transfer
STL as an Attack Vector
Security of Quality Control

Quality 

Control

• Replace / modify firmware

• Machine tampering / modification

• Alter recorded data sets (Wells & Camelio)
We must consider the cyber security of 

our in-situ measurements.

Side channel measurements are 

as important as closed-loop control.
In-Situ Impedance-based Monitoring

Sturm, Albakri, Tarazaga & 

Williams, SFF 2016

Albakri, Sturm, Williams & 

Tarazaga, SFF 2015
Online Side Channel Measurements 

Stage 1

Stage 2

Z direction

Stage 3

Attached part (L) and normal part (R)

G codes are different in stage 2; but the same in stages (1) & (3)

Z. Kong & J. Camelio (Virginia Tech)
Stage 1 Stage 2 Stage 3

Normal

Attacked

• Accelerometer (XYZ) mounted close to extruder

• Spectral graph theory based sensor fusion

• Significant overlap of signal features between normal and 

attacked parts in stages (1) and (3), not separable

• Separable signal features between normal and attacked

parts in stage (2)

Online Side Channel Measurements 

Z. Kong & J. Camelio (Virginia Tech)
Acknowledgements

 Collaborators

 Sponsors

 Industrial Sponsors

 National Science Foundation

 #1436592 (PI: Kong)

 #146804 (PI: Camelio)

 Any opinions, findings, and conclusions or recommendations 

expressed in this material are those of the author(s) and do not 

necessarily reflect the views of the National Science Foundation.

 Virginia Center for Innovation Technology

 VT Institute for Critical Technology & Applied Science

 Callie Zawaski

 Justin Sirrine

 Allison Pekkanen

 Lindsey Bass

 Ivan Vu

 Dr. Amelia Elliott (ORNL)

 Dr. Jacob Moore (PSU-Altoona)

 Dr. Nicholas Meisel (PSU)

 Dr. Prahalad Rao (UNebraska)

 Dr. James Kong

 Dr. Timothy Long

 Dr. David Dillard

 Dr. Jules White
Thank you.

Christopher B. Williams

cbwill@vt.edu

1 mm

Molecules to Manufacturing:

Expanding the Polymeric Materials Toolbox

In-Situ Processing Measurements