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Each overseas military engagement brings a new set of

logistics problems. Traditionally, providing fuel to troops in

the forward battlespace has been a difficult assignment for

logisticians, and delivering fuel to forces in Afghanistan is

no less of a challenge. Currently, logistics teams face the

complex and risk-laden task of

delivering fuel to forward operating locations in a country that

is known for its rugged, mountainous terrain. Recent testimony from the Government

Accountability Office described this particular logistics

challenge. “Transporting large quantities of fuel to forwarddeployed locations presents an enormous logistics burden

and risk. Long truck convoys moving fuel to forwarddeployed locations have encountered enemy attacks, severe

weather, traffic accidents, and pilferage.”[1] While logistics

teams have been successfully providing engaged forces with

the supplies (including fuel) required to carry out their mission, any technology to ease this logistics burden and

reduce the associated risks undoubtedly would be welcome.

The Defense Science Board (DSB), which often assesses the needs and technology gaps that should be filled to

augment and enhance the capability of defense forces,

also recently noted this logistics burden and described a

potential technology solution to ease the challenge. The

DSB report from the Task Force on DoD Energy Strategy

cited the potential value in mobile, on-site fuel production systems.[2]

Synfuel production technologies that can be adapted to

forward deployed locations using local materials (such as

bio-waste) would be valuable because it would directly

reduce the amount of fuel that would have to be moved

and protected in theater.

Mobile, in-theater synfuels processes would address DoD’s

fuel problem by reducing battlespace fuel demand. The

Task Force was briefed on experimental processes that may

be able to produce fuel in the field from military or indigenous biological or waste sources. Such a technology could

have high value for military operations because it would

replace gallon for gallon the amount of fuel needed to be

delivered by fuel convoy into the battlespace.

The Task Force recommends DoD continue research in this

area and invest in full scale development because it

addresses a unique military need.

One system that has been developed for this purpose is

the Tactical Garbage to Energy Refinery (TGER). Not only

does the TGER system tackle the challenge of providing

an on-site fuel and power source, but it has an additional

logistics benefit: it can eliminate waste generated by troops

in the field. The feature article in this issue presents an

introduction and history of the TGER as well as some of

the variant systems that can be used strategically to produce

energy from waste and other sources.

Along the line of reducing waste, the TechSolutions

featured in this issue completes the two-part series on additive manufacturing. This emerging field of manufacturing

offers an alternative to subtractive manufacturing (e.g.,

machining) which typically produces waste that must be

scrapped or recycled. Processes that can minimize or

eliminate waste, and conversely maximize the efficiency of

converting raw material into product, have obvious value.

Ben Craig, Editor

[1] Solis, W. M., “Defense Management: Increased Attention on

Fuel Demand Management at DOD’s Forward-Deployed

Locations Could Reduce Operational Risks and Costs,”

Testimony Before the Subcommittee on Readiness, Committee on

Armed Services, House of Representatives, GAO-09-388T, March

2009. http://www.gao.gov/new.items/d09388t.pdf.

[2] “More Fight, Less Fuel,” Report of the Defense Science Board

Task Force on DoD Energy Strategy, Office of the Undersecretary

of Defense for Acquisition, Technology and Logistics, February

2008, http://www.acq.osd.mil/dsb/reports/2008-02-ESTF.pdf.

Easing a Logistics

Challenge

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The TGER system includes two key components: a gasifier and a bioreactor. This hybrid design enables the production of enough energy via two fuels to mostly replace diesel, which has a high energy content. Syngas contains

20% of the energy content of diesel fuel on a volume-equivalent basis, while ethanol carries 69% of the energy

content compared to an equal volume of diesel. At steady-state the system is nearly self-sustaining. The system is

powered by combining less than 10% diesel with a fraction of the syngas and ethanol produced.

The TGER separates food

and liquid waste from dry solids

and sends it into a bioreactor.

An advanced fermentation

process in the bioreactor uses

enzymes and microorganisms

followed by a distillation process to digest the food and liquid waste and produce fuel grade ethanol. The dry solids,

such as paper, plastic, cardboard, and polystyrene foam, are sent to a down-draft gasifier. Syngas is produced in the

gasifier via the thermal decomposition of the solid wastes. The syngas and ethanol are aspirated into a diesel generator. Once the process has reached full power, 90% of the diesel fuel typically needed to power the electric generator is offset by the syngas and ethanol mixture.

http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 4, Number 3 3

INTRODUCTION

Recent overseas deployments have highlighted several operational

challenges that need to be addressed to improve military readiness

and safety. One challenge is access to dependable energy. Energy

security, particularly with respect to ongoing military operations,

has quickly become a top priority for the Department of Defense

(DoD). Military operations in Southwest Asia have shown that,

despite advanced logistics capabilities, access to fuel can be difficult to achieve, especially during the early months of a crisis. A

second challenge is the cost and logistics problem associated with

the disposal of waste materials created during military operations.

On average, an Army field support unit, which is approximately

600 soldiers, produces nearly one ton of trash per day. This waste

results in an increase in the cost, fuel consumption, and complexity of logistical operations to transport it back to US-based disposal facilities.[1]

One approach to resolving these challenges is based on the idea

that usable energy can be extracted from matter that otherwise

would be disposed of as waste. The conversion of waste to energy

has two additional benefits. First, it provides a renewable source of

energy that alleviates the consumption of nonrenewable energy

resources. Second, it establishes a convenient, alternative method

for eliminating waste products.

In recent years the conversion of waste to energy has become

practical through various technological advancements. Waste-toenergy is a promising concept for both the private and public

sectors including the military. However, since the effectiveness of

US military forces is dependent on being expeditionary, the mobility of their support equipment and systems is essential.

A team of scientists and engineers, therefore, set out to develop a

tactical, mobile, waste-to-energy system for the US Army Research,

Development, and Engineering Command (RDECOM).

While there are other waste-to-energy systems in various stages

of research, development, and evaluation, this article focuses on the

development and deployment of the Tactical Garbage to Energy

Refinery (TGER, pronounced “tiger”). TGER is a unique system

that utilizes a hybridization of advanced fermentation and thermal

decomposition processes to convert military field waste into usable

electric power. The subsequent evolution of this waste-to-energy

system to other formats is also presented in this article.

Transforming field waste into electrical energy (and other forms of

energy) offers a reduced dependence on diesel and other liquid

fuels in theater and provides significant cost savings to the military.

DEVELOPMENT OF A TACTICAL WASTE-TO-ENERGY SYSTEM

In the early part of this decade, internal assessments for the DoD

suggested that the production of alternative energy was one of the

nearest-term applications that could be derived from the field of

biotechnology to support military operations. In 2004, the Army

sponsored a Small Business Technology Transfer (STTR) effort to

Jerry B. Warner

Christopher M. Haggerson

Defense Life Sciences

McLean, VA

Stephanie L. Knoeller

Benjamin D. Craig

Christopher W. Fink

AMMTIAC

Rome, NY

Manufacturing

Energy from

Waste

Dry Solid Waste

Food & Liquid Waste

Syngas

Ethanol TGER

INPUT OUTPUT

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research the feasibility of converting military waste into liquid and

gaseous fuel at forward operating locations. The materials and energy balance mathematical model of a combined thermochemical and

biocatalytic* process showed that the conversion of kitchen waste to

syngas† and ethanol would provide enough

energy to efficiently produce electricity via a

diesel generator.

The results of this feasibility study were subsequently applied under Phase Two of the

STTR to design and fabricate a prototype of

the TGER. The design revolved around two

fundamental unit operations: gasification to

produce syngas via a gasifier and fermentation

to produce ethanol via a bioreactor. In addition

to the production of two renewable fuels, the

selection of gasification and biocatalytic fermentation processes also had strategic value in

that both methods are constantly evolving due

to advanced research efforts. For example, the

introduction of integrated sensors and automated (i.e., computerized) control systems to

the gasification process has led to improved

reliability and efficiency of the biomass to syngas conversion. Moreover, significant increases

in output and efficiency have resulted from biocatalytic fermentation advances, such as evolutionary improvements of genetically modified

enzymes and microorganisms. These developments have enabled the reduction of what would normally be considered unusable biomass waste (e.g., paper fines from shredded

cardboard and other cellulosic wastes) into usable energy, thereby

allowing more energy to be harnessed from the same waste.

Following the initial conceptualization, auxiliary pieces of

equipment were added to create a continuous process for converting waste to energy. Waste processing, separation, and pelletization

were incorporated to prepare and separate the material input for

processing in either the gasifier or bioreactor. The materials preparation process shreds, rinses, augers, and compresses the wastes

along with any residuals from the bioreactor. Following preparation, the solid materials are sent to a pelletizer, which produces

solid pellets of a specified size and shape. Liquid materials, on the

other hand, are sent to the bioreactor where

they are converted to ethanol. After pelletization, an auger or elevator is used to automate

the delivery of the waste-derived pellet fuel to

the downdraft gasifier.

The TGER prototype (see Figure 1), completed in late 2006, demonstrated the ability to

convert waste to useable energy in the form of

electricity. Tests confirmed that the system

produced nine times more energy than it consumed. With evidence of need in Iraq and

Afghanistan, the Army’s Rapid Equipping

Force (REF) supported the upgrade of the first

prototype and the construction of a second.

Upon completion of the second system in

2008, the two prototypes were deployed to Iraq

for field testing and evaluation.

Prototype Performance and Improvements

Two TGER prototypes were fabricated and

deployed to Camp Victory in Baghdad, Iraq, for

a ninety-day field test (see Figures 2 and 3). The

objective of this field test was to demonstrate

and validate the utility of a hybrid biorefinery

capable of converting field waste (see Figure 4) into useable energy

in the forward battle space. While deployed, the TGER systems

demonstrated 90% efficiency and produced nearly 50 kilowatts of

electricity per day. The base camp was able to conserve 62.4 gallons

of diesel fuel per day while consuming 60 pounds per hour of

pelletized waste. During deployment, several potential areas of

improvement were identified for the gasifier, bioreactor, materials

processing and automation portions of the system. Some of these

subsystems were adversely affected when exposed to the desert envi4 The AMMTIAC Quarterly, Volume 4, Number 3

A biofuel is a synthetic fuel manufactured from renewable biomass feedstocks including agricultural crops (e.g., corn),

wood, plants, grasses, agricultural waste, and other waste products.[1, 2] The simple sugars (e.g., glucose) often present in

or readily obtained from biomass are converted to ethanol via fermentation. Ethanol, a volatile and flammable liquid, can

be used as a fuel to power an internal combustion engine. For instance, many flex-fuel vehicles have engines designed to

operate on E-85, a mixture of 85% ethanol and 15% gasoline.

Starch and cellulose are two of the common precursors to ethanol. Starch and cellulose-based ethanols are produced

using similar processes; however, they differ in the methods used to obtain simple sugars (e.g., glucose) from the biomass

feedstocks. Both starches and cellulose must be broken down into simple sugars so that yeast and other enzymes, which

readily consume glucose, can convert them to ethanol. Starches are more readily converted to glucose than cellulose, which

requires a much more complex breakdown process. However, since cellulose is “the most abundant biological molecule in

the world,” cellulosic ethanol is an attractive alternative to starch-based and other types of ethanol.[3]

Corn ethanol is a common starch-based ethanol produced using either a dry grind or wet milling process. In the dry

grind process, the grain residuals are separated at the end, whereas in the wet milling process they are separated in the

beginning.[4]

The dry grind method utilizes a hammer mill to crush the corn kernels into a fine powder or meal. The ‘corn meal’ is

then slurried with water and later combined with a heat stable enzyme, α-amylase. This slurry solution is cooked, in a

process known as liquefaction. The heat from the cooking process mechanically shears the starch granules, while the added

enzyme cleaves the starch polymer into smaller fragments. Following liquefaction, the cooked “corn mash” is further

Figure 1. Original TGER prototype.

Figure 2. TGER prototype in shipping

container.

Ethanol

Biofuel

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ronment (e.g., dust and sand). The TGER is being modified to handle these environments, reduce system complexity, further automate

the system, and incorporate advances in some of the subsystems.

TECHNOLOGY EVOLUTION

Following validation of the TGER design, several variants of the

waste-to-energy system were spawned, each utilizing aspects of its

unique design. These variants, described briefly

in the following sections, can operate on more

than human-generated wastes and produce

more than electrical power. Comprised of several unique features, these variants deviate

strongly from the traditional energy production methods, as they are based on small, distributed systems rather than centralized factories, as demonstrated in Figure 5.

Semi-Permanent Waste-to-Energy Refinery

The POrtable Waste to Energy Refinery

(POWER) is a semi-permanent, non-tactical

variant of TGER intended for strategic placement between food service and barracks locations. This placement permits easy interception

and conversion of waste materials into two biofuels for use in powering barracks or mess utilities. Although designed for fixed locations,

POWER may be transported to training sites

with high population densities. With minimal

manpower the biorefinery is capable of efficiently converting the waste of up to 1000 people to useful energy, thus minimizing the need

for waste removal.

In addition to providing waste to energy

conversion capability for facilities, POWER offsets several of the

direct and indirect costs associated with landfills and utilities by

reducing the amount of waste and providing auxiliary thermal utilities, such as building heat, lot water, and adsorptive air conditioning.

Tree Biomass Waste-to-Energy System

The Poplar Fuel Point (PFP) system is another waste-to-energy variant that produces biofuel from a uniform feedstock of poplar trees

and it is based on the concept of distributed energy manufacturing.

Liquid fuel, in the form of ethanol, is manufactured at decentralized

locations (i.e., close to the feedstock source and final fuel distribution locations). The biofuel product can be used for non-tactical

flex-fuel vehicles (e.g., light trucks and sedans).

Poplar trees are known for their rapid growth

rate and climate resilience. They are commonly

grown for the purpose of producing paper and

other organic-based products. More recently,

the interest in poplar trees has increased because

of their suitability for the production of biofuels. Like most other plants and trees, poplars,

contain cellulose, a glucose polymer that can be

converted to ethanol through biochemical

action. The production method for cellulosic

ethanol is similar to that of corn ethanol; however, pretreatment and hydrolysis are necessary

in the cellulosic process to decompose cellulose

into glucose.

Each PFP unit is designed to produce

120,000 gallons of ethanol per year using

approximately 360 acres of poplar biomass.

This is enough to power one hundred and

fifty E-85 fleet vehicles annually. The 360 acres

of land allotted for production of the biomass

is partitioned into three 120-acre parcels for

seeding, growing, and harvesting. This model

has the potential to reduce carbon dioxide

(CO2) emissions by 132 tons per year, while

simultaneously producing zero greenhouse gas

emissions in the conversion process. Additionally, poplars have the

ability to remove petroleum and explosive material contaminants

from groundwater and soil. Furthermore, competition with food

crops is eliminated and a lower cost fuel is produced.

http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 4, Number 3 5

Figure 4. Some of the garbage at Camp

Victory to be converted to renewable

energy by TGER.

Figure 3. TGER prototype at Camp

Victory in Baghdad, Iraq.

processed to glucose. Saccharification is the process by which the starch from liquefaction is broken down into glucose; this is done through

the addition of another enzyme, glucoamylase.

The corn mash is then combined with yeast in a fermentation tank to convert the glucose to ethanol and carbon dioxide. The liquid

fermentation product is then separated using a distillation process to produce ethanol of the desired purity. The solid fermentation product

is centrifuged to produce distillers’ dried grains with solubles (DDGS).[4]

In the wet milling process, the corn kernels are first soaked in water, making it easier to separate the starch, fiber, and germ from one

another. The separated products follow individual processing steps, ultimately producing a variety of products in addition to ethanol.

Ethanol, in this process, is produced in the same manner as mentioned with the dry grind process using fermentation and distillation.

Cellulosic ethanol is produced similarly to the corn ethanol methods. The difference in these processes is that the cellulosis feedstock must

be pretreated, which typically involves hydrolysis, to convert the cellulose to glucose.[3] Hydrolysis involves the catalytic decomposition

reaction with water to form glucose and carbon dioxide. Acids and enzymes are used to aid in this breakdown process. The glucose is then

fermented and the ethanol product recovered as in the corn ethanol methods. Because the pretreatment process often involves chemicals, this

process is more costly than the corn ethanol methods.

[1] Blackwell, K.E., “Department of Defense and Energy Independence: Optimism Meets Reality,” Air University, April 2007.

[2] Perlack, R.D., L.L. Wright, A.F. Turhollow, R.L. Graham, B.J. Stokes, and D.C. Erbach, “Biomass as a Feedstock for a Bioenergy and Bioproducts

Industry: The Technical Feasibility of a Billion-Ton Annual Supply,” Oak Ridge National Laboratory, Department of Energy, April 2005.

[3] Mosier, N.S., “Cellulosic Ethanol – Biofuel Beyond Corn,” Purdue University, December 2006.

[4] Mosier, N.S. and K.E. Ileleji, “How Fuel Ethanol Is Made from Corn,” Purdue University, December 2006.

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Threat Biomass to Fuel

The Threat Biomass to Fuel (TBF) system is designed to help western states battle the serious ecological and environmental challenges

resulting from bark beetle infected trees and invasive species of

tamarisk trees. This system uses these infected and invasive trees as

the biomass feedstock for bioethanol production. Because the TBF

system is portable (see Figure 6), the biomass can be harvested and

converted to fuel onsite. This eliminates the need to transport the

infected biomass across noninfected regions to the point of processing, thus preventing the spread of these invasive species.

Divided into two compact, portable units, this system has the

ability to efficiently produce two renewable biofuels while simultaneously reducing the impact of forest degradation caused by various

insects and diseases. The first unit contains secondary fermentation

and ethanol storage tanks, the water and pretreatment solvent supplies necessary for cellulose breakdown, and the equipment used

for harvesting and chipping trees. The second unit contains the

material processing equipment and the wood chip storage, drying,

and feeding bins. A local staging area and fuel processing center are

also used for maintenance tasks, storage, finishing, and certification

of raw ethanol to make E-85.

This process is highly efficient and largely self-sustaining due to

its use of “2nd Generation” cellulosic ethanol technology that utilizes biocatalytic and thermochemical processes. A byproduct of the

process is wood lignin, which is used to power the onboard electromechanical systems. This allows the system to be self sustainable,

while the generator exhaust provides the thermal energy needed for

the distillation and other heat exchange operations.

Each of the systems highlighted above evolved from a similar

concept: the need for distributed, portable, small-scale, and efficient

energy production systems. Aside from these foundations, each system is unique in the feedstock consumed and the method by which

energy is produced. Figure 7 outlines some of these differences

along with others, as it compares the waste-to-energy and biomassto-fuel systems.

CONCLUSION

The research, development, and deployment of the original TGER

demonstrated the rapid transition of a concept to an experimental

system for the purpose of meeting a military need. The early deployment of this experimental system validated the utility and identified

areas for design and equipment improvements to achieve even

greater performance. In addition, the technologies developed for

tactical biorefineries have shown potential for scale-up to supply

military installations, such as hospitals and major troop areas, with

power, hot water, and usable fuel while eliminating costly waste

removal expenses. Biorefinery technology applied to several nontactical domestic arenas, such as commercial waste removal, would

provide a viable energy source while reducing the cost and environmental impact of solid waste. The evolution of TGER into more

profound federal and consumer products represents an ideal technological path for a system originally designed and developed to support military operations.

GENERAL REFERENCE

Austin, A., “Trash Tactics in Iraq.” Biomass Magazine, October 2008

http://www.biomassmagazine.com/article-print.jsp?article_id=2064.

NOTES & REFERENCE

*Biocatalytic refers to the use of organisms or enzymes to perform a chemical transformation.

†Syngas is a gaseous mixture that predominantly contains carbon monoxide (CO) and hydrogen.

[1] Behar, M., “Junk In, Power Out.” Popular Science, May 2007, p. 44.

6 The AMMTIAC Quarterly, Volume 4, Number 3

Figure 5. With the continued evolution of energy securing technologies, as with TGER and its variants, greater deviations are apparent

between the new systems and the more traditional as shown.

Figure 6. Illustration of a Threat Biomass to Fuel unit.

Figure 7. Comparison of waste-to-energy and biomass-to-fuel

systems.

Centralized Model

• Traditional industrial model

• Economy of scale for large

manufacturing facility

• Materials transported

to factory

• Products transported to

markets

• Large portion of current

DoD/commercial effort

Distributed Model

• Small systems located

at biomass site

• Economy of scale for high

throughput processing and

local distribution

• Reduced transportation

costs because equipment

is onsite

• Local “energy economies”

rather than multi-national

corporations

TGER

Tactical, mobile, off-grid, expeditionary

Liquid, solid, wet, dry waste, plastic,

cardboard, food, wood

No metal, glass or human waste

Produces electricity & thermal energy

All biofuels used to power

onboard systems

Power

Installation (e.g., brigade

compound, ranges, etc.)

Fixed or mobile

Intercept & convert high energy waste onsite

Avoid landfill, reduce fossil utilities

Biofuels used for thermal utilities

Poplar Fuel Point

Optimized, mobile fuel (E-85) system

Hybrid or transgenic poplar feedstock

1,000 gal/acre/year

Requests no transportation of feedstock

High throughput, self-sustaining, carbon neutral

Phytoemediation of explosives

& oil contamination

Threat Biomass to Fuel

Dual purpose:

protect environment & produce biofuel

Beetle infected pine, tamarisk,

ash tree feedstock

Mobile refinery located at threat site

Harvest & convert – move fuel not biomass

Integrates

Thermochemical

and Biocatalytic

Energy Production

System

Waste to Energy Biomass to Fuel

Comment on this article at

ammtiac@alionscience.com

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techsolutions 13 Christopher W. Fink

AMMTIAC

Rome, NY techsolutions 13

INTRODUCTION

Additive manufacturing (AM) refers to a process that builds up a

component in layers, as opposed to a subtractive operation, which

removes matter from a block of material to form a product.[1,2] An

increase in customer demand for customizable, quick turnaround,

low cost products has opened the door for AM processes to enter the

large scale production market once dominated by subtractive

processes. Compared to AM, subtractive operations have relatively

high capital costs and limited product design flexibility. This article

provides an overview of several AM processes and presents current

and emerging applications and the benefit of AM technology for the

commercial and defense industries.

POWDER-BASED ADDITIVE MANUFACTURING

Powder-based AM processes build layers of metallic and plastic materials by dispersing powders on a substrate. Similar to the liquid-based

processes, the powder is then cured by an ultraviolet (UV) light

source (usually a laser). Powder-based processes, like Laser

Engineered Net ShapingTM (LENS), have found widespread use in

the fabrication and repair of metallic components because of their

ability to deposit metal on an existing substrate. The following sections describe in more detail the processes listed in Table 1.

Electron Beam Melting

Electron beam melting (EBM) was developed in the late 1990s and

is used primarily in the development of fully-dense, functional,

metallic components. The EBM

process uses an

electron beam gun

to create molten

layers from metallic powder in a

vacuum setting.[6]

Each cross-sectional layer is outlined

according to a computer-aided design

(CAD) drawing.

While the layer is still warm, the surrounding area is heated and the

next layer of metallic powder is applied. By heating the surrounding

area, the powdered particulate is sintered, preventing material repulsion and improving the material quality of the downfacing surface.[7] With the ability to create fully-dense, metallic components

EBM is used for the production of parts that require high strength

properties.

As shown in Table 1, titanium and steel alloys are typically used

for the EBM process, and thus it is ideal for the development of

metallic components that have complex surface geometries. In addition, EBM can produce both thick- and thin-walled structures. This

is ideal for applications, such as components for the aerospace and

automotive industries, which require low volume production of

thin-walled parts that possess the strength properties of titanium and

steel alloys. The ability to fabricate complex titanium components has also resulted in the

use of EBM for the production

of knee implants and bone

plates in humans and animals.[7] More applications of

EBM are listed in Table 2.

Laser Engineered Net Shaping

Developed by Sandia National Laboratory in the mid 1990s, Laser

Engineered Net ShapingTM is a process for creating near-net shape

metallic structures.[13] Parts are fabricated by dispersing powdered

metal over a molten pool of metal substrate. The molten substrate is

created by a neodymium-doped yttrium aluminum garnet

(ND:YAG) laser that operates at 500-600W in a closed argon gas*

system.[14,15] The powder and laser dispersion pattern is dictated

by a corresponding CAD model. The molten material solidifies and

cools very quickly, resulting in materials that are fully dense.[16]

The LENSTM process (demonstrated in Figure 1) is capable of

producing materials that possess mechanical properties similar to or

better than those for homogenous materials (see Table 3) as a result

of their densities.[16] The ability to create fully-dense components

eliminates the need for heat-treatment after processing, thereby

http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 4, Number 3 7

An Overview of Additive Manufacturing, Part II

This article is the second part in a two-part series on additive manufacturing. It presents a brief introduction to several additive manufacturing

processes, such as electron beam melting, selective laser sintering and three-dimensional printing. The first installment in this two-part series was

published in AMMTIAC Quarterly, Vol. 4, No. 2, which is available online at http://ammtiac.alionscience.com/quarterly. - Editor

Table 1. Examples of additive manufacturing

processes and materials.[3-5]

Electron beam melting

Superalloys Stainless steels

Tool steels Aluminum

Titanium Copper

Laser Engineered Net ShapingTM

316, 304, 17-4 Nickel-based

stainless steels superalloys

Tungsten Copper

Aluminum M300 steel

H-13 tool steel Titanium

Low alloy steel Nickel aluminides

Selective laser sintering

Polystyrene Sand

Polycarbonate Polyamide

Glass filled polyamide Tungsten

Copper Aluminum

Low alloy steel

Inkjet/3D Printing

316L stainless steel 420 stainless steel

+ bronze + bronze

Wax Starch

Plaster Molding sand

Table 3. Comparison of mechanical properties for wrought homogenous materials and

LENS-produced materials.[17]

Material Ultimate Tensile Strength (ksi) Yield Strength (ksi) Percent Elongation

Wrought LENS Wrought LENS Wrought LENS

316 Stainless Steel 85 110 34 63 50 46

304L Stainless Steel - 95 40 47 55 70

H-13 Tool Steel 250 247 210 212 12 1-3

Annealed Ti-6Al-4V 135 130-145 124 120-140 10 1-16

Inconel 718 200 203 168 162 20 16

Table 2. Industrial applications of

electron beam melting.[8-12]

Industry Application

Medical Canine knee implants

Hip replacements

Aerospace Landing gear components

Impellers

Automotive Turbocharger compressor

wheels

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reducing processing steps and time.[18] In addition, LENSTM can

produce components with complex geometries, which makes it an

optimal solution for the fabrication of new or the repair of used

components.

LENSTM has several applications, but the two most popular are

low volume, custom production runs and repairs to existing components. Certain parts, particularly components that have thin

walls, have been saved from the scrap pile by the LENSTM process.

Since LENSTM can produce a heat affected zone as small as 50

microns, it does not significantly deform or weaken the substrate

material.[19] The DoD has employed LENSTM on several occasions to perform major repairs. At the Anniston Army Depot,

LENSTM was used to repair gas turbines on M1 Abrams

Tanks.[19] LENSTM has also been utilized as a type of ‘hybrid’

manufacturing process because of its ability to add high-resolution

features to forged and cast components (see Table 4).[20] In addition, LENSTM can be employed to protect surfaces through the

application of several layers of wear-resistant materials.

Selective Laser Sintering

Developed in the mid-1980s, selective laser sintering (SLS) added

a new dimension of versatility to AM technologies. For example,

SLS can produce components from elastomers, thermoplastics,

and metals. The metallic laser sintering process is referred to as

direct metal laser sintering (DMLS).

In the SLS process (illustrated in Figure 2), a powdered material is deposited over a surface and then melted and fused by a

carbon dioxide (CO2) laser that moves in a pattern dictated by a

CAD model. Sintering of the powder facilitates adhesion to the

layer below. This process is repeated until the component is fully

formed. While in the sintering phase, a metal component can

receive additional heat treatment or can be infiltrated with a

different metal (e.g., bronze in steel).[3] Components that are

produced using SLS usually require no additional processing after

the sintering process is completed.

The wide range of materials (detailed in Table 1) has made SLS

one of the most widely utilized AM technologies. Based on the

type of material used in a given SLS process, a prototype component can be fabricated to analyze fit and form and then tested in

real time to assess functionality. SLS has become the option of

choice over traditional machining processes for low volume or ‘one

off’ production runs as a result of the ability to develop fully-functioning components. For example, SLS technologies were used to

produce a fuel-vent manifold for first article testing on a carbon

composite race car. SLS was chosen because it could produce the

required complex geometries in less time and at a lower cost than

acquiring conventional tools for the low volume production.[22]

In addition, parts can be produced simultaneously in the SLS

process, making larger volume production a reality. However, the

components produced using SLS tend to be porous and have a

rough surface finish.[23]

Three Dimensional Printing

Developed in the late 1980s, three dimensional printing (3DP) is

a process that uses an inkjet system to deposit a low-viscosity

binder onto a powdered-material bed through the use of a pattern

derived from a CAD model (see Figure 3). Once the binder has

dried, the completed part is removed from the machine and any

excess powder is removed.[7] Plastic components will usually be

infiltrated with a wax or epoxy resin after curing in order to

improve the ability of the part to withstand mechanical stresses.[29] Commonly used for prototyping, 3DP has gained popularity as a method of producing mold cavities for investment cast8 The AMMTIAC Quarterly, Volume 4, Number 3

techsolutions 13

Figure 2. Selective laser sintering process.[3]

Table 5. Industrial applications of selective laser sintering.[24-28]

Industry Company

Racing Prototype fuel vent manifold

Prototype air intake

Production of race car exterior components

Athletic Wear Functional prototype of running shoe

Mechanical Functional prototype for riveting system

Architecture 3D scale model of building

Lawn care Functional mower deck prototype

Electronic surveillance Production of radar housing and components

Medical Customized knee implants

Customized dental implants

Humeral mount for prosthesis

Automotive Gearbox housing components

Aerospace Engine components

Figure 1. Four nozzles

deliver powder sintered

by a laser beam into a

Sandia thunderbird logo

design. (Photo by Randy

Montoya and provided

courtesy of Sandia)

Table 4. Industrial applications of Laser Engineered Net Shaping.TM [21]

Industry Application

Tool and Die Rapid production of improved mold designs

Defense In-field repair of damaged components

Low volume production of specialty and hard-to-find parts

Medical Load-bearing implants

Laser Optics/Scanning Mirrors 50 Watt CO2 Laser

Laser Beam

1. A very thin layer of heatfusible powder is deposited

on top of the build cylinder

2. Laser consolidates a cross

section that matches the

corresponding layer in the .STL

file, bonding the particles and

fusing the adjoining layers

3. The support platform

moves the part downward and

the roller mechanism deposits

another layer of powder

4. The process repeats itself

one layer at a time, until the

part is fully formed

1

2

3

4

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http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 4, Number 3 9

AMMTIAC A D V A N C E D M A T E R I A L S , M A N U F A C T U R I N G A N D T E S T I N G

ing, and as a viable method of rapid tool production. In addition,

3DP technologies set themselves apart from other AM processes in

that they can produce rigid, thin-walled parts. For example, printing

systems like PolyJet Printing can produce parts with wall thicknesses

of less than 1 mm.[30]

The wide range of 3DP applications (shown in Table 6) is a direct

result of the types of materials that can be printed (e.g., metal, plastic,

sand, and wax). The ability to use wax and sand in the printing

process has led to the creation of more complex mold cavities. Similar

to stereolithography and LOM, these materials are less susceptible to

the effects of thermal expansion during the development of a mold

cavity than injection molded processes. A detailed list of 3DP materials is shown in Table 1.

One example of using 3DP to create molded parts is the direct shell

production casting (DSPC) process. In DSPC, a thin layer of aluminum is laid down with a roller and a silica binder material is

sprayed over the aluminum. Once the layers are built up into a completed “green” mold, the mold is fired in preparation of accepting

molten metal.[32] DSPC has been used primarily in the development

of engine components (e.g., intake manifolds, cylinder heads, and fuel

injectors), but it can also be used to cast parts similar to those produced via investment or sand casting.[33]

BENEFITS TO THE DOD

The ability to produce and repair high-strength, metallic parts has

made AM a valuable technology throughout the Department of

Defense (DoD). Advances in electronic controls and modeling interfaces has improved the reliability and repeatability of these AM

processes to the point that they can be reliable for making repairs or

fabricating replacement components for critical applications. As

weapon systems across the services increase in age, the availability of

certain components has decreased significantly. The challenge of supplying an adequate amount of these components to repair depots and

intermediate repair facilities is a challenge that the use of AM technologies can help mitigate. The addition of an AM machine tool to a

repair facility would help improve the availability of a weapon system

by reducing the amount of time and energy spent trying to procure

hard to find components. In cases where metallic components are

heavily worn, bent, or gouged, processes like LENS and EBM can be

used to bring components back to their original dimensions with

comparable physical properties to the homogenous materials.

Several DoD organizations have employed AM processes with

varying degrees of success. The Naval Undersea Warfare Center

(NUWC) at Keyport, WA, operates the Rapid Manufacturing and

Repair (RMR) program. This program employs SLS, DMLS, FDM,

and EBM in the fabrication or repair of legacy parts and tooling.[35]

For example, under the RMR program, AM processes were used in

the production of door handles for the UH-60 helicopter. As a result

of employing these processes, savings of $1.4 million were realized.

The RMR program has been able to achieve an average return on

investment of 10:1 over the life of the program, demonstrating that

AM processes are not only a performance benefit, but a cost-savings

benefit to the DoD.[35]

The US Army Aviation & Missile Research, Development &

Engineering Center (AMRDEC) at Redstone Arsenal, AL, houses the

Prototype Integration Facility (PIF) which employs several AM

processes. Through the use of stereolithography†, fused deposition

modeling†, laminated object manufacturing†, LENSTM, SLS, and

three-dimensional printing, AMRDEC is able to perform design verification and optimization studies in less time and at a lower cost than

previous design assessment techniques. To assess ergonomic features

and performance, AMRDEC used stereolithography to fabricate missile control joysticks for field testing. As a result of using stereolithography, the large time and setup costs associated with traditional production setup were avoided, thereby reducing the overall product cost

and reducing the duration of the development process.

A joint DoD-industry effort recently employed a stereolithography-like fabrication process for the rapid production of titanium

structural components. The process, called laser additive manufacturing (LAM), was able to produce titanium components 80% faster

than traditional titanium fabrication processes.[36] The speed with

which LAM can produce components made it an excellent candidate

for the production of titanium replacement pylon ribs on the F-15

Strike Eagle. The original F-15 ribs, made from aluminum, were failing prematurely and the spare inventory was severely depleted due to

forward deployment of the F-15 in Iraq and Afghanistan. Titanium

was chosen as a replacement material for aluminum in the rib design,

as it had greater strength properties than aluminum. Using LAM, the

surge in part demand was met within two months, keeping aircraft

availability at a maximum.[37] As a result of the success of this effort,

LAM was awarded the 2003 Defense Manufacturing Technology

Achievement Award.

SUMMARY

Advances in materials, electronics, modeling interfaces, and material

distribution over the last two decades have vaulted AM processes from

a simple method for producing three-dimensional plastic design prototypes to a viable option for low-volume production of metallic and

plastic parts. Using processes like stereolithography, three-dimensional printing, fused deposition modeling, and selective laser sintering,

plastic components can be produced to visualize an idea, ensure that

Figure 3. Three-dimensional printing process. (Image courtesy of

CustomPartNet, Copyright © 2008)[31]

Table 6. Industries and applications for three dimensional printing.[34]

Industry Application

Power tools Functioning model for ergonomic testing

Architecture Scale model of facilities

Motorcycle Functional model of accessories for mock-up

Home and office furniture Functional model of furniture designs

Pumping Functional model of pump housing

Underwater exploration Modeling of redesigned diving equipment

Liquid Adhesive Supply

Inkjet Print Head

Powder Bed

Part

Build Piston

Build Chamber

Copyright © 2008 CustomPartNet

Powder Feed Piston

Powder Feed Supply

Leveling Roller

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Mr. Christopher W. Fink is a Manufacturing Engineer and has been supporting AMMTIAC for two years. He received a BS in Industrial

and Systems Engineering from the Rochester Institute of Technology and is currently pursuing an MS at Syracuse University in Engineering

Management. Mr. Fink has authored or co-authored several reports and presentations.

techsolutions 13

10 The AMMTIAC Quarterly, Volume 4, Number 3

newly designed components will fit together correctly, and help

meet a fluctuating demand in production pieces. Laminated

object manufacturing is used in the production of mold cavities

for the rapid production of tools and other cast parts. Electron

beam melting and Laser Engineered Net ShapingTM have made a

significant impact on the ability to repair damaged parts, as they

can build metallic materials on top of an existing substrate. In

addition, the ability of EBM and LENSTM to also build new, fullydense parts has helped to mitigate shortages of hard-to-find parts.

Additive manufacturing technology helped to revolutionize the

design process in the latter part of the 20th century with the

advent of rapid prototyping processes. As these technologies continue to evolve in the 21st century, they will revolutionize the way

parts are manufactured in the same way AM changed how parts

were designed and conceptualized.

Further information on applications, machinery suppliers,

technologies, and countries that employ additive manufacturing

can be found in the “Rapid Prototyping State of the Art Report”

published in 2003. This report is available online: http://

ammtiac.alionscience.com/pdf/MT-93-01.pdf.

NOTES & REFERENCES

*Argon gas is used to prevent oxidation during the deposition process.

†These processes are described in Reference [1]

[1] Fink, C.W., “An Overview of Additive Manufacturing, Part I,”

AMMTIAC Quarterly, Vol. 4, No. 2, 2009.

[2] “What is Direct Digital Manufacturing?”, Society of Manufacturing

Engineers, www.sme.org/ddm, accessed May 2009.

[3] Freitag, D., T. Wohlers, and T. Philippi, Rapid Prototyping: State of the Art,

Advanced Materials, Manufacturing, and Testing Information Analysis Center

(formerly the Manufacturing Technology Information Analysis Center), 2003.

[4] Mueller, B., and D. Kochan, “Laminated Object Manufacturing for Rapid

Tooling and Patternmaking in Foundry Industry,” Computers in Industry, Vol.

39, No. 1, 1999, pp. 47-53.

[5] “Applications,” Arcam AB, http://www.arcam.com/applications/

othermaterials.asp, accessed May 2009.

[6] Lindhe, U., M. Larsson, and O. Harryson, “Rapid Manufacturing with

Electron Beam Melting (EBM) – A Manufacturing Revolution,” Direct Metal

Forum, Society of Manufacturing Engineers, 2003.

[7] Gibson, I., Advanced Manufacturing Technology for Medical Applications -

Reverse Engineering, Software Conversion and Rapid Prototyping, John Wiley &

Sons, 2005.

[8] “New Orthopaedic Implants Improve People’s Quality of Life,” Rapid

News, Arcam AB, http://www.arcam.com/Downloads/PDF/Arcam_Fixa_

Ti-Por_Case_Study.pdf.

[9] “Successful Skull Reconstruction with Rapid Manufacturing,” Rapid

News, Arcam AB, http://www.arcam.com/Downloads/articles/Arcam%20-

%20Maastricht%20Implant%20Case%20Study.pdf.

[10] “Prototal Uses Rapid Manufacturing of Customized Implants for Oral

Surgery,” Rapid News, Arcam AB, http://www.arcam.com/Downloads/

articles/Arcam%20-%20Prototal%20Case%20Study.pdf.

[11] “Aerospace Applications,” Arcam AB, http://www.arcam.com/

applications/aerospace.asp, accessed April 2009.

[12] Cormier, D.R., O.L.A. Harrysson, and H. West, “Characterization of

High Alloy Steel Produced Via Electron Beam Melting,” Solid Freeform

Fabrication Symposium, pp. 440-441, 2003.

[13] Singer, N., “Intense Hopes: Ten Companies Team to Commercialize Sandia’s

Powder-to-Parts Net Shaping Technology,” Sandia Lab News, December 5,

1997, http://www.sandia.gov/LabNews/LN12-05-97/lens_story.html.

[14] Paschotta, R., Encyclopedia of Laser Physics and Technology, Wiley-VCH,

2008.

[15] Kumar, S., and B. Stucker, “Development of a Co-Cr-Mo to Tantalum

Transition Using LENS for Orthopedic Applications,” Solid Freeform

Fabrication Symposium, 2005.

[16] Grylls, R., “Laser Engineered Net Shapes,” Advanced Materials and

Processes, Vol. 161, No. 6, p. 46, January 2003.

[17] “Manufacturing Technologies: Laser Engineered Net Shaping,” Sandia

National Laboratories, http://www.sandia.gov/mst/technologies/net-shaping.

html, accessed April 2009.

[18] Ploude, R., “Laser-Based Repair System Reclaims High Value Military

Components,” NATO RTO-MP-AVT-109, RTO-AVT Specialists Meeting –

The Control and Reduction of Wear in Military Platforms, 2003, DTIC Doc.

ADA441707.

[19] Grylis, R., “Laser System Saves Damaged Military Parts from the Scrap

Heap,” The Fabricator, 27 February 2003, http://www.thefabricator.com/

LaserCutting/LaserCutting_Article.cfm?ID=523.

[20] “LENS Aerospace & Defense,” Optomec, Inc., http://www.

optomec.com/site/lens_2, accessed April 2009.

[21] “The Use of Laser Engineered Net Shaping for Rapid Manufacturing of

Dies with Protective Coatings and Improved Thermal Management,”

Industrial Technologies Program, Office of Energy Efficiency and Renewable

Energy, US Department of Energy, July 2005.

[22] “Advanced Processes and Materials Help Indy Racing League Racecar,”

3D Systems, Inc., http://www.3dsystems.com/products/datafiles/success_

stories/Elan_Motorsports_APP_CS.pdf, accessed April 2009.

[23] Jack, H., “Selective Laser Sintering,” Engineering on a Disk, Vol. 1, Grand

Valley State University, August 2001, http://www.eod.gvsu.edu/eod/

manufact/manufact-309.html.

[24] “Selective Laser Sintering Applications & Case Studies,” 3D Systems, Inc.,

http://www.3dsystems.com/products/sls/applications.asp, accessed April 2009.

[25] “SLS Case Studies,” 3T RPD, LTD., http://www.3trpd.co.uk/sls-casestudies.htm, accessed April 2009.

[26] “e-Manufacturing Solutions for the Orthopedic Market,” EOS,

http://www.eos.info/en/applications/medical/orthopedic-implants.html,

accessed April 2009.

[27] “DirectPart Examples,” EOS, http://www.eos.info/en/applications/

target-metal-parts/directpart-examples.html, accessed April 2009.

[28] “Medical Devices,” EOS, http://www.eos.info/en/applications/

medical/medical-devices.html, accessed April 2009.

[29] Gebhardt, A., Rapid Prototyping, Hanser Gardner Publications, 2003.

[30] “Connex500 – The First Multi-Material 3D Printing System,” Objet,

Inc., http://www.objet.com/Products/Connex500/, accessed April 2009.

[31] “3D Printing,” CustomPartNet, http://www.custompartnet.com

/wu/3d-printing, accessed June 2009.

[32] “Direct Shell Production Casting,” Design Prototyping Technologies,

Inc., http://www.dpt-fast.com/knowledge/direct_shell_production_casting.

asp, accessed May 2009.

[33] “Soligen: Technical Presentations and Case Studies,” Soligen,

http://www.soligen.com/about/casestudies.shtml, accessed May 2009.

[34] “3D Printer Success Stories,” Stratasys, Inc., http://www.dimension

printing.com/successstories/successstories-main.aspx, accessed April 2009.

[35] Delisle, R., M. Tobler, and K. Morris, “Rapid Manufacturing & Repair

Phase II,” Commercial Technologies for Maintenance Activities Symposium,

National Center for Manufacturing Studies, 2008, http://techcon.

ncms.org/Symposium2008/presentations/Plenary%20RM&R%20

ctma%20baltimore-vs3%20REV%204-4.pdf.

[36] “2003 Defense Manufacturing Technology Achievement Award

Recipients,” DoD Manufacturing Technology Program, https://www.

dodmantech.com/award/CY03/index.asp?main=award, accessed August 2009.

[37] “DoD Recognizes Manufacturing Technology Advancements,” Defense

AT&L, March-April 2004, pp. 92-94, http://www.dau.mil/pubs/dam/dam

0204/acq-ma04.pdf.

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http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 4, Number 3 11

INTRODUCTION

Coating and decoating maintenance operations typically rank

among the largest sources of waste and pollution emissions within

the US Navy. Surface coatings often contain solvents that release

volatile organic compounds (VOCs) and hazardous air pollutants

(HAPs; e.g., hexavalent chromium). More than ever, there is a greater

liability for workplace and environmental exposure (e.g., groundwater contamination) claims; therefore, environmental managers

must scrutinize coating operation processes and material requirements. Adding to the burden of managing coating operations, new

regulatory requirements (which are becoming increasingly stringent)

and reduced staffing have led to increased costs for tracking inventories, monitoring emissions, reporting usage of regulated compounds,

and disposal of solid wastes that contain heavy metals.

The extensive coastlines and unique ecological features of Navy

Region Northwest (NRNW) have led to an even greater awareness

of the environmental, safety, and health effects associated with

industrial coating operations. Thus, the Navy has been actively pursuing process improvements, particularly among coating and

decoating operations.

New surface coating technologies have lower contents of VOCs

and HAPs when compared to traditional coating systems because of

the reduced solvent concentration and improved coating

chemistries. These coatings must still be durable, reliable, and corrosion-resistant. In addition to meeting environmental management

requirements, transitioning to new coating processes must result in

minimal downtime of the operation, and the labor required for the

new coating process should be

minimal. This article presents the

benefits, requirements, and concerns associated with the testing and

implementation of several new

coating systems within NRNW,

including various types of powder

coatings, electro-active polymer

coatings, anti-corrosion primers,

and self-healing coatings.

POWDER COATINGS

Powder coatings utilize a solvent-free powder consisting of a resin, a

cross-linking agent, pigments, flow aids, and degassers. The powder

is mixed with compressed air to form a fluidized stream that is

pumped from a hopper to a spray gun for application. Charged

powder particles are propelled towards the substrate, which is electrically grounded and may be pre-heated or at room temperature

(Figure 1). The coated part is then transferred to a curing oven

(Figure 2).[1]

Powder coating systems are efficient and clean, and they significantly reduce hazardous waste when compared to traditional coating processes. The products of powder coating

contain minimal VOCs

and no HAPs, and primers

are not always required for

the application process.

Additionally, system components can be cleaned

solely using compressed

air, and thus toxic cleaning

solvents are not required.

The transfer efficiency of

the powder is high due to the electrostatic attraction between the

powder and the substrate, and overspray can be filtered and reused.

Therefore, the process offers a reduction in material costs compared

to traditional processes. While powder coating is very versatile, it is

not a universally applicable process.[1]

High-Temperature Cure Powder Coatings

There are two types of high-temperature cure powder coatings:

thermoplastic (no chemical reaction during cure phase) and thermoset (chemical reaction during cure phase). Among the thermoset

powder coatings, there are several types, each with different characteristics: epoxy, polyester, urethane, and acrylic.

Polyester triglycidal isocyanurate (TGIC) powder coatings are the

approved powder coatings for US Navy aircraft ground support

equipment and some submarine components. This type of powder

Greg A. Levcun

Naval Facilities Engineering Command Northwest

Christopher S. Mahendra

Naval Air Systems Command

Figure 2. Curing oven.

Figure 1. Powder coating of

a system component.

The EPA has promulgated regulations for several types of industrial surface coating operations and composite material rework operations known collectively as the Coatings and Composites Coordinated Rulemaking (CCCR). These

regulations include the National Emission Standards for Hazardous Air Pollutants (NESHAPs) under Section 112

of the federal Clean Air Act (CAA) and national VOC rules or Control Technique Guidelines (CTG) under Section

183(e) of CAA. Any facility engaged in composites manufacturing or surface coating (including surface preparation,

depainting, and cleaning associated with the coating operation) is affected by these regulations.

Environmental

Regulations

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12 The AMMTIAC Quarterly, Volume 4, Number 3

coating has excellent weathering characteristics, excellent overbake

color stability, and shorter cure times.[1]

The Navy’s Pollution Prevention Equipment Program (PPEP)

provided design, training, and installation of two powder coating

spray systems within NRNW. The first of these systems was dedicated to submarine components. The second system was set up for

aircraft ground support equipment. After six months of operation,

a cost analysis was performed on the first system, which yielded

positive results overall.

The analysis showed that maintenance procedures were improved

and solvent cleaners were phased out, leading to the elimination of

the resultant VOC emissions. The new coating system eliminated

5 gallons of solvent and 20 gallons of solvent-based paint per week.

Paint waste and rags decreased from approximately two drums per

week to one drum picked up every three weeks. Hazardous waste

and hazardous material savings totaled $29,640 per year.

Substantial labor savings resulted from the use of the first new

powder coating spray system. Labor costs were reduced by approximately $146,000 annually. Prior to the installation of the new powder coating spray system, the workers were required to apply as

many as three coats of liquid paint in order to achieve the required

coating thickness, often taking as many as eight hours to cure

between each coat. With the new system, the total part curing time

is only 30 minutes, reducing turn-around time from three days to

one day. In addition, component processing turn-around time was

reduced by 67%, the coating was shown to be more durable by

approximately a factor of ten, and the system payback period was

determined to be 0.8 years.

The need to cure the coating within the range of 350-400°F

restricts the use of high-temperature cure powder coatings to substrates and components that can withstand such temperatures

without degradation. Therefore, temperature-sensitive alloys, such

as aluminum, cannot be coated with high-temperature cure powder,

and alternative processes were considered.

Low-Temperature Cure Powder Coatings

Low-temperature cure powder coatings are thermoset powder coatings designed to cure in the range of 250-275°F. This lower cure temperature results in shorter processing times due to the decreased time

required for the oven to reach temperature, a 20- to 30-minute cure

time, and less time to cool down. These coatings may be epoxybased, TGIC, polyurethane, or a hybrid formulation. In industry,

low-temperature cure powder coatings are used for medium-density

fiberboard (MDF) and plastics, and they are finding increased usage

due to lower cure temperatures and shorter processing time.[2]

As part of the Navy’s PPEP, NRNW initiated an effort that

focused on the testing and evaluation of three commercially available TGIC low-temperature cure powders, comparing them to the

performance of liquid primer/topcoat and high-temperature powder coating systems. The objective of this evaluation was to determine the suitability of commercially available, environmentallyfriendly equipment, systems, and/or technologies for the Navy environment. Additionally, the effort investigated installation ease,

training issues, maintainability/repairability, site interface, future

uses, and lifecycle costs. Booms, pod rails, launch tubes, and bike

racks were used as components for evaluation.

The results showed that the commercially available low-temperature cure coating systems performed well in service compared

to high-temperature cure powder. It was concluded that, for an

activity currently operating a high-temperature cure powder coating spray system, adapting the line to use low-temperature cure

powder coatings would require only an $11,000 investment with

a maximum break-even point of three years. However, these commercial coatings have not been subjected to any Navy laboratoryscale testing, and their ability to comply with military specification testing requirements and performance is unknown.

The second low-temperature cure powder coating evaluation

focused on a coating designed to meet military specification requirements and cure at 120°C within 30 minutes. In addition, this

low-temperature cure coating was developed for application on

aluminum components without the use of a primer. By designing

the coating specifically to meet military requirements, the coating

system should be ideally suited to provide a low-temperature cure

powder for both the military and industry.

Navy Region Northwest is working to determine the potential

uses of this coating system throughout the region. Field testing at

NRNW is ongoing and the ultimate goal is to have a low-temperature cure powder suitable for use on most aluminum and magnesium components, although its performance is currently only being

evaluated on aircraft ground support equipment. Targeted substrates include both steel and aluminum 2024-T3. Key aircraft

ground support equipment components have been identified and

coated. The aesthetics and corrosion protection of coatings being

used at shore-based activities and aboard ships are being evaluated.

The low-temperature cure powder coating system includes a barium

metaborate corrosion inhibitor package, and thus corrosion resistance should be comparable to current coating systems. For this evaluation, the entire coating process is being examined, including labor

savings, hazardous material avoidance, waste stream generation,

worker exposure issues, and implementation obstacles.

Portable Powder Coatings

Some components cannot be removed for processing in an oven.

Consequently, a commercially available, liquid propane (LP),

portable powder coating spray system for in-situ applications was

evaluated. Specifically, NRNW was interested in potentially using

this method for applying TGIC powder coatings and non-skid

coatings on components to include (as a minimum) submarine

components and aircraft ground support equipment.

An initial demonstration preceding the formal evaluation showed

that although this evaluation demonstrated the viability of the equipment for applying and curing the powder coating in-situ, the

implementation obstacles (e.g., high temperatures, air emissions,

open flame, and logistical restrictions) proved insurmountable. The

evaluation was subsequently canceled after the initial demonstration.

Ultraviolet Cure Powder Coatings

As with other powder coatings, ultraviolet (UV) light curable powder coatings contain no solvents (i.e., VOC free), and overspray

can be filtered and re-used. These coatings contain a photoinitiator

that commences the polymerization process when exposed to UV

light. Melting of UV curable powders and flowing of the coating

(which enables it to level prior to crosslinking) occurs at 175-250°F

in approximately two to ten minutes via infrared (IR), convection,

or combination infrared/convection curing ovens. UV curing

takes place in only a few seconds and is dependent on the UV ray

line-of-sight.[3] Consequently, the curing device must be designed

to accommodate components of complex geometries. A robotic

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http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 4, Number 3 13

system can be used to heat and cure the coating, focusing IR rays

for melting and then the UV rays for curing onto geometrically

complex components.

UV curable powder coatings have several advantages over conventional thermoset powder coatings. Conventional powder coatings require time for the oven to heat up to 350-400°F, time to cure

at that temperature, and time to cool down. UV curable powders

do not require those high temperatures, thus the cure time is

drastically reduced. Similarly, since UV curable powders do not

require heat activation for curing, the energy costs are reduced.

Overall, this technology enables increased throughput due to quicker processing times. Additionally, this provides a huge advantage

in the coating of massive metal components. Such components act

as heat sinks and require extensive “oven time” in order to heat the

surface adequately to ensure a proper cure.

The UV curable powder coating evaluation will examine a coating that is currently used for electric motors. The Navy will compare

the performance of four commercially-available UV curable powder

coatings produced by two different manufacturers to have the performance of military specification liquid aerospace coatings. For this

evaluation, the UV curable powder contains a blend of acrylated

polyester and acrylated polyurethane resins.

In industrial applications, one of the primary advantages of UV

curable powder coating is that only one layer of coating is required.

A goal of this project is to determine if this will be viable for the

Navy as well. Candidate components for the Navy include US Navy

aircraft ground support equipment and submarine components of

both metallic and composite substrates. Composite components are

sensitive to the higher cure temperatures and dwell times required

by both high- and low-temperature cure powder coatings.

The most complicated aspect of the UV curing process concerns

the relationship of the optical properties of the heat lamp to the

geometry of the components to be processed. In order to accommodate an assortment of geometrically diverse components, a central

work cell location for coating and curing was used. Location of the

work cell within NRNW will allow the Navy the opportunity to

determine the ergonomic, space limitations, workflow, and disposal

issues resulting from the implementation of the new coating system.

A second hurdle for NRNW is the issue of having trained personnel for the operation of the robotic system. Prior to field evaluation, implementation of the robotically-controlled work cell is

to take place over a span of several months. During that time, the

robot manufacturer will be providing operation and maintenance

training. High personnel turnover due to duty rotation is typical

of Navy installations, but makes it essential that those operators

who are trained initially become thoroughly familiar with all of

the safety, operational, and maintenance aspects of the system.

These operators, in turn, will be expected to train the next group

of operators at some point during the field evaluation phase.

One of the hopes for the UV cure powder coating evaluation is

that it will eventually lead to the ability to provide powder coating

for a variety of different substrates while using minimal space.

Currently, powder coating operations require a large area for the

spray booth and ovens, as well as for staging of components following the curing process. A UV powder curing operation could potentially eliminate this space requirement. Ultimately, NRNW would

like the capability to perform the powder coating operation on the

components in-situ without having to disassemble and transport

them to the powder coating facility. At the very least, the hope is to

augment the existing high-temperature powder coating system with

a manually operated UV curable lamp for curing substrates and

components that cannot currently be subjected to the high temperatures associated with traditional powder coating systems.

This project is scheduled to take two years to complete, with the

field work comprising a substantial portion of that time. At the conclusion, the results and recommendation may lead to further work

in this area.

Electro-Active Polymer Pretreatment Coatings

Preventing corrosion of Navy components is an ongoing challenge.

For aluminum components, a hexavalent chromium (Cr(VI)) conversion coating (CCC) over a Cr(VI) primer and a non-chromated

topcoat has been found to be especially effective. Unfortunately,

Cr(VI) is highly toxic and a known carcinogen.[4] Europe’s

Restriction of Hazardous Substances (RoHS) directive and

California’s Electronic Waste Recycling Act of 2003 (EWRA) are

among the laws forcing commercial users to seek alternatives.[5]

For the Navy, corrosion control operations must comply with regulations from EPA and OSHA concerning worker exposure to

Cr(VI). The permissible exposure limit (PEL) for hexavalent

chromium has been set at 5 μg/m3, calculated as an eight-hour time

weighted average.[6] For operations involving the coating of aircraft

or aircraft components, OSHA has established the PEL for Cr(VI)

at 25 μg/m3.[7]

The Navy has been in the process of evaluating several alternatives

to replace Cr(VI). Navy testing has shown that electro-active polymer (EAP) pretreatments used in combination with Cr(VI) primers

could potentially provide aluminum alloy corrosion protection comparable to that of trivalent and hexavalent chromium conversion

coatings. EAP coatings are advantageous since they are both nonmetallic and non-hazardous. NRNW is currently performing field

testing on EAP coated components. The objective is to determine

whether EAPs can be used successfully with non-chromated primers

on aluminum alloy aircraft ground support equipment components.

Polymers were generally regarded as non-conductive or electrical

insulators until the discovery that polyacetylene doped with iodine

exhibited electrical conductivity many orders of magnitude higher

than the neutral (undoped) polyacetylene.[8] Conductive polymers

and electro-active polymers are terms used to describe conjugated

polymers, regardless of conductivity. When doped, these EAPs

become conductive and have applications ranging from flexible

lighting to electronic paper.[9, 10] EAPs are either insulating or

semi-conducting in their neutral forms but can be converted to the

electrically conductive form via doping. Their conductivities range

from insulators (<10-10 S/cm) to semiconductors (~10-5 S/cm) to

conductors (>104 S/cm).[11]

The EAP evaluated within NRNW is designated poly(2,5-bis-

(N-methyl-N-hexylamino) phenylene vinylene), referred to as

BAM-PPV. Use of this EAP requires that it be dissolved in 4-

chlorobenzotrifluoride (Oxsol-100) solvent and then applied to the

substrate using a high volume, low pressure (HVLP) spray gun.

Although the BAM-PPV has performed equally well after dissolution in xylene and d-limonene, the Oxsol-100 solvent was chosen

for this evaluation since it is the only solvent of the three rated as

VOC-exempt. The dissolution and solvent application constitutes

the pretreatment phase. Typically, it takes nine passes to achieve the

1/100 mil thickness required. Once the EAP is dried, the liquid

primer and standard gloss topcoat can be applied as usual.

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14 The AMMTIAC Quarterly, Volume 4, Number 3

Field testing of this coating system is underway to assess both the

application as well as the performance of the EAP. EAP dissolved in

Oxsol-100 is being applied to aluminum aircraft ground support

equipment components via HVLP spray gun. The evaluation of the

coating will include corrosion resistance, repairability and overall

performance. Impact to the workflow and throughput will also be

examined, along with reliability of the equipment and ease-of-use of

the process. The development of the health and safety procedures at

the test facility is an integral part of the evaluation, although in this

case the existing Environmental, Safety, and Health (ESH) plan was

sufficient for this purpose. Finally, the results of the field testing

will be used to address the feasibility of full-scale implementation

within the Navy.

Anti-Corrosion Inhibiting Primers

In addition to replacing CCC, the Navy is also seeking to eliminate

the use of Cr(VI) from military primers used extensively on aluminum and steel alloys. Compounds have been developed commercially that simulate the corrosion-inhibiting properties of chromium.

These inhibitors would be introduced into formulations made from

Cr(VI)-free epoxy or EAP, which will then be subject to laboratory

testing to ensure compliance with the applicable military specifications. Specifically, the laboratory testing is to include accelerated

weathering testing, adhesion, marine outdoor exposure testing, solvent and jet fuel resistance, and flexibility. After laboratory testing,

the best-performing formulation will be chosen for field testing.

The expected environmental benefits for NRNW resulting from

the incorporation of this Cr(VI)-free primer are similar to those of

EAPs, including reduced disposal of Cr(VI) waste and the associated

costs. The decreased Cr(VI) usage would also reduce worker exposure and enable NRNW to meet future regulatory requirements.

Following the completion of the laboratory testing (scheduled

to be completed in fiscal year 2011), field testing will take place at

NRNW. Should this project prove successful, the Navy hopes to

eliminate the use of Cr(VI) completely by using a Cr(VI)-free pretreatment (BAM-PPV) and the Cr(VI)-free primer.

Plastisol and Self-Healing Coatings

Plastisol, a vinyl compound that exists as a liquid at ambient temperatures, is a thick, non-conductive plastic coating. Like powder coating, plastisol changes its form upon heating from liquid to solid vinyl.

Components are coated with plastisol via a thermal process in which

the components are preheated to about 375°F, dipped, and then post

heated.[12] Historically, the Navy has used plastisol to color code

hand wheels. Identification numbers would be etched into the plastisol, with black paint added into the etching in order to see the numbers. Both powder and liquid forms of plastisol have been used since

the 1970s. Currently within the Navy, plastisol is used for coating

parts ranging from ship components to rocket motors.

Within NRNW, the plastisol coatings currently used contain

PVC and the chemical compounds known as phthalates, which

make the vinyl soft and pliable. However, there are environmental

concerns associated with exposure to phthalates, which has resulted

in plastisol manufacturers offering phthalate-free plastisols.[13]

NRNW plans to introduce a fluidized bed system for plastisol

coatings, which will allow for the use of phthalate-free plastisols. It

will also reduce the use of solvents during the coating process.

Although powder coating is designed to provide a durable finish

requiring only minimal maintenance, aesthetic concerns often dictate when and how the coating is repaired. Stripping of scratched

or chipped powder coated components to bare metal for aesthetic

reasons results in unnecessary labor, waste, and emissions. The use

of self-healing coatings that could resist scratches and chips would

be a significant improvement. Such coatings are currently used in

the automotive industry, and NRNW is exploring the possibility of

using them in the military environment.[14]

CONCLUSION

Navy Region Northwest is under increasing pressure to meet the

demands of increasing workload while providing a safer, cleaner

work environment. Demanding applications and work environments require high performance coatings that achieve reliability

while minimizing environmental impact through their lifespan.

Through the evaluation and incorporation of new coating systems

into their work processes, NRNW have been able to reduce air

emissions, hazardous waste generation, and maintenance expenditures while increasing throughput and operator safety. Due to the

variety and scale of the coating operations taking place within

NRNW, there is ample opportunity to continue to investigate and

use environmentally-friendly coatings. Increased mobility of

repair operations, reduced utility costs, and elimination of chromates are among the primary goals of their investigation into

low-temperature curable, ultraviolet curable, and portable powder

coatings as well as electro-active polymer pretreatments and anticorrosion inhibiting coatings.

REFERENCES

[1] Talbert, R., Powder Coating, 4th Ed., Chemical Coaters Association

International, 2000.

[2] Armstrong, B., “New Benchmarks in Low-Temperature Cure Powder

Technology,” Powder Coating, September 2002.

[3] Mitchell, S., “UV Powders Reaching New Markets,” Fusion UV

Systems, Inc., www.pfonline.com, accessed February 2008.

[4] “OSHA Fact Sheet: Health Effects of Hexavalent Chromium,”

Occupational Safety and Health Administration, www.osha.gov/OshDoc/

data_General_Facts/hexavalent_chromium.pdf.

[5] “Smart Coating Senses and Neutralizes Corrosion,” Crosslink,

www.crosslinkusa.com, accessed February 2008.

[6] “National Emission Standards for Chromium Emissions from Hard

and Decorative Electroplating and Chromium Anodizing Tanks,”

Environmental Protection Agency, Federal Register, RIN 2060-AC14,

January 25, 1995.

[7] “Occupational Safety and Health Standards, Toxic and Hazardous

Substances: Chromium (VI),” Occupational Safety and Health Administration, CFR 1910.1026 (f) (1) (ii).

[8] Shirakawa, H., E. Louis, A. MacDiarmid, and A. Heeger, Journal of the

Chemical Society, Chemical Communications, Vol. 578, 1977.

[9] Electroactive Polymers for Corrosion Control, P. Zarras, J. D. StengerSmith, and Y. Wei, Eds., Oxford University Press, American Chemical

Society, 2003.

[10] “Crystal Clear,” The Economist, December 6, 2007.

[11] Anderson, N., and P. Zarras, “Electro-Active Polymers as Green

Alternatives to Hexavalent Chromium,” Currents: The Navy’s Environmental

Magazine, Spring 2005.

[12] “Plastisol vs. Powder Coating,” www.finishing.com/130/23.shtml.

[13] Beckman, M., “‘Green Printing’ Uses Sustainable Methods and

Materials,” www.impressionsmag.com, accessed July 21, 2008.

[14] Bourzac, K., “First Self-Healing Coatings,” MIT Technology Review,

December 2008.

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