Rapid Pro to Typing

Recent Advances In Rapid Prototyping 2004 – 2005

INTRODUCTION

The term rapid prototyping (RP) refers to a class of technologies that can

automatically construct physical models from Computer-Aided Design (CAD) data.

These "three dimensional printers" allow designers to quickly create tangible

prototypes of their designs, rather than just two-dimensional pictures. Such models

have numerous uses. They make excellent visual aids for communicating ideas with

co-workers or customers. In addition, prototypes can be used for design testing. For

example, an aerospace engineer might mount a model airfoil in a wind tunnel to

measure lift and drag forces. Designers have always utilized prototypes; RP allows

them to be made faster and less expensively.

In addition to prototypes, RP techniques can also be used to make tooling

(referred to as rapid tooling) and even production-quality parts (rapid

manufacturing). For small production runs and complicated objects, rapid prototyping

is often the best manufacturing process available. Of course, "rapid" is a relative term.

Most prototypes require from three to seventy-two hours to build, depending on the

size and complexity of the object. This may seem slow, but it is much faster than the

weeks or months required to make a prototype by traditional means such as

machining. These dramatic time savings allow manufacturers to bring products to

market faster and more cheaply. In 1994, Pratt & Whitney achieved "an order of

magnitude [cost] reduction [and] . . . time savings of 70 to 90 percent" by

incorporating rapid prototyping into their investment casting process.

At least six different rapid prototyping techniques are commercially available,

each with unique strengths. Because RP technologies are being increasingly used in

non-prototyping applications, the techniques are often collectively referred to as solid

free-form fabrication, computer automated manufacturing, or layered manufacturing.

The latter term is particularly descriptive of the manufacturing process used by all

commercial techniques. A software package "slices" the CAD model into a number of

thin (~0.1 mm) layers, which are then built up one atop another. Rapid prototyping is

an "additive" process, combining layers of paper, wax, or plastic to create a solid

object. In contrast, most machining processes (milling, drilling, grinding, etc.) are

"subtractive" processes that remove material from a solid block. RP’s additive nature

Dept. Of Mechanical Engineering, G.V.I.T. , K.G.F. 1


allows it to create objects with complicated internal features that cannot be

manufactured by other means.

Of course, rapid prototyping is not perfect. Part volume is generally limited to

0.125 cubic meters or less, depending on the RP machine. Metal prototypes are

difficult to make, though this should change in the near future. For metal parts, large

production runs, or simple objects, conventional manufacturing techniques are usually

more economical. These limitations aside, rapid prototyping is a remarkable

technology that is revolutionizing the manufacturing process.



THE BASIC PROCESS

Although several rapid prototyping techniques exist, all employ the same basic five-

step process. The steps are:

1. Create a CAD model of the design

2. Convert the CAD model to STL format

3. Slice the STL file into thin cross-sectional layers

4. Construct the model one layer atop another

5. Clean and finish the model

CAD Model Creation: First, the object to be built is modeled using a Computer-

Aided Design (CAD) software package. Solid modelers, such as Pro/ENGINEER,

tend to represent 3-D objects more accurately than wire-frame modelers such as

AutoCAD, and will therefore yield better results. The designer can use a pre-existing

CAD file or may wish to create one expressly for prototyping purposes. This process

is identical for all of the RP build techniques.

Conversion to STL Format: The various CAD packages use a number of different

algorithms to represent solid objects. To establish consistency, the STL

(stereolithography, the first RP technique) format has been adopted as the standard of

the rapid prototyping industry. The second step, therefore, is to convert the CAD file

into STL format. This format represents a three-dimensional surface as an assembly

of planar triangles, "like the facets of a cut jewel." The file contains the coordinates of

the vertices and the direction of the outward normal of each triangle. Because STL

files use planar elements, they cannot represent curved surfaces exactly. Increasing

the number of triangles improves the approximation, but at the cost of bigger file size.

Large, complicated files require more time to pre-process and build, so the designer

must balance accuracy with manageability to produce a useful STL file. Since the .stl

format is universal, this process is identical for all of the RP build techniques.

Slice the STL File: In the third step, a pre-processing program prepares the STL file

to be built. Several programs are available, and most allow the user to adjust the size,

location and orientation of the model. Build orientation is important for several

reasons. First, properties of rapid prototypes vary from one coordinate direction to



another. For example, prototypes are usually weaker and less accurate in the z

(vertical) direction than in the x-y plane. In addition, part orientation partially

determines the amount of time required to build the model. Placing the shortest

dimension in the z direction reduces the number of layers, thereby shortening build

time. The pre-processing software slices the STL model into a number of layers from

0.01 mm to 0.7 mm thick, depending on the build technique. The program may also

generate an auxiliary structure to support the model during the build. Supports are

useful for delicate features such as overhangs, internal cavities, and thin-walled

sections. Each PR machine manufacturer supplies their own proprietary pre-

processing software.

Layer by Layer Construction: The fourth step is the actual construction of the part.

Using one of several techniques (described in the next section) RP machines build one

layer at a time from polymers, paper, or powdered metal. Most machines are fairly

autonomous, needing little human intervention.

Clean and Finish: The final step is post-processing. This involves removing the

prototype from the machine and detaching any supports. Some photosensitive

materials need to be fully cured before use. Prototypes may also require minor

cleaning and surface treatment. Sanding, sealing, and/or painting the model will

improve its appearance and durability.



RAPID PROTOTYPING TECHNIQUES

Most commercially available rapid prototyping machines use one of six

techniques. At present, trade restrictions severely limit the import/export of rapid

prototyping machines, so this guide only covers systems available in the U.S.

A) Stereolithography

Patented in 1986, stereolithography started the rapid prototyping revolution.

The technique builds three-dimensional models from liquid photosensitive polymers

that solidify when exposed to ultraviolet light. As shown in the figure below, the

model is built upon a platform situated just below the surface in a vat of liquid epoxy

or acrylate resin. A low-power highly focused UV laser traces out the first layer,

solidifying the model’s cross section while leaving excess areas liquid.

Figure 1: Schematic diagram of stereolithography.

Next, an elevator incrementally lowers the platform into the liquid polymer. A

sweeper re-coats the solidified layer with liquid, and the laser traces the second layer

atop the first. This process is repeated until the prototype is complete. Afterwards, the

solid part is removed from the vat and rinsed clean of excess liquid. Supports are

broken off and the model is then placed in an ultraviolet oven for complete curing.



Stereolithography Apparatus (SLA) machines have been made since 1988 by

3D Systems of Valencia, CA. To this day, 3D Systems is the industry leader, selling

more RP machines than any other company. Because it was the first technique,

stereolithography is regarded as a benchmark by which other technologies are judged.

Early stereolithography prototypes were fairly brittle and prone to curing-induced

warp age and distortion, but recent modifications have largely corrected these

problems.

Machine : SLA-5000

Manufacturer : 3D Systems

Material : Liquid Photopolymer

Mechanism : 216 mW Solid State Laser

Build Volume : 20" x 20" x 23"

Applications : Produces highly accurate parts for a wide range of

applications.

Stereolithography is a manufacturing process that uses a UV laser to create

successive cross-sections of a three-dimensional object within a vat of liquid

photopolymer. The cross-sections build layers typically of 0.004 inches or 0.006

inches. A platform is placed on top of the vat filled with the polymer (an epoxy resin).

Before the build begins, the platform is moved to a point just below the surface of the



resin. As the solid state UV laser traces the layer in the polymer, the resin begins to

cure; solidifying the part to be manufactured.

Before the part begins to build, supports are created between the platform and

the part, to ensure easier removal of the built part. After the supports are created, the

process to build the part begins. Once the cross-section has been traced with the laser,

a Zephyr blade moves across the platform, leveling the uncured polymer. After a layer

has been completed, the platform drops down again and the same procedure takes

place. The object is manufactured layer by layer, curing the part on each level. When

the build is complete, the platform raises above the vat, draining the excess resin away

from the part.

The platform is then removed and the part is further processed. The fresh part

is bathed in a TPM solution to remove the excess resin. Now that the part has been

sufficiently washed with the TPM solution, it is then sprayed thoroughly with alcohol.

This enables the part to be handled directly by human skin (it removes the stickiness

or tackiness on the outer edges of the part). The face of the part that was attached to

the platform is sanded to remove the support structures. The part is then placed in a

UV oven to finish curing the polymer.

When the curing process has finished, the part can be furthered polished and

processed, if so desired. The part is usually shipped directly to the company whose

design the part was manufactured from, or taken one step further: molding and/or

casting. The parts that are built using the stereolithography machine are durable, but

fragile. These parts must be handled with extreme care. The dimensions of these parts

are very accurate, only varying at times by 0.002 to 0.005 inches. The SLA machine

is also highly accurate with building parts containing complex geometries and

intricate details.

B) Laminated Object Manufacturing

In this technique, developed by Helisys of Torrance, CA, layers of adhesive-

coated sheet material are bonded together to form a prototype. The original material

consists of paper laminated with heat-activated glue and rolled up on spools. A

manufacturing process that uses a carbon-dioxide laser to create successive cross-



sections of a three-dimensional object from layers of paper with a polyethylene

coating on the backside. The first step is to create a base on which the paper can

attach itself to. This is done by placing a special tape down onto the platform. A sheet

of paper is fed through with the aid of small rollers. As the paper is fed through, a

heated roller is used to melt the coating on the paper so that each new layer will

adhere to the previous layer

Machine : LOM 2030E

Manufacturer : Helisys (Cubic Technologies)

Material : Paper

Mechanism : CO2 Laser, Heated Roller

Build Volume : 20" x 30" x 20"

Applications : Produces large prototypes for visualization and assembly

testing.

Figure 2: Schematic diagram of laminated object manufacturing.



Helisys developed several new sheet materials, including plastic, water-repellent

paper, and ceramic and metal powder tapes. The powder tapes produce a "green" part

that must be sintered for maximum strength.

A manufacturing process that uses a carbon-dioxide laser to create successive

cross-sections of a three-dimensional object from layers of paper with a polyethylene

coating on the backside. The first step is to create a base on which the paper can

attach itself to. This is done by placing a special tape down onto the platform. A sheet

of paper is fed through with the aid of small rollers. As the paper is fed through, a

heated roller is used to melt the coating on the paper so that each new layer will

adhere to the previous layer.

The carbon-dioxide laser then cuts the outline of the cross-sectional pattern

into the top layer of paper. Once the laser is done cutting the pattern, it creates a

border around the build that contains the desired part. This enables the part to stay

intact as each new layer is created. Once the border has been cut, the laser then

proceeds to create hatch marks, or cubes that surround the pattern within the border.

The cubes behave as supports for the part to ensure that no shifting or movement

takes place during the entire build.

When the build is completed, the part, attached to the platform, needs to be

removed from the LOM. Depending on the size of the part, the block to be removed

may take more than one person to remove the build from the LOM. After the part has

been successfully removed from the LOM, it must then be removed for the actual

platform. Again this may take the work of more than one individual. A wire is used

and placed between the part and the platform to "cut" the part away from the metal

platform.

The border or frame of the part is then removed. The next step involves

decubing or removing the supports. Often times the supports can be removed from

simple shaking the part; other times it is necessary to use a chisel to pry the cubes

away from the part. When all of the cubes have been removed, the unfinished part is

sanded down and a lacquer is used to seal the part. Being that LOM parts are made for

paper, humidity and temperature affect the structure and composure of the part if it is



not coated; hence, the lacquer serves as a protective measure. The LOM is very useful

in manufacturing large parts quickly.

C) Selective Laser Sintering

Developed by Carl Deckard for his master’s thesis at the University of Texas,

selective laser sintering was patented in 1989. The technique, shown in Figure 3, uses

a laser beam to selectively fuse powdered materials, such as nylon, elastomer, and

metal, into a solid object. Parts are built upon a platform which sits just below the

surface in a bin of the heat-fusable powder. A laser traces the pattern of the first layer,

sintering it together. The platform is lowered by the height of the next layer and

powder is reapplied. This process continues until the part is complete. Excess powder

in each layer helps to support the part during the build. SLS machines are produced by

DTM of Austin, TX.

Figure 3: Schematic diagram of selective laser sintering.

Machine : Sinterstation 2500plus

Manufacturer : 3D Systems

Material : Plastic, Metal, or Elastomeric Powders



Mechanism : CO2 Laser

Build Volume : 14.5" x 12.5" x 17.5"

Applications : No supports allow complex geometries. Durable parts allow

for real-world testing.

Sinterstation systems use the SLS Selective Laser Sintering process to create

solid three-dimensional objects, layer by layer, from plastic, metal, or ceramic

powders that are "sintered" or fused using CO2 laser energy. The inherent materials

versatility of SLS technology allows a broad range of advanced rapid prototyping and

manufacturing applications to be addressed. From aerospace to consumer electronics

and automobiles to appliances, companies around the world use Sinterstation systems

to accelerate the design, development, and market introduction of new products.

Sinterstation systems can process many different types of SLS powders. A

number of plastic-based powders are used to produce functional models directly in the

SLS process. These models have excellent mechanical integrity, heat resistance, and

chemical resistance and can often be used for advanced testing in an environment

similar to that intended for the final product. Many of DTMs new materials are used

for prototype manufacturing applications, where limited quantities of production-

equivalent parts are produced using tooling and patterns made directly in the SLS



process. The tooling and patterns are built from a variety of plastic, metal, and

elastomeric-based powders. In addition, an increasing number of customers are

addressing direct manufacturing applications with SLS technology, using commercial

and custom SLS powders.

D) Fused Deposition Modeling

In this technique, filaments of heated thermoplastic are extruded from a tip

that moves in the x-y plane. Like a baker decorating a cake, the controlled extrusion

head deposits very thin beads of material onto the build platform to form the first

layer. The platform is maintained at a lower temperature, so that the thermoplastic

quickly hardens. After the platform lowers, the extrusion head deposits a second layer

upon the first. Supports are built along the way, fastened to the part either with a

second, weaker material or with a perforated junction.

Stratasys, of Eden Prairie, MN makes a variety of FDM machines ranging

from fast concept modelers to slower, high-precision machines. Materials include

ABS (standard and medical grade), elastomer (96 durometer), polycarbonate,

polyphenolsulfone, and investment casting wax.

Machine : FDM Titan

Manufacturer : STRATASYS

Material : ABS Plastic, Polycarbonate, Polyphenyl Sulfone

Mechanism : FDM Extrusion Head

Build Volume : 16” x 14” x 16”(406.4mm x 355.6mm x 406.4mm)



Fused Deposition Modeling is a manufacturing process that creates successive

cross-sections of a three-dimensional object from threads of plastic. Similar to a hot

glue gun, the FDM first extrudes plastic threads through the support tip to create

support structures for any overhanging portions of the part to be built. The support

continues to build, providing a base for the part to be created on. Once the appropriate

supports are built, plastic is then extruded the desired material through the modeler

tip. The FDM modeler head moves in both the x- and y-axis across a foundation and

deposits a layer of material. This process continues until all layers of the part have

been completed.

The material is heated to a high temperature allowing the material to approach

its melting point. The material is extruded through the head at a temperature just prior

to the melting temperature. This allows the material to become soft enough to push

through the modeler tip, without liquefying the material. Once the material is forced

through the tip, the plastic becomes hard again (again, similar to using a hot glue

gun). The successive layers fused together as the material hardens or solidifies.



Once the part has finished its successive layers and the build is complete, the

part is removed from the FDM. The supports of the part should break away easily

from the completed model. After the supports have been removed successfully, the

completed model is sanded to enhance surface finish. The envelope build space for

the Stratasys Titan is 16"x14"x16".

Figure 4: Schematic diagram of fused deposition modeling.

E) Solid Ground Curing

Developed by Cubital, solid ground curing (SGC) is somewhat similar to

stereolithography (SLA) in that both use ultraviolet light to selectively harden

photosensitive polymers. Unlike SLA, SGC cures an entire layer at a time. Figure 5

depicts solid ground curing, which is also known as the solider process. First,

photosensitive resin is sprayed on the build platform. Next, the machine develops a

photomask (like a stencil) of the layer to be built. This photomask is printed on a glass

plate above the build platform using an electrostatic process similar to that found in

photocopiers. The mask is then exposed to UV light, which only passes through the

transparent portions of the mask to selectively harden the shape of the current layer.



Figure 5: Schematic diagram of solid ground curing.

After the layer is cured, the machine vacuums up the excess liquid resin and

sprays wax in its place to support the model during the build. The top surface is

milled flat, and then the process repeats to build the next layer. When the part is

complete, it must be de-waxed by immersing it in a solvent bath. SGC machines are

distributed in the U.S. by Cubital America Inc. of Troy, MI. The machines are quite

big and can produce large models.

F) 3-D Ink-Jet Printing

Ink-Jet Printing refers to an entire class of machines that employ ink-jet

technology. The first was 3D Printing (3DP), developed at MIT and licensed to

Soligen Corporation, Extrude Hone, and others. The ZCorp 3D printer, produced by Z

Corporation of Burlington, MA is an example of this technology. As shown in Figure

6a, parts are built upon a platform situated in a bin full of powder material. An ink-jet

printing head selectively deposits or "prints" a binder fluid to fuse the powder

together in the desired areas. Unbound powder remains to support the part. The

platform is lowered, more powder added and leveled, and the process repeated. When

finished, the green part is then removed from the unbound powder, and excess

unbound powder is blown off. Finished parts can be infiltrated with wax, CA glue, or

other sealants to improve durability and surface finish. Typical layer thicknesses are



on the order of 0.1 mm. This process is very fast, and produces parts with a slightly

grainy surface. ZCorp uses two different materials, a starch based powder (not as

strong, but can be burned out, for investment casting applications) and a ceramic

powder. Machines with 4 color printing capability are available.

Machine : Z406C Concept Modeler

Manufacturer : Z Corporation

Material : Starch

Mechanism : Print Head, Glue

Build Volume : 8" x 10" x 8" (203 x 254 x 203 mm)

Applications : Produces full-color models primarily for display.

3D Systems' version of the ink-jet based system is called the Thermo-Jet or Multi-Jet

Printer. It uses a linear array of print heads to rapidly produce thermoplastic models

(Figure 6d). If the part is narrow enough, the print head can deposit an entire layer in

one pass. Otherwise, the head makes several passes.

Sanders Prototype of Wilton, NH uses a different ink-jet technique in its Model

Maker line of concept modelers. The machines use two ink-jets (see Figure 6c). One

dispenses low-melt thermoplastic to make the model, while the other prints wax to

form supports. After each layer, a cutting tool mills the top surface to uniform height.

This yields extremely good accuracy, allowing the machines to be used in the jewelry

industry.

Ballistic particle manufacturing, depicted in Figure 6b, was developed by BPM Inc.,

which has since gone out of business.



Figure 6: Schematic diagrams of ink-jet techniques.



FUTURE DEVELOPMENTS

Rapid prototyping is starting to change the way companies design and build

products. On the horizon, though, are several developments that will help to

revolutionize manufacturing as we know it.

One such improvement is increased speed. "Rapid" prototyping machines are

still slow by some standards. By using faster computers, more complex control

systems, and improved materials, RP manufacturers are dramatically reducing build

time. For example, Stratasys recently introduced its FDM Quantum machine, which

can produce ABS plastic models 2.5-5 times faster than previous FDM machines.

Continued reductions in build time will make rapid manufacturing economical for a

wider variety of products.

Another future development is improved accuracy and surface finish. Today’s

commercially available machines are accurate to ~0.08 millimeters in the x-y plane,

but less in the z (vertical) direction. Improvements in laser optics and motor control

should increase accuracy in all three directions. In addition, RP companies are

developing new polymers that will be less prone to curing and temperature-induced

warpage.

Another important development is increased size capacity. Currently most RP

machines are limited to objects 0.125 cubic meters or less. Larger parts must be built

in sections and joined by hand. To remedy this situation, several "large prototype"

techniques are in the works. The most fully developed is Topographic Shell

Fabrication from Formus in San Jose, CA. In this process, a temporary mold is built

from layers of silica powder (high quality sand) bound together with paraffin wax.

The mold is then used to produce fiberglass, epoxy, foam, or concrete models up to

3.3 m x 2 m x 1.2 m in size.

At the University of Utah, Professor Charles Thomas is developing systems to

cut intricate shapes into 1.2 m x 2.4 m sections of foam or paper. Researchers at Penn

State’s Applied Research Lab (ARL) are aiming even higher: to directly build large

metal parts such as tank turrets using robotically guided lasers. Group leader Henry



Watson states that product size is limited only by the size of the robot holding the

laser.

Based on the initial success experienced with Somos® 9120 polypropylene-

like materials for rapid prototyping, AME decided to expand their production

capabilities and product offering to include the new Somos® WaterShed™ resins.

With the intention of being able to produce extremely fine features in a variety of

textures and finishes – including transparency, the technical and aesthetic benefits

offered by this decision were immediately experienced.

The project contracted by the manufacturer Mitrefinch for an employee

logistics system gave AME the opportunity to put WaterShed™ to the test. The

models realized in WaterShed™ showed advantages during the construction process,

as the material allowed the technicians to obtain a superior surface finish that

diminished the time necessary during finishing and preparation of the model for

silicone moulding. The mechanical properties of the material and its resistance to

humidity also gave the technicians the opportunity of using the model for reiterate

tooling processes. These advantages combined with the aesthetic quality of the

models, generated enthusiasm in both the technical and design departments of AME.

AME has also recently completed a project for the design and development of

personal protection accessories, which AME welcomed as particularly challenging:

The design needed to respond to the functional and aesthetic expectations of the pan-

European fire-fighting community, as well as the needs of colleagues in the

paramedic and rescue services.

‘Although there are European Standards for personal protective apparel,’ says

AME designer Andy Rosie ‘the specific expectations of the different countries are

quite distinct.' Prototypes were produced using DSM Somos® ProtoFunctional®

resins. ‘This was an extremely important part in the development phase’, continues

Andy Rosie. The project incorporates a number of unique features which we needed

to check out with the target markets. By using a combination of the 9120 and 11120

WaterShed™ materials, we were able to produce a prototype which was aesthetically

pleasing, highly accurate, and able to withstand the rigours of multiple demonstrations

of the interlocking parts. The parts proved so stable that we were able to retain the



prototype made from Somos® 9120 resin for structural integrity tests, which involves

dropping a 5kg weight onto a helmet: Both helmet and head-cage survived!’

AME’s design and development team were able to present a finished and fully

tested concept four-and-a-half weeks ahead of schedule by avoiding the need for an

aluminium tool. The quality of the original ‘demonstration’ prototypes in Somos®

materials allowed AME to also use these same models for the final tooling process, an

advantage which reduced the client’s total project costs by several thousand Euros.

The quality of the Somos® prototypes is so high that when we produced

replicate vacuum cast parts for the new Irwin Saw’s launched in 2003, product

managers and focus groups were greatly impressed that the quality was the same as

mass production parts.

AME’s blueprint for success not only works for highly technical products but

also for a range of FMCG clients. ‘We’re seeing a surge in demand for consumer

packaging which combines form with function – it’s a major part of the market

differentiation strategy for an increasing number of clients, particularly those serving

the household and cosmetic sectors, ‘ continues Johannessen. We believe that AME

has developed a unique concept within the design community which suits a broad

range of markets: Flair and flexibility combined with technical excellence and the

ability to produce high quality prototypes within a short space of time enables clients

to reach their highest design expectations ahead of schedule and within budget.’

On the horizon, though, are several developments that will help to

revolutionize and enhance the value of rapid prototyping as we know it. Although

most of the machines are approaching the upper limits of speed, due to mechanical or

physical limitations, Choren says further gains in accuracy and surface finish can be

accomplished. Today's commercially available machines are accurate to -0.08

millimeters in the x-y plane at best, but less in the z direction. Improvements in laser

optics and motor control should increase accuracy in all three directions. In addition,

rapid prototyping companies are developing new polymers that will be less prone to

curing and temperature-induced warpage.



The introduction of non-polymeric materials, including metals, ceramics

composites, represents another much anticipated development. These materials would

allow users to produce functional parts. Today's plastic prototypes work well for

visualization and fit tests, but they are too weak for functional testing. More rugged

materials would yield prototypes that could be subjected to actual service conditions.

In addition, metal and composite materials will greatly expand the range of products

that can be made by rapid manufacturing. Another important development is

increased size capacity. Currently, several "large prototype" techniques are being

developed.

"As these advances indicate, the term 'rapid prototyping' is rapidly becoming

somewhat of a misnomer," according to Kruger. As the precision of such systems

continues to improve and the choice of materials grows, the "prototypes" are

increasingly being used for functional testing or to derive tools for pre-production

testing.

This new development-rapid tooling-automatically fabricates production

quality machine tools. This is one of the slowest and most expensive steps in the

manufacturing process because of the high degree of precision required. Some

estimates say tooling costs and development times can be reduced by 75% or more by

using rapid tooling technologies.

Closely related to rapid tooling is the next generation-rapid manufacturing-

which refers to the automated production of salable products directly from CAD data.

Currently only a few final products are produced in this way, but as the number of

materials becomes more widely available, that number will no doubt increase.

"Rapid manufacturing will never completely replace other manufacturing

techniques," says Kruger. "In large production runs, mass production remains more

economical. For short production runs, however, the process is much cheaper since it

does not require tooling. Rapid manufacturing is also ideal for producing custom parts

tailored to the user's exact specifications."

Regardless of whether a company is thinking about rapid prototyping or has

advanced down the path to rapid manufacturing, there can be no escaping the pressure



to get products off the design table and to market faster and faster. While rapid

prototyping provides the tools to help the engineering community accomplish the

objective of reduced time to market, the technologies themselves can accomplish

nothing without the input of a highly skilled and trained workforce that understands

and can manage the process.

One future application is Distance Manufacturing on Demand, a combination

of RP and the Internet that will allow designers to remotely submit designs for

immediate manufacture. Researchers at UC-Berkeley, among others, are developing

such a system. RP enthusiasts believe that RP will even spread to the home, lending

new meaning to the term "cottage industry." Three-dimensional home printers may

seem far-fetched, but the same could be said for color laser printing just fifteen years

ago.

Finally, the rise of rapid prototyping has spurred progress in traditional

subtractive methods as well. Advances in computerized path planning, numeric

control, and machine dynamics are increasing the speed and accuracy of machining.

Modern CNC machining centers can have spindle speeds of up to 100,000 RPM, with

correspondingly fast feed rates. Such high material removal rates translate into short

build times. For certain applications, particularly metals, machining will continue to

be a useful manufacturing process. Rapid prototyping will not make machining

obsolete, but rather complement it.

All the above improvements will help the rapid prototyping industry continue

to grow, both worldwide and at home. The United States currently dominates the

field, but Germany, Japan, and Israel are making inroads. In time RP will spread to

less technologically developed countries as well. With more people and countries in

the field, RP’s growth will accelerate further.

The Wave of the Future

Rapid manufacturing, as differentiated from rapid prototyping, has long hovered as a

possibility that has never quite materialized on a significant scale. According to Terry

Wohlers, “Rapid manufacturing is developing into an intriguing market opportunity.

RM may even become the most significant area of growth in this decade.”



Mervyn Rudgley agrees. The company’s SLA technology is increasingly

being used to generate patterns for short-run parts or tooling. For instance, if a

company needs a short-run of a part, they can produce a soft tool by coating an SLA

pattern with silicone rubber, and then pouring a material like polyurethane into the

pattern, to produce up to 40 or so parts. As Rudgley points out, “For some companies,

forty parts is the entire production. This could include parts like ATM fronts or

casings for certain medical devices.”

There is a significant market for companies that make fewer than 1000 parts in

a run. Rudgley cites the aerospace industry as an example. Boeing uses 3D Systems’

technology to manufacture air ducts for fighter jets. “Traditionally, Boeing used

rotomolding to make the tubing, but rotomolding requires a tool,” says Rudgley.

“Using our SLS technology, they can make the parts without tooling and with greater

complexity.”

According to Wohlers, “It’s unlikely that RM will ever reach the production

capacity of processes such as injection molding, die casting, or sheet metal stamping,

but for some companies, this may not matter.”

The consumer increasingly wants “more customized products, shorter runs,

more complex data in a shorter time,” says Rudgley. This trend could create an even

larger market for rapid manufacturing.

Rapid manufacturing seems to be the wave of the future, but one dilemma

stands out in both rapid prototyping and rapid manufacturing—material selection. “In

terms of materials, there is still a lot of room for improvement,” says Oliveira.

“Today, this is one of the most important issues.”

“Material is really the key limit,” says Rudgley. “We only have 15 in our portfolio,

and we find that people usually want a material that we don’t have.”

Recognizing this need, 3D Systems has developed some more durable

materials to accompany its technology, including DuraForm polyamide and glass-

filled polymers that were developed specifically for creating thermoplastic parts that

withstand aggressive functional testing. A preliminary Accura LaserForm ST-2000



material is a stainless steel composite developed to produce tooling inserts for

injection molding applications. The preliminary Accura SI 40 material is the first SLA

material to mimic nylon 6:6, allowing parts to be used in high-temperature

applications without brittleness or breakage.

“The number one thing users want is better materials—durable, functional

plastics—real engineering plastics used in end products,” says Crump from Stratasys.

The company is developing the use of polyphenylsulfone with its FDM prototypes.

“The selection of materials from Stratasys will offer users such performance

characteristics as improved impact strength, strength at high temperatures, flame-

retardant qualities, sterilization capability, and resistance to oils, gasoline, chemicals,

and acids.”

Michael Littrell, president of C.ideas Inc. (Cary, IL), a service bureau, says

that the availability of materials, whether it is a proprietary issue, or an availability

issue, is a definite limit to the technology. He adds that along with improved

materials, faster speeds and higher resolutions are at the top of the list too.

Oliveira sums up the current state of affairs and points to the future. “More

than actual technology improvements, which have been very significant in the last

few years, the big difference is in the clients’ expectations and perception of what a

prototype should be. Today we are expected to produce a component that is actually

identical to the final part, faster, cheaper, and with the best material.”

The future of rapid prototyping materials

The introduction of non-polymeric materials, including metals, ceramics, and

composites, represents another much anticipated development. These materials would

allow RP users to produce functional parts. Today’s plastic prototypes work well for

visualization and fit tests, but they are often too weak for function testing. More

rugged materials would yield prototypes that could be subjected to actual service

conditions. In addition, metal and composite materials will greatly expand the range

of products that can be made by rapid manufacturing.



Many RP companies and research labs are working to develop new materials.

For example, the University of Dayton is working with Helisys to produce ceramic

matrix composites by laminated object manufacturing. An Advanced Research

Projects Agency / Office of Naval Research sponsored project is investigating ways to

make ceramics using fused deposition modeling. As mentioned earlier,

Sandia/Stanford’s LENS system can create solid metal parts. These three groups are

just a few of the many working on new RP materials.

The future of rapid prototyping materials DSM Somos, a global technology

leader for rapid prototyping (RP) materials and one of DSM Desotech's key strategic

businesses, has announced the launch of a major research and development campaign

aimed at responding to the growing global demand of differentiated material product

lines for the RP industry.

DSM Somos believe that this commitment to enabling research will serve as a

model for the introduction of new materials demanded by the rapid prototyping and

manufacturing industries, as well as by academic and commercial research

organizations."

Introduced were a vast range of R and D materials in various phases of alpha

or beta testing and forecast for commercialization within the next 6-24 months,

depending upon further market analysis.Among those products presented during the

Technology Focus were:

Stereolithography resins for water-clear parts, introduced by John A Lawton,

Research Associate.The need for optical clarity in prototypes has been a consistent

demand from the market place as engineers attempt to understand fluid flow behavior

during design and testing of new components.

Other anticipated applications include stress analysis at the prototype level.A

high modulus material with a superior elongation at break, the properties of the

material are expected to significantly enhance the DSM Somos ProtoFunctional

materials offering.In additional to its optical clarity, the material also offers the

characteristic fast photospeeds for which DSM Somos resins are known and low



viscosity - properties which will increase the overall productivity of the build process.

This material is anticipated to be a "clear" winner for all stereolithography users.

High Temperature / High Resolution Stereolithography Resins, introduced by

Dr Louis H Strong, Research Associate.The ability to produce prototypes which can

be used in high temperature applications is a consistent request from a variety of

sectors, notably the automotive industry for which testing of new design components

in under-the-hood applications is frequently demanded.

Ulterior applications include rapid tooling, thanks to the enhanced resolution

offered, contributing to the overall accuracy improvement in the stereolithography

process.High temperature applications in combination with superior resolution is

expected to open up new applications in a variety of markets.

Experimental Material for Investment Casting, introduced by Dr Glen A

Thommes, Sr Consultant.. The use of stereolithography to create patterns employed in

investment casting foundry applications is growing rapidly, most notably within the

aerospace industry where a small number of custom manufactured parts are needed to

fulfill manufacturing needs.

To respond to the significant accuracy demands in foundry applications, this

resin offers superior water and humidity resistance, preventing the part from growing

when exposed to varying environment conditions. A further benefit is that a

distinctive color can easily be added to effortlessly identify the source of the

prototypes. The advantages offered by this material are expected to expand the use of

stereolithography for investment casting applications.

High modulus and heat-tolerance stereolithography resin for direct injection

mold applications, introduced by Dr Xiaorong You, Research Chemist.The first filled

resin to be introduced in the western world, the material is designed for the realization

of rapid tooling moulds in direct injection applications. The filled resin offers two

significant advantages: high modulus and high heat tolerance, crucial properties for

success in injection moulding applications.



The family of DSM Somos ProtoFunctional materials includes general-

purpose materials with high heat deflection temperatures and high humidity tolerances

(Somos 7100 series) as well as materials that mimic the properties of polyethylene

(Somos 8100 series) and polypropylene (Somos 9100 series). Each resin series has

been individually optimized for Ar-ion, He-Cd, and solid state UV laser systems.

Stronger materials and new build techniques are changing the way companies

use rapid prototypes. Rapid prototypes are available in as little as 24 hr from

Xpress3D.com. E-mail a model and the online system provides a quote. Users can

have parts built on SLA machines from 3D Systems, FDM equipment from Stratasys,

and the Z-Corp. way.

The valve body was printed and assembled by Griffin Industries for spacing

studies at an agricultural equipment manufacturer. It was printed on a Z Corp. 3D

Printer and then infiltrated with Z-Max epoxy to strengthen the part for drilling and

tapping. As a finishing touch, engineers treated the part with a powder-coat paint, a

spray on dry-powder paint. Static charge makes the paint stick to the part. Finally,

they bake the part to create a hard, shiny finish.

Builders of rapid-prototyping equipment have done a good job publicizing the

value of parts made on their machines. After holding an RP part you've designed, it

takes only seconds to tell whether or not it's big enough or shaped right. Handling the

part tells right away what should be done next.

But RP parts can also be assembled into nearly complete products. To some

extent, that unsung capability comes from RP equipment that builds several connected

parts and materials that closely approximate the strength of production plastics.

Stratasys Inc., Eden Prairie, Minn., for example, has been handing out adjustable

wrenches made of three parts built simultaneously. And Z-Corp., Burlington, Mass.,

has passed out full-complement ball bearings made on their equipment. There is more

to these simple assemblies than meets the eye.

Fast and cheap

Several recent build improvements deserve mention. “Revisions to the software that

builds RP parts improve the surface resolution so finishes are more acceptable right



off the machine,” says Jerry Plath, an engineer at Prolific Plastics, a tooling and

service bureau in Opelika, Ala. “Light sanding improves it further so it doesn't look

layered at all,” he adds.

In addition, the newest equipment uses two materials, one for parts and one to

support overhangs and undercuts. “The problem used to be with supports breaking,”

says Plath. “When working with small parts, I had to be careful removing support

plastic so as not to break the parts. But the support material is now water based, so a

simple wash dissolves it. That makes final assembly easier,” he says.

Build tolerances have also improved to as tight as 0.001 in. That's better than

the tolerances on production parts which are often ±0.005 in. What's more, the

machines can make snap fits to aid in assembly.

Along with equipment and material upgrades, savvy engineers like Plath

understand and preach the value of seeing design shortcomings in solid plastic before

committing scarce dollars to production tooling. “We've become the plastics

department for these companies we service,” he says.

Plath uses RP equipment for more than quick parts. For example, he doesn't

charge a company for a prototype unless it's quite complex. The reason? “An RP part

is more than an initial shape. Parts made on a Stratasys Dimension machine, for

instance, cost about $6 to $7 per cubic inch. But when I show a part to a toolmaker,

we look it over and identify features that will be difficult to shape and those that will

be easy, and plan accordingly. Furthermore, I get a part weight, which helps in

quoting. And after talking to the toolmaker, I can go back to designers with

suggestions, such as, ÔIf you move this hole, we can save so much money in

tooling,'” he says.

Trimming costs. “Companies tend to see their products as a series of parts. But

any good molder knows that if you've got six parts, the question to ask is: How can

this be done with three? Reducing part counts trims production costs,” says Plath.

Avoiding assembly steps. When building assemblies, stronger RP materials can be

drilled and tapped. But if you do that, design threads into the part and the machine

will make them. This avoids secondary operations.



Rapid cores

Engineers at Griffin Industries, a pattern and casting company in Green Bay,

Wis., are pushing the manufacturing envelope by printing ceramic molds instead of

just patterns. The process, called Z-Cast, was a cooperative effort between Z-Corp.

and Griffin engineers. In a traditional casting, an RP pattern made of wax would be

dipped in ceramic slurry which would harden. Melting the wax creates a hollow

casting mold. “The Z-Cast method eliminates wax patterns and builds the casting

mold using one of two materials,” says Spike Chronoski, an engineer with Griffin.

“One is for nonferrous materials and the other, still under development, will be for

heavier and hotter ferrous metals.”

Chronoski says his company is dedicated to fast turnarounds using several

newer manufacturing methods. For example, they build complex cores for hydraulic

tool bodies. Traditionally, these have been made in a cast-iron core box. This method

includes designing air-ejection paths, rigging, and lead time. “And costs are

significant,” says Chronoski. “But when we take a day to RP a core instead of making

it in a core box, the whole casting, inside and out, can be done in six weeks instead of

12. And when we push ourselves, the job's finished in just three weeks.”

Accurate RP parts tell more in wind tunnel tests

Airbus in the United Kingdom plans to use RP components for wind-tunnel testing at

its operations in Filton, Bristol. They recently purchased an SLA 7000 system from

3D Systems, Valencia, Calif., to make larger models with tighter tolerances and

higher quality surface finishes than previously possible.

“We were already using RP technology through a service bureau,” says Martin

Aston, wind-tunnel manager for Airbus. “But if we can build models more quickly,

we can enter design cycles sooner, which gives aerodynamicists more time before

committing to a test. Rather than outsourcing prototyping and model production, we

needed to invest in our own to improve cycle times.”

Producing plastic models lets the company explore different shapes and curves

on aircraft components, such as leading and trailing-edge configurations, flap tracks,



pylons and nacelles. Improved geometric forms and dimensional stability means test

data is more accurate. And having technology on-site lets project coordinators define

and control geometry.

Thin layers produce smooth surfaces

RP machines from Objet Geometries Inc., Mountainside, N.J., uses really thin

layers - down to just 16 microns. Eight jetting heads slide back and forth on the X axis

depositing layers of photopolymer onto the build tray. UV bulbs alongside the jetting

bridge cure and harden each layer as it's placed, eliminating additional postbuild

curing.

The system works with two different materials, one for parts and one for

support. Geometry of the support structure is preprogrammed to cope with

complicated shapes, such as cavities, overhangs, undercuts, and delicate features. And

positioning the support material needs no special programming.

The developer says any CAD model can be converted to an STL file for its

Eden system. A preprocessing program suggests a build orientation, but users have

full control over the build process. The technology lets the machine build several

models in the time it takes other technologies to produce one. To shorten build times,

the machine places the shortest dimension in the Z direction to reduce the number of

layers.

The systems are safe for offices because model and support materials

(proprietary photopolymer resins) are environmentally stable. Materials come in 4.5-

lb sealed cartridges and cure to transparent and gray. The developer says running the

Objet Studio Software is simple and intuitive so training isn't needed. Models are

fully cured and can be examined and handled immediately after completion.

The material used in machines from Objet Geometries has a 20% elongation at break

that lets it form snap fits. Materials are fully cured and need no post processing. And

model surfaces readily accept paint.



CONCLUSION

The range of new and usual applications of RP continues to expand. These

uses, combined with the many new developments and innovations around the world,

are leading to advances and trends that are reshaping the RP industry as a whole.

Brace yourself because this is only the tip of the iceberg. Growth into new markets

and industries will redefine the role of RP and this will redefine our future. There are

several advantages to using the tooling for prototypes, including lower cost and less

time that significantly compress the product and production development cycle.

Future work will explore the molding of different geometries of parts, tooling

enhancement such as cores and part ejection systems, different materials systems such

as zirconia and whisker filled ceramic composite materials, and developing a

shrinkage model to predict the dimensions of the fired ceramic part with dimensional

accuracy within 0.1% of design dimensions.



BIBLIOGRAPHY

BOOKS

1. Rapid Prototyping is Coming of Age STEVEN ASHLEY

2. Production Design Tools A. KUMAR DAS

3. Rapid Prototyping AMITABHA GHOSH

4. Design for Assembly and Manufacturing A. KUMAR DAS

5. Rapid Prototyping B. GURUMOORTHY

WEBSITES

1. www.dsmsomos.com

2. www.rapidprototyping.net

3. www.rpc.com

4. www.lf.psu.edu


http://www.lf.psu.edu/

http://www.rpc.com/

http://www.rapidprototyping.net/

http://www.dsmsomos.com/

Documents

Rapid Pro to Typing