Selecting a Rapid Prototype Service Bureau
by Art Siegert
Think of RP as the right process + the
right material = the right part. Do your homework and find a firm you
can depend on to help slash prototyping time and costs
nothing like the rush of a new design idea. Maybe it hit you in the
shower or just clicked when you opened that can of tomato soup. You have
an idea — and it’s your “baby.” But of the hundreds of rapid-prototyping
(RP) firms that will be vying to make the prototype of your baby, how do
you know which to trust? The notion of form following function is only
as good as the appropriateness of the RP process and material selected.
In other words, only the correct RP process will produce a prototype
that acts almost exactly as the product will in the operating
First, accept the premise that you don’t know what you
don’t know. This helps make it clear that you need to educate yourself
and also look for firms that will help educate you. Quickparts founder
Ronald Hollis says, “Designers are too often removed from production
processes. But engineers might make adjustments on the factory floor and
tooling managers could invent a way to enhance manufacturing
efficiencies. Obviously, the more educated the designer, the better. And
this goes for innovators as well.”
A rear section of an electronic housing for a scale (blue part) was made using cast urethane. The part rests atop its mold.
Bottom line: Better informed users get better pricing and better
solutions. Considerations in selecting an RP service bureau include:
processes, timing, expertise, and customer service. Find out whether the
service bureau offers the major RP technologies. They are
stereolithography (SLA), selective laser sintering (SLS), and
fused-deposition modeling (FDM). These firms provide the widest
expertise and generally have the most up-to-date processes and
materials. In addition, their experts have the know-how to steer you
away from making costly mistakes.
How do you know they care enough to make sure you are getting
what you really need? When you submit a CAD model for a quote, better
companies go one step further by alerting you to alternative methods and
explaining the advantages and disadvantages of each one.
The industrial pipes and blue translucent spacer are examples of SLA parts.
For example, say you submitted a CAD model and select SLA — what you
think is the correct process — to build a prototype of a product with a
living hinge. Companies that care will contact you and advise that due
to the living hinge feature, you would be better off with SLS. Use SLA,
and the hinge will just break off.
Along with expertise comes objectivity. Because more successful RP
providers are exposed to so many new designs, processes, and materials
daily, they view designs with a broader perspective. In fact, a good
company will often pick up on and address potential flaws that might not
have otherwise surfaced until the part had been in use for some time.
The cigar cutter and locking knobs were made using FDM.
And never underestimate the advantage of timing. It’s no longer good
enough to be good. What’s needed is an RP bureau that it is both good
and fast. Don’t just take their word for it. Reasonable
turnaround times for most prototypes should range from around one to
Examine the firm’s track record, check references, and ask plenty of
questions. Customer endorsements and case studies will also help you
determine whether a firm has expertise and provides quality prototypes.
The ABCs of AF
To understand the basics of RP, it helps to start with an explanation of
additive fabrication (AF). AF started in the 1980s. It involves the use
of automated equipment to fabricate physical 3D parts from electronic 3D
data by building parts layer-by-layer.
AF is used in every major industry for transitioning design concepts
to physical prototypes to save time and money. It plays a part in
testing form, fit, and function. AF lets users detect and correct design
errors earlier in the cycle, helping to eliminate waste and costly
Today there are more than 40 AF systems in the worldwide market. All
are competing for business from designers, innovators, tool
manufacturers, manufacturing engineers, and ultimately, the end
The clear gaming chair speaker cover was made using the “high-tech” SLA process. The blue industrial motor housing was made with LVIM, while the red rescue launcher and the gray electronic enclosure were made using cast urethane. Although LVIM and cast urethane are both so-called “lowtech” methods, depending on the application, they can provide the best solution.
Individual, specialized technologies fall beneath the umbrella of AF.
SLA is where it all began. The laser-based technique turns virtual
models into plastic parts, usually in a matter of hours. SLA equipment
uses photocurable liquid resin with a UV-laser system to apply
successive layers and build parts. Computer software “slices” the CAD
model and outputs the data to the SLA machine.
SLA works well for form-and-fit testing and for
showroom models. The smooth surfaces can be painted or
plated. Note, however, that SLA and all AF process are
not exact manufacturing techniques, so it’s necessary to
apply tolerances to the design. Tolerance and accuracy
depend on the geometry and build orientation of the
Most SLA resins are epoxy based and provide strong,
durable, and accurate models. They make an excellent
all-around choice for prototypes, but you need to
identify the material that best supports the prototype’s
function. Does the prototype need to be clear, or water
resistant? How durable must it be? Will the part be used
for actual testing or only for trade-show presentations?
SLS makes functional parts from powdered
thermoplastics. This method creates solid 3D objects by
fusing or sintering particles of nylon-based powder
material with a CO2 laser. The technique
produces durable, heat-resistant parts for testing or
actual use in tough environments such as engine blocks,
engine components, mounting brackets, and hot-liquid
dispenser parts. Other examples include trade-show
models, master patterns, low-volume production, snap
fits and living hinges, and airflow models for testing.
SLS primes the creative pump for many engineers. By
getting functional parts directly from CAD, they can cut
out much of the guesswork that would be necessary when
designing for traditional tooling.
Available in a range of materials, including a
glass-filled variety, SLS is a good choice for high-heat
and chemical-resistant applications. For display
purposes, however, its dull, rough surface makes it less
attractive than SLA.
Fused-deposition modeling (FDM) is the strongest, but
slowest, way to produce plastic parts. A heated head
with two extrusion nozzles builds parts from microlayers
of rapidly solidifying melted filament. One nozzle
dispenses melted support material that dissolves away in
water. The other nozzle extrudes the permanent base
FDM produces parts suitable for testing form, fit,
and function. Parts are near-production quality and
resistant to heat, water, and chemicals. FDM parts lack
a sexy, smooth look, so they usually don’t work well for
trade shows and presentations.
A simple approach
Designs don’t always call for the advanced SLA, SLS, or
FDM technologies. Sometimes a simple approach is the
wisest solution. Basic formative and subtractive
fabrication methods provide classic solutions that are
anything but old-fashioned. Often referred to as “low
tech,” these processes can provide a low-cost transition
between prototyping and tooling.
For example, cast urethane (CU) produces real plastic
parts by copying a pattern. Technically speaking, CU
parts are not engineered plastic parts, but they
function well enough to be used in many kinds of
testing. Also, the aesthetic properties of CU, such as
color, texture, and finish, make prototypes look just
like expensive production parts. CU parts work well for
marketing samples, preproduction parts, and low-volume
Computer numerical-control (CNC) machining is a
relatively low-cost method that begins with a block of
material and cuts away unneeded material. It cuts and
shapes parts that call for high accuracy, repeatability,
reliability, and stability. Formerly run by operators,
control modules have made this method almost error-free.
The method cuts automotive parts, compressors, and
high-accuracy components used in aerospace, industrial,
and machining industries. Designers usually like the
many options afforded by CNC because they can shape
almost any material including metal, plastic, wood, and
Low-volume injection molding (LVIM) uses injection
molds or tools of aluminum or soft steel to produce
functional parts from thermoplastic. LVIM is lower in
cost and faster to produce than traditional production
tooling, but the LVIM molds have a much shorter life
span. They can typically withstand up to 50,000 parts,
while high-quality steel production molds have the
strength and durability to make millions. LVIM molds
typically take two to four weeks to make, while
production tools take eight or more weeks.
About the Author
Article edited by Leslie Gordon,
Sr Editor, Machine Design
||Article reprinted by permission of Penton Media,
publisher of Machine Design