Virtual Prototyping
is "computer simulation" of both the styling and internals
of the product. Included in this
may be simulation & analysis of mechanisms,
light pipes, etc. of the product.
This can cut iterations and improve quality;
resulting in a more integrated
final design & often having a lower production
cost. Virtual Prototyping is one
of the most valuable services I offer.
A Breadboard
or "proof-of concept" prototype is a functional collection of
working parts used to verify the
general design intent, but is usually not
self-contained in a product
enclosure. An "inventor's breadboard" is
similar to the above but has the
additional feature of emitting sparks
and fumes and is most likely held
together by the grace of God.
An Appearance
Model or
"Mockup" is usually not much more than a physical
version of a good product
rendering; but something that can be photographed,
held, displayed and of course,
toyed with by the CEO & marketing staff.
An Engineering
Prototype
has an unfinished appearance, but has enough
internal detail to allow
installing some of the internal components, mechanisms
and/or electronics and is used to
verify the earlier design intent.
Over time, this same
"ugly" prototype may be upgraded to the point
where it becomes a fully
functional self-contained product.
A Sales
Prototype
integrates what has been learned from the
Engineering Prototype with the
look and feel of the Appearance Model.
The result usually looks and works
similar to the initial production product.
Significant numbers may be created
for the abuse and use of the marketing dept.
(The following pertains mainly
to the prototyping of plastic parts).
A Very Brief History of Rapid
Prototyping (RP)
No kidding, because the
first commercial RP machine was introduced in 1986!
(3D Systems) This is not to say
someone could have developed it earlier,
because the success of RP was
founded in the commercial viability and
proliferation of 3-Dimensional
CADD (Computer
Aided Design & Drafting).
3-D CADD itself was out of the
financial reach of most small companies
until about the same time as the
introduction of the fist RP machine.
Since then, several manufacturers
have begun offering RP equipment,
and many of these will also build
RP-based prototypes as a separate service.
RP vs Conventional
Prototyping Methods:
Rapid Prototyping is a misleading
term for it's current capability to "simulate"
product components using a narrow
selection of often fragile materials.
The tolerances
advertised for RP processes are usually +/-.003" per inch or more.
However due to warpage and other
correctable problems, it is not unusual to find
features out of tolerance by
more than 4X that amount "Your results may vary".
The conventional alternative that
seems increasingly overlooked is to have the
prototype CNC/Machined
and/or hand-crafted
to achieve the desired result.
If the tolerances, appearance,
materials or precision finishes are paramount,
conventional fabrication is still
the only method to insure such results.
After
creating your original part, more economical and durable copies
of this "master" can be
molded using inexpensive silicone rubber molds.
The copies are usually made of
Polyurethane or Epoxy-based plastics.
Low to meduim volume
production of Injection
molded parts can be
facilitated with relatively low
cost tooling by using RP masters to
cast Epoxy,
Zinc or Rubber mold inserts,
which allows molding
parts in most conventional
thermoplastic injection molding materials.
There are many dual &
single-part Polyurethanes
that can be cast
in relatively low-cost molds to
provide significant quantities of
plastic parts with properties that
range from viscous elastics all the
way up to Shore 90-D hardness and
up to 3~6,000 psi tensile strength,
which is equivalent to the better
grades of injection-molding plastics!
Other notable processes
include Spin-Casting;
A process that uses
similar low-cost molds clamped in
a centrifuge to create both metal
(Aluminum, Brass, Zinc) AND plastic
(Urethanes & Epoxies) parts.
The centrifugal effect boosts the
throughput and quality of the cast parts.
Companies that can economically
provide small production quantities
of parts
are usually not
the same as those that are best suited for your prototyping or
full-volume production purposes. Sorting
through claims and
actual core
competencies of potential
resources can save you both time and money.
Keep me in mind for your future
research, sourcing and quoting challenges.
Assuming the RP materials and
tolerances are adequate for your purposes, here
are the four most
common reasons for opting for RP over conventional prototyping:
1.
Less expensive for validating the digital CADD model prior to using
that same
model in the design &
construction of production tooling.
2.
Less expensive to fabricate parts & enclosures for engineering prototypes.
3.
As a less expensive starting point to fabricate an Appearance Model.
4.
Parts can be obtained in as little as 2 days (depending on the
vendor's schedule).
The (Generic) Rapid
Prototyping Process:
There are at least 6 major
classes of RP processes; Each has it's unique
advantages, depending on the
specific requirements and properties of the
prototype to be created. Rather
than describe the specifics of each process,
I will describe the main theme
common to these processes, and give a simple
explanation of the 3D
Systems SLATM process.
Before
there can be an RP prototype,
there must be a 3D CADD model or digital
representation of each part of the
product (Excluding fasteners & purchased parts).
A typical RP system reads the
digital 3D model and converts that data into thousands
of parallel profiles; Each profile
represents a narrow slice through the part.
The
machine that
actually constructs the part does so by using the data of each
"slice" to define how to
add and/or subtract the "build" material to create
consecutive layers. Thus, current
RP systems either "Grow" or "Laminate"
parts one layer at a time.
The
3D Systems process
takes advantage of specially developed photo-sensitive
pre-polymers (Liquid plastics that
can be selectively cured by a laser beam).
A porous platform is submerged in
this liquid so that only about .005" covers
the platform. The laser then
traces the first profile on the surface of the
liquid plastic. The first profile
is thus hardened on the surface of the platform.
The platform is repeatedly
lowered after the laser cures each profile right atop
the layers previously cured. A
thin, break-away lattice structure is also grown
to support overhanging features
and ensure dimensional stability.
The
average cost of any
single "raw" Rapid Prototyped plastic part has ranged
(In my experience) between a low
of about $200 (US) for small, simple parts to over
$3000 for larger parts. Some of
this cost is related to the curing, lattice
removal and finishing labor
usually required after the part has been grown.
Multiple parts can often be nested
or arrayed together to minimize costs.
The best application of most
RP processes is for parts that are under
1 cubic foot (the smaller the
better) with moderate to intricate details.
RP processes that solidify
material to grow a part are economically better
suited to parts with thin walls.
Others processes, such as LOM
(Laminated
Object Manufacturing)
are more cost-effective with thick walls or solids.
RP for creating harder
(steel) parts and tooling:
There are some new but
relatively convoluted processes that can produce steel
parts or even injection mold
tooling (without machining). However most do not yet
approach the tolerances or finish
quality of conventional machining techniques.
The FUTURE:
On the heels of RP, and
probably sooner than we think, the whole
prototyping and injection
mold-making industry may be subject to upheaval
due to new types of rapid-fabrication
equipment that will
eventually replace
current methods for creating hard
tooling (CNC & EDM machine tools)
and structural metal or plastic prototypes.
Hard tools for injection
molding, stamping and die casting that now cost
$30K (US) or more may eventually
cost less than 1/3rd as much for the
same level of tool accuracy,
finish and durability.
In addition to the molds (cores
& cavities), these new machines could
also fabricate the
sometimes-complicated injection mold bases as well;
Ready for pins, sleeves and
springs (After some finish reaming)!
A Star Trek Replicator Precursor?:
Later "generations"
of such machines will be able to mix all kinds of different
metals, plastics & ceramics
together concurrently during the build process;
Creating "intelligent
matrix" material properties that follow the part geometry,
or building prototypes and
aerospace parts with "unalloyable" metals and other
wildly different materials that
few have dreamed
they would even want alloyed.
Imagine growing an entire assembly
at once complete with plastic, metal and
ceramic parts, including single
materials made of any combination thereof!
Jeff's
"Tribopulselithography" Theory:
I believe this process may
take form as the "Tribofusing"
of material or elemental
powders in
a vacuum to tribologically
alloy micro-thin build layers. Separate
material
powders would be deposited
in the desired proportions and pattern onto a surface
(not necessarily the part surface)
prior to each microseconds-long "tribopulse".
The extremely brief duration
of this pulse or wave through a film or build layer would
help bypass most of the
problems seen when alloying materials or elements with
different structures and/or
of widely different melting points.
It is likely that some
combination of ultrasonics, directed energy, electron-discharge
(as a catalyst) or even consumable
nanotechnology films will be found to execute the
complex, yet rapid protocol
required. Most of the separate technologies are already here.