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By Jeff Krause 11/28/98

    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.

  "UNcopywrite" Jeff Krause 1998

    SLATM is a registered trademark of 3D Systems.
    Read This Disclaimer:
    This page and web site are not intended as more than the opinion &
    experience of the author. As such it should not be relied upon as the
    sole source of information for making decisions or commitments.