RAPID PROTOTYPING(RP&M)

November 16, 2013


Rapid prototyping is definitely a technology that has, and is, changing the way companies and commercial entities do business.   We can certainly say this “emerging technology” has gained tremendous momentum over the past decade.  The applications and uses represent a “best practice” for manufacturers and producers in general.

Being able to obtain prototype parts quickly allows a company to test for component form, fit and function and can help launch a product much faster than its competition.   This can allow for adjustments in design, materials, size, shape, assembly, color and manufacturability of individual components and subassemblies.   Rapid prototyping is one methodology that allows this to happen.   It also is an extremely valuable tool for sales and marketing evaluation at the earliest stages of any program.   Generally, an engineering scope study is initially performed in which all elements of the development program are evaluated.  Having the ability to obtain parts “up front” provides a valuable advantage and definitely complements the decision making process.   Several rapid prototyping processes are available for today’s product design teams while other prototyping processes utilize traditional manufacturing methods, such as 1.)  CNC Machining, 2.)  Laser Cutting, 3.)  Water Jet Cutting, 4.) EDN Machining, etc.   Rapid prototyping technologies emerged in the ‘80s and have improved considerably over a relatively short period of time.   When I started my career as a young engineer, the only process available for obtaining and producing prototype components was as follows:

  • Produce an orthogonal drawing of the component. This drawing was a two-dimensional rendition, including auxiliary views, and generally did NOT use geometrical dimensioning and tolerancing methodologies, which opened the way for various interpretations relative to the part itself.  Solid modeling did not exist at that time.
  • Take that drawing or drawings to the model shop so initial prototypes could be made.     Generally, one prototype would be made for immediate examination.   Any remaining parts would be scheduled depending upon approval of the design engineer or engineering manager. We were after “basic intent”—that came first.  When the first prototype was approved, the model shop made the others required.
  • Wait one, two, three, four, etc weeks for your parts so the initial evaluation process could occur.  From these initial prototypes we would examine form, fit and function.
  •  Apply the component to the assembly or subassembly for initial trials.
  • Alter the drawing(s) to reflect needed changes.
  • Resubmit the revised drawing(s) to the model shop for the first iteration of the design.  (NOTE:  This creates a REV 1 drawing which continues the “paper trail” and hopefully insures proper documentation.)
  • Again, apply the component for evaluation.
  • Repeat the process until engineering, engineering management, quality control and manufacturing management, etc signs off on the components.

The entire process could take weeks or sometimes months to complete.   Things have changed considerably.  The advent of three dimensional modeling; i.e. solid modeling, has given the engineer a tremendous tool for evaluating designs and providing iterations before the very first “hard” prototype has been produced.  As we shall see later on, solid modeling of the component, using CAE and CAD techniques, is the first prerequisite for rapid prototyping.   There are several options available when deciding upon the best approach and means by which RP&M technology is used.   As prototyping processes continue to evolve, product designers will need to determine what technology is best for a specific application.

INDUSTRIES USING RP&M PROCESSES:

As you might expect, there are many disciplines and industries willing to take advantage of new, cost-saving, fast methods of producing component parts.  RP&M has become the “best practice” and the acceptable approach to “one-off” parts.  Progressive companies must look past the prototyping stereotypes and develop manufacturing strategies utilizing additive manufacturing equipment, processes and materials for high volume production. The pie-chart below will indicate several of those industries now taking advantage of the technology and the approximate percentage of use.

Institutions Using RP&M

 

One of the statistics surprising to me is the percentage of use by the medical profession.   I’m not too surprised by the seventeen percent from automotive because the development of stereolithography was actually co-sponsored by Chrysler Automotive.    Consumer electronics is another field at eighteen percent (18.4%) that has adopted the process and another industry benefiting from fast prototyping methodologies. When getting there first is the name of the game, being able to obtain components parts in two to three days is a remarkable advantage.    Many times these products have a “lifetime” of about eighteen month, at best, so time is of the essence.

The bar chart below will give a comparison between sales for RP&M services provided by vendors and companies providing RP&M machines to companies and independent providers.  As you can see, the trends are definitely upward.  Rapid prototyping has found a very real place with progressive companies and progressive institutions in this country and the world over.

Average Uses in Dollars

 

RAPID PROTOTYPING & MANUFACTURING (RP&M) TECHNOLOGIES:

There are several viable options available today that take advantage of rapid prototyping technologies.   All of the methods shown below are considered to be rapid prototyping and manufacturing technologies.

Stereolithography was the first approach to rapid prototyping and all of the other methods represent “offshoots” or variations of this one basic technology.   The processes given above are termed “additative manufacturing” processes because material is “added to” the part, ultimately producing the final form detailed by the 3-D model and companion specifications.  This course will address the existing technology for all of these processes and give comparisons between them so intelligent decisions may be made as to which process is the most viable for any one given part to be prototyped.

As a result of the prototyping options given above, there are many materials available to facilitate assembly and trial after completion of the model.   We are going to discuss processes vs. materials vs. post-forming and secondary operations later in this course.   The variety of materials available today is remarkable and to a great extent, the material selection is dependent upon the process selected.   We will certainly discuss this facet of the technology.

BASIC PROCESSES:

As you might expect, there is a definite methodology for creating actual parts, and the processes do not vary greatly from method to method.    We are going to detail the sequential steps in the process.  This detail will form the “backbone” for later discussions involving the mechanical and electronic operation of the equipment itself.  These steps apply to all of the RP&M processes.

  • Create a 3-D model of the component using a computer aided design (CAD) program.  There are various CAD modeling programs available today, but the “additative manufacturing” process MUST begin by developing a three-dimensional representation of the part to be produced.  It is important to note that an experienced CAD engineer/designer is an indispensable component for success.  As you can see, RP&M processes were required to wait on three-dimensional modeling before the technology came to fruition.
  • Generally, the CAD file must go through a CAD to RP&M translator.  This step assures the CAD data is input to the modeling machine in the “tessellated” STL format.  This format has become the standard for RP&M processes.  With this operation, the boundary surfaces of the object are represented as numerous tiny triangles.  (VERY INDENSABLE TO THE PROCESS!)
  • The next step involves generating supports in a separate CAD file.  CAD designers/engineers may accomplish this task directly, or with special software.  One such software is “Bridgeworks”.  Supports are needed and used for the following three reasons:
  1. To ensure that the re-coater blade will not strike the platform upon which the part is being built.
  2. To ensure that any small distortions of the platform will not lead to problems during part building.
  3. To provide a simple means of removing the part from the platform upon completion.
    1. Leveling—Typical resins undergo about five percent (5%) to seven percent (7%) total volumetric shrinkage.  Of this amount, roughly fifty percent (50%) to seventy percent (70%) occurs in the vat as a result of laser-induced polymerization.  With this being the case, a level compensation module is built into the RP&M software program.  Upon completion of laser drawing, on each layer, a sensor checks the resin level.  In the event the sensor detects a resin level that is not within the tolerance band, a plunger is activated by means of a computer-controlled precision stepper motor and the resin level is corrected to within the needed tolerance.
    2. Deep Dip—Under computer control, the “Z”-stage motor moves the platform down a prescribed amount to insure those parts with large flat areas can be properly recoated.  When the platform is lowered, a substantial depression is generated on the resin surface.  The time required to close the surface depression has been determined from both viscous fluid dynamic analysis and experimental test results.
    3. Elevate—Under the influence of gravity, the resin fills the depression created during the previous step.  The “Z” stage, again under computer control, now elevates the uppermost part layer above the free resin surface.  This is done so that during the next step, only the excess resin beyond the desired layer thickness need be moved.  If this were not the case, additional resin would be disturbed.
    4. Sweep—The re-coater blade traverses the vat from front to back and sweeps the excess resin from the part.  As soon as the re-coater blade has completed its motion, the system is ready for the next step.
    5. Platform Drops–The platform then drops down a fraction of a MM.    The process is then repeated.  This is done layer by layer until the entire model is produced.  As you can see, the thinner the layer, the finer and more detailed the resulting part.
    6. Draining–Part completion and draining.
    7. Removal–The part is then removed from the supporting platform and readied for any post-processing operations. .
  • Next step— the appropriate software will “chop” the CAD model into thin layers—typically 5 to 10 layers per millimeter (MM).  Software has improved greatly over the past years, and these improvements allow for much better surface finishes and much better detail in part description.  The part and supports must be sliced or mathematically sectioned by the computer into a series of parallel and horizontal planes like the floors of a very tall building.  Also during this process, the layer thickness, as discussed above, the intended building style, the cure depth, the desired hatch spacing, the line width compensation values and the shrinkage compensation factor(s) are selected and assigned.
  • Merging is the next step where the supports, the part and any additional supports and parts have their computer representations combined.  This is crucial and allows for the production of multiple parts connected by a “web” which can be broken after the parts are molded.
  • Next, certain operational parameters are selected, such as the number or re-coater blade sweeps per layer, the sweep period, and the desired “Z”-wait.  All of these parameters must be selected by the programmer. “Z”-wait is the time, in seconds, the system is instructed to pause after recoating.  The purpose of this intentional pause is to allow any resin surface non-uniformities to undergo fluid dynamic relaxation.  The output of this step is the selection of the relevant parameters.
  • Now, we “build the model”.  The 3-D printer “paints” one layer exposing the material in the tank and hardening it.    The resin polymerization process begins at this time, and the physical three-dimensional object is created.  The process consists of the following steps:
  • Next, heat treating and firing may occur for further hardening.  This phase is termed the post-cure operation.
  • After heat treating and firing, the part may be machined, sanded, painted, etc until the final product meets initial specifications.  As mentioned earlier, there have been considerable developments in the materials used for the process, and it is entirely possible that the part may be applied to an assembly or subassembly so that the designed function may be observed.  No longer is the component necessarily for “show and tell” only.

The entire procedure may take as long as 72 hours, depending upon size and complexity of the part, but the results are remarkably usable and applications are abundant.

APPICATIONS:

The applications for RP&M technology are as numerous as your imagination.  With the present state of the art, extremely accurate, detailed and refined prototypes may be produced.  Components and structures that were impossible or extremely difficult to model are made possible today with existing methods and equipment.  We will now take a look at figures representing very “real” components fabricated with rapid modeling techniques.   Some of the applications are as follows:

  • Dental Prototypes
  • Orthopedic Prototypes
  • Sculpture prototypes
  • Prototypes for manufactured components
  • Items used to decorate sets for plays, operas, etc
  • Forensic investigations
  • Surgical procedure planning
  • Molds for investment castings
  • Architectural models
  • Scaled models
  • Complex trays for fiber optics
  • Light pipes for electronic devices

In addition to speed, very fine and intricate surface finishes may be had depending upon the material and process used to create the part.    We have taken a look at those industries using RP&M, Figure 1, so let us now consider the various uses for the technology itself.  Looking at Figure 3 below, we find the following major uses for the technology:

  • Visual aids for engineering           16.5 %
  • Functional models                           16.1%
  • Fit and assembly                              15.6%
  • Patterns for prototype tooling   13.4%
  • Patterns for cast metal                  9.2%

Over seventy percent (70%) of the total uses are given by the five categories above.  This in no way negates or lessens the importance of the other uses, but obviously, visual aids, functional models and models to prove form, fit and function top the list.

DIGITAL PHOTOS DEPICTING USES FOR RP&M TECHNOLOGY:

Everyone says a “picture is worth a thousand words” so let’s take a very quick pictorial look at some of the many applications noted by the text and the figures above.  The following JPEGs should give you an idea as to what uses of RP&M technologies exist.  These digital photographs are from actual models created for very specific purposes.  Let’s take a look at parts actually produced by “additative” manufacturing.

Components Made by RP&M

Prototype Engine Block

 

Turbine Rotor

 

These are just a few of the possibilities.  Great detail–with remarkable surface finish.  Just as the technology is improving, the materials are improving also with greater choices for the design engineer.  I definitely hope you will use this post to investigate further this remarkable technology

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4 Responses to “RAPID PROTOTYPING(RP&M)”

  1. Nils Says:

    Hello guys,

    I’m looking for a source:

    INDUSTRIES USING RP&M PROCESSES:

    Where did you get that piep chart?

    Like

    • cielotech Says:

      Hello Nils. I write training courses for professional engineers and publish those through PDHonline.org. I used the work done for that course to show the graphic you saw in the post. I had 56 references but I think the one used for the pie chart came from the following source: 3-D CAM,” Rapid Prototyping Overview”, 2008. Feel free to use it if you wish. Many thanks for taking a look.

      Like

  2. lucas Says:

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    Like

    • cielotech Says:

      Hello Lucas–Thank you so much for your very kind comments. As you can see, my subject matter is fairly narrow. Most of my writing involves STEM (Science, Technology, Engineering and Math ) subjects. I really appreciate you taking a look and hope you will come back soon. Also, any suggestions you have for subjects matter will be greatly appreciated. Take care. Bob

      Like


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