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Rapid Prototyping at Memorial University

The MTC has two rapid prototyping machines which output models for all kinds of applications. The two machines available at the MTC are the FDM (Fuse Deposition Modeler) which outputs plastic prototypes and the LOM (Laminated Object Manufacturing) machine which outputs paper-based prototypes. The following pictures are examples of some of the successful uses of Rapid Protoyping at Memorial. They demonstrate the capabilities of these modelers (click on thumbnail for brief description). Also, see below for additional information about Rapid Prototyping Technology.

 
Stratasys FDM 2000 Helisys LOM 2030

   

 
Information about Rapid Prototyping Technology

History

Prototyping began with Artists/Craftspeople creating hand-made models. Next was the evolution of CAD software. This lead to CAD databases being used to generate CNC programs. Following subtractive processes was the development of additive processes ... generally called “Rapid Prototyping”.
 

Goals of Rapid Prototyping

Rapid prototyping allows for the creation of models at greater speeds and with more precision. With rapid prototyping the design process is improved as designers can experiment with variations of a product until the best results are obtained.

Rapid prototyping can:

  • Substantially reduce product development time, through rapid creation of 3D models.
  • Improve communication (visualization) within multidisciplinary design teams.
  • Address issues of increased flexibility & small batch sizes, while remaining competitive (rapid manufacture).
Basics

First of all to proceed with rapid prototyping a geometric model is required which must include surface information. The model is usually created in a solid modeling system such as CATIA, I-DEAS, Pro/Engineer, Unigraphics II. Surface models require completely bound volume and internal detail. 

3D geometric models are  mathematically sectioned into parallel cross-sections. Each cross-section creates a 2D binding or curing path for model construction. Models are constructed one layer at a time until complete. Supports may also be required.

There are two stages to rapid prototyping: 
(1) Data preparation and (2) model production.
 

(1) Data Preparation:

The CAD data must be converted to .STL format. This format was designed for 3D Systems Inc. Stereolithography Apparatus (SLA). It is characterized by triangular facets  that are used to describe the shape of a closed 3D model. Faceted surfaces must be completely bound. In addition, curved surfaces are approximated.

The .STL Format was developed by Albert Consulting Group. It consists of x, y & z coordinates of triangles. All adjacent triangles must share two vertices.

Translation software is either included in the CAD packages or via third party. The translator should provide the ability to adjust chordal deviation (ie. trade-off accuracy vs file size and processing time).

Virtual Reality Modeling Language (VRML) versus .STL should also be taken into consideration at this point. VRML was developed through Silicon Graphics using their Open Inventor (.iv) standard. This lead to “Tele-Manufacturing” as proposed by Michael Bailey, U. of C., San Diego. It takes advantage of greater development effort and utilizes other features (e.g.. colour, colour gradient,texture).

(2) Model production:

Rapid prototyping production technologies include the Stereolithography Apparatus presented at Autofact show in November, 1987. There are currently upwards of twenty different technologies being developed/marketed. There are major differences in materials used and build techniques within these technologies.

Here are a list of various RP technologies:

  • Stereolithography Apparatus (SLA) - 3D System
               - Laser generated ultraviolet beam traces out cross-sections and              solidifies the liquid polymer.
               - Component is built in vat of liquid resin.
               - Vat size limits prototype 
               - SLA-190 (7.9 x 7.9 x 9.8”) US$105,000
                 SLA-250 (10 x 10 x 10”) US$210,000
                 SLA-250 (20 x 20 x 24”) US$420,000
               - There are five materials currently available for the SLA. All are acrylates (non-reusable thermosets).
               - Accuracy - ranges from 0.1% to 0.5% of overall dimension from small to large parts. 
               - Currently the most accurate RP technology.
               - Curing stability and support structures remain challenges.
 
  • Solid Ground Curing / Photo-masking - Cubital Ltd.
              - Uses photo-masking to solidify whole layers of photopolymer at one time.
              - Solider 5600 (20 x 14 x 20”) US$550,000 
                          - machine dimensions 13.5’ x 5.5’ x 5’
                          - layer thicknesses of .004-.006”
                          - dimensional accuracy of 0.02”, building up to 100 layers/hour.
              - Full cure as built minimizes shrinkage and eliminates post-curing.
              - Wax eliminates need for supports.
              - Fly cutter provides for “undo” operation.
              - System produces a lot of waste; Can’t reuse material picked up during milling; and uncured resin is a hazardous material.
 
  • Selective Laser Sintering - DTM Corp
              - Developed at U. of Texas at Austin
              - Utilizes powder, rather that liquid polymer.
              - Potential exists for different materials including polycarbonate, PVC, ABS, nylon, polyester, polyurethane and casting wax.
              - Sinterstation 2000 (12” dia. x 15” dp) US$425,000. Builds .4 - 2” per hour.
              - Layers from .003 - .02” thick. Accuracy from .005 to .015” depending on  size.
              - Components can be recycled by crushing and converting back to powder.
              - Research is going into materials such as powdered metals, ceramics and composites.
               - Process uses bonded sheet material. Normally paper, but metals, plastics and composites are possible.
             - LOM-1015 (14 x 15 x 10”) US$95,000 LOM-2030 (30 x 20 x 20”) US$180,000
             - Sheets of .002 - .02” thick.
             - Accuracy of +/- 0.005” achievable.
             - Support provided by remainder of sheet.
             - Prototypes less fragile than polymers.
             - No internal stresses or curing shrinkage.
             - Paper waste is non-hazardous.
             - Machine can be operated in an office environment.
             - Cannot build hollow cavities as single part.
 
  • Three Dimensional Printing - MIT
             - Utilizes powdered material, spread out one layer at a time.
             - Adhesive is applied in droplets through a device similar to an inkjet printer head.
             - Limited quantitative data available on accuracy.
             - 3DP licensed to Soligen Inc. for Direct Shell Production Casting process.
             - Internal supports not required.
             - May require post processing, depending on material and binder.
             - Work continues on limiting impact of binder drops, reducing jagged “print” edges and flow control for the binder.
             - Consortium includes Boeing, Hasbro, Johnson & Johnson, 3M & United Tech.
 
  • Other RP Systems
             - Fused Deposition Modeling - Stratasys uses .050” dia. thermoplastic filament 

             - Ballistic Particle Manufacturing - BPM
                      - uses three axis robotic system controlling an ink jet like deposition head. 
                      - Low cost, easy to operate system.

             - Electrosetting - U.S. Navy.
                      - 2D profiles are used to “plot” electrode shapes which are attached to foil. 
                      - Multi-layer foil sandwich is immersed in liquid and energized. Material inside electrode solidifies. Separately controllable voltage and current provides for programmable density, hardness, etc.

             - Masking & Depositing - Carnegie Mellon
                      - robotic control of metal spraying through a disposable, laser cut, mask. A complementary mask is used to spray low melting point support alloy.

             - Shape Melting - Babcock & Wilcox
                      - controlled placement of gas metal arc welding wire weld deposit. 
                      - Very closely controlled and monitored thermal conditions with localized cooling allow for control over material properties.
 
 

Research and Development in Rapid Prototyping

  Areas of R&D dealing with Part Accuracy Improvement:

        Mathematical area:
             - potential use of CSG and ray tracing vs .STL
             - improving facet approximations
        Process related area:
             - increasing z step resolution
             - developing layer registration
        Material related area:
             - material selection/development
             - considerations ofstress relief, alternate build techniques to reduce deformation
             - additional processing (eg. shot peening)

  Areas of R&D dealing with Materials:

        Improvements to current materials:
             - current materials weak and fragile
             - development of low-shrink, less brittle plastics
             - introduction of glass, carbon or graphite fibre
         mixtures including ceramics are being tested
             - focus on end-use material requirement
             - develop techniques to build with metal
             - low melting point, binary metal powders
             - deposition of droplets of molten metal from a moving nozzle

  Areas of R&D dealing with Systems:

        Improvements to current technologies:
             - incremental improvements to specific RP technologies
             - generic improvements, applicable to several RP types
             - development of new RP technology
             - development of implementation knowledge
             - desktop manufacturing, automated fabrication, tool-less manufacturing, free form fabrication
             - workplace implications
             - application identification and development
             - virtual manufacturing, communications
             - the personal factory
 

Examples of RP in Research

    Molecular Modeling
        - Protein Kinase
        - Molecular Docking Sites

    Earth Science
        - Bathymetry
        - Fault modeling
        - Terrain surfaces
        - Hurricane / meteorological modeling
        - Ozone Hole over Antarctica

    Mechanical
        - Specific component models
        - Clearance, fit, function verification
        - Design process development

    Medical
        - Creation of mold blanks
        - Customized devices for specific patients
        - Mathematical Surface Visualization

Selected Product Development / Prototyping Bookmarks