Model Maker

From: Albin Hastbacka (E-Systems , Inc.)
To: RP-ML
Date: Monday, April 17, 1995
Subject: Model Maker
Based upon a question that appeared last week, I wanted to clarify the fact
that Sanders Prototype, Inc. was NOT bought up by STRATASYS.  We are
producing Model Makers and enjoying life in Wilton, NH.  We got the Best of
Show award at the Jewelry Show in Providence, RI during April 10-12.  We
got that award because we made several different rings using our 1/2 mill
slice thickness capability.  These rings were made on the Model Maker and
investment cast with NO POSTPROCESSING beyond a hands free ten minute cycle
to remove the support structure.  These rings were absolutely beautiful.

For your information, I am emclosing a summary writeup on the Model Maker.

Al Hastbacka (SPI President)

Model Maker 3D Modeling System Technical Description.

Enabling Technology

 Sanders Prototype, Inc. (SPI) desktop modeling technology advances the
state-of-the-art for computer controlled fabrication of solid models. The
Model Maker 3D Plotting System is currently the only three dimensional
modeling machine available for true desktop use. Non-toxic materials are
used to ensure safe use in the designers work station environment.
 SPI introduces new improvements to inkjet printer technology that enables
the fabrication of solid models with excellent dimensional tolerance and
smooth surface finish. The Model Maker System produces thermoplastic models
in a timely manner and allows the designer to visualize new products,
validate and alter designs, and obtain inexpensive, functional prototypes
through molding and casting suppliers. This enabling technology promotes
concurrent engineering and diminishes time-to-market and design-to-cost
considerations for critical product releases.

Desktop Modeling System
 The SPI Model "MM-6B" is a true desktop "Design Engineer's Associate"
modeling system with a footprint of 17.5" deep x 20.5" wide x 23" high and
a model build volume of six inches per axis. The MM-6B produces precision
three dimensional (3-D) models using a stack of successive layers or
cross-sectional slices of the CAD 3D surface model.  The MM-6B produces the
output product by building the model from the bottom up using the slice
data.

Inkjet Modeling Technology
 The MM-6B plotting system is a liquid-to-solid inkjet plotter with a
separate Z-axis input.  The dual inkjet subsystem rides on a precision X/Y
drive carriage and deposits both thermoplastic and wax materials on the
build substrate under program control.  The X/Y drive carriage also
energizes a flatbed milling subsystem for maintaining precise Z-axis
dimensioning of the model by milling off the excess vertical height of the
current build layer. Thus, subsequent layers will have a known surface
reference layer to build upon.
  The superior dimensional tolerance and smooth surface finish are based on
the innovative features of the Model Maker System for model building and
tolerance control, namely - the 3D plotting process and the variable slice
thickness control process.  The 3D plotting process consists of the
deposition of the build and support materials on a substrate mounted on the
Z-axis build
table whose elevation is determined within 0.000125 inches (0.125 mils)
under strict program control. Smooth surface quality is ensured by
pre-tracing the perimeter and cavity surface outlines with deposited
materials to establish the surface wall finish prior to filling the
interior with build material.
 The support material is used to support overhangs and cavities in the
model during the model build sequence.  The build and support materials are
digitally deposited onto the build substrate as a series of uniformly
spaced "micro-droplets" incorporating a Sanders Prototype, Inc. proprietary
"drop-on-demand" inkjet process. Utilizing patented technology, these
droplets may be placed at any desired location upon the build substrate to
within 0.00025 inches (0.25 mils) in the X and Y  directions. The
droplets adhere to each other during the liquid-to-solid phase transition
to form a uniform mass. The drying process is fast enough to allow milling
of the layers immediately following the deposition cycle.

Build and Support Materials
 The ProtoBuild material is a Sanders proprietary thermoplastic material
and is used to produce the final part geometry.  This build material is
compatible with investment casting and other mold making processes and has
excellent burn-out characteristics. The ProtoSupport material is also an
SPI proprietary wax material designed to be removed with a solvent without
damage to the build material.  The color of the ProtoBuild material is
significantly different from the Support material so the two materials may
be differentiated from one another.  The ProtoBuild material is dyed a
green color, whereas, the ProtoSupport material is dyed a red color.
 The X and Y axis speed and positional controls allow the Model Maker
System to produce vertical free standing walls as narrow as 0.004 inches
thick with smooth side walls.  The Model Maker also has the ability to
provide different specified cellular fill patterns, such as, solid fill or
honeycomb fill within the wall structures. Positional accuracy is
determined and maintained under control of the associated control program.

Positional Accuracy
 The X and Y micro-droplet placement can be specified to within 0.00025
inches (0.25 mils) under program control.  The resultant line width
deposition is typically 0.004 inches and compensation is provided to offset
the line from prior depositions to make a physical model of the correct
dimensions.  Smooth model surface finishes are ensured by tracing the model
surface outlines on each build cycle prior to the subsequent internal fill
process. Very smooth surface finishes may be obtained by building a series
of contiguous walls prior to the interior fill process.

Variable Slice Thickness Control
 The Z-axis control can be stepped under program control in increments of
0.000125 inches (0.125 mils), thereby giving very close dimensional control
to the designer.  Nominal Z-axis slice thicknesses are 0.002 inches (2
mils) per slice although the experienced user can adaptively control the
horizontal slice thickness to 0.001 inches (1 mil)  at different regions of
the constructed model to improve surface finish. Thus, the designer has
control over the building of very intricate models and surfaces to within
100 micro-inches.

Continuous Modeling Operation
 The Model Maker will operate continuously for long periods of time based
upon the model size and volume fill requirements.  The operator will need
to replenish the material supplies at 12 hour intervals under rapid
building conditions.  The machine may be stopped and restarted for
unscheduled maintenance or manual intervention in the building process -
without loss of the model build file and positional accuracy.  A number of
operational conditions are automatically monitored and controlled,
including the proper operation of the inkjets and the status of the model.
Automated service actions are used to sustain the proper jetting of the
materials.

CAD Software Compatibility
 The Model Maker System is designed to work with current workstation based
Computer-Aided Design (CAD) systems. Software tools are provided within the
system to translate the files from these CAD systems into the proprietary
binary format (.BIN) required by the Model Maker System.
 A program called TMM accepts an industry standard Stereo-Lithography
(.STL)  file and creates a set of two-dimensional slices of the model. A
binary file is then created that contains the instructions for the Model
Maker System to fabricate the part. TMM also allows the user to view the
entire model or individual slices, make simple corrections, and create
support structures as necessary. A variety of process parameters can be set
to control model fabrication.
 The TMM program will accept pre-sliced data as a set of two-dimensional
HPGL files. A separate guide file is provided to order the slices and other
process parameters. TMM will also accept data from CAD programs that don't
support the .STL format.
 The Model Maker System has a user program to control and monitor the
building process. This program accepts the binary data file from either TMM
or a third party software package and uses the data to fabricate the
physical model.

Third Party Software Support
 Third party vendors may develop proprietary software tools that support
the Model Maker System binary file format directly. These tools provide
various additional capabilities, including alternate data input formats.
 POGO, International has developed a powerful Windows based pre-processor
program called "Model-Win" for the Model Maker System . It has a graphical
user interface with many convenient features to make the preparation of
files easy and efficient. It imports .STL & AutoCAD DXF files, orients
parts in the build volume, moves and scales parts, finds holes and open
surfaces, view 3D shaded images of parts, find & repair bad surface
normals, slices & rasterizes models, view binary slice files graphically,
and combines multiple parts for a single build cycle.

Notice:
 Model Maker, 3D Plotting, and Variable Slice Thickness are all registered
trademarks of Sanders Prototype, Inc. All rights are reserved. Windows is a
registered trademark of Microsoft Corporation and Model-Win is a registered
trademark of POGO, Int'l.