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Another way to use the stereolithography
technology is to insure that the CAD solid model is complete.
Sometimes, a designer will not close a line and the model will not be
complete. It
is better to find that out in the production of a prototype part rather than in
the manufacture of the production mold which could cost both time and money.
In all of these processes, part complexity is
not a factor. By
that I mean that for all practical purposes, it takes the same amount of time to
produce a simple part as a very complex part.
By exporting a 3D stereolithography file (*.stl) from your CAD software,
and sending it over the internet to a stereolithography service bureau anywhere
in the world, it’s possible to
have a part back in about a week or two, no matter how complex the part,
to an accuracy of typically .002 to .005 inch.
PROTOTYPE MOLDS
If
life testing, mechanical testing, or any other testing is needed to validate the
design, then prototype molds may be needed to mold the part out of the actual
resin that will be used in production. This
is still an approximation since the part will not be produced from production
molds. All the test data produced
from parts made from prototype molds would have to be re-validated using parts
molded from the production molds. The
reason for this is that the process parameters set on the injection molding
machine and the characteristics of the mold can impact part quality.
For example, a prototype mold may not have very good cooling resulting in
a longer cycle time, while the production mold may have better cooling and a
faster cycle time. The production mold may cool the part faster and cause more
molded-in stress than with parts molded from the prototype mold.
We’ll talk more about process validation in a later article.
DTM
Corporation has developed a process to produce prototype molds similar to how
they produce prototype parts. Per
DTM, the accuracy of molds produced by this method is reported to be about .006
inch. This is not a precision mold,
but it can be produced in a week or two.
There
are other ways to use stereolithography. A
silicone rubber mold can be made from an over sized model. The silicone rubber mold can be used to make multiple samples
using cast urethane or cast epoxy. When
making the stereolithography model, the shrinkage of the silicone rubber mold
and the cast resin shrinkage need to be added to the part dimensions to make the
model oversize.
PROTOTYPE METAL PARTS
Another
way to use stereolithography is to make a model from wax rather from resin.
Using the “lost wax” process
for casting metal, a metal part can be cast.
A very complex geometry metal part can be produced with no machining.
SUMMARY
Advances
in Prototype Technology provide a manufacturer a means to develop products
faster and get them to market faster, providing a competitive advantage.
In the medical products industry, it is not unusual for the company that
gets to market first will capture an 80% share of that market.
Vendor Contact Information:
3D
Systems
26081
Avenue Hall
Valencia,
CA 91355
Phone:
805-295-5600
Fax:
805-257-1200
DTM
Corp.
1611
Head Way Circle
Building
#2
Austin,
TX 78754
Phone:
512-425-2830
Fax:
512-832-6753
Cubital
America, Inc.
1307F
Allen Drive
Troy,
MI 48083
Phone:
313-585-7880
Fax:
313-585-7884
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Robert A. Beard is
president of Robert A. Beard & Associates, Inc. which was formed in
1984. Mr. Beard received his Bachelor of Science Degree in
Mechanical Engineering from the University of Wisconsin-Madison and is
also a registered professional engineer. He has been elected to the
prestigious grade of Fellow in the Society of Plastics Engineers.
Robert A. Beard &
Associates, Inc. provides consulting services on product design and
development (CAE and FEA), computer process simulations for injection
molding, and process trouble shooting in injection molding. Mr.
Beard also presents seminars on plastics and injection molding and has
taught thermodynamics, plastics, kitnematics, and advanced machine design
at such universities as the University of Wisconsin, Pennsylvania State
University and New York State University.
He has been a General
Manager for a custom injection molding division, spent 10 years with
Abbott Laboratories in engineering management, and has been R&D
Manager for plastic coextrusion technology at National Can Corpn. |
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