[Jewelry making - Article 00425] - Re: [Orchid] CAD/CAM grown model woes

[Steven Adler]

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Richard

    First it is important to differentiate the materials. The term
    "resin" does little to define what type of material is being cast.
    There are two basic types of materials being used for 3D printing
    (RP) by jewelers, photopolymers and thermal plastics. 

    The documented history of ALL photopolymers is that they are
    hygroscopic, meaning that they will expand when exposed to water.
    Photopolymers are also subject to thermal expansion at higher
    temperatures. When you invest these patterns, the warm and wet
    environment in the flask will cause them to expand. As the investment
    dries, the pattern gives up the moisture and contracts away from the
    boundary between the pattern and the investment. This can cause small
    or sometimes large surface defects in the investment surface before
    the burnout phase. These defects are greatly dependant on the
    geometry, volume, and surface area of the pattern. The larger the
    design, the less likely you will achieve success. In the second phase
    of burnout, which is where the investment companies have focused
    their effort, the pattern expands again when subjected to heat and
    may damage the boundary between pattern and investment as well. To
    the degree one can control the time that a pattern is exposed to
    water in phase one and the strength of the investment in phase two,
    you will achieve a level of success. I know of some companies using
    small flasks that are doing OK with photopolymers but, I know of none
    who are getting results "just like wax" every time. The best solution
    has been to cast several patterns and to cherry pick the best result
    or to be satisfied with a less than pristine surface finish 

    The thermal plastics will dissolve in water and even faster in
    alcohol or acetone. They are also much more fragile but, they will
    hold up very well during the investment phase. They do not absorb
    water or expand. In the burnout phase, the thermal plastics behave
    exactly like wax. There is no expansion and thus a regular investment
    and burnout cycle will work just fine. The only caution with these
    materials is to keep them away from de-bubbler solutions that contain
    alcohol and not to over vacuum the flask. 

    I did a scientific study on this subject with Teresa Frye at Techform
    Casting not too long ago for the Santa Fe Symposium which is
    available on the MJSA site and goes into more detail.
    http://www.mjsajournal.org/features/0508 

    If you need more information, feel free to contact me off-line.. I
    have been on the bleeding edge of this subject for quite some time
    and will be happy to provide some guidance 

Steven Adler
A3DM
www.a3dm.com
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