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Andy recently wrote approximately the following:

...an Ec of 5 makes a resin the fastest on the planet...

Looking at Ec alone to determine the speed of a resin is a mistake. One

must consider both the Ec and Dp. The exposure required to expose a

layer is given by the formula:

Energy = Ec * e ^ (Thickness / Dp) or

E = Ec * e ^ (T / Dp),

Where:

Energy (E) is the energy required to produce a layer of Thickness (T)

E = mJ /cm^2

Thickness (T) is the thickness of the desired layer (mils or mm)

Ec = mJ / cm^2 from the working curve

Dp = Slope of the Working curve (mils or mm)

For example:

To produce a layer 10 mils (0.25 mm) thick,

using a resin with Ec = 8 mJ/cm^2 and Dp = 5.6 mils (~0.14mm),

one would calculate:

E = 8 * e ^ (10/5.6) = 47.7 mJ/cm^2

DuPont, 3D and Ciba have used the terminology E-10 to refer to such a

number, where E-10 is to be interpreted as "the energy required to cure a

layer 10 mils thick".

Other layer thicknesses can be reported, for example, E-5 would refer to

a 5 mil layer.

One must still be careful when using such an approach. Real parts in

real equipment have many different exposures used to create the layers.

A more careful analysis of the actual typical or dominate exposures is

required to make the most meaningful comparison. At the simplest level

one should compare the hatching exposures since hatching tends to

predominate in typical part geometries. If one images a free floating

layer of a part and measures the actual thickness produced you may find

that for a 6 mil (0.15 mm) layer, the total thickness, with overcure, is

around 10 mils (0.25 mm). Consequently the E-10 comparison is not a bad

one to make when comparing materials being used for 6 mil layers.

In the example cited earlier, an Ec of 5 was mentioned, Dp was not

mentioned. Consider the following E-10 values computed for 3 different

Dp values:

Dp = 4, Ec = 5, E-10 = 5 * e^(10/4) = 61 mJ/cm^2

Dp = 5, Ec = 5, E-10 = 5 * e^(10/5) = 37 mJ/cm^2

Dp = 6, Ec = 5, E-10 = 5 * e^(10/6) = 26 mJ/cm^2

The third material is twice as fast as the first by this measure, even

though they all have the same Ec of 5.

Historically we were able to compare the earliest resins by only looking

at Ec, since they all had approximately the same Dp. We can no longer do

this. We must take both Ec & Dp into account.

Thanks, Bronson

PS. The opinions are my own, don't blame anybody else!

================================================================

Bronson R. Hokuf USMail: DuPont Company

DuPont Company (NCCC/PWay) 2 Penn's Way, Suite 401

Advanced Material Systems (P&IP) New Castle, DE 19720

Somos(tm) Solid Imaging Materials Tel: 302-328-5635

E-Mail: hokufbr@esvax.dnet.dupont.com Fax: 302-328-5693

================================================================

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