Re: invesment casting from desktop printers (and high performance RP machines)

From: Christian_Nelson/
Date: Fri Mar 03 2000 - 01:06:38 EET

I want to also tell you about CastForm PS, the investment casting material
available for Selective Laser Sintering (SLS). CastForm PS was introduced to
the market last April. It is an polystyrene material that is processed in the
SLS machine to form the shape of the pattern. After SLS processing, the loose
powder (unsintered material) is brushed off of the part and the pattern is
dipped in a gating wax to fill all porosity. Both of these materials
(polystryene and wax) are foundry friendly materials that burn-out cleanly using
a standard autoclave and firing oven cycle.

What are the benefits of CastForm PS?
1) Shell cracking. Their have only been 2 instances of shell cracking with this
material (remember that even wax parts can crack shells). That includes
thousands of parts of all geometries; thin walls, thick walls, posts, and holes.
This is a huge improvement over our previous casting materials. The material
begins to soften at 60C. The flash point of the polystyrene is 350C, and the
flash point of the wax is around 200C.

2) The material burns out cleanly using times and temperatures very similar to
those used with typical wax patterns. This means that every foundry in the
world can process this material (Casting prototype patterns shouldn't be limited
only to foundries with flash-fire furnaces). This saves time at the foundries
because they can process these rapid prototype patterns on the same trees as wax
parts, using similar firing temperatures.

This also allows foundries to burn-out the patterns during normal operating
hours. I don't know if you are aware, but some foundries in urban areas burnout
epoxy, paper, and ABS materials under the cover of darkness to hide the black
smoke piped out of their flash-fire furnaces.

3) The ash content of the CastForm is less than 0.02%. There is effectively no
ash residue in the shell.

4) The SLS process doesn't use support structures. The unsintered material
(loose powder) acts as the support medium as the part is being built. This
build method eliminates constraints on pattern complexity because it is easy and
quick to remove the unsintered material for holes and blind passages.
(Thermojet, SLA, and FDM patterns are built on a support structure that has to
be removed)

5) Speed. SLS is a fast process, and it is getting faster with machine and
software enhancements. The NASA web site (
mentioned in a previous post has some build times that can be compared for a
part built on different platforms. I need to add that the Sinterstation
2500plus builds parts faster than the Sinterstation 2000 used to create that

For a material data sheet for the CastForm material, visit the DTM web site.

If you need a list of SLS service bureaus, I have a list of a dozen companies in
North America that are providing quality investment casting patterns made with
the CastForm PS material. Inquiries about SLS service bureaus in Europe and the
Pacific Rim will be appropriately redirected.

I also have a long list of foundries that have used CastForm PS patterns and
welcome more patterns. This list includes contact information and a summary of
metals cast.

Christian Nelson
DTM Corporation

Kevin Dyer <> on 03/01/2000 11:30:41 AM

cc: (bcc: Christian Nelson/DTM)
Subject: invesment casting from desktop printers

I would be interested in hearing from others who have used ThermoJet, Z
Corp or Genisys systems to produce investment castings. This information
would be helpful in preparing for an upcoming presentation that contrasts
these technologies with 'industrial strength' RP systems like SLA. If you
have anything you would like to share it would be appreciated. Thanks!

Kevin Dyer
InterPRO Rapid Technologies

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