Shaw Process Casting of RP Tools

From: Greg Redden (CSIRO  Institute of Industrial Technologies)
To: RP-ML
Date: Tuesday, April 11, 1995
Subject: Shaw Process Casting of RP Tools

Despite there being some interest in my comments (including requests to
describe the Shaw process) I was unable to reply as I was unavoidably
nowhere near a computer for the past three weeks.

Anyway, apologies aside.....

The Shaw process for the casting of steel is in many ways similar to the
plaster mold casting process (A good article on cast aluminium injection
molds from rapid prototype masters recently appeared in the March edition of
the Rapid Prototyping Report).  

The plaster mold casting process is good in that it avoids the loss of an
expensive RP pattern, which can be reused (unlike investment casting) also,
much smaller RP patterns can sometimes be included as part of a large
conventional pattern which, I expect, would otherwise need to be wholly
constructed by RP. 

The Shaw casting process offers a number of further advantages when
producing castings of parts without undercuts (eg tools):
1. The Shaw process can be used for ferrous metals.  Plaster casting is
usually limited to casting non-ferrous metals as plaster undergoes a phase
transformation to calcium oxide at 1195 deg C (2183 deg F) resulting in
mould decomposition.
2. The Shaw process does not necessarily use the intermediate step of a
rubber or polyurethane pattern, thus it would be expected to yeild improved
dimensional accuracy.  The avoidance of the polyurethane or rubber pattern
is possible as the Shaw mold is slightly flexible when it is stripped from
the RP pattern.

I hope this answers some questions.  If more info is wanted on Shaw process
then let me know.  (BTW the Shaw process is VERY similar to a process known
as the Unicast process which some mail group members be more familiar with.)
************************************
Question: Is anybody familiar with foundries in either the US or UK/Europe
who specialise in Shaw/Unicast process or plaster mold casting ?
************************************
Greg Redden