2) A set up board is built to
establish the parting line, incorporating the gating system
and non-shift buttons. This consists of mounting the pattern
on a wooden board with a workable material which can be
machined or sanded to establish the parting line. During
this step the non-shift buttons are added.
3) A negative impression is made of
the set up board.
4) The negative impression and the
pattern are then removed from the set up board exposing the
other side of the pattern. An impression is then made of the
other side of the pattern which is set in the negative
impression made in step 3.
At this stage 2 pieces of the
tooling required in the RPM process have been completed, the
master pattern (model) and a hard urethane negative.
5) The next step is to build the
foundry working tool or "Rubber Tool". This is done by
making an impression of each piece of the negative using
soft urethane rubber.
The rubber tool is what is used to
create the plaster molds into which the aluminum will be
poured. A plaster mold must be made for each part needed.
The Plaster Mold Process
1) A plaster slurry is poured onto
the rubber tool and allowed to set. When set, the plaster
mold is removed from the tool, assembled and racked for
drying. Plaster molds are dried for 10 to 14 hours.
2) The dry plaster molds are
removed from the drying ovens and the metal is poured.
3) Once the metal has cooled, the
plaster is removed, commonly referred to as shake out.
4) The gates are then removed from
the casting.
5) The casting is washed to remove
any remaining plaster residue.
6) The casting is now ready for
grinding, straightening, heat treating and any additional
secondary operations.
.JPG)