Appendix I
ZCast Design Guide - 9
5.2.1
Direct Pour
A mold designed by this method incorporates the cavity of the casting and the entire gating
system, including risers and vents. This keeps the mold setup simple by minimizing parts. It is
most handy for small molds: up to 5 lbs in aluminum or 15 lbs in bronze. Larger castings can be
feasible if the gating system is kept simple, for example, a short sprue leading to a single gate.
These molds are least complicated, usually only two or three parts.
Using the Direct Pour method, the parting surface need not be a flat plane, as usually is the case
in conventional sand casting. Nor does the gating system need be constrained to the parting
surface. The requirement for “draft” with respect to the parting surface is absent as well.
This method is ideal for molds for which the components (entire cope, entire drag, and cores) can
each be printed out in their own build without modification.
5.2.2
Shell Method
In this method, the mold cavity is formed by a ½” thick shell of ZCast material and is held in place
by backing it with conventional sand. The gating system: sprue, wells, runners, and risers are
constructed in the foundry sand, merging with ingates and riser holes that penetrate the ZCast
shells. This method is conceived for larger molds than the Direct-Pour method and when the
gating system would require very large ZCast components. If the size of the mold exceeds the
working volume of the printer the Shell Method is recommended.
These molds are more complicated to design than Direct-Pour molds, and require the designer to
be familiar with tool design for conventional sand casting. The designer must allow for the ZCast
pieces to mount to a pattern board, which aligns them with respect to the rest of the mold. The
ZCast shells must provide connections to the gating system, vents, and risers, and they must
have features that anchor them to the backing of foundry sand. Finally, the ZCast shells must be
structurally sound by themselves so they can be handled and baked individually.
The printed mold pieces consist of cores and a uniform shell (at least 12mm or ½” thick) that
surrounds the mold cavity. A flange of similar thickness extends out on the parting line. The
flange contains vent holes, core prints and alignment pins. The mold pieces can be built in
sections and aligned together on a blocking board (usually a plywood construction). The blocking
board assembly is placed in a mold box, standard gating forms can be positioned and foundry
sand is packed around the printed parts.
Figure 4: Shell Method – ZCast components of a shell mold (left).
Assembled mold with ZCast components packed in foundry sand. Note
the risers, runners and sprue have been formed in the foundry sand
(right).
