Process
Description:
1) Master Pattern:
Precise Cast will convert your 3D CAD data into
a master pattern. This usually consists of an
SLA model or a pattern precision machined from
Renboard. It is during this process that machine
stock, gating, risering, and shrink compensation
occur. Depending on part geometry FEA solidification
analysis is run to optimize the tooling design
and quality of the eventual casting.
2) 1st Stage of Tooling:
From the master pattern, a negative cavity of
the geometry is produced either by surrounding
the master pattern with silicone or by machining
the negative geometry into Renboard. This is where
the parting lines for mold halves and cores/slides
are generated.
3) 2nd Stage of Tooling:
A urethane or silicone material is then poured
over the 1st stage of tooling. This creates a
positive geometry of the part in individual cope,
drag, and core segments. The resulting tool is
used repeatedly to produce each plaster mold.
2nd stage tooling life varies, but generally yields
100 -300 plaster molds, this can result in many
more parts than 100-300 depending on how many
cavities each plaster mold has in it. Tooling
life depends on part geometry and material used
to produce the tool. If the 2nd stage of tooling
wears out, new tooling can be quickly produced
at a fraction of the original cost using the 1st
stage of tooling described in step 2.
4) Plaster Molds:
Plaster and water are mixed to form a plaster
slurry. This plaster slurry is poured into the
2nd stage of tooling and the plaster is given
time to solidify. After the plaster is firm, the
mold is removed from the tooling. The plaster
molds contain the negative part geometry. The
mold halves (cope/drag) and cores are carefully
assembled into a complete mold. They are then
baked for 1-2 days to remove all moisture content.
5) Metal Pouring:
Plaster casting utilizes a gravity pour method
of filling the cavity. Several techniques are
used when pouring metal to ensure that a high
quality part is produced. Some of the variables
that can affect casting quality are metal temperature,
mold temperature, active chilling, mold tilt,
riser size/location, and metal filtering. To ensure
optimum metal quality Precise Cast uses certified
virgin metal, rotary degassing, and a continuous
melt furnace. Precise Cast’s metal pouring department
utilizes strict quality control of all materials
including multiple RATS (Reduced atmospheric testing
system) testing throughout the day. All data is
electronically documented and archived. Throughout
the process each mold and corresponding part made
is internally serialized and all known variables
are tracked and archived.
6) Break-Out and Clean-Up:
After the metal has solidified and the plaster
has cooled, the plaster is carefully broken away
to reveal the metal casting. Remaining plaster
is removed via pressure washing and the part is
then hand cleaned and detailed. During this process
gates and risers are removed and the part is prepped
for machining.
7) Machining:
Final machining is often used to create high-tolerance
geometries that are beyond the capabilities of
the casting process. Our machining centers are
specifically designed for the special requirements
of prototype and casting work. Each machine has
4th axis capability, built-in CMM touch probes,
and tool height sensing probes to ensure consistent
and accurate machining of each casting.
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