very old and common casting process begins with a pattern
made in the shape of the desired part. The pattern can
be made from wood, plastic, metal or other material.
Simple parts can be made from a single piece or solid
pattern. More complex items are made
in two parts called "split patterns."
A split pattern has a top or upper section called a cope,
and a bottom section called a drag.
Both solid and split patterns can have cores
inserted to complete the final part shape. Where the cope
and drag separate is called the "parting
line." Typically a well-designed pattern
has tapered edges so that the pattern can be removed without
breaking the edges of the mold.
are packed into sand that is mixed with binding agents.
This helps harden the sand into a semi-permanent shape.
Once the sand mold cures, the pattern is removed, leaving
a hollow space in the sand in the shape of the desired
part. The pattern is purposely made larger than the cast
part to allow for shrinkage during cooling. Sand "cores"
can be inserted in the mold to create holes and improve
the casting's final shape. Simple patterns are usually
open on top, and the melted metal is poured into them.
Two-piece molds are clamped together, and the melted metal
is then poured into an opening called a gate.
Sometimes, vent holes are created to allow hot gases to
escape during the pour.
temperature of the metal is a few hundred degrees higher
than its melting point to assure good fluidity.
This ensures that the part won't cool prematurely, resulting
in voids and porosity. Bruin Metal Works casts from
a variety of aluminum and brass alloys.
When the metal
cools, the sand is removed and the metal part is ready
for use or for secondary operations such as tumbling/deburring,
machining, polishing, plating, etc. One of the biggest
advantages of sand casting is that it's the least expensive
of the range of casting processes. Sand casting
is ideally suited for low-volume runs, prototypes and