The Tooling for
Sand Casting, the Classifications of Pattern in Sand Casting
The main tooling for sand casting is the pattern that is used to
create the mold cavity. The pattern is a full size model of the
part that makes an impression in the sand mold. However, some
internal surfaces may not be included in the pattern, as they
will be created by separate cores. The pattern is actually made
to be slightly larger than the part because the casting will
shrink inside the mold cavity. Also, several identical patterns
may be used to create multiple impressions in the sand mold,
thus creating multiple cavities that will produce as many parts
in one casting.
Several different materials can be used to fabricate a pattern,
including wood, plastic, and metal. Wood is very common because
it is easy to shape and is inexpensive, however it can warp and
deform easily. Wood also will wear quicker from the sand. Metal,
on the other hand, is more expensive, but will last longer and
has higher tolerances. The pattern can be reused to create the
cavity for many molds of the same part. Therefore, a pattern
that lasts longer will reduce tooling costs. A pattern for a
part can be made many different ways, which are classified into
the following four types:
Solid pattern - A solid pattern is a model of the part as
a single piece. It is the easiest to fabricate, but can cause
some difficulties in making the mold. The parting line and
runner system must be determined separately. Solid patterns are
typically used for geometrically simple parts that are produced
in low quantities.
Split pattern - A split pattern models the part as two
separate pieces that meet along the parting line of the mold.
Using two separate pieces allows the mold cavities in the cope
and drag to be made separately and the parting line is already
determined. Split patterns are typically used for parts that are
geometrically complex and are produced in moderate quantities.
Match-plate pattern - A match-plate pattern is similar to
a split pattern, except that each half of the pattern is
attached to opposite sides of a single plate. The plate is
usually made from wood or metal. This pattern design ensures
proper alignment of the mold cavities in the cope and drag and
the runner system can be included on the match plate.
Match-plate patterns are used for larger production quantities
and are often used when the process is automated.
Cope and drag pattern - A cope and drag pattern is
similar to a match plate pattern, except that each half of the
pattern is attached to a separate plate and the mold halves are
made independently. Just as with a match plate pattern, the
plates ensure proper alignment of the mold cavities in the cope
and drag and the runner system can be included on the plates.
Cope and drag patterns are often desirable for larger castings,
where a match-plate pattern would be too heavy and cumbersome.
They are also used for larger production quantities and are
often used when the process is automated.
Cope and drag pattern
Another piece of tooling used in sand casting is a core-box. If
the casting requires sand cores, the cores are formed in these
boxes, which are similar to a die and can be made of wood,
plastic, or metal just like the pattern. The core-boxes can also
contain multiple cavities to produce several identical cores.
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