The parting or separation between two or more segments of a mould is
necessary to create the mould cavity (as in sand casting) and also to
remove the manufactured part from the mould (as in die casting).
For any given casting geometry, a number of parting alternatives may
exist; visualizing and selecting the best alternative is a non-trivial
task even for simple shapes. Variations in customer requirements,
quality specifications, manufacturing facilities and economical
considerations may lead to different parting solutions for the same
shape. For intricate parts, there is a high possibility of overlooking
feasible alternatives and difficulty in assuring that the selected
alternative is the indeed the best one.
To evolve a scientific approach to parting line design and
analysis, unambiguous definitions of parting and related features are
required, valid for all types of tooling being considered. The following
definitions are proposed.
- Mould segment is a distinct body, at least one face
of which is in contact with the casting.
- Parting direction of a mould segment is the direction
along which it is withdrawn from the adjacent mould segment,
usually along the axis of the mould segments. It is also
referred to as draw direction.
- Draw distance is the minimum length of movement
required to completely disengage one mould segment from the
adjacent one.
- Parting surface is the surface of contact between any
two segments of the mould.
- Parting line is the contour of intersection of a
parting surface with casting surface.
- Undercut is a part feature (pocket or protrusion)
located with respect to the parting direction and parting line
such that it hinders withdrawal of the part from the mould.
|
Parting surfaces may be classified based on the type of mould segments
at the interface. Considering three types of mould segments: cope, drag
and cores, we have cope-drag, cope-core, drag-core and core-core parting
surface. In practice, only cope-drag interface is referred to as the
parting surface. The logic can be extended to die casting, by replacing
cope and drag with the moving and fixed die half. The cope-core and
drag-core interfaces correspond to the portions of mould that are
contact with a core. The core-core interface is encountered in core
assemblies (or dies with multiple inserts in contact with each other).
The interfaces between the segments of a three-part mould (cope, cheek
and drag) can be treated similar to those in a two-part mould.
Parting line is the contour of intersection of mould
parting surface (cope-drag or mould-core) with part surface.
Parting lines may be classified based on the number and orientation of
planes containing the different segments of a parting line. A flat
parting line lies entirely in a single plane. A stepped parting line
lies in two or more planes, all of them normal to a single plane usually
parallel to the parting direction. The segments of a complex parting
line lie in multiple planes in different directions.
Pattern,
Mould & Core Design