must be understood that the pin and the collapsible core
sleeves float in the mold base and will be positioned in
center by the retaining diameter. (Stripper ring,
slides, or in the case of a side action the cavity and
core inserts) This requires that the pin expands the
fingers of the core while being contained to avoid
unnecessary wear on the shut off of the core.
molded part is required to be held centered during
ejection, as the collapsible core is collapsed. This is
so as not to hang the part up on one side of the core.
This could be accomplished through the use of a part
detail or molding part of the outside diameter on the
stripper ring, etc. On side actions, the part needs to
be held in place (centered) as the core is removed from
the molding area. The mold function will dictate the
most advantageous design.
with all mechanism with moving parts, venting must be
away from the core. Preferably along the parting line,
vent to the outside of the mold. In some cases, when the
core is a side action, it may be necessary to vent along
the outside diameter of the core. The fingers of the
core have clearances of +0.0000/-0.0002”, this
requires that the core remain clean of gassing and
residue produced in the molding process.
pin diameter has similar clearances to the inside
diameter of the fingers of the core. As was stated
earlier, the pin and the core are centered by these
diameters fitting within the containment ring (stripper
ring, side actions, etc.) You should never vent along
is essential to maintaining the endurance of the core.
Mattering on the material being molded and the
effectiveness of the venting, a schedule for cleaning
the cores needs to be established. If the fingers become
too dirty or gummed up with residue from the molding
process, they will not close properly, which will cause
damage to the core. It is better to clean the cores more
often than to allow the dirt to build up to an
unacceptable level. The mold design should incorporate
an easy way for removing the cores for cleaning.
with all injection molding, having the mold close on a
part that did not eject properly will cause damage. When
the part is molded and hardens, the part shrinks smaller
than the cavity. This situation will cause breakage to
the core, since it will not be able to open the fingers
into the molded part. There are many safe guards which
can be installed to avoid this situation.