Molded Part: Design and Function
A cubic molded part of impact-resistant polystyrene forms the main body of a tape-cassette
holder consisting of a number of injectionmolded
parts. Several cassette holders can be
stacked on top of each other by snap fits to yield
a tower that can accommodate more cassettes.
The molded part, which has a base measuring
162mm x 162mm and is 110mm tall, consists of a
central square-section rod whose two ends are
bounded by two square plates. Between these plates,
and parallel to the central rod, are the walls, forming
four bays for holding the cassettes.
Single-Cavity Mold with Four Splits
The mold, with mold fixing dimensions of
525mm x 530mm and 500mm mold height, is
designed as a single-cavity mold with four
mechanical splits (Fig. 3). The movable splits (9) are
mounted on the ejector side of the mold with guide
plates (21) and on guide bars (20). The splits form
the external side walls of the molded part while the
internal contours of the bay’s comprising ribs, spring
latches and apertures are made by punches (34) that
are fitted into the splits and bolted to them. Core (6),
which is mounted along with punch (7) on platen
(23), forms the bore for the square-section rod. The
punch (7) and the runner plate (14) form the top and
bottom sides of the molded part.
When the mold is closed, the four splits are
supported by the punch (7) and each other via
clamping surfaces that are inclined at less than 45.
Furthermore, the apertures in the molded part ensure
good support between punches (34) on the splits,
core (6) and runner plate (14).
The closed splits brace themselves outwardly against
four wedge plates (12) which are mounted on the
insert plate (18) with the aid of wear plates (13).
Adjusting plates (11) ensure accurate fitting of the
splits. Each slide is driven by two angle pins (8),
located in insert plate (18) on the feed side. Pillars
(39) and bushings (37) serve to guide the mold
halves. The plates of each mold half are fixed to
each other with locating pins (27).
The molded part is released from the core by ejector
pins (25), which are mounted in the ejector plates (3,
4). Plate (23) is supported on the ejector side against
the clamping plate via two rails (40) and, in the
region of the ejector plates beneath the cavity, by
rolls (2).
Feeding via Runners
The molding compound reaches the feed points in
the corners of the square-section rod via sprue
bushing (16) and four runners. The rod’s corners
have a slightly larger flow channel than the other
walls of the molded part. The sprue bushing is
secured against turning by pin (15).
Mold Temperature Control
Cooling channels are located in the core retainer
plate (22) and the insert plate (18). Punch (7) is
cooled as shown in Fig. 4. Core (6) is fitted with two
cooling pipes, while punch (34) is fitted with cooling
pipe (35). Furthermore, the slide (9) are cooled.
Demolding: Latches Spring Back
As the mold opens, the slides (9) are moved by the
angle pins (8) to the outside until the punches (34)
are retracted from the side bays of the molded part.
As Fig. 5 shows, the cavities of the spring latches Z
are located on the one hand between the faces of the
four punches (34) and runner plate (14) and, on the
other, between the two adjacent side faces of the
punches (34).
On opening of the mold, the ratio of the distance
moved by the slides to the opening stroke between
runner plate (14) and slides is the tangent of the
angle formed by the angle pins and the longitudinal
axis of the mold. Thus, when the mold
opens, enough space is created behind the latches Z
to enable them to spring back when the punches (34)
slide over the wedge-shaped elevations (a) of the
latches (Fig. 5). The situation is similar for ejecting
latches between adjacent punch faces. As the mold
opens further, the angle pins and the guide bores in
the slides can no longer come into play. The open
position of the slides is secured by the ball catches
(33). The molded part remains on core (6) until stop
plate (29) comes into contact with the ejector stop of
the machine and displaces ejector plates (3, 4) with
ejector pins (24, 25). The molded part is ejected
from the core, and the sprue from the runners. When
the stop plates are actuated, helical springs are
compressed (30) that, as the mold is closing, retract
the ejector pins before the slides close. Return pins
(26) and buffer pins (19) ensure that the ejector
system is pushed back when the mold closes
completely.
