Showing posts with label Design and Function. Show all posts
Showing posts with label Design and Function. Show all posts

Injection Mold for the Body of a Tape Cassette

product design development
Injection Mold for the Body of a Tape-Cassette Holder Made from High-Impact Polystyrene.
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.