硬质聚氯乙烯管接头模具设计英文文献和中文翻译(8)
are mounted in the same way in their holders, although the sectional view does not
show this. The whole set of collapsible cores is then mounted to the sliding plates
to provide the means of actuation and enable the sequence of motion.
Figure 16(a–c) shows the assembly of the collapsible core unit and the complete
assembly of the injection mould. As shown in the figure, the segments are pivoted at
one end on pins and supported by their inpidual holders. The sleeve or bush (number
8) is mounted on a slide (number 10). Segment A (number 2) and its holders are
contained in a slide plate A (number 16), while segment B and its holders are in
slide plate B (number 17). Slide plate A, which contains segment A, is mounted to
the slide support (number 15). When the mould opens, the cam block will activate
the slide, thus withdrawing the bush and causing the segments to collapse. Slide
plate A and slide support, which are mounted together, then start to withdraw
further, resulting in the bush and segment A moving with them until they hit the stopper. A hydraulic motor is used to control this movement. Finally, segment B col-
lapses and thus clears the undercut and the whole unit moves away from the cavity,
allowing the moulded part to be ejected. A Ø30 mm shaft with one end mounted on
the moving half cavity and the other end on a stopper is used to guide the movement
of the plates. Guide rails are used to guide the movement of the entire unit.
5. Design evaluation
The main criteria for the evaluation of injection mould design include the function-
ality of design, the manufacturing process and the cost of manufacturing. The func-
tionality of the injection mould can be evaluated based on the injection moulding
process, which involves mould filling, cooling and demoulding.
The purpose of mould-filling analysis is to ensure that, with the designed runner
system, the mould will definitely be filled up during the injection process. Based on
the result obtained from the analysis, modifications can be suggested to ensure the
quality of the moulded part meets specifications. Plastic Advisor is one of the
mould-filling analysis programs available in Pro/Engineer design solutions. The soft-
ware is capable of suggesting the location of gates, the number of gates, the kind of
material, thicker wall section, size of runners and gates, and so on. It can also simulate
mould filling for injection-moulded plastic parts, thus providing manufacturability
insights for reducing design changes and mould costs. In Plastic Advisor, designers
start from a solid model (for example, figure 4) and subsequently conduct such ana-
lyses as determining the fill time of the cavities, confidence of fill, injection pressure,
flow front temperature, weld lines and air traps.
A sufficient cooling system has been designed to run on the cavities and the core. It
helps make the molten plastic into shape as soon as possible. These designs help
prevent the mould from overheating and ensure the moulded part is cooled as soon
as possible so as to reduce the cycle time. In addition to cooling, the moulded part
has to be ejected with no damage. This stage depends a lot on how the mechanism
is designed and incorporated to the mould. Using the side core and the collapsible
core unit helps solve problems in demoulding the undercut. With the development
of CAD models, the mechanism can be verified to function virtually through the com-
puter. Interference between the core and the moulded part during demoulding has been
checked using the commands available in the software.
To minimize the cost of the mould, most of the parts are designed with minimum
complexity. Only such simple manufacturing processes as milling, turning, electrode
deposition machining and wire cutting are needed to produce the mould to the
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