actuated collapsible core design is proposed in industry (Wong 1997). Tor et al.
(2000a, 2000b) have established geometrical features for such a core with the motiv-
ation towards the automation of the design process (Chung 1999). This moulding
tool is designed for UPVC pipe fittings of size from Ø100 mm to Ø350 mm. For the
groove of the 87.58 elbow with a diameter of Ø50 mm, however, such a two-stage
design is not workable because the diameter of the moulded part is too small to
provide enough space for segments to collapse in two stages. In light of this, we
propose a modified design; that is, an additional stage is added to the original two-
stage system. In this modified design, two different patterns of segments are designed
in different lengths.
The operating sequence of this three-stage collapsible core is illustrated in
figure 13. At the starting position, the two different patterns of segments are placed
one after another. This is the moulding position of the core. A bush is used to
support segments and keep them in position during the injection process. When
the injection process is over and the moulded part has solidified, the bush starts to withdraw (step 1). A spring force causes the set of small segments to collapse at the
moment the bush leaves the inner surface of the segments. This is the first stage of
collapse (step 2). Coinciding with the collapse of small segments, the spring force
on the large segments starts to collapse as well. Due to the small diameter of the
groove undercut, there is no enough space for the set of large segment to collapse
and clear the undercut. To solve this, we use a method that lets both the set of
small segments and the bush withdraw further (step 3). This clears more space for
the set of large segments to retract inwards and thus to clear the undercut for demould-
ing (step 4). This is the additional movement added to the original two-stage mechan-
ism. Reverse procedures take place when the bush is return to the original position for
the next moulding cycle.
4.5. Interference check
The interference for the segments of the collapsible core was checked using Pro/
Engineer software. Within the software environment, all parts are modelled together
with assembly relations among them. A trial and error method is used to find out all
related dimensions and the interference. The software enables interactive changing of
the input values of variables until there is no interference between related parts. For
example, the angle at the interface between two segments is found interactively
through a few runs of trial and error until the retraction of the segments can be satisfac-
tory. Using the commands available in the software (e.g. the ‘Model Analysis’ function),
the interference between segments and the moulded part during retraction can also
be checked interactively. The segments are modelled and assembled together in the
assembly mode. Then the segments of the core are interrelated using relations and set
parameters for user input. This helps simplify the whole trial and error process.
Figure 14 shows the interference result calculated by the software, in which all
intersecting parts are listed. The volume of each intersection is also shown. Three- 4.6. Housing and moving mechanism
Plates and holders for mounting the spring and the pivot of the segments need to be
designed at this stage. Accordingly, the actuating mechanism used for creating the
operating sequence of the collapsible core can be detailed. A cut-away section of
the holder in three-dimensional views is shown in figure 15. The small segments of
the collapsible core are pivoted by a pin and secured in their respective holders.
Slots enable the mounting of springs to retract the segments. The large segments 硬质聚氯乙烯管接头模具设计英文文献和中文翻译(7):http://www.751com.cn/fanyi/lunwen_18127.html