TABLE OF CONTENTS As mentioned previously there are two basic types of collapsible coring:
Two-segment cores
Multisegment cores
There are many applications for which a complete thread form is unnecessary. Bottle closures, for example, only use the simplest of thread forms, often consisting of partial threads.
If they cannot be made using two-plate tools (as they often can be, where perhaps a longer thread length is required), two-segment cores may be used. Figure 13.11 is a more detailed view of the two-segment core shown earlier in Figure 13.7.
Collapsible cores are like mini side core units but placed at an angle to the axis of the core. In Figure 13.11 the central core is withdrawn downward (action C) away from the moulding. As it moves it forces the two small side cores SC to move inwards (action B). This clears the cores from the moulded thread. Finally, the part is stripped off the tool face (action A).
Clearly an undercut form cannot be placed on the non-side core areas, as it would not be released when the central core withdraws.
As the name implies, multisegment collapsible cores consist of a number of segments, which are constrained to move inwards or outwards by the action of a tapered sleeve expanding and collapsing all the individual segments. This system is very similar to the two-segment system but in this the undercut thread form cut be machined...
