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a_knecht
15th September 2013, 01:58 PM
Hello Everybody,

I'm new in this forum, and I need your hep with this VERY big and difficult part, to be moulded in one piece.

Do you have any idea on how to build the tool for the inner part ??

Thanks in advance for you help,

A_knecht

pjhall
15th September 2013, 07:43 PM
A collapsible Core would be the only way.

http://www.youtube.com/watch?v=rfxpD1rlZ90

Suhas
16th September 2013, 04:13 PM
Agreed with PJ. If you can make it in two parts and assemble them, that will also work. But you will not get a smooth surface.
Suhas

a_knecht
16th September 2013, 07:29 PM
Thanks for your help. Of course in two parts moulding would be very easy, but this is not possible. Do you think collapsible core can be feasible with such dimensions (diameter 800 mm) ?

pjhall
17th September 2013, 03:48 AM
Not sure about the size...that's BIG. I did a project way back in my U-mass Lowell days about "lost core molding". Freudenberg in New Hampshire was making nylon intake manifolds and the core would dissolve when immersed in glycol. They would then get the core material out of the glycol, remold the core and insert it and REPEAT. Obviously, this will not work for you application, but there are methods out there.

rickbatey
17th September 2013, 05:36 PM
One question not asked is what resin? I remember working in a shop years ago that ran PS parts in a three plate mold. The parts were popped off threads on the B-side with a stripper plate as the mold opened. They ran fine, so might yours depending in resin and tolerances

Rick.

a_knecht
17th September 2013, 07:43 PM
you are right, rick. it is polyurethane. probably we will use a compact formulation, with no expansion during polymerization, to avoid as much as possible leakage inside the core system during injection.
and that's also the problem with the collapsible system: the sealing has to be done perfectly, because as you know material is injected in liquid form.

Team JAG
18th September 2013, 12:54 PM
Some parts can be stripped off of undercuts provided that the part is free on the cavity side to flex outwards. Ofcourse, this depends on the amount of undercut, molding material, process conditions etc. Its hard to tell from the pictures but as far as I can see a stripper ring would not pass by the core upon ejection since the part has an "outward bulge".

Collabsible cores are a likely option although I'm not certain about issues with the resin you plan to mold it out of. I have done alot of lifters and collapsing cores in the past when working in design at a mold making company. You should contact a local tool shop and they should be able to guide you in the right direction.