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Hercules28 (Materials)
16 Feb 12 11:14
Hi,

Does anybody know of Bulge forming for metals?
Essentialy you have an outer die and you put your tube inside. Inside the tube you put a rubber bladder and pressurize it. The bladder forces the metal tube to get the shape of the outer dies.

Is there something similar for plastic? let's say forming elbows or other pipe shapes?

Regards,

Herc
Hercules28 (Materials)
16 Feb 12 11:14
Actually I am looking to make elbows so just bulge forming won't do. Is there a combination of bulge and Injection?
ornerynorsk (Industrial)
16 Feb 12 11:31
Check out tube hydroforming.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

MacGyverS2000 (Electrical)
16 Feb 12 11:31
If you're injection molding, any reason why the standard faire won't work?  If I can get a dozen PVC elbows for $10 at the local Borg, well, that should tell you how economical it can be.

Dan - Owner
http://www.Hi-TecDesigns.com

Hercules28 (Materials)
16 Feb 12 11:34
Regular injection molding limits you to the length of the elbow.
If I would like to design a long radius...? then how would I do it?
Hercules28 (Materials)
16 Feb 12 11:37
ornerynorsk, any companies to recommend?
Pud (Mechanical)
16 Feb 12 12:33
If it's a constant rad, not too many degrees, you made be able to withdraw a curved core. Think of those tubes they stick down your throat in ER!

Alternatively, use a lost metal process. This used to be used (may still be) to make automotive inlet manifolds.

H

www.tynevalleyplastics.co.uk

Why be happy when you can be normal?

ornerynorsk (Industrial)
16 Feb 12 13:51
I've never actually had a part commissioned in tube hydroforming, so I cannot make a specific recommendation.

A quick query of google yielded 200,000 + hits.  If you're in the US, I'd personally start with ThomasNet.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

patprimmer (Publican)
16 Feb 12 19:20
Plastics won't normally hydroform like metals, but I'm not saying it can't be done at all.

The bag or tube is not used. The process is called blow moulding. Billions of bottles are made from the process every year.

As Pud says, curved cores can be used within limits and this is used for pipe fittings with an inside rad on the elbow.

Lost core can also be used. Typically a bismuth tin alloy with a melting point a bit below the softening point for the polymer. This is expensive as you need to cast the cores first and they are use once only. The bismuth tin is very expensive and there are always some losses in reclaiming. There are also toxicological and EPA issues, but it still make a better manifold than a welded together one. I have heard of people experimenting with ice cores. Precision was an issue as was handling and time and mould temperatures and flow lengths with glass filled nylon 6.6 at least.

Rotational moulding can also be used for hollow parts. It is often used for very large parts due to the much lower tooling and machine costs.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
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ornerynorsk (Industrial)
17 Feb 12 11:09
Hercules28, could you clarify ~ are you wishing to make plastic or metal parts?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

Hercules28 (Materials)
16 Mar 12 11:21
Plastic parts
Richar24 (Industrial)
19 Mar 12 4:20
Hello Hercules

Yes a process that may work for you of injection blow molding assuming the wall sections do not have very tight tolerances.

With air injection molding and water inject assisted molding, you fill the mold part way by injecting plastic in the mold, then an air or water valve opens in the mold forcing the plastic to continue to fill the mold and creating a hollow part. This is how they do the air duct work in automobiles, etc.

Not a lot of people doing this, using this process you do not have to deal with retracting out the core. But the ends will need to be cut off. Part with bulges in the middle of the part can be produced that can't be produced with convention injection molding.

Hope this helps
 

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