Re: hydroforming : was water spark gaps

["Tesla list" <tesla-at-xxxxxxxxxx>]

Original poster: "Jim Lux" <jimlux-at-jpl.nasa.gov> 

spark hydroforming is very practical.  As Terry points out, explosives are
also used.

The advantage of explosives is higher energy density... getting 50 kJ out
of some high explosive is easy (typical: 50 kJ/gram).. getting 50 kJ out of
an energy storage cap is a bit bulkier.  However, in a production
environment, the electrical approach is much easier: all you buy is
electricity (and replacement caps periodically), and you don't have the
byzantine laws and regulations surrounding the purchase, storage, and use
of explosives.  By the way, I haven't tried it, but I suspect that low
explosives (like black powder) wouldn't work too well. All the explosive
hydroforming I've done has been with real stuff (PETN in the form of
detonating cord) which has a very high detonation velocity.

Before you embark on electrical hydroforming, it's a good idea to get an
feel for how much energy you're going to need to do your forming.  10 kJ is
like dropping a 1 ton weight 1 meter... Your spark gap is going to
essentially radiate the energy in a sphere, so much of the shock wave won't
intercept your work piece.

However, it is interesting and fun to try...  There are books on this
available, as well.

----------
> From: Tesla list <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: hydroforming : was water spark gaps
> Date: Friday, December 01, 2000 5:32 PM
> 
> Original poster: "bob golding" <yubba-at-clara-dot-net> 
> 
> 
> 
> Tesla list wrote:
> > 
> > Original poster: "Ed Phillips" <evp-at-pacbell-dot-net>
> 
> .  I used to wander down the line for amusement, and
> > remember one of the machines they used for forming fairly large
aluminum
> > panels.  It was a tank of water with a female cavity in the bottom. A
> > sheet of aluminum was placed over the cavity, and a great big capacitor
> > bank discharged into a spark gap in the water.  This created a pressure
> > wave which then forced the aluminum into the die.  Think the process is
> > called hydroforming, but that may be a generic name.
> 
> Hi all,
> 	Ok guys and girls, who will be the first to produce an hydroformed
> toroid. It sounds like it might be easier than spinning. Get a big piece
> of steel pipe bent into shape, chop it in half, weld to the bottom of a
> tank, place aluminium sheet in bottom of tank, fill with water, insert
> spark gap, cover and stand clear, throw switch. BANG!! one half toriod,
> maybe... Anyone fill us in on the details, or let me know off list if
> Terry thinks it is getting off topic*.
> 
> cheers
> bob golding
> 
> >>*perfectly on-topic and above the completely impractical cutoff.  I
think
> conventional explosives my be more practical than a spark gap thing. 
There
> are a few explosive experts on the list... - Terry<< 
> 
>