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Re: explosive hydroforming for toroids and spheres
From: D.C. Cox[SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent: Thursday, December 04, 1997 5:09 PM
To: Tesla List
Subject: Re: explosive hydroforming for toroids and spheres
to: Gary
Another method similar to explosive hydroforming but without the hassle of
explosives, permits, regulations, etc, is to discharge a large energy
storage capacitor in which the tungsten discharge terminals are placed in a
pan of water. An ignitron is usually used as the switch and the values of
the cap would be around 20 MFD at 10-15 KV DC. The shock wave is very
similar to an explosive shockwave and the forming is completely repeatable
in a relatively short time span.
DR.RESONANCE-at-next-wave-dot-net
----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-poodle.pupman-dot-com>
> Subject: Re: explosive hydroforming for toroids and spheres
> Date: Wednesday, December 03, 1997 6:55 AM
>
>
> From: gweaver[SMTP:gweaver-at-earthlink-dot-net]
> Sent: Tuesday, December 02, 1997 10:39 PM
> To: Tesla List
> Subject: Re: explosive hydroforming for toroids and spheres
>
> At 12:03 AM 12/3/97 -0600, you wrote:
> >
> >From: Jim Lux[SMTP:jimlux-at-earthlink-dot-net]
> >Sent: Tuesday, December 02, 1997 10:50 AM
> >To: Tesla List
> >Subject: Re: explosive hydroforming for toroids and spheres
> >
> >
> >
> >> Explosive forming is much easier than metal spinning. Dig a dish
shaped
> >> hole in the ground. Lay a sheet of metal over the hole. Lay a 1/4"
> >thick
> >> layer of plastic explosives over the sheet of metal. Place the
detonator
> >in
> >> the exact center of the explosives. The shock wave travels out from
the
> >> center to the edges. The metal is blasted into the hole and it will
take
> >> the shape of the hole. It really works. The metal thickness has to
be
> >> calculated so not to blast a hole in it.
> >
> >Of course, digging the hole is the easy part. Actually, this sort of
work
> >is usually done under water. The water helps transmit the shock wave and
> >also reduces the air blast. The air blast is what annoys the neighbors,
> >since you don't need much explosive for this.
> >
> >The tricky part is getting the explosives (legally) and determining the
> >amount to use. I have done some preliminary research in this area with
> >respect to the Los Angeles region and have discovered that there is
truly
> >stunning amount of regulation. You need a permit from the ATF to
purchase
> >and use the explosives. To get that, you need either a pyrotechnician
> >license or a blaster's license from the state of California. A suitable
> >pyro card will take 4 years licensed experience, and wouldn't even be
> >technically legal for this use. A blaster's license takes 3 years
> >experience, and there isn't a box to check for "manufacturing" or "R&D"
on
> >the application form: you get to choose mining, excavation, or seismic
> >work. Finally, the local fire department will look somewhat askance at
your
> >activities, not to mention the problems with storage, since most
explosives
> >dealers don't want to work in small quantities (i.e. < 50 pounds).
> >
> >Now, if you live in Nevada, or a similarly enlightened state, go to it.
The
> >regulations are much looser there.
> >
> >Actually, a few phone calls to the local explosives dealers found me a
few
> >firms that do this sort of work, have the water tanks, can do the
> >calculations, etc. There is a substantial NRE cost, but the per shot
cost
> >is very low. Explosives are quite cheap, a buck a pound in small
> >quantities, and, for this application, a pound is a lot. It is cheaper
to
> >do spinnings for very small quantities and simple axially symmetric
shapes.
> >Explosive hydroforming is more suited to complex shapes with lots of
> >detail, rather than big spheres and toroids. Imagine stamping out a
> >refrigerator door (the inside, with all the shelves) in one shot. For a
> >production run in the 100 to 10,000 pieces range it is very attractive.
> >When you start getting a lot of pieces, a conventional die and press
system
> >becomes more attractive.
> >
> >For larger shapes than can be done by spinning, why not go with internal
> >ribs and structure covered by a thin flexible outer layer. This is how
> >airplanes are built. Compound curves aren't too tough if the segments
are
> >chosen properly, and if you do a little hammer work on the pieces ahead
of
> >time to get the cross axis curvature. Any auto body guy could help here,
> >and their hourly rates aren't too high, and you can learn to do it
yourself
> >in a few months practice, particularly with aluminum, which is soft.
>
>
> In the state of TN anyone can buy explosives over the counter with out
any
> type of permit. I bought some Jellmax in 1 lb sticks which is basically
> jelly nitroglycerine for a $1.00 a lbs. I tryed making a small dish shape
> for a stirling engine project I was working on. I turned the dish shape
in
> a piece of thich steel in the lathe instead of diging a hole in the
ground
> because my shape is not very large like a toriod. I laid the sheet metal
on
> the piece of steel and put a thin layer of jellmax over the top of the
metal
> with a blasting cap in the center. It worked the 1st shot but not
perfect
> so I tried again. After several trys I layed a 1/2" thick sheet of black
> neopream rubber on top of the sheet metal then put the explosives on the
> rubber. This shot worked perfect without any inperfections of any kind
in
> the dish shaped sheet metal. I made a few more and found that lower
speed
> explosives like dynamite would work fine also. Hell with taking classes
to
> learn how to do this or getting permits. A few hours of practice and I
made
> 3 good parts and it cost me less than $20.00 for everything and I had fun
> doing it. And for ATF they can go to HELL, I have no use for those
people.
> This same method might work fine for making toroids.
>
> Gary Weaver
>
>