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.


> 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
> >> 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
> >in
> >> the exact center of the explosives.  The shock wave travels out from
> >> center to the edges.  The metal is blasted into the hole and it will
> >> the shape of the hole.  It really works.  The metal thickness has to
> >> calculated so not to blast a hole in it.
> >
> >Of course, digging the hole is the easy part. Actually, this sort of
> >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 
> >stunning amount of regulation. You need a permit from the ATF to
> >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"
> >the application form: you get to choose mining, excavation, or seismic
> >work. Finally, the local fire department will look somewhat askance at
> >activities, not to mention the problems with storage, since most
> >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.
> >regulations are much looser there. 
> >
> >Actually, a few phone calls to the local explosives dealers found me a
> >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
> >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
> >do spinnings for very small quantities and simple axially symmetric
> >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
> >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
> >chosen properly, and if you do a little hammer work on the pieces ahead
> >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
> >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
> 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
> a piece of thich steel in the lathe instead of diging a hole in the
> because my shape is not very large like a toriod.  I laid the sheet metal
> the piece of steel and put a thin layer of jellmax over the top of the
> with a blasting cap in the center.  It worked the 1st shot but not
> 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
> the dish shaped sheet metal.  I made a few more and found that lower
> explosives like dynamite would work fine also.  Hell with taking classes
> learn how to do this or getting permits.  A few hours of practice and I
> 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
> This same method might work fine for making toroids.
> Gary Weaver