Crimping using pulsed power

[MRMILSTAR]

I was playing around with my pulsed power machine a few days ago and decided to try something different. I took a 2 inch long piece of 0.875 inch diameter copper pipe and did a shrinking experiment. I placed the piece inside a 12-turn 12 AWG work coil and hit it with 7000 Joules. The result was an almost-perfect hourglass pinch. The work coil wasn't wound tightly against the pipe so I could have done the same thing with less energy with a tighter coil (better coupling) but I already had a few of these spare work coils made for quarter shrinking laying around.

This technique is actually used in industry where one piece has to be crimped on to another piece. Supposedly this method produces a better more uniform crimp than can be accomplished mechanically.

[davekni]

Steve,

Nice crimping demo!  I'd done the same thing with my 3kV setup, but I think your pipe piece came out a bit more uniform.  Perhaps it helps to have some spacing.  I also crimped one onto a wood dowel. 

[klugesmith]

Very nice.  Does the work coil get damaged?  Is it mechanically reinforced on the outside?

Long ago I thought of making very durable work coils in the style of flexible shaft couplings:
thick bushing with helical saw slot.

[johnf]

Kludge
Woundnt you need to put some mica in the slots as the coil would compress Yes /No ?

[MRMILSTAR]

The work coil is completely sacrificial. Being sacrificial is actually good for the capacitor because the work coil disintegrates before any voltage reversals occur.  I had considered the idea of machining a heavy-duty G10 containment structure for the work coil just to hold it together a little longer to allow more work shrinkage.

I wonder what the re-usable work coil for the commercial pulse power crimpers looks like?

[klugesmith]

I agree with John's point that the saw kerf (in shaft coupler) would tend to close up, and should be stuffed with insulator.
We might jokingly call the phenomenon magnetostriction.

Durable work coils might be a good application for copper alloys with high strength, in spite of electrical conductivity far below IACS.  I think they use something like that in world class resistive Bitter electromagnets, the kind that can continuously dissipate many kilowatts per cubic centimeter.

[MRMILSTAR]

Doing this little experiment made me think of the huge problems encountered during the WW2 plutonium bomb development. They had to determine a way to use explosives rather than magnetic fields to compress a plutonium core with practically perfect spherical symmetry. Its sort of a similar problem as crushing this copper cylinder with perfect symmetry minus one dimension, except that I didn't achieve perfect cylindrical symmetry by any means.

[davekni]

I think Maxwell Magniform is the only company making magnetic forming machines commercially.  I heard somewhere that some of their coils us solid copper wire with a triangular cross-section, cast in epoxy.

Their most fascinating machines were made for Boeing, for taking dents out of airplane skins from the outside.  More complex control to get an attractive impulse!  Current needs to ramp up slowly, then suddenly drop in half.