High Energy Metal Forming

https://apps.dtic.mil/dtic/tr/fulltext/u2/681248.pdf

I believe this technique is also used for making large rocket nozzles.

When I first read about it in high school, that was what was mentioned.

We've used a related method. called electromagnetic forming, for 22 years to magnetically "shrink" coins as a novelty. An ultrastrong pulsed magnetic field is created by discharging a high voltage capacitor through an expendable coil. The coin is centered inside the single-layer magnet wire work coil. The process must be done inside a blast shield since deadly coil fragments are ejected at supersonic velocities as the coil explodes. Following are images of a clad Kennedy Half-Dollar as its being shrunk and the results.

Interestingly, US clad coins are themselves made from sheets of explosively-bonded cupro-nickel alloy on either side of a sheet of copper using high explosives. The process creates a molten metal jet at the contact point that creates an interlocking weld between the outer and inner sheets that is stronger than the parent materials.

I didn’t know that’s how they bonded the coin... thanks...

reminds my of high speed tooling inserts that hold the cutter bits,... when you exchange tools insert on a high speed CNC machine spindle, you always wipe out the the spindle insert on the machine and the tool holder,... if you don’t, the dust dust that might be there dust will creat a high speed vibration and micro weld the tool ibetween the spindle and the tool holder that’s called fretting (page three). It can be tough getting these apart,... and what happens the fretting gets passed on to other tool holder, that pass is them on other spindles.

on another note about coins...

My fabricators used to put pennies in my 300 lb break press with flattening dies and flatten them... (I wonder what else they did...

Growing up, had a friend in Chicago, they used to put the on the railroad tracks for similar effects.

One application where electromagnetic forming is used is on wire strainers and filter screens. A pulse coil is used against the face of the flat screen and the pulse blows the screen away from the coil into a forming die.

That would be similar to a sintering for a filter/strainer.

Not really. Sintering is where a loose media of metal particles are compressed and then heated in a controlled atmosphere so that the loose particles stick together in a solid part.

Electroforming of a screen involves taking a flat piece of screen, placing it over a forming cavity and then using a high energy, short duration magnetic field to press the screen into and against the form cavity. The starting screen remains screen, but in a different shape.

I'm more familiar with superplastic forming of titanium. If you tried the explosive forming with titanium, it would just shatter. Instead, the titanium is heated in a vacuum furnace to a very specific temperature not too far below the melting point, then low pressure (a few psi) argon slowly inflates it into the mold over a period of a significant fraction of an hour.

That’s the problem with the physical metallurgical property’s with the more ‘exotic’ metals. For strength or hardness, you’ll compromise with say fracturability. Titanium wouldn't be a good candidate for explosive forming...

This method is used to bond super hard wearing metals to more weldable material to make bulldozer blades. Also used to make material for wear plates.

I have been told that after the forming the two materials are only slightly thicker than the parent metal. I saw a demonstration of this process on a small scale once from a long way away. the hard metal was coated with the HE and then detonated. I was suitably impressed but not as impressed as the two metals were.

That’s a great example.
I had only heard of joining dissimilar sheet metals together and forming into a single cavity die.

You’d want to be sure not to overdo the charge.

When I worked at in the shipyard,... weight played a huge factor in ships, either designing or retrofitting.

there was a time, were we wanted to mount a pilot house made ot of aluminum to a steel deck,... it couldn’t be bolted,... so there were a number of tests made for the ‘bonding’.

I’m not sure how they did it, but there was a aluminum/steel coupon that was floating around engineering, about 3” x 3” x 3”... of which 1-1/2” was aluminum, and the same with steel.

when you picked up the coupon, with half being aluminum, and the other half being steel, it felt like you were holding a running gyroscope.