Electrochemical machining cuts almost any metal, has reasonably high material removal rates, has no side loading or heat affected zone, and permits cutting fairly free-form parts in 3-D, much like CNC milling. But in its ordinary form it can’t cut parts with complex internal spaces, and in a pure 3-axis form it can’t even cut overhangs.
Watching demo videos of ZURAD Engineering’s ECM jet-cutting machines, though, it occurred to me that we can go further still. If we use ECM cut layers of the 3-D shape we want, then stack them up, we should be able to get not only much freer-form shapes, but also effectively a higher material removal rate, since we only need to remove a perimeter of stock around the shape of each layer, while if we were cutting the same part out of a solid block of stock, we’d have to remove all the material all the way to the surface of the stock.
There are many possible ways to manage the layer stackup, but locator pins for alignment and thin plastic backing for each layer seem like one straightforward option; the pins can instead be replaced with thin strips that are cut out with ECM in the same way.. The plastic backing can be burned away after the layers are stacked up.
After roughing out the shape in layers this way and stacking them up, you can do the final precision shaping work with ECM on the stacked-up part.
ZURAD’s soon-to-be-open-source ZURAD Two EC Jet Cutter evidently cuts 1mm-thick sheet steel with a gentle stream of water with 100 grams of NaCl per liter of water (or was it 200?), with the metal nozzle about 2.5 mm away from the steel. For some reason he positions the sheet steel horizontally instead of vertically. The video looks like it cuts at about 2mm/sec, but at one point the guy holds up a part (“a simple mechanical pawl”) with a perimeter of about 100mm, and says it took an hour and a half to cut completely through, so maybe it took 50 passes. I have no idea what current or voltage he’s seeing; on his die-sink ECM machine he uses 12 volts.