Using electrochemical machining, steel can be molded with a soft, cheap piece of tin without any physical contact
Posted 08.06.2009 at 9:16 am
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The tin peace-sign earring acts as an electrode, etching away the metal in the hardened steel washer [left]. The imperfect results are due to the difficulty of manually maintaining an exact thousandths-of-an-inch distance between the two. Commercial electrochemically machined pieces, like this microturbine for a water pump, use sophisticated electronics to monitor the current flow and carve precise pieces [right]
Courtesy ECM Technologies BV/ ECM Productions BV; Mike Walker
I remember seeing a demonstration of a seemingly magic process at an engineering open house decades ago, in which a soft metal bit carved detailed shapes into far harder metals. It's called electrochemical machining (ECM), and it's so simple in principle that you can do it at home with a drill press, a battery charger and a pump for a garden fountain.
ECM is basically electroplating in reverse. In electroplating, you start with a solution of dissolved metal ions and run an electric current through the liquid between a positive electrode and the object you want to plate (the negative side). The ions deposit themselves as solid metal onto the surface of the object.
Etching Apparatus: Clamps from a battery charger run about 10 amps between an electrode and the metal being machined. The flowing saltwater acts as a conductor. The drill press simply moves the electrode Mike Walker
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DIY, Gray Matter, Theodore Gray, diy projects, electrodes, electroplating, gray matter, How 2.0, july 2009, Theodore GrayThis process is used industrially to create extremely delicate, detailed shapes in very hard metals. Since there is zero force exerted on the part being machined, it's possible to make fine shapes that would break if you tried to cut them with a milling machine.
Without the precise current control of those commercial systems, my home setup produced a disappointingly blurry copy of the earring's shape. But it's still amazing that in a contest between a tin earring and hardened steel, the earring won.
See our gallery of electrochemically machined parts
Achtung! When your hands are wet with saltwater, even 12 volts is potentially dangerous. Wear rubber gloves.
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How does this differ from EDM? Popular Science had a project for a home EDM machine back in the 60's.
EDM and ECM both use Electricity to machine metal.
EDM = Electric Displacement Machining,
ECM = ElectroChemical Machining.
The difference comes in how they are applied. ECM Means that you will have a pattern that is not conductive and the part being "Machined" is in electrical conductive solution and the current etches the design. EDM's typically use a wire or a steel wheel that the electrical conductive solution flows over. By moving the wire or wheel the solution forms the shape and cuts it out of the material. My dad operates a Wheel EDM to cut Stainless Tubing into sharp points without burrs.
This is an interesting demo, but without a mechanism to better control the movement of the "cutter" it is pretty useless, except for making blurry blobby indentations.
I am sure there is an increase in electrical current before it actually starts arcing, so using that increase to control a servo driving a screw drive would seem to be fairly simple compared to making your own cnc milling machine.
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The examples in the gallery seem to be of extremely fine and high quality. I guess this method also means that the metal has not received any stresses in the machining process.
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I read recently of a well known gun engraver using only sharpened concrete nails for the basic outlining on his engravings. Also, the usual engraving chisel shape is not round, but square, with one corner making the v-shaped cut. I suggest annealing your steel thoroughly before engraving it. I used the diamond-abrasive burr for the final smoothing and finishing.
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Well, Without the precise current control of those commercial systems, my home setup produced a disappointingly blurry copy of the earring's shape. But it's still amazing that in a contest between a tin earring and hardened steel, the earring won.
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