Electrochemical Machining
electrochemical machining
The electrochemical machining (ECM) process electrochemically dissolves material -- "reverse electroplating" -- until only the desired shape remains.
A RepRap has the potential to make its own circuit boards by equipping it with an electrochemical printed circuit board head. With this ElectrochemicalMillingDrillingHead, it could mill a copper clad board. With this tool head, the tool head is the cathode, with a negative voltage, and the copper board is the positive anode. The workpiece is immersed in an electrolyte and the filtered electrolyte flows through or around the tool head. This is one of several Automated Circuitry Making ways for the RepRap project to produce its own circuit boards.
There is a thread on mentioning electrochemical board milling at:
http://blog.reprap.org/2006/11/universal-pcb-test.html
From that thread, Adrian mentioned that:
The Reprappers had an alternative idea: put a (bunch of) electrode(s) in a RepRap head and use electrochemical machining to make the PCB. Best electrolyte, according to my colleague Tony Mileham who's a world authority, would be sodium chlorate. Bit dodgy as it's
1. Horribly Poisonous, and
2. A fierce oxidsing agent...
Vik mentioned:
I'm,er, familiar with sodium chlorate. I've been accidentally poisoned by it and to be honest it wasn't a big deal. I wasn't even really sick after accidentally consuming a teaspoonful or so of the stuff. Wouldn't recommend it though, even if the LD50 is a few hundred grams (1200mg/kg in rabbits,apparently).
I must say, it's very easy to produce though. Fire 12V into salty water through a couple of old carbon battery rods and there she is.
The proximity of clorates and finely divided long-chain ketones would be a problem, however.
-- Main.EnriquePerez - 04 Dec 2008
Is it possible to make PCBs using electrochemical machining (ECM)? With this method, you move the tool head over the isolation gaps near (but not touching) the copper clad board, immersed in a shallow pan of saltwater. A positive voltage wired to the copper clad board and a negative voltage wired to the tool head drives a current through the saltwater that dissolves the workpiece near the tool head.
Perhaps: Use the extruder board's current-limited stepper motor driver to, instead, drive a constant current.
Perhaps: use the thermistor ADC to, instead, measure the analog voltage from the PCB (positive) to the stiff wire tool head (negative).
- wire touching PCB gives zero volts: too close, drive the Z axis to pull the wire away from the PCB
- wire far from the PCB gives high voltage: too far away, drive the Z axis to push the wire closer to the PCB.
(Once an isolation gap is cut completely around a region, it's impossible to ECM inside that region. How to avoid painting yourself into a corner?) (Is it possible to use the ECM tip as a probe to detect holes already drilled in the PCB, and semi-automatically compensate for any small misalignment to make perfectly centered pads and fan-out traces?)
"Carve Steel with Saltwater, Electricity and a Tin Earring (Popsci)"
electric discharge machining
The electric discharge machining (EDM) process cuts away material using dielectric breakdown (sparks) until only the desired shape remains.
Forrest Higgs is considering "Going for an EDM toolhead"[1]
Wikipedia: electric discharge machining
ECM vs EDM
The equipment for EDM milling appears similar to the equipment for ECM milling -- a high-power electric power supply, a submersed block of raw material in a water-tight tray, and a tool head focusing the electric current on the unwanted material to be eroded away. Both systems are non-contact -- the machine maintains a small but nonzero gap between the tool and the workpiece. (And therefore puts much less stress on the positioning system than mechanical milling). Both system require electrically conductive raw material.
The differences are less obvious: ECM requires a conductive fluid (typically salt water), while EDM requires non-conductive fluid (typically oil). ECM requires the tool head to have a negative voltage, while EDM works with positive, negative, or AC voltage. ECM has no tool head wear, while EDM has heavy tool head erosion. ECM pulls a more or less continuous current from the power supply, while EDM pulls a pulse of current for each spark.
