How a wire EDM works?

[ali_asadzadeh]

Hi,
I wanted to know the principle behind a wire edm and how they are working? do we have any open source projects for them? I can not understand the wiki

https://en.wikipedia.org/wiki/Electrical_discharge_machining

[Seekonk]

The short course.  EDM only cares about the melting point of a metal and how well it conducts heat.  Copper is very hard to EDM.  In an arc the two end points are the hottest, not so much the plasma which is low resistance.  So, little chunks of metal blow off. The electrode can wear as much as the work piece.  A moving wire always gives a new surface. The cut rate speed is determined by the arc voltage, increasing distance is higher voltage.

[ali_asadzadeh]

Thanks, then is there any kind of waveform that we should make? what are the voltages and Currents? is there any open source projects?

[Seekonk]

The circuits are quite simple.  Usually around a 60-90V supply is used with just a FET with
resistor limiting the current. Resistors can be switched in, but usually a 1,2,4,8 binary
with a FET for each resistor. The range of 1-10K generated by a SG3524 or similar switching
regulator to give frequency and duty cycle. A 150V low current pulsed same as the main high
current supply is sometimes used to help initiate the arc.Sinker machines use a kerosene
like oil for the dielectric and wire machines use water. High duty cycles and low frequencies
give a rougher finish.  Distance control is critical. In sinker machines hydraulics work best
for precise movement. All rather simple till you want to do real precision.  Then it is experience
and art in selecting electrode material, speed, currents,frequency and duty cycle. There
ought to be circuits online. Used machines for cheap are plentiful here. Mechanicals are the
toughest to build. Some good articles that can be sourced online of this magazines archive.

http://www.edmtodaymagazine.com

[ali_asadzadeh]

Dear Seekonk thanks for sharing, is there a simple block diagram or a circuit? I do not get it fully yet.
what do you mean by

The range of 1-10K generated by a SG3524 or similar switching
regulator to give frequency and duty cycle.  150V low current pulsed same as the main high
current supply is sometimes used to help initiate the arc.

[DTJ]

About 15 years ago (I think) the "Model Engineers Workshop" magazine had a construction article on a EDM machine.

From memory it was a simple transformer / rectifier / capacitor power supply and used a stepper motor to advance the electrode.
Perhaps some searching would turn up  a scan of the old article or the magazine publishers may sell back issues or scans to you.


This is the magazine:
http://www.model-engineer.co.uk/


EDIT: Some interesting links


http://homebuiltedm.tripod.com/

http://mikesworkshop.weebly.com/a-spark-erosion-apparatus-mk-3.html

https://groups.yahoo.com/neo/groups/EDMHomeBuilders/info

http://www.homebuiltedmmachines.com/

[Seekonk]

I'm sorry, but I do not draw schematics just for anyone that asks. The information
provided is clear enough to follow. I would add that if a servo motor is used for
die sinking that the traveling head be counterbalanced with a weight so the speed
down is not faster than the speed up. I'm confused at this change to sinkers when
wire EDM was first mentioned.  Wire EDM is expensive to operate because it uses enormous
amounts of wire that can not be reused. Building such a machine is a difficult endeavor
because of mechanical and CNC drive issues. A small sinker machine is fun. I admit that
what I have seen on the internet has not impressed me. If you care to submit a drawing
or direct me to one you have found on the internet, I will evaluate it.

[Conrad Hoffman]

I think http://www.homeshopmachinist.net/ had a multi-part article on building a diy edm a couple years ago.

[Seekonk]

For a pulse supply circuit that is relatively simple to build, I almost defy anyone to come up with a schematic from a google search of EDM without having to pay.