Re: Wire ECM for the home shop

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler" <eexgs@...>
wrote:

>
>
> This is a bit of a brain fart so appologies.
>
> Firstly note the C, this is electroCHEMICAL machining I am refering

to.

>
> The basic concept is metal forming by the un-electroplating of the
> workpiece. It is fast compared to EDM has less complex control and
> can, like EDM, machine hard materials. It is however isotropic not
> "closest point first" so the gap between electrode and workpiece must
> me small to ensure a high current density and low side cutting. The
> electrolyte can range from salt water to weird acids. Unlike EDM the
> electrode is NOT eroded!
>
> As some may know I am working on a micro wire EDM machine and I have
> been playing with a RC supply based on Ben Flemming's book. I am
> setting myself up to do some single axis wire EDM to assess the needs
> of the supply and the cutting speed etc. It got me thinking that a
> simple supply of that sort might also be used for ECM, and then I
> started to wonder about wire-ECM.
>
> I have never seen or heard of a wire ECM, I can think of many reasons
> why. Even if you can insulate the rear 180 degrees of the electrode
> and rotate it to follow the cutting vector it will cut sideways. If
> the material thickness varies, the gap control becomes more complex,
> it must be measured. So for precision, wire EDM wins hands down.
>
> what about general profiling? Well water jet obviously or laser.
> What about at home? Well there is plasma for steel and a CNC mill or
> router for aluminium a cnc router.......
>
> So here is my idea, build a simple wire ECM machine for doing basic
> cutting jobs in sheet metal from steel a few mm thick to alumnium an
> inch thick.
>
> The concept, you need a tank in which the work can be positioned.
> Unlike wire EDM the wire is not eroded, therefore it does not need to
> be a moving wire system. If stainless wire is used there will be
> little plating of the wire and it should be quite strong. Control is
> via the current, we assume a sheet material so that the thickness
> should remain the same roughly and current control should work, so you
> do some experients in test pieces. You set up mach for constant
> velocity and a slow feedate, the wire advances, if the current goes up
> too much you pause mach until it drops, if the current gets too low
> you tweak the feedrate (perhaps do that with the modbus stuff). If
> the kerf is too big you increase the current.
>
> Another important design feature is that the wire should be insulated
> above and below the work. If the lower wire holder is of fixed height
> then it can protrude through a insulating block. The upper wire could
> have a block of insulating material that slides up and down it and
> sits on the work piece.
>
> so that's the idea, burr free wire style cutting of sheet metals at

home.

>
> Power supply BTW should be about 15v and whatever current you think
> you need, for a thin wire not all that thick. I'll try and find out
> what the cutting speed might be.
>
> worth a play, it will all depend on that speed and cut quality!
>
> Graham

I looked at your site, but have questions about how you did some of
the stuff.

Can one just put a unit together much like a home brew EDM and monitor
the current to hold the proper cutting distance without a short ?

I'm thinking of making lathe tools.

I'm thinking that one could make an inside threading tool or boring
bar with all the proper relief, and no grinding and get a better
finish than if one hand ground.

Filter ? can one just use a car engine oil filter ? gas filter ? I
already know that a Mr. Coffee filter will clog quickly under gravity
when used on EDM stuff.

Also, you mentioned coating the electrode to reduce unwanted etching.
What about painting the part ? seems a layer of DyKem might prevent
some of the excess etching.

Is the feed generally the same as EDM ? on my EDM, I have a very
rapid response or pecking.

How much etching occurs at greater distances ?

If you are doing a deep hole, could (would) one use something like a
glass tube with a flat head screw, so the flat head was wider than the
tube to allow for clearances when cutting ?

Is the surface effected ? I was thinking about making shaped lathe
tools, but if the surface requires a post process re-grind, the idea
looses some of it's appeal for that use.

Dave



Dave