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Min wire cut radius size.

CarbideBob

Diamond
Joined
Jan 14, 2007
Location
Flushing/Flint, Michigan
Sooo, I don't do wire and job it out.
Help educate me. My sources are running away like chicken little.
Internal corners 90 and more with a max of .003 inch.
Carbide, .1875 thick and some different rake angles in the cut. (think multi-tooth groover 11 front plus the extra 2 on the sides of the teeth)

Everyone talks about over burn when holding this so wire size is teeny.
And then that small wires have a very limited current (which is in the duh, makes sense).
How much slower in such an application do you have to run against say a .010 radius?

At this size is this like micro-machining where all the rules change?

I can grind this with some effort but with many tips across a profile it seems a wire would be easier .
Bob
 
Depending on current settings and wire size, wire overburn can be under 5 tenths to over 2 thou. I use a rule of thumb for 10 wire of about 1.2 thou, at that the min radius is around .006.
 
Hi Carbide Bob:
I've screwed around a fair bit with making form cutters on the wire EDM and I've become disenchanted with all of what it takes to try to make the kind of shape you're talking about.
Here's why:
When you cut a vee notch into the sides of a milling cutter (I presume that's what you're describing) you have an increasingly difficult problem as the root radius approaches the wire radius, and that's the risk of gouging in the root.

It happens because that's the transition where the wire has to go from your 2 degree side clearance to whatever front clearance you need to accommodate the diameter of the cutter which of course gets more and more acute as the diameter of the cutter gets smaller.
(For those of you who can't quite picture it, imagine a parallel sided cutter with zero rake.
As the cutter gets smaller and smaller you need to increase the front clearance more and more or make the land skinnier and skinnier to avoid heeling with the cutter unless you can put secondary relief on it which of course is why endmills are ground with secondary relief as well as primary relief.)

This transition from side clearance to end clearance forces the wire to describe a complicated conic path with continuously changing taper; from 2 degrees to perhaps 10 degrees back to 2 degrees.
This has to happen all while at the plane at which the cutting edge sits, the wire cannot describe much if any arc but essentially must pivot in place if the radius of the cut is close to the radius of the wire.
That's hard to do.
It's doubly hard to do with fine wire.
It's triply hard to do with big taper angles and continuously changing taper angles.
So it becomes a God forsaken shit miserable job that's impossible to control.

A tiny wire flutter and the geometry is toast.
Ditto if you get an error in the taper angle; even a small one will move the transition point where the wire is pivoting in place out of the cutting edge plane and you're hooped again.
On every modern wire that I'm aware of the upper head moves out of alignment relative to the lower in order to cut tapers but the guides stay vertical, so the wire has to bend around the donut shaped wire guides making the determination of the actual taper complex.
It depends on the hardness of the wire, as well as the wire tension; with fine wire you don't get to play with these at all.

The very best machines ever devised for this sort of work are obsolete now; these are the old tilting head Agies, and they could do amazing taper cuts because they didn't bend the wire in this way; they tilted the guides and the flush cups so they were always pointing perfectly toward one another as the upper head was displaced relative to the lower.
So you knew to a much higher level of confidence where the wire was relative to the plane at which you defined the taper.

Too bad precisionmetal doesn't run his own wire anymore...he had the PERFECT machine to do work like this with confidence (a 170 HSS I believe) and he also has the skills to take it on and deliver what you want.
You'd need to find someone like him: I don't know how many really good tilt head Agie drivers there are anymore, but probably not many.
Maybe Larry McNamee from EDM Network can point you to someone.
He's the premier guy in North America for fixing this vintage of Agie so if anybody knows of someone, he'd probably be your man.

Ultimately though, I think you're probably going to have to bite the bitter pill and figure out how to grind it.
Good thing is you'll get a WAY better cutter when you're done; I've become disappointed with the longevity of carbide cutters made on a conventional water dielectric wire EDM because of the cobalt leaching.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 








 
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