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Sinker electrode for Tungsten, Niobium, refractories etc

claya

Cast Iron
Joined
Aug 6, 2006
Location
california
Can someone suggest electrode options for the refractory materials? Someone recommended Copper but which copper (P ure, C110 or C145 Tellurium)?

Current projects are Tungsten and Niobium. Pure copper (C101) is wearing faster than expected.

The electrodes are VERY small 0.02" x 0.117" (Area= 0.002in-sq) and 0.02" x 0.03" (A=0.0006"in-sq). What is the max roughing amps I should use to minimize electrode wear? Test cuts with copper @15.5A are wearing more than I like. @9A the burn is too long & still have too much wear. Obvious other variables like on/off time, plunge times etc. But I suspect amperage kills electrodes the most.
 

Bud Guitrau

Aluminum
Joined
May 8, 2006
Location
SoCal
Claya,

I suggest switching to CopperTungsten using negative polarity and high-frequencies. Maybe 25µ secs ON/OFF to start, with incremental reduction in OFF-time to increase speed, depending upon flushing.

Pure copper electrodes cannot survive at the current densities you are using
(Note: the small amount of Tellurium is added to aid free-machining and does not affect EDM cutting speed).

With the accepted maximum amperage for copper electrodes to be 50A/in2, almost any setting you can select will exceed this ratio, but the tungsten (70%) within the copper matrix (30%) will "take the heat" better.

Because of CuW's lower conductivity (42-45 IACS vs. Cu at 100), increase your open-gap voltage in increments to help increase cutting speed. (IE: 60V to 120V, 120V to 180V, etc.). However, with electrodes this small against tungsten and Niobium, success will be limited even on the best machine executed by the best applications engineer.

I'n my job-shop days, I called jobs like these, "TTQ!" Triple The Quote!
(...and hope we didn't get it!)

Wishing you luck...

Bud
 

plastikdreams

Diamond
Joined
May 31, 2011
Location
upstate nj
Claya,

I suggest switching to CopperTungsten using negative polarity and high-frequencies. Maybe 25µ secs ON/OFF to start, with incremental reduction in OFF-time to increase speed, depending upon flushing.

Pure copper electrodes cannot survive at the current densities you are using
(Note: the small amount of Tellurium is added to aid free-machining and does not affect EDM cutting speed).

With the accepted maximum amperage for copper electrodes to be 50A/in2, almost any setting you can select will exceed this ratio, but the tungsten (70%) within the copper matrix (30%) will "take the heat" better.

Because of CuW's lower conductivity (42-45 IACS vs. Cu at 100), increase your open-gap voltage in increments to help increase cutting speed. (IE: 60V to 120V, 120V to 180V, etc.). However, with electrodes this small against tungsten and Niobium, success will be limited even on the best machine executed by the best applications engineer.

I'n my job-shop days, I called jobs like these, "TTQ!" Triple The Quote!
(...and hope we didn't get it!)

Wishing you luck...

Bud
Excellent info!
 








 
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