Thread: removal rate for aluminum (and 300 stainless)

Hello again,

I'll lay out what I'm doing, the research I've done, and ask a general question or two. thanks ahead.

I have been experimenting with my new old edm. a Raycon R20 20 amp hydraulic manual sinker. It's fun. Ive found the ability to slice things without slitting saw constraints to be very sweet. so far I have done more work that is actually suitable for wire than ram. but anyway.......

I've been using .012" brass shim stock on edge as a knife to slice .015" wide aluminum slots. it takes a lot of experimentation to figure out what consumes less brass.
I've got a new requirement: a 1" deep, 1" wide (and open on the ends slot) by around .050" thick slot. I bought some .046" Poco-3 sheet and
I am set up to plunge it with the .046" sheet on end. I'm really just roughing cutting a groove in a part which will allow it to flex. surface finish is unimportant.

I have been searching the internet for "recommended" current density. What I have found is 50 amps per sq inch is about all you want to push through graphite @ %100 duty. and I probably really want to do less, but I believe my duty cycle is about 75% so I intend to shoot for that density unless told differently. By duty cycle I mean I am retracting about .01" for flushing about every 2 seconds and I estimate the duty cycle by sound. there is no numerical value setting.

so my .046" sheet would get about 2 amps when in the cut. or 1.5 amp average



general questions:

is 50 amp/ sq in reasonable for me with an old 20 amp machine? thank goodness I'm burning such small area features.

what volume of material per current density should I be hoping for? Aluminum and stainless. MY THIS IS A SLOW PROCESS!!!!!

I also got some copper impregnated graphite. what is a good density guideline for that?

Dan

fastes time I could plunge with reasonable results using my .049 poco 3 was 2 minutes per .1" or about 23 minutes an inch.

I did this at 4 amps and 85 volts on the meter. I'm just wondering if this is even anywhere near "right".

if anyone is familiar with these machines.... my settings.

10 servo feed.
10volts
1&2 amp board switches
4 peak
10 avg
6 surf finish
rev polarity
graphite

my panel:


my cut setup used .049 poco 3 sheet stock on edge. into 1" wide 6061.

Been a long time since I ran a sinker, so I won't even attempt to assess your numbers.
But I do recall aluminum being the fastest burning metal I worked with due to it's low melt temp.
One of the dirtiest too, but maintaining a large spark gap lets it flush clean.
I usually tuned the settings by the sound of the cut (think frying eggs) and smoothness of the depth indicator.
Small or deep cuts can be made more audible by sitting a radio next to the machine, tuned between AM stations.

Also, Poco (Unical) used to publish a wealth of info on electrode wear in different materials. Had lots of good info on methods of determining best wear/erosion rate per machine. (But I don't see that info on their website)

Since you seem to be in the experimental mode....one of the neatest attachments I saw for a sinker was a horizontal wire drive attached to the ram so that you could make slice cuts in your work piece. Same principle as a WEDM.

I think it was made or sold by Eltee Pulsitron in the '70s before WEDM was popular.

I know it's been a month but I'm also slotting AL with graphite. I'm using a Hansvedt sinker with .048 thk graphite and it is SLOW. I need a pretty good finish in the slot though so I'm using pos. polarity on the electrode servo at 6 and 16 microsecond duration. The current switch is on 1/4 whatever that means. Meter shows about an amp in the cut. I can get the frying egg sound especially if I open the gap up.
Dan, where did you get the sheet material? What grade is it?

Thanks,

Tim in D

I bought from saturn industries

I bought both poco 3 and some copper impreg. the plain poco sheet is more rigid and flat.

Graphite:Plates, Sheets, Blocks, Bulk:Poco EDM-AF5

POCO3 (AKA compressed smoke) is nice stuff, but pricey. For just fooling around, burning slots with no surface finish requirement, you can do as well with less expensive materials. I buy a lot from Ohio carbon Blank:

Ohio Carbon Blank

The AR-12 has worked well for what I do, and I've been able to machine ribs .010" thick.

Copper Graphite has no real advantage - it costs more, burns slower, and wears faster - unless you need ribs less that .005" thick. I've done some contoured ribs .004 wide, .040 high using copper graphite.

When burning aluminum, watch out for the "burn berries". Burn berries are little bumps that form on the electrode... poor flushing leaves a lot of particles in the gap, which weld together, and the point formed on the trode then takes the majority of the discharge, which only makes it continue to grow. You'll be watching the ram cycle, everything looks normal, but it doesn't seem to be making any progress. Retract the trode, and see a black spot in the bottom of the burn. Poke at it with a scriber, and find to your horror that it's .010" or .015" deep, well past your intended finish depth. You can burn aluminum fast, but it's easier to put a good finish in steel.

Dennis

Dennis