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Wire cutting small hole in AL 6065?

Dial EDM

Plastic
Joined
Nov 16, 2008
Location
Buffalo, NY
Hi,

I got an application where we need to machine a .095 diameter hole thru 4 inches. Currently we have EDM drilled the wire start hole at about 0.060. But when we put the part into the wire the hole popper has left a non-conductive film on the hole. So we try drilling it with an undersized drill. Big pain in the butt and sometimes the drill walks.

Any other suggestions on how to do this. We’re using a Agie Charmilles Drill 20amd a 440ccS wire machine.

Any suggestions would be great.

Bill
 
Bill,

The 6XXX series Aluminums are very prone to this. Quite frankly, I tend to avoid hole popping it if at all possible. But that doesn't help you right now. You might try a mild acid to wash out the popped hole and remove the non conductive oxidization layer. We've also had reasonable success with making a special nozzle for our bead blast gun to slip into the hole and blast out the oxidized layer.

Good luck.
 
Why not hole pop it on size? Asking for a friend.

I'm not the OP, don't play them on TV, and haven't slept at a Holiday Inn for at least two decades, but mostly because hole popping is typically a preparatory operation and not a finishing one. ( there are always exceptions and caveats ) In AL, the holes can often wander a little bit. Less than drilling, but easily out of spec/tolerance if there is one. ( and there usually is ) Too, they're actually not usually actually round. Same disclaimer regarding specs and tolerances. So, we tend to use it as a preparation for finishing up with Wire, where we like to pretend we can better control outcomes. :D
 
Start-holes in 6061

Hi,

I got an application where we need to machine a .095 diameter hole thru 4 inches. Currently we have EDM drilled the wire start hole at about 0.060. But when we put the part into the wire the hole popper has left a non-conductive film on the hole. So we try drilling it with an undersized drill. Big pain in the butt and sometimes the drill walks.

Any other suggestions on how to do this. We’re using a Agie Charmilles Drill 20amd a 440ccS wire machine.

Any suggestions would be great.

Bill

Hi Dial,

A drill should work, but if you're truly, "at or about" .060", I would float a 1/16" (.0625") or larger, metric reamer through it from both sides to remove the thin, oxide layer that makes wire-starting problematic. Note: A reamer cannot "walk", but it will "follow" the pre-existing hole (however inaccurate).

As for the logical suggestion of "popping it to size", IMO, this concept is not possible without precautions except in the most-open of tolerances and applications. The hole's "Edge-Quality" must be considered, as electrode entrance in conjunction with high-pressure flushing with a water-based dielectric will produce "cratering", which is exactly as it sounds - a high-speed expulsion of molten material from the entrance-site, which will be larger than the hole-size.

Additionally, upon electrode exit, we can also suffer from "ejection" or "spatter", the same as "cratering", but to a lesser degree. Both conditions can produce through-holes with inaccurate edges. To combat these conditions, clamp a conductive sheet of aluminum shims (min .062"), to the top and bottom of the part before machining. "Cratering" and "ejection" will still occur, but on the outer, sacrificial "bread" of this EDM "sandwich", instead of the "good-stuff" in the middle.

Note: This will contribute to increased electrode wear and machining time which must be considered, but will produce a "popped" hole with better edge-quality.

Hoped this helped with both posts.

BG
 








 
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