Need to drill 63,000 .020" dia. holes 6

[buckley8]

I am trying to find a machining process for making 63,000 very small (.020” dia) holes through .200” thick 6061 aluminum with .050” layer of epoxy (Scotch-Weld, Shore D hardness = 55) bonded to it. Hole spacing is .056” resulting in 318 holes per square inch. The holes do not have to be perfectly round, and the diameter tolerance is generous (.019-.024”)

This is for a rub strip over the rotor on a turbofan inlet for a test rig. The epoxy serves as a sacrificial abradable surface in case the rotor tips contact the nacelle and this is the only approved method/material for doing so. The holes are the focus of acoustic testing so they are not negotiable.

EDM can not be used since it requires electrically conductive material and epoxy is not.
Electron beam drilling (e.g. Acceleron Inc.) can not be used as the epoxy will off-gas and ruin the laser hardware. Anyway, this process is limited to .200” deep holes.
I fear that good-old-fashioned mechanical drilling is the only way this can be done and I figure that it will take 3 months or more to make this part (at 30 seconds per hole, 8 hours per day)= $$$$.

To make matters worse, the rub strip is not a flat plate but is a cylinder, 22” ID, 3” long.

I would also appreciate suggestions to "build-up" the aluminum/epoxy rub-strip with holes instead of drilling the holes from the rub-strip.


Jim Buckley
ASRC Aerospace
at NASA Glenn Research Center
Cleveland, OH

 

[Timelord]

Check out laser drilling with real high power. With enough power, a pulsed laser beam should be able to ablate the hole without any local temperature rise that would affect the epoxy. It may take some development work to get a proper nozzle that will prevent contamination of the final optic. You need to look for a shop that has a lot of experience with laser drilling and has a high power pulse laser. I'm not in that business, but I deal with high power pulse lasers for paint stripping and weapons and I have expermented with drilling so I know it is possible.

Timelord

 

[TVP]

I agree with Timelord that laser drilling may be a viable option. I would contact Nuvonyx or Trumpf to discuss the feasibility of using their equipment for this application.

 

[rb1957]

if you can make do with 52 holes per row (3"/53 = 0.0566"), then you could probably drill 4 holes at a time (3/4" apart) and reduce your time to 3/4 month !

would a water jet work for you ?

 

[TheTick]

It is possible.

I've DONE THIS with mechanical drills! No kidding. Making melt-blow die nose-pieces w/ thousands of Ø0.025" holes through 1/8" D2 steel. 30 seconds/hole is sci-fi. Plan on 90.

Perhaps drill through the epoxy to make way for EDM.

 

[buckley8]

Actually, the holes go through both the aluminum and epoxy so laser is out. This is what I meant when I wrote that the epoxy will off-gas and ruin the laser.

I do like TheTick's suggestion to drill the epoxy to make way for EDM. However, we are still talking lots of machine time and $$$. BTW, how much did that nose-piece cost?

Jim Buckley
ASRC Aerospace
at NASA Glenn Research Center
Cleveland, OH

 

[MintJulep]

My first thought was also laser.

I would think you could set up to laser from the non-epoxy side, with appropriate scavenging exhaust to control the outgasing.

Alternately, EDM from the non-epoxy side through the depth of the metal, then chemical etch through the epoxy. Might have a tough time finding something that eats the epoxy but not the aluminum.

Or it might be possible to hydraulically blow-out the epoxy "plug" over each hole after EDM from the aluminum side.

 

[TheTick]

Literally, nose-pieces are worth more than their weight in gold. Much precision labor and heartache goes into each one.

They (my Dad's company) have since upgraded to EDM and laser welding. Still an intensive effort.

 

[CoryPad]

Mr. Buckley,

You will have to forgive the responders of this thread when they don't understand your limitations. For example, you refer to an ELECTRON BEAM, then say that the laser will be ruined. That doesn't make sense, which is why you have people recommending lasers.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[jistre]

Hmm. Would it be possible to use a turret punch to pop the holes in a flat state, then form it into a ring afterwards and then only have to worry about manually doing a relatively small number of holes?

 

[jistre]

If manual drilling is the only method, could you possibly have a special tool built that would drill multiple holes at once to cut down on the time required?

 

[buckley8]

Thanks for your help so far.

Corypad: I was told that the $8,000 electron-beam thingamajig would be ruined and only received a no-quote. The electron beam works in a vacuum and the epoxy particles (molecules?) would collect on the optics. I guess the off-gas problem would affect the optics of laser the same as electron-beam, but it's probably a mute issue since I can't find a laser to that can do .250" deep or epoxy without making a mess of it.

jistre: Someone here suggested that too. We're pretty sure that the compressive stress on the epoxy side (the inside), when the plate is bent into a cylinder, would cause the epoxy to come-off the aluminum, chip-out, or form cracks/craters around the holes. Anyway, the cylinder needs to be very accurately round since the rotor tip clearance is very small. Also, welding is a last resort due to the massive quality and safety concerns that NASA has about welds. The easiest parts to make with welds are almost always made from solid blocks of aluminum.

Jim Buckley
ASRC Aerospace

 

[MadMango]

You could punch the holes in your 22" dia cylinder, if the holes were larger. I think at .020" thru .200" is the problem. There would be a lot of broken dies.

Can you EDM the holes first, then coat with the epoxy after the holes are formed? You could probably use silicon plugs in the holes, and machine the outer surface to remove any build-up around the plugs.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[jistre]

Hmm. NC machining center or five-axis machine, then? You can program the holes, turn the machine on, and just let it run. It's got to be cheaper than paying labor to do it by hand for three months, it will be more accurate than manually doing it, and you'll have the program if you ever need to make another.

 

[jistre]

Plus, with the machining center or 5-axis, you could drop a disk of aluminum in the center of the part to support the whole thing during machining and help prevent the epoxy from chipping when the drill bit comes through.

 

[btrueblood]

Could the holes be stepped, i.e. counterbore at something reasonable (say 0.06" dia x .15-.18 deep), then drill thru the remainder with .02 drill, or waterjet.

How is the epoxy applied, as a film/tape, or is it centrifugally cast to the i.d.? If cast, pre-drilling the aluminum and putting wax or similar erodable cores in the holes will keep them clear while the epoxy cures.

 

[TheTick]

proposed alternate method...

EDM holes before epoxy is applied. Plug holes w/ wire to prevent filling, plus enough wire to stick through epoxy. Apply/cure epoxy and then have an intern yank out the wires.

 

[jistre]

I'm probably not understanding exactly what the epoxy does, but do you have to have it? If I read it right, it's there so that if the fan blade touches this shroud, it'll ablate. If the rotor tips cut so deep that they go completely through the epoxy, they'll hit the aluminum anyway, so it doesn't help you. If they are just slightly grazing the epoxy, removing it means they'll hit nothing and keep going. If you can eliminate the epoxy layer, then you're back to being able to use beam based solutions.

Like I said, though, I'm probably not fully understanding the purpose of the epoxy layer or perhaps the geometry of it.

 

[rb1957]

how were you planning on making the tube ? rolling and welding a plate ? if you're not fussy about the roundness of the holes, couldn't you cut the holes first, much easier on a flat surface.

i too thought maybe you could add the epoxy after machining ?

don't think the counter-bore idea will work, the holes are 0.053" apart, and what does it gain you ?

 

[eromlignod]

I agree with the multiple-spindle drill head ideas. You can get them made for a reasonable amount of money (several companies make them).

http://www.multi-spindle-heads.com/

If your holes are spaced in a regular pattern, a head with, say, six spindles could be spaced every ten holes for a center spacing of .56". Then just index one hole-spacing(.056") for each drilling and in ten hits you've got 60 holes. If you do it in a straight line, you can drill along the tangent line of the cylinder, then index the cylinder for the next row.

Don
Kansas City