Need to drill 63,000 .020" dia. holes
Need to drill 63,000 .020" dia. holes
(OP)
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)= $$$$.
To make matters worse, the rub strip is not a flat plate but is a cylinder, 22” ID, 3” long.
I would also appreciate suggestions to "build-up" the aluminum/epoxy rub-strip with holes instead of drilling the holes from the rub-strip.
This is for a rub strip over the rotor on a turbofan inlet for a test rig. The epoxy serves as a sacrificial abradable surface in case the rotor tips contact the nacelle and this is the only approved method/material for doing so. The holes are the focus of acoustic testing so they are not negotiable.
EDM can not be used since it requires electrically conductive material and epoxy is not.
Electron beam drilling (e.g. Acceleron Inc.) can not be used as the epoxy will off-gas and ruin the laser hardware. Anyway, this process is limited to .200” deep holes.
I fear that good-old-fashioned mechanical drilling is the only way this can be done and I figure that it will take 3 months or more to make this part (at 30 seconds per hole, 8 hours per day)= $$$$.
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





RE: Need to drill 63,000 .020" dia. holes
Timelord
RE: Need to drill 63,000 .020" dia. holes
RE: Need to drill 63,000 .020" dia. holes
would a water jet work for you ?
RE: Need to drill 63,000 .020" dia. holes
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.
RE: Need to drill 63,000 .020" dia. holes
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
RE: Need to drill 63,000 .020" dia. holes
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.
RE: Need to drill 63,000 .020" dia. holes
They (my Dad's company) have since upgraded to EDM and laser welding. Still an intensive effort.
RE: Need to drill 63,000 .020" dia. holes
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
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RE: Need to drill 63,000 .020" dia. holes
RE: Need to drill 63,000 .020" dia. holes
RE: Need to drill 63,000 .020" dia. holes
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
RE: Need to drill 63,000 .020" dia. holes
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."
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RE: Need to drill 63,000 .020" dia. holes
RE: Need to drill 63,000 .020" dia. holes
RE: Need to drill 63,000 .020" dia. holes
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.
RE: Need to drill 63,000 .020" dia. holes
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.
RE: Need to drill 63,000 .020" dia. holes
Like I said, though, I'm probably not fully understanding the purpose of the epoxy layer or perhaps the geometry of it.
RE: Need to drill 63,000 .020" dia. holes
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 ?
RE: Need to drill 63,000 .020" dia. holes
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
RE: Need to drill 63,000 .020" dia. holes
RE: Need to drill 63,000 .020" dia. holes
http://www.pcbdriller.com/sz1000.htm
They quote 350 hpm, which works out to 21,000 holes per hour. Assuming that they're optimistic by a factor of 5, it would still only take about 16 hours to drill your device. Note that these guys are drilling 0.006" holes routinely, a 0.020" hole is probably gigantic to them.
TTFN
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RE: Need to drill 63,000 .020" dia. holes
Are you suggesting an automated process for plugging the holes? How does the wire plug stay in the hole? Interference fit?
The abradable rub-strip is a safety requirement.
The two-part epoxy (3M p/n:EC-3524) is applied with a spatula or trowel and cures at room temp.
jistre: You are very close to understanding the rub-strip. The rub-strip is for a worst-case scenario. If the centrifugal force (from overspeed), excessive vibration, or temperature (or some other force) of the rotor blades is great enough to cause the blade to contact the inlet wall, the wall will be abraded, saving the expensive rotor blade and preventing fragmentation (at 10,000 rpm). It would only need to be used once. The epoxy is .050" thick. If the rotor goes through that, it has already come out of the hub and is on its way to doing some serious damage. You can't just have a lot of air clearance since it would seriously affect the efficiency of the compression of the fan. Clearance is ideally <.004". Therefore, a small excursion of the blade tip could cause it to scrape the rub strip.
Jim Buckley
ASRC Aerospace
RE: Need to drill 63,000 .020" dia. holes
PCB are a lot less than .2 thick and probably easier to drill than AL.
KENAT, probably the least qualified checker you'll ever meet...
RE: Need to drill 63,000 .020" dia. holes
RE: Need to drill 63,000 .020" dia. holes
RE: Need to drill 63,000 .020" dia. holes
Then I still like the idea of using some sort of NC automation to get the holes drilled. Once it's set up and running, you should see a finished part in days, not months. Plus, if the pattern is regular, you can set up to drill by rows, which should make creating the tool path much less taxing. You just hit a hole, and then rotate through the proper angle and hit another. Jumping between rows should take just a lateral movement and a rotation to locate the first hole of that row, and you're set to repeat the rotate, plunge, rotate, plunge drill.
At 3 holes a minute, total drilling time would be about two weeks, and you should be able to get way more than 3 holes a minute.
RE: Need to drill 63,000 .020" dia. holes
You are wrong about the laser. Reread my post. If you use a PULSE laser of sufficient power you can ABLATE (not melt) the holes thru both the aluminum and the epoxy without heating up either. We use this technique to remove paint with a 1 in square focal spot and a 30 joule per pulse laser (at 200pps). We can remove paint one layer at a time without heating the substrate or the remaining paint. It will not ruin the epoxy. The blow back (off gas) can be handled by using a final optic with a long enough focal length and a special nozzle. You just need to locate a laser vendor who understands the problem and is willing to work with you.
Timelord
RE: Need to drill 63,000 .020" dia. holes
with a spatula inside a 21" dia tube ?
i think there has to be a better way; I mean, you are NASA.
RE: Need to drill 63,000 .020" dia. holes
The ID is machined after the epoxy cures. This has been done before several times. I didn't mention it since I didn't think it mattered how the epoxy thickness was arrived at. :) It's the holes that are new.
I just work for a contractor. NASA comes up with the far-out ideas. We then make them work. This is for aeronautical acoustic research (why aircraft engines are already so much quieter than they used to be and will eventually be virtually inaudible outside an airport).
I'm sure there's a better way. That's why I'm here! :) :)
Jim Buckley
ASRC Aerospace
RE: Need to drill 63,000 .020" dia. holes
cats tend not to like any of them !
RE: Need to drill 63,000 .020" dia. holes
htt
http://w
Ted
RE: Need to drill 63,000 .020" dia. holes
flow does make a 5-axis machine, but I do not know if they can hold that tight of a tolerance on those .020" dia holes
RE: Need to drill 63,000 .020" dia. holes
RE: Need to drill 63,000 .020" dia. holes
vesselfab, rb1957 has stated no positional tolerance. The hole tolerance is .019 to .024 inch.
Use two aligned jets and cut holes half depth from each side if taper exceeds the tolerance range.
Drilling the holes with a drill bit will leave a burr that probably will have to be removed. Water jet will leave no burr.
Ted
RE: Need to drill 63,000 .020" dia. holes
That's why I downgraded by a factor of 5...
Actually, not, but the point was that even at a much slower step rate, it wouldn't take 3 months to drill. The full stroke retract time on drill is 18 ms. Assuming a drill rate of 20 in/min, the drill dwell time is 0.6 seconds.
Based on the manufacturer's velocity spec, it should take less than 10 milliseconds to move to the next drill position. The estimated cycle time is therefore less than 0.7 seconds per hole, resulting in a single piece drill time of about 25 hours, so 3 days, instead of my WAG of 2 days.
In any case, substantially shorter than 3 months, so definitely worth checking out.
TTFN
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RE: Need to drill 63,000 .020" dia. holes
The part in the spindle rotates at constant RPM and the laser is fired based on hardware position matches in the controller. It is fired briefly for each hole. This has two advantages;
No time is lost from starting and stoping.
The holes are drilled a little bit with each laser pulse (minimizes heating and the ablated material chuff is small for each pulse).
Many modern machine tool controllers have the hardware match feature to drive the laser trigger input.
RE: Need to drill 63,000 .020" dia. holes
1) laser teh holes in teh Al.
2) Fill holes w/ wax (also wrap a matching mold on the ID, that creates a waxbutton .075" tall from each hole.)
3) Machine ID to get tight ID tolerance.
4) Melt the wax off and clean the part.
Hmmm?
(think casting, not machining) Cast the holes in the Epoxy.
RE: Need to drill 63,000 .020" dia. holes
Insert the pins into the holes until the parallel portion protrudes no more than necessary. Apply the epoxy. Make a small slide hammer with a claw on the end that will just fit over the pin dia. Pull all of the pins out!
Stodge.
RE: Need to drill 63,000 .020" dia. holes
Drill blind holes from the outside on a CNC machine.
Turn the inner ring to chips.
Mike Halloran
Pembroke Pines, FL, USA
RE: Need to drill 63,000 .020" dia. holes
If the surface is flat, any electronic printed circuit board manufacturer could probably do the job for you. It just requires the supply of a computer drill file giving the X and Y coordinates of every hole.
Normally circuit boards are drilled stacked four at a time, and the fiberglass board is typically 1.6mm thick, so thickness is not a problem.
It might be at least worth asking.
RE: Need to drill 63,000 .020" dia. holes
http://www.ergaerospace.com/index.htm
http://www.porvairadvancedmaterials.com/index.htm
http://www.ultramet.com/index.html
http://mot
RE: Need to drill 63,000 .020" dia. holes