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

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.

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

RE: Need to drill 63,000 .020" dia. holes

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

RE: Need to drill 63,000 .020" dia. holes

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.

RE: Need to drill 63,000 .020" dia. holes

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 ?

RE: Need to drill 63,000 .020" dia. holes

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.

RE: Need to drill 63,000 .020" dia. holes

(OP)
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

RE: Need to drill 63,000 .020" dia. holes

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.

RE: Need to drill 63,000 .020" dia. holes

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.

RE: Need to drill 63,000 .020" dia. holes

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: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.

RE: Need to drill 63,000 .020" dia. holes

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?

RE: Need to drill 63,000 .020" dia. holes

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?

RE: Need to drill 63,000 .020" dia. holes

(OP)
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

RE: Need to drill 63,000 .020" dia. holes

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: Eng-Tips.com Forum Policies to make the best use of Eng-Tips Forums?

RE: Need to drill 63,000 .020" dia. holes

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.

RE: Need to drill 63,000 .020" dia. holes

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.

RE: Need to drill 63,000 .020" dia. holes

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.  

RE: Need to drill 63,000 .020" dia. holes

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.

RE: Need to drill 63,000 .020" dia. holes

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.

RE: Need to drill 63,000 .020" dia. holes

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 ?

RE: Need to drill 63,000 .020" dia. holes

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

RE: Need to drill 63,000 .020" dia. holes

Why not woven aluminum mesh, 20 mesh, with 25, 27, or 30 thousandths, flattened (a little) and then coated. The square openings will round a little when coated and might look like round holes.

RE: Need to drill 63,000 .020" dia. holes

All very high tech solutions, but people seemed to blow off drilling way too quickly.  Your time estimate for mechanical drilling is absurdly high.  see:
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

(OP)
I definitely like the idea of edm-ing the holes before the epoxy is applied.  Of course, plugging the holes and then de-plugging them would not be much fun...
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

IRstuff, the different materials/material thickness might be the killer though.

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

Many hush kits for jets are made from carbon fabric prepreg and hard plastic pin blankets. After the epoxy is cured the pin blanet is pulled off leaving the holes. The pins are pushed through the prepreg with pneumatic hammers.

RE: Need to drill 63,000 .020" dia. holes

Drill the holes, aplly the epoxy and force air through before the epoxy dries, thus clearing the holes?

RE: Need to drill 63,000 .020" dia. holes

Ahh, it's the need for the tight air clearances that didn't click.  Removing the epoxy and having a larger gap just won't work in that case, will it?

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

buckley8,

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

"The two-part epoxy (3M p/n:EC-3524) is applied with a spatula or trowel and cures at room temp" ... and you think you're going to get a constant thickness of 0.05" ??

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

(OP)
To rb1957:

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

many ways to skin a cat ...

cats tend not to like any of them !

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

Water jets tend to enlarge the holes at the bottom of the cut.  Would it be possible to make the holes, THEN machine the epoxy?

RE: Need to drill 63,000 .020" dia. holes

minerk, according to Flow the hole is larger at the entrance not the exit.

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

Kenat,

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

FAQ731-376: Eng-Tips.com Forum Policies

RE: Need to drill 63,000 .020" dia. holes

I'm all for the laser.  We do this on a lathe (much smaller, fewer holes but still the same concept).

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

     steps:

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

I wish I hadn't read this thread. I have not been able to sleep thinking of a solution. Anyway, try this: Purchase 63,000 sewing pins. The ones in my wifes sewing tin are 0.5mm dia. EDM drill the holes in the aluminium cylinder.
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

Sandwich the epoxy between two aluminum rings... yes, bonded to both.

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

Looking at this, the hole size and hole pitch seems very reminiscent of drilling holes in electronic circuit boards.

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

Modern turbine engine combustors have a profusion of small holes for cooling. Go to the Aero engineering site with your question.

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