Best way to create 1/8" holes in 1" steel plate?

[structuresguy]

I am one of the structural engineers working on a project where we need to create a perforated steel plate. The plate is nominally going to be 1" thick, grade 50 structural steel (ASTM A572). We need to create thousands of 1/8" diameter holes through the plate. Some of the holes are perpendicular to the surface, and some of the holes will be at a 30° angle to perpendicular. The tolerance on the hole size, and the smoothness of the interior of the hole are very important, as is the entry and exit profiles. We need it to be smooth inside, and without any burrs on the entry and exits. In total, we will have something like 45,000 holes in varying density patterns over a surface area of about 1500 SF.

I am looking for recommendations as to how to create the holes, along with pros and cons of each method. Possible methods I can think of are drilling, laser, waterjet, or plasma cutting. However, I have little experience with the latter three methods, and dont know how focused they can be, or if they work on such thick steel plate. Also, I am concerned with all the methods for the holes that are at the 30° angle.

To add to the complexity, some of the plate will need to be rolled to a 25 ft radius bend. In the radius area, the holes are all perpendicular. So I am imagining that the holes are made first, then the plates are rolled.

Any help you guys can offer is much appreciated. Thanks.

 

[SwinnyGG]

If the holes in the rolled area must be round or close to round, they can't be cut before the rolling process- that operation will distort their cross section. They will wind up round on the inside and oval on the outside, with the long axis of the ellipse perpendicular to the centerline of the radius of the rolled section.

1/8" is way too small for plasma cutting with any appreciable level of accuracy or surface finish quality.

Drilling 45,000 holes at 1/8" through 1" plate is going to be VERY time consuming, and your holes will not likely be very accurately placed or very round.

The fastest processes for this type of work are going to be laser drilling or wire EDM. Either one is going to be very expensive on a part of this scale.

When you say:

The tolerance on the hole size, and the smoothness of the interior of the hole are very important, as is the entry and exit profiles. We need it to be smooth inside, and without any burrs on the entry and exits.

What exactly do you mean? What are the positional tolerances, diameter/perpendicularity/circularity tolerances, and surface finish targets you are trying to hit?

I'm having a hard time imagining an application for what you're describing.. what is this part designed to do?

 

[structuresguy]

Thanks for the reply. Good points about the ovalling of the holes. I was operating on the assumption that the bend radius was not tight enough to make an appreciable difference on a 1/8" hole. I will discuss with the client.

We definitely understand that whatever process could be very costly and time consuming. The more automated the process, the quicker and more consistent the holes can be made, I'm sure.

I don't have all the dimensional tolerances on the holes yet. And I can't say much about the function, other than to say a fluid has to pass through the holes under pressure, and we need to control flow rates and pressure loss. So things like interior smoothness and inlet shape could have a significant impact on pressure loss.

So for instance, i imagine a plasma cut hole would be very rough, as the metal slags off as it melts, and would have a ragged edge, possibly worse on the downstream edge. I say this from experience with plasma cut structural steel shapes. I don't know how laser cutting would compare, as it is only melting the steel. But from what I have seen in thin metals cut be laser, it is much cleaner than plasma cut.

Hope that helps clear up some of our requirements. Thanks.

 

[SwinnyGG]

Much depends on how the holes are spec'ed.

Wire EDM will almost certainly provide the best surface finish, most accurate positioning, best circularity, and shortest production time- but will be far and away most expensive.

Laser can provide comparable finish and accuracy to EDM, or can be merely 'very good' depending on the specifics of the process used- there are several variations.

 

[hendersdc]

You haven't given us much to go off of for function but parts of this concept might be useful.

Could you use a bunch of precision inserts that are brazed into your larger sheet?

This would allow you to cut larger and uglier holes with a plasma cutter and get the precision from the inserts which could be thick walled tubing cut to length or bar stock that was drilled or reamed on a lathe. Assembly could be relatively easy and a batch process.

This could allow you to use a base sheet that is thinner than 1" as well if the thickness was driven by the length of the holes instead of structural requirements.

 

[MikeHalloran]

Laser-drilled holes, at least in 12Ga ss sheet, come out round with sharp entry and exit.
... until you look at them closely. Under magnification, they look like a big hole drilled with a small bit, maybe .007" diameter, arrayed on ~.010" centers, with the core punched out.
The holes are not truly smooth, but they do flow consistently.

It's usually very hard to get a machinist to NOT deburr holes by breaking the edges, ESPECIALLY if they find out that flow is involved, in which case they will use multiple chamfers or a radius, 'so it will flow better'. ... which it does, but the flow coefficient for a hole is extraordinarily sensitive to the entry and exit geometry, so the resulting holes will have a coefficient somewhere between 0.7 and 1.0 , with a lot of scatter, whereas 'no burr, no chamfer' will usually produce a coefficient of 0.6 , with just a little scatter.

Thirty holes per square foot could be achieved with say five inserts per square foot, each insert having six holes. ... if 'uniform hole spacing' is not dogmatic.

Even at that density, the needed volume of inserts would be enough to justify production on a screw machine.
... if you can get 20 foot rounds in the alloy you want,
... or, better, if your customer can tolerate a free-machining alloy like 1212L,
... which is leaded; that may be an issue.

Screw machine production of multi-hole inserts could allow pressing or pressing and welding the inserts into punched holes.

Plasma cutting can't get even close to what you want.

Absent inserts, drilling is possible, and will probably go much faster with carbide drills.
... but definitely talk to a drill bit supplier about it when you have a range of alloy selections.
Somebody will buy a lot of drill bits for a job like this, and sometimes the expensive ones are cheaper.





Mike Halloran
Pembroke Pines, FL, USA

 

[dvd]

wire edm requires a hole to start the wire - probably want an electrode edm process.

 

[tygerdawg]

You've got to cough up some specs for any type of intelligent answer:
[ul]
[li]hole interior surface finish[/li]
[li]entrance profile & surface finish[/li]
[li]exit hole & surface finish[/li]
[li]acceptable size of burrs entrance / exit[/li]
[li]tolerance of hole-to-hole or hole-to-datum spacing[/li]
[li]tolerance of hole diameter[/li]
[li]axis of hole-to-surface angle tolerance[/li]
[/ul]

Thinking way out of the box, I see a solution of one or more six axis robots with either end effectors of
[ol a]
[li]spindles & automatic drill chucks & common + custom drills[/li]
[li]electrode EDM heads[/li]
[/ol]
Long-reach robots are amazingly inexpensive these days. Offline programming software (like that of which I resell, but that's another - private - discussion) can produce the locations & orientations easily for 45K holes. Very good (but not 0.0000 perfect) robot positional tolerances are possible from modern robots. A custom-built solution like this can run 24x7 with minimal skilled labor. The Manufacturing Engineer in me says that some rework & repair will be inevitable. But if your tolerances are reasonable, then this could be done. And probably for a lot less cost of the total skilled labor cost.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[dicer]

And with the last poster, I'd like to see dimensions of the parts.
And second question is why? Why to all of it, why the fussy entry exit, why the finish etc.
All the holes will need to be spotted, and small through spindle coolant Guhring drills are the way to go and will give
good life with correct feeds and speeds. The angled holes may need to be spotted first with a small end mill.