Punching angles prior to rolling. 1

[SJMoore]

I'm looking for the formula to calculate the hole layout for a large angle flange punched prior to rolling. The angle is 3" x 3" x 1/4" rolled leg out to a 60" inside radius with holes in the outstanding leg on a 2" gauge.I know the spaces will stretch some since they're outside the neutral axis, but I haven't been able to find out how much. Can anyone help?

Thanks,
Scotty

 

[dhengr]

SJMoore:
I don’t think you are going to find any such formula. The pre-punched holes will certainly lead to localized stretching, at each hole, during the rolling process, and they may mess a bit with the rolling process. And, this could lead to some radial cracking at the holes too. I think I would roll the angles first, and let them relax for a short time. Then tack the two angles back to back, do your layout on one, and match drill them.

 

[Ron]

SJMoore...what tolerance is required on the holes? If your tolerances are acceptable to this, you can slightly underdrill or underpunch the holes and then ream them after rolling. You will get stretching on the outside radius and some compression on the inside radius, but unless your holes are relatively large, I wouldn't worry too much about that.

As dhengr notes, you might get some cracking. Inspect closely after rolling.

 

[dik]

As Ron noted they can be reamed to fit after rolling. If it's important that dimensions be maintained, they can be mag drilled after rolling to suit the hole requirements.

Dik

 

[SJMoore]

I should have mentioned that these are 7/8" x 1 7/8" slots so that gives me some amount of tolerance. However you've given me concern over the cracking aspect. I think we'll do a test piece. I'd still like to now that formula if anyone has it.

Thanks,
Scotty

 

[dik]

Punch, then roll...

Dik

 

[BAretired]

Well, I don't know the formula but if R is the inside radius, the radius to the neutral axis would be R + x where x is 0.84" for L3x3x1/4. I would assume that the N.A. remains the same length before and after bending although I'm not sure if that is true. If the hole is y from the inside face then the stretched spacing s' would be s(R + y)/R + x) where s is the spacing before bending.

I tend to think that the term 'x' should by closer to t/2 than the position of the N.A. because I think yielding will be in tension, not compression. If you are doing a test case, why not measure s' after bending?

BA

 

[dhengr]

BA:
There is a whole vert. leg and some inner part of the horiz. leg on the compression side of the N.A./centroid of the static section. The horiz. leg also has the punched slot in it on the tension side of the N.A., so the static/calculated centroid will be moved further toward the vert. leg even before yielding. Then it will be moved still further toward the vert. leg (compression leg) during the rolling process (partial hinge formation?). Over the 1.875" slot length the section stiffness and Sx/Z will be significantly reduced, with fairly significant yielding/strain outside of the slotted hole, almost to the point of producing a flat spot or different rolled radius at the slots. Unless they really dress the slot edges and corners, I’ll bet they will get some ripping or cracking in the radial direction. The only saving grace is that this ripping will propagate across the rolling grain of angle material.

 

[Lnewqban]

I should have mentioned that these are 7/8" x 1 7/8" slots so that gives me some amount of tolerance.

Consider that the neutral line may move outwards because there is more sectional material to compress (3" x 1/4" non-perforated leg) and much less to stretch, mainly the 1"x1/4" above the holes.
I would run a test first with a few feet of perforated angle, mainly to estimate the resultant inner diameter (critical in the case of a flange).
Once you have the actual diameter and total length figured, you could just divide a straight length in equal parts, according to the number of slots.

You will be rolling around 31 feet of 3"x3" angle and welding its ends.
Consider that the first and last few feet will not be curved by the machine.

"God will not look you over for medals, degrees or diplomas, but for scars." - Elbert Hubbard

 

[SJMoore]

Just an update.

We punched a trial piece of angle. It didn't crack but we did get a small amount of thinning between the edge of the hole and the toe of the angle. I don't know my customer's usage so I sent them pictures and asked for their blessing. On the vertical leg there is an ever so little bit of a ripple at the hole but if you weren't looking for it I don't think you'd even notice it.

We laid out our 7/8" x 1 7/8" slots on 16 7/8" centers prior to rolling. After rolling they're on 17 3/16" centers. An increase of 5/16". I expected some but not that much. I'd still like to find a proven formula for figuring this in the future.

Thanks for your suggestions.

Scotty