help on sheet forming process!

dear all

I'm going to create a ring with special criteria some pictures of it can be seen here:

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?d=415042 in fact its a half ring with an outer diameter of about 1900 mm, its shape is some how difficult in some aspects :

- as shown in attached pictures a portion of structure is just an easy cylinder form but the other portion is conical shaped

- it must be seamless, coldworked and made from stainless steel sheet

- thickness of the sheet is 15 mm

- it must be produced with a good telorance ( the bend shape must b axact)

my questions are : which forming process is the best for it?(rolling , spinning , any other forming process? these are just my guesses ) can it be formed in a full ring and then splited into two halves? or residual stresses would not let me do something like this even if I anneal it , and I should form it in a half ring from the begining?

can anybody provide me some information? any kind of information or sugestion would be precious. thanks in advance for your care best regards, Shantia

Reply to
shantia
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The easiest way to do this is in a good sized roll bender with special dies. Roll a full ring, weld the end together, continue rolling to get the thing round and the angle fully formed. Cut it apart into 2 completed units.

Most any good structural steel fabricati> dear all

Reply to
RoyJ

How much money do you have? You're going to need a bundle.

-- Ed Huntress

Reply to
Ed Huntress

"Good sized"? Roy, 15mm material thickness is over 0.59". The cone is attached to the straight cylinder, so one edge is going to have to be stretched or the other is going to have to be shrunk -- or a little bit of both -- while you keep that blend radius intact.. And this is stainless! You can't just roll it. you have to iron it at the same time, and ironing it out so it doesn't twist is going to be an extreme metalworking job.

Unless you have access to the machines used for making Saturn V rocket nozzles, I think there is a problem here. d8-) The forces involved are astronomical.

-- Ed Huntress

Reply to
Ed Huntress

That 15mm must a typo. If the ring is truly that thick, a blank ring could be rolled and welded, then turned on a lathe.

Reply to
Chas Hurst

With a 1900 mm diameter? Even for a VTL, that's a big piece of work, and it isn't going to be cheap to get it done. The material cost alone -- especially if you roll the cone section, which would have to be cut out of a pretty large plate of 15 mm stock (assuming it's not a typo) -- would be a hefty chunk of change -- over $3,000 for that one piece of plate. The stock for the cylindrical ring will be on the same order. Then there's rolling, and welding, and turning. That assumes it was done by someone who is really expert and that it doesn't wind up being all distorted out of shape. With

1/2" - plus stainless, that's more than a little problematic, matching a cone to a cylinder.

As I said, it's all a matter of how much money one has. The total job is going to run into five figures. This is extreme stuff. I think the first point here is to see if the OP is aware of what the cost is likely to be.

-- Ed Huntress

Reply to
Ed Huntress

I'd didn't say it would be cheap. There are companies that specialize in rings and one this size is would be no problem at all. I think the whole ring could be made from one piece and turned on a vertical lathe, eliminating welding.

Reply to
Chas Hurst

These guys are somewhat local to me. IIRC, they have a suitable roller.

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I'm inclined to believe the OP is real on the thickness, the drawings show a pretty hefty thickness in relation to the width. The blank would be a 20' piece of 5/8"x 8"(?) 304. Calculated weight would be 336 pounds. I haven't priced stainless lately, not calibrated on that one. I'd certainly hope to get it for less that $5 a pound, that would put the piece under $2000.

My biggest concern is the OP may think that a fabricated piece will hold the same tolerances as a machined piece. BTDT, had a very unhappy customer.

Ed Huntress wrote:

Reply to
RoyJ

I agree a fabrication would present problems. It's possible a casting could be made. A quick search just dug up a few companies that have the capability.

Reply to
Chas Hurst

I can't see how you'd do the angle (cone) and the cylinder (flat) on a pipe bender, Roy, but I'll be interested to hear if they'll give a quote, and what it is.

-- Ed Huntress

Reply to
Ed Huntress

It's especially inspiring that the OP doesn't seem to know how to make such a part, nor does he have any actual tolerance.

A part like this would be *very* difficult to measure without the use of a CMM. Application-based gauging would be important, especially when the customer says "no" and the builder says "yes". A good description of the part's function would be nearly a requirement to avoid shenanigans.

Regards,

Robin

Reply to
Robin S.

Operative word is 'roller'

A quick google brought up this mfg: The largest unit on this page

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easily handle this cross section. Most of these roll benders will operate in either the vertical position (shown) or horizontal position (better for this project) There is a max size calculator at the bottom of the page.

You would need to make one male roller and two female rollers. These would be some pretty massive chunks of tool steel, probably 8" in diameter by 9" long (1/2" flanges to contain the 8" material on each side). The rollers are easy to make: turn on a lathe, bore the center hole, broach the keyway, heat treat.

The OP's shape would require that one side would need to shrink, hard to do in a roller. In real life, multiple passes through the roller will likely stretch the outside some. That makes the final diameter a bit of a guess.

Final process would probably be: roll with flat roller (or in a big slip roll), weld the ends together, start forming the angle leg of the ring. I'd expect that you would need to cut out a section and reweld to get the diameter just right. This is not an easy part to make but I'd hope to get one finished ring out per 8 hour shift with a team of two.

BTW: the equipment >> These guys are somewhat local to me. IIRC, they have a suitable roller.

Reply to
RoyJ

OK, but I don't see it, Roy. The angled flange, or cone section if you prefer, is going to wrinkle like crazy if you try to do this on a roll former. Custom roller profiles won't help, IMO. Rolling a perpendicular angle is a lot easier, because the leg is not trying to spring to the outside -- they just constrain it like the walls on a piece of rectangular tube.

There just is no way I can see to apply the force necessary to compress an angled flange progressively, so that it doesn't wrinkle, with a normal roll former. The forces required would be huge.

But maybe the OP will want to call a roller manufacturer or a jobber and see what they say.

-- Ed Huntress

Reply to
Ed Huntress

If you read up on the roller mfg, they do ANGLE IRON rolls with the leg

***IN***. Sure, they have limitations on how long the leg is but it can and is done every day. For the angle iron, the roller die has to have a suitable slot so the inward leg is constrained while bending. It is being compressed so it will expand (the web will get thicker).

For the >> Operative word is 'roller'

Reply to
RoyJ

Yeah, I read it, and I visited a number of roll-forming operations when I was writing for fabricating magazines. Again, the thing to do here is to talk to a jobber or equipment manufacturer. I don't think the dynamics will work out, Roy.

Without making a long story out of it, the forces involved in bending angle iron or channel apply the stretching (outside leg) or shrinking (inside leg) to the web (the leg) in such a way that there is no lateral load on the web. Yes, it needs constraint, because it will seek relief by moving in or out, but there is no *resisting force* encouraging it one way or the other. If you can keep it from starting to wrinkle with a lateral guide roller, you can overcome that tendency of the web to move sideways to seek relief, and you'll get it to shrink, if you apply enough force.

With the angled web (the flange, or the cone shape) the resisting force is trying to flatten the web back into its original plane all the time. It's always pushing against the outside restraining roller, assuming you're using an outside restraining roller. And the force trying to press that web flat is considerable. In this case there is not only a tendency for the web to resist compression (shrinking) but there also is a force trying to *relieve* it: the resisting force that's trying to flatten the web back to its original plane.

This is going to produce a lot of wrinkling. I'd bet on it. But I would talk to an equipment manufacturer before betting money on anything here one way or the other.

Reply to
Ed Huntress

well I think Ed is right , the conical part will wrinkle without any doubt if I just use a simple roll forming.

but no one had seen how such part is created? I myself think of spin forming , maybe shear spin forming or flow forming

the fact is we don't concern about the money , even about 16000 $ is just fine , but we don't know investing in which way would be better.

as I mentioned before , casting is not allowed , it should be formed from sheet.

once someone mentioned of machines used for making Saturn V rocket nozzles , anybody know what machines do they use for that forming process , I'm sure theire material is much more stronger than stainless steel.

Reply to
shantia

Reply to
RoyJ

I was joking about the Saturn V. The engine (Rocketdyne F-1) has several sections of curved shapes and most of them are double-walled, so I don't now how relevant it would be.

Have you called any fabricators who specialize in thick metal, to see what they say?

-- Ed Huntress

Reply to
Ed Huntress

in fact we have called some , but no one accept the risk of it.

they just suggest to thinking on roll forming , spin forming , stretching or a mixed up of them!

Reply to
shantia

I spent a couple years off and on designing equipment and tooling for GE's medium steam turbine division while they were in the process of consolidating several plants. I saw plenty of parts not so different from what you've got. They were generally fabricated, welded, stress relieved, and machined. Most internal parts were 400 series stainless steel. I'm sure the more complicated parts bounced back and forth between those processes several times.

Which is my long winded way of getting around to the suggestion that you check with companies that rebuild and repair turbines, for example:

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Reply to
Ned Simmons

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