Here's a tough one -- rolling ribs in a cone

On Thu, 5 Feb 2004 20:37:02 -0800, Bruce Simpson wrote (in message ):

I don't know the end use of your cone or how many you need. If it's a small number could you fabricate a graduated series of solid rings and bond/screw/rivet/weld them to the cone, either inside or outside?

Just an off-the-top-of-my-head thought.

A low tech version of hydroforming might be what you are looking for, if you can make a complete outside form in 2 or more parts, split lengthwise (to remove after the ribs are formed). Alternatively it could be made in shorter split sections and the ribs put in a few at a time, the tradeoff being a new tool for each section.

A heavy rubber bladder is made to roughly fit the inside and all hydraulic escape paths accounted for, forming a cavity. High pressure fluid is pumped in to expand the metal into the die, and the bladder and die removed. Lacking a pump, low explosives could be employed. I have even heard of hydroforming using a simple wire to generate the pulse with a tremendous current from a cap bank.

In industrial use, the bladder design is carefully tuned to the application to get the most uses before it wears out. Yours need not be as exacting as long as the function is there once.

Just thinking out loud...

Or revising the solid female die approach to just another cone cut into sections with enough removed to just expose to the air the places you want ribs, giving weaker single wall area where you want them and double or more if thicker material is employed for the straight sections.

There is probably an easier way, but I'll leave it to someone else to think up.

Glad to hear you are still around and kicking. Did you get some kind of resolution to all the trouble over the big CM project?

StaticsJason

...

Option the first - TIG a bead around the cone every 8"

Option the second - the matching backup form to your "inside the cone roller" is a bearing with appropriate groove on a metalspinning tool, freehanded or held in a cross-slide toolholder. I think you only want a single wheel inside with an arrangement to push it out from the support, but perhaps you could use 3 grooved bearings on a steady-rest and 3 wheels inside to match - that would reduce springing, but increase complexity a bit. You want the wheel and bearing positions to match up.

Details get a bit messy, but I'll give it a whirl. You need to hold and drive the cone from the headstock end of the lathe, and you also need a support for the inside wheel or wheels. I think the easiest approach to the inside support is to have it fixed, and then have a bearing (essentially a live center) where it picks up support at the headstock end. The tailstock supports the far end, and the expandable wheel or wheels sit in there, opposite the grooved bearing or bearings.

Unfortunately that's a lot of jingging and tooling to make for a one-off build. Since I'm prototyping rather than manufacturing, I was hoping for some technique or tool that could be (re)used across a wide range of different sizes of workpiece.

Not yet -- the whole thing still smacks of political agendas and much going on behind closed doors. But trust me, from where I sit, the fat lady hasn't sung yet :-)

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Nope, that won't work because of other factors.

The cone in question is subjected to huge levels of vibration and rapid temperature cycling (about 40 times a second) which means that any thickness variation in the metal (such as a weld bead) creates significant stresses that manifest themselves as fatigue, and within a very short period of time, cracking.

The problem with this approach is that I don't have a lathe that is

6.5 feet between centers :-(

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Hmmm, reminds me of 55 gallon drums.

Maybe you can apply them before rolling the cone?

Tim

-- "That's for the courts to decide." - Homer Simpson Website @

Ah, but then they'd have to be made in an arc on the flat sheet or they wouldn't line up once the cone was rolled (tubes are much easier).

There's also the problem that the rolling process would tend to crush the ribs :-(

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Hi Bruce,

Here is a thought to kick around. I imagine that you guys have formed these cones on some kind of slip or pyramid rolls.

Make up the required number of male positives of the bead shape that are tubes. These tubes fit the upper roll of your slip roll on the inside and have the bead form on the outside. These can be attached to the upper roll with set screws or some kind of split clamp collar. You could even use one and just reposition it for each bead along the cone axis.

Now I am assuming that you have already formed the cone and welded the seam. The next step is to re-roll the cone with the male bead rolls mounted to the upper roll. The only problem is the outer backup rolls will deform the beads. You need to provide a female shape or place for the newly formed bead. I would suggest re-rolling with a semi stiff urethane or rubber sheet as a backup. This can be fed through the rolls at the same time as the cone.

.04 stainless sheet should not be too bad. Remember that the bead is forming as almost a rolling point loading so not a lot of tonnage is needed. I would use a fairly high durometer elastomer as the backup. The rubber sheet should be cut like the flat pattern of the cone with added length in the circumference.

Stainless, and in particulair T316 work hardens rapidly. Try to form the bead in as few passes as possible.

This method assumes a couple of things. That you have a set of rolls, the upper roll is powered, and that the upper roll will accomodate the bead rolls added to the diameter and still fit inside the cone.

A second method would be to form the bead features in the flat pattern using a Pullmax machine (reciprocating tool) And then roll the flat pattern using the rubber backup and the normal upper rolls.

Or a third method might be to form the beads with a Pullmax and bump the cone in a pressbrake with a urethane lower die.

Tom Lipton

Have someone with a CNC plasma(theyr'e alot more available than you think) burn you out some smaller cones sized to match up with where you want the beads. Mark then with a Sharpie and bead there so the lines match up when rolled.

Set your front roller to the thickness of the metal _and_ the beads, that way it should not crush the beads as you roll. This is the biggest mistake most people make when rolling sheetmetal, they throw the metal up there and then wonder why they can't get less tha a 4" roll out of their 3" rollers. I usually set mine hand tight on both ends of the roll, then back off maybe

1/4 turn. Be sure to set the thickness at both ends of the roll, otherwise yo will get different diameters depending on where you set up on the roller.

Hope the above doesn't sound preachy, it is alot easier to show you than try to get it into this keyboard. :)

Regards, Jim C Roberts

The problem remains that if I'm rolling the rib onto the metal before I form ti into a cone, I'll have to roll an arc with a suitable radius

-- although I can mark that out before I do the rolling operation -- however, there's still the small problem of actuall forming that rib.

Using a regular rotary machine, I would still face the same problem as if I tried to do it *after* I'd rolled the cone -- ie: not enough reach. I guess I could use a two-part form (male & female) plus a bnammer to beat the rib into the flat sheet -- although I wonder if that might not create some significant distortion along the way.

I might mill up a couple of forms tomorrow and give this a try anyway. They'll have to be relatively narrow so that I can form the arc of the ribs relatively smothly -- it could be quite a tedious process when there are nine ribs involved -- but if it does the job and doesn't cost too much :-)

When rolling cones with a regular slip-roll you usually have no alterantive but to set the main rollers loose so that you can slide the wide end of the cone around, so that the rollers always lay on a line that is exactly perpendicular to the tangent that intersects the arc of the sheet being rolled.

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You do come up with interesting problems. I think I would make or buy a regular bead forming machine. At least it would work for some of the beads. And would give you a feel on how much pressure is needed to form .040 material. Making a longer frame for the beading roller shouldn't be too hard, but you can't have a very thick frame to fit in the 100 mm end and even the 150 mm end isn't all that big. Would having the beads mostly at each end of the cone work? Maybe a two foot section in the center with no beads, but four beads spaced over two feet at each end of the cone?

Dan