Making steel "flat" is generally not an easy process - typically done by rolling or peening. Good luck..

It was originally on a coil, then pressed into a sheet, then parts cut from the sheet. As the parts are small they are quite flat now. I just want them flatter. I could get a roller rather than press I guess, what is peening?

Regards,

Ant.

Beat it with a hammer.

How flat is flat?? There are actually methods for describing "flatness"

It is for an ultrasonic device, the device works but as the steel isn't completely flat is has an audible ticking noise too. The device needs to be silent which means making quite flat into micro metre flat - flat enough to be quiet.

Will I be able to use an arbour press? Flattening 0.2mm thick stainless shouldn't be that hard should it?

You cannot make a steel sheet perfectly flat just by pressing on it. Coiled steel is flattened by roller levelers and then parts are stamped. As Mike said it's not that simple.

Anyone care to explain? Regards Ant

Try this as an explanation: The steel has a certain amount of springiness in it. If it's nearly flat now and you use a device to just squash it 100% flat by pressing against a 100% flat surface then, when you let go, your part will simply spring back a little to a "still not flat" shape. You need to over-bend it to beyond the flat condition you're looking for. You need to make it change shape just the right amount so that, when it subsequently springs back, the shape it springs back into is your desired degree of flatness. This isn't easy. This is what the rollers would be doing.

If you examine some old telephone relays, ...
Belay that.
If you can _find_ some old telephone relays, examine them.

You may find that the parts that have to be flat have been planished, i.e. pressed between flat dies whose faces are covered with arrays of small pyramidal teeth. The resulting pseudoplanar surfaces are obviously not optically flat, but they are mechanically flat.

You can buy aluminum sheets that have been 'stretcher leveled', or basically stretched in two dimensions until they begin to yield. I do not know if the stretcher leveling process would work on stainless steel; since I have never seen such sheet offered, I suspect not.

My theory is that planishing effectively performs stretcher leveling on a macro level, between the pyramids. Maybe it could work on stainless. You would probably need carbide dies, but if your workpieces are not large, the dies need not by hugely expensive. I don't know if planished surfaces would work in your application; only you can answer that.

Recent Trumpf CNC punch presses can be had with a marking head, that probably could planish parts like yours, one impression at a time (more rapidly than you can imagine) before blanking them. It might be worth a try.

Mike Halloran
Pembroke Pines, FL, USA

Yes that is a problem isn't it. I was assuming there would be a simple solution. What are the "methods of describing flatness" mentioned by miketheengineer?

I could buy a roller and get it into what I thought was flat but it probably still wouldn't be. A mammoth industrial press would presumably leave it a bit flatter but it'd still spring back to not quite flat. I will read up about planishing. Hmmmm.

Antknee
If the parts were cut out with a punch and die, they are likely to have a slight bow or dome from the punching process. To get them flat you have to stress relieve the part by stretching around the edge of the part.
Whilst a fly press can do this, it is hard on a hand operated press to control the pressure from stroke to stroke.
( As an apprentice I spent many an unhappy hour on one of these fiendish devices.) you would be better off limiting the travel against a hard stop.
A small hydraulic press that you can press to a known pressure will give you better results, for what you are doing 10 tons should be enough.You can buy one of these for about 140 Pounds Sterling
Also you only need pressure on the edge of the part, if you give it too much stretch on the periphery then the part will warp with a floppy edge, not enough and you still have the dome.
Good luck with this,
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

The parts were laser cut so aren't domed on the edge. I'm minded to think a 10 tonne hydraulic press will do the job and at £140 its not a startling amount of money. A new fly press can be >£2000 alone. Thanks.

I've found a 20 tonne hydraulic press for £140. Does anyone disagree about it doing the job? I'm thinking at some point just the sheer weight will flatten anything, but I'm not sure. I know from the earlier discussion a roller is preferred, opinions? Thanks, Ant.

Ant knee
Just to be sure we are talking the same loads your tonne is 2204.62 lbs, correct?
That should be more than enough to straighten your discs.The rest will depend on your tooling.
If they are lazer cut you will still have a small heat affected zone around the periphery.
You should not need as much straightening effort as with a punched blank.
Remember at this point you are hand straightening these parts, while the basic principles are as I described in my first post, this is still very much a trial and error process.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

Hi Berkshire, the press I saw is at the link below. It doesn't indicate if the tonne is 2204 lbs or not, but it probably will be.

http://www.ebay.co.uk/itm/200647032212?ssPageName=...

I can imagine I'll make a few mistake, at some point further down the line I'll also need to coin these parts with a punch of some description. It looks like this will be the right equipment, i'll just have to chuck some away! Thanks, Ant.

Antknee,
I was thinking something more like this, you can get this style in 20 tonne also but they are over 200 Pounds stirling.
http://www.ebay.co.uk/itm/BENCH-PRESS-10-TON-CAP-H...

B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

Yes that is much better, I don't want to be walking around the press all day. Made me chuckle that I hadn't thought it possible to get one in this size! Thanks, Ant.

Do you think the one I linked to could be used as a bench press? as I'd be putting it together myself it may be possible to adjust the legs and shorten them, getting the 20 Tonnes for £140. Thanks, Ant.

You could, But I do not think it is worth the trouble to modify it, when you can buy what you want readymade.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

Agree. Thanks for the spot on comments. Regards, Ant.

If you really want them flat then lapp them. adding force will change the distortion but not likely get them any flatter.

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Plymouth Tube

If you're serious about your flatness range then I'm not sure pressing will do it. If you really need to get down I think you probably need to grind or even lap as Ed says.

Flatness can be measured by the difference in height from edge to edge or to center line.


Look into "coining" - the US Mint does a pretty good job of this....

If they had been fine blanked in the first place they would be flat.
I would still try to lap them, you will get flatness better than you can measure and there is no tooling, just machining costs. Very low stress process also.

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Plymouth Tube

Lapping is rather labor intensive - BUT it will be FLAT!!!

If a 12" square of 0.020" shim stock is not flat, it will not be made flat by lapping. Just one example.

These are 1" diameter, easy enough to polish flat by hand.

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Plymouth Tube

Since you indicated an intention to coin the parts at a later process step, I fail to see the added value of lapping or even pressing them 'flatter' now.

Mike Halloran
Pembroke Pines, FL, USA