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Hydraulic Press For Flattening MS Plates

09/08/2008 12:25 PM

Could anyone suggest to me the method of calculating the load required to flatten a MS plate of size 425mm x 180mm x 8mm thick on a hydraulic press to eliminate waviness on the surfaces from 0.5mm/1mm to 0.1mm and to subsequently eliminate the grinding operation? The plate is opticully cut to profile from a larger plate, which has waviness on the surfaces up to 0.5mm to 1mm at various locations. The flattened plate is used, after eliminating waviness as a mounting plate. Presently, I am using a small flywheel press and manually identifying the areas where there is waviness (after locating the plate between supports) and trying to smoothen out the surfaces. Thank you.

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Guru
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#1

Re: Hydraulic Press For Flattening MS Plates

09/08/2008 1:33 PM

If I understand it was lasered

The plate may not have been stressed relieved fully or the heat generated from cutting induced the stress.

This is difficult because of the little amount you want to grind off.

The only thing I can think of is to roll it (in a pinch roll) on one side only slightly

Flip it and then roll the other side.

But with the information no matter how much info you can supply, results can vary.

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#2

Re: Hydraulic Press For Flattening MS Plates

09/08/2008 11:42 PM

From your post, I have to guess that you are using hot rolled plate such as A-36. If so, this is commonly flattened by bumping it on a press brake followed by Blanchard grinding one or both sides as needed. For long term stability, you may wish to stress relieve this plate after the press brake operation and before the grinding. You are not going to easily squash this plate flat. Good luck with your project.

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#3

Re: Hydraulic Press For Flattening MS Plates

09/09/2008 5:06 AM

Hi There,

You won't flatten a MS plate to the tolerance you require, 0.1mm {0.004"} on any press unless you coined it flat & to size, the press tonage would be huge & even in MS there will be some springback. The plate would need to be ground on a surface grinder & shimmed as it is ground if you want to keep both flatness & parallelism, probably doesn't need stress relieving if you are only trying to achieve 0.1mm

Compare the cost of using ground stock [O1] instead of MS & its subsequent operations costs added although you may need to cut the GS to the sizes & this is an added cost.

You could get a lot of plates properly blocked to stop movement on a close pole spaced magnetic chuck Blanchard or similar grinder, 8 mm is a reasonable thickness to hold down.

Although I once saw a toolmaker accidentally engage the rapid traverse down on a Blanchard with about 150 small parts on a 3ft dia. table, spectacular fireworks display & bits flying everwhere.

Regards,

Brien.

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#5
In reply to #3

Re: Hydraulic Press For Flattening MS Plates

09/09/2008 2:55 PM

Hi,

Thanks a lot for your suggestions.

You do mention about coining / sizing operation. I agree that very high tonnage would be involved. The off take of these plates is very high and would therefore justify the cost of the capital outlay. Hence the requirement of a press.

What I am looking for is to theoretically determine the load required. For instance, if we talk about straightening, we do have a empirical formula (Force = 6UZ / 2000L) to at least get an idea of the tonnage of the press we would be looking for. I am looking for a similar formula to get an idea of the load requirement.

I have seen a press (250T capacity) for coining aircraft brake pads, although the material here was a composition of brass and ceramic (I am not sure of the exact composition of the ceramic) and the surface defects were minimal. Also, the area was much smaller.

I am wondering if there would be any method in determining the approx. load required to flatten the plate so I could at least conduct some trials on a press of such capacity as determined by the method.

Regards,

Kulalli

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Guru
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#6
In reply to #5

Re: Hydraulic Press For Flattening MS Plates

09/11/2008 1:51 AM

Irrespective of theoretical pressing force, I am doubtful about possibility of flattening the plate. This I had tried on just 1 mm MS plate with small area of 150 mm X 400 mm. We could not suceed with simple high force pressing.

We could do it only when we introduced some small sharp points of tool, which created small pin marks on the plate. The reason I do not understand.

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Guru

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#4

Re: Hydraulic Press For Flattening MS Plates

09/09/2008 8:41 AM

The press load would vary dramatically with the nature of the waviness. If the curves are compound, the the load would be far higher than for simple curves. Getting flatness to less than .1mm with a press would require a lot of trial and error, end each piece is likely to be different.

Eitel makes automatic straighten presses, used for, among other things, to straighten automotive camshafts after heat treating. The presses for this application have several arbors in a row and measurement probes at several locations along the length of the cam. The cam is spun, the runout automatically recorded at several places, and then the amount of correction for eash arbor location calculated. The press is actuated accordingly, and the the process repeats. Often one shot is all that is required.

A similar technique could be used for a plate, although the measurement and calculation of spring back would be trickier.

Probably easiest and most reliable to grind it flat.

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