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Perforated Metal Warping

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Perforated Metal Warping

Perforated Metal Warping

steris

(Mechanical)

(OP)

22 Sep 09 13:23

I am working on a design where we are looking to replace wire rack shelving with perforated metal.  The shelves will hold liquid containers and need to be fairly flat.  However, all the prototypes we have constructed suffer from an oil can type warping.  The rack will bow up in the center and then as you put weight on it, it will suddenly pop down.  We installed a support in the center however now we have two sections that bow - one on each side of the support that bow about half as much.  Adding more supports creates more sections that bow however each section bows less.

I understand that the perforating process stretches the material, however I am at a loss of how to address this.  Adding lots of supports solves the problem but yields a fairly ugly and time consuming product.  Anyone have any ideas on how to reduce the warping?

RE: Perforated Metal Warping

BrianPetersen

(Mechanical)

22 Sep 09 13:29

Form ridges or grooves into the shelves at periodic intervals. The ridges/grooves can point down to avoid causing trouble with whatever is on the shelf.

RE: Perforated Metal Warping

rstupplebeen

(Mechanical)

22 Sep 09 13:34
A picture would be more helpful.  How are the perforations made?  I hope this helps.

Rob Stupplebeen

Try stamping a channel in it similar to gas cans. http://www.okoffroad.com/gifs/stuff/gascan-1.jpg A picture would be more helpful. How are the perforations made? I hope this helps.Rob Stupplebeen

Rob Stupplebeen

RE: Perforated Metal Warping

steris

(Mechanical)

(OP)

22 Sep 09 14:59

Thanks for the suggestions!  I am unable to place a channel or grooves into the shelf because the surface must be flat.  Also, I am worried about tearing the material along the perforations with any sharp bends.  Is there some way to mildly stretch the other side too?  Would annealing or bead blasting help reduce the residual stresses from the stamping?

-Steris

We are purchasing the material from a perforated metal supplier. The material is fabricated out of 16 gage 316L stainless sheet stock. It is punched 1/2" holes on 11/16" centers on a staggered 60deg pitch. http://www.accurateperforating.com/images/patterns/large/RS096.jpg Thanks for the suggestions! I am unable to place a channel or grooves into the shelf because the surface must be flat. Also, I am worried about tearing the material along the perforations with any sharp bends. Is there some way to mildly stretch the other side too? Would annealing or bead blasting help reduce the residual stresses from the stamping?-Steris

RE: Perforated Metal Warping

SnTMan

(Mechanical)

22 Sep 09 15:07

You may find something else is more practical to use.

http://www.iperf.org/perfhandbook.html

Regards,

Mike

steris, there is just about no way to prevent punched perf metal from warping, however some suppliers can have the sheets levelled after perforation. Not cheap though.You may find something else is more practical to use.Regards,Mike

RE: Perforated Metal Warping

MTPipeliner

(Structural)

22 Sep 09 15:10

This is way outside my area of expertise so maybe this won't even work, but is it possible to punch half the holes, then flip it over to punch the other half?   

RE: Perforated Metal Warping

mcgyvr

(Mechanical)

22 Sep 09 16:18

The bottom surface of the shelf has to be flat also? Your putting supports on the bottom surface of the shelf aren't you? Those supports obviously aren't flat. I think you missed the fact of having beads formed on the bottom side of the shelf. So the bottom will have the bumps and the top is still flat with grooves indented down.  

If you want to learn more, please visit our website gaite.

RE: Perforated Metal Warping

dvd

(Mechanical)

22 Sep 09 16:45

I think your corners are overly constrained.  Try fully constraining one corner and let the other corners float.  You may need to use slots and shoulder screws to accomplish this.

RE: Perforated Metal Warping

berkshire

(Aeronautics)

23 Sep 09 01:06

Have the sheets stretch leveled after punching and before continuing with the rest of the fabrication.
Per SnTMans suggesion.
 The punching stretches the metal around the holes and will cause the oil canning you describe.
B.E.

RE: Perforated Metal Warping

steris

(Mechanical)

(OP)

23 Sep 09 12:24

Thanks for all the suggestions.  I am looking into the stretch leveling to see if that is cost feasible.  That solution seems like it should be easily doable.

As far as the bottom being flat - I meant that the top surface (where the containers rest) must be flat.  Stamping a channel similar to gas cans, while an excellent idea, would not work for our situation.  The supports I've already tried are attached to the bottom surface of the shelf and do not disturb the surface where the containers rest.

Thanks again for all the help!!

RE: Perforated Metal Warping

SnTMan

(Mechanical)

24 Sep 09 17:55

steris, you may find 16 ga. oilcanning anyway without some means of stffening it.

Good luck,

Mike

RE: Perforated Metal Warping

ginsoakedboy

(Mechanical)

25 Sep 09 12:03

Have a diagonal brace tack-welded to the bottom after the perforation process. Then you will not need the levelling process.  

RE: Perforated Metal Warping

MikeHalloran

(Mechanical)

25 Sep 09 14:15

Another option:  Use much thicker sheet, and have it perforated by laser or waterjet.  No warping, no limits on 'punch' shape, no limits on spacing.

The only limit on complexity is that the cutters price their work by length of cut or machine time (same thing, really).

 

16 gage is too thin for even a solid flat shelf, much less a perforated one with minimal support.Another option: Use much thicker sheet, and have it perforated by laser or waterjet. No warping, no limits on 'punch' shape, no limits on spacing.The only limit on complexity is that the cutters price their work by length of cut or machine time (same thing, really).

Mike Halloran
Pembroke Pines, FL, USA

RE: Perforated Metal Warping

StoneCold

(Chemical)

25 Sep 09 16:45

What about making the shelf out of wedge wire?
I like that stuff.

RE: Perforated Metal Warping

CorBlimeyLimey

(Mechanical)

26 Sep 09 15:16

What size is the shelf?
How is it supported?
What shape, size and weight are the liquid containers?
Does it absolutely have to be stainless steel?
Without little details like those, the best answers you get will be pure guesswork.

Instead of trying to fix the problem, eliminate it.
If the material is creating the problem, then use something else.

A thinner material with suitable edge forms and stiffening ribs can be surprisingly rigid.

Have you considered laminating a thin sheet of material onto a honeycomb/lattice structure?

Ore even the same perf sheet you have, but suitably reinforced with stiffening ribs, and with a very thin sheet of material bonded on top to give the flat surface?

RE: Perforated Metal Warping

rb1957

(Aerospace)

28 Sep 09 11:51

weld angle of tee extrusions onto the lower face.  how heavy are the liquid containers ?  how wide and long are the shelves ?

RE: Perforated Metal Warping

steris

(Mechanical)

(OP)

29 Sep 09 18:03

Thanks for all the help.  I looked into the stretch leveling but the perf manufacturers are fairly confident that it won't solve much of the problem.

I will look into the diagonal braces as well as the water jet cutting.  It turns out the laser cutting is really expensive but with the waterjet they may be able to stack multiple sheets on top of each other.  Also, I am examining the possibility of bumping to 14 gage.

The laminate or solid sheet over honeycomb is an interesting idea.  That could work but I also need drainage in case the containers leak.  These shelves are 22" wide by 30"-55" long and will hold no more than 100 lbs UDL.

RE: Perforated Metal Warping

MikeHalloran

(Mechanical)

29 Sep 09 20:39
Obvious question:  Does it have to contain _all_ of the possible leakage, i.e., is it secondary containment or just for nuisances?

Another question that has a bearing on what's appropriate:  How many shelves will you be making or buying?

And:  What's the environment?  By which I mean, oilcanning and deflection of sheet shelving is largely a cosmetic consideration.  Is the shelving in a retail or other environment where appearance is important?

 

You might have mentioned the need for a drip tray earlier.Obvious question: Does it have to contain _all_ of the possible leakage, i.e., is it secondary containment or just for nuisances?Another question that has a bearing on what's appropriate: How many shelves will you be making or buying?And: What's the environment? By which I mean, oilcanning and deflection of sheet shelving is largely a cosmetic consideration. Is the shelving in a retail or other environment where appearance is important?

Mike Halloran
Pembroke Pines, FL, USA

RE: Perforated Metal Warping

berkshire

(Aeronautics)

30 Sep 09 00:04

Steris
It should be possible to make a shelf out of 16 Ga perf SS that size that does not, oilcan.
 Are you bending flanges on the outside of the shelf, if so how deep?
 If they are 1.5" to 2" deep, you should be able to run the edges through a 3 roll bending roller clamped tight,( not a pyramid roller) to pre-stretch the material before you form the flanges. There is a fine line to this, not enough and the part will oilcan, too much and the part will flip flop diagonally across the corners. The shelf will still deflect under load but should not oilcan. If possible put a 1/2" return under the bottom of the flange, and tack weld there, try to avoid welding the vertical corners.
B.E.

RE: Perforated Metal Warping

macthenife

(Mechanical)

4 Dec 09 18:33

Cut the shelf into wide strips.
Bend and reverse the long sides to form a "shelf slat."

A typical slat could be say 30 inches long by 6 inches wide
by 1/2 deep.

These will not oil can but  rivet,screw or bond in position to avoid twist.

 

RE: Perforated Metal Warping

mfgenggear

(Aerospace)

7 Dec 09 19:57

why not tack weld the sheet onto the frame.
restrain it?

RE: Perforated Metal Warping

EngineerTex

(Mechanical)

9 Dec 09 17:04

Here's what I think your problem is:

The punching operation distorts and stretches the material in the middle, but not around the edges.  This makes the problem that there's too much material in the middle of the shelf.  So, how can you shrink this (slight) overabundance of material?  

You might try either of these:

1) Run a weld bead in a large "X" on the underside of the shelf.  As the bead cools, it contracts, pulling the material inwards.  This is done in the manufacture of safes when a panel is bowed out after the heavy welding around the edges.  The large "X" is done on the inside and then covered with insulating material and is never seen.  Depending on the amount of initial distortion, I would imagine that your welding techs can get a feel for how long/what size the weld bead would need to be.  Though I'm guessing you don't need much.  The only issue I can see with this is that it may discolor the top side of the shelf which may or may not be a problem for you.  

2) Keep the outer edges of the shelf cool with a copper heat sink or jig or by clamping it with some long flat bar.  Next, heat the middle of the shelf with a rosebud torch and use separate supports to keep the shelf as flat as possible.  After the middle of the shelf is red hot and well supported, cool it with water or ice or compressed air.  You may find that you don't need to do any sort of forced cooling beyond just still air.  BUT MAKE SURE THAT IT IS SUPPORTED WHILE IT IS COOLING.  What this process is doing is introducing residual tensile stresses in the material.  Just make sure that you keep the outer edges cool, get the majority of the inner area glowing red hot and don't allow the weight of gravity to distort it while it is hot.  

Either way, you are making the shelf more like a trampoline which is preloaded with tensile stresses before service, as opposed to being like the top of a paint can which will be unpredictable and annoying in use.  

If you try #2, you may also go to a local auto body shop, as this is a process that they use to remove minor dents from body panels if the distortion isn't too great.  
 

Are you using a press brake to make flanges around the edges of the shelf piece? I couldn't imagine a shelf being made out of simple flat sheet without incorporating flanges around the edge. Even if you're not using flanges, I don't think that adding flanges will prevent the problem you're encountering.Here's what I think your problem is:The punching operation distorts and stretches the material in the middle, but not around the edges. This makes the problem that there's too much material in the middle of the shelf. So, how can you shrink this (slight) overabundance of material?You might try either of these:1) Run a weld bead in a large "X" on the underside of the shelf. As the bead cools, it contracts, pulling the material inwards. This is done in the manufacture of safes when a panel is bowed out after the heavy welding around the edges. The large "X" is done on the inside and then covered with insulating material and is never seen. Depending on the amount of initial distortion, I would imagine that your welding techs can get a feel for how long/what size the weld bead would need to be. Though I'm guessing you don't need much. The only issue I can see with this is that it may discolor the top side of the shelf which may or may not be a problem for you.2) Keep the outer edges of the shelf cool with a copper heat sink or jig or by clamping it with some long flat bar. Next, heat the middle of the shelf with a rosebud torch and use separate supports to keep the shelf as flat as possible. After the middle of the shelf is red hot and well supported, cool it with water or ice or compressed air. You may find that you don't need to do any sort of forced cooling beyond just still air. BUT MAKE SURE THAT IT IS SUPPORTED WHILE IT IS COOLING. What this process is doing is introducing residual tensile stresses in the material. Just make sure that you keep the outer edges cool, get the majority of the inner area glowing red hot and don't allow the weight of gravity to distort it while it is hot.Either way, you are making the shelf more like a trampoline which is preloaded with tensile stresses before service, as opposed to being like the top of a paint can which will be unpredictable and annoying in use.If you try #2, you may also go to a local auto body shop, as this is a process that they use to remove minor dents from body panels if the distortion isn't too great.

Engineering is not the science behind building.  It is the science behind not building.   

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