Electronics > Mechanical & Automation Engineering

Remove warp from aluminium plate?

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beanflying:

--- Quote from: aneevuser on May 24, 2022, 07:41:04 am ---
--- Quote from: beanflying on May 24, 2022, 02:41:59 am ---Chances are whatever you do to reverse that bend caused by the saw cut you will add reversed stress into a bit of material still containing residual stresses. This sort of Aluminium is formed by rolling to a Temper in one direction and it is not normalised in anyway after as far as I know or remember.

--- End quote ---
I didn't cut this - I bought it cut-to-size, and it was fine on arrival. The warp has been caused by drilling, AFAICS - no warp before drilling, warp after drilling.


--- Quote ---Other than that you will need likely to look at a different grade of Aluminium. You might get lucky locally and find an offcut of Tooling Plate which is typically Cast. There was some bits floating around on evilbay US a while ago.

--- End quote ---
Is tooling plate less likely to have residual internal stresses? If so, may be useful to know about for future reference.

--- End quote ---

Yes as it is cast rather than mechanically worked into shape via a roller or forced extrusion process. There is some in the UK on evilbay marketed for 3D printer beds too eBay auction: #265311533227

The long cut will be why it warped the stress relief from the holes will be minor in comparison.

By all means try reversing the bend and holding it too, unlikely you will break it but also it is unlikely you will get it 'flat' and have it stay that way. You could also try a long soak of a few hours in your home oven to try and reduce the stresses (normalize) it but generally you need a higher temperature typically 300-400C the downside to this is you will also change the temper (generally soften it).

aneevuser:

--- Quote from: beanflying on May 24, 2022, 07:52:35 am ---
Yes as it is cast rather than mechanically worked into shape via a roller or forced extrusion process. There is some in the UK on evilbay marketed for 3D printer beds too eBay auction: #265311533227

--- End quote ---
Thanks. That is very useful to know. These residual stresses in formed metal seem to be quite a problem - I'm no great metal worker, and am quite surprised by how tricky it is to work some materials.


--- Quote ---The long cut will be why it warped the stress relief from the holes will be minor in comparison.

--- End quote ---
I'm not sure what you mean by "long cut" - I haven't cut this, I have only drilled it.


--- Quote ---By all means try reversing the bend and holding it too, unlikely you will break it but also it is unlikely you will get it 'flat' and have it stay that way. You could also try a long soak of a few hours in your home oven to try and reduce the stresses (normalize) it but generally you need a higher temperature typically 300-400C the downside to this is you will also change the temper (generally soften it).

--- End quote ---
I think that I shall avoid any kind of heat treatment - seems to easy to screw alu. up by doing that. If my hammering goes horribly wrong, I may treat this piece as a learning experience and see what happens when I heat it.

And re: tooling plate - it looks like there's a hefty premium over standard rolled plate.

jpanhalt:
I think "the long cut" may apply to the sheared edge in your top photo.  Although, the curl looks to be in both directions.  One sees curl like that when relatively narrow strips are sheared from larger plates.  Are you sure there was no curl before drilling?  Was it fully supported while drilling?

As mentioned slip rolling would be my first choice as it is easiest to control.  If you have a press, my second choice would be to try to bend back between two supports.  I would put a 3rd piece under it to limit the amount of deflection.  Assume you will need to go past flat for the bend to take.  I prefer to bend less and repeat than to straighten from the other direction.  I tend to go about 5° past vertical for 90° bends starting with flat stock.

beanflying:
The obvious shear marks on the photo above. When you get to thicker sheets like this a shear really becomes an issue as it is not a simple knife moving vertically down against a lower blade but the two are at a slight angle so it is a shallow scissor type of action which tend to create a curling force. There is ways to minimise the deformation and stresses but when you shear metal but over a certain thickness best thing to do is look at another cut method. This will vary a lot depending on the shear as it is quite possible to shear stock of 25-30mm with the really heavy ones. Preferably I guess you would use some form of cold saw over a certain thickness but this comes at a time cost. So Bandsaws, Cold Cutting saws or Waterjet are some of the alternates all of these put very low stresses into the metal across a longer length.

Typically as your part was fairly small it likely came off the back side of the shear meaning it wouldn't have been supported by the clamping jaws of the shear either. That is just speculation without knowing your source but it would be uncommon to poke the large part of the sheet out the back and keep the small bit to hold onto.

aneevuser:
OK, with much more vigorous clamping than I tried before, I have eliminated most of the deflection. I've attached a couple of images for comparison.

It's not perfect, but good enough for my purposes, and I don't want to go any further as I seem to be introducing a small amount of deflection along the long axis, as I reduce it along the short one.

Anyway, thanks to all for the suggestions and info.

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