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Old 02-08-2016, 05:18 PM
foamcar foamcar is offline
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Default Shrinking metal thickness change

Is the thickness change in the haz measurable with a mic? Anyone done a study on this?

Thanks - Phil
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Old 02-08-2016, 06:01 PM
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I have shrunk a part in a dedicated recip machine with nice dies, shrunk the bejeepers out of it, and I found no discernible thickness change. The mic didnt have a tenths scale, I have been planning on trying it again to see if I can repeat this really odd sounding result.

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Old 02-08-2016, 07:43 PM
AllyBill AllyBill is offline
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Depends on how hard you go at the shrinking but you're talking very small values. I've run the digital verniers over the offcuts a time or two out of curiosity and never been sure if I was measuring surface irregularities or a genuine increase in thickness.
You're better measuring the other way. Wheel a shape in a piece of material then measure how small a change in thickness you need to push quite a lot of shape. Unless I'm making extreme shapes and in danger of going under a stipulated thickness or causing a failure in the material I don't give it a thought.

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Old 02-08-2016, 08:11 PM
mark g mark g is offline
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Some processes can cause shrinking and stretching at the same time which to varying degrees, cancels out the change in thickness. Shrinking parallel to an edge and stretching perpendicular to the edge in the same instant. It goes back to the plastic flow conversation.
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Old 02-08-2016, 09:19 PM
Kidpaint Kidpaint is offline
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I may not be understanding this right, but in one of Ron Covells videos "English Wheel Techniques" He does a quick over view on how the thickness and length changes with wheeling. Where is compares and measures metal as he wheels it. They all start the same gauge and length. He does measure a change in each piece as he wheels it more than the last. Its not very scientific as in there are lots of variables that arent accounted for.
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Old 02-08-2016, 09:21 PM
Kidpaint Kidpaint is offline
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Okay I wasnt sure what HAZ was, so after I wrote that I did a search. So my previous post means nothing. sorry lol
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Old 02-08-2016, 11:26 PM
crystallographic crystallographic is offline
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Quote:
Originally Posted by foamcar View Post
Is the thickness change in the haz measurable with a mic? Anyone done a study on this?

Thanks - Phil
Hi Phil,
I haven't done a "study" on this, per se, but I have made measurements over the years.
A few items of note:
Shrinking methods of varying types yield varying thickness increases.
Using a "grab and shove" machine (Eckold, ERCO, Marchant, YandE and ... etc) can yield thickness increases of 20-25%, in 3003 - no annealing, work until fatigue fracture.
Thumbnails, depending on setup, can see 15 -20% increases, in 3003- no annealing, work until fatigue fracture.
My APH can make increases in 3003 to 40% - no annealing, work until fatigue fracture.
... and in 2024-0 to 25% - no annealing, work until fatigue fracture. (no other machine or method makes it past 15% without failure, according to my tests.)
In one case, I used hand tools to increase thickness 300% in 3003, hot working with a rivet gun.
I wanted to prove to myself that a Vignale rear lid skin could be made in one piece, and without darts.
Unfortunately, I had to sand down most of that excess in order to be able to hem it over the dang frame...



(hope this helps?)
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Old 02-09-2016, 09:44 AM
foamcar foamcar is offline
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Thanks for all of the informative responses.
Phil
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Old 02-09-2016, 10:42 AM
Marc Bourget Marc Bourget is offline
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If you want further, technical, insight to thickness change google on "Poisson's Ratio."

FWIW

mjb
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Old 02-09-2016, 10:43 AM
crystallographic crystallographic is offline
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... if the metal does not gain thickness then it must be flowing in another dimension - as in spreading the edge out, as Mark G mentioned. There are 3 dimensions, and the metal has to move in one of them to see movement in another ....

If the frame of the shrinking machine is stiff and the dies/jaws are not permitted to respond to the increase in thickness, then the metal flows away.
It's actually simple when you think about what you are actually seeing.
(I teach this in my classes with a fresh deck of cards.)

As a corollary to the example above, simply scribe a line in from the edge of the metal and parallel to it 2in. - 50mm and shrink the edge without increasing the edge-to-line distance.
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Last edited by crystallographic; 02-09-2016 at 10:47 AM.
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