Home sheet metal stamping help needed!!! - rec.crafts.metalworking

Message from discussion Home sheet metal stamping help needed!!!

F. George McDuffee

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More options Sep 27 2006, 12:36 pm

Newsgroups: rec.crafts.metalworking, alt.machines.cnc

From: F. George McDuffee <gmcduf...@mcduffee-associates.us>

Date: Tue, 26 Sep 2006 21:36:14 -0500

Local: Wed, Sep 27 2006 12:36 pm

Subject: Re: Home sheet metal stamping help needed!!!

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On 26 Sep 2006 17:24:53 -0700, "super88" <tdebo...@gatecom.com>
wrote:

>I'm going to post this message to all groups that I feel may be able to
>help. Bear with me, I'm ignorant, but ambitous. I'm tryng to make
>something similar to a cookie sheet. A little larger radius (2 1/2")on
>the corners and about 1 1/4" deep out of 22 ga. cold rolled steel. I've
>built a "press" using I beams and 25 ton bottle jacks to do the
>job.(Keep in mind if I could afford to job this out, or pruchase a
>press, things would be different.) Anyways, I've managed to make the
>part except for the corners wrinkle badly. I'm in the process of
>casting the female to allow me to use binders. The question is where is
>the best place to bind the blank? In the corners, or along the
>straights? Any help, opinions, suggestions, ideas are appreciated! I'm
>doing this with determination and junk layin around the yard. Buy a 10K
>press, hire a die maker...etc. are not the answers I'm looking for.
>Unless someone is willing to produce this for less than a grand. Thanks
>again!!

==============

The ingenuity and dynamism of participants of these groups
continues to impress me.

I think I understand your product/problem (and then again maybe
not.)

The sides and ends form well because these are flat curves. The
corners however are compound curves that bend two directions at
the same time with the result there is an excess of material and
it wrinkles. This is the same problem that you encounter when
you wrap a package, and have to fold the corners over to make
everything fit. Indeed, many cookie sheets have "envelope" or
folded ends, or the corners are "fluted" for just this reason.
Therefore, it is doubtful that binders will help the problem,
because the [extra] material is not moving in from the sides/ends
during forming, but is preexisting in the flat sheet.

In some deep draw products (such as sinks) the extra corner
material problem is "solved" by placing anchors completely around
the part. This forces the edges and ends to stretch and get
thinner, thus there is no "extra" material in the corners, but
just enough. The trade-off is the tooling is complex, the
presses big [i.e. expensive] (or they use stretcher-hydro forming
and expensive tooling) and the material gets thinner, and is
deformed extensively, which may cause problems with work
hardening, i.e. stainless.

As anyone who has attempted automotive bodywork knows, shrinking
metal, i.e. pounding out dents where the material was actually
stretched is very difficult. Indeed, it is so difficult that
normal practice is to "get it pretty close" and fill in the rest
of the way with lead or Bondo, which is then planed/sanded to
fit.

See
http://www.polyprod.com/successful-applications.html

http://www.polyprod.com/customtooling.html

http://cumahome.org/Brochures/Castable-Ureth-Elast_You.pdf#search=%22...

http://web.me.unr.edu/me353/pdf/smf.pdf#search=%22forming%20%22uretha...

http://beckwoodpress.com/store2.asp?item=0224&cat=Application%20Speci...

And about 890 more when googling on < forming "urethane pad">

Good luck on your product, what ever it may be.

One final thought - have you contacted Elko or other cookie sheet
manufacturers? They may have something off the shelf.

Unka George (George McDuffee)
...............................
So long as a man rides his Hobby-Horse peaceably and quietly
along the King's highway, and neither compels you or me
to get up behind him-pray, Sir, what have either you or I
to do with it?
Laurence Sterne (1713-68), English author.
Tristram Shandy, bk. 1, ch. 7 (1759-67).

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