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Posted by rashid111 on May 19, 2008, 2:31 pm
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Folx,
what kind of surface finish can one expect punching holes (say 1.5"
long by .150 wide) in
1/8" thick 7075 Al ? The application is punching of reed holes in
accordion reed plates.
I have seen some that have near-mirror surface finish and am puzzled
as to how can it be
achieved ?
I have made some dies/punches, with .005 clearance all around. With my
hand-operated
flywheel press I can get holes in a single punch, but surface finish
if rather rough, so I have
to file the edges to get the smooth finish I require.
What factors could be affecting it ? In a factory condition, much
higher forces and speeds
can be obtained, but would it affect the surface finish ? With higher
forces, one can reduce
die/punch clearance - what kind of effect would that have on surface
finish ?
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Posted by Ned Simmons on May 19, 2008, 3:01 pm
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On Mon, 19 May 2008 11:31:22 -0700 (PDT), rashid111
>Folx,
>
>what kind of surface finish can one expect punching holes (say 1.5"
>long by .150 wide) in
>1/8" thick 7075 Al ? The application is punching of reed holes in
>accordion reed plates.
>
Google "fine blanking," e.g.:
http://www.fineblanking.org/process/howitworks.htm
--
Ned Simmons
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Posted by rashid111 on May 19, 2008, 3:47 pm
Please log in for more thread options Ned - that is an excellent link, thank you very much !
I now believe this is exactly how they make the parts
I mentioned .
> On Mon, 19 May 2008 11:31:22 -0700 (PDT), rashid111
>
> >Folx,
>
> >what kind of surface finish can one expect punching holes (say 1.5"
> >long by .150 wide) in
> >1/8" thick 7075 Al ? The application is punching of reed holes in
> >accordion reed plates.
>
> Google "fine blanking," e.g.:http://www.fineblanking.org/process/howitworks.htm
>
> --
> Ned Simmons
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Posted by on May 19, 2008, 6:10 pm
Please log in for more thread options > Ned - that is an excellent link, thank you very much !
> I now believe this is exactly how they make the parts
> I mentioned .
It sounds like you probably don't want a fine-blanking die.
They have (comparitively) high tonnage requirements because of the
virtually zero punch-to-die clearance (in the low tenths). Tonnage
requirement increases as clearance decreases.
They are fairly complicated and require excellent workmanship/accuracy
as there is virtually zero punch-to-die clearance. Slight wear/
deformation over the life of the tool with cause crashes and the
punches/dies will be difficult/expensive to replace.
They require a triple-action press (not really common/cheap).
Are you going to build the die yourself? How many parts are you
making?
There are other options.
You can run a second punch through as a single-tooth broach (taking
off perhpas .001-.002" per side), and you will likely get a machined
finish without the workmanship/accuracy requirements of a fine-
blanking die. Mind you, now you have to deal with the silly little
chips that will be generated by the cutting action. These are a pain
in the butt because you'll likely need a lubrication to prevent cold-
welding so they'll stick to everything. You can take off more of a
bite to yield a thicker slug, but your finish will suffer.
Depending on other requriements, you can burnish the inside of the
hole with a punch that has a taper, and then flairs out to your final
dimension. This is a forming operation so there is no cutting
involved, but you'll likely get a certain amount of bulging around the
edges of the hole, and the finish you'll get will likely be dependant
on the finish from the original punching operation. This means
lubrication, and you'll have to keep the cutting and forming punches
well polished to prevent cold-working.
If you're not making many parts, finishing the holes with some type of
abrasive may be most cost effective as you can get rolling
immidiately.
Regards,
Robin
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Posted by rashid111 on May 19, 2008, 7:55 pm
Please log in for more thread options Robin,
thank you for your post :)
Before I made my own set of punches/dies (I actually made a few for
different reed styles - italian and russian),
I read a bit about die making. I started with .002 clearance which I
had to expand to .005 to reduce the effort
required when punching.
The punches and dies are A2, milled and heat treated by truly yours.
To file the edges, I made a set of thin, wide
and tapered files - 2" wide tapering to about 1" (and few smaller
ones), 1/8" thick (and thinner). Milled the single
cut pattern on a mill with rotating head. These sure eat Al for
lunch !
I think I got as close to the best recipe for what I need to do, in my
conditions, as I possibly can .
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>
>what kind of surface finish can one expect punching holes (say 1.5"
>long by .150 wide) in
>1/8" thick 7075 Al ? The application is punching of reed holes in
>accordion reed plates.
>