STAMPING SHEET METAL

The preform stations of the progressive die keep it from wrinkling. :)
That's sort of a joke, because it doesn't appear that you are trying to "deep draw" your AL stock......so I wouldn't think you would have any wrinkling problem.
How many of these parts are you trying to produce? If not too many, you may just be able to take an appropriate sized ball bearing, fit it to a fixture that holds it in the top of any type of press (i.e., jack screw or hydraulic etc.), make an appropriate sized female receptor and mount that in the bottom of the press, form your parts using that set up, and then simply make a circular punch die to punch the finished hemisperes out of the sheet of formed AL.
Actually, when deep drawing metal, it gets alot more complicated and I am tired now, so I am not going to write a book. Dave

Shouldn't take much force at all. The will depend on the alloy and on the clearance between the punch and the die.

Not much force at all. The force will depend on the alloy and on the clearance between the punch and the die. Low end will be one ton to get good deformation. More will be required to get a clean sharp bend around the edges. Gathering shouldn't be a problem. For best results use grade 3003 aluminum or maybe 5005 but avoid 6061.
starbolin

The long explination is... Long..
But, you should try experimenting, if you have more time than money. If you find there is more wrinkling than you want, you will need a pressure pad which surrounds your punch (the male half of the tool) to apply pressure to the surrounding sheet metal to reduce/prevent wrinkling. The pressure pad will likely be spring loaded, so you'll have to add that force to your total force calculation.
If you're using small blanks as opposed to large sheets, you can just use some c-clamps to clamp the blank between the pressure pad and the die section (the female half of the tool). If you clamp really tightly, you'll get virtually zero wrinkling, but the sheetmetal will be stretched, which *could* created issues with thinning/cracking (may not be an issue in your case, however).
What's the part for? Will you punch out the hemisphere after you've produced it, or is it only a portion of the finished product? Application has a lot to do with the details of a press tool.
Regards,
Robin

Nice explanation, Robin. Thanx.
Bob Swinney

Thanks Robin. The shape I need is a bit more complicated than a hemisphere, but a ball bearing is a good "ferinstance" shape to give an idea of the size. The finished item will be a "hold-down" bracket to keep a laptop computer in place on a flat surface (four required per each). If it works out I'll likely need a couple hundred of them made-- which leads me to my next question:
Can I make the dies from a harder grade of solid aluminum? Or do I need to use steel if it's only going to be for this small run?
Maybe I'm kidding myself here. Maybe this wouldn't be as expensive to have made by a job shop as I'm thinking. It's just that, whenever I hear the word "custom tooling charge" my eyes start to roll like a slot machine... Thank you, --Max

At this point, I think you should look at trunk corners, and see if they wouldn't do the trick. A trunk corner is a pyramidal piece of stamped sheet metal riveted to the corners of luggage, roadie-cases, and equipment boxes. Since they're regular tetrahedra with 90-degree apex angles, a simple "L" bracket could fasten the thing down to the table in such a way that the fasteners weren't visible or accessible. If the bracket were spot-welded to the inside of the piece, it would look "custom made", and should serve the purpose.
Take a look at any high-end portable electronics or the road cases used to move it, and you'll see the corner guards I'm talking about.
LLoyd

Then I take back what I said.
I don't like the idea . AL on AL tends to gall. Depending on the actual shape mild steel might work. The contact surfaces are usually pollished. Everything depends on the shape. Might be able to use soft tooling for the die or off the shelf tooling or something else. If you're trying to make a sharp corner or a return then that would be more difficult. Could you come up with a design that used just bends?
If you have the design finallized then fax a print off to a bunch of shops. Someone will give you a low enough qoute.
starbolin