pressing indentations in sheet metal

I'm trying to make some parts that require indentations in sheet metal (see Fig. 1.). The metal used is .040" 1/4 hard copper sheet. The indentations are .750" OD, ~.656" ID, and .156" deep. As you can see, the sides of these dimples are close to perpindicular; they are pretty sharp bends.

I made the jig in Fig. 2 to form these bends. The hole in the bottom half is .750 x .156. The top half has a .625 hole. I put a piece of sheet on the bottom half, slide the top half over the pins to align the pin with the hole, put a .625 pin in the hole, and squeeze the crap out the whole thing in a vise (I have no press).

The problem is that the plates that I make are sometimes cut either around the upper edge of the .075 hole or around the bottom edge of the .625 pin (see Fig. 3). I have chamfered the edge of the .750 hole, and the pin already has rounded edges. I can't think it will get any better ifI move up to a .656 drive pin and the bends get even sharper.

I am using a .625 drive pin because a) I don't have a bit to drill a .656 hole, and b) I don't have a .656 pin or a lathe on which to turn one. Unless I can get this cutting problem solved, I am loath to invest in new tools.

Questions:
- Is there a real name for these indentations other than just "identations"?
- I'm just guessing on the 1/4 hard temper (although I know .040" copper is right). Would I have better luck with different material?
- Are there standards/specs for bends, punching, chamfering, etc?
- Are there special tools to take the sharp lip off a drilled hole? I just used a grinding bit on a Dremel tool, but that's a bit sleazy. I'm thinking a smoothly rounded lip (with a real tool)might help.
- Any suggestions on an easier/better way to do this?

Thanks.

Fig. 1:


Fig. 2:


Fig. 3:

Can you anneal the copper? Those will form a hell of a lot easier.

-Jacob

Kongaman, your material needs to be dead soft. (In fact, you probably will have to do the embossing twice, annealing in between the steps.) You need nice, polished radii on all of the edges, not chamfers.

As others have said the copper needs to be dead soft and you need smooth radiuses. I have made dies to make impressions in sheet metal but use a single pin in the center to guide the two parts together squarely in a press. When you use a vice the jaws are probably not closing squarely and this is causing some of the tearing that you are experiencing. Give yourself a little more clearance and let the metal flow freely to the shape you want. What kind of tolerances are you looking for?

Hope this helps.

Joe

Annealling? You guys are freaking genii. I never thought of that. I fired up the torch and had at it. It works great now. Thanks. BTW, these parts are going to be plated - will a buffing wheel take of the "scale" from the annealling?

How do I get the aforementioned radii on the edges? Are there special tools/bits for this?

As to tolerances - there aren't any to speak of, in that I'm not making precision parts here. My measurements were based on a) the preexisting sample part, and b) the functional need to get a 1/2" nut on the indented flat. Truth be told, the ID of the existing part is a little small, as you can't get a socket on the 1/2" nut. As such, I'd like to increase the ID to something greater than .694" (based on the OD of a 1/2" nut driver). But then, I'm faced with the prospect of either buying a bunch of bits in strange sizes that I'll probably never use again, or increasing the pin to 3/4" and reboring the bottom hole to 7/8". Or using thinner stock; switching to 20 gauge (.032") would gain me the clearance I need (but I don't know if it's sturdy enough).

Skip the buffing wheel and take care of it at the source. Get some firescale preventative...

Boric Acid mixed in denatured alcohol to a nice paste consistency. Brush this on. Use a slightly reducing flame. After heating, quench in water. You may have some "glass" on the part from the boric acid. Easiest way to take care of this is to put it in a pickle solution. Pickle is basically boric acid again, but a little different. I'll have to find an MSDS to figure out exactly what's in it.

Boric acid can be purchased at your local ceramics supply store...shouldn't be more than a couple bucks a pound.

Pickle works best if you heat it in a crock pot...just dump your piece in there afterward. Only use copper tongs in the pickle or it will become contaminated.

After this, if you want a really shiny surface, use a little tripoly followed by some jewelers rouge (different buffs, tripoli will contaminate the rouge and make it a tripoly buff wheel)

-Jacob

Oh...if you want a better way to make your die, get somethign from called liquid steel. It's basically JB weld. You can use your good piece as a pattern for the die.

You can press this whole thing out on a hydraulic press much easier. Go to:

Bonny Doon

And check out their presses. Basically, by using a hard die and a urethane "punch", you can hydraulically form the part. 18 gauge copper will probably take 95 durometer urethane. www.mcmaster.com sells urethane rubber

If you are making a bunch of these, it might be better to do something like that.

-Jacob

A generic name for the tooling would be "form punch/die. You could also call it "coining" as that's what shallow forming in material is called. The others are correct in annealing the material as copper will work harden and the radii are essential in forming material in this manner. For deburring you could either use a chamfering tool in a drill press/ by hand or there are also many deburring tools that are inexpensive in catalogs that use replacable tips that rotate in a plastic handle.