Punching vs Cutting


I need to figure out a way to punch out shapes from .025 aluminum sheet.
I've got the little taig mill of course, but I'm thinking it will be
incredibley slow, and if the project works I'll want to punch a lot of them.
The shape is roughly triangular with an outside shear length of
approximately 6 inches.
I also considered the idea of making some kind of punch that I could use in
my press, but I haven't any idea how to start or what material to use for
the punch itself. Also, I am thinking something as slow as a hydraulic
press is going to tear and distort the metal rather than punch it out. I
made a couple of custom punches out of some stainless rod stock for another
project a while back and even for paper they only lasted a very short time.
Going back to the idea of using the mill. What do you think is the most
aggressive cut and cutter I could use? The spindle RPM maxes at 10,000 and
my max IPM is about 30 for rapids, but with any force for feeding is 20. I
have a couple details on the cut that could double as holding tabs and be
cut as a seperate operation.
Reply to
Bob La Londe
Loading thread data ...
Stack up a bunch of blanks and chew them all out at once. Could also do the same and use a pin router with a template on top or bottom. Usually uses handfeeding against the guide pin. Quite common to use wood-cutting router bits on aluminum, too.
Stan
Reply to
stans4
Yep. I use some carbide wood bits on aluminum all the time because they just don't make certain sizes and shapes of mill bits that will fit my little mill.
Reply to
Bob La Londe
Tell me about your press. Make your punch and die out of O-1, you can harden it easily with an OA torch and quench it in oil. Easy-peasy! I'd be glad to quote the part if you like.
Reply to
Buerste
Consider a Beverly shear to cut them out. You didn't say how much "a lot of them" is, but a Beverly shear can cut them out pretty fast. This kind of shear cuts around curves, too. Harbor Freight has a knock-off model for something around $100 that would work well for this. I have had one for several years and it's one of the neatest tools in my shop. If you lived around Baldwin Wisconsin, I'd be glad to let you try it out.
Pete Stanaitis ----------------------------
Bob La L> I need to figure out a way to punch out shapes from .025 aluminum sheet.
Reply to
spaco
Well, I just have a generic open frame 12 ton air over hydraulic H-frame, but I was thinking something like a compound lever action arbor press might work better if it will produce enough force.
I'll have to look see what O-1 is. If it machines well I guess I could just make it with my little mill easily enough.
Hmmm.... that is an option.

Reply to
Bob La Londe
Initially maybe 100 or so. Give or take. They need to be pretty identical though and have exactly the same weight.
Watch it. That's the kind of thing that's likely to get me to roll the bike out of the garage.
Reply to
Bob La Londe
Hmm ... for distortion -- make the punch nose flat, and the die angled so it starts cutting near the middle of one side and at the point opposite (assuming that the triangle is equilateral) so the distortion is in the waste stock instead of the workpiece. (This probably means that you want to shear to blanks not too much oversized to start with.)
Hmm ... this sounds like a job for a flywheel punch press. But with a 6" perimeter, my little 1-1/4 ton one would not have a chance.
O.K. A bit of calculation, with a full perimeter of 6", a thickness of 0.025" and 6061-T6 aluminum at 30,000 PSI shear strength gives 2.25 tons using the formula:
Tons=Pi*D*S*T/2000
and replacing the Pi*D with your 6" perimeter.
Here is a 7-1/2 ton one on eBay if you are near New Jersey:
320556364771
And a 10 ton one:
360275737690
And a 5 ton one:
360268548345
Search for "punch press"
These essentially have a flywheel spinning around a shaft with an eccentric which drives the punch holder a short distance. There is a dog clutch which is tripped by some mechanism or other (some are air, other mechanical) after which there is a quick up-and-down stroke and then the clutch releases and pauses for the next trip.
Note that these strokes are quick and thus quite dangerous to the user. Probably best if you set it up so both hands are required to trip it.
Which stainless? They are not what I would choose for a punch anway. And paper has clay in it, so it is rather abrasive compared to aluminum.
I would use a high carbon steel (and did -- D2 air hardening -- to make some punches to cut out circles). Machine it to near the desired shape, harden and temper it, and then grind it to final dimensions.
And make sure that there are guide pins to keep the punch and die aligned.
And add a stripper to pull the workpiece off of the punch on the retract stroke.
Part of the problem is that you need a way to pull the chips out as the workpiece is cut. Since you are cutting through, put some sacrificial material below it. Use a shop vac with a reduced nozzle to pull air quickly past the cutter.
Perhaps have a toggle clamp which you can swing into place after the cutter passes so you don't need the tabs.
But if you want quick -- you are really talking about a punch press job here.
Or perhaps a waterjet cutter with a stack of plates to perhaps 1" thick or so (depending on precision needed) so you make a lot of them in one machine pass. (This means contracting it out, of course.)
FWIW -- the 1 ton punch press (or is it 1-1/4 Ton?) that I have I can just barely carry from one horizontal surface to another not too far away. Anything bigger -- expect to use something to help lift it.
Good Luck, DoN.
Reply to
DoN. Nichols
FWIW, the recommendations to make punch and die sets for this job seem a little cavalier. The punch/die clearance will be rather small and difficult to keep consistent with a manual mill, unless one is very good and has the right tools.
Tawwwwwm mentioned O1, which would do it easily for a few hundred parts, but heating a die of that size with a torch, as he recommends, sounds like a disaster waiting to happen. O1 is forgiving but this is an inside shape, fer chrissakes. I wouldn't try it without a decent heat-treating furnace.
D2 is overkill. It would work fine, but you're making the job more difficult than it has to be.
If I had to do it (and I wouldn't -- I'd have it wirecut; I think the clearance is enough that you can do a one-shot punch/die set from a single piece of steel) I'd make it from a free-machining grade made for case hardening and have it case hardened by a heat treating service. The cost is modest and it beats the heck out of doing a high-wire act with a torch.
As for curving the die set (cutting "shear" into the die, if the saved piece is the inside piece of the punching) to reduce forces, it's not a bad idea if you really have to. But if you can't develop 2.5 tons of force with your press, you have another problem. A press lighter than that is likely to strain, trying to keep the die centered in the punch. You'd need guide pins. Building a punch and die with guide pins and bushings is not for tyros. And don't forget to file some clearance into the die -- or make it thin, and make a die shoe with a slightly larger hole.
This is not a trivial job. If the stock was 0.006", it *could* be trivial.
Reply to
Ed Huntress
[ ... ]
O-1 is a high carbon oil hardening tool steel. You heat it up until it no longer attracts a magnet, then quench it in oil. Then, if you don't want it to be too hard and brittle, heat it up again, to a temperature determined by what hardness you want. I would suggest about Rockwell C 59 to 61 as being reasonable. From the tables in:
formatting link
you heat it to about 475 F (should be able to do it in the kitchen oven, if SWMBO does not object).
They suggest an hour per inch of thickness to get the tempering done all the way through.
Since you want a precise clearance between punch and die, and since the steel expands slightly when hardened -- you want to make it with overlap between the punch and die, and after hardening, use a die grinder to adjust to the desired final dimensions.
Make the hole too small, because it will grow with the material surrounding it. Make the punch just slightly too big to give room to grind back to a clean surface.
BTW You want the hole in the die to be the right size at the surface, and to taper larger behind the surface, so you don't wind up with the slugs getting stuck in the dies. (Especially here, where the slug is what you actually want to make. :-)
I *think* (but you should verify this first) that the usual clearance angle in the die is 7 degrees.
Good Luck, DoN.
Reply to
DoN. Nichols
Almost all my O-1 dies are full hard with no tempering. I counterbore the dies rather than taper, I leave 1/4" of land. Usually, I machine to size and not grind to size. O-1 doesn't move that much for me. But, 95% of my dies are for round parts in 19-11 ga. mild steel.
Reply to
Buerste
Wow! It doesn't have to be that complicated. I have O-1 dies, full hard with a torch and a bucket of quenching oil, that have served for decades making many hundreds of thousands if not millions of steel parts. A lot of them are on shoe plates not die sets unless there is more than one operation. But, I've made hundreds of die parts and have a knack for machining and heat treating them trouble free. OTOH, I've had some give me real headaches. For most of the high production or complex parts, the dies and punches are D-2 on die sets professionally heat treated. The OP job isn't above the hobby category, it can be way less complicated than a real production die.
Reply to
Buerste
I mentioned to a friend recently that the dishwasher would be a good way to clean some copper parts prior to patination. The alkali nature of the wash agent being good at removing finger prints etc. Apparently that and the patination worked a treat although she said her husband did give her a few odd looks when he saw the stuff in the dishwasher, it didn't bother her.
Reply to
David Billington
Weeeeeelll.... I think I'm gonna give punch making a try again. I got to thinking about it and its not much different than using a slug buster. A tool of which I have a couple. One hydraulic and one manual. The key being I'll have to design my irregular shape slug buster to use a c-clamp type configuration instead of a bolt through configuration.
Reply to
Bob La Londe

Site Timeline

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.