The material is 7075 Al and 360 brass - .062" and .050", holes are rectangular in shape, ranging from 1/16 x .5 to
1/8 to 2 ".Will any of cheap Arbor presses do (5 ton for example ) ? For now I mill these out, but it is tough to mill with
1/16" endmills :) 1/8 slots are much less of a problem when millingWhat other alternatives are there - ideally small and inexpensive nuff to fit into one's garage ?
Lots of tricks for this. Do you have any press now? How many/time? A small arbor press or even air press with the right die work. Your punches can be ground different ways to minimize pressure. Think of a "W" or "V" shape will spread out the pressure over the stroke. You must configure the punch to keep the material from being squirted out the side. Is there a common denominator so as to minimize the number of punches and dies so you can do bigger holes with multiple hits? Keep clearances tight, maybe 2% thickness per side. Put it on a shoe if at all possible, used shoes are cheap.
Define "shoe" in this usage
Keep your eyes open for a "fly press" - size 2 or so is small enough to be (vaguely) portable.[1]
Punches can be made with 40mm (1 5/8") bar drilled out to accept 13mm (1/2") tool steel inserts (or even centre punches) - drill and tap a hole horizontally to put a bolt in to hold tools in place.
[1] About a cwt (50kgs)-- BigEgg
Die set would be another term. See:
Why a "W"?
The distance between the peak and valley of the "v" should be about one material thickness. This varies based on material thickness and type.
As the clearance decreases, the tonnage (and punch wear) increases.
Assuming 7075-T6 (I know, assumptions...) Tensile is about 85ksi so we'll go
70ksi for shear strength. This number is probably high.Shear area is .062*.125*2" = .0155in^2
Force required to shear is .0155*70,000 = 1085lbs (~1/2 ton).
If you go nuts and grind your punch face into a concave "v", you can cut the required force by two thirds, but this may be more trouble than it's worth. If you're not concerned about the burr, got larger on your punch to die clearance to reduce tonnage. Punch to die clearance is specified as a percentage of the material thickness on each side of the punch:
The pierced hole conforms to the punch, the slug conforms to the die.
Pierced hole: 1/8"x2" Punch: .125"x2.000"
Resulting die opening: .125+(2*.02*.062) = .1275"
2.000+(2*.02*.062) = 2.0025"Aluminium is pretty forgiving so you've got some tolerance here. I would say you could easily exceed .005" or more over the die opening sizes listed above and you'll still get a decent part (more burr mostly).
A die set (consisting of an upper shoe and lower shoe) will prevent your punch from smashing into your die, and give a more consistant appearance...
HTH.
Regards,
Robin
That's what I would have said if I had Robin's eloquence and smarts!
Interesting reference:
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