For tubing assemblies, we used to blind punch the top surface of the
tube with no backing, got the shape you are referring to. Usually
referred to as as "pierce and tap" or "extrude and tap"
You can get a much better form for the hole if you grind the end of the
punch pin to a taper with the main section of the pin the size of the
desired tap drill size. For the punch block, use a hole about tap drill
size + 2x diameter + .010" or a bit more. Chamfer, round, and polish the
hole edge to allow metal to ease over the corner and give thicker sides
as well as minimize tearing.
Andre Majorel wrote:
Yeah. If you Google "extruded nut" you'll find what you're looking
for. This process is technically not extrusion or drawing. It's a
bending operation.
I designed/built the tooling for such nuts during my apprenticeship. I
recommend a roll-form tap. You should get roughly 30% more strength in
the threads, which is important as there is sooo little meat in the
wee tube.
We actually drilled a small hole in each nut before using the forming
punch. We found that if there was no hole, you would end up with a
ragged hole at the other end of the tube and it would typically split
off-center. We only needed about 200pcs so we drilled them. In normal
production, the hole would be pierced. Indeed, you can combine the
pierce and forming punch. The pierce will not be supported, but it's
only a little wee hole anyway (like 1mm pierce for an M6 thread).
Using 16ga mild steel sheet, we could easily get the forming punch
using a 5 ton arbor press.
We used a urethane stripper cause it's really simple and the nut
*will* get stuck on the punch without a stripper of some kind.
As I remember, we left the die hole sharp or perhaps with a slight
countersink. This may or may not be important. The application was
pretty relaxed so we didn't spend the time to test a sharp/countersunk/
radiused hole. YMMV
"Bob La Londe" wrote: Why not go with a riv-nut or a two piece threadsert
rivet? Cost? Time?
^^^^^^^^^^^^^^^^^^
In an application where a drilled hole and self-tapping sheet metal screw
are good enough, or almost good enough, this would be better. Threaded
inserts would, of course, be better. They cost more and take longer. They
also require access to the lower sheet prior to assembly.
Did you mean tap drill size + 2x *thickness* + .010" ?
Thanks folks. The application is 19" cases.
The sides are usually pieces of relatively thick (perhaps 1.5 mm)
steel sheet with four 1-cm wide "ears". The front panel and back
panels can be attached to the corresponding ears with whatever
screws suit you.
The top and and bottom covers are made of thin (<= 1 mm) sheet
metal. They are often attached to the sides' top and bottom ears
with button head screws. Obviously that's not ideal because when
you insert or remove the unit from the rack, the screw heads
scratch and get caught in the units above and below.
I'd like to use countersunk heads. Problem is, the head of an M3
screw is thicker than the covers by at least 0.5 mm. So I'm
thinking of either making a 0.5 mm-deep countersink in a PEM nut
or pierce and tap using an ad-hoc die with a 0.5-mm deep
countersink.
--
André Majorel <URL:http://www.teaser.fr/~amajorel/
"Buy in bulk, that's my advice." -- Lemmy
Yeah, I caught the error later. my bad. indeed: 2x the material thickness.
You might have to do the countersink as a second op. Same press, same
die block different pin, different hole in the block.
Andre Majorel wrote:
Been a while for me too! You are correct, the shape of the punch is
fairly critical to getting a consistent result. You want to leave a bit
of a flat end on the punch pin to get a consistent starting hole and the
taper is adjusted to maximize the usable hole length. Using a roll form
tap is an excellent idea, this thing wants to be machine formed.
The results are fairly fussy about material thickness and ductility. The
die/punch combination that worked great on the last run may be miserable
on the next run.
snipped-for-privacy@gmail.com wrote:
--Check this out: http://www.formdrill.com/english/index.html
--Generic term maybe "flow drilling" or some such.. Here's a link to
the video: http://www.formdrill.com/english/pop_formdrillvideo.htm
--
"Steamboat Ed" Haas : "Hold on! we're passing
Hacking the Trailing Edge! : through the moronosphere!"
interesting. I thought I'd buy a couple common size formdrills. Till I seen
the price. Small sizes start at 45 euro up to 325 euro for large. The darn
thing is just a center punch, I'll try to make my own. If anybody has one,
I'd love to reverse engineer (that is copy) the angles.
karl
--Well it's more than a center punch: for a #10 size bolt the
recommended speed is something like 2700 rpm. And those suckers get *hot*!
If ya try it with a centerpunch it may anneal the tip. Dunno what they make
the formdrill out of, but the ones I have show no evidence of wear after a
few hundred holes...
--
"Steamboat Ed" Haas : "Hold on! we're passing
Hacking the Trailing Edge! : through the moronosphere!"
Couldn't sleep... (common problem for me) so I just read all I could find
about flow and form drills. They are made of tungsten carbide. So, I'm going
to grind one up. By chance, do you have an optical comparator so you could
get a measurement of the angles involved? Also, they mention applying a
paste after each cycle. Do you know what it is and where to get it?
If this trial don't work, I'll buy a set. I've got a project right now that
needs this solution.
Karl
I went down and tried a few different shapes, mainly center punches
made from broken taps. It looks like a sharp punch drills faster but
raises a tube on the top surface as well as the bottom. A rounded tip
with tapered sides, ground by hand from a broken drill bit, pushed the
metal mostly out the bottom into a tube. The flange on the tool in the
photo squashes down the raised metal on top, but for low volumes it
might be easier to knock it down with a punch and hammer rather than
grind away so much metal. You need a backup underneath or the sheet
will wrinkle. A drilled pilot hole helped. Cutting oil was OK as a
lube and the tool didn't get hot enough to make it smoke drilling one
or two holes in 6061 Aluminum 0.062" thick.
--Actually there are two different style bits: one that produces the
flange and one that cuts it off. Mostly I prefer to keep the flange on as it
means no material removal and therefore less weakening of the part.
--
"Steamboat Ed" Haas : "Hold on! we're passing
Hacking the Trailing Edge! : through the moronosphere!"
There is a competitor to them called (interesting enough) Flowdrill.
http://www.flowdrill.com /
Still expensive, but if you have a *lot* of these to do, then an automated
process using these is a good option.
We've sold equipment to run them, and have learned it's a balancing act of
sorts... If you go too slow or with too little feed (or the other way
around) you really don't get what you want... But when set up correctly,
this is a great option for thin material, pre-tapped holes.
It can be done on a drill press... But again, it's a balancing act and
requires a good amount of HP / thrust.
Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com
V8013-R
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