(Tooling design help please) Die Cutting / Punching non ferrous sheet

I'd like to stamp/die cut some copper or aluminium disks using a home made 2 piece punch & die (silver steel?) - does anyone know what the clearance should be to produce a nice burr free edge or have any advice, I'm just making it up as I go along at the minute!

- back ground info (as there may be a better way!)

I'd like to make a simple heat exchanger consisting of aluminium or copper disks slid over a copper pipe and soldered to it.

I would guess the best way would be to turn a two piece tool out of silver steel (Die + punch) with a clearance specific to the material type and thickness and use an arbor press to stamp out of a stack of disks.

And going to the next stage............ all these disks would ideally have a formed hole in the middle, providing a natural land and spacer to the next fin in the stack, as per the below image (which may be upsidedown.......). This is a beautifully clean cut multiple heatpipe example of the type of cooler I'm trying to build. Mine will obviously be much simpler, just a single copper pipe with round disks on it and a generous gap to allow convection.

When I have wanted a batch of washers I just drill and rough cut them. Then bolt them all to an arbor and turn the OD may be an easier option and nice crisp edges.

Usual clearance is 10% of material thickness for each cutting edge, if you are using .5 sheet then that would be a total die clearance of .1mm. With very thin sheet it is usual to use no clearance, harden the punch and then use the punch to size the die.

Unless you need loads I would use Jason's method, you might need a backing plate each end to support the blanks.

Michael

I'd be interested to hear how you propose to solder aluminium to copper

Roy

This piece of tooling i made about 20 years ago originally to punch
and form the holes in this gas turbine combustion chamber,since then it
it has been used for all sorts of sheet metal work.The original design
was from the Gas turbine builders association and was the work
of Terry Lee.
The 5.5 mm punch in the tray is exactly 5.5 mm diameter the hole in the die
is 5.65 mm diameter.
The punches and dies are silver steel .With a little imagination it would be
possible to accurately punch the holes and using an additional punch
and die to form a flange on the inner diameter as in your original photo
forming a greater contact area and providing automatic spacing of the
individual fins.
Drilling these holes is the least likely solution for a successful outcome
for obvious reasons.

John

JasonB, thanks - yes I'm getting a bit carried away with the manufacture of tooling, but I imagine if I like the results, I'll want to make a few more for other bits and pieces.

Michael, that's the same clearance I use on my 3in1 machine for steel, so an easy one to remember thanks!

Roy, it would need to be plated or simply push fitted with a thermal interface material (paste) - I hadn't thought about that! That eliminates aluminium from my line of enquiries, as its quicker/easier to just use copper, and it's probably easier to source, and certainly performs far better.

John, that tool looks really handy!! I feel a hex bar stock project coming!! How bigger hole do you think it could cut in 0.5mm copper sheet? - I've sent a quick message to the Gas Turbine Builders Association to see if those plans are still available.

If you are not set on making the punch, after making the smaller hole you could use a Q-max cutter.

The problem with Q-max and other knock out tools is that they give a wavy washer due to the scalloped shape of the punch part, not usually a problem if it is the hole you want but bit of a pain if making washers/discs

Edited By JasonB on 22/08/2017 13:30:29

Russ- for some good background engineering info about punches and dies, clearance, etc you can find a great deal at the link below to Dayton Progress Co's website. They supply many std items to the punch press trade in North America. Have used their products for many years in industry with every success. They wrote the book, basically. JD

http://www.daytonlamina.com/776

Hi Russ,

Not sure what size, but old (Copper) coins have their uses.

Russ B, industrial heat exchangers such as air conditioner coils use aluminium fins over copper tube.

Their process however uses thin wall tube, the fins are positioned and then a ball bearing, eg, is pushed down the tube to make it slightly oversize and thereby grip the fins.

Jeff that Dayton page is superb thanks, a very interesting and informative read, I've downloaded their PDF version and will certainly keep that for reference indefinitely.

I'm going to have to drop the silver steel for the main outer cut to make the disks as I need them around 30mm diameter, so the die would have be circa 40mm minimum and It's very pricey!

I think I'll just use EN8 and harden and temper, I might case harden too as I have stash of kasenit, I'm not overly experienced with heat treatment, I tend to just follow the basics and it seems to have an effect!

Why not use a bit of flat gauge plate and cut a hole through that, can screw it onto a bit of mild steel to stiffen it up if needed.

Jason, thanks, I'm lacking knowledge on these things, but wow, double the carbon content of EN8, practically the same as silver steel, but more chromium, plus a bit of vanadium, and a sprinkling of tungsten to boot! Would I be correct in thinking this will harden more than silversteel, I'm not totally sure, the carbon content is practically equal.

I'll look in to prices, I wouldn't mind ordering more than I need as it seems like it would be very useful.

I'm also beginning to come back around to your orignal suggestion of rough cutting and machining the OD, but we'll see, it's certainly looking like the cheap and easy (less a bit of elbow grease rough cutting) option to attain good results.

In simple terms Gauge plate also known as "Ground Flat Stock" is the flat or square version of silver steel so can be hardened in a similar way.

You could also fit a round disc of it to the end of your die which could then also be mild steel.

J

Russ, the clearance depends on the thickness of the material. The thinner the material the less clearance you should have. Your biggest problem will be holding the punch and die in line, that is unless you have access to a fly press or similar. I can recommend Jasons' suggestion of gauge plate. For short runs you can even use it unhardened as we used to when the development Lab wanted a couple of dozen components for evaluation, obviously you cannot use material more than about .75mm for a job like that. Going back to clearance, if your clearance is to much the punch tries to drag the material through the die, this causes the burrs you wish to avoid and a radius on the top of the hole and on the underside of your washer.

Look like Gauge Plate is the way to go folks!

Do you think I'd get away with 2mm thick plate, bearing locked into/onto mild steel or would I need thicker?

I could easily afford a 2mm thick piece 100mm wide and 500mm long (£22.79 delivered) and this could be useful for all sorts of things in the future. The next step up is 3mm and its 50% more (thinner is the same price on the width I was looking at)

Edited By Russ B on 28/08/2017 17:09:00

should be fine.