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Making a punch for a thin laminated plastic

Wade C

Stainless
Joined
Jul 21, 2004
Location
Wiggins CO. USA
Not sure where I should have put this post, so figured best to aim here, and then go to a different topic if needed.

Im working on a "simple" punch that I use for punching a thin laminated plastic (.009 - .016" thick - similar to Mylar). Ive built a few over the years, and most have worked well - but I recently decided to try using D2 instead of A2 for the punch and die (top guide plate and bottom cutting plate) - both materials were 58HRc range. I am fighting delamination of the material when punched suddenly and it has me baffled.

I guess Im getting smart enough these days to know when there must be something going on that I dont know about... and realize that sometimes you can get lucky for a while then it runs out.

The design is just a punch cut out with the wire edm, with a handle to smack with a hammer, and then the top and bottom die plates are ground flat, then grind a step on the top of the bottom plate and bottom of the top plate to make the gap for the material to slide in, dowel pinned, and bolted together with a base plate with a hole to give clearance below the die plates for the part to fall out.

I wire out the punch, leaving a good tab to hold it by, and run 4 skim passes. Then cut off the part and take it to the surface grinder to dial in on the surfaces on both sides of the tab, so I can grind the tab off as accurately as I can. Then, the plates that have already been ground, step ground in, doweled and bolted together go in the wire. I cut out the shape, and run about 3 skim passes and then start testing fit after each skim pass. Run the following skim by changing the wire offset by .0001" until the punch will just start in the wired hole (Id guess by time its cleaned up and any recast layer rubbed/worn off that I have around .0003-.0005" clearance per side). Take it out, take it apart, dry, oil and put back together - and usually Im good to go. But not these latest ones Ive tried to do. I thought maybe it was the change from A2 to D2, but I have A2 and D2 versions doing the same exact thing - so Im starting to think its me. Ive made punches before that were looser (on my older wire thats not as accurate as the newer FX10)- and didnt delaminate, so Im a little perplexed.

So Im starting to wonder if Im missing something in the operational theory, or some trick or secret about punching laminated material, or maybe just not holding my mouth right? Im wondering if Im getting a couple tenths worth of misalignment from when the die plates are assembled and then cut to when they are taken apart, dried, oiled and then blown off, and put back together?

Any one willing to share any expertise or thoughts on punch making for thin laminated material where one of the requirements is that the material does NOT delaminate? Feeling dumber and dumber the more I try things to cure it, and it either gets worse, or at least not any better.

Thanks
 
Does your punch have a flat face? Are you trying to punch so the entire periphery is being cut at once? Sounds like some kind of stretching is going with the material. I wonder if putting a little bit of a concavity on the punch face might help?
 
Yes, the punch face is flat as is the die plate cutting face. When you say concavity on the punch face, do you mean as in making the face concave like you mount the punch in a vise, and used a huge ball endmill to plunge into the face? Or as in, lay it on its side and cut a radius into the face so that the two ends would cut first, then shear towards the middle where that is the last portion cut?

I have tried the arc cut into the face (if you lay the punch on its side and looked down on it, the side where the handle screws on is flat and the opposite has an arc. It dramatically reduced cutting and seemed to reduce delaminating on I tried. I had intended to try that next on this one that Im focusing on first, but the hard-head in me wants to know why ones in the past were fine, and now, I have 5 that are all giving me fits. You know, that good ole "why did those others work fine, and these dont" question. :D

If youre meaning making the face of the punch sort of a "dish" like the theoretical plunge a ball nose into it, Im not sure how I can do that - as the shapes are odd. But always eager to learn :D

Thanks a bunch!
Wade
 
Did you change plastic lots or suppliers about the time your problem started?
I have run into tough lots of material.. even some that was just plain unusable. But in this case, the material Im using now, punches fine in my old punches, as well does some other sample material I was given. But, Im going to try some other batches that I have that are varying ages just to see if any one of them acts better than the other.

Thanks!
 
Can this be made as a simple steel rule die ?
Not familiar with them... so I dont know. I would imagine it could be possible. Ill have to do some search-fu on steel rule dies and see what I can learn about them.

Though, that still wont quench my "why the heck am I having problems now" mental problem :D
 
Do you have a microscope? Seems since your old punches work fine, a very close comparison old vs new might be informative. If they're all made to the same spec, try using an old punch or die with the new counterpart and maybe it'll shed some light on the problem.
 
Can this be made as a simple steel rule die ?
Looking at a few sites... the way they seem to operate, I suspect they would be painfully slow without expensive equipment to run it or at least the time put in to making something to run it - where as what Ive been doing can be run with a cheap hammer :D With these punches Ive been making/fighting recently... Ive been able to get 50k+ pieces per punch before its worn enough that it wont punch cleanly (at least on the ones that dont delaminate the material when its first made).

I could see other issues come up, such as sharp corners etc. But I guess the more pertinent for me, is, its not really something I have the equipment to make, but I do have the stuff (other than apparently the knowledge) to make the punch and die setup.
 
Do you have a microscope? Seems since your old punches work fine, a very close comparison old vs new might be informative. If they're all made to the same spec, try using an old punch or die with the new counterpart and maybe it'll shed some light on the problem.

Wish I did... best I have is a 10x loupe, but Im not seeing anything that sticks out.
 
"Or as in, lay it on its side and cut a radius into the face so that the two ends would cut first, then shear towards the middle where that is the last portion cut?"

Yes, this was what I was trying to say. Didn't help?
 
Seems the dish concave face punch would be good but a bugger to make or re-sharpen for an odd shape part/punch.
cnc grider could do that but big bucks there
flat end and quick/easy grind to skim .005 or so every 30k parts likely best, with focus at super sharp.
What wheel do you use for sharpening?
 
"Or as in, lay it on its side and cut a radius into the face so that the two ends would cut first, then shear towards the middle where that is the last portion cut?"

Yes, this was what I was trying to say. Didn't help?

I had tried it on an old punch that was worn out and delaminating badly because of loose fit. It fixed the delaminating on that one. And I do plan, as a final step before building a new one, I planned on trying it on this one. My worry was, that it was a bandaid and it might start doing it again in the near future if Im not catching what is really causing it. I was wondering if a light bit of misalignment might be being imparted when I take it apart after wiring it to dry it out and get some oil in between the plates... and if its just enough. Or maybe the dowel pin holes are a touch too tight and causing some deformation (plates are about .4" thick) when they are driven in. Just grasping at straws... Had thought about putting something like LPS3 between the plates before wiring, so that when it comes off the wire, it doesnt have to come apart again, but seems like that just alleviates the potential for misalignment now, but when it needs sharpened, then its coming apart anyway - and were right back at square one.

Im probably just overthinking this about 40 fold... :o
 
Set it up and grind the punch from both ends. High in the middle the thickness of the material you are cutting. Makes it like a pair of scissors it puts shear in it the tonnage goes way down. I don’t know how big these dues are but that will help. Take a pair of scissors and cut up a bunch of the material. Does it delaminate with the scissors?
Don


Sent from my iPhone using Tapatalk Pro
 
Seems the dish concave face punch would be good but a bugger to make or re-sharpen for an odd shape part/punch.
cnc grider could do that but big bucks there
flat end and quick/easy grind to skim .005 or so every 30k parts likely best, with focus at super sharp.
What wheel do you use for sharpening?

Yeah thats my thought... tough to do, or expensive... and when it comes to resharpening... repeat expensive.

Wheel wise, (I fully admit I am not a skilled grinder hand by the way - sort of a case of I know enough to be a bit better than dangerous, but far from accomplished), I have tried two wheels, the one I had been using on so many punches before and tried on this one as well, was a Norton 46grit SG wheel, 5SG46-IVS and the other I tried, was an old wheel that I got with the grinder, a Bay-State Abrasives 9A-80-H8-V52
Obviously the 80grit was a finer finish, but both yielded a very sharp feeling corner. If I had a softer stone, Id have given that a whirl too, but H was the softest I had.

I have also tried "sharpening" the punch side with the wire edm, and just doing a rough and 4 skims across the face on one punch that Im fighting (yeah fighting more than one at the moment) and it did improve notably. But I also didnt try that one on the grinder either. I may just have to grind one side of that punch and see what the change is.

On many of the punches in the past (well, the ones I make for me - where I can track usage and life) I usually get about 50k pieces from a punch, and then I start getting a little delamination going around the 6-6.5k mark, so I pull it, grind it and back together and rolling again every 5-5.5k pieces. So roughly about 10 sharpenings before its getting loose enough that it will still delaminate depsite being sharpened.

I really wish I were better on the grinder, but dont know anyone local. Ive read and watched a lot on it, but it just seems like there are enough variables that you just have to sort of learn the feel... and I dont grind regularly enough to build that experience to gain the feel. Add in its an old Reid grinder with an unknown past... there could be some lacking with the grinder too.
 
Set it up and grind the punch from both ends. High in the middle the thickness of the material you are cutting. Makes it like a pair of scissors it puts shear in it the tonnage goes way down. I don’t know how big these dues are but that will help. Take a pair of scissors and cut up a bunch of the material. Does it delaminate with the scissors?
Don


Sent from my iPhone using Tapatalk Pro

Doesnt delaminate with scissor cuts or paper cutter cuts. And doesnt delaminate when run in other punches. So feel pretty good that its not just the material.

My only concern about going that direction (as opposed to making the two ends cut first by wiring in a radius to the punch face), is that the main area that delamination is problematic, is on the ends. So if its ground that way, it would put a negative "rake" to the end where its "nipping" the ends instead of shearing. But then again, I have nothing to lose - if I can get this to punch without delaminating, Im making a new one anyway.

Pieces are typically somewhere between .5"W x 1.7"L and .62"W x 1.3"L. Shorter ones usually have a "critical" radius on both ends, the narrower ones usually are just rectangles with enough radius on the corner to allow for the spark gap radius plus a touch to bring it to a round number (typically .015-.020"
 
Looking at a few sites... the way they seem to operate, I suspect they would be painfully slow without expensive equipment to run it or at least the time put in to making something to run it - where as what Ive been doing can be run with a cheap hammer :D With these punches Ive been making/fighting recently... Ive been able to get 50k+ pieces per punch before its worn enough that it wont punch cleanly (at least on the ones that dont delaminate the material when its first made).

I could see other issues come up, such as sharp corners etc. But I guess the more pertinent for me, is, its not really something I have the equipment to make, but I do have the stuff (other than apparently the knowledge) to make the punch and die setup.
Huh ? Steel rules dies are made very inexpensively, and they run on any kind of press, I've seen a stack old newspapers for the pad (sacrificial part that the die overcuts into)
 
Some sort of image/drawing would help. Problem sounds like something in method/outcome of how you made the punch/die if the old version worked. Change of material from A-2 to D-2 should have been an improvement in wear on the punch. Other suggestions of magnification, even with just a 10x eye loupe, should reveal something to help you if you know what to look for. Dowel pin fitment that is a "tap fit" should not deform .4 thick plate enough to cause problems in hardened tool steel. Allowing punch to shear instead of setting up a fracture plane (flat faced punch) may be your solution. Finding a solution to material delamination may offer an explanation to why it's happening now, the solution can possibly be tailored to your application afterwards. Determine what works before determining why there's a problem is just flipping the variables in an equation to find the answer. Sometimes that's what has to happen. Steel rule dies are cheap, no special press like a "clicker press" is really required. Tolerances and shape may be limiting factors.
 
Huh ? Steel rules dies are made very inexpensively, and they run on any kind of press, I've seen a stack old newspapers for the pad (sacrificial part that the die overcuts into)
Everything I was seeing had a "clicker" presses being used with them and those were 1500+ new from what I was seeing.
 








 
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