Punch clearance for .125" 6061-T6

DanielG · Dec 8, 2017

We're currently putting holes in .125" 6061-T6 aluminum standard unipunches, but now we want to improve the process.

I'm speccing out some punches and dies, and most of the information I'm finding on punch clearance for aluminum is saying 7.5% per side, although the old die design reference books suggest smaller clearances. For .125" thick material, this is roughly .009" per side

I have two punches/dies I'm speccing:

1:
punch: .354" square with .015 radius
die: .373" square with .024 radius

2:
punch: .625" x .500" with .059" radius
die: .644" x .519" with .069 radius*

Does this sound correct?

Thanks,
Daniel

WILLEO6709 · Dec 8, 2017

it depends how much burnish you need, but for general work I'd go up to 10%. for what its worth I don't punch much aluminum... just a lot of 1010 steel....

check out dayton progress, they should have tech data and clearance recomendations.

DanielG · Dec 8, 2017

WILLEO6709 said:
it depends how much burnish you need, but for general work I'd go up to 10%. for what its worth I don't punch much aluminum... just a lot of 1010 steel....

check out dayton progress, they should have tech data and clearance recomendations.

Thanks, they're running larger clearance on Jektol punches than on the regular punches. I've never worked with Jektol punches, but I've also not had problems with getting rid of the slug. It probably helps we're not running a really high speed, high performance system.

JRIowa · Dec 9, 2017

OK, lots of stuff that needs to be mentioned.

1. "Standard" clearance is 7.5%/side. That's a place to start from. Raising the clearance will take less tonage, but create a larger burr. Decreasing the clearance does the opposite. You have to be careful when decreasing the clearance with how accurate the equipment that you are using is. I've built stuff that ran 2.5%/side clearance, but it was in a ball bushing die set.

2. What was beat into me years ago: punched determines hole size and the die determines slug size. So simple, but it gets lost a lot of times.

3. The "die life" determines how many slugs atay in the punch. The "usual" spec for die life if 3X material thichness. Now, here's where there can be a lot of different opinions, how far should the punch enter the die? In the perfect world, no more than is necessay to leave the slug in the hole. That's usually around 20% of material thickness. Bad things happen when you start going deeper. Usually, you go with ejector punches or special end grinds to avoid this, but sometimes you just have to.

4. "Jetkole" is a Dayton trade name for their high $ punches and dies. Years ago, they called them VSD which we took to mean Very Slow Delivery. I can't tell you how many Dayton or Richardson or other brands of punches that I reworked. We'd buy the punches 0.001" big and 1/8" longers to polish all of the grind marks out of the punches. This kept the sheet from sticking to the punches so that we could use less of a stripper.

Well, not bad for a Saturday morning with only 1 cup of Joe in me. Material makes all the difference. A press and die set-up might run really good until you switch coils and then it goes to Hell. I'm retired, I don't have to worry about that crap anymore.
JR

AD Design · Dec 9, 2017

JRIowa said:
OK, lots of stuff that needs to be mentioned.

2. What was beat into me years ago: punched determines hole size and the die determines slug size. So simple, but it gets lost a lot of times.

Would also suggest that if you're looking to improve the process like you stated that you use inserts for the die to change the clearance to find what does work best for you. Die/punch clearance is often a trade-off of burr height, tonnage, and hits per sharpening. It's all about what you determine to be "improvement". Don't neglect the application of a thin even layer of cutting fluid either as aluminum likes to micro weld to the punch and lead to poor performance from perforators/punches, hole shape, slug pulling, etc. Every part of the process affects the results like JR stated above. With experimentation and documenting it you'll get it down to a process, and then you'll change the coil....

DanielG · Dec 11, 2017

AD Design said:
Would also suggest that if you're looking to improve the process like you stated that you use inserts for the die to change the clearance to find what does work best for you. Die/punch clearance is often a trade-off of burr height, tonnage, and hits per sharpening. It's all about what you determine to be "improvement". Don't neglect the application of a thin even layer of cutting fluid either as aluminum likes to micro weld to the punch and lead to poor performance from perforators/punches, hole shape, slug pulling, etc. Every part of the process affects the results like JR stated above. With experimentation and documenting it you'll get it down to a process, and then you'll change the coil....

Thank you all for the advice.

Are die inserts the same as button dies? That's what I was planning to use.

Any specific recommendations on cutting fluid? Looking at what's easily available in small quantities at Grainger or Fastenal, I see LPS Tapmatic Aquacut, which they say can be used for stamping?

AD Design · Dec 15, 2017

Yes inserts can also be called "buttons" , just nomenclature. It's about using tool steel only where the cutting/forming occurs and it's easier to pop out a smaller section for sharpening. If you use a c'bored hole with a shoulder a shcs can secure the section/button/insert in place and can be extracted without removing the entire die set from the press. You can also change for different clearance "buttons" while you test for maximum results. The cutting fluid can be kerosene/mineral spirits if there's no chance of igniting the fluid. I've even used a strong soap/water solution in a pinch for short run jobs. Use something that will justify the cost, short testing can be any of the above. Long run should have something that works well for aluminum, you can look this up. It's the longer run jobs where micro welding of material to the perforator/punch or forming present the problems. The cutting fluid selection is less important on short run/testing so long as something is present to lube the punch walls as it passes through the material and the surfaces on the die face the material is dragged over if it's a progressive die. Smooth radii and ramps on all lifters and contact areas or you'll get build up of material. Inspect the punch/perforator under magnification to determine material as it wipes off on the walls, do not allow it to build up or it will cause acceleration of aluminum deposits as it drags on the material for each successive hole. Aluminum sticks to itself quickly. High polish on contact surfaces helps avoid material galling but that's for longer runs. You just want to concern yourself, for now, with improving the basics. The rest will come through documenting your results.

Rewt · Dec 15, 2017

Don't use jektol (ejector) punches unless you're having problems with slug control, because you're introducing a weakness into the operation. Even then I'd use a button (matrix) with a "glitch" in it to hold the slug, which works particularly well with Aluminum. I think Dayton actually calls it "slug control". For 1/8" 6061, I would go with 10% per side and call it good. After that I'd call Dayton and ask what coating they recommend for aluminum, and order that punch. Because, like AD said, aluminum loves to stick to stuff, to itself more than anything.

EPAIII · Dec 15, 2017

Boy, thanks for that. I think my knowledge of punching just increased by 2X or more.

JRIowa said:
OK, lots of stuff that needs to be mentioned.

1. "Standard" clearance is 7.5%/side. That's a place to start from. Raising the clearance will take less tonage, but create a larger burr. Decreasing the clearance does the opposite. You have to be careful when decreasing the clearance with how accurate the equipment that you are using is. I've built stuff that ran 2.5%/side clearance, but it was in a ball bushing die set.

2. What was beat into me years ago: punched determines hole size and the die determines slug size. So simple, but it gets lost a lot of times.

3. The "die life" determines how many slugs atay in the punch. The "usual" spec for die life if 3X material thichness. Now, here's where there can be a lot of different opinions, how far should the punch enter the die? In the perfect world, no more than is necessay to leave the slug in the hole. That's usually around 20% of material thickness. Bad things happen when you start going deeper. Usually, you go with ejector punches or special end grinds to avoid this, but sometimes you just have to.

4. "Jetkole" is a Dayton trade name for their high $ punches and dies. Years ago, they called them VSD which we took to mean Very Slow Delivery. I can't tell you how many Dayton or Richardson or other brands of punches that I reworked. We'd buy the punches 0.001" big and 1/8" longers to polish all of the grind marks out of the punches. This kept the sheet from sticking to the punches so that we could use less of a stripper.

Well, not bad for a Saturday morning with only 1 cup of Joe in me. Material makes all the difference. A press and die set-up might run really good until you switch coils and then it goes to Hell. I'm retired, I don't have to worry about that crap anymore.
JR

AD Design · Dec 16, 2017

Not to dispute what Rewt has stated, an ejector punch IS weaker than a solid punch but several places I've worked used ejector punches (on steel) without breakage. There is the possibility of the ejector pin breaking if it's left too long or the spring collapsing and then you've lost the benefit but that doesn't happen very often. You will have to address slug control one way or another, that's your call on that one. Coatings can be quite beneficial but sharpening them chews the grinding wheel at resharpening. Also, if the coating gets flaked/wiped off due to material sticking you might as well just toss the punch as you can't even polish the surface like you can with an uncoated one. Inspection of the cutting edge will reveal what's happening and is recommended. That's just a personal opinion, coated perforators outperform regular ones provided the coating remains intact. There are at least 3-4 other strategies to slug control if you don't want to use the ejector pin punch, look them up. Lots of good info from the other members that posted. Report your findings if you want further help.

DanielG · Jan 13, 2018

I finished building the punch press today and ran some test pieces. For the first iteration, I have 7.5% per side clearance, and the punch goes 20% of material thickness into the die. The slugs are staying in the die, and the urethane strippers are working well.

A few concerns:

1) I'm running about 50% burnish most places, although there are 2 (out of 12) sides where the burnish is much higher (e.g. middle slug in first picture). My understanding is that high burnish is from low clearance, in this case, it's probably an alignment issue because it only happens in 2 places. Is the easiest solution a slightly larger die?

2) The slugs are cupping. I'm not sure if the degree to which this is happening is normal. On the 9mm slug (picture 2). The slug is dished. On the 1/2" x 5/8" slug (picture 3), the top of the slug is pretty flat, but the corners are significantly smashed.

The punches and dies have corner radii. The corner radius of the punch is based on what I can have on the hole. I calculated the corner radius of the die by just adding the per side clearance. Is this correct, or are there tricks you can play to get it to punch better?

Thank you all again for your help. I've learned a lot doing this project.

-Daniel

JRIowa · Jan 14, 2018

clearance looks to be about right with 1/3 shear and 2/3 fracture. If the burr isn't bothering you, run it like that.
JR

DanielG · Jan 14, 2018

JRIowa said:
clearance looks to be about right with 1/3 shear and 2/3 fracture. If the burr isn't bothering you, run it like that.
JR

Thank you!

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