Problem stamping inconel

We are having a real problem stamping spring from annealed Inconel 718.

We have a die that makes this same spring from .006" thick 302FH and Elgiloy with no problem.

It will punch and form hundreds of feet, 12 slots at a time.

New customer wants this spring, and several others, from annealed Inconel 718 … no problem right?

Wrong!!!

We've had to reduce the punch count to four and reduce the die block thickness just to get a few dozen feet before the punches wear out and/or break.

Punches and die blocks are made of PMM4 @ 65 Rc. Punches have 4 degrees shear from open end of slot to closed.

We have tried switching to Z-TUFF PM and Z-MAX PM with no appreciable improvement.

Reversing the direction of the shear is the only thing that as yielded positive results and that not much.

Cannot show you pictures of die, but pictures of spring I can.

Have you tried to get some hardness reading (maybe micro hardness ?) around the sheared areas ?

Suspect work hardening.

If so, maybe fool it by getting rid of all the shear angle.

yes, tonnage will go way up, yes it will sound like a 30-06 going off.

Slots are .008" wide.

Reducing the shear from 4 degrees to 2 degrees results in broken punches after only a few hits.

Eliminating the shear results in broken punches and die blocks with first hit.

These are all powder-metal based steels? Are the dies EDM'd? We had a thread here recently about how the effect of EDM was somehow depleting some of the alloy constituents at the cutting edge, but since you seemed to have success with other materials perhaps that's not the issue here.

Metallurgy? Wire EDM? Black Magic? Issues with HSS wear and looking for answers [check posts #13 and #16]

Have you done physical properties testing of the 718 sheet? Does it meet spec for expected tensile strength, or is it higher? Is the material annealed or at full hardness from the rolling?

I've never stamped Inconel so I'm just throwing suggestions out there. How long is the unsupported length of the .008 punches at material entry? Guided box stripper supporting the punch? How much die clearance per side? Is the punch flat faced or can you dome/angle the face for shear? Have you tried this on a hydraulic or screw press to control the speed of entry? If the punch breaks how does the CE of the die section look under magnification? Cutting fluid used? Allowable burr tolerance? I'm wondering if this is a job for carbide at slow(er) ram speed but that may be grasping at straws.

I'm with AD, never stamped iconel so this might be worthless thoughts. Is the shear one direction? Are the punches/can the punches be polished in the direction of the stamping to reduce any friction? Coatings? We used to see an increase in punch life (depending on a few factors but) by altering shear, even a little bit- for example on some round punches we could get improved life by grinding a conical shear on them, or grinding the shear in a "V" shape.

KilrB said:

New customer wants this spring, and several others, from annealed Inconel 718 … no problem right?

Wrong!!!

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I got nothing except that the word Inconel should never be used in a sentence with "no problem". That shit just sucks no matter what you need to do to it.

With inconel, you really have no choice but to go with carbide punch and die. Make punch tip as short as possible. Die clearance should be .0005 per side and stripper should be .0002/.0003 clearance per side. (Based on .006 thick inconel).
Punch holder should be .0001/.0002 clearance per side and should be allowed to "float" up/down about .001/.002. Use a toe clamp to stop the punch from falling out. Do not let the die hold more than 3 slugs. Proper die relief should be 1½ degrees with approx .050 land. Hope that helps.
Garry

Is it Gregormawick who calls it ''inconasty'' ? ..apt name.

Limy Sami said:

Is it Gregormawick who calls it ''inconasty'' ? ..apt name.

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I remember running it on Swiss cam autos back in the day before insert tooling, what a pain in the butt. I had a part where I remember getting 5 parts on a set of tools before regrinding.

Dualkit said:

I remember running it on Swiss cam autos back in the day before insert tooling, what a pain in the butt. I had a part where I remember getting 5 parts on a set of tools before regrinding.

Click to expand...

YIKES Dual, ...…...5? that is

Limy Sami said:

YIKES Dual, ...…...5? that is

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I've got an Inconel job where I need to replace a $100 tap every 4 parts. Not a big deal when it's worked into the price.

Have you considered cutting this with a laser instead of a punch?

Philabuster said:

I got nothing except that the word Inconel should never be used in a sentence with "no problem". That shit just sucks no matter what you need to do to it.

Click to expand...

Especially when it is Inconel 718 !!! Must be for another part for the oilfield, spring energizer for a seal. Oh, could be for the petrochemical industry, too. Most made from X750.

4GSR said:

Especially when it is Inconel 718 !!!

Click to expand...

I have an Inco718 HT job coming up this week (aerospace). Not looking forward to it.

Thank you all for your suggestions and observations so far, I am looking forward to any more.

Yes, this is a spring energizer.

Yes, all the tool steels used are powdered metal.

Yes, they are being cut on our wire-edms.

I had a much longer and more detailed reply ready to post and got kicked offline and lost it.

I will try to recreate it tomorrow.

Maybe get permission to post some photos of the die.

For now:

Die block clearance for our standard materials is 6%/side per Arnold's suggestion for notching ss up to .060".

This produced an unsatisfactory burr on the annealed Inconel that would hang in the die block and prevent feeding.

Reducing the clearance to 3%/side cured this.

The punches run through a .500" thick spring loaded stripper that leads them by .010"-.015" and has the same clearance as the die block.

Could this part be made using 718 wire, bend formed to the "zig-zag" geometry, then flattened using carbide roll dies, and finally folded over to create the proper form? Not solving your die cutting problem, but if that continues to be an issue it's another approach.

Hi KilrB:
Some things I'd consider:

1) I notice the strip appears to have been slit...have you checked if the edges are still soft (per digger doug post # 2 and Milland post # 4)?
I wonder if it's work hardened at the slit edges.
I ask because you posted that you do better when you reverse the shear and punch first into the center of the strip.
Could the local work hardening be shifting the punches laterally or shifting the strip?
Could you have some test strips water jet or laser cut or wire cut and see if it makes a difference?
Alternatively, could you have some slit oversize and surface grind the edges just to make test pieces you can punch?

2) Do the punch and die corners look crumbled or rounded over on the ones that didn't break yet when the die first failed?
If not, it gets harder to condemn the wire EDM as the source of your crappy punch performance.

3) Can you do a simple test die with a ground punch and die section vs a wire cut set?
Make it an easy shape to build (like a simple Vee notch), because you just want to find out if ground works better and lasts longer than wired.

4) Can you find a vendor who runs an oil filled wire and try making a set from carbide as gwbolton recommends in post # 8?
I know Agie/Charmilles makes an oil dielectric machine and Makino and Sodick do too.
Maybe call them and ask who has bought one in your neighbourhood.

5) If ground is good, do you think you could even build a set of punches and dies by grinding them, or is there no realistic way to grind what you need?

6) Are alternative processes even on the table? Fine blanking? Laser cutting? Wire EDM cutting?

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Oh yeah; while I'm thinking of it; when you reduced the die clearance from 6% to 3% to eliminate the exit burr, did you evaluate the edges of the punched strip to see how it was shearing and breaking?
Did you check for evidence of punches binding in the die?
Did you check to see how the punching forces changed?
Basic questions I know but sometimes I've been guilty of getting so far into the weeds that I forget to ask these simple things while I'm busy cursing and swearing over the details, so I just had to ask.

MC

Photo-etching?

Gentlemen, sorry about the slow response time. It's eom and the rush is on, plus a lot of other things came up.

Still not permission or opportunity to get any good photos of the die(s).

We have made some progress on a slightly larger spring from this same annealed Inconel 718.

That spring is from .010" (instead of .006") thick material and the punches are .012" wide (instead of .008").

And there are only 6 punches (instead of 12).

In addition to going to a "tougher" punch material (Z-TUFF PM) and reversing the direction of the shear some of your comments led me to suggest something we've never tried before. In fact, we usually strive to do just the opposite.

Slow the press down.

Slowing the press from 72 strokes per minute to 51, it's minimum, got us from a couple dozen feet between sharpenings to 300-350 between.

Seems like we are work hardening the strip ourselves.

To answer a few questions now …

Inconel is highly resistant to photoetching. Any chemicals that will etch it … you don't want to be around.

Laser … we're already work hardening it in a die, I can only imagine what a laser is going to do to it.

There are several other reasons I think laser is unworkable here. A larger spring … maybe, but not these two.

Making it from round wire and flattening it in a set of rolls, I don't think we could (1) feed it (it's a slinky) (2) hit the print dimensions.

WEDM, we have cut some sample spring (and forms) in our wedm's and formed it in our brake press. Too slow.

We currently have seven 25ton Stamtecs running 16 hours a day Mon-Fri and 8 hours on Sat.

If for no other reason than volume and time this has got to run in a press, and we're getting there.

If I haven't responded to your particular comment yet, I will get to it asap.

Once we get some more stable run times we will be doing further tests between tough and wear resistant tool steels.

We will also be revisiting carbide, I hope.

We got 4 of the smaller punches ground from carbide (expensive) but no one would quote the die block.

I've got a piece of Leech LC112 waiting for some time in our CUT-200.

.004" ST10 through 1" of carbide … I'm pretty sure grass grows faster.

Thanks again guys.