Carbide grade help

Here's a pic of part of a wire cutter. It cuts 3 pieces of .110" x .017" oil tempered flat wire at a time. There are three 3/4" x 1/4" square carbides. They are red in the model. The wire advances 3" out of the lower carbide through a 1/8" square mouse hole. (Yes, we have square mice) The arm then moves up and snips the wire driven by a cam follower in eccentric. Each carbide has 8 cutting edges and I would be thrilled to get a week from each edge or 200,000 cuts. That's about what I get on my other machine using round carbides, so it's not unreasonable.

The problem I'm having is the top carbide is chipping after 200 cuts, the arm carbide seems not to chip. It is C5 TiN coated. The arm is in tapered roller bearings an is very ridged. The green block behind the carbides has a fine thread adjustment screw and caps that clamp the carbides are not shown but mount using the visible holes.

Since the mechanism is already built and mounted, I'd prefer not to build a new design. Once I figure this out, the machine is done!

I have no idea what grades to try next and I wonder how much pressure to apply to the carbides.

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Reply to
Tom Gardner
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I also seek advice about the amount of overlapp I would need after the cut. Curently, it's about .025"

Reply to
Tom Gardner

"Tom Gardner" wrote in news:_m1Jg.12292$% snipped-for-privacy@newssvr29.news.prodigy.net:

Tom,

Switching to C2 would give you a "tougher" grade which would be less likely to chip. But I wonder if the problem is with the wires impacting the top block too sharply more than anything else.

You could try putting the carbide on the moving pice on an angle, or changing the ramp on the cam, so that the moving cutter moves slowly until it starts to bite the wire then accelerates quickly after that point.

You could also see if you can get the carbide inserts made in a die grade of carbide rather than a cutting grade, then have them coated to give a decently hard cutting edge.

Hmm. Well you could try this MF30 grade from Mitsubishi or see if you can get something similar from your current supplier.

I doubt pressure is the problem. I think what you need is impact strength. If the failure were caused by pressure, the carbide would rupture after the first cut. And it would be a catastrophic failure rather than a chipped edge.

The comparitive number you are looking for is "Fracture toughness" as given in the Mitsubishi link above.

But I would also think about simple ways that you can mod the machine to reduce the impact on the carbide.

Reply to
D Murphy

Reply to
bamboo

Are you absolutely sure that your shear edges are not overlapping during the cut?

Wes S

Reply to
clutch

I'm not sure what you mean, please explain.

Reply to
Tom Gardner

Edges contacting edges.

Reply to
clutch

Never mind my overlap comments. You would know it just from listening to it run.

Wes S

Reply to
clutch

Tom,

You might try shimm> Here's a pic of part of a wire cutter. It cuts 3 pieces of .110" x .017"

Reply to
Fred R

Tom, I am probably talking out my backside with this, but even tho you may lose a couple of cutting edges, you could try to grind a relief on the arm carbide of 6 or 7 degrees so it would act more like a cutting wedge rather than a hard shear. The arm carbide is probably producing a "sliding" motion, even though minute, and may be the reason it is not chipping, and giving a little relief to the shear may stop the shock the upper carbide is receiving. Worth a try, anyway. HTH Ken.

Reply to
Ken Sterling

D, I believe that C2 is not "tougher", but harder instead, so it would be inclined to chip easier. It has good wear characteristics, thus its use for non-ferrous, stainless, cast iron and circular saw blades for wood. Could be I'm misinformed, though, I've been away from the shop for a long time.

Harold

Reply to
Harold and Susan Vordos

I can't help but think that the wire isn't cutting clean, and pulling the edge off the carbide on the return stroke. All it has to do is remove a tiny amount from the edge and it will go down hill quickly. As you know, carbide has very little tensile strength. Narrow down the clearance so you achieve a dead clean cut, or improvise a way for the machine to pull back the wire between cuts, so it can't make contact with the carbide while it's moving back to location. .

Harold

Reply to
Harold and Susan Vordos

Hi Harold! I talked to a billion carbide people and have a billion inserts shipping to me. Supposedly, the C2 is less brittle and intended for interrupted cuts. As a standard grade, I hope it does the trick as they will be cheap. My TiN coating buddy says the design is all wrong but he has a tendency to Escher type mechanisms. Once I explained that I don't have a quantum singularity to power the unit, he acquiesced. He's working on a process called "Ion Implantation", he explained it to me but lost me in 40 seconds.

Reply to
Tom Gardner

No edge-to-edge contact. In fact, I even tried .005" clearance that worked for a short time. The moving carbide is always in contact sliding face to face on the other two. I can vary the pressure with an adjustment screw that pushes the back-up block into the stationary inserts then lock it down with the cap not shown. Thanks for your thoughts.

Reply to
Tom Gardner

Great link with lots of info, thanks! I'll post the answer when all my samples are tried.

Reply to
Tom Gardner

Hmmm!

Reply to
Tom Gardner

I see it!

Reply to
Tom Gardner

Wouldn't that situation wipe out the moving insert rather than the stationary insert?

Reply to
Tom Gardner

It's hard to see this in my mind's eye----too bad I'm not there to see it in person. If there's any movement under pressure away from compression, the carbide would be subject to edge chipping. If, in the process of the moving carbide returning to the shear position, it drags any portion of the wire with it, and it laps the non-moving carbide, I'd suggest it may be pulling off a bit of the edge. Once you lose the sharp edge, failure is imminent. It also may be chipping the edge as it snaps back to position after it reaches the end of the return stroke and it releases the wire. Eliminate, or minimize the clearance and it may not be able to do that. Just thinking out loud.

H
Reply to
Harold and Susan Vordos

What's different about the problematic machine versus the machine that works?

Are you getting any burr at all?

Does the movable insert flex away from the stationary insert during/after the cut? Even a couple thou could be important.

Is the stationary insert moving *at all* during the cut?

Regards,

Robin

Reply to
Robin S.

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