Insert recommendations for nitinol

[zrobitaille37]

I have an endless supply of nitinol bars I need to face to clean. 3/8" diameter to 1" or so. Only taking off .01" at most usually. Have tried various manufacturers and grades but nothing has really stood out. Used mostly cnmg432 and a couple snmg432. Has anyone worked with this enough to suggest a good carbide grade or particular insert? These are being done manually for now, with the hope of moving facing and pilot drilling the end of the bar to a small cnc lathe.

 

[SShep71]

When you say that nothing has "stood out" what exactly do you mean. Are the inserts wearing prematurely, and the chips uncontrollable, are the inserts cracking, etc. A material like Nitinol is not a standard material that has a huge amount of readily available data to consider.

The basic questions:
What is the SFM of the spindle?
What is the state of the material?
Are you approaching in Z or X?
Are you taking the full DOC?
What is your surface finish?
What inserts have you tried?
Are you using coolant?
What do the chips look like?

These are the most likely questions that need to be answered so anyone on here can answer with any reasonable degree of certainty. Just guessing and throwing down is just pissing in the wind. All you will do is waste money on useless inserts and time. Nitinol is a common material in the medical or medical related field, i.e. stints, guide wires, frames and optical components, etc. Are you just doing this for the hell of it or is this for a job?

 

[EmGo]

Why would you even consider negative rake inserts on an alloy of titanium and nickel ? self-abuse ?

 

[michiganbuck]

You might state what failure condition you are having with current inserts. likely having flank wear rather than chipping or cratering. That might suggest you could use a harder-grade carbide. A grade equivalent to Carbloy CP50 might be good/better (a fine grain very hard carbide as opposed to a tough grade that would be better for cast iron). Consider also insert geometry, so you might try a positive rake angle. Then edge factors, you might try very sharp uncoated insert. Negative inserts can often have a sharper edge when uncoated, the shaving a fingernail test tells if an edge is sharp.
You might state how many parts per insert, or how many minutes you get from an insert (roughly 30 minutes in the cutting action is (ballpark average) decent insert life.
Having a surface grinder, you might compare grinding the parts... most efficiently for a take of .010 you might set the parts standing in a V block with a single-point diamond very close by, with it having a height of the diamond making part height zero...This is so each very quick tickle dress makes the part exactly correct and eliminates measuring time. Always try both down grinding and incremental crossing for production or one-up grinding to determine the best process for a certain part.

A down-grinding test might be grind side down feed only (no down-feeding on the climb side)..and try passes of .0005 / ,001 / 003 /, and .005 to see what your set-up, wheel and horsepower can handle...yes for down grinding you might wish to put a block-in block on the go-side of your V block because in serious down grinding operation you may put a 20-pound side push on a part
(X) Coming into the part on the Climb-Side when down-grinding can throw a part off the chuck.

 

[zrobitaille37]

When you say that nothing has "stood out" what exactly do you mean. Are the inserts wearing prematurely, and the chips uncontrollable, are the inserts cracking, etc. A material like Nitinol is not a standard material that has a huge amount of readily available data to consider.

The basic questions:
What is the SFM of the spindle?
What is the state of the material?
Are you approaching in Z or X?
Are you taking the full DOC?
What is your surface finish?
What inserts have you tried?
Are you using coolant?
What do the chips look like?

These are the most likely questions that need to be answered so anyone on here can answer with any reasonable degree of certainty. Just guessing and throwing down is just pissing in the wind. All you will do is waste money on useless inserts and time. Nitinol is a common material in the medical or medical related field, i.e. stints, guide wires, frames and optical components, etc. Are you just doing this for the hell of it or is this for a job?

This is an ongoing job. For now 1/2" dia bars. Approching in X.Haven't been using coolant. Have tried spindle speeds from 300 to 1200 or so. The big change here is at slow rpm the chips stay the same color. High rpm they get super hot and turn all sorts of colors. The chips don't break. Surface finish isn't really critical. They are just face to clean in prep to be gundrilled. The ones I've used the most are a kyocera cnmg432 pr1535 grade. I think it's a stainless roughing insert. This is what was used before I got to that job so it's what I used. Now I'm working for a new company and don't feel like sticking with what we always did just because that was how we did it. Trying to branch out and see if there's something better. Oh and the tool holder/holders I've had to use were dclnr or mclnr. New company doesn't have an issue buying new tooling if it's beneficial. Like I said were hoping to move this off the manual lathe and get it on the cnc so we can face and pilot drill for the gundrill in one op. Sorry it took me a while to get back to this, I didn't have the info on that insert. I used a few others, general purpose Corloy and some snmg Walter that I liked mostly because I got to use all the corners. I'm sure I've missed something but if there is more info I can provide I will. I was hoping maybe someone had more experience with machining this material and had some suggestions. Thanks

 

[michiganbuck]

*QT: Zorb 37 (what are your tool-fail conditions/attributes)
cratering, chipping, flank wear, other?

Special tooling may be beneficial. Instead of using inserts regrindable carbide blade that is reground at .015(or what) wear land, super heavy lathe, perhaps the blade up-standing so to absorb heat.
Reverse direction spindle and cutter on the other side so heat goes up, quick tool change to re-use tooling with the regrind amount such adjusted that part size remains in control.
Big old Gishollt or Warner Swasey with stepping motor feeds and CNC control would be the berries...perhaps/likely upping the spindle RPM

(Even a small Gishollt or Warner Swasey might be the berries)

 

[zrobitaille37]

This is the Kyocera insert that my old shop used. And this is typical failure. Sometimes 25 bars. Less if taking too big of a cut.

 

[michiganbuck]

The insert doesn't look very sharp from here. Even a negative insert can be sharp-edged to shave your fingernail.
25 parts per corner..is that about 25 minutes of cutting..not that bad.

You might try an old-fashioned flat top insert because they can stand up to heat better, it looks like there is no flank wear so your insert may just be burning up.

Chip breaker inserts actually have less mass at the cutting edge so can absorb less heat..if the chip control is not needed the sometimes a flat to can be better.

Some uncoated inserts may be less surface hard at the cutting edge but very often are sharper.

 

[SShep71]

This is an ongoing job. For now 1/2" dia bars. Approching in X.Haven't been using coolant. Have tried spindle speeds from 300 to 1200 or so. The big change here is at slow rpm the chips stay the same color. High rpm they get super hot and turn all sorts of colors. The chips don't break. Surface finish isn't really critical. They are just face to clean in prep to be gundrilled. The ones I've used the most are a kyocera cnmg432 pr1535 grade. I think it's a stainless roughing insert. This is what was used before I got to that job so it's what I used. Now I'm working for a new company and don't feel like sticking with what we always did just because that was how we did it. Trying to branch out and see if there's something better. Oh and the tool holder/holders I've had to use were dclnr or mclnr. New company doesn't have an issue buying new tooling if it's beneficial. Like I said were hoping to move this off the manual lathe and get it on the cnc so we can face and pilot drill for the gundrill in one op. Sorry it took me a while to get back to this, I didn't have the info on that insert. I used a few others, general purpose Corloy and some snmg Walter that I liked mostly because I got to use all the corners. I'm sure I've missed something but if there is more info I can provide I will. I was hoping maybe someone had more experience with machining this material and had some suggestions. Thanks

Since the Nitinol is a Nickel Titanium alloy is it no surprise that there is no change in color until higher RPMs are used. The nickel aids the titanium in temperature resistance, but the titanium will make the chip a bear to form and break properly. The insert shown has a shallow chip breaker. This is most likely an insert geared for stainless cutting at higher surface speeds and deeper depths of cut. You mentioned you are running this on a manual machine, the most wear that inserts get are in the very introduction into the cut and at the center of the rotating component when surface speeds approach zero. The benefit of CNC is the constant pressure applied to the part along with the constant RPM ramping to accommodate the reduction in surface speed as the tool approaches the center of the part (variable surface speed). This is a huge change and improvement over the manual machine capabilities.
The insert shown doesn't show any significant heat damage or wear but then again if you were running at a low enough RPM you wouldn't see it. If I were in your situation, I would look for an insert with a chip breaker more suited for the material and the manual machine aspect. Maybe even try a CBN or coated insert to see if there any changes. Really nailing down the issue with a material like this being cut with carbide on a manual lathe isn't going to be easy.

One last thing, and I hope someone else can step in here as my experience with gun drilling is low, but I thought the benefit of predrilling before gun drilling was so the gun drill would follow the concentricity of the predrilled material. If you faced and predrilled on one machine and moved the part to gun drilling the concentricity of the predrilled hole would be lost and the gun drill would walk all over the place, if not just fail all together. I could be completely wrong, best to get some input from some with the gun drilling experience.