Chips stuck on External Groove

[mooses]

Hey Everyone,

I'm turning a small diameter part, Nitronic 40 (21% chrome, 6% nickel, 9% manganese) and I'm having a ton of trouble clearing chips from an external groove. The groove is .200" wide and .055" deep.

Mainly after finishing, it's leaving a hanging chip that prevents me from being able to grab it with the sub spindle without scarring the part up. Running roughing @ 250 SFM and .007" feed with a 3mm iscar insert and finishing @ 250 SFM with .002" feed. Current doing the finishing pass in one go from one side to the other to try to remove that chip, but not working too well. Iscar tells me that even with a diff chip break, it's not gonna help finishing too much.

Would super appreciate any thoughts on this, been working on it nonstop for about a week and nada. Tried all sorts of speeds and feeds from 80 SFM and .002" to this. Not allowed to show the part, but here's the chip, it's basically the same swirl that continues around the part 2x.

 

[sfriedberg]

It would slow you down, but can you peck to break the chip into shorter segments?

 

[mooses]

It would slow you down, but can you peck to break the chip into shorter segments?

Yeah that would pretty much removes the roughing issue since I'm plunging, but I'm turning the finish so I can't peck that.

 

[sfriedberg]

For Z feed, you can do something similar to pecking. Feed a small amount, halt feed, resume feed for another cutter width. You would be rubbing at the cutting edge during the halt, but it can be a pretty short halt.

 

[plastikdreams]

As backwards as it sounds what about a m00 and reach in and pull it off. If nothing else works, somethings gotta be better.

 

[implmex]

Hi mooses:
I've never tried with Nitronic 60 but I have been successful (mostly) controlling the chip in PEEK by either air blasting it or vacuuming it so it never gets a chance to snarl around the workpiece but streams away in a direction I can sort of control.

Another tactic I've used successfully in PEEK is to plow a ball mill along the profile first so when I rough the chip is broken up by the groove.

The third tactic I've sometimes had success with in 17-4 PH H900 and Ti-6Al-4V is to run two finishing passes and make the second as tiny as I can get away with and still have the tool take a chip.
I'd let the first pass do whatever it was going to do, manually clear off the chips or back out the tool after the pass by following along the contour with the lathe still going in M03 but the toolpath reversed so it would follow the contour feeding back out away from the chuck and stripping the snarl as it went.
Then I'd take the final whisker pass.

Sometimes I'd need to use a dedicated tool for that whisker pass because I'd be taking half a thou or a thou or so per side, so the chip was like steel wool and would clump itself into a mat that would fall away in one big ball.
That pass would fix all the welded on chip remnants and give me the pristine surface I needed.
I needed a separate very sharp tool for that because of the nutso shallow DOC.

Back feeding away from the chuck was often the desired strategy for that whisker pass too, and I accepted 3 times the cycle time for finishing, and the two tools just to be able to actually make the part unattended.

I have found, that for peck roughing with super stringy material, the peck increment had to be so short the machine sounded like a machine gun and the tool life suffered, if the tactic was to be successful.

I always had far better luck grooving out the part in successive steps, stepping down the length of the part in Z but then pecking in X rather than in Z.
But I still had the problem you're having while finishing.

Interestingly I was able to do better sometimes with box tooling like you'd use for an old fashioned turret lathe (obviously not for contoured parts but for cylinders) because they would direct the chip better, but with stringy materials it's always a problem.

I'm not sure there's a magic solution...I've certainly never found one.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

 

[guythatbrews]

Whether turning in the x or z direction i peck stuff like this. Very short pecks, only a few thousandths but don't dwell to break the chip, reverse the feed.

G1 W.004 F.004 (turn)
W-.005 F.015 (back up)
W.004 ( approach next cut)
W.004 F.004 (turn)

Cycle time is slightly longer. I do not see significant loss of tool life. The addition of properly directed hi pressure coolant helps a bunch!

When the feature is complete come back with the groove tool, position a few thousandths above the diameter, and feed the tool off the end of the part. This will often snag chips and pop them off the end of the part. Again, hi pressure coolant makes a huge difference.

Although it is a big pain i have a few parts with a program stop before the pickoff. Parts that just won't always cooperate. Just be right there when the program stop happens to intervene as required. Not terribly high production, 1000-1500 pieces. But this way I don't loose any to hanging chips. If you've been struggling for a week this might be one of those parts.

 

[mooses]

Really appreciate everyone's shared experiences and advice. I'll certainly give the peck turning and second raised pass a try. We have about 10k of these a year so I really really wanted to get it to unattended running with a barfeed. Doing m00 after every grooving OP right now and removing them manually, I'm gonna wear out this door before I wear out my machine! I had a bit more success in somewhat similar part using a smaller cutting width for finish I just remembered, will also try that on this part and see what happens.

 

[sinha]

Pecking with G75 would be very convenient, specially when the width of the groove is more than the width of the tool, requiring another grooving operation after a lateral shift of the tool. This will be just two blocks of program.

 

[michiganbuck]

Not likely possible but I wonder if a small spinning wire brush and a comb to clear the brush could be used?
I could see/imagin such a device on a turret lathe, to drop in when needed.
I have used tool-designed to chip-break or steer the chip a certain direction

 

[Ox]

Like the ball end mill idea above, you could try a quick pass with a threading tool to just above your finish diameter.
2-4 TPI sorts? (wouldn't need to use a threading cycle, just F150. or some such...)
Not sure if that would show up in the finish or not?


... b ut then maybe you end up with a thread ratts nest hanging in stead of what you have?

------------------

Think Snow Eh!
Ox

 

[couch]

When you say it’s from finishing is this finishing the groove or finishing the rest of the part?

Have you tried finishing from back to front instead of front to back, to push the burrs off the front of the part?

 

[guythatbrews]

I use a do-while loop to peck. Also Marcus' thought of a very low DOC finish cut will help. Almost a dead pass.

You might still loose a few parts with chip marks. I'm currently running some small rings losing about 1/750. Very acceptable. The parts get a 100% visual inspection during packing.

 

[csteen]

Totally different take on this. Get a right and left hand 35 degree or 55 degree diamond tool holders then just cut it and ditch the grooving tool. Without knowing more about the part length or where the groove is you may be able to turn the entire part with a left hand tool mounted right hand orientation from the chuck out and the lead angle will be driving the chip ahead the entire time, then clean up the corner with a tool mounted the correct orientation. Another option would be back turning tools for swiss type machining.