Insert recommendation for turning ductile iron
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  1. #1
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    Default Insert recommendation for turning ductile iron

    Hi all. It's been a while since I've done any turning on ductile. I'm setting a job up with some steel cutting carbide inserts, and it's wearing them out crazy fast. I'm taking light, very interrupted cuts at about 350 sfm. What have you had success with in turning interrupted cuts in ductile? Or what brand seems to have the best offering for this? Thanks.

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    You might try a flat top insert (no chip breaker) with a small negative land.

    A tool holder that takes a thicker insert for better hear absorbing.

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    The interruptions in the part leave some fragile bits that I was afraid to use a flat top insert on. I might give it a try, though.

    Inserts I'm using are WNMG432 for roughing and DNMG431 for finishing.

    Should I be running dry?

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    One insert to try would be Ingersoll's TT7015 grade in an RT chipbreaker.
    It's designed for heavy interrupted cut in DI with a robust chipbreaker.
    Or, Seco has a TP3501 grade that is very tough, too.

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    Walter is a market leader with their Cast Iron grades WKK10S & WKK20S.

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    You might run a snu 433 (432/434) in a c2 grade Flat top, Negative, 8 corners.
    SECO tk grade (tk 1501 or tk 0501 the one that is C grade.)
    Kennametal K-1 was a good interrupted cut c-2.

    https://www.mscdirect.com/product/details/37816725

    TK1501 and TK0501 Insert Grades | Cutting Tool Engineering
    you might call and ask SECO rep what is their c-2 grade. phone 248-528-5200

    Some old Valenite grades were good likey now the Walter grades perhaps the 10s and 20s ?.

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    I've got a Walter WKK20S for the roughing and a Seco TK1501 for the finishing scheduled to be delivered tomorrow, so I'll see how those cut. I've also got some other inserts From Tungaloy, Sumitomo, and Sandvik coming in case those don't work out. Thanks for all the suggestions so far.

    Any advice on running these wet or dry?

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    What’s the diameter you’re starting at where are you ending up at? How bad is the interruption? What machine do you have? How long is the workpiece?

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    Diameter is about 2.5". Length is less than 1". We're just turning to clean up the casting- I'd say about .050" per side. There are 6 large windows in the part. There are more voids than there is material to cut. I'd say it's about 30% material, 70% open voids. Currently in a Hardinge Conquest 42.

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    It is my understanding CBN works well in interrupted cuts if you run stupid fast SFM. IIRC if you are missing 70% of the material you would run around 3 times faster SFM than a continuous cut. I've never done it but know people that have/do. Basically CBN wants the polar opposite of carbide and requires speed/heat to soften and cut the material.

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    Quote Originally Posted by wmpy View Post
    I've got a Walter WKK20S for the roughing and a Seco TK1501 for the finishing scheduled to be delivered tomorrow, so I'll see how those cut. I've also got some other inserts From Tungaloy, Sumitomo, and Sandvik coming in case those don't work out. Thanks for all the suggestions so far.

    Any advice on running these wet or dry?
    If they are chip breaker type, they will not be as good as flat tops. Unground U are better than ground G for cast iron. Us are just ground on the top and bottom with the sdes as pressed. Us can have a sive variance due to the quality of each ingredient in the mix..but in the same run number they are near dead nuts the same..Dimensionally the whole package will be as close as ground, one insert to the other.
    iron is more like Ice. the pressure pushes hard enough to case fractures ahead of the cutter. much more heat and cratering behind the cutting edge...Chip breaker inserts have less material to absorb that heat and the chip breaker allows that cratering to do more damage.
    I used to be right in the front line with Carboloy and Vaenite and did some testing on experimental hones and grades. We (with Carboloy) took a positive rake insert and put a negative hone to get outstanding life per edge..but because it was positive lost the 8 corners or 6 in a triangle so it was not cost worthy.

    If you can find Valenite Vc 101 in a shape you need for iron in the used carbide ..That was very good C-2 carbide. Carboloy 883 was good for interupted iron..We ran much of iron dry and some flooded..light coolant never worked.

    Again, the tolerance given is one run number to another run number ...not the variance you will get in a package of inserts. Because they are the same run and nearly dead on the same.

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    For the WNMG 432 MK5 WKK20S I would suggest 625 SFM .012" IPR at as much depth you can give it. For that much of a interruption the WKP30S is a tougher grade probably would have been better.

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    Thanks for all the good info. Once this goes into full production, I'll have more time to dial it in. Hopefully, the few inserts I ordered to test will get me through this prototype run. On my list of things to try are flat top inserts, CBN, and ceramic inserts. This will be a repeat job, so finding the right tool will be worth it.

    The one thing I'm worried about on this part is that on the OD with all the interruptions, there are these thin "fingers". I'm afraid of snapping one off while turning. I guess I have to find the right balance between pushing hard enough so that the tool cuts like it's supposed to and not pushing so hard as to snap those little guys off. There's only one way to find out, right?

    I'm just remembering now that the foundry that made these said that they held some parts back in case I needed some annealed. Like I said before, I don't have much experience with cast iron. Is it not very machinable in the un-annealed state? I'm confused about this.

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    If you can show the fingers perhaps a PM guy could give advise on shoeing that.

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    A lot depends on what type of cast it is and how it was let cool. A good friend of mine spent the last 30 so years machining cast pump parts that the inhouse foundry machine shop couldn't or didn't want to do. So I've had a lot of convos with him about it. Even the difficult alloys aren't super bad if they are allowed to cool to room temp before the sand/mold is busted apart. But when they get in a rush and don't allow them to fully cool they tend to be harder and more difficult to work with. They don't like to anneal them cause it costs money and also makes them softer and not wear as well in abrasive conditions. My friend used to tell me stories about turning along just fine and poof he would hit an inclusion and his $100 insert would explode. Keep in mind this was many years ago when the cost of ceramics and CBN were much higher.

    I always get a kick out of going to his shop and seeing a dozen of so turning centers with big 4 jaw independent chucks on them

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    You might consider to pick up a carbide grinder with perhaps a 150-diamond wheel, run the insert on enough parts to get a .015 wear land then change the corner only so not to change the IC and get a second or third run from each insert. With doing this on a surface grinder you can grind them in sets so a whole package of inserts will have the same numbers so to ease programing a run.

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    Danger, danger Will Robinson.
    This does not compute.....not enough information.

    You tell of interruptions and then thin sections.
    Not a world for steel cutting inserts but then the tool pressure on the thin sections where normally you would push lots of pressure.
    Bob

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    I just wanted to update you all on my troubles with this job. Once we got the parts annealed, things got a whole lot better. The material cut the way I remember ductile iron cutting in the past. There was no more chipping out of the part in the thin sections, and tool life went up dramatically. This was just a trial run, so I can't say what the best tool was. Once the job goes into production, I'll have plenty of opportunity to test some inserts.

    The lesson learned is that if asked if you want your ductile parts annealed, you should definitely say yes!

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