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insert life in stainless steel (304)

SDConcepts

Stainless
Joined
Mar 1, 2007
Location
warren, mi
some previous threads about running lights out has got me thinking... i know its dangerous, but i run alot of stainless parts and for the life of me i can't get inserts to live longer than about 30 parts. i can't imagine trying to run lights out on these jobs. what kind of jobs are people running that they can run lights out? and also for those that turn stainless any recommendations for inserts that can last? i've tried kennemetal and kyocera and the ones that seems to work for me are the TMX bison ones. i am taking pretty aggressive cuts as i'm trying to cut my part cycle time to below three minutes. my lathe has a peak RPM of 5000 and my parts are less than 1.5" od and most are smaller than 1".
 
some previous threads about running lights out has got me thinking... i know its dangerous, but i run alot of stainless parts and for the life of me i can't get inserts to live longer than about 30 parts. i can't imagine trying to run lights out on these jobs. what kind of jobs are people running that they can run lights out? and also for those that turn stainless any recommendations for inserts that can last? i've tried kennemetal and kyocera and the ones that seems to work for me are the TMX bison ones. i am taking pretty aggressive cuts as i'm trying to cut my part cycle time to below three minutes. my lathe has a peak RPM of 5000 and my parts are less than 1.5" od and most are smaller than 1".

I can't testify as to their longevity (inserts in my shop don't ware out. They usually die a sudden violent death), but the TMX have worked great for me in a ccmt config. However the insert I have recently found the best for stainless was the Seco TM2000 series. I have one (CNMG) that was cutting all day the other day and I cant see any appreciable wear. I was cutting mostly 303 with some 316.
 
I'll second Sandvik 2025. They rocked in 310 SS. Ran them at 450sfm, although the pack said between ~500-750sfm. Could have run it that faster but tool life would go down. FYI, DOC was .04 and feed was .016/ipr and was the MM chipbreaker. Get the MR (I think that's the one) for serious roughing.

Toshiba Tungaloy 6020 is another good grade.
 
I can't testify as to their longevity (inserts in my shop don't ware out. They usually die a sudden violent death), but the TMX have worked great for me in a ccmt config. However the insert I have recently found the best for stainless was the Seco TM2000 series. I have one (CNMG) that was cutting all day the other day and I cant see any appreciable wear. I was cutting mostly 303 with some 316.

303 is a far cry (best pc game ever-"Far Cry") from 304 and 316. :willy_nilly:

I use the Sandviks and I index roughers 1/day in at least 10 hours. Still would not want to run lights out on anything other than soft, easy stuff with wide tols, say +/-.01. I know some guys claim lights out in tuff stuff and +/-.005, but...:crazy:
 
well thats kind of what i was thinking too. i would hate to try and run lights out on 304 no matter what the tolerances. so that brings me back to what inserts can be used to get more life out of them? i'm using tmx nc3020, i'm thinking of trying the nc9020 and seeing if that will hold up longer. all my work is stainless and i rarely do anything else.
 
SD concepts,

No wonder your insert life sucks, you're using inserts rated for steel. The 9020 grade is comparable to Sandvik's 2025. Just how aggresive are you being with the roughing. There are a few more grades on the TMX website that are more suited to roughing stainless, PC9030 & NC330.

What style of insert are you using? I'm guessing CNMG.
 
I have been wondering about the lights out business also.I hear that kennametal 5010 is
pretty good. I wish my boss would buy some to try out. He thinks that KC850 is the greatest
insert ever, for everything! I beg to differ.

Jeff
 
I really like the Sandvick 2025, I do run some 2015 in a couple sizes that I couldn't get 2025. The 2015 may last longer in CNC applications? I just do manual stuff, but lots of SS.
 
some previous threads about running lights out has got me thinking... i know its dangerous, but i run alot of stainless parts and for the life of me i can't get inserts to live longer than about 30 parts. i can't imagine trying to run lights out on these jobs. what kind of jobs are people running that they can run lights out? and also for those that turn stainless any recommendations for inserts that can last? i've tried kennemetal and kyocera and the ones that seems to work for me are the TMX bison ones. i am taking pretty aggressive cuts as i'm trying to cut my part cycle time to below three minutes. my lathe has a peak RPM of 5000 and my parts are less than 1.5" od and most are smaller than 1".

Look, I'm straight up and honest with you. Look at your tooling, negative rake holders and inserts are not the way to go with the smaller dias. Reject the whole 4-6 edged inserts seated in neg rake holders. With that speed and dia (yes, even the 1.5") will push and ride on the insert. Seek your local Sanvik sales rep and discuss true pos rake holders that will not accept the 4 edged jobs. SCLCR/L stick tools with the CCMT's. Guys will argue that the CNMG's are really pos inserts sitting in a neg holder, but the actual cutting edge is unsupported, thus 'flecting to a neg cutter. Better tol hold with the finish that everyone loves! :smoking:
 
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re: TMX grades
If there are no interruptions you should be using PC9020 with the proper geometry ( HA chip breaker)
Here it is:
84827211.jpg


For interrupted cuts or slight scale use PC9030 (slightly tougher) and the HS chip breaker. It still has some positive geometry but with more land for edge strength:
cb933b03.jpg


The trick in 304 is to take a hefty cut and feed the crap out of it and force that gummy chip to roll over and pop. The insert in picture one will do that for you.

For extreme roughing go with NC3030 (updated version of 330).
 
Metlhed, I'll argue with you, or at least play devils advocate, if for no other reason than to learn more.

I think we can both agree that a CNMG with a 20 degree positive chip breaker sitting in the holder will give you 15 degrees as the workpiece sees it, and 70 degrees of solid carbide supporting the edge. A CCMT with a 15 positive chip breaker will show the workpiece 15 degrees in a neutral holder and 68 degrees of solid carbide supporting it. Unless your sitting in a positive holder, which I've only seen once(never looked for one).

On the unsupported edge, I just went and looked at some DNMG, WNMG, DNMG 432s(431s) some finishers some roughers, generic job shop stuff. They are ground on both sides, so that the high parts of one side of the insert support the cutting side, most are pretty close out to the cutting edge(.020-.040 or so) .

However, I also have some Taegutec(ingersol) CNMG 432 ML TT3050s, pretty darn positive, no T-land, just a medium hone, and the nearest underside support is about .115" from the cutting radius. I understand what you are saying, but I'm finding it hard to believe that the insert will actually bend signifigantly. 3/16" thick(minus double chipbreaker depth), approx .200 wide, hanging out .115". Seems far more likely that your toolholder or especially your workpiece will flex first and much further, especially on a finish pass. I have seen carbide bend and not break, so I know it can happen, but in turning the insert seems to be the most stable part of the whole mess.

A reason you might actually like negative holders, you can get single sided, very positive inserts for them when you need them, and revert back to the more common stuff when you don't.

I'm not discounting what you are saying, and have filed it away hoping it comes in handy some day, I just need more convincing.
 
metlhed,

I have to disagree. If the holder that he has is for CN?? inserts, it already has relief built into it. Add a CC?? insert with another 7 degrees of relief and now you have 12+ degrees total relief. This will leave the cutting edge with even less support. Besides why would you use an insert with only two cutting edges versus four, it's doubling tooling costs. The only thing I would use a CCMT insert on is easy to machine materials, like aluminum.

Just because an insert is in a negative holder doesn't mean it's negative geometery. The only part of the insert that actually does the cutting is the thin ~.010" land (I think that's the right word) on the edge. If you find exploded views of different inserts you'll see that manufacturers change the angle of the land for machining different materials. Inserts for roughing steel usually have a negative edge because it creates a stronger edge and there's no worry of work hardening. Stainless, Aluminum and super alloy inserts have a positive edge to reduce built up edge and/or work hardening.
 
SDConcepts,

Have you tried backing off your SFM? Let the chip load rise to maintain your cycle time assuming you have enough rigidity. Tool life is directly related to SFM while chip thickness has very little effect unless you get so thin that you are rubbing or so thick that you run out of rigidity.

Gotta agree with Bobw, there is no way you are going to "bend" a CNMG-43x in a steel cutting grade. There isn't enough cobalt content to allow it to happen. Your toolholder and/or clamp is going to move first.
On the flip side of the CCMT vs. CNMG is the fact that the CCMT has more clearance on the side or flank of the tool helping to give a cleaner cut because there is less rubbing as the material "springs back" after the compression from cutting. This extra clearance also helps prevent the flank wear from progressing down the side of the tool.

The key to lights out running is some sort of automatic probing/gauging. Kinda sucks when your machine calls you up at 2:30 in the morning to tell you it has shut down but it's better than coming in and finding 500 scrap parts.:)
Bob
 
There are at least 2 different ways to look at your cutting tool.
What some refer to as "rake angle" is actually called the inclination angle.
This is the front to back view. Technically speaking, it's the plane parallel to the main cutting edge of the tool. If you held your hand straight out with your palm down and tilted your fingertips up slightly you would be altering the angle of inclination.

Rake angle is perpendicular to the main cutting edge and is the measure of the cutting edge in relation to the cut itself. Once again, holding your arm straight out palm down (for a right handed person) fingers extended, tilt the left side of your hand down slightly. Hopefully I have described this accurately and this will be your thumb side.
If your hand were the cutting tool and you are turning from right to left, this is your rake angle.

The cutting edge as it is presented to the work piece can be positive in a negative rake tool holder.
 
metlhed is not wrong with what he said. There's arguments for both neg and pos insert/holders. When you get down to smaller diameters, especially in stainless steels and super alloys, positive inserts generally will work better. This is not opinion...just fact through the materials I run and have tested.

Forget your opinions for a sec and imagine how the insert tip is presented to the work piece...imagining also the workpiece diameter and how it curves away from the tool tip.
With a positive insert (CCMT, TCMT, etc...) you have a sharper cutting action. Therefore, a lower cutting temp at the same SFM as a negative insert (CNMG, TNMG, etc...). Lower temp equals less plastic deformation of the tool tip...longer tool life. Time to speed it up a bit.

On my larger lathes (over 1-1/16") I'm running CNMG, TNMG, & VNMG. Under, I'm running CCMT, TCMT, but still running a VNMG for finishing...currently testing Sandvik's TR inserts (T-rail) with excellent tool life and repeatability.

Why am I running the positive rake angles? Because productivity and tool life outweigh the cost. Overall lower cost per part...that's the goal!
 
ok, the tooling i'm using for roughing is a TNMG. this insert will last a long while. where i run into a problem is on the VNMG inserts that are doing the semi finish and finish turn profile. i will be trying the nc9030 in the tnmg the next time i'm doing this job and i will be going with the nc9020 for the vnmg as thats all they make in the size i need. my next up coming job is another stainless peice but i need to use two ccmt inserts for it. and i will be getting these in nc9020 as well since i have to do 2800 pcs.
 








 
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