Greenleaf inserts for Inconel - turning

[P_Scott]

Lathe gurus,

 

I have a customer that is turning Inconel and stainless for aerospace industry. They have been using Greenleaf WG 300 "whisker" impgregnated ceramic button inserts for roughing large diameter parts. They are learning and using Mcam X after using a proprietary programming software. They have to change the inserts on their standard OD roughing tools every few passes. They were told by the Greenleaf representative to flood the tool with as much coolant as possible. They have a hose the size of a clothes washer drain line attached just below the turret on several Mori-Seiki's. My question is this. I've always been told that ceramic inserts should be run without coolant. Is my customer being "hosed" into buying inserts more frequently, or does this situation sound legitimate? It just seems unreasonable that they would have to change an insert every few roughing passes when it is supposed to be an "oustanding" new insert material designed to be far superior in longevity to carbide inserts. The shape of the insert actually looks more like an insert seat than an insert. There's no chip breaker molded into the insert shape. I just want to understand so I can work with my client to help them in programming their parts properly. If I can save them some cash in the process, that would be an added benefit. TIA.

[Tim Simmermon]

Peter,

 

Attached is an article I found on a shop that uses those inserts:

 

http://www.americanmachinist.com/304/Issue...lse/12112/Issue

 

They seem to take lighter DOC's (.030 - .040) at higher SFM. It does not say anything about using coolant or not. When we turn stainless steel or "Super Alloys" we don't use ceramics, but rather a grade of carbide that can stand up to the heat generated. And we use coolant. They say the insert is supposed to stand up to thermal shock, and that is why coolant is not used in some applications.

 

HTH

[CAM-mando]

Peter, my understanding of cutting with ceramics (milling and turning) is that the DOC and surface speed combination are critical to generating the heat REQUIRED for the cut. As I understand it, creamics rely on plastic deformation of the material ahead of the cut.

 

Without the enough heat, the inserts don't hold up.

 

The only thing I can think is that the the speeds and feeds are so high in this application that even with copious amounts of coolant the work piece is getting hot enough in the cut and that without the coolant the workpiece is suffering thermal micro cracks or something.

 

As for tool life, it often appears the life is too short, but when you compare it to the volume of material that could be removed with carbide you get a better perspective.

 

Out of curiosity, how big is the part ?

 

BTW we run them dry on our lathes.

 

 

EDIT: Peter check page 27 of the PDF. The "Paradox" is explained.

http://www.greenleafcorporation.com/images/PDF/WG-300.pdf

 

[ 05-30-2006, 02:56 PM: Message edited by: CAM-mando ]

[88Matt]

Peter,

 

How are the inserts failing? Wear? Fracture? Build-up? etc... Examining the used inserts is a HUGE resource of info. IMHO a must.

 

You are correct, ceramics are meant to be run dry. They are very hard and can withstand extremely high temps (actually they thrive at high temps), but are extremely brittle. They dont like coolant or heavy interrupted cuts. Ceramic inserts need the high temp at the cut with a DOC deep enough to cut under any possible workhardened material.

 

Ive never used Greenleaf's inserts, but ceramic is ceramic. Have them contact another insert vendor (we use Kennemetal or Seco) and see what they say.

 

Please post what u find out. I'm highly curious to hear Greenleafs reasoning behind using coolant.

 

Matt

 

Hope Y'all had a safe and "HICUP" fun holiday!

[P_Scott]

Thanks for the info guys. Keep it coming. I will ask my client how the inserts fail and see if they can give me some more specifics. Thanks again.

[JG]

Peter,

If the inserts are wearing to quickly it is probably due to depth of cut notching, you need to continuously vary the DOC or if the part and machine are capable, plunge perpendicular to the contour using full depth of cut (button insert only)

 

thanks,

 

Jg

[mcpgmr]

Never used coolant. Dry cutting only with fairly good results. Used the WG300's in milling and turning applications. Turning and grooving dia's in inconel 939 up to 96" with the chips on fire and floating back to the floor. This was on a Dorries CNC VBM and the parts were Vane segments for a gas turbine engine. There were 32 segments being machined with approx .100 gap between each part so the cut was intermitant and the inserts still held up fairly well. Milling with 4.0 face mills taking .075 to .100 d.o.c. in Inconel and cobalt aloys at 3500 rpm and 50 ipm. I was told by the Greenleaf guy never to use coolant. Worked for us.

[Randy Morton @ Clem Industrial]

Myself, I use ceramics both dry and with coolant. Truthfully, I have not notcied any difference, from my application, in life of the tooling either way. We mostly use Kennametal and have found them good, but not for monster hogging (now thinking back to my last shop).

 

A good grade of carbide with a good chipbreak (or not...) is better suited and ceramics for smaller cuts, higher SFPM, almost finishing like ops.

 

This is just my opionion.

[CAM-mando]

From the link above, Greenleaf claims that flood coolant does not decrease the temperature in the cutting zone but can as much as double tool life for WG 3000.

[P_Scott]

Tim Simmermon,

 

Great article but they never mentioned whether coolant was used or not. From the first picture at the bottom, it appears like they had an air line on the milling part.

 

CAM-mando,

 

The pdf seems like the inserts should last longer than they appear to be. Also according to mcpgmr, those inserts work well without coolant as he was told by their Greenleaf rep.

 

mcpgmr,

 

Thanks for the input. the application you described seems very similar to the one my client is using the inserts for. I will find out how the inserts are failing and what speeds and feeds they are currently running at.

 

Thanks to All for your replies. I'll keep things updated.

[88Matt]

:Bump:

 

How about an update Peter?

 

Matt

[OK-KO]

We also use ceramics both wet and dry (lathes), dry runs are through interuptions (thru impeller vane segments) where insert thermo shock starts to be a problem with coolant. Running dry in a continuous cut causes the parts to over heat and distort so we have had good results with heavy coolant flow. We have found Indexables inserts out of Canada to be top notch, with differnt pressure angles and edge preps in lots of styles.

We cut mostly 718 Inconel. for us .100 to .150 d.o.c. is about average for roughing, about 800-900 sfm and a .004/.006 feed. At these numbers you can expect about a 4 min max tool (edge) life at these speeds, but as CAM-mando says, the shear volume of material removed in such a short time sets these inserts miles ahead of carbide. We use round inserts when possible for more cutting edges. with ceramics it takes a while to find the "sweet spot" where that part wants to run, but then you will never go back to carbide.

 

Kelly

CNC Programming

Hanard Machine Inc.

Salem, Oregon