PDA

View Full Version : Advice needed on using ceramic turning tips.



old mart
02-04-2017, 03:40 PM
I picked up a box of SPK (German) SNGN 120716 T03030 SN80 ceramic inserts for 10 cents on the dollar from eBay the other week.
They are thick square*white tips, some variation on aluminium oxide probably. I bought them just for fun to play with.
Rod made a 45 degree holder with a 7 degree recess to use a corner*and we had a pathetic trial with an old MT2 holder which was the only bit of hardened steel to hand.
I know that interrupted cuts are a no no, but don't know much else. Do you need to take big cuts or small?

rklopp
02-04-2017, 04:06 PM
You probably need to use these in a super-rigid machine that can handle a deep cut and high feed. Ceramic inserts are brittle as all getout and the route to success is compressive stresses in the ceramic. Hence the negative rake. They probably have a hefty chamfer or "hone" on the cutting edge to keep it from chipping. Your depth of cut needs to be much bigger than the chamfer so that the peeling chip bridges the "pre-dulled" edge caused by the chamfer. These inserts are probably meant for roughing cast iron dry at 600 ft/min speeds and up. That's tough to do at home, and you don't want to be in the spray of hot chips coming off.

JRouche
02-04-2017, 04:25 PM
Haha! You sound like me. I bought hundreds of them on ebay years ago and have never used them. I imagine some serious speed (SFM) is needed. I have holders for all of them. From what I remember the dark colored type are "better". Better how, I dont know.

Ill be watching this thread. Maybe Ill play around with them also. I have two lathes that will reach 4000rpm and both have some decent power. I just dont know what to cut with the ceramic.. Thanks, JR

http://i1183.photobucket.com/albums/x461/_GLE_/HSM/ceramic_zpshtxvrrbk.jpg (http://s1183.photobucket.com/user/_GLE_/media/HSM/ceramic_zpshtxvrrbk.jpg.html)

old mart
02-04-2017, 04:44 PM
The old Smart &*Brown will manage cuts of up to 20 thou in steel on say, 1.5" stock before the belts slip. I noticed the chamfer round the ceramics, I will set one up in the mill and use the optical scope to measure just how big it is and try at least that depth of cut.
What we got with the tip were lots of red hot sparks and a trace of steel welded to the tip.
The S & B will only reach 1375 rpm and has only a 1.5 hp motor, so ceramics may be just a*pipe dream for us. Never mind, we have lots of carbide tips of all shapes to use.

bobw53
02-04-2017, 05:47 PM
Ceramics are completely the opposite of every conventional cutting tool you've ever used...

They DO NOT "CUT"... They work by generating HEAT, they plasticize the metal ahead of the cutter, and the next time around (or next insert around),
the plasticized (HOT!!!!) metal gets wiped away and more heat is generated ahead of the cutter.

HEAT is the key... That leads to several odd things.. You need to stay in the cut, entering a cut is when the damage to the inserts occurs(primarily),
because the metal is COLD and HARD.. so ramping back and forth is what you need to do...

Interrupted cuts.. Complete opposite of conventional tooling.. In interrupted cutting, milling or turning a hex or square shaft, you need to INCREASE the speed,
the inserts have a chance to cool when they are not in the cut, and you need to get them back in the cut before they cool too much, and then you need
to pile a whole lot more heat into them before they exit the cut.

If you are chipping carbide, you slow down.. If you are chipping ceramics, you speed up....

If you aren't throwing flames and fire everywhere, you are WAY TOO SLOW...

Ceramics are nasty and violent, they generally require a ton of horsepower, rigidity and speed...

I did one job years ago in A286, (also known as Incoloy).. Milling.. I took my roughing time down from
over 30 minutes with carbide to 30 seconds with ceramics.. 2" cutter, 11700rpms and 240ish ipm.. It
was nasty violent and LOUD.. It was AWESOME!!!! Ceramics saved 3 weeks on that job...

I wouldn't run it at night it was so LOUD!!! and violent, people would come out of the office to watch the roughing op several times
a day.. It was quite the fireworks show..

http://www.mmsonline.com/articles/successful-application-of-ceramic-inserts
Here is an article from MMSonline. They have a few more that are good also, look for the older stuff from back when their articles had really good technical content. Not
"XYZ saved $$$ by using BLAHBLAH tool"

duckman
02-04-2017, 06:53 PM
I use them at work when we get our check rings back after heat treating (D2 at 60-62 Rockwell C) they are left over size so if there is any warping it can be turned off, 1 1/2" dia. usually run about 1,000+ RPM .002 feed and about .003 DOC love watching the fire works.

becksmachine
02-04-2017, 06:58 PM
One problem I had with ceramics when turning in the lathe, the insert would survive the cut just fine and then get destroyed by the 1 or 2 turns of ragged edge as it ran past a shoulder.

Putting a heavy chamfer where the tool enters or leaves the cut helps this.

Dave

MattiJ
02-05-2017, 03:50 AM
Agains all conventional visdom some ceramics (kenna ky1615)seem to work very well when finishing soft steels like 1018.

I have been playing with hard turning on a 11x36 kerry with suprisingly good insert life. Its only a 500 pound lightweight and worn out machine but seems to work.

Jaakko Fagerlund
02-05-2017, 04:19 AM
As always, te best advice is this: experiment, you have nothing to lose but time. If I'm turning a case hardened something something, I'll start off with around 100 m/min surface speed and a feed of say 0.015 mm on a R0.8 nose radius insert.

Those black ones we have had at work and they were for "roughing", meaning they could take way more pounding and variable cutting conditions than regular ceramic inserts meant for semi-/finishing.

DR
02-05-2017, 10:54 AM
There are "cermet" inserts which I use exclusively turning steel on my CNC lathe. They can be used wherever "conventional" carbide is used including interrupted cuts.

I'm not quite sure of their distinction from regular carbide. It seems they were slightly less expensive.

MattiJ
02-05-2017, 11:16 AM
There are "cermet" inserts which I use exclusively turning steel on my CNC lathe. They can be used wherever "conventional" carbide is used including interrupted cuts.

I'm not quite sure of their distinction from regular carbide. It seems they were slightly less expensive.
You can think that Cermet is just a variation of regular carbide. Ceramics are much different animal..

old mart
02-05-2017, 01:15 PM
Thanks for all the advice, we probably will not use the ceramics very often,*I don't fancy having too many of those red hot balls of fire dropping on my arm.

j king
02-05-2017, 01:27 PM
I have 2 diamond tipped tools. Have had them for years. Brand new ..I always wondered what I could use them on but never really bothered to try them. I figured I would ruin them playing around..any suggestions?

JRouche
02-05-2017, 05:14 PM
I have 2 diamond tipped tools. Have had them for years. Brand new ..I always wondered what I could use them on but never really bothered to try them. I figured I would ruin them playing around..any suggestions?

Aluminum.. JR

Jaakko Fagerlund
02-05-2017, 11:53 PM
I have 2 diamond tipped tools. Have had them for years. Brand new ..I always wondered what I could use them on but never really bothered to try them. I figured I would ruin them playing around..any suggestions?
As JRouche said, aluminum. Diamond and aluminum is the best combination, as the alminum can not cold weld itself to the diamond tool. In industry they can do mirror like surface facing cut to aluminum with such a tool.

boslab
02-06-2017, 12:04 AM
I have a diamond tool, the diamond is quite large and flat, I've machined Ali several times with it, mirror finish, light cut and lathe flat out, I'm told to avoid interrupted cuts, works well on copper too.
Mark

dian
02-06-2017, 12:49 AM
concerning interrupted cuts, i own a single ceramic insert and use it for hard turning chuck jaws. its still like new, but what bobw53 said about speed. the insert has a single edge and was around $100, a "special" price a shop made me, because they didnt need it. so no idea if that works with any inserts out there.

btw, how do you tell a reinforced insert? because its black?

MattiJ
02-06-2017, 01:20 AM
concerning interrupted cuts, i own a single ceramic insert and use it for hard turning chuck jaws. its still like new, but what bobw53 said about speed. the insert has a single edge and was around $100, a "special" price a shop made me, because they didnt need it. so no idea if that works with any inserts out there.

btw, how do you tell a reinforced insert? because its black?

Pricing and having only one edge suggest that its a cbn- insert.

dian
02-06-2017, 03:11 AM
sorry, your right, i wrote this before having the morning coffee.