Coolant on PCD (turning) tools in aluminum?

[GiroDyno]

I've seen conflicting reports, what's the consensus on using coolant when running PCD inserts when cutting 6061-T6?
We are using PCD inserts for finishing operations in our lathes and the guy who originally set up the machines said coolant was bad so they've always run dry. Fast-forward two years and I'm trying to improve our reliability and wondering if coolant would help with our chip management...
We get fine/stringy chips caught between parts and pie jaws during main/sub spindle transfers more often than I'd like and I bet a well aimed stream of coolant would blast those chips to pieces and save us a lot of headache.

 

[nihilistic]

I've seen both arguments.

Coolant could cause thermal expansion/cracking.
OR
Coolant adds lubricity/removes chips/etc.

Personally, I use coolant by default as I don't see the thermal issue occurring if coolant is steady and consistent.

So, try it out and see what works for you.

 

[guythatbrews]

If the coolant is high pressure it will help little to none with chip control.

 

[ManualEd]

FWIW, Sumitomo makes coolant thru inserts for facemills, so its not a hard no.

I would run a PCD insert with lasered chip breaker, and if you have HP coolant, a tool holder with the coolant nozzle integrated in the clamp.

I doubt you'll get enough SFM in alu in a lathe to make it hot enough to fail with coolant.

 

[EmGo]

Shops that turn wheels do not use coolant. They take a really light cut, fast tho.

 

[boosted]

FWIW, Sumitomo makes coolant thru inserts for facemills, so its not a hard no.

We often use thru spindle air for PCD as well as high feed and HSM in hard metals.

I am surprised that more tooling suppliers don’t offer explicit recommendations for coolant va air, because it is frequently a question over here.

I think conventional wisdom is that PCD or slippery coatings perform best without coolant, but that recutting chips is worse for tool life than thermal shock.

 

[DavidScott]

In case it matters diamond conducts heat 3 times better than pure copper.

 

[crossthread82]

I get better finishes running my Sumitomo PCD facemill dry vs wet. The finish with coolant is cloudy but a mirror when cut dry. That PCD insert isn't going to get hot enough to worry about thermal shock, so for roughing I'd run coolant but for the finish I'd run dry with an airblast.

 

[GiroDyno]

I saw through tool coolant on PCD milling tools so I figured it isn't totally forbidden.
Ideally I'd be able to break the chip, but try as I might its just too gummy. We take a .005" deep cut for finishing and it just makes a stringy mess. Surface finish is like a mirror but all these parts get anodized so I'd be willing to sacrifice a bit of the finish.
My hope is the the weight of coolant soaked chips and the gentle "push" of coolant pressure might help them get to the conveyor before wadding up around the holder or chuck.

 

[EmGo]

My hope is the the weight of coolant soaked chips and the gentle "push" of coolant pressure might help them get to the conveyor before wadding up around the holder or chuck.

6061 ? Good luck with that

Remember the separate chip breaker pieces we used to put on top of brazed carbide tools ? Came close to the cutting edge and made the chip deform away badly enough to break it ?

I wonder if this, or some other sort of physical breaking thing, wouldn't work for you. I don't see coolant doing much more than making a little hurricane when that nasty rat's nest flails it.

Or just change to 6262 T9, that stuff makes chips like snowflakes and it's still a 6000-series material. If you can.

 

[GiroDyno]

There is a .01" undercut/groove in either side of the part, I rearranged the process so that the groove is cut between rough/finish ops to make the rats nest half as big.
I also ran a heavy coolant blast pointed just under the tip of the boring bar and it seemed to pin the chip against the part. You we're right about the hurricane-I had absolutely no visibility through the window but when the tool pulled away there were no chips left dangling so I think I'll keep running it like that, at least until I come up with a better plan.

 

[Milling man]

I've done quite a bit of aluminum with Sumitomo diamond inserts. Haven't noticed any problems with coolant supply - only benefits.
High pressure coolant will be able to break chips even in very soft materials, but the pressure must be really high - 100 bar or so.

 

[hi-fly-cnc]

I get better finishes running my Sumitomo PCD facemill dry vs wet. The finish with coolant is cloudy but a mirror when cut dry. That PCD insert isn't going to get hot enough to worry about thermal shock, so for roughing I'd run coolant but for the finish I'd run dry with an airblast.

Can I ask what depth of cut you run for that final pass if you are chasing mirrors?

 

[crossthread82]

Can I ask what depth of cut you run for that final pass if you are chasing mirrors?

0.003"-0.005"

 

[hi-fly-cnc]

0.003"-0.005"

That's helpful, thanks.

My Sandvik apps guy has advised me not to go under 0.25mm (0.01") for finishing passes (on Alu), with their CD10 grade inserts on my R590 Century. (Otherwise they might not be sharp enough to have a negative rake and the tool is just rubbing). That seems like a rather big cut to me for a finishing cut though... (On a BT30 spindle)

On end mills I've often found that a cloudy finish is a result of having too high a surface speed. Knock the rpms down a bit and the finish quality gets better.

 

[gkoenig]

Roughing or drilling? Yes. Coolant on/through the PCD.

Finishing applications or fine reaming? No coolant on the PCD.