Minimum quantity lubrication - MQL

Hello! So, I'm not an engineer, unfortunately, so I have fairly limited technical knowledge, as a disclaimer.

I've been doing research into MQL, and am trying to get a sense of why its adoption rate is fairly low (at least in the US). I've been reading a bunch of materials and even research studies into MQL and its benefits and effects on various materials, but a lot of it seems like marketing collateral (UNIST's MQL Handbook, for one). I've come across studies of it being integrated into Ford and VW's manufacturing floors, but maybe that's just in Europe.

Have you, or do you know of any shop that has adopted MQL into their processes?

Or anyone who has looked into MQL but ultimately chose not to use it? Or I guess, can anyone hazard a guess as to why that would be the case? Is the stereotypical "old school" nature of the industry preventing adoption of these new tech? Is it because materials aren't compatible? Initial costs? Lack of awareness of the technology itself, as well as its benefits? Or they simply don't want or need it? All of it?

Any thoughts would be greatly appreciated!

I smell spam.

Oh no. Why do you think this is spam? (it's not, btw, if that matters)

If it feels like spam, tastes like spam and smells like spam, it's spam.

Ok, what is spam then? I'm not selling anything - I associate that with spam, but I guess anything can be considered it these days.

Or, spam is just spam, i.e., meat in a can.

By my understanding of it, "Minimum Quantity Lubrication" is essentially just mist coolant and air blast instead of traditional flood. It IS in widespread use already, but I don't see how or why it would take over all coolant needs. Both systems have strengths and draw-backs.

For one, mist coolant may provide necessary lubrication, but it doesn't clear out the cutting area quite the same as flood does. If your tool paths are creating lots of fines, then it's going to leave a mess for the operator to clean out when he loads the next part. It also provides less room for error in that if you don't have everything set-up just right, you can get zero lubrication, where-as with flood if your nozzles are not set right or you don't have optimal pressure, there's still some getting where you need it. There are some operations where you can stand to just cool the cutting edge, others where you really what to keep the whole part saturated.

In certain apps like engines, the flood coolant helps stabilize the parts from a dimensional standpoint. Thousands upon thousands of gallons are held in a specific temp window.

Obviously energy savings are possible but who wants to take the risk in all of the variation?

Limy Sami said:

I smell spam.

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Sami,

For some reason, I smell pineapples, as well......which reminds me of the old joke--What did one snowman say to the other snowman?




"Do you smell carrots?"

hrchrc said:

Ok, what is spam then? I'm not selling anything - I associate that with spam, but I guess anything can be considered it these days.

Or, spam is just spam, i.e., meat in a can.

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I guess my sense of smell failed this time. I hope it's not a sign of coronavirus...

I was reading an article in fabricator, yrs ago? and guy 'mention mist and you will get laughed outta detroit'. We tried it on a saw (unist), and wow- not worth it. Surface finish is not our concerns, and on the few times I really need it I run dry, mql is/was a trend word for industry 2.0 or 3.0. Sorry I forget which version of industry that update came out in.

On my manual unenclosed machines, I generally cut dry or with cutting oil applied locally by a brush or lab squeeze bottle. However, some jobs call for something more.

I use a Noga MiniCool in the home shop, and had the opportunity to use a FogBuster at a school shop this year. Both deliver mostly air with a little liquid. The Noga will adjust from airblast to very wet spray, but it's not as easy to adjust at the dry end of the range. The FogBuster is much easier to adjust for minimal liquid, enough that I'm planning to get one. Both systems were used with a water-based coolant (KoolMist 77 in 1:20 dilution) rather than straight cutting fluid, which differs from other MQL systems which deliver tiny droplets of more concentrated fluid. I like the FogBuster's approach of pressurizing the coolant reservoir over the MiniCool's venturi suction hose.

In my limited experience, the mostly air blast of these systems cleans swarf out of the cutter flutes/gullets better than a low-pressure flood of cutting fluid. (High pressure coolant is completely another story.) And it definitely has a strong local cooling effect. When adjusted toward the dry end of the spray, machine cleanup is minimal, even on machines not designed for flood coolant.

I was not completely happy with using the MiniCool on a manual surface grinder, unless cranked up to a very wet spray. I will be reverting to a liquid flood once I get a new reservoir and pump.

I cut only with MQL, my flood coolant is only used to wash off parts. Air oil mist gives better tool life hardmilling compared to flood, also it's nice to see what the hell your doing.

memphisjed said:

I was reading an article in fabricator, yrs ago? and guy 'mention mist and you will get laughed outta detroit'. We tried it on a saw (unist), and wow- not worth it. Surface finish is not our concerns, and on the few times I really need it I run dry, mql is/was a trend word for industry 2.0 or 3.0. Sorry I forget which version of industry that update came out in.

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You have an awesome memory- I was actually able to find that article (or, one similar) on CTE from 2017!

5 axis Fidia guy said:

I cut only with MQL, my flood coolant is only used to wash off parts. Air oil mist gives better tool life hardmilling compared to flood, also it's nice to see what the hell your doing.

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So you use both MQL and flood coolant, but coolant only to wash off parts -- is that different from chip evacuating? (sorry i realize this question sounds quite elementary)

MichaelP said:

I guess my sense of smell failed this time. I hope it's not a sign of coronavirus...

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too soon!

but seriously, hope everyone's doing all right

Years ago in a mold shop we had 2 Yasdas. They never came with a coolant tank. These were high speed core and cavity machines. Used MQL or ran dry like Fidia Guy says. Much better tool life and part finish. The secret is in "minimim" part. We went through about a gallon a month of non-stop machining. I do have a white paper on the use of different oils used in a MQL system. More subject to benefits of the oils themselves than the MQL system itself. Private message me and I will send it to you. It's a rather large PDF.

Paul

I use MQL for my very low production/one-off stuff. Usually with mundane materials (6061, 1018, 303 etc). I initially started using it because my CNC mill has only a partial enclosure and can sit unused for weeks at a time. So both control of mist/splash and minimizing sump maintenance are concerns for me. I use a fogbuster system which is well made and reliable, although I have never been able to completely dial out "fog" like they promise.

Two issues that bug me with the system:

Chip cleanup SUCKS! Little sticky shards everywhere. As I don't have a sump full of coolant I cannot just wash down my parts/fixtures. So I spend a lot of time wiping stuff down with rags. Everything goes into an ultrasonic cleaner after machining (the ultrasonic has to be cleaned more often because it gets tons of shavings and oil residue in it). With single operation parts, its fine because they go from the mill directly to the cleaner anyway. I'm not usually trying to optimize parts/hour so its workable but man it is annoying. Of course I could keep coolant for washdown but then I have to maintain a coolant sump which negates an advantage of MQL for me.

Second issue, is that depending on the tools you are using and your part geometry, making sure you get flow to the tool cutting surface(s) can be problematic. More nozzles is better (I started with one, but now I would consider two to be the absolute minimum). Spray "shadows" from part geometry can cause issues as can slotting operations. Depending on your tools and parts this may be a non-issue. I have also seen servo-controlled nozzles that could help.

I can't speak to benefits or drawbacks of MQL for MRR or cutting behavior otherwise. Again due to the nature of my business and the low volumes I work at I'm optimizing for stability of process rather than speed of operations. I am usually using HSM style paths with conservatively low width of cut, as especially in aluminum this gives me lowest chance of clogging flutes or recutting chips. Perhaps I could push harder with flood but I have never been in a position to do controlled testing of that hypothesis.

IMHO.
Kinda agree with all posters.

MQL.
It´s not too common,
can work great,
"works great" given parameters a,b,c** etc,
does not usually easily work so well for flushing chips, with "bigger" chips and in bigger quantities.

But..
MQL has been proven to work well in endless particular work cases, sometimes even better than traditional flood coolant strategies.
In specific apps.
But not overall for everything.

My opinion / guesstimate.
MQL is likely to become more and more common, and become prevalent in probably about 60% of machining apps, within x time.
At the same time, I estimate it will be a std feature of all new machine tools with one or multiple servo coolant nozzles as standard.

It is probably not better, but not worse, in productivity, and may be better for tool life / predictability in a significant % of cases.
But tools, tooltips, parts can be potentially clean and well visible throughout the production process.
This usually has high value.
Likewise, high-speed MQL air-blast should have more uniform tooltip and part temperatures.
Uniform leading to better productivity// stability with less loss on possible breakage.

But most importantly, I think, MQL may make the parts produced "near-clean".

So most-any part is almost-clean and easily handled, and final cleanup is potentially minimal.
Like dump in degreaser 5 secs, hot water 5 secs, second cleaner 5 secs, stabiliser, hot water, done.

Effluent and chemical usage may reduce by a factor of 20x.
While parts QC may speed up, and reliability may speed up.

--
I think "better" MQL will become very common in new machine tools, and vastly reduce coolant use and waste products.
I also think it will become a std feature for all MT builders.

LockNut said:

Years ago in a mold shop we had 2 Yasdas. They never came with a coolant tank. These were high speed core and cavity machines. Used MQL or ran dry like Fidia Guy says. Much better tool life and part finish. The secret is in "minimim" part. We went through about a gallon a month of non-stop machining. I do have a white paper on the use of different oils used in a MQL system. More subject to benefits of the oils themselves than the MQL system itself. Private message me and I will send it to you. It's a rather large PDF.

Paul

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How about a synopsis?

hrchrc said:

So you use both MQL and flood coolant, but coolant only to wash off parts -- is that different from chip evacuating? (sorry i realize this question sounds quite elementary)

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Maybe I was not clear in my post. I only CUT with MQL, when the job is finished to get all the chips and leftover MQL oil off the finished part, I use high pressure coolant hose on the machine.