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Hard Milling over 60Rc? Coolant/Air

Apparently not that common / generally overlooked, but a very capable solution is MQL (minimum quantity lubrication) as it gives the greasing ability of the coolant without the thermal shock problem. The air is enriched with oil mist and sprayed on / through the tool. Best if your tool or at least the holder is capable of through coolant/air. And yes, i am aware of the risks in regards to explosive atmospheres. Please make sure you buy a system that uses less then 20ml/h or install a fire suppression system. This is not a small shop solution but very capable if you have the volume to make the investment viable.
We are running 3 mid sized horizontals with 42CrMo4 with 44-48 HRC parts. Tool life is double compared to same application with coolant.
What fluid do you use, and do you have problems with mess/residue?
 
We use oil from the supplier of the MQL system, which is Knoll. As the amount per hour is around 15ml so less then a shot glas full, you wont see any residue on the part. To even see the oil you need to hold a paper before your tool for quite a while before you will see something
 
We use oil from the supplier of the MQL system, which is Knoll. As the amount per hour is around 15ml so less then a shot glas full, you wont see any residue on the part. To even see the oil you need to hold a paper before your tool for quite a while before you will see something

Not on the part, but on the machine?

I used a similar system, with a vegetable oil base, I forget the brand. About the same oil usage, but over time it left a grimy residue on the inside of the machine that didn't wash off with coolant.
 
We use it for over a year now and we don't see any residue / problems. I am sure it is an artificial / non-vegetable oil. AerosolMaster c-st is the name. I think "natural" oil is not a good idea in machining, because that sounds like a bacteria problem you encountered. But i know we have some stamping applications that still run best on olive oil ...
 
We use it for over a year now and we don't see any residue / problems. I am sure it is an artificial / non-vegetable oil. AerosolMaster c-st is the name. I think "natural" oil is not a good idea in machining, because that sounds like a bacteria problem you encountered. But i know we have some stamping applications that still run best on olive oil ...

Definitely not bacterial, just greasy oil residue. Vegetable base for the MQL I was told by the manufacturer was because it was less toxic as an aerosol compared to synthetics. Active extraction and filtration on that machine anyway so no risk to operators, but that was the reason given.
 
i mill a lot of 1.2436 in the 60+ range for finishing i always use coolant.
for roughing i run with airblast or with tsc trough the holder but it just depends how well you are able to flush chips out sometimes are works better or coolant.

i try to use endmills with a radius and those seem to give me the best results for roughing.
we are making tooling here so no production but i have a 8mm endmill which has around 3h of cutting time and still looks good.
 








 
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