Thoughts on dry machining

Hi,

What are your thoughts or experiences with dry machining? I never really tried it and only have a very theoretical book that goes into CAM compensation of the generated heat....

The usual applications for me are precision parts in alu (or other soft stuff) or stainless that in de end need to go into the cleanroom. The end application is for example semicon or medical, thus cleanliness is key. My first machining experience was with a DATRON, which was great because we were not specialized in machining (that machine is really easy to operate) and the ethanol cooling meant that parts came clean of the machine. Then there was a job where we made huge parts for semicon and everything was cut with standard coolant but cleaning afterwards needed to be very thorough.

- Did you try it? How did it effect tool wear or feed?
- How did it affect precision? I can imagine the heat is not helping you reach tolerances, especially with thin walled parts. Any examples of what could be made still? Do you air cool it to make it better or does that make warping worse?
- What percentage of the hourly machine rate do you estimate coolant is? (Does potential extra tool wear with dry machining compensate this?)

Thanks!

Tool wear isn't the only factor you need to compensate for. In a material like aluminum, machining times will increase when dry vs. wet. The newer generations of DLC coatings can make up some of this difference, but you'll pay more for the tools.

The name "coolant" only tells part of the story as well. While it does do some amount of "cooling," the added lubricity helps prevent chip welding and edge buildup and the stream removes chips from the cut. Do you have air blast available?


I'll be interested to see what others who have experience in your applications have to say.

You specifically mention alu (most that I do is 5083), so is it not slower in other materials ? And what kind of % slowdown in feed/depth/volume would you guess the impact is?

What I did not mention in my start post is that I'm also quite motivated to 'go dry' for health-related reasons. A lot of chemicals have been removed from the coolant over-time and only time will tell how good/bad the replacement chemicals are. It really struck me when I switched from a cleaner field (cleanroom mostly) to machining and welding how many people get seriously in their fifties... I'm hesitant, possibly over-concerned

I don't thing bulk coolants in closed machines are a huge problem if you have decent ventilation, but IMO mist units are to be avoided at all costs. IMO, eliminating coolant eliminates a tuning parameter and opens one up to all sorts of new problems. Even a dry part off a machine will need cleaning before it can go to a clean room, so what have you really gained? I'd look into better cleaning procedures. Probably start with bulk removal followed by precision cleaning. Alconox has a book you can get on precision cleaning- Aqueous Cleaning Handbook - Alconox Inc. They also have various downloads that might be useful.

bla_bledass said:

.......It really struck me when I switched from a cleaner field (cleanroom mostly) to machining and welding how many people get seriously in their fifties... I'm hesitant, possibly over-concerned

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Trying to understand this paragraph. Are you saying that folks into machining and welding die young? I sure haven't seen that.

1. Choose a good coolant. I cut medical device parts using Hangsterfer's 5080. It's food grade; I've splashed it in my eye and it didn't even sting. It never develops a bad smell (which is indicative of bacteria growth.)
2. Get a good cleaning setup and procedure. For example, 5 minutes in an ultrasonic bath with Liquinox solution, followed by two 3-minute rinse cycles in DI water in the ultrasonic, followed by one 3 minute cycle in the ultrasonic with 99% isopropyl alcohol, then lay on lint free dry wipes for 30 minutes to dry. This procedure is suitable for implantable parts to be assembled in the cleanroom.

Trying to machine aluminum dry will cause all kinds of problems. Glacial production rates, surface finish and tolerance issues, low process reliability. Just don't do it unless there really is no other option.

I machine dry in 2024 aluminium, I wouldn't try it in 6061. Even in 2024 when I'm really hogging I can get a built up edge...6061 just melts and clogs the flutes. Airblast helps

MQL's main appeal is elimination of sump maintenance.

The part still needs to be cleaned just as thoroughly, and the machine can be more difficult to clean without the aid of a washdown. Might even pose chip evac issues in a lot of machines.

Yeah that's what I write. It's nothing statistically significant or scientific, but it really does seem like there are more long term and serious illnesses compared to my previous job at a similar-sized company. Could also be lifestyle related, but my 1+1=2 assumption was to relate it to all the chemcials that used to be normal...

bla_bledass said:

You specifically mention alu (most that I do is 5083), so is it not slower in other materials ? And what kind of % slowdown in feed/depth/volume would you guess the impact is?

What I did not mention in my start post is that I'm also quite motivated to 'go dry' for health-related reasons. A lot of chemicals have been removed from the coolant over-time and only time will tell how good/bad the replacement chemicals are. It really struck me when I switched from a cleaner field (cleanroom mostly) to machining and welding how many people get seriously in their fifties... I'm hesitant, possibly over-concerned

Click to expand...

There are materials that do want to be machined dry. Many insert tools in stainless, however. (Stainless doesn't conduct heat well so it stays in the tool -- the thermal shock can cause early fracture in many insert grades.) But solid carbide in alu and stainless will both want coolant.

You're going to need a good cleaning procedure regardless. Vast majority of coolants are not harsh chemicals -- I feel like you're making things harder on yourself if you avoid it. Just my 2c.

In some fields, the manufacturers have gone to great lengths to make dry cutting work. Steel and gears, in particular. Water-based ruins machines and is a hassle to deal with, oil-base is also a giant hassle to deal with so most new production gear machines run dry. Even spiral bevels, where you have to deal with really big distortion problems. But the tools have to be designed for it, steel doesn't mind dry, don't know if it would work with aluminum, and the machines are designed to get the chips away and out fast so that heat is not a problem.

Another thought is that most way cover wipers (at least on older machines) need coolant for lubrication. I ran some dry for a while and the way covers got pretty loud and the chips would melt into them. Could probably run wash down while it’s machining to avoid this issue.

Most coolants these days are pretty benign. Probably the most that happens is a few can get contact dermatitis from certain coolants. Mist control can help with airborne particles. I've never heard of or known someone who's health declined from coolant.