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Ever wondered how much tool life can deteriorate when using coolant with High Speed Machining (HSM)?
Or maybe you never really saw the boost in tool life when using HSM techniques because you had to use coolant?

Well here is a test results I just got from running the same tool at the same Speed and Feed with and without coolant.

A short preamble: 
I had to machine a 1080 steel component where chip clearance was an issue. Without programmable airblast and due to non-attended run of the machine I  decided to try and see how long the tool is going to last with coolant turned on.

I calculated cutting parameters using HSMAdvisor Speed and Feed Calculator and came up with the following data:

Tool: 0.5" 4Flute High-Performance  End Mill from Kennametal
Depth of Cut: 0.8"
Width of Cut: 0.025" (5%)
RPM: 10000
Feed: 400 ipm

Because I had hundreds of parts to machine I could really get a good sample data.

So I ran each tool for as long as I was comfortable with the noise level.

Results of the test surprised me quite a bit.
Yes, I knew tool life with coolant would be less than without, but I did not expect such dramatic difference:

  With Through Spindle Coolant.
Perfect chip removal.

Dry.
No Airblast - some chips recuting in the pocket

Number of Parts 45 pcs 400 pcs !! Could do another 400 easy.
Tool after the run
Comments

Run stopped when tool was making a lot of noise and pushing too much burr up the wall.

Coating totally stripped from cutting edges. Lots of plastic deformation.

Tool survived barely touched! Finished the rest of batch with the same cutter and could run the same amount easily.

No considerable wear on cutting edges and no built-up edge.

We got almost 10 fold improvement in cutter life just by turning off the coolant.

Counter-intuitive, but that is High Speed Machining for you. It does not have to make sense!


If fact we know that the bad tool life is caused by thermal shocking of the tool coating and the carbide itself at high temperatures that are produced by high cutting speeds.
You can read more on the theory behind HSM in this article->How to: High Speed Machining (HSM), CNC Milling
Here is a small excerpt from it:

Quote:
....Increased cutting speed makes use of coolant not advisable.

As hot swarf contacts coolant it may harden (in case of tool steels) and when re-cut it will damage the cutting edges.
Also contact of the coolant with overheated cutting edge will cause thermal cracking and premature wear of the endmill.

Popular AlTiN and TiAlN coatings, for example, actually require heat to "activate" coating and make it work properly.

Air blast is required not to cool the tool, but actually to clear the chips from the cutting zone...

How about that gummy stainless?

I know what you are going to say: "Let's see you try no coolant with some 304 Stainless Steel"
And I totally agree with you. Sometimes when we are getting a lot of built up edge on gummy tough materials we just have to use coolant. And that will negatively impact your tool life!

There are, however a few tips on dry HSM-machining gummy stainless:

  • Use less radial engagement (about 5%).
  • Use heavy feed.
  • As a result of above you can use higher cutting speed

What this less radial engagement does it allows you to surpass the "no man's land" between 300 and 900 SFM where built up edge forms on the cutting edge.
In addition to Chip Thinning our HSMAdvisor accounts for the SFM boost you can get in that case. Just turn on the "HSM" check box! 

If you tried everything and you are still getting chip weld, you might have no other option than to turn on your coolant and suck up the bad tool life.

Some materials are just crap to machine and that's the end of it.

Happy Millin'!

--Eldar Gerfanov

Comments:

Pages:(1) [1]

By tom

May 19, 2016, 6:24 am
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I'm surprised that it was that big of a difference! Good read!

By Dawn Smith

May 19, 2016, 1:04 pm
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Wow! That is a HUGE difference! Thank you for posting and sharing this info.

By Eldar Gerfanov

May 19, 2016, 10:11 pm
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Yes, the difference in tool life is huge. I did not expect it to be such.

By Paul Roe

May 22, 2016, 5:55 pm
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How about the material your cutting? Any adverse heat affected zones?

By Eldar Gerfanov

May 22, 2016, 7:01 pm
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To be honest the part was barelly warm to the touch.
And it was a thin walled part too. When HSM is done properly the heat is carried away with the swarf.

By Seki90@gmail.com

May 24, 2016, 5:27 pm
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I was work stainless steel 316 with 250 cutting speed 33 mm depth and 1 mm by side, dry of course . I have 23 pieces and still is ok

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