Troubles milling 4140 Normalized with BP mill

keeena

keeena

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I've been having a heck of a time trying to get a good cut in 4140 Normalized on a 2hp BP knee mill.

The cutter is a USA (?) manufacturer 0.5" diameter 4FL solid carbide endmill. I started with 0.5" DOC, 0.2" WOC, 12 IPM at 1400 RPM. Per FSWizard this is a Vc of 185 f/min, fz 0.0022 in/th, and MRR 1.25 in^3/min. I'm just hogging material - alternating between conventional and climb milling as I move back/forth. The few 0.5" carbide EMs I have used but reasonably good shape.

The finish seems OK but the chips are very dark blue (I'd actually say purple) and I get a good amount of sparking. I feel like its cutting way too hot; the part is getting somewhat hot too. I've played with the feed (7-15IPM), speed (1200-2000RPM), WOC (0.150" and 0.100", haven't tried higher than 0.200") : nothing seems to fix the problem.

Thoughts?
 
Milling steel with carbide at the appropriate speed will yield blue chips and the occasional spark. Keep in mind that published speed and feed values are based on a finite tool life. Normally hey do not publish what tool life they are assuming.
 
Normalized is similar to annealed; slight bit harder due to how the material is cooled.

100FPM seems low for carbide. In my hunting around I've seen 200-500 for carbide endmills.
 
This endmill is used? You might consider trying a new endmill. Your symptoms are what I would expect from a dull one.
 
I myself have had issues like this I’ll be following to learn more .
 
Are you using any coolant? I think the cutting charts assume coolant. Blue chips mean that the heat is being carried away in the chip, which is as it should be. Your cutting parameters seem reasonable for carbide. As said above, maybe a dull end mill?
 
rabler said:
This endmill is used? You might consider trying a new endmill. Your symptoms are what I would expect from a dull one.
Click to expand...
I think this is probably the main reason I was having trouble. I also had much better results with indexable carbide which also made me realize my feed / chip load per tooth was probably too low for the solid EM. I think I was too conservative as I'm more used to using HSS and thought that charging in at high IPM would be bad. Nope!
JimDawson said:
Are you using any coolant? I think the cutting charts assume coolant. Blue chips mean that the heat is being carried away in the chip, which is as it should be. Your cutting parameters seem reasonable for carbide. As said above, maybe a dull end mill?
Click to expand...
No coolant; my mill isn't configured to handle it (no collection tray and whatnot). I would like to get a fogbuster setup at some point though.

Anyway, an update:

I switched to a 3/4" 3FL indexable carbide and woah: big difference. Chips a more normal blue color, zero sparking. I did have to use a small DOC (0.060") to avoid chatter. These inserts are designed for up to a ~0.375" DOC but I couldn't come anywhere near that in the 4140. I'm sure I could do better DOC with some tuning and if I shorten the EM. Here's a vid of the cutter in 1018 from the previous owner who I bought the mill from; looks to be about a 0.120"? DOC:
This feed rate is so much faster than the HSS than I'm used to...guess you just gotta send it. :)

I also tried out a 2", 4 insert indexable face mill using params from FS Wizard. Small DOC (0.040") but decent MRR due to the full 2" WOC. This one made perfect chips dark straw-to-blue and nice chip formation...really cut like a dream.
2inch_FM_chips.jpg

I plan to buy a couple new solid carbide EMs since I would like to get a higher DOC for certain ops. I was getting pretty frustrated earlier thinking I might have to abandon this particular project; glad to be on-track.
 
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