A customer recently asked what end mill to run for a full-slotting application in stainless steel and for some general recommendations about high speed vs. carbide and how many flutes to use. Listen in to our reply:
The 2 flute is usually used when you have a
material that produces long stringy chips that get clogged in the flutes. That
is usually referred to as 'chip evacuation'. The 2 flute has more room to clear
the chips, however it does not leave as good of a finish as the 4 flute. So you
can get from 2 to 6 flutes, and as you go up in flutes you get better finish
and more work, or cutting action, per rotation of the tool. For example, if you
were taking a chip load of .001" per tooth, you would be removing only
.002" per rotation of the tool with the 2 flute, as opposed to .004" per
revolution with the 4 flute. The tool is
also more engaged with the workpiece when you have more flutes, so you have
less chance of chatter and poor surface finish. For tools that produce stringy,
chips like aluminum, brass and other mostly non-ferrous materials we offer 2
and 3 flute tools that have a higher degree of helix than the standard 30
degree. These aluminum tools are available in 2 or 3 flute and have a 45 degree
helix which creates a shearing action and gives a better finish because of
that. We have some high performance tools for stainless that also have a higher
helix.
We
would definitely recommend carbide as long and you have a good rigid
toolholding and workholding setup. These days high speed steel is usually used
on older machines that cannot generate the spindle speed or are not rigid
enough for carbide. Carbide used to be more expensive than high speed steel, as
usage and volume has shifted to carbide, they have become the less expensive in
many cases than the high speed counterparts. Especially on the smaller diameter tools.
So
depending on the amount you have to do and the capability of you machine, you
would have to decide to run a high performance tool or the standard end mill.
It also depends on the depth of your slot. For the standard tools you can do
full slotting at 1x's the diameter on the tool. If you go with the VI-Pro high
performance end mill, you can slot at 2x's the diameter. So with most grades of
stainless you should not have a chip evacuation problem, so you should use 4 or
more flutes. However, a common reason for end mill failure is caused by 're-cutting'
a chip. So it is important to have some means of removing the chips from the
workpiece as you go to avoid any re-cutting. The carbide is capable of doing a
lot of work, but it is also brittle to some degree. So the chips can get
work-hardened from the initial cutting and then if the tool re-cuts a chip it
can cause the tool to chip. The only chips you want are from the workpiece. The
rule of thumb is to use as short of a flute length as possible, which produces
the most rigid setup. However you want to make sure you have enough flute to
get the chips up and out of there. Especially in a full-slotting application. We
would recommend the ALTiN coating for stainless. Below we have listed the
different series of tools that you might consider and a link the reference
documents.
These are all stub length. Go for a longer
tool if you need one, but start here - these are also the least expensive
option.
Good:
standard 4 flute stub length for max 1xs
diameter slotting per pass http://www.kodiakcuttingtools.com/viewproducts/carbide-end-mills-4-flute-single-end-stub-altin-coated/
standard end mill speeds, feeds and recommendations
http://www.kodiakcuttingtools.com/CarbideEndMillSpeedsAndFeeds.asp
you can plug the figures
from the above chart into this milling calculator:
http://www.kodiakcuttingtools.com/calculators.asp
Best for higher production
and max 2xs diameter slotting per pass:
VI-Pro variable index high
performance end mill (less chatter with high speeds and feeds)http://www.kodiakcuttingtools.com/viewproducts/carbide-end-mills-vi-pro-4-flute-stub-altin-coated/
Vi-Pro speeds and feeds
http://www.kodiakcuttingtools.com/ViProSpeedsAndFeeds.pdf
Another option for better
chip removal:
3 flute high performance
with 45 degree helix (this would give you more chip clearance if that is an
issue)
http://www.kodiakcuttingtools.com/viewproducts/carbide-end-mills-3-flute-single-end-45-degree-altin-coated/
high performance speeds and
feeds
http://www.kodiakcuttingtools.com/Kodiak2014HighPerformanceCarbideEndMillSpeedsAndFeeds.pdf