304 ss-will it work harden?

Fred.Rowe

Fred.Rowe

Joined
May 2, 2004
Messages
6,848
I am milling some 304 ss for guards. My speed is around 400 rpm with a feed rate of 50 sfm. It feels like the material is work hardening. Is it possible for 304ss to work harden at this slow a speed. I am using a new carbide 4 flute ball mill. Any information would be appreciated. Fred
 
How deep a cut are you taking and what is your feed rate? You quote your feed rate as 50 sfm??? Normally, feed rates are given in inches/millimeters per minute. 50 SFPM is a reasonable material speed to use to calculate your RPM. I don't know what size your cutter is, so I can't tell you if your RPM is correct.

You have to take off enough material and fast enough to avoid work hardening with 304 stainless. It hardens by cold working, not by heat. 304 is famous for work hardening. At the right feeds and speeds it cuts very nicely. At low feed rates, it hardens dramatically.

Normally, with a carbide tool you can increase RPM by 2-3 times over HSS. Feeds increased by 50 -100% (versus HSS tooling). Flood coolant helps a lot, but carbide tooling generally doesn't like intermittant cooling - the thermal shock cracks it.

If your RPMs are correct for the material, then my guess is your chip load is too small. Try increasing the feed rate or taking a bigger cut.

Hope this helps,

George
 
The 300 series of SS is notoriously nasty to machine. Engravers don't like it and many refuse to engrave it, so you get the idea.:eek:

If it's for guards and bolsters, try 416 SS. It works a lot better.
 
Work hardening is the only way to harden 300 series stainless. In the aircraft industry we buy it 1/4 hard and 1/2 hard and the way the mill gets it there is to work harden it by rolling it. I use 303 and 416 for guards and such and they both work well. I cut an undersized slot with my bandsaw first on guards and that reduces side cut loads on the 1/8" cutter and makes it faster.
Jim
 
Of the 300 series 301 work hardens far faster than the rest, we used to make springs with it ! 305 work hardens least. 303 is a free machining grade if you want that.Don't baby it , proper speed, feed and lube should prevent problems.
 
You must log in or register to reply here.
Back
Top