Run time 4340 VS. 1018, using indexable tooling.

[Brian FRF]

Getting some 4340 in for a project.
I know what I can comfortably run 1018 for feed/speed.
Thinking somewhere 1/2-3/4 as fast for the 4340?

The 4340 Im getting in is pre treated, ~30 RC. Im going to have it annealed down to ~15 RC.

This is all milling, making better than 1/2 the part into chips.

Running indexable face mill, end mill, etc. I run a 2 flute 1" cutter at 25 ipm, at 2200 RPM now, .250 depth, at ~50-60% spindle load in 1018. Thinking back down to ~1800/20ipm/.200 for the 4340?

Other suggestions?

[RICHARD ZASTROW]

Why get pre-heat treated then anneal it? Your just paying for a throw away heat treating.

30 Rc isn't all that hard. I believe your pre-heat treated 4340 is closer to 34-38 Rc and that is machinable. A bit stiffer than 1018 though.LOL

Dick Z

[Brian FRF]

Originally Posted by RICHARD ZASTROW Why get pre-heat treated then anneal it? Your just paying for a throw away heat treating. 30 Rc isn't all that hard. I believe your pre-heat treated 4340 is closer to 34-38 Rc and that is machinable. A bit stiffer than 1018 though.LOL Dick Z

The material being pre-treated is just what I happen to be able to find for the size I need. That, and Im pretty sure I can take care of annealing myself, in small batches. Ive got a small oven.

[Cmailco]

I agree with Rich, 4340 machines quite nicely at 28-32 (pre-heat) HRC, there really is no reason to anneal. It will actually finish better in the pre-heat condition. Let's also not forget, your time is never free... at least it shouldn't be.

Very general guidelines but, you will probably machine at 65-70% the rates you're seeing in 1018. Solid carbide end mills; 70-170 sfm for slots, 125-225 sfm for peripheral cuts. Use the high range for lighter peripheral (~.1D) and the lower range for heavier cuts; same for slotting.

I don't know your part geometry but if you really want to get serious about MRR in this material, look to hi-feed mills. The Mitsubishi AJX and Hitachi ASR are two of my favorites. Speeds will be in the 350-550 sfm range, 120-300 in/min dependent on axial depth. A 1" diameter hi-feed can easily achieve 2.75-4.5 in³ in 4340 at ~30 HRC.

For the tooling you have, really need to know what you plan to use. The more info, the better.

Regards,
Chuck

[TR MFG]

+ 100 for The Mitsubishi AJX cutters in this stuff.