Acheiving good finish on 440C

[icentropy]

Hello, I'm new to the forum and have a question that i think Moldmakers might be able to help me with. I'm an aluminum guy and mostly work on machine from plate, flat surfaces simple radii etc. but now i have a job that i can't figure out. I think it's closer to mold making than general machining.

I'm profiling complex curves on 440C (annealed) and trying to leave as good of a finish as possible within a reasonable amount of time. Currently my stepover is set at .005", DOC on final pass is .002", I'm using a .25" 4fl ball endmill coated TiAlN, Speed 6000rpm at 50IPM.

What we're getting is a surface that looks like the cutter is pulling the metal fibers out and leaving pinhole looking rough finish.

I know 440C isn't exactly mold making material but have any of you acheived a decent finish with something similar? I'm completely out of my element here and am probably off on everything. Any help would be very appreciated.

I'm not limited on the cutter size and could go up to 1/2" if it would help, but since i'm only cutting with the very tip, a 1/2" cutter would wear out just as fast and i'd be out a lot more $$ per cutter.

Oh, I should add, I'm using a Haas VF-3 with 15K max RPM. so i can raise it up still quite a bit. I tried a higher speed (again since i'm only cutting with the very end of the cutter) but it just seemed to burn it up, acted more like a grinding than cutting op.

How would you guys cut the finishing pass on a mold out of 440C if you wanted the surface finish to be as good as possible?

[txcncman]

Climb or conventional? Probably too light of a finish cut.

[icentropy]

Climb or conventional? Probably too light of a finish cut.

Both, it's a zigzag cut so it cuts climb and conventional every other stepover. We basically rough it out leaving .010" for the finishing pass. The .010" finishing pass leaves a terrible finish so we take another .002" and it gets better but still not very good, certainly not as good as i'd expect from a correctly dialed in setup. I just figured we are way off perhaps in all variables and maybe needed to step back and ask for an experienced mold maker's opinion. Maybe start from scratch with completely different feeds/speeds/DOC/stepover, etc.