I am turning Drill steel used in oil drilling operations. to the best of my knowledge it is 4140 at about 40HRC, it turns pretty closely to 4140 QT. I want to improve my cycle times and have been doing research on it. I was hoping that the folks around here have some pointers. I am using Sandvik Coromant - CCMT32.52 PM Grade 4325, I am running it at 130SFM with at .06 - .1 depth of cut, and .006 per rev. I am getting good chip breakage and a good finish. but the MRR is terrible at 1.43 cu inch per minute. I can do a .012" / rev and have good chips but I can seem to move the speed up without greying out the chips. right now they are just turning blue. I get decent life from the insert but even that seem a little bit low. I burn out the insert every 200 or so cu inches.
I have a few parts I make that use this material but as an example 233RPM 24 inch long 3.5 inch diameter turned down to 2.5" 29 inch OAL with a 1.5" hole in the center. it takes me about 80 min to cut the feature. insert angle to workpiece is about 87 deg.
The lathe is a Colchester Clausing mastiff 1400 that I converted to a CNC Lathe with a 12.5HP spindle. 5% emulsion coolant
I suspect I am using the insert wrong. I read it is normal to reduce the speeds significantly when cutting harder steels. but it seems pretty slow compared to the 1130 FPM that the insert says for low alloy steel. or maybe someone knows a good insert for 35-40HRC?
I use the same insert for 1045 and can get about 10 Cu inch/min MRR at about 945SFM .1 DOC .009 feed/rev , I cant get any faster though as this gets to my max spindle speed.
thanks for any input.
