Anyone with experience machining 99.95% Molybdenum?

We have a customer that is requesting some parts to be made from pure moly. This has not been a fun experience and am hoping someone can give some hints and maybe a direction to head in. They are requesting an 8 finish on the O.D. of the part, all the around a full radius to the I.D. of the part. On the O.D. there is a shoulder that tends to get in the way.

Is it extruded, cast, ...?

Depending on what you have it can machine like anything from cast iron to stainless steel.

You need to have new carbide inserts and plenty of coolant. Molybdenum is abrasive and dulls tools very quickly.

We usually start with tools that have a geometry suitable for cast iron at 200fpm @ 1/20" DOC. For finish try 400fpm @ <5 thou DOC. Start with a feed of 0.01 ipr. Push too hard and it will chip/tear.

I know it is ASTM-B-387 Type 361, but not sure if it is Cast or Extruded. We have seen the chip and tear issue you speak of, and the customer wants no nicks or dings under 10x magnification. Well, even small pits in the material show at that level. Trying to get it to a 8RMS finish is like trying to polish cast/ductile Iron. They keep making changes to the print and not in a good way, that keep making it harder and harder. I will pass your info on the our programmer and see how close he is to what you suggest.

The only way to do it is on a Bridgeport J-head (pre-Textron era). Something about the "feel"...

(This is not going to be helpful, sorry.)

Pure molybdenum with an 8 microinch finish? Your customer making reflectors for Martian heat rays by any chance?

I use to do production turning of pure arc cast moly. The parts were small just under 1/2 inch in diameter and thin with grooves, shoulders and so forth. It can be a bear until you learn the rules. I would start with jwbaldwin's numbers.

We used a mitsubishi insert for roughing (I no longer recall the insert number, sorry) and finished with our own custom ground brazed carbide turning too. I believe we were using Micro 100 3/8 screw machine cutters. We ground them with a 15 degree face angle clearance, zero on the leading face and 17 degrees relief angle. The tip was left almost sharp with a hand stoned radius of about .003.

We were able to get about 150 to 200 parts per custom tool and the same for the rougher then the finish would start degrading. We made about a thousand to three thousand of each type per run.

Unfortunately, here is the kicker. We had a government waver to use 1,1,1-Trichloroethane as it was for the government and commercial aircraft parts. This not to be confused with other Trichlor's that are toxic. A lot of people do that. We could run all day on a half cup of the Tri. then we would have to add another to the VG 68. We had 3 little micro nozzles with around .003 holes in them for splashing on the part which was caught in a recycling long tube and filtered back through. Also the vapors, which was not much, were pulled away from the operator so he wasn't getting a whiff everytime he opened the door. It was about 15 to 20% Trichlor. and Blaser VG-68. You could just try using the Blaser, but it was the chlorine produced under the heat and cut pressure in the Tri. that I believe made it work.

1,1,1-Trichloroethane - Wikipedia, the free encyclopedia

fresh inserts in whatever you are using. 3 flute uncoated carbide endmills, speeds/feeds similar to cast iron flood coolant. and no more than .030" DOC if it has a lot of stress in it. also, as with all stressed metals, switch sides cut often. and as for the surface finish, only way to get there that i know of, is with surface grinding, start with 60 grit and go down (coarser) from there. probably not less than 40 grit though. and keep it a pretty airy (low density wheel) silicon carbide. if you can talk with your wheel vendor.
i used to work at a place that pressed, cintered, and hot rolled its own ingots of basically pure moly. stuff was a PITA!

You would think so, but they apparently go in some X-Ray equipment or something. The kicker is, they asked us to make some parts out of 316 Stainless that they liked, but they need to test before they can approve. How could you go from a material like Moly to 316? I hope they can, because we can make the part on our screw machine all day long and meet the print. Just super frustrating, and now they want to get credit on close to $15,000 of parts. If it was up to me, I would tell them to take a hike and move the part back to their old vendor. Oh wait, he couldn't do it either.

sfriedberg said:

(This is not going to be helpful, sorry.)

Pure molybdenum with an 8 microinch finish? Your customer making reflectors for Martian heat rays by any chance?

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