Insert for interrupted/broken cut.

[mick1985]

Guys,

Im having a problem finding an insert grade that will provide me with reasonable life per edge whilst machining one particular component. it is a cast steel component (cant remember hardness offhand, but it is VERY hard) and changing the materials properties is not an option.

The machine is setup to run Sandvik Capto Tooling (due to the diverse amount of products we turn on the particular machine - a Mazak Quick Turn 40) and the particular tool I am having issues with (which is being used to rough turn the face/OD on the part) is a CNMG 120412 4025 (can't remember the otherinformation offhand - can supply later).

At the minute, I am currently getting a Maximum of 3 parts per edge using the above insert due to the broken/interrupted cut on the OD ONLY. if i do more than 3 parts per edge i am causing premature faailure of the finishing insert.

the part is similar to the picture i have inserted below (so you can see the broken cut i have to make machining the OD)



as ive said changing the material is NOT an option. I understand with a material this hard and the broken cut, im never going to get 20+ parts an edge, but i think I should be able to get it better than 3 somehow.

Please help as im

[mick1985]

Just had a check there and the Inserts being used ATM are Sandvik CNMG 160612 KR 3215.

any help appreciated.

[mick1985]

anybody? have I perhaps posted this in the wrong section?

[3illmesmart]

Does the OD of you gear carrier needs really need to be finish turned, if that is what it is. Why not finish to size before hardening. That being said, we used to use silicon wisker reinforced carbide inserts from Greenleaf that were very durable. I always found as big a rad as possible, and very high speed will help turning interrupted cuts. Button inserts seemed to stand up the best.

[mick1985]

Does the OD of you gear carrier needs really need to be finish turned, if that is what it is. Why not finish to size before hardening. That being said, we used to use silicon wisker reinforced carbide inserts from Greenleaf that were very durable. I always found as big a rad as possible, and very high speed will help turning interrupted cuts. Button inserts seemed to stand up the best.

thanks for the reply

Yes, the OD needs to be turned down, leaving it rough is not an option im afraid, as the customer I am supplying will not allow it. they also will not allow us to change the castings slightly so that the part that causes the interrupted cut would sit below the flush, hence not be machined.

Yes, it is a planet gear carrier, you are correct. I think you misunderstand though (perhaps due to my original post being somewhat misleading) the part is not case hardened. it is just an extremely hard steel casting we are working with, although not hard in the heat treated sense.

It is still a rough casting at the first stage of machining when this interrupted cut takes place (which im led to believe could also be a contributary factor, being that the "skin" of these castings is also slightly harder than the clean steel within, hence punishing the inserts moreso)

when you say high speed, are you referring to spindle speed, surface feedrate, or a combination of the two? I assume a combination would work best.

I have thought about using a button tool, even if to just use it to do the majority of the interrupted cut. so may be something to look at.

Ill have a look into reinforced carbide inserts as well, thanks for all your help thus far. theres definately got to be something I can do to improve the situation, as getting 3 parts per edge is not really efficient, when im getting nearer 20 parts from all the other roughers not doing any interrupted cuts.

Cheers

Mick

[neilw20]

Have you considered ceramic button inserts?

[3illmesmart]

Ah yes, the customer... I was assuming it was rough turned and then hardened. I miss typed, I should have said silicon wisker reinforced ceramic and I was referring to spindle speed. Even with your carbide you should get better life if you speed the spindle up, it seems to reduce the fracture of the insert and is contrary to what I always thought.

[PixMan]

Steels are generally not a good application for the whisker-reinforced ceramics. Those type of inserts work best in high-temp alloys.

That 3215 grade is ALL WRONG for that application. It is a wear resitant (NOT impact resistant) grade meant for cast irons. You want a steel-turning grade for roughing STEEL, and I would go with a Sandvik Coromant CNMG160616 MR GC4235 or a Walter CNMG160616 NM9 grade WPP30. You could also they the same inserts in the CNMG160612 if you really need the smaller tool nose radius.

You'll see a night & day difference in tool life.