Single Point Diamond Turning 7

[Plako]

Is it possible to machine a series of very small "v" grooves on a maraging steel roll with single point diamond turning? I understand that SPDT cannot be done on steel because of the carbon content. We have already had a roll with an electroless nickel deposition machined and it looked great. But when heat treating (at 590 deg F for 3 hrs.) it developed fine cracks. When we made a trial run trying to roll the form into solder coated copper wire (.085 x .017), the EN began to disintegrate, falling off the substrate roll.

I have been reading about maraging steels. Would one of these alloys be a candidate for directly turning of the grooves using the SPDT? From what I've read, carbon content is nil. I am looking for a finished roll with a hardness somewhere around a Rc 54 to 56.

I appreciate the knowledge and experience so many of you have demonstrated in your replies to other questions. Surely one or several of you will be able to point me in the right direction in solving this problem.

 

[unclesyd]

Can you comeback with the details of your groove?

We made very small grooves in different steels using several different methods,single point and multi point tools.

 

[IRstuff]

> EN can be deposited VERY hard or moderately hard, so there may be some wiggle room on the processing parameters

> SPDT is done on EN, which can be quite hard, so it's unclear why that wouldn't work on steel

TTFN

FAQ731-376

 

[Plako]

The grooves are in the form of a "v". They are .002 deep with a progression (peak to peak) of .008. The reason I keep going back to SPDT centers around profile and surface finish. The radius at the bottom of each "v" cannot exceed .0005. That radius has proven to be the problem. We have tried producing a roll by grinding (CBN wheel) and have only had minimal success. The radius at the bottom of the groove tends to creep up to .0007 or .0008.

The other critical area centers around surface finish on the roll. We need to maintain an Ra of 3 or less. It looked like SPDT on the EN deposition really was going to meet our criteria for this project, but apparently the EN would not hold up under a production environment.

 

[CoryPad]

The idea of avoiding diamond tooling with steel is that at high temperature you may get carbon diffusion from the diamond into the steel. You can avoid this by keeping the temperature low (e.g. use a lubricant/coolant during turning). The other options are use single point tools made with tungsten carbide or cubic boron nitride.

The carbon concentration for maraging steels is intentionally low, but that means it would be more likely to pick up carbon during manufacturing. It can be treated to a hardness level of 54 HRC to 56 HRC, so it is a candidate.

 

[saberblue]

I would agree with CoryPad on this one you need to approach any material containing iron Fe with a great deal of caution when you are using diamond in any form -- cBN was specifically manufactured to address these issues


A.R. "Andy" Nelson
Engineering Consultant
anelson@arnengineering.com

 

[TVP]

Use cubic boron nitride inserts specifically for hard turning of steel. There are many suppliers of these, including all of the major players. Diamond tools will just be a waste of time.

 

[Plako]

It seems that the only tooling available to produce a .0005 radius at the bottom of each groove is a single point diamond. I have looked at CBN tooling, but can't find anything that even comes close to that small of a radius.

This project is really becoming a challenge (which I enjoy).

 

[Ceramicguy]

Try contacting some of the superabrasive tooling vendors that can grind/lap the fine point on a single crystal cutting tool. Two I can suggest are Keenkut,

http://www.keenkut.com

and J&M Diamond Tool,

http://www.diamondtool.com.

If worse comes to worse, you can purchase a single point tool and lap the point yourself on diamond lapping film. An excellent film product is 3M Imperial diamond lapping film.
I agree with all comments above re diamond vs CBN. You will lose your tip radius almost immediately if you try to turn the steel with diamond. Iron has a tremendous affinity for carbon. The diffusion of carbon into iron or steel happens quickly and at surprisingly low temperatures.

Bruce

http://www.accuratus.com