Burnishing Counterbore face

[A1BERZ]

Hello,
We have a custom burnish tool from Cogsdill made to burnish the face of a .440 diameter counterbore with a .281 through hole in Stainless 316L. We have been running these parts for a little over a month and we are having a very difficult time getting consistent finishes. The burinsher it self is a three roller that gets its compression set to - .066 and 50lbs of pressure. We get our best results cycling the burinsher at 3ipm (feed in feed out) and 750rpm contacting the counterbore 3 separate times for dwells of 4sec, 4sec, and finally 2 sec. Our finishes typically look very orange peelish or almost flakey. When we start to see inconsistencies it can be anything from dents along the outside edge (not caused by mashing chips into material) to black grime marks all on the surface to what looks like wavy flakey chatter. We have no real good understanding of what is causing these inconsistences and are honestly very unfamiliar with burnishing this being our first time doing so. We are using a Haas DM2. If anyone has any experience with burnishing or can point me in the direction of some good info on it that would be amazing.
Thanks for your time! - Jake

 

[TeachMePlease]

Not that I know anything about burnishing, but what coolant are you using, what's your concentration, and how fine of a filter do you have on your coolant pump?
Seems like those could be factors at this point. Also, how's your coolant delivery to the tool/part interface?

 

[Omega]

I would call Cogsdill, if your just trying to get a good finish a .437 dia endmill with the bottom ground flat would do the trick.

 

[Rstewart]

What is the reasoning behind burnishing a counterbore? Are you talking about the walls, or the lower face?

 

[Mtndew]

What micro is your finish before burnishing? There is a range it needs to be at typically.
Also make sure your coolant doesn't have any grit.
I would suggest not using coolant and using an oil lube spray out of a spray can/bottle.

 

[Booze Daily]

I can't tell if you're if you're burnishing the dia? If so, you need to feed a lot faster. One shot, in and out. How much stock is in the bore? Sounds like a lot.
You only need a thou or two. The burnisher smooths out the high spots. It sounds like you are compressing way too much material and that is what is giving you issues.

 

[A1BERZ]

What is the reasoning behind burnishing a counterbore? Are you talking about the walls, or the

I can't tell if you're if you're burnishing the dia? If so, you need to feed a lot faster. One shot, in and out. How much stock is in the bore? Sounds like a lot.
You only need a thou or two. The burnisher smooths out the high spots. It sounds like you are compressing way too much material and that is what is giving you issues.

No material is being left behind it is just attempting to smooth out highs and lows left from our 2 flute cutter that brings it to its finished size.

 

[A1BERZ]

Not that I know anything about burnishing, but what coolant are you using, what's your concentration, and how fine of a filter do you have on your coolant pump?
Seems like those could be factors at this point. Also, how's your coolant delivery to the tool/part interface?

Hangsterfers 5080 coolant running anywhere from 16% - 22% concentration. Our DM2 has no coolant filters on it besides what comes with the machine, and we also run these parts on our Robodrill Plus K which has a 5 micron filter added on and we see the inconstancies on both machines. Also we believe we have adequate coolant delivery to the tool.

 

[dandrummerman21]

How are you creating the counterbore? Are you simply plunging a 7/16 endmill down into it, or using a smaller endmill and interpolating the hole?

I only ask because if plunging an endmill straight down, you will have a counterbore that isn't flat already, which might contribute to problems with your burnisher.

If you just need a nice floor but not necessarily a burnished finish, I'd just follow up your current tool with a smaller (1/4") endmill to finish interpolating the bottom the last few thousanths, at a higher rpm and slower feedrate.

 

[A1BERZ]

What is the reasoning behind burnishing a counterbore? Are you talking about the walls, or the lower face?

We are burnishing to achieve a number 8 finish and burnishing also work hardens our parts.
Essentially we are creating a leak proof seal that will let no more than a couple part per million of helium through per year.

 

[A1BERZ]

How are you creating the counterbore? Are you simply plunging a 7/16 endmill down into it, or using a smaller endmill and interpolating the hole?

I only ask because if plunging an endmill straight down, you will have a counterbore that isn't flat already, which might contribute to problems with your burnisher.

If you just need a nice floor but not necessarily a burnished finish, I'd just follow up your current tool with a smaller (1/4") endmill to finish interpolating the bottom the last few thousanths, at a higher rpm and slower feedrate.

It is being roughed out with a 6mm end mill which interpolates the counterbore leaving .01 on the floor. Then we have a 2 flute cutter which cleans the remaining .01 and that plunges straight down. with a .4 sec dwell. then finally the burnish tool comes in to finish. Also the burnished finish is required.

 

[memphisjed]

I only know hand burnishing and the orange peel is from over burnishing and not working the metal. The surface is getting work hardened on the first passes, subsequent passes are moving the subsurface, like a gel filled stress ball. The wake of the sub surface metal is seen as the ripples. As you make more passes the working layer is going deeper, making larger spacing in orange peel until the top surface fails into flakes.
being stainless the work harden happens shallower and faster, so you get less distance from just right going to far.

 

[Milland]

I would look into getting a stub 3-flute carbide endmill ground flat as a finishing tool, it would be much more stable than the 2-flute you're using now. I'd keep the dwell as short as possible, but still ensure at least a full revolution occurred during it. Mount it in a short, rigid holder for best effect.

I think the point about the burnisher being used for too long is a good one, but it's worth some careful experimenting on some scrap 316L before you commit. You can work harden 316 very quickly, and going beyond that surface hardening "ideal time" may lead to fatigue failure and spalling of the upper surface.

 

[dandrummerman21]

It is being roughed out with a 6mm end mill which interpolates the counterbore leaving .01 on the floor. Then we have a 2 flute cutter which cleans the remaining .01 and that plunges straight down. with a .4 sec dwell. then finally the burnish tool comes in to finish. Also the burnished finish is required.

But does your 2 flute endmill have a true flat bottom? Or is it a regular endmill?

Because endmills have a bit of dish at the bottom. The center will be a few thousanths shorter than the tips. And I was wondering if that was causing you issues.

 

[doug925]

Two flute end mills have relief called 'dish angle' (taper up towards the center) that is going to be heck on your finish.

Use the 6mm endmill to interpolate the bottom of the counterbore ~flat~ and not plunge to the bottom with a 2fl end mill.
This will guarantee it is flat prior to burnishing.
I can imagine the inconsistencies with roughly +0.002" more material at the Ø.281" diameter from the Ø.437" diameter
(caveat: assuming 1.5° dish angle & I did my math correctly. Carbide Bob will know the exact amount)

 

[guythatbrews]

Get Cogsdill involved! And you must start with a true flat bottom hole.

 

[Mtndew]

Harvey sells flat bottom end mills with no dish.

https://www.harveytool.com/products/counterbores---flat-bottom

 

[Sam L]

Burnishing is HIGHLY dependent on the pre-finish.
If the finish is not consistent you will be chasing your tail forever

I've burnished thousands of tubes made from aluminum, stainless & titanium.
Each one had different running parameters, but all needed to have a specific pre finish roughness so the burnishing process would work.
If the pre-finish is too smooth, its just as bad as being too rough.

 

[Nmbmxer]

I've never burnished a hole bottom that wasn't faced in a lathe, I don't have much to add but it seems challenging for sure.

 

[A1BERZ]

But does your 2 flute endmill have a true flat bottom? Or is it a regular endmill?

Because endmills have a bit of dish at the bottom. The center will be a few thousanths shorter than the tips. And I was wondering if that was causing you issues.

yes these are custom 2 flute cutters ground flat, we also seem to get good results when grinding off the second flute and just letting one flute do the cutting.