Roller Burnishing Aluminium

[Rickabilly]

Long ago in a Forum a Far, Far away away,

OK, about eight months ago, while chatting on H-M about Knurling, DaveH and I started on about roller burnishing Aluminium in a lathe, Is it possible, what will the results be like etc,

At the time I was doing a little favour for a neighbour, when there just happened to be a left over track roller, a 3/4" diameter 3/8" wide roller bearing with integral 8mm mounting stud, I said I now had all the gear required to test the process, and Poooff, Some thing happened and DaveH vanished without a trace.

Anyway now that I've tracked him down again, when I spotted that track roller this morning I thought why not,

so I mounted a steel bar in the tool post and an 8mm drill in the three jaw chuck, while running the lathe at 800 Rpm I simply moved the carriage in towards the chuck drilling the mounting hole to take the 8mm stud,

I then simply slipped the stud into the hole, tightened the nut and presto, one roller burnishing tool.
   

The aluminium tube shown on the preceding photo is a piece of 60mm od x 10mm wall ally tube of unknown grade however I suspect it was 5083.

I had wanted to test on a pretty rough surface finish so i started with a standard turning tool in HSS but the finish was actually really good, almost "silky", so I went to carbide in the hope that the tip might tear the surface a little, no luck, smooth again

So how to get a dodgy finish, I tried this;
   
A carbide parting tool, the finish was still OK but it really "picked up" as I ran my finger nail across the surface,

So I went back to the roller burnisher, and using it just like a bump knurling tool, I proceeded to Knurl/Burnish, Burl? Knurnish? using machine way oil as a lubricant, just coating the surface with a squirt from an oil can.

Whatever it's called, I ran the machine at about 300RPM, brought the tool up to the surface and then applied about ten thou of preload, then fed along the piece at about 0.004"/Rev,
   
I did this three times and the result;
   

While the photos look like the Knurlished surface is less shiny than the machined surface, surface finish is about more than lustre, when I run my finger nail across this surface there are no hangups at all, it doesn't feel as smooth as silk it is just so smooth that it doesn't feel at all, the nail simply glides across.

the other benefit of burnishing apparently is that the grain boundaries are closed up by the process, not torn open as in machining, and also in rolling the boundaries closed in the presence of oil, locks some of that oil into the surface of the metal helping to guard against corrosion.

As far as dimensional changes go I could not measure any with my digital verniers, I will have a closer look later on with Mics but I feel that as the surface finish was not very rough before, there was only a very small movement of surface material so no great change in diameter.

So, I hope this of interest to some one out there,

Best regards
Rick

[EdK]

Rick,

When would one use that process and why?

Thanks,
Ed

[DaveH]

Hi Rick,

I'm glad you found me, I was just lost but found again.

I'm still very interested in this burnishing idea.
I had one go on some ally 2" diameter using an 8mm wide bearing, all I can say is the results were outstandingly rubbish. The problem now I realise is too slow, I was doing it at 100 to 500 rpm.

Also my thoughts (no idea why) were the 8mm wide bearing was too wide and it may be better with something like a 4mm wide bearing.

Also I thought it would and should looked polished

Any more views Rick


DaveH

[Mayhem]

(07-02-2012, 07:30 AM)EdK Wrote: When would one use that process and why?

When one has too much time on their hands Ed

Just kidding Rick - interesting experiment.

[Highpower]

The only burnishing I have ever done was on some clock pivots and bushings. But I can see this as perhaps being useful for making rollers for something like a belt grinder/sander? Might be good for making slight adjustments for press fits on shafts as well?

Do tell Rick. Any particular uses in mind?

Willie

[Bill Gruby]

One has to be careful when Burnishing. Smaller parts especially. Heat is generated and will distort the part. As said though this is an interesting thread.

"Billy G"

[Rickabilly]

(07-02-2012, 07:30 AM)EdK Wrote: Rick,

When would one use that process and why?

Thanks,
Ed

Well, Of course, when you Ummm, and also when Hmmm.

I dunno

No seriously, when you want a smooth finish that can't afford to pick up on another part or material, so a roller that has cloth or paper run over it for example, or a bearing fit that needs some precision to it, that is; a really tight transition fit.

Also anywhere that fatigue is a problem as there are no machining marks left there are no propagation lines to start fatigue from, and the surface is under compression so reducing the tendancy to fatigue also.

Or where you want to finish with a polish, burnishing first starts the process off much better than turning, and there is the benefit of reducing corrosion, which works on all sorts of parts, the "cloudy" appearance looks a lot like clear anodizing as it happens.

My opinion too Dave is that a thinner roller might be better, so what I am thinking as a next step is to set up a really highly crowned roller, maybe with a width od 6mm but a crown radius of 4mm?

I am just thinking out loud here, what do you all think?

Best Regards
Rick

[krv3000]

hi interesting

[DaveH]

Hi,

It also tends to (work) harden the surface therefore takes a polish a bit better.

Plus messing about with this keeps Rick and myself off the streets.

DaveH

[Mayhem]

I think keep experimenting Rick and keep posting the findings please.