high speed machining (High RPM)

Hi, it the first time I post on this forum but I found some solutions to my problems in the past thanks to everyone sharing their experience.


We recently acquiered an high speed air-turbine spindle that runs at 150 000 RPM. I'm trying to mill with our Hurco 3-axis with a 1/32'' dia(0.031'') ball nose tool :

Harvey Tool - Miniature Ball End Mills | Carbide, 2 Flute, 45° Helix

I'm machining in aluminum 6061-T6 and so I took the TiB2 coating.

My problem:

I keep breaking the tool. I've been using the company feeds and depths but it seems to me that it's going too fast and too deep.


I need help. I think that if I go too slow, the tool will heat up and will not cut.
I've noticed that conventional milling does not cut at all, it melts the metal.
Also, I'm not using any coolant.

Thanks

6061-T6 has got to be the gummiest of all.

Use coolant

nuf said

At 150 000 RPM, I can't use regular coolant since it wont even reach the tool because of its high vicosity. I know that ethanol might be the solution here but I would like to not have to use it.

Also, the TiB2 coating should help preventing the aluminum from sticking to the tool.

The problem is that I can't mill for more then 15 sec without breaking the tool. I would simply need a guideline for feeds and depths of cut.

thanks for your reply.

I think you are melting it.
20-30K and 3-5IPM slower if in a slot. Really short tool stick out.
Depth of cut. no more than cutter diameter/3
Watery flood coolant - lots of it. Kerosene is excellent. Fire extinguisher??
WD40 is nice too.
Don't recut the chips!! (or melt them)
Plenty of calculator online: first one I looked at.
Milling Speed and Feed Calculator

At that rpm, a high pressure spray mist in the only thing that's gonna get in and clear chips. I don't know that your coating isn't actually hampering in this case. Aluminum will adhere to many coatings at high speeds (read that temps).

Your SFM should be ok, but unless you're running in the 50IPM+ feed range, I'd tend to think you're just rubbing the tool to death. .... At 127k RPM and 50IPM, that's only .0002"/tooth on a 2 flute. (that's 3000SFM)

The U.S. Navy has run aluminum at 20,000 to 30,000SFM in testing... successfully... But they've got access to funds we (at least me, anyway) don't.

Thank you for your replies. I feel like we're moving toward a solution here.

I guess I could tried at 50-75IPM to start (instead of 90IPM) but with an axial depth of 10-20% of the tool dia.

I do not have the control on the RPM. The spindle is built to run at 150 000 RPM and it is not recommended to use it at other speeds for long periods of time.

@fizzissist

The TiB2 coating is supposed to work up to 1500°F. I don't know yet what temp I am reaching.

Also, a high pressure spray mist of kerosene or ethanol.....looks like an engine to me XD. I guess they had some componant in it so it tends less to catch on fire.

Quote:

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Originally Posted by bucketbot

...The TiB2 coating is supposed to work up to 1500°F. I don't know yet what temp I am reaching.....

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Aluminum melts around 1200F so I doubt you are at 1500.:D

You do need some form of lubrication/cooling/chip removal. Misting is a good approach but at those speeds you are going to create a lot of aerosol which is not good for breathing.

This is one application where a cold air nozzle might be worthwhile to get good cooling. If you can keep the temperature down the TiB2 (theoretically) will prevent aluminum adhesion to the tool.

Quote:

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Originally Posted by Geof

Aluminum melts around 1200F so I doubt you are at 1500.:D

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I tried surface finish with a zigzag toolpath and when the tool was doing conventionnal milling, you could see that the surface finish was weird and nothing like when the tool was doing climb milling.

I looked at the part closer with a microcope and your can clearly see something that looks very familiar to melted aluminum.

I was going at about 40IPM so that may be the problem here. Anyways, since conventionnal looks to be giving poor results, I will do only climb.

Your cold air idea might work. I know some use dry ice but is need the part to be clean right after being machined.

It does look like I need some form of lubrication/cooling/chip removal. The light air spray I'm using is just not enough.

Thanks

I think you should try a tool without coating. In these dimensions and for that workpiecematerial you need a razorsharp tool. But each coating brings a little fillet at the edge.
And you should use a oilmistlubricating, with a really thin oil like petroleum or kerosene.

The most important point is, you must roughing your surface to a definite amount of 1/10mm or 4mil, not more.
If I calculate right, you have a resulting maxSFV of 240m/min or 775ft/min. Thats good enough for Alu, more should be better, for feed i would try a maximum of 1/100mm, 0,4mil per teeth. If your ballnosemill is 2 fluted you can try 3m/min, 120IPM.

HSC with Alu begins with 1000m/min, 3200fpm.

Quote:

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Originally Posted by bucketbot

Your cold air idea might work. I know some use dry ice but is need the part to be clean right after being machined.

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There are a lot of products that will easily remove dry ice residue. I've often used air, but that'll still leave a slight .039% CO2 film on the surface. Water is excellent, but when it dries, you could be back where you started. I think WD-40 is probably the best thing to use, since it's designed to displace water, and in the process leaves the parts smelling CO2 free.

Putting plants in the shop near the machine will help absorb excess dry ice fumes. Ferns in particular.

Only cooling isn't a good solution, the problem is that your ally sticks on your tool, but not because it melts, it needs a little bit liquid between each chip, to inhibit sticking. Thats the reason, why spiritus works, although it has no lubricating action. I haven't tested it yet, but I think adding some drops of dishwasher liquid will improve the action drastically. CO2 is dangerous, in the best case you get only headache, but if you have to much in the air you can die.

Thank you for your ideas.

I successfully mill at 14 IPM with .005" axial depth and 10%dia radial depth without coolant, just air jet to help blow the chips away. The program runned for 2 hours XD.

I'm looking foward to bump this up to at least 50IPM and see what happens. I'll try to go deeper too.

I'll look for a supplier of ethanol cooling system like Datron. do you know any other company?

If you use air to remove your chips, you can simply add a pneumatic oiler and fill it with sewingmachine oil or similiar. You need a thin oil who doesn't become resinous.

You can increase your feed up to .4mil/tooth but don't go deeper, that will be the best method to destroy your tool.

If you search for oil mist lubrication, you will find some threads here, to make a good solution DIY.