[Pondo]

Very interesting thread. I've never thought about chilling the workpiece or the coolant.
One thing to consider is the exaggerated effect of really cold coolant hitting a hot cutting edge. That is the #1 reason for not using coolant on inserted carbide face mills. The repeated heating-cooling and "thermal shock" causes the cutting edge to crack and chip giving very short insert life. This is not really an issue with HSS tools, but it will effect solid and cemented carbide tools a lot more than you'd think. Modern coated carbide mills are best run dry in just about all steels - really in about all materials except for aluminum and Ampco-Moldmax type copper alloys.
Also, the #1 purpose of using air on carbide tools is to clear chips to avoid chip recutting. Cooling is a distant #2 reason. Carbide can take high temperatures, but recutting chips will eat up a cutting edge real quick. The workpiece should not get very hot at all if the chipload is kept high enough and the speed high enough - the chip carries the heat, not the workpiece.
As for chilled coolant on aluminum, the reasons already given about thermal expansion/contraction are definitely true. Room temp coolant will allow for holding tolerances while keeping the material from melting in the cut, sticking to the cutting edge, or wadding up in the flutes. For copper alloys, the tendency of the material to push back as it is cut (due to it being highly malleable) makes it almost impossible to keep the heat out of the workpiece. That, along with the high coefficient of thermal expansion, make it necessary to flood the fock out of the cutter and the workpiece.
If anyone tries it out, I'd be interested to know how it works out.

[twocik]

Pondo this is good info. !

I've been using my tormach face mill with coolant, is this something I shouldn't be doing ? I haven't had any cracked inserts yet and have only witnessed wear from use.

Now this would make a lot of sense because I've noticed my end mills and chamfer bits chip and crack a lot more than expected. I use a lot of carbide tooling, mostly 1/8 - 3/8 2 aluminum FL end mills, 1/8 - 1/2 2 FL chamfer bits some with TIN coating some without. What temp should the coolant be shot out at so that I don't damage these bits faster or should I be using compressed air ?

[Pondo]

Pondo this is good info. !

I've been using my tormach face mill with coolant, is this something I shouldn't be doing ? I haven't had any cracked inserts yet and have only witnessed wear from use.

Now this would make a lot of sense because I've noticed my end mills and chamfer bits chip and crack a lot more than expected. I use a lot of carbide tooling, mostly 1/8 - 3/8 2 aluminum FL end mills, 1/8 - 1/2 2 FL chamfer bits some with TIN coating some without. What temp should the coolant be shot out at so that I don't damage these bits faster or should I be using compressed air ?

Thanks!

If you are just cutting aluminum, then use coolant (room temp) for everything. It is not nearly the same as cutting steel. The aluminum will melt way before you will have problems with heat checking the carbide. The important thing for milling aluminum is getting the coolant into the cut and getting the chips out. I use fewer flutes on my milling cutters on aluminum than for steel, and even prefer HSS over carbide for some cutters. A 1/2" 3 flute mill can way outperform a 4 flute in aluminum. The flutes are deeper so the chips can clear out and the coolant can get in. The problem with mills for steel when used on aluminum is that the flutes are usually too shallow and there is not enough positive rake on the cutting edge. This causes the aluminum to have a tendency to stick to the cutting edge and either wad up in the flutes or pull off tiny pieces of carbide - the chip gets welded (more like brazed) onto the cutting edge, then the next cut forces it off and it can pull a bit of carbide with it. If the edge is even slightly dull then it's way worse. This is what you may be having happen to your mills. It looks like excessive flank wear on the tool, like when an insert's being run in steel with too low of a chipload. The TiALN coating (gold color) or a silver "chrome" coating is designed to be really slippery to avoid that and to let the chip slide off the face. Those coatings are usually on mills designed for aluminum - deeper flutes, more positive rake, and usually a different cutting edge/flute face geometry.
I don't know what kind of inserts a Tormach face mill uses, but for most common ADKT/APKT style inserts and even hexagonal or button inserts you can get inserts that have been ground on the face to get a sharp edge. They are specifically for aluminum and cut it like butter. I use a 1" 2-flute insert mill with them for a lot of roughing and have a 2" 5-flute hex insert face mill that leaves better than a 32 finish with them. Ask your tool rep about them. It's cheaper to just change out inserts in a tool you have than to buy an aluminum specific cutter body + inserts.

[benji2505]

concerning cooling the raw material itself: the raw material block should be in the temperature range in which it will be inspected later on. If one machines the block at very low temperatures it will be out of whack at room temperature. Ultra-precision shops are always temperature controlled at exactly the temp where they inspect the parts later on.

concerning influencing the coolant: blowing cold air onto the coolant will have no measurable effect with these flow rates. Putting the whole coolant tank into a fridge or running the coolant through coolant tubes should bring down the temp maybe 10 degrees to put a number on the board, but how much does that help inside the direct cutting area that reaches a couple of hundred degrees or more?

My best guess is that the wear and the melting problems with cutters is due to bad chip evacuation and insufficient access of coolant. That won't be solved with cooler fluents, cutters or raw material.

Overall I think it is a "cool" idea but a new FEM every once in a while will always be cheaper.

benji

[davidperry3]

I really appreciate info like what "Pondo" has put up. Maby he could give a short list of favorite cutters for various materials and where to get them.

[Magnum164]

concerning cooling the raw material itself: the raw material block should be in the temperature range in which it will be inspected later on. If one machines the block at very low temperatures it will be out of whack at room temperature. Ultra-precision shops are always temperature controlled at exactly the temp where they inspect the parts later on.

Agreed..Inspection is everything.

concerning influencing the coolant: blowing cold air onto the coolant will have no measurable effect with these flow rates. Putting the whole coolant tank into a fridge or running the coolant through coolant tubes should bring down the temp maybe 10 degrees to put a number on the board, but how much does that help inside the direct cutting area that reaches a couple of hundred degrees or more?

Think you missed the point on the fridge. The idea was not to really cool the fluid further, but more designed to keep the fluid at a constant temperature. Almost like your radiator in your car. It's actually designed to keep the car at a certain optimal temperature, not cool it down. I am no expert, but I would think too much variation in temperature during cutting would wear a tool out faster than if it stayed hot all the time.

Should note that when used like I mentioned in a PC, you are really trying to cool down some hot fluid. A high end PC can raise a room temperature by 10-15 degrees. I don;t need much of a heater in my PC room in the winter, but in the summer I need tons of AC.

[Scott_M]

I am also a water cooled computer guy. Pretty cool stuff. No pun intended.
That being said I have run some pretty intense machining cycles on 4140 HT and many other materials. After a hour or so of continuous cutting I doubt I raised the temp of the nearly 10 gallons of coolant. Remember it is flowing back to the tank over a lot of room temp steel. This is as good as a radiator or cooling tower. Maybe if the Tormach had a 15 HP spindle and you were using ceramic inserts that were glowing red the whole time cooling the coolant may be an issue. But in the scope of what we have I really do not think it is a problem.
I also agree that coolant for the most part ( On steels ) is for chip evacuation. It is also said that for carbide "If you cannot supply coolant in sufficient quantity then do not use it" The thermal shock of intermittent cooling is far more detrimental to carbide than no coolant at all.

I say.. keep your coolant tank full and let er rip.

Scott

[plasmator]

I used to do liquid cooling of my computers, but eventually decided it wasn't worth the hassle... Now I just upgrade every 6 months.

On the topic of coolant, I've heard it said that flood coolant with high-speed spindles is pointless because it the spindle creates a boundary layer of air that keeps the coolant from making contact. Has anyone else heard of this or seen it in action?

[Scott_M]

Yes. And I am pretty sure that is why they started using coolant through the tool. To feed it at the cutting point.

Scott

[Magnum164]

Now I just upgrade every 6 months.

At $7K a pop I would go broke fast.:nono: