Hi,
the real killer for aluminum cutting tools is heat.....and I don't mean necessarily heat of the tool or workpiece. Its more about
the heat of the chips.
There are some excellent videos on you-tube about chip formation, every mechanical engineer has to be intimately familiar with this process
AND the calculations that result. I'm only very fair with the calculations myself.
Amongst the objectives of forming a chip is to have the energy of the shearing work to enter the chip rather than the workpiece or the tool. You'd
say that the chip is 'hot'. You will of course have seen 'blue' hot steel chips forming when drilling steel. The same thing happens with aluminum but
without the change in color. Also the melting point of aluminum is only about 780 C whereas steel is about 1480 C.
If by a combination of heat and pressure aluminum chips adhere to the edge of the tool the energy (heat) required for the now blunt tool, by virtue
of the rounded built up edge, to create fresh chips increases dramatically. This results in now very very hot aluminum chips and will have a great propensity
to stick to the already built up edge. Breakage is now imminent.
It is a similar line of reasoning that recutting chips must be avoided. When an aluminum chip is formed it gets hot, lets say 400C. Should that same chip
get recut by the next flute it will get hotter again....lets say 700 C. At that elevated temperature the likelihood of it sticking to the tool goes up hugely.
Thus if you use means like flood cooling or air to remove the chip from the cutzone, it will still get hot, 400 C, air or coolant doesn't change the physics
of chip formation, but air/flood will prevent the chip from getting recut. If you haven't given some thought to trying flood cooling, think again, and if you
decide you can't do it, think a third time until you do it.
Flood coolant or air will have significance for tool life. Lets say that a new and sharp tool will produce chips of 300 C at normal cutting parameters. As the tool
wears and becomes less sharp the temperature of the chips will go up, lets say to 500 C, at which point they adhere to the tool and that tool is now worn out.
If you have flood cooling or compressed air in operation you may be able to cool the chips to the extent that they do not adhere and can carry on using the tool,
extending its life.
I use very small (0.5mm) and tender two flute carbide endmills to cut a thick (0.42mm) copper layer on a circuit board. Without flood cooling I get about 1/2 hour
life for a tool with decreasing cut quality, burrs etc. WITH flood cooling I get about 10 hours, and MUCH BETTER cut quality.
I have had similar experience in aluminum. At 500m/min surface speed my 3mm two flute endmills will last a few minutes before BUE (built up edge) and
subsequent breakage. WITH flood cooling the same endmills last for hours and NO BUE!!
I know a lot of highly authoritative sources say don't use coolant on aluminum but I have found an immense increase in performance if I do.
Craig