Slotting aluminum with small (sub 5mm) tools

[rando]

Hi,
for a past few years I've been struggling with slotting aluminum with small 3-5mm tools.
Like right now I'm machining small-ish parts from these big 2x3m 5083 H111 sheets. Cutting (essentially slotting) around the parts at 20 000rpm at 8mm/sec with cutting depth of 1.5mm with mist coolant and I just can't push the machine harder unless I up the rpms and that helps only so little.
All the calculators are suggesting I should be flying at like 20mm/sec or faster but that would either break the carbide, TiAIN coated endmill or coat it with molten aluminum within seconds. I also keep seeing these videos of people slotting at like 12-15mm/sec with 4mm endmills with no coolant and they go through the material like butter.
What am I doing wrong?
The rigidity of the machine is not a problem, neither is the spindle power I think.

[dazp1976]

I found slotting is slow with anything.
The calculators don't take into account the force involved with slotting. If machining around the outside you only have say 1/4 of the tool side engaged (woc) at half tool depth (doc). (this is what the calculators are based on). When you slot you have double the tool engagement / double the force,
ergo- you have to HALVE the calculation figures. So: half the speed and 1/4 tool depth.
That's how I figure it anyway.
I always end up halving the HSMworks calculation.
It is what it is!!!.


Milling at home I go 1/4 shallow with a 3mm. I doc at 0.75mm, 2500rpm, 300mm/min. I'm limited by my rpm.

[m_c]

You may find it's quicker to use some form of full depth helical cutting (my mind has gone completely blank on the proper name for this style of machining!), however whether that is an option depends on what CAM you're using.

Using that alleviates the common issues of slotting, which are chip clearance, and the cutter resonating/chattering in the slot due to no clearance.

[dazp1976]

You may find it's quicker to use some form of full depth helical cutting (my mind has gone completely blank on the proper name for this style of machining!), however whether that is an option depends on what CAM you're using.

Using that alleviates the common issues of slotting, which are chip clearance, and the cutter resonating/chattering in the slot due to no clearance.

I forget what it's called too. It's something to do with 'Adaptive' in the cam. However, you use a smaller tool than the slot itself. For a 3-6mm slot it's prob not a viable option. It's used more for wider slots.

[Voicecoil]

Do you mean trochoidal cutting m_c? It does help with chip clearance in my experience, though because of the extra movement I've not found it gives a great improvement in overall speed. Offset overlapping toolpaths can also help, I sometimes use those when deep slotting.

[m_c]

Do you mean trochoidal cutting m_c? It does help with chip clearance in my experience, though because of the extra movement I've not found it gives a great improvement in overall speed. Offset overlapping toolpaths can also help, I sometimes use those when deep slotting.

That's the one.
I almost said Polygonal in my original post, but that's what my lathe does.

On the rare occasion I need to slot something on the mill, I've used a mix of techniques.
Generally once you go deeper than 1.5x-2 times diameter, basic slotting is a risk, more so if you don't have good coolant to flush chips out.
It's worth running various options through your CAM and comparing times.

Trochoidal/Adaptive might appear slower, but since it uses a lot more cutter depth, it can be quicker than multiple passes.
Offset slotting is also worth a try.

It's a case of experimenting to see what works best on the parts you're doing, and with your machine.
A super rigid flex/backlash free machine with through cooolant might be able to rip through slots at 2-3D, but something with a bit flex/backlash and minimal coolant is likely to struggle.