using external coolant for drilling Aluminuim

[khalchris]

I am trying to drill some holes in Aluminium plates AL 2024-T351 ,I am not sure how much coolant to use for that (Pressure,flow rate) , my coolant is Liquid nitrogen but it will be coming out in its gaseous state, is there any equation that relates the amount of coolant pressure and flow rate to be used with respect to the drilling speeds and feeds ?

As the coolant will be supplied externally which position/location is best for the coolant to target, should it be targeted on the drill bit tip and the top surface of the plate or just the drill bit or just the plate? any suggestions?

Thanks a lot

 

[TVP]

I'm only familiar with liquid nitrogen used for hard turning, not drilling. Air Products and their ICEFLY® Cryogenic Machining Technology is probably the best place to obtain information on the subject:

http://www.airproducts.com/industri....aspx?itemId=2105045D6A774F1783B913A25D359ADF

 

[BillPSU]

Coolant is used for more than cooling the tool and work piece it also adds lubricity for contact between the tool and the work piece and the expelling of chips out of the hole. Aluminum is notorius for plugging up drill flutes and causing the drill to break. There are several things which impact this problem.
Diameter of the hole and the depth of the hole to size of the hole ratio. Small diameter holes < .060". Hole depth to diameter ratio greater than 3/1 will need to be peck drilled.
Peck length if peck drilling. Peck length should decrease with depth.
The type of drill being used. Polished flute fast spiral drills would be the preferred type.
The material and condition. Aluminum machines with less complications when heat treated. Some aluminums are just gummy and will be more difficult to machine.

You are doing some things where very few people have experience and you will have to learn by trial and error.

Good Luck
Bill

 

[MikeHalloran]

Luckily, 2024-, other than -O, machines like a dream.
Unluckily, gaseous nitrogen does not provide lubricity or chip flotation.
Unluckily, providing enough mass flow of nitrogen gas to even begin to affect cooling and chip flow will also produce a serious suffocation hazard, unless you are working in a hurricane.
... which in this case is a good idea, because the rainwater would provide lubricity and chip flotation.

DO read up on the hazards of using nitrogen; it can be very dangerous, mostly because it produces no useable physiological response; you just go to sleep. ... a don't wake up.

IF you can get a high enough spindle speed to produce ideal chips (short, hot, curly, friable), they will fly out of the drill flutes without encouragement or coolant or substantial heating of the workpiece. For small drills in aluminum, that's scary fast, but if you back off the speed, you get long stringy chips that form birdsnests, wrap around the drill, break the drill, and ruin the hole.



Mike Halloran
Pembroke Pines, FL, USA

 

[khalchris]

Thank you all for your tips and advise , I really appreciate that

@ Mike , I have thought about the fact that LN2 won't give any lubrication for the drilling process, hence I will later try to use LN2 with MQL in a single system which might help to improve the drilling process and reduce the tool wear and improve the hole quality.

Initially I will be using a 6 mm twist drill for the tests and I will use two hoses for supplying the liquid nitrogen from two opposite sides being focused on the drill bit tip and slightly on the top surface of the Al plates, the plates are 15 mm thick and I will be using speeds varying from 1000 up to 6000 rpm .

As bill mentioned not many have actually used LN2 for drilling and I would have to explore a lot before I can come to some good conclusions but I will try do my best

Thank you all again for your suggestion and advice

Khaled

 

[ornerynorsk]

What is your concern for not using a liquid coolant? Is it part cleanliness? There are many details which you have not mentioned, such as the overall size (heatsinking ability) of the workpiece, how many holes it will have, and if the equipment is manual or cnc, sustained duration of the operation (do you have 2 pieces or 200,000?), metal removal rate cc per minute or hour, All of these factors will have an effect on determining what kind of coolant system will be most effective, or if any coolant system is needed at all. LN2 may prove more costly than you are imagining, unless this is for pure research purposes.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[MikeHalloran]

Start at 6000 rpm.

Don't bother trying slower speeds, you'll just break drills.



Mike Halloran
Pembroke Pines, FL, USA