Adam's Tips - Cutting Aluminium Sheet

Cutting aluminium can be challenging, but it doesn't have to be. The following tips can help increase your confidence when cutting aluminium with a CNC machine: This guide is suitable for CNC machines of all levels, as the principles are the same. However, you may need to adjust settings to suit your machine's capabilities. 

The guide applies to CNC router machines for cutting, slotting and basic profiling applications. CNC milling on the other hand has its own nuances and requires appropriate tool-paths, coolant, and 2 or 3-flute end mills. Keep in mind that it's essential to choose the right tool and adjust settings to achieve the desired results.

Safety

It's essential to prioritize safety when cutting aluminum with a CNC machine. Always wear approved safety glasses as a minimum. Keep in mind that a gummed up router bit can quickly shoot chunks of aluminium or parts of the router bit itself. 

Before starting each cut, take the following steps: 

• Inspect the condition of the router bit for chips and aluminium reweld. A damaged or gummed end mill will not perform well. 
• Ensure that the waste board is levelled and the material is flat. This can help prevent cutting too deep on the first pass. 
• Secure the material to the waste board to prevent vibration, which can generate unnecessary heat and noise. 
• Use a tool like FSWizard, a handy smartphone app and online web calculator, to determine optimal feeds and speeds. Keep in mind that the rigidity of the CNC machine will impact the recommended feed and speed. By following these steps, you can safely and effectively cut aluminium with a CNC machine.

Tip #1 - What aluminium are you using?

Not all aluminium should be treated equally. The first question I ask when someone calls about cutting aluminium is "What aluminium are you using?". This is usually because the grade of aluminium used causes the majority of issues they are experiencing. It is true that all aluminium grades are machinable but each grade will require a different approach.

The going rate is... the lower the thermal conductive of the grade, the lower the temperature generated when cutting. If you want to get all nerdy, read this paper. There are two types of grades that are commonly found at your local aluminium merchant for sheet between 1 and 6mm.

5005 has a thermal conductivity value of 201 W / m. °C. From experience this grade of aluminium will gum almost instantly if cut dry (without coolant) due to excessive heat. This grade is common for 1-6mm aluminium and is called aluminium sheet. Do not despair if you have bought yourself a sheet of 5005 as there are ways to cut without any hassle. Refer to "the exceptions" in tip 3 regarding use of coolant to keep the heat down while cutting. A notable mention is 3003, also known as propeller plate which has the same thermal conductivity as 5005 at 192 W / m. °C.

5083 has a thermal conductivity value of 122 W / m. °C and makes for a much better cutting experience than 5005. The difference in cutting is like day and night due to the low heat generated while cutting this grade. At the local aluminium merchant, they will call this aluminium plate. 

6061 has a thermal conductivity value of 166 W / m. °C and is also called aluminium plate. 6061 sits in between 5005 and 5083 from the perspective of work-ability. 

6060 is used for extruding aluminium and has a thermal conductivity value of 209 W / m. °C. 

Tip #2 – Use a single flute spiral up cut CNC router bit (for aluminium)

When cutting aluminum with a CNC machine, one of the main challenges to overcome is material gumminess. Due to its low melting point of 660C, aluminum can easily reweld back onto the router bit, making it useless. To avoid this problem, a single or 1 flute router bit is recommended for cutting aluminum. These bits are made from larger carbide grains with a lower cobalt content, making them harder and sharper than traditional router bits. The single tooth design, similar to a velociraptor's nail, allows for maximum chip evacuation and minimal heat generation. This allows for a smoother and more efficient cutting process. 

While it is possible to use 2 or 3 flute carbide CNC router bits to profile and slot cut aluminium, it is recommended to keep to smaller diameter bits (4mm or less) to avoid excessive heat. Additionally, it is important to have a good understanding of the cutting process when using 2 flute end mills to slot aluminium. It is important to use the correct cutting parameters and coolant while machining with the 2 or 3 flute end mills to achieve the desired result.

Here it is the link if you were wondering

Adam’s Tips

When using a high-quality 1 flute up spiral router bit for cutting aluminum, you can expect to get a significant amount of cutting before needing to replace the bit. However, it is important to regularly check the condition of the bit after every cut to check for any chips or material reweld that may have accumulated on the cutting edge. This can help prolong the life of the bit and ensure optimal performance. 

It's important to know that, even with good quality bit, sometimes you may need to replace the bit due to unforeseen circumstances, such as hitting a screw or other foreign object, snapping the bit due to loose material or due to an action caused by user error. By following proper safety protocols, monitoring the cutting process, and making sure to use the correct cutting parameters, you can help prevent these types of accidents and prolong the life of your router bit.

Tip #3 – Use a coolant 

I will admit that I have ping ponged between using and not using coolants. Where as you can avoid using coolants on 5083, it is not the same with every other aluminium grade.

My current stance on the use of coolant is use it where you can! Coolants provide a better cutting experience by reducing the chance of gumming your material and therefore providing a cleaner and quieter cut.

My coolant suggestions include:

• Isopropyl Alcohol
• Purple Methylated Spirits

Isopropyl is actually the best in my opinion to use for tapping aluminium and the same goes for cutting. It does not leave a residue, flashes at 80c, cleans your hands, can be used as an antiseptic for cuts and great for cleaning windows. I buy it by the 5ltr bottle and decant into a spray bottle.

Do not use WD40 or something similar as these are lubricants, not coolants. You are wanting to cool the material you are cutting, not the bit itself.

Tip #4 – Use appropriate hold down methods and tabs

A lot of force is generated when cutting aluminium so you need to use appropriate hold down methods and tabs to secure your material to your wasteboard. Clamps and screws are some of the better options while super glue + masking tape has its time and place. Securing around the parameter might not always suffice as the internal stresses will have a tendency to warp your material over medium distances. So if you are planning on using tabs, be over cautious and make them high so that if your material does warp, it will account for the new height.

Also, aluminium likes to be cut with maximum rigidity as any vibration will increase heat and therefore degrade your finish. I have found that the use of a vacuum bed can cause issues with vibration and the tell tale sign is the loud noise generated when cutting.

Adam’s Tips

Compared to cutting timbers, cutting aluminium should be surprisingly much quieter. If your cutting operation is generating unbearable noise (without a dust vacuum on), it’s a quick way to determine that something isn’t right. This is especially true if you have previously cut with the same settings before with no issues. Check your end mill condition for chips or material reweld.

Tip #5 – Choose the right direction of cutting

Last of all, the direction of cutting makes a huge difference to your finish. Conventional cutting/counter clockwise should be used for cutting out holes so as to leave a nice finish on the hole, not the material you just cut out. For example you would leave a great finish on the inside of a cut out letter “O”. Climb cutting/ clock wise should ideally be used for cutting out objects like the outside of a letter “O”

Adam’s Tips

Shallow passes will give you a much nicer finish than aggressive passes. This is due to the sheer amount of force generated when cutting. If you cannot get away from using the correct cut direction, you can still get an excellent finish by using a coolant like isopropyl alcohol. 

So hopefully your confidence in cutting aluminium has increased and you are ready to do some yourself. Any feedback on this article is welcomed and you can email me at adam@endmill.com.au