Routing of Aluminum

When routing aluminum there are two basic conditions. They are treated which is hard and untreated (annealed) which is soft. The harder alloys are actually routed more easily than softer materials.
Traditionally, high speed steel tools in spiral flutes were used in routing aluminum. This tool consists of a very hard material and carries a very sharp edge. These bits were originally used for hand held routing applications and could handle vibration and adversities in hand fed or hand controlled routing. At the time solid carbide tooling was too brittle to be used in these applications.
The advent of more advanced CNC routers which have excellent control and feed has created more uses for the more refined solid carbide tooling. These newer solid carbide tools have stronger sharper edges and are more shock resistant than the earlier ones.
As a rule of thumb use single edge tools for "O" condition aluminum (soft) and double edge tools for the "T" condition (Hard).
It is also very important to keep your bits as cool as possible. The chances of heat build up is very high when cutting aluminum. It is wise to have your tool lubricated using a vegetable based lubricant or at the very least compressed air.
As with all routing, good hold down, collet condition, proper tooling and feeds and speeds are important factors.
A typical feed rate example in aluminum is as follows:

1/8 cutting edge diameter- .060 depth of cut (Single sheet)

Solid carbide spiral "O" flutes: 150 IPM to 300 IPM

Solid carbide standard spiral: 60 IPM to 125 IPM

When cutting into aluminum it is a good idea the cutting depth to be 1/2 the diameter of the router bit.
Many CNC operators end up breaking bits because of the feed and speeds are off or the depth of the cut is too deep.
A conventional cut path is recommended. However, I suggest to check out the scrap pieces. If they have a cleaner edge finish than the part being cut switch over to climb cut direction.
Chip welding is a popular problem. This is caused by many different factors or a combination of them. Dull tools, poor chip loads, wrong feed direction, loss of coolant during the cut are all common errors. Chips welding back into the cut path occurs when the chip load is too light or the flute of the tool cannot eject it. This can happen when the cutting edge length is not long enough to clear the top of the deep cuts.
If you are novice to routing aluminum you may break a tool or two at the beginning stages yet if you go by the rules I described you will most certainly achieve a superior cut and the smooth finish you desire.