Aluminum is one of the most popular materials for machining, and milling in particular. Its alloys are light, resistant to corrosion, and durable; also have very good heat conductivity, and can be easily machined and improved in further processes (e.g. anodizing).
These features of aluminum alloys make them a perfect base to produce many types of parts for many industries – from home decor and automotive, to the airplane and even space industries.
On the other hand – aluminum milling, as a process of machining alloys – is one of the most popular ways of producing aluminum parts and elements.
Aluminum milling - why is that alloy so machinable?
Aluminum is a name used to describe the whole family of aluminum alloys (Al in the periodic table) and clean aluminum (within the processes it is possible to refine aluminum with 99,9% purity). A vast variety of aluminum alloys provides many possibilities to select the right one for a particular application.
Among the most popular additives for aluminum alloys it is worth mentioning:
- silicon (Si),
- magnesium (Mg),
- zinc (Zn),
- copper (Cu)
- manganese (Mn).
These elements give an alloy additional features and change its characteristics (about their impact on machinability in a further part of the article).
Such a vast variety of "types of aluminum alloys" makes that metal almost perfect for many types of machining.
These additives can make aluminum alloy safe to have contact with food, to mill complicated parts from it, or to produce light, yet durable parts for airplanes.
In addition: the aluminum itself is very machinable, easy to work with proper tools, and can be surface improved (e.g. anodizing).
Machining and milling different types of aluminum - what are the differences?
An important part of milling aluminum is the machining parameters for a particular alloy.
Such parameters consist of information like:
- smoothness index – which describes the surface of the machined element,
- hardness index – which correlates with milling speed, that includes:
- the insensitivity of cutting tool deterioration (in other words: how long a particular tool remains at its optimal sharpness during machining aluminum),
- relative machinability index (in other words: how fast it is possible to mill a particular element, made of a particular aluminum alloy while using particular types of cutting tools),
- the durability of the cutting tool (in nomenclature described usually as "T”).
Among the auxiliary indicators, that have a direct impact on aluminum machining, it is worth mentioning:
- chemical composition of the machined alloy (e.g.: type of the alloy),
- the temperature of milling,
- overall machinable of the material (described usually as kc1),
- stretching resistance,
- metallurgical structure,
- type and shape of shavings cut from the aluminum block. Perfect are 0.2 mm thick, but it should be more than 0.1 mm, to avoid blocking the router or mill spindle,
- mechanical properties of the particular alloy,
As you can see, there are a lot of these parameters. From the perspective of an average person, these pieces of information are secondary due to the quality of an element made in the aluminum milling process.
That is why professional CNC milling operators can include these parameters on the fly and program the right type of work for the expected element.
Types of aluminum alloys and their machinability
There are many methods of categorization of aluminum alloys. For the purpose of the following categorization, we use the International Alloy Designation System (the most popular and widely accepted).
That system is based on the 8 series, which divides alloy types by their additives. Such information is important for the client, as for the CNC machining company.
According to that, we can describe the following types of aluminum alloys:
- series 1xxx – it is basically pure aluminum. Such material is soft and flexible.
Characterized by excellent heat and electricity conductivity, thus used in radiators and
older types of electrical installation. Rarely used in milling,
- series 2xxx – an alloy of aluminum and copper. It is harder but has worse corrosion
resistance. Among these types of aluminum alloys we can highlight aluminum PA7
(2024), often used as a material to produce airplane interior parts,
- series 3xxx – aluminum alloy with the manganese additive. Such alloys are relatively
soft, thus often used for plastic machining, but retain their features even at higher
temperatures. That type of aluminum is weldable and safe to use around food,
- series 4xxx – an alloy of aluminum and silica. Has good corrosion resistance. Some of
its versions (AK7 and AK9) can be used around food,
- series 5xxx – alloys with additives of magnesium. Has even better corrosion resistance
and is easy to machine. Due to its weldability, it is used often in the marine industry. Its
flexibility makes it also perfect for the production of aluminum sheets,
- series 6xxx - an aluminum alloy with additives of magnesium and silica. On top of the
great corrosion resistance, such material is robust and has great mechanical strength.
Such type of alloy is very machinable and often used in CNC milling of aluminum. One of
the most popular types is PA45 (6061), often used to produce bike frames,
- series 7xxx - alloys with the additive of zinc and magnesium. Has very good mechanical
strength and is easy to machine in mills and lathes (CNC and automatically). Such alloys
are the go-to material in the production of crucial elements of cars (e.g. internal frames)
and are widely used in many industries. One of the most popular types is 7075 alloy. On
the other hand – in that series, we can also mention trademark alloys such as
HOKOTOL® or ALUMOLD®,
- series 8xxx – all of the other alloy types that do not fit in any of the mentioned series.
Key information related to aluminum milling (CNC and automatic)
Although classic milling is still one of the most popular methods of shaping aluminum, the usage of CNC milling machines makes it more efficient.
Automatisation of that process allows for an increase in production volume, a decrease in tolerance of produced elements, and the number of elements declined by quality control.
A vast variety of aluminum alloys have different hardness and overall machinability. That is why professional CNC machine operators must be focused on many parameters that have a direct impact not only on the surface finish but also on the cutting tool life.
Right cutting edge, proper cutting speed, or feed rates makes it more challenging due to the speed of numerically controlled CNC routers. Because of that, there are a handful of aluminum alloys treated as go-to for machining. The high hardness of alloy makes it easier to mill in CNC machines, especially due to the ease of chip clearance (such are fragile and easy to remove). For that reason, refined aluminum (series 1xxx) is suboptimal material to the machine in CNC mills.
Another important factor is the temperature of the whole process. Due to good thermal conductivity (and its extensibility), these alloys require good cooling to maintain small tolerances. Heat removal systems (dry or wet) can improve the quality of machined elements and decrease the risk of damaging cutting tools in the process.
It is worth mentioning that usage of higher helix angle cutting tools (made of solid carbide) can
decrease build-up on the blades. That is why the overall "machinability" of aluminum alloys is important. Such susceptibility for that process allows for an increase in RPM of the spindle and material removal rates. As shown, aluminum milling is a complex process that requires knowledge of metallurgy and milling. That is why outsourcing aluminum part production can be a perfect business decision.
Further processing of parts milled from aluminum
Machining aluminum is often the last step in the production of a part or element. Just like in producing steel parts, milled elements can be subjected to additional processes. It can improve the physical properties of parts, like increasing hardness or corrosion resistance.
Among these processes we can mention:
- anodizing – that process creates a coat of aluminum oxide on the surface of the part. In addition, can improve the aesthetic of an element,
- hardening – improving the rigidity of the part and its physical properties by heating and rapid cooling,
- polishing – the surface of milled aluminum can contain marks of cutting tool, thus such can be sanded and polished,
- laser marking/engraving – the surface of a milled aluminum part can be marked by these
Aluminum milling - contact us
At RADMOT, we can offer CNC milling services, CNC turning services as well as many additional services, including washing, aluminum anodizing, laser marking and assembly.
Contact us and tell us what you need. We have been providing CNC services for almost 40 years. Our quote is completely free. And if you have any doubts about what technology will work best for you, our expertise is at your service.