There are many reasons why aluminum CNC machining is the most commonly used in metal CNC machining. Aluminum is very ductile and malleable, making it suitable for a wide range of applications. Its ductility allows it to be made into aluminum foil, and its ductility allows aluminum to be drawn into rods and wires.
Aluminum CNC machining is very popular in metal CNC machining. The other reason is aluminum have highly resistant to corrosion, as a protective oxide layer naturally forms when it is exposed to air. This oxidation can also be artificially induced to provide even stronger protection.
Aluminum’s natural protective layer makes it more resistant to corrosion than carbon steel. In addition, aluminum is a good thermal and electrical conductor, better than both carbon and stainless steel.
Aluminum Advantage and Disadvantages in Aluminum CNC Machining
In metal CNC machining, aluminum is faster and easier to work with than steel, and its strength-to-weight ratio makes it a good choice for many applications requiring strong, hard materials. Finally, aluminum can be recycled well compared to other materials, so more of the chip material can be saved, melted and reused. Compared to the energy required to produce pure aluminum, recycling aluminum can save up to 95% of the energy needed.
Of course, there are some disadvantages to using aluminum in metal CNC machining, especially when compared to steel. It is not as hard as steel, which makes it a poor choice for parts that are subjected to greater impact or extremely high load-bearing forces.
In special areas, aluminum CNC machining also has a significantly lower melting point ( just 660℃, compared to steel’s lower melting point of about 1400℃), so it cannot withstand extreme high temperature applications. It also has a high coefficient of thermal expansion, so if the temperature is too high during CNC machining, it will deform and have difficulty holding tight tolerances.
Aluminum Alloys in Aluminum CNC Aachining
In usual, aluminum alloys is almost used for aluminum CNC machining. It is not hard to got aluminum alloys which can be made by slightly adjusting the amount of aluminum alloy elements. However, some combinations have proven to be more useful than others.
These common aluminum alloys are grouped according to the major alloying elements. Each series has some common properties. For example, the 3000, 4000, and 5000 series aluminum alloys cannot be heat treated, so they are cold worked, also known as work hardened.
Types of Aluminum Alloys Used in Aluminum CNC Machining
1000 Series
Aluminum 1xxx alloys contain the most pure aluminum, with at least 99% aluminum by weight. There are no specific alloying elements, and most of them are almost always pure aluminum. For example, aluminum 1199 contains 99.99% aluminum by weight and is used to make aluminum foil. These are the softest grades, but they can be work hardened, which means they become stronger when repeatedly deformed.
2000 Series
The primary alloying element in 2xxx series aluminum is copper. These grades of aluminum can be precipitation hardened, which makes them almost as strong as steel. Precipitation hardening involves heating the metal to a temperature at which precipitates of other metals precipitate out of the metal solution (while the metal remains solid) and helps increase the yield strength.
However, due to the addition of copper, 2xxx aluminum grades have lower corrosion resistance. Aluminum 2024 also contains manganese and magnesium and is used in aerospace parts in aluminum CNC machining.
3000 Series
Manganese is the most important element added to the aluminum 3000 series. These aluminum alloys can also be work hardened (which is necessary to achieve adequate levels of hardness, as these grades cannot be heat treated).
Aluminum 3004 also contains magnesium, which is commonly used in aluminum CNC machining to make soft drink cans.
4000 Series
4000 series aluminum includes silicon as the primary alloying element. Silicon lowers the melting point of 4xxx grade aluminum. Aluminum 4043 is used as filler bar material for welding 6000 series aluminum alloys, while aluminum 4047 is used as sheet and cladding.
5000 Series
Magnesium is the primary alloying element in the 5000 series. These grades have some of the best corrosion resistance, so they are commonly used in marine applications or other situations where they face extreme environments. Aluminum 5083 is an alloy commonly used for marine parts in aluminum CNC machining.
6000 Series
Both magnesium and silicon are used to create some of the most common aluminum alloys.
The combination of these elements is used to create the 6000 series, which is typically easy to machine and can be precipitation hardened. 6061 in particular is one of the most common aluminum alloys and has high corrosion resistance. It is commonly used in structural and aerospace applications in aluminum CNC machining.
7000 Series
These aluminum alloys are made from zinc and sometimes contain copper, chromium and magnesium and can be precipitation hardened to be the strongest of all aluminum alloys. 7000 grades are commonly used in aerospace applications in aluminum CNC machining because of their high strength.
7075 is a common grade and while it has higher corrosion resistance than 2000 series materials, it has lower corrosion resistance than other alloys. This alloy is commonly used, but is particularly suited for aerospace applications.
These alloys are made of zinc, and sometimes copper, chromium and magnesium, and can be the strongest of all aluminum alloys through precipitation hardening. 7000 grade is commonly used in aerospace applications due to its high strength. 7075 is a common grade with lower corrosion resistance than the other alloys.
8000 Series
The 8000 series is a general term for aluminum alloys that do not apply to any other category. These alloys can include many other elements, including iron and lithium. For example, 8176 aluminum contains 0.6% iron and 0.1% silicon by weight and is used in the manufacture of electrical wire.
Surface Finishing in Aluminum CNC Machining
There are many surface finishes that can be applied to aluminum, each with appearance and protective properties suitable for different applications.
There is no effect on the material after polishing. This finish requires less time and effort, but is usually insufficient for decorative parts and is best suited for prototypes that are only tested for function and fit.
Sanding is the next step up from the machined surface. More attention is paid to the use of sharp tools and finishing passes to produce a smoother surface finish. This is also a more precise method of machining and is often used to test parts. However, this process still leaves machine marks and therefore is not usually used for the final product.
Sandblasting produces a matte finish by spraying tiny glass beads on the aluminum part. This removes most (but not all) of the machining marks and gives it a smooth but grainy appearance. The signature look and feel of some popular laptops comes from sandblasting prior to anodizing.
In aluminum CNC machining, anodizing is a common surface treatment that is a protective oxide layer that forms naturally on the surface of aluminum when exposed to air. In the manual process, the aluminum part is suspended on a conductive support and immersed in an electrolytic solution in which a direct current is introduced. As the acidity of the solution dissolves the naturally occurring oxide layer, the current releases oxygen on its surface, resulting in the formation of a new protective layer of aluminum oxide.
Tips of Aluminum CNC Machining
1. The high coefficient of thermal expansion of aluminum can affect tolerances, especially for thin parts, if the part is overheated during machining. To prevent any negative effects, heat concentration can be avoided by creating toolpaths that are not concentrated in one area for too long. This method dissipates heat and allows the toolpath to be viewed and modified in the CAM software that generates the aluminum CNC machining program.
2. The softness of some aluminum alloys can promote distortion during aluminum CNC machining if the force is too great. Therefore, follow the recommended feeds and speeds for machining specific grades of aluminum to produce the proper forces during machining. Another rule of thumb to prevent distortion is to maintain part thickness greater than 0.020 inch in all areas.
3. In some process of aluminum CNC machining, another effect of aluminum’s ductility is that it can create a combined edge of material on the tool. This can obscure the sharp cutting surface of the tool, dulling it and reducing its cutting efficiency.
This build-up of edges can also create a poor surface finish on the part. To avoid accumulated build-up of edges, experiment with tool materials; try replacing HSS (high-speed steel) with carbide inserts and vice versa, and adjust the cutting speed. You can also try adjusting the amount and type of cutting fluid.