A Comprehensive Guide to Aluminum Machining Properties
Aluminum’s machinability makes it a top metal for machining. Its material properties make it easy to mill, drill, cut and stamp, and aluminum machining parts are durable and aesthetically pleasing. All in all, aluminum is the easiest metal to machine on the market.
Still, aluminum is far from perfect. Aluminum’s ease of machining is limited by certain issues, including long, sticky, obstructive chips; chip entanglement; rough thread finish; an overly “machined” appearance and straightness issues.
Fortunately for those in the machining industry, engineers and metallurgists are continually working to find solutions to improve the machinability of aluminum and its various alloys—through improvements to the material itself, improved machining methods and selection of the right alloys.
1.Metallurgy
The first way to improve aluminum machining performance is to simplify the metallurgical process for making aluminum workpieces. Currently, the most widely used aluminum extrusion method uses a direct press, in which a punch presses an aluminum billet through a die with great force. In this process, often called “forward extrusion,” the aluminum billet and punch move forward in the same direction.
While forward extrusion can be used to quickly create large pieces of aluminum, it also has disadvantages. It takes a lot of force to push the billet through the die, but this force is not uniform throughout the process: it is greatest at the beginning and decreases as the billet moves forward. This variation in force can lead to inconsistent grains, which often renders one end of the billet unusable.
More consistent, higher quality workpieces can be made by using an indirect press and a process called “reverse extrusion.” An indirect press pushes the container and billet while the punch and die remain stationary. This is achieved using a rod, which reduces friction and thus the potential for cracking. However, the process is less versatile than forward extrusion.
2.Alloy Selection
It goes without saying that not all aluminum is created equal in terms of machinability. While A6061 remains the most common aluminum alloy used in machining, it is neither the only choice nor the ideal metal for all projects. A6061 has good mechanical properties and corrosion resistance, making it suitable for machined parts and consumer products, but it can produce chips that are difficult to break in certain tempering conditions.
Other alloys, such as A6042 and A6262, have material properties that improve machinability. The former produces smaller chips than A6061, which was developed specifically for machining applications. Like A6042, A6262 produces small, curled chips, but has the added benefit of good finishing characteristics and heat-treatable properties.
3.Aluminum Machining Tools
Aluminum machinability can also be improved in other ways, such as paying close attention to the tools and machining techniques used when machining the metal. In general, aluminum is better suited to tools made from tool steels, high-speed steels, carbides, and diamonds than tools made from ceramics or synthetic materials.
Maintaining cutting tools also has a big impact on machinability. By keeping cutting edges sharp, maintaining finely ground edges, using proper rake angles, and using a coolant feed system, machine shops can ensure that aluminum is machined optimally (and that they get the longest possible life from their tools). Chips should also be kept away from the workpiece or into a chip breaker, especially when working with less machinable alloys.