Affects the Machinability of Aluminum

Metallurgical Structure Affects the Machinability of Aluminum
Advancements in grain structure consistency and mechanical properties help to make this extremely machinable metal suitable for an ever growing range of applications.
The term “machinability” refers to the ease with which a metal can be machined to an acceptable surface finish. But maximizing machinability is a complex, sometimes trial-and-error process that is influenced by a number of factors that often must be fine-tuned.
Fortunately, compared with other construction materials, aluminum is relatively easy to machine. It responds well to most fabrication methods, including milling, drilling, cutting, punching and bending. Despite the “machine friendliness” of aluminum, though, machine shops have a number of specific concerns when it comes to working with this material, including long, stringy chips, chips wrapping on parts, machined surface finish, rough thread finish, dimensions, diameter to fit in collets, straightness, good tool life, and high production rates.
At Production Machining, our job is to help you stay on top of the latest trends and developments in the precision machining industry, which includes parts cleaning processes and best practices. Here is a collection of four PM features that delve into the technologies, processes and the people working to provide the most efficient and effective parts cleaning experiences for you, the end user.
The metallurgical field is making advances every day that are producing better results with materials such as aluminum in machine shops around the world. the goal is to provide machine shops with product that is unmatched in consistency and tolerance control.
Aluminum Machinability
Three factors affect the machinability of aluminum. The first factor is the machining process, which includes the type of equipment, the cutting tools, cutting speeds, feed rates and lubricants. The second factor involves the material—specifically, the particular alloy and temper of the aluminum, its microstructure, and how uniform its mechanical properties are. The third factor is the material processing, which involves the alloy chemistry and heat treatment, the extrusion process controls, the reduction ratio and die design, and whether direct or indirect presses were used in extruding the aluminum.
Machinability Ratings
Machinability ratings for aluminum are based on chipping characteristics. Because of the volume of chips created while machining aluminum, their form takes on great significance. Generally, the goal in machining aluminum is to generate short, tight chips that do not interfere with tooling or mar the surface of the part. Machinability ratings for aluminum specify expectations for chips and surface finish:
A-rated: Very small chips, excellent surface finish
B-rated: Curled or easily broken chips, good to excellent finish
C-rated: Continuous chips, good surface finish
D-rated: Continuous chips, satisfactory finish
E-rated: Long, continuous chips, difficult to maintain finish
An array of chip forms can be created; depending on the aluminum alloy selected, almost all forms of chips can be produced. As a general rule, the harder and stronger the aluminum alloy, the shorter the chips. Because of that, pure aluminum and soft wrought alloys produce extremely long chips. Special corrective measures, such as adding chipbreakers to the tools, are essential with these materials.
High strength wrought alloys present no issues in terms of chip form, and hypoeutectic casting alloys form short-coiled and spiral chips, which are easy to remove. Additionally, eutectic casting alloys tend to produce longer chips, while hypereutectic casting alloys result in short, fragmented chips, which can be hard to remove.
Alloys that are best suited to machining contain alloying elements with low melting temperatures, which help in the formation of the preferred, shorter chips.
Enhancing Metallurgy for Machining
One of the great advances in extrusion metallurgy has been the advent of the indirect extrusion process. The most common type of extrusion in the aluminum industryoccurs on a direct press, a process in which a ram pushes a billet through the container and the metal flows through a die. Direct presses can produce larger and wider shapes than can an indirect press. But because the direct extrusion process generates tremendous friction and heat between the billet and the container wall, pressure and temperature vary as the billet extrudes. The result is inconsistent grain structure and compromised metallurgical properties in the finished product.
An indirect press, on the other hand, pushes the container, billet and ram together over the die. Extrusions of harder alloys and thinner shapes are created using a lower tonnage press. Because there is less frictional heat and more constancy in pressure and temperature, the extruded product is more consistent, both from a metallurgical as well as a dimensional standpoint.
GPT precision operates an extensive line of presses with indirect extrusion technology. The company is able to supply the production industry with machine-grade rod, bar and hex products that have consistent grain structure, tight dimensions and high mechanical properties. and alloy options in 6061, 6042, 6082 and 6262. GPT precision can produce products with special tempers to enhance formability and machinability.