You can assess chip breakage with chip maps or chip counting. The first gives you a good overview of chip breakage at different cutting parameters, while the latter provides you with a more accurate measurement.

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One final point: Aluminium producers have traditionally added the low melting-point alloying elements lead (Pb) and bismuth (Bi) to 6xxx-series alloys to achieve good machinability. Examples are the 6042 and Hydro 6262 alloys.

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That said, lead and bismuth are banned as alloying elements in some regions and applications. Where this is the case, good machinability alloys are 6061M and 6082M. These are special versions that are based on 6061 and 6082 with both tailored temper and composition for machinability.

For 6xxx alloys, the general trend is that chip breakage increases with strength, both with harder alloys and tempers. However, this cannot always be translated to other alloy systems. For instance, it can be very difficult with some 7xxx alloys, despite their high strength, to get good chip breakage.

Let me conclude simply by stating that excellent machinability of aluminium alloys is achieved by careful control of the alloy’s chemical composition and the parameters in all process steps.

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You can view this issue in the same way as a restaurant chef does when preparing a meal: The raw material matters. With aluminium, having the right material will improve machinability and thereby the final product.

Aluminium is a relatively easy material to machine. It is also relatively easy to excel in this work, as long as you understand the three factors that affect the machinability of the metal.

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The machinability of aluminium alloys can be difficult to predict, even for machinists. There are so many variables. One is the condition of the material, not to mention its physical properties – alloying elements, microstructure, hardness, yield strength, tensile strength, elongation, work hardening.

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Let me start with the two principal classifications of aluminium alloys: cast alloys and wrought alloys. Each classification is further divided into the categories heat treatable and non-heat-treatable. About 85% of aluminium is used for wrought products, such as rolled plate and foils, and extrusions. Here you can find large variations, with some alloys forming very small nice chips whereas others struggle with chip breakage.

David has a Bachelor of Science degree in metallurgical engineering from Michigan Technological University as well as master's and doctorate degrees in metal science and engineering from The Pennsylvania State University.

In general, machining aluminium profiles is relatively inexpensive. I’m talking about processes such as sawing, turning, drilling, milling, threading and punching. One reason is that tool costs tend to be competitive due to low tool wear as a result of low specific cutting force. The cutting force in Al is only about a 1/3 of that with steel. In addition, the cutting speeds attainable with aluminium are much higher than for steel, thus leading to less-expensive machining compared to steel.