Which metal is likely to not require lubrication while drilling?

Cast iron is known for its excellent properties when it comes to machining, particularly in drilling operations. The material is relatively brittle compared to other metals, which reduces the tendency for it to gum up or form chips during the drilling process. This characteristic allows for easier operation without the need for lubrication, as the cutting process can proceed efficiently without the potential for overheating or excessive friction that lubrication typically mitigates.

Additionally, cast iron has a high graphite content, which not only makes it self-lubricating to some extent but also helps to dissipate heat, reducing wear on the drilling tools. This combination of properties makes cast iron a suitable choice for scenarios where lubrication may not be necessary.

In contrast, metals like aluminum, steel, and copper tend to require lubrication during drilling to improve cutting efficiency, extend tool life, and manage heat generated during the drilling process. Therefore, cast iron stands out as the metal that is less dependent on lubrication while drilling.