Induction furnaces are commonly used for heating metals in casting, forging, and heat treating. They are classified according to their use, such as foundry melting furnaces for casting or quenching furnaces for heat treating. They are also classified based on the material melted, such as aluminum melting furnaces. Additionally, induction furnaces are classified by their power supply structure, such as single or multiple power supply configurations. The document provides an overview of common induction furnace types and classifications.