Before revision: The disadvantages are: Undesirable reactions between the metal and the surrounding atmosphere (scaling or rapid oxidation of the workpiece) Less precise tolerances due to thermal contraction and warping from uneven cooling Grain structure may vary throughout the metal for various reasons Requires a heating unit of some kind such as a gas or diesel furnace or an induction heater, which can be very expensive Processes Rolling Hot rolling Hot Spinning Extrusion Forging Drawing Rotary piercing References Notes Bibliography .
After revision: The disadvantages are: Undesirable reactions between the metal and the surrounding atmosphere (scaling or rapid oxidation of the workpiece) Less precise tolerances due to thermal contraction and warping from uneven cooling Grain structure may vary throughout the metal for various reasons Requires a heating unit of some kind such as a gas or diesel furnace or an induction heater, which can be very expensive Processes Rolling Hot rolling Hot spinning Extrusion Forging Drawing Rotary piercing References Notes Bibliography .