The two primary processes are hot rolling and cold rolling/forming.
Hot Rolling: This is the predominant method. Steel billets are heated above their recrystallization temperature (typically above 1100°C) and passed through a series of rolls to progressively form the L-shape. This process produces a characteristic mill scale on the surface and allows for the manufacture of a wide range of sizes and thicknesses with good mechanical properties. It is more economical for large sections.
Cold Rolling/Forming: This process shapes steel strips or sheets at room temperature through a series of shaped rolls (roll forming). It produces angles with smoother surfaces, sharper corners, and tighter dimensional tolerances. The process induces work hardening, increasing the yield strength but potentially reducing ductility. It is typically used for thinner sections.