Roll forming refers to the operation of rolling raw materials with smooth surface or with a certain shape by using a rotary roller to make products of a certain shape.

During the rolling operation, the material directly contacts with the roller and deforms. The material thickness before and after rolling is called the absolute reduction, contact angle or feeding angle. In the process of rolling, the inner part of the material layer presents different flow states due to different pressure directions. At the initial stage of rolling in the front section of the roll working area, due to the small radial pressure of the roll on the material layer, the surface speed of the material layer is close to the surface speed of the roll due to friction, while the internal flow is in reverse direction with respect to the material layer surface, and its speed value is even greater than the forward movement speed value of the material surface.

After entering the vicinity of the rolling distance, the roll pressure increases sharply, the pressure inside the material layer is close to the pressure on the surface, and the relative motion between the surface and the interior of the material layer is reduced, and the overall motion speed is accelerated. At the moment after passing the rolling distance, due to the roll pressure, the material inside begins to flow forward relative to the surface, and the forward movement speed of the central part of the material layer is higher than the speed of the roll surface, so the radial pressure of the roll drops rapidly.