Deformation and kinematic parameters of roll forming

Currently, the manufacture of large-diameter pipes is performed on pipe-welding units using press or roll forming. In both cases, there is an unevenness of the stress-strain state of the pipe billet after forming, which leads to a decrease in the geometric parameters of the finished pipes and the formation of residual technological stresses in the pipes. In the case of roll forming, synchronous rotation of the rolls and immersion of the upper roll are used to obtain a blank of monotonic curvature. This technology is relatively new and does not have a full theoretical description. On the basis of the energy approach, the equations of the energy balance of the forming process in rollers are obtained and a method for calculating the forming force is proposed. The expressions for calculating the forming force include such parameters as: resistance of the metal to plastic deformation, sheet thickness, the center distance of the lower rolls, the radius of the workpiece after forming, radius of the lower roll; speed of vertical movement of the upper roll, the rotation speed of the rolls, is the coefficient of friction. Also, the dependences for calculating the length of the arc of contact between the workpiece and the upper roll were obtained, and a method for calculating the amount of immersion of the upper roll was proposed. The verification calculation of the forming parameters was carried out for a billet with a radius of 300 mm, a thickness of 18 mm, and with a yield point 520 MPa. The dependences of the change in the forming force and on the radius of the workpiece are presented graphically and are consistent with the data of the real process. The obtained analytical dependences make it possible to predict the working loads on the rolls at the given settings of the bending machine and the standard size of the pipe, which will avoid breakdowns of the roll drive elements and emergency shutdowns of the unit.