Control for Straightening Process of Seamless Pipe

Seamless pipes have some terminal end bends which must be eliminated before shipment. This paper describes a real-time control system for a press straightening process. The straightening process must account for elastic springback, which is a strong function of the material properties of the pipe. On-line measurements of reactive forces and deflection of the pipe during the early part of the bending process are performed to form an elastic-plastic model in a microcomputer. The final correct die position to yield the desired unloaded shape is predicted using the elastic-plastic model. Through a series of experiments on different materials and different sizes and shapes, the resulting straightness of the pipes was within 0.18 mm, which is sufficiently smaller than product allowance.