Springback Theory Of Small Curvature Plane Bending And Experimental Verification

With the rapid development of science and technology as well as increasingly fierce competition in product manufacturing, the accurate prediction and precise control of bending springback has been the key issues to solve. Springback is the most common metal forming phenomenon and in the past several decades, a lot of research work about plane bending springback has been done by experts in the world. However, due to the diversity of bending mode and bending objects, yet there is a complete and unified theory or methods to analyse springback of plane bending.In this paper, geometric model and mechanical model of plane bending are established at first. Based on them, geometric constraint equations and springback equation of straight beam plane bending, curved beam stretch-bending and curved beam compress-bending are derived. The concepts of initial equivalent strain and equivalent strain neutral layer are introduced in the analysis of curved beam plane bending, with which the strain of curved beam plane bending can be expressed more accurately. According to the force, curved beam plane bending can be divided into stretch-bending and compress-bending. According to the bending direction, it can be divided into equidirection bending and redirection bending. Different cases correspond to different geometric constraint equations and springback equation.In the defined symbol system, the unified expressions of geometric constraint equations and springback equation of different plane bending situations are given. The process forms the basic framework of the plane bending theoretical system. The results can be successfully conversed to straight beam plane bending and pure bending, that proofs the correctness of the springback theory from the theoretical point of view.Expanding and setting round and compression and setting round respectively belong to curved beam stretch-bending and curved beam compress-bending. The springback equation is used to analyse these two kinds of plane bending situations and curvature radius after unloading of pipe is given. With the help of the molds designed by author own and high precision equipments and measuring instruments, expanding and setting round and compression and setting round experiment are successfully done. Theoretical predictions and experimental results agree very well, that proofs the correctness of the springback theory from the experimental point of view.The establishing of small curvature springback equation and the successful prediction of expanding and setting round as well as compression and setting round settle a solid foundation for springback theory of small curvature plane bending. The results not only further enrich the content of the classical theory of elastic-plastic bending, but also successfully apply it to solve engineering problems, which provide a theoretical basis and technical support for engineering.