中文摘要：

提出了一种大型直缝焊管生产的新工艺——四点弯曲JCO成形，采用该工艺最终成形的管坯径向截面的几何形状为曲率一致的圆，且成形道次少，生产效率高。通过宽板四点弯曲试验，验证了理论解析的正确性，为将来实际生产中通过调整凸模行程控制成形管坯曲率提供了理论依据。理论和试验数据均表明弹复前后的曲率为线性关系，这为四点弯曲JCO成形过程智能化控制提供了便捷。基于上述理论进行了管坯四点弯曲JCO成形试验，获得了理想成形管坯，且成形道次仅13道次，相对传统工艺25道次，生产效率得到显著提高。

英文摘要：

This paper presented a new technology for forming LSAW pipes called by ＂four--point bending JCO process＂. In the manufacture of LSAW pipes through this new technology, the end sur- face is a circle of equal curvature. Other advantages of the new technology include fewer steps in for- mation and higher productivity. The theoretical analysis was verified by the experimental results. These will provide a theoretical basis to control the forming curvature by adjusting the punch displace- ment during each stage of bending in real manufacturing. Both the theoretical and the experimental re- sults show the linear relation between bending and forming curvatures, thus provide a convenient means to intelligent control over the four--point bending JCO forming process. Based on the above theory and with the help of the new technology,the ideal LSAW forming pipe is obtained in only 13 steps. Since the traditional process entails 25 steps, productivity is significantly increased.