With the development of society and economy in China, the demand for oil, gas and other energy resources is increasing day by day for the construction of long-distance oil and gas pipeline engineering for large diameter, high strength and high toughness of large straight seam welded pipe.  This provides the development opportunity for the steel pipe manufacturing industry, but also poses a greater challenge to the large straight seam welded pipe manufacturing technology.  JCOE and UOE are common forming methods of large straight seam welded pipe billet, and JCOE forming method is common because of its characteristics of less investment and strong adaptability.  The JCOE forming process of large straight seam welded pipe includes plate edge pre-bending,JCO forming and mechanical diameter expansion.  JCO forming is a typical progressive multi-pass die forming process, and mechanical diameter expansion is a complex elastoplastic deformation process with obvious local small deformation characteristics.  Due to the influence of springback in sheet metal bending, it is a difficult engineering problem to accurately predict the process parameters of tube billet JCOE forming.  At present, the production mainly relies on experience or trial-and-error method to formulate and adjust the JCOE forming process parameters. This method has many problems, such as large parameter adjustment error, long process parameter formulation cycle, large product quality fluctuation and so on.  Therefore, it is necessary to study the theory and application of pipe billet JCOE forming process systematically, so as to provide theoretical basis and technical support for the actual production process design of enterprises.  Firstly, based on the traditional elastic-plastic theory and the elastic theory of small curvature plane bending, the theoretical analysis of the sheet edge pre-bending, sheet metal three-point bending and mechanical diameter expansion forming process is carried out.  

The latching machine is a large straight seam welded pipe forming process, the theoretical research structure of various forming processes, as well as the JCOE forming production line for large straight seam welded pipe forming process design and process parameters formulation of the actual demand,  By using VC+ +6.0 software programming tool, the main function modules of CAPP system for JCOE forming of large straight seam welded pipe billet were developed. The system realized the basic functions of theoretical calculation and prediction of main process parameters of JCOE forming.  The feasibility of the main functional modules of the system in the formulation and prediction of JCOE forming process parameters was verified by an actual production example of a certain specification of large straight seam welded pipe.