Bending Theory And Technical Study Of FFX Forming In Straight Seam Welded Pipes

With the rapid development of the domestic economy,people pay more and more attention to high grade straight seam welded pipes.High grade straight seam welded pipe mainly for oil wells tubes,submarine pipelines,oil and gas delivery pipes and Some other professional tubes for special application.At present,there are two types of the forming process for producing the high grade straight seam welded pipes.One is the abreast roll forming,the other is FFX(Flexible Forming Excellent)forming.Where in the FFX forming is a more advanced forming process.Although FFX forming technology has been developed for several decades,few researches in this field have been done in China.The researches mainly focus on the introduction of FFX's advanced technology and process characteristics,but there is no more theoretical study on FFX forming technology.Therefore,it has great social significance to carry out relevant researches on FFX forming process of straight seam welded pipe.This paper mainly focuses on a series of researches on the theoretical derivation of forming bending analysis and the roll flowers design of FFX forming process.The former is based on the classical elastic-plastic bending theory,analysising the contact state between the strip and roller system in FFX forming process.Based on three-point bending and four-point bending analysis of the broad plate,we establish the “W” five-point bending model.And after calculating this process,the corresponding analytical formulas are derived.So we can calculate the bending curvature and the spring back of curvature.The theoretical analysis results are verified by experimental method.In the aspect on the roller flowers design of FFX forming process,we study the strip deformation characteristics in FFX forming,and deduce the marginal end-point equation and horizontal projection equation for the roller flowers of FFX forming,combining with the traditional roll bending theory and the design method of cage roll forming.Besides,we have used the finite element method to analysis the Mises stress,the distribution of the equivalent plastic strain,the shape curve of roller flowers and the down hill amount in different formingprocess.Finally,by comparing the the simulation results and the experimental results,we prove that the finite element model and the roll design theory are correct.