Research On The Forming Mechanism And Process Design Method Of Cage Roll-forming Of ERW Pipes

ERW (electric resistance welded) pipes have been increasingly applied in variousindustries, due to their advantages of high efficiency, low energy consumption, goodforming quality and high dimensional accuracy. The seamless pipes have been completelyreplaced with ERW pipes not only in the low-strength application fields such as coal gaspipeline, building structure pipe, but also in the high-strength application fields such ashigh pressure boiler tube, gas and oil line pipe. With quality improvement of ERW pipesand concern for the environment and energy, ERW pipes will be found in more extensiveapplications in future. Therefore, cold roll-forming technologies of ERW pipes have beenpaid much attention in recent years.At present, there are two major cold roll-forming processes for ERW pipes. One isconventional contour roll-forming process, and the other is the cage roll-forming process.The cage roll-forming is developed from the conventional contour roll-forming. In the cageroll-forming process, for reducing springback, improving forming quality and enhancingroll common use, many small rolls with same shape are used before fin pass stands toreplace horizontal and vertical rolls in conventional roll forming mills. Although manyresearchers have done a lot of work on the conventional roll-forming process of ERWpipes, there are few theoretical studies on the cage roll-forming process. Design of cageroll-forming process is a formidable process, so it is impossible to get satisfactory designresult just by the traditional “trial and error method”. Theoretical design of cageroll-forming process of ERW pipes is an challenge in the cold roll-forming field.In this thesis, the research on the process design of the cage roll-forming is conductedbased on the ERW610cage roll forming mill introduced by Baosteel in2005. Experiment,numerical simulation and theoretical analysis are combined to systematically study thedeformation behavior of strip, pattern design, forming parameters design and roll design.Through uniaxial tension tests, the required material property data are obtained. Based onADPL language, CAD/CAE parametric modeling of cage roll-forming mill is realized. Thewhole cage roll-forming process of ERW pipes is simulated by dynamic explicitelastic-plastic finite element method. The deformation behavior of strip in different forming sections has been analyzed from different aspects such as plastic strain (transverseand longitudinal), relative curvature and forming shape. The non-bending phenomenon isdiscovered. The numerical simulation is also verified through measurement of openingvalue, strip width and section profile. In order to overcome the limit of traditional patterndesign methods, a new method of pattern design, which is suitable for cage roll-formingprocess, has been put forward based on the non-bending phenomenon and is applied todesign parameters of forming flower diagram in the ERW Φ325mm cage roll-forming mill.According to frame mechanism in cage roll stands of the cage roll-forming mill, a designmethod of forming parameters for cage roll-forming process is presented. The cage rollssurface equation related to forming parameters is constructed, and geometry constraintconditions for solving initial forming parameters are determined. In combination with theproposed new pattern design method, a general algorithm for solving the formingparameters is proposed. As an illustrative case, the new forming parameters of a Φ244.5mm ERW pipe cage roll-forming mill are designed, and the practicality and validity of thedesign method of forming parameters are also proved by comparison of simulation resultsunder new and old forming parameters. According to different geometric shape of rolls, aknowledge base of roll design is built up. Based on BP neutral network algorithm, ageneral roll design method of cage roll-forming mills is implemented. Roll profiles designof the Φ377mm cage roll-forming mill is performed with the proposed roll design method,and reliability of general roll design method of cage roll-forming mills is verified. At last,in combination of above research results, modules of CAD/CAE parametric modeling,pattern design, forming parameters and roll design for cage roll-forming are developedrespectively. Through integrating these modules with parameters management and usermanagement modules, a design system of cage roll-forming process of ERW pipes isdeveloped.The research of this thesis is helpful to break through foreign trade blockade andtechnology monopoly. By developing the basic theory of cage roll-forming process forERW pipes, the design of cage roll-forming process can be realized by “theoretical design”instead of traditional “empirical design”. This research also contributes to the applicationof cage roll-forming technology in domestic ERW pipe manufacturing industry.