【作者】 高颖；

【导师】 李强；

【作者基本信息】 燕山大学 ， 材料加工工程， 2011， 博士

【摘要】 随着全球石油、天然气等能源消耗速度的不断加快,输送管线建设得到迅猛发展,大口径直缝焊管的需求量日益增加,这对大口径直缝焊管的生产技术与产品质量提出了更高要求。JCO渐进式多步模压成形工艺作为大口径直缝焊管制造工艺的一种,尽管人们对相关技术进行了部分研究,但由于JCO工艺路线比较长,影响参数众多,仍然需要深入全面系统的进行研究,以合理制定成形工艺、提高产品质量、保证生产稳定性。首先,本研究基于塑性弯曲理论,根据大口径直缝焊管成形特点,在对预弯与JCO成形合理假设和简化的基础上,采用数学解析方法,对大口径直缝焊管预弯过程及JCO成形过程进行理论分析。根据预弯模具与板坯的几何关系,推导出了上下模间距、预弯板坯任意卷角处曲率半径求解公式;同时利用宽板大曲率半径纯弯曲与非圆弧弯曲计算模型,推导出了预弯回弹后曲线方程与板坯各点卷角解析式,以及预弯任意时刻的成形力、预弯回弹后残余应力分布解析式;并分别针对JCO成形中的末次对称弯曲与其它道次非对称弯曲进行理论建模,给出了弯矩、加载弯曲角、回弹角、成形力与凸模位移解析式。其次,以塑性弯曲理论为指导,以X80管线钢为主要研究对象,利用大型非线性有限元分析软件ABAQUS,建立了无底凹模自由弯曲成形有限元仿真计算模型,通过讨论不同有限元算法、不同单元模型、不同网格密度等对自由弯曲成形及回弹仿真计算精度的影响,确定了适合自由弯曲成形的有限元数值模拟参数。同时,通过实验研究验证了自由弯曲有限元模型的有效性。并以此为基础,针对X80钢普遍存在的材料性能波动与厚度变化问题,采用正交设计与全因子设计思想制定了仿真实验方案,依据响应面模型、径向基神经网络等数据分析技术,探讨了材料初始屈服应力、杨氏模量、硬化系数、硬化指数与厚度变化等因素对回弹的影响规律,建立了关键参数预测模型。为研究模具结构参数对成形的影响规律,进行了凸模曲率半径、凹模曲率半径、凹模跨距等参数对回弹角、回弹后弯曲角、成形力、最大残余应力影响敏感性分析,并利用多目标遗传算法与序列二次规划法,建立了模具参数优化模型。综合考虑凸模曲率半径与应力/应变场、弯曲角、成形力之间的关系,确定了凸模选择策略。最后,基于弹塑性材料模型和平面应变的假设条件,以X80-Φ1219×22×12000(mm)直缝焊管成形为例,建立了预弯与JCO成形过程的计算机连续仿真系统。在实验验证仿真模型正确性的基础上,分析了预弯与JCO渐进式多步弯曲成形应力应变场特点,揭示了预弯成形和JCO成形的变形特征。通过改变预弯模具形面尺寸与装配关系,给出了预弯力、下模行程及板料预弯形状变化规律。针对JCO工艺中末次对称弯曲与其余道次非对称弯曲,探讨了压下量与回弹后弯曲角之间的关系,建立了目标压下量预测模型,实现了对不同道次压下时目标弯曲角所需目标压下量的预测;讨论了模具结构参数、凸模位移等对JCO非对称弯曲成形的影响,分析了不同道次成形时管坯最终形状特点。通过对大口径直缝焊管预弯与JCO成形过程进行理论分析、计算机仿真与实验研究,归纳总结出了一些规律,为成形设备的选择、模具设计以及JCO成形工艺的制定和优化提供了重要的指导方法和参考,具有一定的工程应用价值。更多还原

【Abstract】 With the more energy consumption such as global oil and natural gas, pipeline construction has been developed rapidly and the demand of large-diameter straight-welded welded pipe (LSAW) is increasing, which increases the production technology of LSAW and put forward higher requirements of product quality. JCO forming, as one of the production technique for LSAW, requires systematic and comprehensive investigation due to a long process line of JCO and too many parameters with improved steel levels and pipe quality, although the research on deformation characteristics of JCO forming process and comprehensive influence of multi-parameter related technologies have carried out.Firstly, according to forming characteristics of large-diameter longitudinal welded pipe, based on theory of plastic bending, the reasonable assumptions was considered and the forming model was simplified in the paper. The theory description with the mathematical methods is performed for pre-bending and JCO process of LSAW. According to geometric relations between pre-bending moulds and slab, the spacing from upper die to lower die, radius of curvature at any angle of pre-bending slab were deduced. Simultaneously regarding forming characteristics of wide-punch pure bending with large curvature radius, the slab shape curve equation after pre-bending springback, analytic expression at any angle of the slab, pre-bend forming force at any time, and the analytic equation of the residual stress distribution was obtained by the non-arc bending calculation model. Then, the two modes for the symmetric bending and asymmetric bending for JCO forming were analyzed theoretically. In theoretical analytical study on common air bending, mathematical model of JCO forming for the last bending was established. The analytic expression of bending moment, bending angle before and after springback, springback angle, forming force and punch die displacement was obtained, as well as forming force and punch die displacement of unsymmetrical bending.Then,in the base of the previous theoretical analysis, considering X80 pipe steel as the main study issue, the finite element simulation model on air-bending without bottoming was established and the deformation characteristics was investigated using orthogonal experimental design and numerical simulation. The effect of different finite element algorithm, different element type, and different meshing on spingback were discussed and the parameters of the finite element simulation were determined, which were suitable for air-bending without bottoming. Then simulation experiments were performed and the effect of punch and die radius, dies opening on springback angle, bending angle after spingback, forming force and maximum residual stress were discussed based on orthogonal design, combining response surface model technology and radial basis function neural network. Parameters prediction and optimization model was established combining multi-objective genetic algorithm and sequential quadratic programming. Simultaneously, the sensitivity of material property parameters and thickness variation on sheet springback has been analyzed based on orthogonal experimental design and FEM simulation, including initial yield stress, Young’s modulus, hardening coefficient, hardening index and material thickness.Finally,the assumption of elastic-plastic material model and plane strain was adopted, continuous simulation model for pipe manufacturing of X80-Φ1219×22 (mm) as example has been established. The experimental investigation on pre-bending and JCO forming was performed to verify the simulation model effective. The characteristics of stress-strain field of pre-bending and JCO forming was analyzed and their deformation characteristics were revealed. By changing the pre-bending mold geometries and the assembly relationship, the variation of pre-bending force, lower die stroke and pre-bending shape was described. For the final symmetric bending and the other asymmetric bending during JCO forming, the relationship between punch insertion and bending angle after spingback was discussed. Prediction model of punch insertion was put forward to predict target punch insertion for required bending angle. The effect of mold structure parameters and punch die displacement on asymmetric forming was discussed and the analysis on the final forming shape of steel tube for different bending times was performed.Through the systematical research on pre-bending and JCO forming for large diameter longitudinal welded pipe, it provides important guidance for the choice of forming equipment, the design of dies and the establishment of forming process project, and has greater engineering application prospect.更多还原