【作者】 李任君；

【导师】 李明哲；

【作者基本信息】 吉林大学 ， 材料加工工程， 2014， 博士

【摘要】 曲面柔性轧制是一种新型的三维曲面板类件成形方法，在某种程度上可以认为是传统轧制与多点调形技术的结合，其基本原理是采用两根轴线方向可弯曲且径向强度与刚度足够大的柔性工作辊作为成形工具，通过辊的旋转实现三维曲面板类件的连续成形。通过不同的工作辊弯曲形状及辊缝分布形式，曲面柔性轧制可以成形不同形状的凸曲面件、鞍面件等典型三维曲面件。曲面柔性轧制的关键为形状可调整工作辊的结构设计。本文选用直线光轴作为工作辊，钢丝软轴作为支撑辊，提出了工作辊总成的设计思路。相比于以上几种成形方式，曲面柔性轧制实现了真正的成形连续化与柔性化，具有较高的工程应用与学术研究价值。本文的主要研究内容与结论如下：一、在理论研究及成形设备研制方面曲面柔性轧制采用整体式可弯曲柔性工作辊作为成形工具，通过调形单元来调整工作辊弯曲形状，使其可以在弯曲状态下绕其轴线旋转。工作辊的弯曲使板料在横向产生一定的弯曲变形，而在板厚方向的不均匀压缩则导致了板料沿轧制方向的不均匀伸长。通过工作辊旋转板料不断进给并最终成形出三维曲面板类件；分析成形过程中板材的成形机理，并说明成形凸曲面件与鞍面件时辊缝调节方法；建立曲面轧制成形控制理论与方法；给出了当工作辊弯曲形状为弧形时，弯曲半径的计算方法；分析曲面柔性轧制的特点。叙述了曲面柔性轧制设备的设计方案、主要结构及参数；完成设备整体结构及关键部件设计，包括可换芯式调形单元总成、工作辊总成、变速箱总成等；给出了工作辊总成的设计方案，对工作辊与支撑辊的选择进行说明，直线轴符合可弯柔性辊要求且表面光滑硬度高，因此选择直线轴作为工作辊，而钢丝软轴具有良好的挠性及可传递性，从而选择表面经过磨削处理的钢丝软轴作为支撑辊；对设备中关键零部件进行校核及有限元分析，包括丝母、三横梁、导柱等，结果表明，这些关键部件均满足设计要求。二、在成形工艺探索及实验研究方面总结了工作辊调形方式，包括渐进调形与一次调形方式。渐进调形应用于调形量大，一次完成调形较困难而进行的多次形状调整。一次调形应用于调形量小，只需一次调整即可完成目标形状；对工作辊驱动方式进行研究，包括单端驱动与双端驱动，双端驱动工作辊转动均匀，不产生滞后；提出曲面柔性轧制的三种典型成形工艺，即一次、渐进及闭环成形工艺。一次成形工艺工作辊调整一次，即可完成成形。渐进成形工艺需多次成形才能逐渐贴近目标件形状。闭环成形工艺可在成形过程中根据成形要求及信息反馈实时调整辊形状，要求自动化控制程度高。得到效果较好的实验件，包括凸曲面件与鞍面件；应用三维光学扫描仪对实验件进行扫描并通过逆向工程手段将扫描结果还原成曲面，在这个基础上对成形结果进行分析；对比了成形参数变化对成形件形状的影响，参数包括辊缝高度、弯曲半径与板料厚度；对曲面柔性轧制的成形缺陷进行研究，包括“中浪”、“边浪”与条状压痕等。三、在曲面柔性轧制数值模拟研究方面对数值模拟中的理论进行说明，包括显式动力学、连续介质力学、弹塑性材料本构关系等；提出整体工作辊离散化的建模方案，即应用若干刚性短辊组成整体工作辊，在模拟时这些被调整形态的短辊围绕自身轴线旋转，恰当地模拟了弯曲辊旋转形态；对数值模拟时刚性短辊的局部坐标系与整体模型的全局坐标系关系进行说明，并通过矢量合成手段解决短辊下压时产生的偏差问题；最后给出数值模拟结果，效果较好，与实验件基本吻合。研究了不同参数对曲面柔性轧制成形件形状及应力应变影响，参数包括辊缝高度、弯曲半径、成形速度及摩擦力；随着辊缝高度的减小，成形件两个方向的曲率都有所增加；随着弯曲半径的增大，成形件纵向曲率增加，而横向曲率减小；随着成形速度的增加，纵向曲率减小而横向曲率略有减少；随着摩擦力的增加，纵向曲率与横向曲率均有所减少；参数对成形件形状影响的研究可以为工作辊形状调节、板形控制等提供理论基础。整体来讲，曲面柔性轧制的应力分布较均匀，应力应变分布都随参数变化而发生特定的变化；在数值模拟基础上，对成形件的形状精度及厚度变化进行研究。介绍了数值模拟中载荷的计算过程；采用数值模拟的手段，对成形载荷进行分析，得出x、y、z三方向载荷的变化趋势，指出z方向载荷是板材产生塑性变形的主要来源，而y方向载荷可以近似认为是板材运动的驱动力；分析了辊缝高度、工作辊弯曲半径、摩擦系数及板料材质对z向载荷的影响；分析了曲面柔性轧制成形载荷的特点：成形载荷由轧制力与弹性力共同组成，其中轧制力引起板材的塑性变形，而弹性力引起了板料的横向弯曲变形；分别给出了两部分力的计算方法，对比了载荷理论计算数值与数值模拟值之间的区别与联系。更多还原

【Abstract】 Surface flexible rolling (SFR) is a novel method to form3D sheet metal parts and to someextent, it can be considered as the combination of the traditional rolling and Multi-pointadjusting technology. The basic principle of SFR is to employ two bendable working rolls,whose strength and stiffness in radial direction are sufficient enough, as the forming tool. As therolls rotating,3D sheet metal parts will be formed continuously. Through the different workingroll bending shapes and roll gap distribution modes, the typical formed parts such as convexand saddle surface with different shapes will be formed. The critical content of SFR is thestructural design and shape adjusting of the bendable working rolls and in this study, the idea ofworking roll assembly is put forward and linear axis is selected as the working rolls and wireflexible shaft ground is used as the supporting rolls. Compared with the forming method above,SFR realizes the continuum and flexibility of forming for3D sheet metal parts and has a highvalue in the aspects of engineering application and academic. The specific research contentsand conclusions are summarized as followings,Theory research and forming equipment development of SFR:Surface flexible rolling employs two integral bendable working rolls, which still can rotatearound their axis despite in the state of being bended, as the forming tool. The bending shape ofworking rolls is regulated by the adjusting units. In the forming process, the bending of workingrolls causes the plate to produce a bending deformation in the transversal direction; that thenon-uniform roll gap makes an uneven compression in the thickness direction of sheet metalcauses the different elongations in the longitudinal direction. As the rolls rotating, the plate isfeeding constantly and3D sheet metal parts will be formed finally. The forming mechanism ofthe formed parts in the processing process was analyzed and the roll gap adjusting method ofconvex and saddle surface parts was explained; the controlling theory and method of SFR wasestablished; the calculating method of bending radius was showed when the roll shape is arc;the characteristics of SFR was introduced.The design scheme, main structure and parameters of the SFR forming equipment were introduced; the overall structure and the design of key parts including the adjusting unitassembly whose copper set are replaceable, working roll assembly and gearbox assembly, etc.were accomplished; the design scheme of the assembly of working rolls were showed and theselecting process of working roll and supporting rolls was introduced. Linear axis meets therequirements of bendable flexible rolls and has a smooth and hard surface, so it is used as theworking rolls. The flexibleness and transitivity of wire flexible shaft are favorable, so the wireflexible shaft is selected as the supporting rolls; the critical parts including the big nut, threebeams and guiding pillar, etc. in the forming equipment were checked and the result is thatthese components can satisfy the design demand.Forming technology exploration and experimental study of SFR:The adjusting modes of the working rolls were summarized, including gradual and oncemode. The gradual one is applied when the adjusting amount is large and the rolls needregulating many times to finish the target shape. The once one is applied when the amount issmall and need adjusting only once; the driving mode including single-end and both-end of theworking rolls were studied and in the both-end mode, the working roll rotates uniformly andproduces no lagging; three typical technology of SFR were put forward, namely, once, gradualand closed-loop technology. In the once mode, the working rolls are regulated once toaccomplish the processing. In the gradual mode, the roll shape needs regulating many times tofinish the forming. In the closed-loop mode, the roll shape can be regulated in the formingprocess according to the forming requirements and feedback information and this mode requiresa very high degree of controlling automation.The fine experimental parts has been obtained, including convex and saddle surface parts;the experimental parts were sensed by3D binocular optical sensing device and the results weremade into surface by means of the reverse engineering and based on the surface, the formingresults were analyzed; the impacts of forming parameters on the shapes of the formed partswere compared and analyzed, the parameters include roll gap height, bending radius and sheetmetal thickness; the forming defects in the SFR forming process were researched, the defectsinclude middle wave, side wave and stripe pressure mark.Numerical simulation of SFR:The theories in the model building process were explained, including explicit dynamics, continuum mechanics and elastic-plastic material constitutive relations, etc.; the model schemeof the working roll discretion was put forward, namely, the whole working roll is dispersed byseveral short rigid rollers and in the simulation process, the rollers are rotating around their axisand simulating the working roll rotation appropriately; the relations between the localcoordinate system of the rigid short rollers and the global one of the overall model wereexplained and the approach of vector synthesis was applied to solve the deviation problem ofthe short rollers moving down in the local one; finally, the numerical simulation results, whichare in accordance with the experimental ones, were displayed.The different parameter influences on the shape and stress-strain of the formed parts werestudied and the parameters are including roll gap height, bending radius, forming speed andfriction. Along with the roll gap height decreasing, the two main curvatures of the formed partare increasing. Along with the bending radius of the working rolls, the longitudinal curvature isincreasing and the transversal one is decreasing. Along with the forming speed increasing, thelongitudinal curvature decreases and the transversal decreases a little. Along with the increasingof the friction, the longitudinal and transversal curvatures are both decreases. The research ofparameter impact on the shape of formed parts will supply the theoretical foundation for theworking roll regulation and part shape controlling. Generally speaking, the stress distribution ofthe stress in the SFR is uniform and stress-strain distributions will change specificallyaccording with the parameters changing; the numerical simulation method was employed tostudy the shape error and the thickness changing.The load calculating method in the numerical simulation was investigated; based on thenumerical simulation method, the forming load was analyzed and the load changing trends inthe directions x, y and z have been obtained; the load in z-direction is the major source of plateplastic deformation and the one in y-direction can be considered approximately as the power todrive the plate to move forward; the influences of roll gap height, working roll bending radius,friction factor and materials on the z-direction load were analyzed; the characteristic of the loadin the SFR was analyzed and the load is composed of the rolling force and elastic force. Therolling force causes the sheet metal to be deformed plastically and the elastic one causes theplate to be bended in the transversal direction; the load calculating method was introducedsystematically; the load values calculated by the theory and that of the simulation were compared and analyzed.更多还原