【作者】 贾彬彬；

【导师】 苑世剑； 王卫卫；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2018， 博士

【摘要】 航空、航天、船舶等行业板材零件具有批量少、品种多的特点,适合采用多点模具成形技术进行生产。为解决传统多点模具成形存在的回弹大和易起皱难题,本文提出了力-位移可调多点模具成形新工艺。核心思想是将力和位移分别控制,使板材各区域始终在法向约束下发生变形,实现曲面件精密成形。本文以圆柱面件和马鞍面件为研究对象,通过理论分析、数值模拟和实验研究,阐明不同力和位移加载条件下的变形规律和回弹规律,揭示全区域法向约束条件下起皱和回弹抑制机制,为曲面件力-位移可调多点模具成形提供理论指导和技术支持。通过力-位移可调多点模具成形过程力学分析,阐明了不同成形阶段各区域板材应力状态,分别给出了法向约束力上限值和下限值。上限值与压头和板材之间摩擦系数成反比,高于上限时出现减薄、开裂缺陷;下限值与板材厚度成正比,低于下限时出现欠成形缺陷;推导了板材在法向约束条件下的弯矩计算公式,揭示了全区域法向约束对减小回弹的作用机制。板材截面受面内切向拉应力作用,使板材拉应力区增加、压应力区减小,中性层向内移动,导致弹复弯矩减小,进而减小了板材回弹量;获得了双向弯曲作用下的板材变形规律。双向弯曲使板材反复受拉应力和压应力作用,能够显著增加内层和外层的塑性变形量,其分布具有中心区小、边缘区大的特征;采用能量法建立了板材临界起皱应力模型,揭示了法向约束力抑制起皱的机制。因法向约束力的作用,板材抗失稳能力明显增加,临界起皱应力提高与法向约束力成正比。利用Python语言二次开发实现参数化建模,建立了力-位移可调多点模具成形数值模型,分析了不同加载条件下圆柱面件和马鞍面件应力应变状态与变形行为。板材由传统多点成形的整体弯曲变形变为分段分区双向反复弯曲变形,通过不同阶段局部双向弯曲变形的累积实现整体变形。与传统多点模具成形相比,弹复弯矩下降了17%,因而使回弹量显著下降;与先边缘后中心加载相比,先中心后边缘加载的板材塑性变形和厚度分布更加均匀。与压头对称排布相比,压头非对称排布的板材塑性变形和厚度分布更加均匀。在力-位移可调多点成形中,马鞍面件中心区经向和纬向均为拉应力状态,因此不出现起皱缺陷。研制出力-位移可调多点成形装置,通过实验研究了不同约束力条件的缺陷形式,建立了约束力加载成形窗口。在过夹持区,两列压头之间板材产生台阶式变形,进而产生减薄、开裂缺陷;在欠夹持区,过渡区和中心区板材与上压头之间出现间隙,导致板材出现欠成形缺陷。通过圆柱面件力-位移可调多点成形实验研究,获得了不同位移加载方式和压头排布方式下壁厚与回弹分布规律。板材壁厚均呈现出边缘区小、中心区大的分布趋势,且随约束力增加,减薄率增加,但最大减薄率仅为2.2%,表明力-位移可调多点成形件壁厚分布均匀。对于铝合金和低碳钢,回弹量比传统多点成形分别下降了83.7%和43.6%。建立了基于分段调形的回弹补偿方法,获得了不同材料板材回弹补偿规律。回弹补偿能够显著改善工件贴模效果,提高工件曲率分布均匀性。进行了马鞍面件力-位移可调多点成形起皱行为实验研究,揭示了起皱抑制机理。马鞍面件力-位移可调多点模具成形中,板材在成形全过程中均受法向力约束,不存在悬空区,板材起皱现象被显著抑制。通过实验获得了不同约束力条件下缺陷形式。当约束力低于下限时,出现欠成形缺陷。进行了不同压头排布方式的实验研究,获得了不同接触条件下的马鞍面件变形规律。与对称排布相比,非对称排布时,马鞍面件折痕显著减弱。更多还原

【Abstract】 The sheet metal parts in aviation,aerospace,shipbuilding and other industries have the characteristics of small batch and multiple varieties,and are suitable for multi-point die forming technology for production.In order to solve the problem of large springback and wrinkling inclination in traditional multi-point die forming,a new technology of multi-point forming by adjusting force-displacement is proposed.The core idea of the technology is to control the force and displacement separately,thus the plates are always deformed under normal constraints,so as to realize the precision forming of curved parts.In this paper,theoretical analysis,numerical simulation and experiment are used to study cylindrical parts and saddle parts.The laws of deformation and springback under different loading and displacement loading conditions are clarified,and the mechanism of wrinkle and springb ack suppression under the normal constraint condition is revealed.The aim is to provide theoretical guidance and technical support for the realization of multi-point forming by adjusting force-displacement for curved parts.Through the mechanical analysis of multi-point forming by adjusting force-displacement,the stress state of the plate in different forming stages is clarified,and the upper and lower limits of the normal binding force are given respectively.The upper limit is inversely proportional to the friction coefficient between the indenter and the plate,and the crack appears when the binding force is higher than the upper limit.The lower limit value is directly proportional to the thickness of the plate,and the defect occurs when the binding force is lower than the lower limit.The formula of the plate at bending moment under normal constraint condition is deduced,and the mechanism of normal constraint on reducing the springback is revealed.Under the action of tangential tensile stress,the tensile stress zone of the plate increases,the compressive stress zone decreases,and the neutral layer moves inward,which leads to the reduction of the elastic bending moment,thus significantly reducing the resilience of the plate.The deformation law of plates under two-way bending is obtained.Two-way bending makes the plate repeatedly subjected to tensile stress and compressive stress,which can significantly increase the plastic deformation of the inner and outer layers,and its distribution characteristics are smaller in the central area and larger in the marginal area.The critical wrinkling stress model of sheet metal is established by energy method,and the restraining mechanism of normal constraint on wrinkling is revealed.Due to the effect of normal constraint,the anti-buckling ability of sheet metal is obviously increased,and the critical wrinkling stress is proportional to the normal constraint force.The parameterized modeling of the numerical model was realized by the secondary development of the Python language.The numerical model of multi-point forming by adjusting force-displacement was established.The stress-strain state and deformation behavior of the cylindrical parts and saddle parts under different loading conditions were analyzed.The plates are subjected to piecewise and bidirectional repeated bending deformation rather than the whole bending deformation of traditional multi-point forming process,and the whole deformation is realized through the accumulation of local bi-directional bending deformation at different stages.Compared with the traditional multi point die forming,the elastic bending moment decreased by 17%,and the rebound amount was reduced significantly.Compared with the loading mode of the center forming after the first edge forming,the plastic deformation and the thickness distribution of the plate are more uniform in the loading mode of the edge forming after the center forming.Compared with the symmetrical arrangement of the indenter,the plastic deformation and thickness distribution of the asymmetrical arrangement of the indenter are more uniform.In the multi-point forming by adjusting force-displacement,the longitude direction and the latitudinal direction of the center part of the saddle piece is a tensile stress state,so there is no wrinkling defect.A multi-point forming by adjusting force-displacement experiment device is developed,and the defect mechanism under different binding conditions is studied by experiment.A binding loading forming window is established.The defects in the cracking area is caused by the step deformation of the plate between two columns.In the insufficient deformation area,there plates in the transition zone and the central area cannot be completely in contact with the upper punch,resulting in insufficient deformation of the sheet metal.Experimentally research of cylindrical parts in multi-point forming by adjusting force-displacement were studied.The law of wall thickness and springback distribution under different displacement loading ways and punch arrangement are obtained.The thickness of the plate shows the same distribution trend,that is,the numerical value in the center area is la rge,and the value in the edge area is small.With the increase of binding force,the thinning rate is also increased.The maximum thinning rate is only 2.2%,indicating that the parts produced by multi-point forming by adjusting force-displacement have good wall thickness distribution uniformity.For aluminum alloy and low carbon steel,the resilience decreased by 83.7% and 43.6% respectively compared with traditional multi-point forming.A springback compensation method based on sectional shape adjustment is established,and the springback compensation law of plates with different materials is obtained.Springback compensation can significantly improve the matching effect between workpiece and die,and improve the curvature distribution uniformity of workpiece.The wrinkling behavior of saddle parts in multi-point forming by adjusting force-displacement is experimentally studied,and the mechanism of wrinkle inhibition is revealed.When the saddle parts are deformed by the multi-point forming by adjusting force-displacement,the sheet is restrained by the normal force during the whole forming process,and there is no suspension zone,therefore the wrinkling phenomenon of the plate is greatly suppressed.When the normal force is lower than the lower limit,there is a defect of insufficient deformation.The experimental study on different arrangement methods of punch was carried out,and the deformation rules of saddle parts under different contact conditions were obtained.Compared with the symmetrical arrangement of the punch,the fold of the saddle part is significantly weakened when the punch is asymmetrically arranged.更多还原