Optimization on springback reduction in cold stretch forming of titanium-alloy aircraft skin

An optimization method was presented for cold stretch forming of titanium-alloy aircraft skin to determine process parameters and to reduce springback.In the optimization model,a mathematical formulation of stress difference was developed as an indicator of the degree of springback instead of implicit springback analysis.Explicit finite element method(FEM)was used to analyze the forming process and to provide the stress distribution for calculating the amount of the stress indicator.In addition,multi-island genetic algorithm(MGA)was employed to seek the optimal loading condition.A case study was performed to demonstrate the potential of the suggested method.The results show that the optimization design of process parameters effectively reduces the amount of springback and improves the part shape accuracy.It provides a guideline for controlling springback in stretch forming of aircraft skin.

Process design for multi-stage stretch forming of aluminium alloy aircraft skin

A process design approach for multi-stage stretch forming was proposed by combining the strain distribution method and finite element method(FEM)to determine the minimum stage number and deformation amount of each stage.The strain distribution method was used to calculate the deformation amount of each stage and evaluate the formability through a safety criterion.FE simulation was taken as an analysis tool to reveal the deformation behaviour,to predict the strain contour and to determine the process parameters at each stage.To evaluate the effect of heat treatment after pre-strain on occurrence of deformation defects during the subsequent deformation,a multi-stage uniaxial tension test for 2B06 aluminium alloy sheet was carried out.A case study demonstrates that the approach has high reliability and good practicability.

Simulated and experimental investigation of stretch sheet forming of commercial AA1200 aluminum alloy

The simulation and experimental results obtained from stretching test of a commercial sheet of AA1200 aluminum alloy were compared and evaluated. Uniaxial tensile tests were carried out to obtain the required input parameters for simulation. Finite element analysis of the forming process was carried out using Abaqus/Explicit by considering von Mises and Hill-1948 yield criteria. Simulation results including punch force and strain distribution were compared and validated with the experimental results. The results reveal that using anisotropic yield criteria for simulation has a better match in both cases with the experiments.

Stretch Forming Simulation of Woven Composites Based on an Orthotropic Non-Linear Material Model

Characterisation experiments have been conducted on a woven self-reinforced polypropylene composite (SRPP) including uniaxial and bias extension tests. Outcomes of these experiments were employed to develop a non-linear orthotropic material model within an incremental deformation framework. The material model of the woven composite was implemented into a finite element simulation to predict stretch forming behaviour of SRPP specimens. The predicted strain paths at the pole of specimens were verified against experimental outcomes. It was shown that specimens possessing different aspect ratios deform under a wide range of deformation modes from uniaxial extension to biaxial stretch modes. Finally, the effect of different forming parameters on the strain path evolution of the woven composite was elucidated through numerical simulations. It was shown that the aspect ratio of the samples plays an important role in forming behaviour of woven composites. Development of a reliable and accurate numerical model for predicting forming behaviour of woven composites and understanding their main forming mechanisms promote and encourage the extensive application of these materials systems in a wide range of mass producing industries. Adopting woven composites in manufacturing industrial components facilitates addressing environmental concerns such as recyclability and sustainability issues.

Unveiling the planar deformation mechanisms for improved formability in pre-twinned AZ31 Mg alloy sheet at warm temperature

To investigate the role of pre-twins in Mg alloy sheets during warm planar deformation,the stretch forming is conducted at 200℃.Results suggest the formability of the pre-twinned AZ31 Mg alloy sheet is enhanced to 11.30 mm.The mechanisms for the improved formability and the deformation behaviors during the planar stretch forming are systematically investigated based on the planar stress states.The Schmid factor for deformation mechanisms are calculated,the results reveal that planar stress states extremely affect the Schmid factor for{10-12}twinning.The detwinning is activated and the prismatic slip is enhanced in the pre-twinned sheet,especially under the planar extension stress state in the outer region.Consequently,the thickness-direction strain is accommodated better.The dynamic recrystallization(DRX)type is continuous DRX(CDRX)regardless of the planar stress state.However,the CDRX degree is greater under the planar extension stress state.Some twin lattices deviate from the perfect{10-12}twinning relation due to the planar compression stress state and the CDRX.The basal texture is weakened when the planar stress state tends to change the texture components.

T型截面铝合金型材零件成组加工技术研究与应用

针对目前飞机T型材零件单件弯曲成形效率低成形精确差的问题,提出了T型材弯曲件成组拉弯成形的成组加工方法。基于截面尺寸、引导线的曲率半径等信息建立了成组分析算法,对T型材进行分组,使用长型材拉弯成形后切割分段得到符合精确外形要求的T型材零件。通过理论计算、模拟分析和拉弯试验,验证了T型材拉弯成形成组加工技术的可行性,该方法提高了零件的制造效率和成形精度,可以大幅度降低人工矫正的工作量和加工成本。

TiAl基合金格栅结构预制空位拉制成形研究

为解决TiAl基合金板材制备困难、成形性能差以及难以采用传统方法制造格栅结构的问题,采用预置空位拉制成形方法制造TiAl基合金格栅结构。在烧结温度1150℃、烧结压力30 MPa、保温时间2 h条件下,通过预合金粉末热压烧结工艺制备TiAl基合金。TiAl基合金板料预制空位拉制成形温度为990℃,应变速率为0.001 s^(-1)。结果表明,随着板材变形长度增加,空位形状变化为纵向菱形→正方形→横向菱形,空位沿板材分布比较均匀,与模拟结果相符;板材最大拉应变位置由空位圆角处转移到空位交叉处,最大拉应变值为0.5。当TiAl基合金预置空位板材变形长度最大达到89 mm时,变形区伸长率为112%。

后拉伸条件对羟基化聚丙烯中空纤维膜性能影响的研究

合成研究了不同羟基插入率的羟基化聚丙烯(PPOH),使用熔融纺丝-拉伸法(MS-S)制备了PPOH中空纤维膜并探究了热拉伸温度、热拉伸比例对其孔径分布、孔隙率、水通量和力学性能的影响。相比聚丙烯(PP)中空纤维膜,相同条件下制备的PPOH中空纤维膜的水通量更高,孔径更大,拉伸强度和孔隙率则较低。当热拉伸温度为110℃、热拉伸比例为150%时,PPOH中空纤维膜的孔径为0.139μm,孔隙率为22.1%,水通量为1 822 L/(m2·h),拉伸强度为123 MPa。

马鞍形蒙皮拉形工艺参数仿真优化与试验验证

对某马鞍形蒙皮零件在拉形过程中的起皱和破裂现象进行了研究,以得到消除缺陷的方法。采用作图法,对该蒙皮零件进行了工艺性分析,确定了工艺参数的范围,用正交试验方法设计了数值模拟方案,利用AI-FORM软件拉形模块进行了模拟仿真,并对仿真结果进行了评估,确定了一种最优的方案,并再次进行了有限元仿真验证,最后在拉形机上进行了拉形试验。发现试验结果与有限元仿真结果吻合很好,消除了起皱和破裂等缺陷,提高了零件的成形质量。结果表明,对此蒙皮零件,拉形轨迹前部分采用较大伸长率,拉伸到4.9%,后部分采用较小伸长率,最终拉伸到7%,有利于避免起皱和破裂。另外,相较于FormCAM,AI-FORM在起皱模拟方面具有明显优势。

铝合金双曲率薄壁件电磁渐进辅助拉伸成形工艺方案设计与开发

目的针对铝合金双曲率薄壁件传统拉伸成形工艺成形均匀性差的问题,提出一种采用电磁渐进辅助拉伸成形的高精度成形工艺。方法设计电磁渐进辅助拉伸成形工艺方案,基于有限元仿真软件LS-DYNA R13.0,建立拉伸成形和电磁成形有限元模型。通过数值仿真研究线圈移动路径和放电电压组合对成形质量的影响以及薄壁件的整体贴模成形过程和等效塑性应变。结果与单程放电相比,双程放电能够大幅度提高板材变形均匀性。与以中间值电压连续放电以及先大电压后小电压的放电电压组合相比,在先小电压后大电压的放电电压组合下,板材的成形质量更高。选择线圈双程顺序移动路径和7 kV-10 kV放电电压组合,通过10次拉伸和9层54次放电,得到了减薄率仅为3%的贴模性良好的双曲率薄壁件。变形量基本呈现随着放电层数的增加而不断降低的趋势。电磁放电仅扩展更大的塑性应变区域,不改变已贴模区板材的塑性应变值。结论与拉伸成形相比,电磁渐进辅助拉伸成形工艺有效提高了板材的塑性变形程度并极大控制了回弹的发生。

火箭箱底大型薄壁零件拉形工艺及回弹补偿研究

根据单拉实验获得火箭箱底大型薄壁零件所使用的硬化不锈钢材料力学性能参数。通过分析薄壁曲面件的结构特点,制定拉形工艺参数并研究回弹补偿系数对成形贴胎度的影响,通过数值模拟与实验验证的结果获得该类硬化不锈钢回弹补偿系数为1.588。拉形工艺回弹补偿系数的运用为实际生产提供理论基础和实践经验,并且对该类硬化不锈钢薄壁双曲类零件的批量化生产具有深远的指导意义。

2024T3铝合金蒙皮拉形数值模拟与试验验证

蒙皮是构成飞机气动外形的关键零件,通常采用拉形工艺进行生产。基于通用分析软件ABAQUS,对2024T3铝合金蒙皮拉形进行了数值模拟,研究了板料尺寸、夹钳移动距离、模具上顶高度、摩擦因数对拉形主应变、次应变和厚度的影响,并通过试验进行验证。研究结果表明,当板料尺寸增大、夹钳移动距离减小、模具上顶高度减小、摩擦因数减小时,蒙皮的主应变减小、厚度增大,成形质量较好。

薄壁曲面拉伸成形失稳起皱数值模拟

起皱作为薄板成形中的常见缺陷,严重影响曲面成形质量。为研究不同加载路径下的曲面失稳起皱现象,设计了三种加载路径,并对相应成形过程进行数值模拟。结果表明,加载路径对成形曲面起皱现象具有较大影响;受到较大压应力时,处于悬空状态的板料因约束不足易产生面外失稳而出现起皱;板料与模具间的摩擦力可减小板料承受压应力,可通过调整板料与模具的接触状态,进而对起皱有效抑制;采用最小变形加载路径,板料与模具接触良好,可获取光滑、无起皱缺陷曲面。

核能发电用主设备封头锻件制造技术的选择与应用

基于实际研发制造业绩,重点介绍了反应堆压力壳封头、蒸汽发生器封头、稳压器封头、补水箱封头等多种典型核电主设备封头锻件的制造技术及应用情况,讲述了热拉伸成形工艺、胎模旋压全仿形锻造工艺、胎模旋压与热拉伸复合成形工艺、胎模旋压半仿形锻造与气割修刨组合成形工艺、拉伸成形与管嘴翻边复合成形工艺等典型工艺的优缺点,总结了封头制造技术的选用原则,为核电封头制造的质量稳定性和标准化生产提供依据。

矩形截面型材拉弯成形

针对铝合金矩形中空截面挤压型材进行了不同预拉和补拉的拉弯成形试验研究 ,获取了预拉和补拉对成形精度的影响规律 .截面畸变是影响成形精度最主要的因素 ,由弯曲过程中的径向压力引起 .试验表明 ,型材靠模弯曲即发生截面畸变 ,主要表现为上腹板的塌陷 ,沿型材长度方向截面畸变量不同 ,最大畸变量并不位于型材中间对称截面处 ;增大预拉和补拉 ,截面畸变增大 .弯曲卸载回弹是影响零件贴模度的主要因素 ,其大小受多种因素影响 ,规律复杂 .增大预拉和补拉 ,回弹减小 ;当预拉和补拉增大到一定值时 ,增大拉伸量减小回弹的效果不再明显 .

柔性三维拉弯成形零件的形状控制

对柔性三维拉弯成形工艺进行了研究,给出了三维弯曲成形件的数学表达式.通过分析柔性三维拉弯成形过程中型材的水平和垂直方向的变形,给出了控制成形件水平方向和垂直方向形状的单元体调形方法与夹钳的拉弯轨迹计算方法.根据柔性三维拉弯工艺中单元体调形多点控制的特点,定义了多点模具的调形参数,给出了单元体与成形件接触的几何关系,并给出了描述单元体上多点模具包络形状的三次B样条插值方法.基于上述的几何关系和多点模具的调形参数,使用圆弧对夹钳的拉弯轨迹进行计算.对L形截面铝型材的三维拉弯成形实验结果表明,成形件轮廓误差小于0.7%,验证了上述方法的实用性.

VTL1000型数控蒙皮拉形机运动仿真系统

为预先发现并避免拉形过程中可能出现的轨迹错误、意外碰撞等缺陷,开发了VTL1000型数控蒙皮拉形机运动仿真系统。给出了系统的流程和体系结构,研究了拉形轨迹的计算、拉形轨迹与机床运动参数的转换两项关键技术及相关算法。在CATIA环境下,采用组件应用架构二次开发技术,实现了系统的开发。通过对实际蒙皮零件拉形过程机床的运动仿真,验证了系统的实用性和稳定性。

镜面蒙皮拉形工艺参数研究

滑移带是导致飞机镜面蒙皮报废的主要原因之一。通过分析镜面蒙皮拉形中变形程度、拉形速度、毛料几何尺寸、润滑与操作方式对滑移带的影响，确定了临界变形程度和拉形应变速率的合理范围。毛料几何尺寸的影响，反映在悬空段板料的宽长比值上，宽长比值增加，变形趋向于平面应变状态，易出现滑移带。良好的润滑方式有利于改善板料变形的均匀性，增加成形面内材料的变形程度。操作方式的选择，应充分考虑模具拉胀的作用，严格控制夹钳预拉量和补拉量，避免冲击和阶跃式的加载方式。

铝合金型材拉弯成形研究进展

文章着重对封闭截面型材的拉弯成形 ,从型材力学性能研究、起皱、截面畸变和回弹 4个方面简述目前研究状况 ,提出了若干需着重研究的基础性问题和今后研究发展的方向 。