Multi-Point Forming Technology for Sheet Metal

Multi-point forming (MPF) is an advanced manufacturing technology for three-dimensional sheet metal parts. In this paper, the MPF integrated system is described that can form a variety of part shapes without the need for solid dies, and given only geometry and material information about the desired part. The central component of this system is a pair of matrices of punches, and the desired discrete die surface is constructed by changing the positions of punches though the CAD and control system. The basic MPF process is introduced and the typical application examples show the applicability of the MPF technology. Wrinkle and dimple are the major forming defects in MPF process, numerical simulation is a feasible way to predict forming defects in MPF. In conventional stamping, the mode to form sheet metal with blankholder is an effective way to suppress wrinkling; the same is true in MPF. A MPF press with flexible blankholder was developed, and the forming results indicated the forming stability of this technique. Based on the flexibility of MPF, varying deformation path MPF and sectional MPF were explored that cannot be realized in conventional stamping. By controlling each punch in real-time, a sheet part can be manufactured along a specific forming path. When the path of deformation in MPF is designed properly, forming defects will be avoided completely and lager deformation is achieved. A work piece can be formed section by section though the sectional MPF, and this technique makes it possible to manufacture large size parts in a small MPF press. Some critical experiments were performed that confirmed the validity of two special MPF techniques.

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.

Numerical simulation of wrinkle phenomenon during multi-point forming process of shallow rectangle cup

In this paper, the principle of multi-point forming (MPF) technique is presented. One of the most serious defects, wrinkling, during the multi-point forming process of a shallow rectangle cup is discussed by means of numerical simulation on the shallow rectangle cup forming process. The effects of thickness, material of sheet metal and the pressure of the blank holder are investigated. Based on the simulation results, the reasons and control methods of wrinkling are pointed out. Moreover, the experiment on the multi-point die forming of the shallow rectangle cup by the MPF machine is done to validate the efficiency of the numerical simulation, and the result proves that the application of an elastic cushion in the forming can restrain wrinkling efficiently.

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.

Numerical simulation on the process of multi-point forming for tube

To apply the multi-point forming technology to the field of tube processing,the process of multi-point forming for tube is studied.Numerical simulation for the process of multi-point forming for tube is achieved by using elastic-plastic FEM in ABAQUS.During simulation,reasonable coefficient of mass scaling and friction model of penalty function are used.The influence of several major technological parameters on the process is analyzed.When the tube diameter is 60 mm and the forming curvature radius is 1000 mm,the distortion rate of cross-section and the absolute forming error gradually decrease with the increasing of tube wall thickness;However,when the tube wall thickness is constant,the smaller the curvature radius,the larger the distortion rate of cross-section,but as to forming part,its absolute forming error becomes smaller.

Improving effect on forming quality and accuracy using a polyurethane board positioning/resetting the discrete steel pad in multi-point forming

To improve the quality of multi-point die forming, a new approach using discrete steel pads was proposed. The formability of three different multi-point die forming processes was analyzed through numerical simulation and experiments. Numerical simulation and experimental results showed that the use of discrete steel pads in the multi-point forming process can substantially improve the stress–strain state on the plate and suppress dimple, straight-edge, and wrinkle defects. This analysis verified that the use of discrete steel pads in a multi-point forming process can effectively improve the quality and accuracy with which sheet metal is formed.

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。

精密金属丝网拉伸成形有限元分析及工艺优化

目的针对喇叭防尘网罩在拉伸成形过程中的起皱、折叠和断裂等质量问题,研究工艺参数对拉伸质量的影响特性,探寻较佳工艺参数。方法应用Deform软件模拟喇叭防尘网罩的拉伸成形过程并进行仿真验证。在单一条件下分别研究冲压速度、压边间隙、摩擦因数以及凹凸模圆角半径对喇叭网罩拉伸极限的影响规律。以拉伸极限为评判标准,对丝网直径、压边间隙、摩擦因数和冲压速度4个工艺参数进行正交试验优化,结合极差分析研究以上4个因素对评判标准影响的主次关系及最佳工艺参数。结果各参数按对拉伸极限的影响由大到小的顺序依次是丝网直径、压边间隙、摩擦因数、冲压速度,最佳工艺参数如下:丝网直径为0.065mm、压边间隙为0.2mm、摩擦因数为0.05、冲压速度为30mm/s。结论通过有限元模拟与分析,确定了影响产品质量的主要工艺参数及影响特性,通过试验实现了最佳工艺参数组合,提高了产品质量。

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。