新型热冲压高强钢22MnB5(Nb&V)的热变形本构关系

为了研究新型热冲压高强钢22MnB5 (Nb&V)高温流变力学行为,采用热模拟试验机Gleeble-1500D,在550～850℃温度区间,分别以0. 1、0. 5、1和5 s~(-1)的应变速率进行等温单向拉伸实验,得到相应实验条件下的真应力-应变曲线。综合考虑应变量、加工硬化、应变速率和温度等因素的影响,采用Johnson-Cook模型描述了流变应力方程,将建立的新型高强钢本构模型应用于热冲压数值模拟中,得到板料变形过程的载荷变化曲线,并与实验数据进行对比表明,该模型能准确描述不同变形条件下的流变应力-应变曲线,较好地再现了变形过程中的加工硬化、应变速率强化以及温度软化等效应。     

轿车侧围零件冲压开裂网格应变分析

网格应变测量系统是专用于测量汽车车身用钢在冲压过程中变形的分析设备.以某国产轿车侧围零件为例,选择ARGUS网格应变测量系统为工具,通过网格应变分析,找到了冲压开裂的原因,并从模具和材料两个方面提出了优化方案,在实际生产中得到了较好地验证.     

汽车用5182铝合金板温冲压实验研究及数值模拟

以5182铝合金板本构方程为基础,采用ABAQUS有限元模拟软件对5182铝合金板温冲压过程进行数值模拟,研究冲压温度和冲压速度等工艺因素对板材成形性能的影响;通过温冲压实验探讨5182铝合金板在不同冲压温度、冲压速度下的极限拉深比(LDR)。实验及模拟结果表明:冲压速度为0.1 mm/s时,合金的LDR值并非随着温度的升高而单调增加;冲压温度为523 K时,随着冲压速度的增加,LDR值逐渐降低;5182铝合金板的冲压性能主要受变形过程中板材的温度梯度与应变速率的影响;模拟结果与实验结果具有良好的一致性。     

基于DEFORM 2D的纯铜管热挤压过程的数值模拟

通过二维建模软件建立管材立式挤压模型,采用DEFORM2D大型有限元数值模拟软件进行纯铜管热挤压过程的数值模拟,获得了不同挤压速度下变形材料内部的温度场、应力场、应变场及应变速率场的变化规律。分析结果表明,随着挤压速度的提高,变形材料内部的温升和等效应变速率明显提高;等效应力是先提高,而在高速挤压时又下降;等效应变则无明显变化。     

模具温度和凸模速度对超高强钢热冲压成形的影响(英文)

高强钢板热冲压作为一种创新工艺逐渐被用于汽车领域制造超高强度的零件。实际上,由于在热冲压过程中材料表现出高度非线性的弹塑性以及热固响应行为,实验很难全面考察热成形过程。因此,有必要建立超高强钢板热冲压三维弹塑性热固耦合的有限元模型。同时,在高温拉伸试验的基础上,测试超高强钢的高温力学性能,并建立和应变、应变速率、温度相关的材料本构模型。此外,采用热冲压试验结合数值模拟研究模具温度和凸模速度对方盒形件超高强钢热冲压的影响规律,在测试热成形零件性能的基础上,得到优化的模具温度和冲压速度。     

基于DEFORM 2D的纯铜管热挤压过程的数值模拟

通过二维建模软件建立管材立式挤压模型，采用DEFORM2D大型有限元数值模拟软件进行纯铜管热挤压过程的数值模拟，获得了不同挤压速度下变形材料内部的温度场、应力场、应变场及应变速率场的变化规律。分析结果表明，随着挤压速度的提高，变形材料内部的温升和等效应变速率明显提高；等效应力是先提高，而在高速挤压时又下降；等效应变则无明显变化。     

材料流变行为的温度和应变速率补偿研究

采用Gleeble-3500热模拟试验机,对实验材料进行热压缩变形,研究了该材料在850~1000℃和应变速率为5~20s-1条件下的高温流变应力行为。考虑到实验过程的实际温度及应变速率与实验设定值存在差异,实验对材料高温变形过程进行了温度补偿和应变速率补偿,并给出了实验材料的变形常数(β、α、激活能Q)在材料高温变形过程中的连续变化规律,使传统的本构方程更加准确。     

铝合金板料多道次成形极限预测研究

为了解决轻量化车身铝合金板料多道次冲压成形有限元仿真的准确性问题,以各向异性铝合金板料在非线性应变路径下的成形极限预测为研究对象,讨论了预变形对后工序成形极限图的影响,研究了获得预变形均匀应变场的试验方法,引入了与应变路径无关的成形极限预测模型,并介绍了PEPS模型的极坐标转换方法,结果表明：成形极限应力图可以更准确地预测轻量化车身铝合金板料二次加载条件下的成形极限,优于目前仅依赖材料供应态FLD模型的有限元分析准确性。     

基于Zener-Hollomon因子的Ti40阻燃合金开裂准则研究

采用热模拟压缩试验与有限元分析相结合的方法,对Ti40阻燃合金在温度900～1100℃、应变速率0.01～10 s-1范围内的热变形开裂问题进行了研究.发现Ti40合金的临界开裂变形量εf随变形温度和应变速率的变化规律可用一个单变量Zener-Hollomon因子表示,并与1nZ成线性关系.在此基础上,运用冷成形过程广泛采用的Oyane准则对Ti40合金的开裂行为进行了分析.发现Oyane准则能够准确地预测Ti40合金压缩过程中开裂发生在最大臌肚的外表面处,且开裂的临界Cf值随变形温度升高和应变速率降低而增加,与1nZ也成线性关系.由此得到的Ti40合金高温变形下的开裂准则能够更直观地反映变形参数与开裂的临界Cf值之间的关系,为成功地预测Ti40合金高温变形时的开裂提供了有力的依据.     

冲压速度对高温合金卡圈成形的影响

为了研究冲压速度对高温合金卡圈在高温下冲压成形的影响,基于ABQUES/Explicit有限元软件对GH4169高温合金卡圈热冲压过程进行数值模拟,对比分析了不同冲压速度下卡圈残余应力、等效塑性应变和厚度的变化,并与试验数据进行对比,验证了冲压有限元模拟的准确性.结果 表明:在不同冲压速度下,卡圈的残余应力、应变以及厚...     

钛合金空心风扇叶片成形三维有限元分析

随着高旁路涡扇发动机在军用、民用飞机上的应用,采用超塑成形/扩散连接(SPF/DB)技术制造大尺寸钛合金宽弦风扇叶片已经成为涡扇发动机的一项关键制造技术.钛合金空心风扇叶片的成形过程包括3个阶段:扭转成形、热成形、超塑成形.在本研究中,为了分析空心风扇叶片的成形过程,建立了一个三维有限元模型,钛合金的变形行为符合Backofen方程.通过三维有限元模型,分析扭转速率、热成形模具下落速度、超塑成形目标应变速率、板材与模具之间的摩擦系数、芯板和面板的厚度比等参数对成形力的影响规律.研究表明,随着扭转速度、热成形模具的下落速度、目标应变速率、板材厚度比的提高,成形力将提高,而摩擦系数对成形力的影响很小.     

轿车非典型U形件冲压成形工艺及模拟研究

利用板料成形模拟软件Dynaform对某轿车非典型U形件的冲压成形过程进行模拟,研究凸、凹模间隙、凸模速度、摩擦因数等对板料成形后厚度的影响,经多次模拟及对模拟结果进行分析,确定可行的成形工艺参数,用于指导实际生产。     

基于刚黏塑性本构关系的钛合金空心整体结构成形过程三维有限元分析

建立了钛合金空心整体结构成形过程的三维有限元模型.采用刚黏塑性本构关系,基于Marc有限元程序,分析了工艺参数对成形的影响.研究表明,扭转速度的提高使扭矩仅有较小的变化;当模具速度和应变速率提高时,热成形的成形力和超塑性成形的气压将提高.随成形温度降低,成形力显著提高,当温度高于900℃时,扭转成形的扭矩、热成形的成形力和超塑性成形的气体压力随温度的变化均不明显.在有限元分析的基础上,选取合适的工艺参数制备了钛合金空心整体结构模拟件,成形后的钛合金空心整体结构件面板厚度的实测值和模拟计算值具有相同的变化趋势,两者吻合良好.     

Combined experimental and numerical analysis of bulge test at high strain rates using split Hopkinson pressure bar apparatus

High strain rate bulge test technique which is introduced in this paper adopts a rubber-pad as pressure carrying medium to bulge a sheet metal at high velocity using split Hopkinson pressure bar (SHPB) system. The experimental set-up is based on conventional hydraulic bulge test which is modified to mount on SHPB. The thickness thinning of the sheet metal during the test will be considered as a measure of true strain of the bulged sheet. The theoretical approach is developed in this study to attain pressure–strain curves of sheet metals during high strain rate bulge forming process. This approach is followed by a finite element simulation of the process in ABAQUS/Explicit software. To verify the developed method, analytical and finite element methods are compared with experiments.     

Experimental characterization of sheet metal deformation during electro-hydraulic forming

A novel experimental technique, that combines high-speed imaging and digital image correlation techniques, has been developed and applied to investigate the high-rate deformation behavior of aluminum sheet during electro-hydraulic forming (EHF). Aluminum alloy AA5182-O sheets (1 mm thick and ∼152 mm diameter) were EHF deformed by high-energy (up to ∼21 kJ) pressure-pulse and the time-evolution of sheet-displacement, velocity, strain and strain-rate quantified. The data shows that different locations on the sheet undergo unique deformation history that is not apparent from the conventional post-mortem strain measurement (using etched circle/grid pattern) approach. Under the experimental conditions used in this work, the sheets were formed into domes and the maximum strain-rate observed was ∼664/s. Further, this maximum strain-rate was observed at an off-apex location and was ∼2.5 times greater than the maximum strain-rate at the dome apex. The maximum velocity observed was ∼100 m/s and the velocity-time data showed evidence of pressure-wave reverberations during the forming process. We believe that knowledge of such time-evolution of sheet deformation is necessary for a better understanding and accurate modeling of sheet formability that has often been reported to exceed quasi-static forming limits under high-rate forming conditions.     

Reduction of a pre-formed radius in aluminium sheet using electromagnetic and conventional forming

Electromagnetic (EM) forming is a high-speed forming process that uses the forces induced on a conductive workpiece by a transient high frequency magnetic field to form the workpiece into a desired shape. This paper describes the results of a work undertaken to study the reduction of a 20 mm radius to 5 mm in 1 mm AA 5754 sheet by conventional metal forming process and by electromagnetic forming. The combination of conventional and EM forming will be referred to as “hybrid forming”. The 20 mm radius was pre-formed from flat sheet using a conventional die, punch and binder that allowed the material to draw in. The radius was then reduced to 5 mm, with no draw-in allowed for either process. Sheets were studied in the as-received condition and were also pre-strained to 5%, 10% and 15% to simulate strain path effects in a multiple stage forming operation. The process was modelled numerically to gain insight into the stress, strain and strain rate histories. The research indicates that features that are not achievable using traditional stamping techniques can be obtained with the aid of EM forming.     

Improvement of formability of 6xxx aluminum alloys using incremental forming technology

Aluminum sheet is becoming increasingly common as an automotive body panel material. The heat-treatable aluminum alloys of the 6xxx series are widely used as an outer panel material, due to their ability to precipitation harden during the paint-bake cycle, resulting in improved dent resistance. Increasing the formability of these alloys would allow for multiple parts of less complex geometry to be combined into a single more complex part, thereby avoiding the costs associated with any subsequent joining operations. Incremental forming is a process that can improve material formability through the use of short, recovery heat treatments applied between increments of deformation. The objective of this study was to investigate the incremental forming behavior of 6111-T4 an alloy, which is often used for exterior body panel applications. Interrupted tensile testing was used to simulate the incremental forming process. The effect of different heat-treatment parameters on mechanical properties was analyzed. The heat treat regimen developed for uniaxial testing was then applied to a series of plane strain tests using a hemispherical punch, to simulate the more complex states of stress found in forming operations.     

固体颗粒介质成形新工艺及变形研究

固体颗粒介质成形新工艺,是采用固体颗粒代替刚性凸模(或弹性体、液体)的作用,对金属板料成形的工艺。固体颗粒介质成形新工艺,即可以解决流体介质、粘性介质的密封难题,又具有内压非均匀分布、便于控制成形、提高材料成形极限、降低投资成本、所得零件表面质量高、成品率高的优点,且固体颗粒无工业污染,可重复使用。该工艺为材料的加工制备提供了新的方法和手段。利用塑性增量理论,对自由变形区任意一点的应变进行了分析,得到了自由变形区任一点的应变及厚度计算公式。采用固体颗粒介质成形工艺,进行板料成形试验,成功试制出多种典型工件;对试验件壁厚分布的计算值和实测值进行了比较,证明理论正确。     

Determination of the flow curve at high strain rates using electromagnetic punch stretching

A simple new method is proposed and applied to determine the flow curve of aluminum alloy 1100-O at high strain rates. A high-speed camera was used to record the free flying process, from which the retrieved images were used to characterize the impacting velocity. The determined flow curve was established by combining the effective stress retrieved from the simulation and the effective strain measured from the deformed workpiece. Moreover, an iteration procedure was utilized to improve the accuracy of the determined flow curve. Using the determined flow curve to simulate the forming process, the simulated deformation performed good agreement with the experimental result, where the deviation of effective strain could be reduced from 17.9% to 6.74%. Besides, the effective strains reached in these high rate forming experiments exceed the effective strain at failure determined in a quasi-static tensile test. The material could be deformed to the effective strain of 0.56 without any fracture.     

Superplastic forming characteristics of fine-grained 5083 aluminum

Superplastic forming characteristics of a fine-grained 5083 aluminum sheet have been investigated by means of gas-pressure forming of a rectangular pan. This part geometry lends itself to a simple representation in terms of nearly one-dimensional sheet stretching and permits reasonably rigorous control of strain rate throughout the forming cycle. This study followed a study of the uniaxial tensile properties carried out on this alloy. A two-stage forming cycle, which comprised a short, rapid prestraining stage followed by a stage of slower rate of superplastic straining, was used because the uniaxial tensile work showed enhancement of superplastic response of this alloy under this condition. The study examined the effect of process parameters such as initial gas pressurization rate, level of hydrostatic pressure, and lubricants on the thinning characteristics of the sheet, especially along the die entry radii. The gas pressure/time cycle was suitably modified to avoid premature sheet failure due to excessive sheet thinning or cavitation. Cavitation under the biaxial forming condition and the effect of hydrostatic pressure on cavitation suppression were evaluated. A defect-free pan with sharp corners was formed.