耦合温度和应变率的铝合金板成形极限预测方法

为了提高铝合金板成形能力,一些先进成形工艺已经被开发。温成形是实现铝合金高成形能力和高成形精度的一种有效方法。温度和成形速度是影响铝合金板温成形工艺的重要参数,对其成形性能影响十分显著。提出一种综合考虑温度和应变率影响的铝合金板成形极限预测方法。采用响应面法建立铝合金板应变硬化指数n、应变率敏感度指数m与成形温度、应变率条件之间的力学性能函数关系;基于M-K理论,并结合Logan-Hosford屈服函数,推导出耦合温度和应变率的铝合金板成形极限图计算模型。模型检验表明力学性能响应面方程具有较高精度。成形极限的计算结果与已有的试验值对比表明,二者吻合较好,这证实耦合温度和应变率的铝板成形极限预测方法是正确和可靠的。     

Effects of temperature and driver sheet for magnesium alloy sheet in magnetic pulse forming

Thermal effect from warm temperature is always used to improve the formability of AZ31 magnesium alloy sheet. However, it is seldom employed to deform AZ31 sheet in magnetic pulse forming process, due to increasing resistivity and decreasing effect of high strain rate. In this study, Al driver sheets without heating were used to strength effect of high strain rate and drive AZ31 sheet with warm temperature to deform. Method of numerical simulation was used to analyze magnetic pulse forming of AZ31 sheet with driver sheet and temperature. Magnetic flux density and magnetic force with and without Al driver sheet (thickness of 1, 1.5, and 2 mm) and different temperature (25, 100, 150, 200, and 250°C) were investigated. Deformation processes and velocity with Al driver sheet and different temperature were analyzed. The results indicate that it is better for formability of AZ31 sheet to adopt 1-mm Al driver sheet at higher discharge energy and warm temperature.     

板材粘性介质压力成形粘性附着力影响因素试验研究

针对粘性介质压力成形过程是粘性介质与板材耦合的变形过程,不易确定板材在粘着应力作用下变形行为的情况,自行设计了粘性附着力拉伸试验装置,将粘着应力作为板材拉伸力,直接测量粘着应力对板材变形的作用。采用聚甲基乙烯基聚合物作为成形传力介质,初步研究了粘性附着力拉伸过程板材受到的粘性介质粘性附着力对板材变形的影响以及粘性附着力的影响因素。试验结果表明,增大板材表面压力差、提高粘性介质流动速度及提高粘性介质压力有利于提高粘性附着力的作用。研究结果可为合理利用粘性附着应力作用,提高板材成形性提供理论基础。     

Analysis of the bulging process of an AZ31B magnesium alloy sheet with a uniform pressure coil

As the lightest metal material, magnesium alloy is widely used in the aerospace, automobile, and consumer electronic industries. However, magnesium alloy sheet has poor formability at room temperature. Electromagnetic forming is a high velocity forming technique that can promote the formability of low ductility materials, improve the strain distribution of workpieces, and reduce their wrinkling and springback. In this work, a uniform pressure coil was used to bulge AZ31B magnesium alloy sheets. The finite element method was then used to analyze this bulging process. The bulging contours and displacements of AZ31B magnesium alloy sheets were consistent with the experiment results. The distribution of the magnetic field intensity and magnetic field forces were found to be better than using a flat spiral coil. The deformation rule of AZ31B magnesium alloy sheet using the uniform pressure coil differed from that using the flat spiral coil. The largest strain occurred at the center of the sheet.     

A novel approach for temperature control in ISF supported by laser and resistance heating

Aeronautical applications often require small batches of large-scale sheet metal parts made from titanium and its alloys. Due to the low formability of titanium at room temperature, warm forming processes are necessary. Incremental sheet metal forming (ISF) is suitable for production of prototypes and small batches as well as large-scale parts. A short review of the experimental work done by international scientists in the field of warm ISF including stationary and moved temperature sensors will be presented mostly applied from the backside of the sheet metal. The present paper shows a new approach for a tool setup including a thermocouple inside of the tool. Hence, the sensor for temperature measurement was moved with the forming zone. Furthermore, a suitable closed loop control including a PID controller will be presented. The characteristics of the controller will be discussed. By means of two different warm ISF processes (ISF with resistance heating and laser-assisted ISF), the applicability of the developed setup will be analysed and evaluated. It will be shown that the experimental setup is capable to ensure minimal temperatures needed to ensure adequate formability of Ti grade 5.     

利用激光局部硬化效应提高2B06铝合金板材拉深成形性研究

针对2B06铝合金复杂零件成形困难问题,提出了利用激光热处理局部硬化提高板材成形性的思路。在通过激光热处理试验研究了铝合金板的激光硬化效应的基础上,采用数值模拟计算了铝合金板激光热处理过程中激光光斑路径和其周边热影响区域的峰值温度场,并通过实际测温验证了其准确性。提出并构建了耦合性能梯度的差性坯料模型,对激光局部硬化的杯形件拉深成形性进行了模拟和试验研究。结果表明,激光扫描方式可以形成稳定的梯度温度场并对周边非加热区影响较小,且可以通过多道次扫描方式设计不同宽度范围的大梯度差性板材坯料。力学性能试验表明激光热处理可以有效地提高铝合金的局部加工硬化能力,这种效应可以有效抑制杯形件拉深时圆角大变形区的减薄,从而提升了板材的拉深性能。在上述基础上,将激光局部热处理用于2B06铝合金航空复杂口框零件的成形,通过设计激光处理路径和参数,获得合理的局部硬化区域,可有效地避免在加强筋处出现过度减薄导致的破裂,大大提高复杂零件的成形性。     

铝合金磁脉冲辅助板材冲压技术研究进展

铝合金板材室温下的成形性较差,但在高速变形条件下成形极限大幅提高。为了促进铝合金板材在汽车制造、航空航天及3G领域的应用,需要开发先进的板材成形技术。磁脉冲辅助板材冲压成形技术（EMAS）通过在普通冲压模具中嵌入线圈,能有效控制和改善变形板料的应变分布。针对这些问题,重点介绍和讨论了EMAS技术的国内外研发现状,阐明了开展该技术研究的必要性和重要意义。     

Formability analysis on the process of multi-point forming for titanium alloy retiary sheet

The multi-point forming (MPF) process of spherical surface parts of titanium alloy retiary sheet and titanium alloy sheet metal with different thickness and curvature radius was simulated by an explicit finite element software. Contradistinctive analysis between retiary sheet and sheet metal forming parts with different modes were done. The simulation results show that under the same forming conditions, titanium alloy retiary sheet is not easy to wrinkle and springback, whereas it is easy to form. The reason for differences in the formability of above-mentioned sheet metal is also analyzed. A non-wrinkling limited graph and a fracture critical graph for spherical surface parts of retiary metal sheet and metal sheet were obtained. Finally a forming test of titanium alloy cranial prosthesis was done in MPF press. Testing results indicate the customized 3D curved surface of prosthesis can be adequately shaped and the forming quality was guaranteed.     

镁合金板成形工艺参数对其成形性能的影响

镁合金热成形时的工艺参数对其成形性能有很大的影响,探讨该影响规律具有重要研究意义。基于国内外镁合金板热拉深的研究现状,论述了成形温度、模具结构与尺寸、压边条件、拉深速度、摩擦和润滑条件等工艺参数对镁合金热成形性能(极限拉深比LDR)的影响规律,指出未来镁合金塑性成形技术的研究方向。     

Process metallurgy design of aluminum alloy sheet rolling by using two-scale finite element analysis and optimization algorithm

Recently, the asymmetric rolling (ASR) process was applied to the aluminum alloy sheet generation to control the micro-crystal structure in order to improve the formability and the strength. Until now, many experimental and numerical studies of ASR process have been carried out, but these schemes have not enough capability to predict the texture evolution at the micro-scale and the sheet formability at the macro-scale. In this study, we develop a process metallurgy design code to analyze and optimize the sheet rolling process. At first, our dynamic-explicit crystallographic homogenized elasto/viscoplastic finite element (two-scale FE) code was applied to analyze ASR sheet deformation and optimized ASR process to generate a high formability sheet metal by employing the response surface method. A texture evolution of ASR sheet metal under an optimum process condition was compared with the experimental results, and the availability of our design code was confirmed. Next, an initial texture for the symmetrical warm rolling was optimized to generate a better formability sheet metal. Consequently, our two-scale FE code combined with the optimization algorithm was verified as a comprehensive tool in the process metallurgy design to predict plastic induced texture evolutions and optimize a rolling process and an initial texture for a high formability sheet generation.     

点阵热源加热板料成形技术研究

初步试验验证板料温成形中,采用离散化热源和均匀热源相比能够进一步提高板料成形性能的基础上,提出点阵热源加热板料温成形新技术。基于有限元仿真,采用0Cr18Ni9不锈钢板料对点阵热源加热成形过程进行验证和初步研究。研究结果表明,点阵热源加热板料成形工艺是完全可行的,在相同热量的情况下,通过控制点阵热源的分布可以得到比均匀热流加热更大的极限拉深比;采用点阵热源加热拉深得到的零件壁厚分布一般存在两个明显的谷值,第一个谷值点在凸模圆角处,和最大拉深力有关,第二个谷值点在零件直壁上,是由于凸缘部位的高温材料拉深成直壁变成传力区以后因温度高承载能力下降引起的。     

Experimental and numerical study of stamp hydroforming of sheet metals

The objectives of this research was to experimentally and numerically study the stamp hydroforming process as a means for shaping aluminum alloy sheets. In stamp hydroforming, one or both surfaces of the sheet metal are supported with a pressurized viscous fluid to assist with the stamping of the part thereby eliminating the need for a female die. The pressurized fluid serves several purposes: (1) supports the sheet metal from the start to the end of the forming process, thus yielding a better formed part, (2) delays the onset of material failure and (3) reduces wrinkle formation. This paper focuses on the experimental and numerical results of the stamp hydroforming process utilizing a fluid pressure applied to one surface of the sheet metal. The effects of applying a constant, varying and localized pressure to the surface of 3003-H14-aluminum sheet alloy were evaluated. Experiments demonstrated draw depths improvements up to 31% before the material failed. A failure prediction analysis by Hsu was also carried out to predict an optimal fluid pressure path for the varying fluid pressure case. The commercial finite element analysis code Ls-Dyna3D was used to numerically simulate the stamp hydroforming process. Both isotropic and anisotropic material models were used and their predictions compared against the experimental results. The numerical simulations utilizing Barlat's anisotropic yield function accurately predicted the location of the material failure and the wrinkling characteristics of the aluminum sheet.     

金属微弯曲成形方法的研究

介绍微弯曲成形方法——激光微弯曲成形以及塑性微成形方法。并提出了激光辅助加热微弯曲成形方法。即激光辅助加热待加工件使其达到合适的温度范围后进行微弯曲成形的方法，提高难成形材料的微塑性成形能力和质量。     

镁合金板材温热成形韧性破裂准则

针对镁合金板材温热成形数值模拟过程中无法精确判断材料损伤破裂失稳的技术难题,建立考虑温度效应的镁合金板材温热成形韧性破裂准则;基于单向拉伸试验和温热成形极限试验,采用试验和数值模拟相结合的研究方法,确定镁合金板材温热成形韧性破裂准则中的材料参数;以建立的考虑温度效应的镁合金板材韧性破裂准则作为判断破裂的标准,对AZ31镁合金板材的温热成形极限进行预测,并且通过温热拉延试验进行试验验证。研究结果表明,考虑温度效应的镁合金板材韧性破裂准则适合镁合金温热成形数值模拟,应用建立的韧性破裂准则成功的预测板材温热破裂方式,揭示板材温热成形韧性破裂机理,预测结果与试验结果体现较好的一致性。     

AZ31镁合金盒形件变压边力温热拉延工艺

通过温热交叉轧制工艺制备了板形以及成形性能良好的AZ31镁合金薄板;开发了可加热的变压边力双动液压机,并详述其工作原理;采用不同的压边力方案,对盒形件进行温热拉延实验,分析了变压边力对AZ31镁合金板材温热拉延性能的影响。结果表明:最佳的压边力变化方案是压边力随凸模行程先增后减的模式;采用变压边力技术可以将AZ31镁合金盒形件的拉深深度提高13·2%。     

铝合金阶梯形件粘性介质压力成形的研究

通过压缩试验得到了粘性介质的应力－－应变关系、压力衰减随冲头加载速率及时间变化的规律。采用有限元软件DEFORM分析了在不同压边力下分别用钢凸模和粘性介质成形铝合金阶梯形件的工艺过程。结果显示，采用VPF可以提高板料的成形性。根据模拟结果，采用VPF成功地制备了阶梯形件，这表明有限元法对VPF试验具有很好的指导意义。     

A new approach for deformation history of material elements in hole-flanging produced by single point incremental forming

This paper combines plasticity and circle grid analysis to investigate the deformation mechanics and failure in hole-flanging produced by single point incremental forming (SPIF). The approach is based on circle grid analysis and allows tracing strains and stresses along the deformation history of material to compare their maximum achievable values against necking and fracture limits in the principal strain and stress spaces. The overall methodology draws from the independent characterization of necking and fracture limits by means of sheet metal formability tests to the appraisal of strain loading paths in hole-flanging with blanks having different pre-cut hole diameters. The work is supported by experimentation in aluminium AA1050-H111 and the overall investigation widens previous research in the field by presenting the first set of experimental data covering the history of material strains, stresses and their corresponding formability limits.     

T6态7075铝合金的温拉深成形研究

温热成形是铝合金板料成形的重要方法。通过改造后的极限拉深比试验与方形盒试验,研究了T6态的7075板料在不同温度下的等温以及非等温拉深性能,并通过对成形后材料强度进行单向拉深试验,分析了经过温成形后材料强度和硬度的变化。结果表明,T6态铝合金在140～220℃左右拉深性能最好,且成形后可以保持足够的强度和硬度,所以最佳的温拉深成形温度为140～220℃。     

润滑条件下铝合金板成形模拟中摩擦模型的研究

对润滑条件下铝合金薄板筒形件拉深成形过程进行了工艺分析，在作出一些简化和假设的基础上，建立了基于流体润滑的筒形件拉深成形过程摩擦模型；将该模型运用到板料成形过程有限元分析中，计算出筒形件成形时摩擦系数动态变化的数值；开发出基于探针测试的铝合金板温成形动态过程摩擦测试系统，并对筒形件成形时的摩擦系数进行了测试实验。计算结果与实验数据表明，板料成形过程中的摩擦系数不是一个常数，随着凸模行程的增加，摩擦系数具有增加的趋势。     

Al-Mg-Si基合金车身板材成形极限及数值应用

采用成形极限图（FLD）试验,运用网格应变自动测试分析系统ASAME,对Al-Mg-Si基合金车身板的成形极限进行了检测,同时,将FLD应用于有限元分析作为成形时出现破裂缺陷的判据,并分析车门外板在冲压成形过程中破裂危险部位主应变在FLD上分布。结果表明：Al-Mg-Si基合金板材的成形极限高于目前常用的AA6111铝合金车身板;拉延筋的形状和位置对成形过程的影响很大,采用双曲面法设计车门可以改善车门腹部拉深不充分引起的刚度问题。