成形极限图的测试、应用和可信度分析

成形极限图也称成形极限曲线,常用FLD或FLC表示.成形极限图是判断和评定金属薄板成形性的最为简便和直观的方法,是对板材成形性能的一种定量描述,是解决板材冲压问题的一个非常有效的工具,同时也是对冲压工艺成败性的一种判断曲线.相对于通常使用的基本成形性能指标(σs、σb、δ10)及杯突值而言,成形极限图可以较好地反映材料的极限变形能力,定量衡量钢板冲压成形性能的好坏.对具体冲压零件成形后的应变进行测试和分析,得到零件表面应变分布情况,将应变分布点放在该材料的成形极限图中,有助于科学评估板材对零件的实际成形效果,通过分析零件变形大小与成形极限的关系,可以确定零件冲压成形的危险部位、材料使用是否合理.     

东汽EQ153柴油车油底壳应变分析与选材预测

用ＳＰＣＥＮ和０８Ａｌ两种薄板材料坟东汽ＥＱ１５３柴油车油度壳，用应自动测试系统（ＡＳＡＭＥ）对成形后的应变进行分析。作出成形极奶图，确定了危险部位；评价了两种钢板的成形效果，对优化选材进行预测，指出了应变硬化指数ｎ为０．２１的钢板是冲压该油底壳的最佳网板。     

汽车冲压零件分类的一种新方法

提出了一种汽车冲压零件分类的新方法,根据零件的几何形状和实际冲压成形过程中危险部位的变形特点,将汽车零件分为3种类型,并对32种汽车零件进行了分类。     

成形极限图的测试、应用和可信度分析

成形极限图通常是通过钢模胀形试验测得，实际测量的成形极限图与ASAME自动应变测试分析系统模拟计算的成形极限曲线吻合较好。应用成形极限图分析冲压零件成形的安全裕度和进行选材预测时，对以平面应变和胀形为主的成形零件具有较高的可信度，而对以深拉延变形为主的成形零件可信度不高。     

提高网格数据处理精度的新方法

介绍了在板材冲压智能化研究中,用坐标网格法分析锥形件形成规律时采用的更精确的数据处理方法,给出了各变形质点精确的应变值（而不是一个小区域内的平均值）,并与以往所用方法得到的结果进行了比较,该方法对更准确地分析锥形件及其它形状零件在冲压成形过程中应力、应变的分布特点及冲压成形机理,进而实现成形过程的智能化控制具有重要意义。     

平面应变用于评定薄钢板成形性能的研究

对大量汽车零件进行冲压成形分析，表明平面应变在零件的危险区域中是个重要因素。用两种方法测定了薄钢板的平面应变值，其结果接近，但拉伸试验法较成形极限试验简单。此外还探讨了平面应变在评定薄钢板成形性能方面的实际应用。     

汽车翼子板零件应用技术研究

通过对汽车翼子板零件投料冲压试验，对零件进行了应变测试分析，评价试验钢板的成形效果；分析了冲压工艺，表面粗糙度和板厚等条件零件冲压生产的影响，得到翼子板零件的最佳用材方案及冲压工艺条件。     

润滑条件对汽车零件冲压成形的影响

用３种润滑条件进行了一种汽车零件的冲压，对零件盛开有后的应变进行分析，比较了３种润滑条件下的成形效果。并对无润滑条件下的优化选材进行预测，认为该零件可以实行无润滑冲压。     

网格应变技术在汽车门内板开裂分析中的应用

利用网格应变技术对汽车门内板DC56D+Z潜在开裂位置进行了分析,测量了零件冲压过程中风险位置的减薄率、主次应变等数据,掌握了材料的流动规律。同时,将测量数据与成形极限图FLD进行对比分析,计算出零件的成形安全裕度。结果表明,试验钢的冲压减薄率25%,且沿轧向45°方向减薄率最大;材料整体的安全裕度为9. 5%,存在潜在失稳风险;主应变较大区域发生于凹槽偏上侧壁处。实际生产中,可通过减少板面尺寸,优化压延筋位置和尺寸,降低材料的局部压边力,提高成形效果。     

应变分析方法在金属薄板拉深成形中的应用

用应变分析方法测量和分析接深试验过程中拉深杯件各个区域的应变分布情况和应变变化历史,还分析了典型实物拉深零件JD90型摩托车油箱的应变分布特点,最后提出了确定接深成形零件危险部位的方法。     

Material Determination of Vehicle Part Using Strain Analysis Method

The experiment regarding material determination of a vehicle part was conducted.The experiment on stamping production of a part using the steels A, B and C was made. The strain data on the deformed parts were measured. The forming limit diagrams for the steels were examined and evaluated. The results show that three steels are unsuitable for this stamping part. The desired material properties with an optimal strain hardening exponent value were determined using experimental and analytical methods. The steel D was chosen as a desired material. The results show that the steel D is appropriate for mass production. In addition, the feasibility of the application of thinner material to this part was studied. The validity of the material selection was verified theoretically and experimentally.     

Peter Groche

Tube hydroforming (THF) is a relatively new but established technology among metal tube forming processes. It is the technology of forming closed sections, hollow parts with different cross‐sections by applying an internal hydraulic pressure and sometimes additional axial compressive loads to force a tubular blank to conform to the shape of a given die cavity. Material properties have a significant influence on the process stability. Often roll‐formed, non‐heat treated tubular materials made of steel with longitudinally oriented welding lines are used in tube hydroforming. Different production processes involve a change of the material properties from the initial flat sheet to the hydroformable tube. Testing methods such as tensile tests and conventional forming limit diagrams do not accurately reflect the state of stress and strain conditions seen in the tubular blank during the hydroforming process. Thus, inaccuracies in FEA predictions and design failures occur. Test methods were developed to characterize the relevant geometrical and mechanical properties of tubular semi‐finished products.     

汽车用高强低合金钢成形性能的研究

对本钢HC260LA、HC340LA、HC420LA系列汽车用高强低合金钢进行金相组织检验、常温力学性能测试和成形极限试验,并将力学性能试验和成形试验结果导入AUTOFORM仿真软件,进行冲压仿真模拟。结果表明:本钢汽车用高强低合金钢系列产品力学性能和成形性能良好,加工硬化指数n≥0.11,塑性应变比r值约1.0,伸长率A_g≥12%,在平面应变状态下的极限应变值FLD0大于20%,满足生产汽车纵梁等结构件的要求。     

Experimental and Numerical Failure Criteria for Sheet Metal Forming

For sheet metal forming, often the forming limit diagram (FLD) is used as failure criterion as it can be derived easily in experiments. It is based on the assumption that localization of strain in the sheet plane is responsible for crack initiation, but application of FLD is limited to linear strain paths. Hence, only forming processes with approximately the same deformation history as the experiments carried out for FLD determination should be evaluated by this criterion. Forming limit stress diagrams (FLSD) do not exhibit such strict limitations. They are based on the assumption that principal stresses in the sheet plane are responsible for crack initiation. As these stresses are usually calculated by FE analysis using elastic plastic material laws, strain hardening is considered. Two‐step forming tests as application examples prove the FLSD to be adequate for evaluation of non‐linear forming processes with alternating forming directions. Nevertheless, FLSD are derived in extensive investigations which makes them unattractive for most industrial applications. Furthermore, both FLD and FLSD do not consider the physical background of ductile crack initiation which is provoked by an interaction of local stress triaxiality and equivalent plastic strain. Hence, a reliable failure criterion should concentrate on these two parameters. The Gurson‐Tvergaard‐Needleman‐ (GTN‐) damage model can predict crack initiation during sheet metal forming. Application of the GTN model to 2 step forming tests with the bake hardening steel H220BD+Z showed good agreement to experimental results although a sensitivity of the model to mesh size and stress triaxiality is observed.     

Experimental and Numerical Study of Electromagnetic Forming of AZ31B Magnesium Alloy Sheet

Wrought magnesium alloys are interesting materials for automotive and aeronautical industries due to their low density in comparison to steel and aluminium alloys, making them ideal candidates when designing a lower weight vehicle. However, due to their hexagonal close‐packed (hcp) crystal structure, magnesium alloys exhibit low formability at room temperature. For that reason, in this study a high velocity forming process, electromagnetic forming (EMF), was used to study the formability of AZ31B magnesium alloy sheet at high strain rates. In the first stage of this work, specimens of AZ31B magnesium alloy sheet have been characterised by uniaxial tensile tests at quasi‐static and dynamic strain rates at room temperature. The influence of the strain rate is outlined and the parameters of Johnson‐Cook constitutive material model were fit to experimental results. In the second stage, sheets of AZ31B magnesium alloy have been biaxially deformed by electromagnetic forming process using different coil and die configurations. Deformation values measured from electromagnetically formed parts are compared to the ones achieved by conventional forming technologies. Finally, numerical study using an alternative method for computing the electromagnetic fields in the EMF process simulation, a combination of Finite Element Method (FEM) for conductor parts and Boundary Element Method (BEM) for insulators, is shown.     

应变分析方法用于汽车零件选材的研究

用 0 8AL、0 3AL、WIF钢三种板材冲压一种汽车零件 ,利用应变分析方法评价了三种板材的成形效果 ,对优化选材进行研究 ,预测了最佳使用材料的应变硬化指数n值。     

三通阀体零件多向主动加载成形过程数值模拟

利用有限元分析软件Msc.marc模拟三通阀体零件多向主动加载成形过程。通过分析各种多向主动加载的等效应变云图及凸模的受力情况，确定最佳的工艺成形方案，并通过速度矢量图详细论述其金属成形时的流动规律，为此类零件的工艺设计提供依据。