Effect of stamping deformation on microstructure and properties evolution of an Al–Mg–Si–Cu alloy for automotive panels

The effect of 5 % tensile deformation, which simulates the stamping process of Al–Mg–Si–Cu automotive outer panels, on the microstructural evolution during age strengthening, has been investigated. In addition, its benefit on key mechanical properties including hardness, yield strength, ductility, and corrosion resistance has been linked to the microstructural features. It was found that the aging precipitation sequence, SSSS → clusters and G.P. zones → β″ → β′ + Q′ → Q, was not influenced by the dislocations introduced through the stamping deformation prior to aging. On the other hand, stamping deformation could promote the formation of precipitates and refine the precipitates because of the enhanced heterogeneous nucleation and the accelerated precipitation kinetics, leading to superior strength of the alloy at the early stage. Meanwhile, the larger amount of Cu incorporated into nanoprecipitates leads to better intergranular corrosion resistance of the stamped alloy compared with the unstamped one. Due to the reduction in free Si amount at grain boundaries, the formation of fine subgrain structures and the increase of dislocation accumulation, the ductility of the stamped alloy was increased.     

Materials selection for hot stamped automotive body parts: An application of the Ashby approach based on the strain hardening exponent and stacking fault energy of materials

Complex stamping operations are becoming widespread in the automotive industry to produce vehicle body parts with adequate mechanical strength and reduced wall thickness. The need for weight reduction drives the development of new metallic materials capable of achieving a good balance between formability and mechanical properties. Advanced high strength steels play a major role in this scenario. The aim of this work was to develop a materials selection strategy for hot stamped automotive body parts using the Ashby approach. The selection process was based on the formability of metallic alloys derived from two fundamentals materials properties, the strain hardening exponent and the stacking fault energy.     

Experimental investigation of stamp forming of unconsolidated commingled E-glass/polypropylene fabrics

Stamp forming of two unconsolidated commingled E-glass fiber/polypropylene fabric composites with nominal weights of 743 and 1485 g/m² has been studied for simple mold geometry. For this manufacturing process, unconsolidated commingled fabrics are transferred directly from an oven to a press where they are stamped using a matched-dies metal mold to achieve simultaneous consolidation and conformation to the mold shape. In this study, the influence of the stamping parameters such as the stamping pressure, stamping temperature, mold temperature, loading rate and holding time are determined on the flexural properties, void content and void distribution. Results obtained for the stamp forming process of the unconsolidated fabrics were compared with results obtained by compression molding of the unconsolidated fabrics and by stamping pre-consolidated fabrics. For the fabric with the higher nominal weight, the flexural properties were found to be lower than the optimal properties, while for the fabric with the lower nominal weight the flexural properties were equivalent to the optimal properties determined by compression molding. Good correspondence was found between the variation of the flexural properties and the variation of the void content. This allows the mechanical properties to be approximated by only measuring the void content. Finally, the minimum temperature at which the stamping pressure has to be applied in order to successfully process the unconsolidated fabrics is determined.     

Multi-regression modeling for springback effect on automotive body in white stamped parts

The use of high strength steel (HSS) materials in automotive body in white (BIW) stamped parts has increased the occurrence of springback after the forming process. Although HSS exhibits superior strength, weight reduction, and crash energy, it strongly influences springback impact on the sustainable development of BIW stamped parts. In this study, an empirical springback prediction model was synthesized based on the contemporary data sets of springback-prone components of automotive BIW stamped parts. Two different BIW stamped parts from an actual industrial stamping production line were selected as pilot parts for this study. A statistical multi-regression (MR) analysis was used to model the springback prediction effect by examining the sensitivity of springback input parameters on existing die geometry. The outputs represent the total springback values of the stamped parts. A total of 240 data from samples of selected stamped parts were tabulated to synthesize the springback prediction model. The results show that the MR models for the two parts were linear with the springback estimated errors between the measured and predicted values between 0.5° and 3°, which is acceptable from an industrial viewpoint. The proposed MR models are capable of predicting the springback effect with minimal error by incorporating all possible variations that are inherent in the shop floor process.     

汽车立柱加强板成形分析

目的轻量化是汽车零部件设计的发展方向,汽车立柱因需要在碰撞中承受外力而变形,并为其他零件提供足够强度和刚度的安装点,一般都使用高强钢材料制造,以达到轻量化的要求。方法对采用DP590高强钢制造的典型结构汽车B柱加强板进行了工艺分析,以提出高强钢立柱加强板零件的设计及成形工艺优化方案。通过AutoForm软件的板料仿真技术,对采用590DP高强钢的典型汽车B柱加强板的冲压工艺进行了数值模拟分析。结果成功预测了板料成形过程中可能存在的起皱、开裂等问题。结论分析结果为汽车立柱加强板冲压工艺提出了改进方案,实现了模具的设计及优化。     

Virtual material testing for stamping simulations based on polycrystal plasticity

In the modern practice of stamping simulation of complex industrial parts the prediction of springback still lacks accuracy. In commercial software packages various empirical constitutive laws for stamping are available. Limited to simple empirical models for material anisotropy they do not take into account in a full manner the effects of microstructure and its evolution during the deformation process. The crystal plasticity finite element method bridges the gap between the polycrystalline texture and macroscopic mechanical properties that opens the way for more profound consideration of metal anisotropy in the stamping process simulation. In this paper the application of crystal plasticity FEM within the concept of virtual material testing with a representative volume element (RVE) is demonstrated. Using virtual tests it becomes possible, for example, to determine the actual shape of the yield locus and Lankford parameters and to use this information to calibrate empirical constitutive models. Along with standard uniaxial tensile tests other strain paths can be investigated like biaxial tensile, compressive or shear tests. The application of the crystal plasticity FEM for the virtual testing is demonstrated for DC04 and H320LA steel grades. The parameters of the Vegter yield locus are calibrated and the use case demonstration is completed by simulation of a typical industrial part in PAMSTAMP 2G.     

Stamp forming of hydroxyapatite filled ethylene vinyl acetate co-polymers: Process optimization using a right angle V-mould

Hydroxyapatite (HAP) filled ethylene vinyl acetate co-polymer (EVA) composites are developed in an attempt to formulate a surgeon friendly material for renovating impaired skull contours. A cost effective technique for obtaining these composites in the clinically significant forms would indeed be a landmark accomplishment. Stamp forming is one of such processes where the cost as well as the performance of the product strikes the right balance. This study was carried out prior to the stamp forming process optimization of the composites into three-dimensional (3-D) contours, essential for applications like cranioplasty. This paper discusses the V-bending results for HAP filled EVA and an attempt to identify a processing window for real manufacturing situations (3-D forming) is made. The processing conditions, such as the stamping temperature, time, and stamping rate, required to give high-quality right angle bends, have been established. The quality of stamped forms is also examined in terms of shape conformance and variation in wall thickness. It has been found that the stamping temperature and velocity were the key factors, which determined the quality of the stamped part. Too high temperatures as well as too high stamping rates lead to severe thinning and degradation of the formed parts. On the other hand, when the temperatures and the stamping rates are too low, the composites do not conform to the mould contour.     

Influence of stamping on the compressive behavior and the damage mechanisms of C/PEEK laminates bolted joints under severe conditions

Bolted joint tests have been performed in order to evaluate the influence of stamping on the behavior of thermoplastic-based woven-ply laminates subjected to structural loadings under severe service conditions (120 °C after hygrothermal aging). Compressive tests have been carried out on carbon fabrics reinforced PolyEtherEtherKetone (PEEK) laminates to investigate fibers buckling due to changes induced by stamping on the non-planar interply structure of woven-ply laminates. As compressive strength decreases by 13% in stamped laminates, it facilitates the plastic buckling of 0° and ±45° oriented fibers due to compressive loads in bolted joints. Contrary to double-lap joints, stamping does not affect the strength of single-lap joints, as the geometry of single-lap joints is non-symmetric. Stamping modifies the damage mechanisms of PEEK-based laminates under bolt-bearing loadings, such as the failure of stamped bolted joints is dominated by bearing failure mode.     

超级钢板料冲压性能的拉伸试验研究

将超级钢应用于国产汽车冲压件的生产中不仅可以提高汽车质量,而且可以降低汽车的成本、减小汽车重量、降低能源消耗和减少环境污染.为了在汽车工业中更好地使用超级钢,概述了板材冲压性能的评价指标,介绍了拉伸试验值对板材冲压性能的影响,并对超级钢进行了拉伸试验.研究了超级钢板的硬化指数、塑性应变比、屈服强度、极限强度、均匀延伸率等机械性能,并分析了超级钢板的冲压成形性能,超级刚具有较好的胀形性能、拉深性能、弯曲性能,抗起皱性能等冲压性能,可以广泛地应用于汽车冲压零件生产中.     

Numerical and Experimental Investigations on Deep Drawing of G1151 Carbon Fiber Woven Composites

This study proposes to simulate the deep drawing on carbon woven composites in order to reduce the manufacturing cost and waste of composite material during the stamping process, The multi-scale anisotropic approach of woven composite was used to develop a finite element model for simulating the orientation of fibers accurately and predicting the deformation of composite during mechanical tests and forming process. The proposed experimental investigation for bias test and hemispherical deep drawing process is investigated in the G1151 Interlock. The mechanical properties of carbon fiber have great influence on the deformation of carbon fiber composites. In this study, shear angle–displacement curves and shear load–shear angle curves were obtained from a bias extension test. Deep drawing experiments and simulation were conducted, and the shear load–displacement curves under different forming depths and shear angle–displacement curves were obtained. The results showed that the compression and shear between fibers bundles were the main deformation mechanism of carbon fiber woven composite, as well as the maximum shear angle for the composites with G1151 woven fiber was 58°. In addition, during the drawing process, it has been found that the forming depth has a significant influence on the drawing force. It increases rapidly with the increasing of forming depth. In this approach the suitable forming depth deep drawing of the sheet carbon fiber woven composite was approximately 45 mm.     

Interface sheet-constrained groove pressing as a modified severe plastic deformation process

In this paper, a new severe plastic deformation (SPD) process entitled interface sheet-constrained groove pressing (ISCGP) as a new variant of conventional CGP has been developed for producing ultrafine-grained metallic materials. In this process, repetitive shear deformation is imposed into the sheet material by utilising symmetrically grooved die along with two interface sheet on both sides. To study the applicability, mild steel sheets were processed by both ISCGP and CGP processes, and mechanical and microstructural properties of the processed samples were investigated. The results show a considerable improvement in mechanical properties including hardness, yield strength, and ultimate tensile strength, though the ductility sacrifice was reduced. Comparing ISCGP and conventional CGP revealed interesting results, which are shown that ISCGP can result in better surface quality and ductility.     

先进高强钢DP1000地板中央通道的成形回弹及补偿研究

高强度钢板因具有较高的强度而易产生严重的回弹缺陷,已成为其应用的最主要瓶颈.为此,本文以某车型地板中央通道零件为载体,针对其几何型面复杂、材料变形程度大的特点,研究先进高强度钢板DP1000的冲压成形回弹及补偿特性.通过对该零件的冲压成形工艺方案进行优化设计和全工序回弹数值模拟,并结合零件的几何特征和变形模式,对各成形工序的回弹进行精确预测.基于预测结果对模具型面采用折入处理的方式进行全工序几何补偿,实现回弹补偿的自工序完结.最后以补偿后的型面进行冲压实验,并对零件的型面尺寸进行检测分析.结果表明,全工序回弹数值模拟和型面几何补偿是解决复杂零件多工序冲压成形回弹问题的最有效方法.通过两次回弹补偿后,该零件的回弹得到完全控制,尺寸精度达到要求且成形质量良好.     

电流辅助高强钢板热成形工艺数值模拟研究

目的探究电流辅助高强钢板热成形工艺中坯料自阻加热的加热机理,揭示电一热一力三场耦合条件下金属板材的塑形变形规律,为工艺方案及工艺参数的制定提供理论依据。方法利用FEM软件对电流辅助高强钢板的热成形过程进行了数值模拟研究。结果获得了通电加热时坯料的温度场,并通过热一力耦合分析,得到了板材热成形时的应力及应变的分布规律。结论采用该加热方式可极大地提高加热速率,经过几十秒的加热即在变形坯料上获得了较均匀的温度场,满足板材热成形要求。应力、应变分析表明,加热时产生的压应力缓解了坯料变形时的应力集中,有助于板料塑性成形。     

碳纤维织物力学性能和冲压成形实验研究

在实际成形过程中,碳纤维复合材料往往处于复杂的应力状态,开展近于真实载荷环境下的力学试验分析,能够更准确地认识实际应用中材料的成形性能和变形机理.为获得碳纤维织物的基本力学特性,设计了平纹碳纤维织物拉伸试样及成形试样,进行了单轴拉伸、双轴拉伸、镜框剪切试验和方盒冲压成形实验研究,对比了不同双拉比及纱线取向对力学性能及成形性能的影响.研究结果表明:碳纤维织物具有高度的非线性、各向异性和双拉耦合特性,即经纬向纤维的力学性能会相互影响;剪切变形是成形过程中的主要变形模式,当剪切角达到临界锁死角时,织物发生起皱现象;同种织物不同纱线取向试样表现出不同的成形性能,因此可以根据零件几何形状选择合适纤维取向的织物,从而减少缺陷,优化成形零件的力学性能.研究结果为后续建立碳纤维织物本构模型和成形仿真奠定了基础.     

Limit Strains Comparison during Tube and Sheet Hydroforming and Sheet Stamping Processes by Numerical Simulation

Hydroforming is a manufacturing process that uses a fluid medium to form a component by using high internal pressure. Tube and sheet hydroforming has gained increasing interest in the automotive and aerospace industries because of its many advantages such as part consolidation, good quality of the formed parts etc. The main advantage is that the uniform pressure can be transferred to every where at the same time. Forming limit is the limit of the component up to that extent it can be formed safely. While analyzing hydroforming process, it is often assumed that the limit strains are identical as that of stamped sheet metal of equivalent material properties. It is not clear if such an assumption is valid. In this paper the forming limit strains during hydroforming is predicted. A series of tube bulge tests for tube hydroforming and limiting dome height test for sheet hydroforming and sheet stamping processes are simulated by a commercial finite element solver to predict the limit strains. Numerical simulation of forming limit strains in tube hydroforming with different internal pressure and different simulation set up with or without axial feeding, while in sheet hydroforming and sheet stamping, by changing the specimen geometry are considered to develop wide range of strain paths in the present work. The effects of process conditions on the forming limit strains are detailed. The comparison of limits strains during hydroforming and stamping processes is presented. Prediction of limits strains is based on a novel thickness based necking criterion.     

Changements of mechanical properties of alloyed steels by Thermomechanical Processing

Two high alloy tool steels of a similar type were ausformed in the temperature range of the metastable austenite. Swaging and forward extrusion were chosen as deformation process. As long as characteristic properties such as deformation velocities, deformation temperatures and the local distribution of deformation temperatures are similar, the mechanical behaviour of the material is mostly independent of the deformation processes. Mechanical properties, such as tensile strength and yield point, increase by ausforming in comparison to the quenched and annealed material condition. Values for ductility slightly drop. The work hardening capability cannot be related to any specific ausforming process.     

冷却速率对聚乙烯管材专用料力学性能的影响

采用不同的冷却方式研究冷却速率对聚乙烯管材专用料力学性能的影响,发现随冷却速率减小,其屈服强度增大,冲击强度先升高后降低,空气冷却时最高,最大差值达12 kJ/m2。通过扫描电子显微镜、热分析、热台偏光及密度法对韧性提高的机理进行了研究,发现PE100管材料在塑性形变中产生的银纹化与其晶片厚度和结晶度相关,空气冷却时,晶片较厚,晶片数目较多,塑性形变中产生空隙较多,冲击断面中形成的银纹较致密,吸收的能量更多,裂纹更难扩展。     

400MPa超级钢板材冲压性能的实验

对400MPa超级钢板材进行了拉伸试验、冷弯试验和金相组织检验,获得了超级钢板的硬化指数、塑性应变比、屈服强度、极限强度等力学性能,并分析了400MPa超级钢板的冲压成形性能,了解这些性能对超级钢冲压件在汽车行业里的应用与生产具有一定的指导作用.     

基于Yoshida-Uemori材料模型的汽车结构件冲压回弹分析

Yoshida-Uemori随动硬化材料模型能够准确描述应变路径发生变化时材料性能的改变,从而较好地反映复杂加载情况下材料的各向异性.本文基于JSTAMP件分别采用Yoshida-Uemori随动硬化材料模型和各向同性硬化材料模型对汽车高强钢结构件的冲压成形进行了仿真分析与回弹预测,研究了不同材料硬化模型对回弹预测精度...     

Evaluation of high temperature mechanical strength of Cr–Mo grade steel through small punch test technique

Remaining life assessment (RLA) of high temperature components calls for estimation current mechanical properties of the component material. For determination of mechanical properties of in-service components, large volumes of samples are required to be cut from components. The sample() removal warrants post-sampling repair by welding and mandatory post weld heat treatment. The time and the efforts involved in these exercises often limits the RLA to less reliable levels relying on the material’s original properties at the time of fabrication leading to over prediction.Research is being carried out for estimation of mechanical properties of materials by destructive testing of miniature samples under various modes. Small punch test (SPT) technology is one such technique which has generated significant interest of the researchers. However challenges exist to establish procedure of testing and development of field implementable characteristic co-relation between SPT parameters and material properties. Though reports are available on room temperature (RT) properties on variety of materials to a great extent, studies on estimation of high temperature properties through SPT are sparingly available. An attempt has been made to develop correlations between SPT parameters and high temperature mechanical properties of Cr–Mo grade material. This paper describes salient features of the test setup developed and used for conducting test at high temperature, experimental results on one of the Cr–Mo grade material followed by development of correlation equation for estimating tensile properties.