Formabilities of steel/aluminium alloy laminated composite sheets

The tensile properties and press formabilities of laminates experimentally produced from mild steel and various aluminium alloy sheets are examined. The tensile properties of the laminates are approximately predictable by the mixture rule of the properties of the individual sheets. The forming limits in deep drawing, as well as stretch forming due to various types of fractures of the laminated composite sheets, cannot be predicted without considering the stress and strain histories of the individual sheets during forming. Furthermore, it is found that the drawability, as well as the stretch formability, is improved by setting the mild steel sheet on the punch side for the case of aluminium alloy sheet with comparatively high ductility, and by sandwiching the aluminium alloy sheet with the mild steel sheets for the case of low ductility.     

Negative and positive incremental forming: Comparison by geometrical,experimental, and FEM considerations

This study compares negative incremental forming (NIF) and positive incremental forming (PIF) processes by geometrical considerations, finite element method (FEM) analyses, and experimental evaluations. Conical frusta were manufactured starting from AA5052H19 aluminum alloy sheets using both techniques. The processes were also simulated with LS-DYNA software and a close correlation between the experimental and numerical results was observed. The analysis of forming forces, forming limit diagrams (FLDs), and sheets thinning highlights that the PIF technique allows one to reach higher formability and geometrical accuracy. Finally, the differences in terms of surface quality were also discussed.     

Deep drawing process of steel/brass laminated sheets

In this paper, the effects of several parameters on the deep drawing process of laminated sheets are comprehensively studied. The main reason to carry out such a process is taking the advantages of different materials, such as high strength, low density and corrosion resistibility, at the same time and in a single component. With this regard, it is possible to take the benefits of the forming processes, such as low waste of material and high directional strength of the components. This research work is concerned with the experimental and finite element studies of the deep drawing process of steel/brass laminated sheets. Several tests were conducted to investigate the influences of some variables, such as the stacking sequence of the layers, lubrication, blank-holder force and the diameter of the composite blank on the load–displacement curve and the final shape of the produced components. Investigation of stress and strain distributions in the deep drawn cup were also done and the FE results showed that the numerical method can predict the same place of tearing for bimetal cup as occurred in experimental tests. The main issues studied in this work are the material flow (occurrence of defects such as wrinkling and fracture) of the layers of the specimen and the required drawing force.     

不锈钢外板对 2219 铝合金拼焊板胀形性能的影响

目的现有2219铝合金板材宽度不能满足大型复杂曲面件整体流体高压成形需要,仍需采用焊接方法制备成形坯料,焊缝的存在导致铝合金拼焊板整体性能不均匀,影响成形性能及壁厚分布。方法提出2219铝合金拼焊板的双层板流体高压成形方法,采用1.8 mm厚铝合金拼焊板作为内层板,1mm厚不锈钢板作为外层板,进行双层板胀形实验研究。对比分析了单层板与双层板条件下2219铝合金拼焊板的成形极限、应变及壁厚分布。结果外层板的存在能够使板材的极限成形高度和极限应变增加,同时使壁厚分布更加均匀。结论双层板之间存在界面摩擦,可以提高内层拼焊板的成形极限、改善壁厚分布。     

Experimental evaluation and prediction of deep drawability of adhesive bonded steel sheets

The main aim of the present work is to experimentally evaluate the deep drawing behaviour of adhesive bonded sheets at different adhesive properties and predict the same using finite element simulations. The deep drawing quality steel and SS316L stainless steel are used as base materials for experiments and simulations. The deep drawing behaviour is also predicted using available analytical equations and proposed semi‐empirical equations. Such predictions are validated with experimental results. It is observed that due to increased plasticity of adhesive layer, the hardener rich formulation of adhesive improves the deep drawability of adhesive bonded blanks. The presence of carbon black in the adhesive has improved the drawability of bonded sheets up to a certain limit, say 2% by weight in the present work. The deep drawing behaviour predicted either by approach 1 (by giving experimentally evaluated adhesive properties as input) and by approach 2 (adhesive properties evaluated from rule of mixtures) are almost same, which indicates that both the methods can be used for forming behaviour prediction. The deep drawability predictions are moderately accurate with respect to experimental observation. The accuracy of analytical models for maximum load predictions is encouraging while comparing it with experimental results and numerical predictions. The proposed semi‐empirical equations show promising results to obtain initial estimate about the load‐progression behaviour of bonded sheets.     

软封装锂电池铝塑膜成形性能研究进展

目的 综述铝塑膜成形性能的影响因素和研究现状,为锂电池铝塑膜领域的科研,以及工程技术人员进行深入研究,提升产品性能提供参考。方法 首先介绍铝塑膜多层复合材料的结构、各层的作用,接着讨论冲压模具、冲压工艺以及基层材料的选择对铝塑膜成形性能的影响,并详细综述铝箔基层合金成分、微观组织和晶粒尺寸对铝箔性能的影响。结论 为了加快锂电池铝塑膜的国产化进程,未来需要加强铝塑膜对电解液耐久性的研究,同时进一步提升铝箔的成形性能,加强铝箔界面性质对铝塑复合性能和铝塑膜耐久性影响机理的研究,为增强下游用户对国产铝塑膜的信心提供理论支持。     

Forming limit evaluation of adhesive bonded sandwich steel sheets and numerical prediction

In the present work, the effect of hardener to resin ratio of epoxy adhesive on the formability of adhesive bonded steel sheets has been studied. Forming limit curve has been evaluated by hemispherical dome tests at predefined strain-paths. They are predicted by finite element simulations using strain mapping method. Cohesive zone model has been used to model the interface between skin and adhesive core. An improvement in the forming limit of sandwich steel sheets has been observed when the hardener to resin ratio is changed from 0.6 : 1 to 1 : 1 due to the improved plasticity of adhesive core layer at 1 : 1 ratio as compared to others. The forming limit of sandwich sheet made at 1 : 1 ratio is equivalent to base steel sheet of same thickness and grade. This shows the potential use of sandwich sheet in place of base steel sheet. The forming limit curve predictions agree well with experimental data for base sheet, while reasonable agreement is observed in case of sandwich sheet. Numerical prediction of interface delamination show insignificant influence of hardener to resin ratio on the onset of delamination and significant effect of strain-paths.     

A study on sheet formability by a stretch-forming process using assumed strain FEM

The effects of sheet thickness and frictional condition between the punch and sheet on formability is predicted and compared with the experimental results of the Erichsen test as a stretch-forming process. The material and geometrical nonlinearity are considered. A hypoelastic–plastic model is used and strain-field stabilization is taken into account using the Assumed Strain Finite-Element Method. By considering the contact problem and applying the nonlinear finite-element method, the force and dome height for aluminum and steel sheets are computed and compared with the experimental results. The Oyane criterion is used to access the formability of the sheet. A good agreement was found between the experimental and predicted formability results of aluminum and steel sheets. The results show that for decreasing friction coefficient the position of tearing is moved from the rim to the pole. Also, by increasing the work-hardening exponent, formability is increased.     

Improvement in formability of aluminum alloy sheet by enhancing geometrical hardening

Individual grains in a polycrystal rotate during plastic deformation. This leads to a change in the crystallographic texture, and results in an increase or decrease of the macroscopic flow stress of the material. Such a change of strength as a result of grain rotations is called geometrical or texture hardening/softening. In the present study, for textured aluminum alloy sheets, the geometrical hardening/softening effect in the in-plane plane-strain stretching mode is numerically investigated using a generalized Taylor-type polycrystalline model. It is found that the cube texture () exhibits significant geometrical hardening when the major stretching direction is inclined at 45° relative to the orthotropic axes, and that a cube texture rotated about the normal direction (ND) shows a notable degree of geometrical hardening for any in-plane orientation of the sheet. Using the Marciniak-Kuczyński-type approach, forming limits for these textured sheets are analyzed. It is found that geometrical hardening definitely enhances the formability. It is, therefore, strongly suggested that texture control guided by the present results may be highly effective in producing aluminum alloy sheets with higher formability.     

Blast impact response of aluminum foam sandwich composites

Military and civilian structures can be exposed to intentional or accidental blasts. Aluminum foam sandwich structures are being considered for energy absorption applications in blast resistant cargo containers, ordnance boxes, transformer box pads, etc. This study examines the modeling of aluminum foam sandwich composites subjected to blast loads using LS-DYNA software. The sandwich composite was designed using laminated face sheets (S2 glass/epoxy and aluminum foam core. The aluminum foam core was modeled using an anisotropic material model. The laminated face sheets were modeled using material models that implement the Tsai-Wu and Hashin failure theories. Ablast load was applied using the CONWEP blast equations (*LOAD_BLAST) in LS-DYNA. This paper discusses the blast response of constituent S2-glass/epoxy face sheets, the closed cell aluminum foam core as well as the sandwich composite plate.     

铝合金复杂曲面薄壁件液压成形技术

介绍了适合于制造铝合金复杂曲面薄壁件的液压成形技术,包括充液拉深、可控径向加压充液拉深和液体凸模拉深。由于充液拉深能提高成形极限,适合于制造铝合金复杂型面零件。可控径向加压充液拉深通过径向压力向内推料,进一步提高了成形极限,适合于成形大高径比筒形件。液体凸模拉深适合于获得深度较大、形状复杂、尤其底部具有小过渡圆角的复杂形状零件。     

An analytical model for bending and springback of bimetallic sheets

Springback is an inevitable phenomenon due to elastic redistribution of internal stresses occurring in sheet metal forming operations. Most of the research reported in this area has been concerned with the components formed from single metal. This article deals with the analytical solution for prediction of springback in bending of bimetallic sheets. A mathematical model is derived based on Woo and Marshall's constitutive equation, considering logarithmic strain (nonlinear) distribution across the thickness and thickness change during bending. Analytical modeling, based on logarithmic strain distribution across the thickness, can be used for accurate springback predictions in the case of smaller bend radius to the thickness ratio. The results of the springback and thickness change are validated using experimental results for the aluminum sheet layered with steel. Further, springback variation in bimetallic sheets is studied, with a change in material properties and thickness of each layer.     

Effects of Loading Paths on Hydrodynamic Deep Drawing with Independent Radial Hydraulic Pressure of Aluminum Alloy Based on Numerical Simulation

In order to meet the forming demands for low plasticity materials and large height-diameter ratio parts, a new process of hydrodynamic deep drawing （HDD） with independent radial hydraulic pressure is proposed. To investigate the effects of loading paths on the HDD with independent radial hydraulic pressure, the forming process of 5A06 aluminum alloy cylindrical cup with a hemispherical bottom was studied by numerical simulation. By employing the dynamic explicit analytical software ETA/Dynaform based on LS-DYNA3D, the effects of loading paths on the sheet-thickness distribution and surface quality were analyzed. The corresponding relations of the radial hydraulic pressure loading paths and the part＇s strain status on the forming limit diagram （FLD） were also discussed. The results indicated that a sound match between liquid chamber pressure and independent radial hydraulic pressure could restrain the serious thinning at the hemisphere bottom and that through adjusting radial hydraulic pressure could reduce the radial tensile strain and change the strain paths. Therefore, the drawing limit of the aluminum cylindrical cup with a hemispherical bottom could be increased significantly.     

金刚石表面激光熔覆Cu-金刚石超硬涂层的组织及摩擦性能

为了提高金刚石刀具的耐摩擦性能,利用激光熔覆在其表面制得Cu-金刚石的涂层,实验测试分析了涂层的组织及摩擦性能。研究结果表明:涂层形成了清晰的断面结构,涂层能够和硬质合金形成紧密结合状态,并没有发生剥落。经测试发现单层涂层的厚度约30μm,双层涂层厚度约50μm,并且双层涂层形成了更致密的上砂量。大部分金刚石颗粒都是沉积在涂层的(101)晶面,添加金刚石颗粒后并没有引起Cu晶体组织的改变。单层涂层形成了宽度较大而深度较小的众多表面犁沟结构,双层涂层在磨损表面形成了许多深度较大并且密集分布犁沟,表现出更优的耐磨特性。双层结构涂层摩擦测试也表现为先减小后到达3 min之后则表现为规律变化的特征。     

树脂复合减振钢板U型弯曲回弹实验与数值模拟研究

通过带法兰边的U型弯曲成形实验研究,考察了树脂复合减振钢板在不同压边力下的回弹特性.实验结果表明:压边力对树脂复合减振钢板回弹特性影响显著.较大的压边力有利于减小回弹缺陷.其次,考虑树脂层的粘弹性特性,采用非线性粘弹性模型来描述树脂层的力学变形行为,并采用Cohesive单元和固体壳单元分别对树脂层和表层钢板进行离散,进行了树脂复合减振钢板在不同压边力下的U型弯曲有限元数值模拟研究.和实验结果比较表明,所建立的有限元模型能够较好的模拟U型弯曲成形过程.最后,基于建立的有限元模型,考查了成形速度,树脂层厚度和表层钢板初始屈服应力对回弹的影响.参数分析结果表明:这三个参数对回弹角的影响显著.该研究对树脂复合减振钢板冲压工艺设计具有一定的指导意义.     

An experimental investigation into the warm deep-drawing process on laminated sheets under various grain sizes

It has been proved by many researchers that increasing the temperature in warm deep-drawing process of single layer sheets decreases the forming load, however, this phenomenon is not necessarily the case in warm deep-drawing process of laminate sheet. The objective of the present paper is to carry out a comprehensive investigation on warm deep-drawing process on laminated sheets experimentally. Based on the results of this study, it can be observed that by raising the temperature, variation of forming load more depends on blank holder force (BHF). In this study, thinning and wrinkling in Al 1050/St 304 and Al 5052/St 304 samples for each layer in warm deep-drawing process are evaluated individually. In addition, the effects of various grain sizes, blank temperatures and sequence layer on forming load are investigated. In order to carry out a comprehensive survey of warm deep-drawing; three blank temperatures namely, 25 °C, 100 °C and 160 °C are examined. Furthermore, to achieve various grain sizes, the aluminum sheets are annealed at 350 °C, 400 °C and 450 °C for 1 h. Finally, several tests are conducted to obtain the influences of grain size on some material characteristics such as stress, elongation and friction coefficient.     

Effects of Constituents and Lay-up Configuration on Drop-Weight Tests of Fiber-Metal Laminates

Impact responses and damage of various fiber-metal laminates were studied using a drop-weight instrument with the post-impact damage characteristics being evaluated through ultrasonic and mechanical sectioning techniques. The first severe failure induced by the low-velocity drop-weight impact occurred as delamination between the aluminum and fiber-epoxy layers at the non-impact side. It was followed by a visible shear crack in the outer aluminum layer on the non-impact face. Through-thickness shear cracks in the aluminum sheets and severe damage in the fiber laminated layers (including delamination between adjacent fiber-epoxy laminae with different fiber orientations) developed under higher energy impacts. The impact properties of fiber-metal laminates varied with different constituent materials and fiber orientations. Since it was punched through easily, the aramid-fiber reinforced fiber-metal laminates (ARALL) offered poorer impact resistance than the glass-fiber reinforced fiber-metal laminates (GLARE). Tougher and more ductile aluminum alloys improved the impact resistance. GLARE made of cross-ply prepregs provided better impact resistance than GLARE with unidirectional plies.     

Material saving and cost reduction with hot forming of U‐shaped titanium part

Titanium alloy sheets are widely used for highly loaded components in the aerospace industry as well as spacecrafts. The unique combination of high strength, outstanding corrosion resistance and thermal endurance makes titanium alloys the preferred material for applications with severe requirements. Due to the limited formability at room temperature, forming processes have to be conducted in a multitude of steps what is costly and labour intensive. Additionally, typical titanium alloy sheets show a significant anisotropy of mechanical properties and material flow. Undesired earing, wall thickness variation and residual stresses are the result. Complex shaped parts can be produced at elevated temperatures to avoid named drawbacks. The present work introduces a newly developed hot deep drawing process, applied to titanium sheets at FormTech. In comparison with conventional superplastic forming processes via gas pressure, hot deep drawing comes with a significantly reduced process time and hence, increased output over time. Titanium sheets of the work horse alloy Ti–6Al–4V were formed in a single stroke to a U‐shaped component at process temperatures ranging from 750 to 890 °C. Specimens were extracted to validate the neglectable influence of the hot forming process on mechanical properties and fatigue behaviour. In conclusion, hot deep drawing of titanium sheets offers a cost efficient alternative to a gas pressure superplastic forming process, while maintaining its main benefits such as significantly improved formability, low residual stresses and tight tolerances.     

Today's sheet metal materials and their forming properties

The production and processing of sheet metals of high‐strength steels, titanium, aluminum or magnesium alloys is investigated intensively at universities and in the industry. The main emphasis is put for example on the aluminum space frame concept as well as on the succeeding projects of the ULSAB‐study in the field of the steel sheet metals. Within this article the qualification of the above mentioned materials for the application as deep‐drawing materials will be discussed. The aim of the development for new deep‐drawing sheet metals is to decrease the elastic part of the forming, which means to lower the yield point. A high elastic portion would cause a high resilience after the forming of the sheet metals and therefore an increased requirement of force and form error during the forming process. Furthermore the optimized sheet metal material should have a great uniform elongation, so that it can be plastically deformed in a wide range. The beginning of the deformation should be possible at low forming forces but due to the deformation an increase of the hardening should be caused, so that the finished component has high strength. But it is not possible to realize both aims, high strength and great uniform elongation, at the same time.