方盒形件混合分块压边拉深工艺研究

目的 提高盒形件拉深成形过程中的成形件质量及成形极限。方法 提出混合分块压边方法,即将法兰区的4个直边区和4个圆角区沿周向分开进行压边,并在每个圆角区分别采用径向分块压边。采用有限元方法,结合正交试验,对压边圈的分块位置及压边力的分配方案进行优化设计,并通过实验比较分别采用混合分块压边方法和整体压边方法时方盒形件拉深成形的抑制起皱效果及成形极限。结果 有限元模拟和实验结果表明,采用混合分块压边方法,成形件皱纹最大幅值及最大减薄率显著减小,板料最小厚度增加,有效降低了成形件的起皱和破裂风险。结论 新方法抑制起皱的效果显著优于普通压边方法,在合理的工艺条件下,板料的成形极限也得到明显的提高。     

Research on Thermal Deep-drawing Technology of Magnesium Alloy (AZ31B) Sheets

Forming technology of Mg alloy (AZ31B) sheets can be investigated by thermal deep drawing experiments. In the experiments, the blank holder and die contacting with the blank were heated to the same temperature as the blank by using the heating facility. The circular blank heated in an oven is formed at a temperature range of 100~400℃ to obtain the optimum forming temperature range and the effects of major technical parameters on the workpiece quality.It is found that the blank is brittle at temperatures lower than 200℃.Temperatures higher than 400℃ are not suitable for forming of the sheets because of severe oxidation and wrinkling.AZ31B shows an excellent formability at temperatures from 300 to 350℃ and can be formed into a workpiece with good quality. When the blank holder force is 9 kN, extruded sheets with a thickness of 1 mm can be formed into cups without wrinkling. Workpieces show strong anisotropic deformation behavior on the flanges.     

Simulation of wrinkling during textile composite reinforcement forming. Influence of tensile, in-plane shear and bending stiffnesses

Wrinkling is one of the most common flaws that occur during textile composite reinforcement forming processes. These wrinkles are frequent because of the possible relative motion of fibres making up the reinforcement, leading to a very weak textile bending stiffness. It is necessary to simulate their onset but also their growth and their shape in order to verify that they do not extend to the useful part of the preform. In this paper the simulation of textile composite reinforcement forming and wrinkling is based on a simplified form of virtual internal work defined according to tensions, in-plane shear and bending moments on a unit woven cell. The role of the three rigidities (tensile, in-plane shear and bending) in wrinkling simulations is analysed. If in-plane shear stiffness plays a main role for onset of wrinkles in double-curved shape forming, there is no direct relation between shear angle and wrinkling. Wrinkling is a global phenomenon depending on all strains and stiffnesses and on boundary conditions. The bending stiffness mainly determines the shape of the wrinkles and it is not possible to perform a wrinkle simulation using a membrane approach.     

Experimental and numerical evaluation of multilayer sheet forming process parameters for light weight structures using innovative methodology

Being light weight and superior in characteristics, hybrid materials such as fiber metal laminate (FMLs) and functionally graded structures (FGS) are becoming increasingly popular in aeronautical, automobile and military industries. In the present work, an innovative methodology which hereafter will be named as “3A method” has been proposed to replace complex shaped, monolithic, metallic sheet parts with hybrid parts. This method is based on simultaneous forming of any number of multiple metallic blanks in required shape by applying hydroforming (HF) technology. Based on numerical simulations, forming limit diagrams (FLDs) are established for three types of blanks forming hemispherical shaped parts using Barlat 2000 yield criteria/DYNA Form/LS Dyna. To validate the simulation results, experimental study is accomplished and optimal process parameters are determined by varying the cavity pressure under constant die-binder gap. Effects of number of layers and thickness of blanks on thinning, wrinkling and punch force have been well studied for three types of blanks and a comparative analysis is made to investigate various failure modes. To achieve a composite layered structure, post forming procedure has been devised and implemented to get a final hybrid part. Furthermore, limitations of the 3A method in terms of final shape of parts are discussed. Good agreement can be found between numerical and experimental research. The new methodology is capable of employing any types of resins and composite materials at any required place in parts for desired characteristics. Elimination of repeated heating and solidification of blank assembly as well as precise punch force and speed requirements make this multilayer blank forming method more efficient, economical and user friendly for manufacturing of FMLs and FGSs at commercial scales.     

铝合金汽车顶盖充液成形的数值模拟

目的研究铝合金汽车顶盖拉延工序的充液成形工艺。方法基于有限元分析软件Dynaform,利用带局部刚性凹模整形的被动式充液成形工艺,通过建立有限元分析模型,优化成形过程中的关键工艺参数,分析变形规律并进行质量控制。结果成形过程中的液室压力加载路径、压边力、拉延筋,以及坯料形状等工艺参数对成形影响较大。液室压力不宜过早加载。液室压力过大或压边力过小不利于顶部产生充分塑性变形。压边力过大极易造成顶盖圆角处的破裂。结论该成形工艺可行,且数值模拟的准确性及适用性较高,采用该成形工艺可得到表面质量良好,未出现起皱、破裂缺陷的合格零件。     

Drawing behaviour of metal–composite sandwich structures

The drawing behaviour of metal–composite sandwich structures is investigated as a function of the constituent material properties and the process variables of blank preheat temperature and blank-holder force. Materials include three grades of aluminium alloy as the skin layer material and two types of reinforced polypropylene composite as the core layer material. Blank-holder force has a significant effect on the failure mode of the metal–composite system with lower forces resulting in wrinkling as the dominate mode and higher forces resulting in splitting and fracture. Increasing preheat temperature decreases the failure in the composite core however it will increase the severity of wrinkling in the outer flange and sidewall.     

Textile composite double dome stamping simulation using a non-orthogonal constitutive model

Stamping is one of the most effective ways to form textile composites in industry for providing high-strength, low-weight and cost-effective products. This paper presents a fully continuum mechanics-based approach for stamping simulation of textile fiber reinforced composites by using finite element (FE) method. A previously developed non-orthogonal constitutive model is used to represent the anisotropic mechanical behavior of textile composites under large deformation during stamping. Simulation are performed on a balanced plain weave composite with 0°/90° and ±45° as initial yarn orientation over a benchmark double dome device. Simulation results show good agreement with experimental output in terms of a number of parameters selected for comparison. The effects of meshing and shear moduli obtained from bias extension test and picture frame test on forming simulation results are also investigated.     

FE analysis of coupled thermo-mechanical behaviors in radial–axial rolling of alloy steel large ring

Radial–axial rolling of alloy steel large ring (ASLR) is an advanced plastic forming process with complex coupled thermo-mechanical deformation behaviors which have significant influences on the microstructure and properties of the product. In this paper, the stable forming conditions and ranges of key forming parameters for the radial–axial rolling process of ASLR are determined reasonably. Then a 3D elastic–plastic and coupled thermo-mechanical FE model of radial–axial ring rolling is explored using the dynamic explicit code ABAQUS/Explicit, and its reliability is verified theoretically and experimentally. Using FE simulation and analysis, the effects of key forming parameters on the uniformity of deformation and temperature distribution of ASLR are investigated. The main results show that: (1) The deformation and temperature distribution of the ASLR are nonuniform in radial–axial ring rolling. The PEEQ gradually decreases from the surface region to the central region of the ASLR while the temperature distribution is reverse. The largest PEEQ and smallest temperature appear in the edge region of the ASLR. (2) With increasing the feed speeds of rolls, initial temperature of blank or decreasing the rotation speeds of rolls, the deformation of the ASLR becomes more uniform. (3) With increasing the feed speeds of rolls, rotation speeds of rolls or decreasing the initial temperature of blank, the temperature distribution of the ASLR becomes more homogeneous. (4) The friction coefficient has a slight effect on the uniformity of deformation and temperature distribution of the ASLR. The results provide an important basis for improving the microstructure and forming quality of ASLR through optimization of forming parameters.     

飞机铝合金深锥型面零件多道次充液拉深技术

目的随着新一代飞机在隐身和战斗性能方面的提高,飞机钣金零件的复杂程度和制造精度要求也越来越高。对于深型腔复杂型面零件,充液拉深是一种有效的精密制造方法。方法针对难成形、复杂型面的某型飞机铝合金深锥零件,利用理论分析、有限元模拟和工艺试验相结合的方法,设计了多道次充液拉深技术方案,并建立有限元分析模型。基于等裕量函数法和零件锥面特征,分配并优化了不同道次的材料变形量。结果对多道次充液拉深成形过程中出现的起皱和破裂的失效形式进行了研究,分析了预成形高度,液室压力和压边力等关键工艺参数对零件成形质量的影响,获得了优化的预成形高度和液室压力加载轨迹。结论结果表明,提出的多道次充液成形技术能够实现复杂型面,大拉深比的铝合金零件的整体精确成形,采用优化的工艺参数能够成形出壁厚均匀,表面质量好,锥面精度高的零件。     

Experimental measurement of wrinkle formation during draping of non-crimp fabric

A rig and image analysis methodology is described to characterise wrinkle formation during draping of non-crimp fabrics. The circular fabric blank is draped over a male hemispherical mould, partly constrained by a circular clamping ring around the periphery of the blank. The three-dimensional shape of the fabric is derived from a shape-from-focus analysis of a stack of photographs of the deformed blank. Wrinkles are identified from the deviation of the shape from a smoothed shape. Wrinkle formation is strongly dependent on the fabric architecture and increases progressively with increased punch displacement. Triaxial fabrics have the highest wrinkle amplitude, unidirectional and 0/90° biaxial fabrics the lowest amplitude. The clamping force reduces the wrinkling for some fabrics but, for the maximum force applied, is not effective at eliminating wrinkling.     

轻质高强异形管件充液压制成形技术

目的 针对轻质高强异形管状构件的迫切需求,研发了充液压制成形技术,以在低载荷下成形出具有高强度、大尺寸、小圆角等特征的异形空心薄壁管状构件。方法 给出了充液压制成形的力学原理,建立了成形过程压制力计算模型与临界支撑内压理论模型,分析了充液压制成形过程失稳屈曲/起皱规律、圆角充填机理与壁厚分布规律。结果 当管材充液压制过程所需的支撑内压为内高压成形压力的1/10~1/20时,就可以避免管坯发生失稳屈曲与起皱,同时使压制力大幅降低。在弯曲与压缩应力复合作用下对管坯进行圆角充填,充液压制成形得到的管件壁厚减薄非常小。结论 利用小吨位合模压力机在超低压条件下可以充液压制成形出具有小圆角与均匀壁厚的轻质高强异形管件,解决了传统内高压成形压力高、易发生开裂等难题。     

钛/铁复合板平底球形薄壁件充液拉深工艺研究

目的 选用充液拉深先进成形技术制备钛/铁复合板平底球形薄壁件,并研究其充液拉深变形行为,以解决传统拉深工艺制备平底球形薄壁件极易产生褶皱的问题。方法 对钛/铁复合板平底球形薄壁件在不同液压力、压边间隙及凸模与板料间摩擦因数等工艺参数下的充液拉深过程进行数值模拟。对数值模拟结果进行分析,讨论工艺参数对零件成形性能的影响以及抑制起皱的机理。最后在不同拉深工艺下进行成形试验,制备钛/铁复合板平底球形薄壁件并与数值模拟结果进行对比。结果 数值模拟和成形试验结果表明,传统拉深工艺制备的钛/铁复合板平底球形薄壁件出现了明显的褶皱,采用充液拉深工艺可以有效解决零件侧壁起皱的问题。增大液压力、减小压边间隙或增大凸模与板料间摩擦因数会导致零件减薄率的提高并降低零件侧壁起皱的风险。在压边间隙1.5 mm、液压力25 MPa的条件下,采用充液拉深工艺可以制备出侧壁无褶皱的平底球形薄壁件。结论 通过充液拉深工艺可以有效解决钛/铁复合板平底球形薄壁件成形过程中起皱的问题。     

矩形盒拉深变压边力加载规律及预测

目的解决板料拉深过程中出现拉裂、起皱、拉深不充分等缺陷的问题。方法利用专业分析板料成形的软件Dynaform,研究分析了非轴对称件矩形盒,在几种典型的变压边力下的拉深成形性能,获得了成形效果较好的加载模式,进而利用仿真软件Dynaform获取了样本数据。结果建立了矩形盒拉深成形变压边力网络模型并对其学习训练,最后对神经网络预测结果及仿真结果所得到的变压边力加载曲线进行多项式拟合,获取了最佳压边力控制曲线。结论在板料拉深过程中,通过控制压边力的大小,能够较好地发挥材料的流动性,改善制件的最终成形效果。     

An approach in modeling the temperature effect in thermo-stamping of woven composites

Made with high-strength continuous fibers, textile composites are of increasing interest in automotive and aerospace industries due to their high-strength/weight performance as compared to sheet metals. Nevertheless, significant reduction in manufacturing cost is required to use textile composites for mass production applications. Highly efficient thermo-stamping operations possess the potential to substantially reduce fabrication time and cost compared to the much slower autoclave forming process. In this paper, thermo-forming of woven fabric-reinforced thermo-plastic composites is simulated using a non-orthogonal material model. The temperature effect is taken into account by modifying the equivalent material properties for the composite sheet based on the contact status between the tooling and the blank. The approach is exemplified on the hemispherical thermo-stamping of a plain weave composite sheet.     

Forming sheet metals by means of multi-point deep drawing method

Multi-point deep drawing (MPDD) is an advanced manufacturing technology for 3D sheet metal parts and it can form a variety of part shapes without the need for solid dies. In this study, a test set has been prepared for multi-point deep drawing process utilizing the multi-point forming technology. Drawability attributes of gradually rectangular shaped container have been observed using a sheet, which has the quality of Erdemir 7114 and is suitable for deep drawing process, and also using multi-pointed punch with a given tool geometry and a draw velocity. The blank shape to be drawn without wrinkling and tearing has been determined. Wrinkles and dimples are the major forming defects in the MPDD process. In conventional deep drawing, the method to form sheet metal with a blank holder is an effective way to suppress wrinkling; and the same is true in MPDD. The process of multi-point forming technology decreases production cost of die, provides flexible usage, and it is convenient to achieve the most even deformation distribution.     

Investigation of material deformation in multi-pass conventional metal spinning

This paper reports a study on material deformation during a multi-pass conventional spinning. A Finite Element (FE) analysis model has been developed based on a 5-pass conventional spinning experiment. The explicit Finite Element solution method has been used to model this multi-pass spinning process. Effects of mass scaling and reduced integration linear element used in the FE simulation have been evaluated by using various energy histories obtained from the FE analysis. The numerical results suggest that among three tool force components the axial force is the highest while the tangential force is the lowest. Certain correlations have been found between the FE analysis results and measured dimensions of the spun part. The blank thickness decreases after each forward pass and there are almost no thickness changes during the backward pass. Stress distributions of the local forming zone of the workpiece in both forward and backward passes have also been analysed, which gives an insight into the material deformation during the spinning process.     

AZ41 镁合金管材充液压形规律探究

目的实现镁合金管材的室温成形。方法利用物理实验的方法研究AZ41镁合金薄壁管材充液压形过程中的成形规律,分析主要缺陷形式,并揭示圆角填充过程和壁厚分布规律。结果 AZ41镁合金管材充液压形易发生破裂和失稳缺陷。内压过低变形部位难以转移,导致弯曲破裂的发生;内压过高,管坯合模前膨胀,导致截面周长大于零件截面周长,进而发生起皱。结论最终在5.6 MPa的支撑内压下成功成形出了最小圆角5 mm的零件,最大减薄率小于5%。     

A simplified rate dependent model of forming and wrinkling of pre-impregnated woven composites

A simplified finite element model is developed and validated for the forming/draping of pre-impregnated woven composites, incorporating the effects of wrinkling and strain rate dependence. The model development builds upon previous work on simulation of fabric draping using a truss representation of the woven material. Tows are modelled by stiff elastic bar elements, and the non-linear rate dependent shear behaviour is incorporated in elastic-viscoplastic elements that follow an appropriate phenomenological constitutive model. Wrinkling due to tow buckling is simulated by allowing the deactivation of tow elements that undergo compressive deformation. The model convergence is tested and its validity is checked against experimental results from the forming of pre-impregnated woven carbon hemispheres. It is found that the model reproduces successfully experimental measurements of shear and wrinkling with a relative error of approximately 4%, while solution times are kept below 60 s on a conventional PC. These features allow potential iterative use of the model within a process optimisation scheme. The sensitivity of the process outcome to process parameters such as blank holder force and forming speed is investigated.     

芯轴摩擦系数对推压-拉拔复合缩径的影响

推压-拉拔复合缩径工艺是管坯减径的新方法,芯轴外表面与管坯内表面之间摩擦系数对工艺有重要的影响。通过建立推压-拉拔复合缩径变形过程中变形管坯的力学模型,分析了芯轴外表面与管坯内表面之间摩擦系数对成形的影响规律。针对某载重6.5 t胀压成形汽车桥壳管件的第一道次推压-拉拔复合缩径,设定不同的芯轴摩擦系数,进行了有限元仿真,得到了芯轴摩擦系数对管坯变形的影响规律,并基于管坯传力区不失稳以及变形所需凹模推力和芯轴拉拔力较小,给出了芯轴摩擦系数的设定范围。进行了缩径实验,实验和有限元模拟的结果接近。较小的芯轴摩擦系数可能造成管坯起皱失稳,而较大的芯轴摩擦系数,有利于降低管坯轴向压应力、凹模推力和芯轴拉拔力,但可能造成管坯表面划伤。     

Study on plastic deformation behavior of hot splitting spinning of TA15 titanium alloy

The plastic deformation behavior of hot splitting spinning of TA15 titanium alloy is a complex metal forming problem with multi-factor coupling interactive effects. In this paper, on condition of considering various thermal effects, a three-dimensional (3D) elastic–plastic coupled thermo-mechanical finite element (FE) model of hot splitting spinning of TA15 titanium alloy is established using the dynamic, temp-disp, explicit module of FE software ABAQUS. Based on the analysis of flow behaviors of TA15 titanium alloy, the mechanism and influence of materials plastic deformation behavior during the forming process are studied. The results show that, the flow stress of TA15 titanium alloy generally decreases with the increase of deformation temperature; at the same strain rate, the higher temperature is, the lower flow stress is. The temperature distributions along the circumferential direction of disk blank are even and the temperature of plastic deformation area is about 984 °C. The heat from plastic deformation and friction at local plastic deformation area is less than the dissipated heat, so the temperature just falls into approximately 945 °C. Radial spinning force as the driving force of plastic deformation increases gradually and reaches about 35 kN at the end. The maximum value of equivalent stress is presented in fillet part between disk blank and two mandrels. The distributions of equivalent plastic strain appear the large strain gradients and the obvious characteristics of inhomogeneous deformation. When friction factor on interfaces between disk blank and dies ranges from 0.4 to 0.6, the forming quality and precision are highest.