Severe plastic deformation by incremental bulk metal forming

Incremental bulk forming technologies are investigated with respect to the creation of ultrafine-grained aluminium material. Based on first investigations of spin extrusion the technology of gradation rolling for rod shaped billets was developed. High strain generation as precondition for grain refinement is caused by the so called knead effect during processing in incremental rolling. Cross sections of processed billets show a demarcated area of different reflexion behaviour and a corresponding increase in hardness. In this area a gradient with decreasing grain size in surface direction is shown by crystallographic mapping. A several millimetre thick layer of refined material has been obtained.     

Sheet metal forming limit prediction based on plastic deformation energy

For sheet metals, the endurance to fracture under different strain paths may be different. Based on plastic deformation energy, the sheet metal forming limit is calculated, and the relationship model between maximum allowable integral value of the general plastic work criterion and the strain path is built. In addition, the strain-hardening exponent, anisotropy coefficient and the initial thickness of the material are also taken into account to consider their effects on forming limit. In order to simplify the process of parameter determination, only uniaxial tension test is used to calculate the material property parameters and necessary limit strain, and the expression of the criterion is determined finally. Then the limit strains under other strain paths between uniaxial tension to equi-biaxial tension are predicted by the criterion combined with numerical simulation of the forming process. The criterion is also applied to limit strain prediction under bilinear strain path.     

电磁平板自由胀形3D数值模拟(英文)

电磁成形是一种高速率成形方法,它能够有效提高金属板材的成形极限。但是电磁成形过程复杂,涉及到磁场?结构场之间的耦合分析。数值模拟提供一种手段去解决耦合问题。然而,大多数的数值模拟都限于2D。建立3D有限元模型去分析电磁平板胀形。成形过程中考虑了板料与底模的接触和板料变形对磁场的影响。板料中心节点和半径20mm处节点的位移随着时间的变化与实验结果一致。分析了塑性应变能和塑性应变。     

基于代理模型的板料成形优化技术进展

综述了板料成形优化技术现状,针对优化中计算成本高的问题,提出了基于代理模型的优化技术,包括可立格模型、响应面模型、神经网络模型等。从实验设计、代理模型的建立,以及优化求解等方面进行了阐述。针对产品设计中因素的随机性和不确定性,为减小目标函数对设计变量的敏感性,将稳健设计理论应用于板料成形优化中,以提高产品的可靠性和稳健性。     

Dynamic correction of oscillatory forces during ultrasonic-assisted metal forming

Numerous investigations in the past decades reported that the forces required for forming processes can be reduced by superimposing high frequency oscillation. Even though many studies have been carried out identifying and assessing the complex cause of this reduction, cause-effect relationships are generally not yet established in detail. Since the measurement of dynamic forces plays a key role in clarifying the causes, a precise measurement of the forming forces oscillating with high frequency is necessary. Although dynamic force measurement is a well-known field of research, this study focuses on its utilisation for ultrasonic-assisted forming processes. Since dynamic effects distort original measurements in this frequency range, adjustment is required. Based on measurement instruments with high temporal resolution the present study introduces an approach for creating and employing a frequency dependent force correction in the high dynamic range. The experimental procedure for creating a transfer function up to a limiting frequency of 40 kHz is later analysed and verified by numerical modal and transient simulations. The results indicate that the highly location dependent dynamic force detection has major influence on peak forces. Observed deviations can be precisely corrected using the generated frequency dependent transfer function.     

凝固微观组织的多层次模拟

通过引入溶质再分配、溶质扩散、界面能各向异性和界面曲率,构建了描述合金凝固微观组织形态演变的元胞自动机模型.在介观和微观尺度上的模拟结果表明,该模型可有效地解决微观组织形成的多尺度问题.模拟结果清晰地再现了与实测结果相一致的枝晶形态和生长现象.根据分形理论采用分维定量比较了模拟结果和实验结果,两者的计盒维数分别为1.703和1.694,阐述了分维定量表征枝晶形貌的物理含义.模拟结果表明熔体过冷度和树枝晶的计盒维数呈近似抛物线关系.     

Plastic deformation of magnesium alloy with different forming parameters during ultrasonic vibration-assisted single-point incremental forming

The research of forming parameters on the ultrasonic vibration single-point incremental forming of magnesium alloy plastic deformation can provide a theoretical basis for the establishment of the forming parameters.According to the forming characteristics of magnesium alloy sheet,a new method of ultrasonic vibration-as sis ted single-point incremental forming was proposed.The influence of forming parameters on the plastic deformation of magnesium alloy was studied by finite element simulation an...     

Destruction of metal during bulk and surface plastic deformation

Conclusions Plastic deformation in tension (compression) occurs in stages associated with the development and accumulation of microdamage — destruction of the material. The mechanics of the deformation process, each stage of which depends on the characteristics of the deformation mechanism, can be judged from the S vs ^1/2 diagram. On diagrams of true stress vs residual deformation there is a critical point — the point of inflection — which determines the beginning of destruction during plastic deformation and makes it possible to characterize the condition of the body in the process of deformation by the coefficients of destruction and quality, indicating the extent of the development of microdamage. The laws governing the development and accumulation of damage in plastically deformed material make it possible to characterize the behavior of the material in the region where neither the mechanical macromodels (mainly for the continuous solid state) nor micromodels of the physics of metals and alloys based on data concerning lattice defects can be used. Concepts of the plastic-destructional deformation and methods for quantitative determination of the degree of destruction make it possible to solve problems of material sciences associated with the quality of a material, its reliability, and service life. Concepts of the development of destruction in plastically deformed material are useful in studying the laws governing the accumulation of damage under different deformation conditions, particularly with surface treatments. They are of particular importance in order to explain the role of surface layers of metal in the overall macroscopic process, since they may determine the behavior of the material as a whole.Institute of Machine Sciences. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 17–22, August, 1980.     

基于ABAQUS的汽车板材成形性能及变形规律研究

在板料液压成形过程中,由于流体压力的施加,对板材的受力状态会产生不同程度的影响,同时可以在一定范围内有效提高板材的成形性能。为了分析流体压力下板材成形性能的变化规律,基于有限元软件模拟软件ABAQUS,对不同流体压力条件下的2024铝合金的单向拉伸过程分别进行数值模拟研究,得出了流体压力对板材米塞斯应力分布、轴向应力分布、伸长率及颈缩区厚度的影响规律。研究结果表明,在流体压力作用下,板材的变形更加均匀;并随着流体压力的增大,板材表现出更大的变形潜力,可以达到更大的伸长量。     

Thermal and mechanical finite element modeling of laser forming from metal and ceramic powders

A 3D thermomechanical finite element model including the effect of the powder-to-solid transition has been developed to investigate the transient temperature, transient stresses, residual stresses and warpage of the component made of multiple materials produced using a laser-assisted layer-by-layer fabrication approach. The model encompasses the effects of the temperature- and porosity-dependent thermal conduction and radiation as well as the temperature-dependent natural convection. It is found that changing from the initial solid elements to powder elements results in higher temperature gradients, larger transient and residual stresses, and increased warpage. Mechanisms responsible for these phenomena are discussed based on heat transfer capabilities and constraints resulting from different initial materials.     

板料多步冲压回弹的数值模拟研究

回弹是板料冲压成形过程中一种常见但很难解决的现象。首先研究了板料弯曲变形中卸载回弹的原理,然后以依维柯侧壁上内板为例,采用动态和静态算法相结合的方法,在考虑每道工序板料回弹的基础上,对其进行多步冲压回弹的数值模拟,最后对模拟结果和实验结果进行比较,验证该模拟方法提高回弹计算精度的有效性,为板料冲压成形工艺的制定提供科学依据。     

Conformal mapping modeling of metal plastic deformation and die cavity in special-shaped extrusion

With the help of Complex Function Mapping studied results,the analysis function of Conformal Mapping is set up.Since the complicated three dimension‘s deformation problems are transferred into two dimension problems,both the stream function and strain ratio field are analyzed in the metal plastic deformation.Using the upper-bound principles the theory of metal deformation and die cavity optimized modeling is established for random special-shaped product extrusion.As a result,this enables the realization of intelligent technique arget in the die cavity of CAD/CAM integration.     

Flexibility in metal forming

Flexibility in metal forming is needed more than ever before due to rapidly changing customer demands. It paves the way for a better control of uncertainties in development and application of metal forming processes. Although flexibility has been pursued from various viewpoints in terms of machines, material, process, working environment and properties, etc., a thorough study of the concept was undertaken in order to with problems of manufacturing competiveness and tackle new challenges of manufacturing surroundings. Therefore, in this paper, flexibility in forming is reviewed from the viewpoints of process, material, manufacturing environment, new process combinations and machine–system–software interactions.     

Damage in metal forming

Physical mechanisms of ductile damage in metal forming, experimental characterization methods for damage, and models predicting the damage level in formed components are reviewed. Applications of damage analysis in metal forming processes reveal that damage in metal formed parts is not failure, but a product property that accumulates between processes. Various metal forming process designs demonstrate that damage in formed products can be reduced and their performance can be increased. Static and fatigue strength, impact toughness, stiffness, and formability are typical examples of performance indicators that can be improved by damage-based process design. Potential scientific and technological challenges are addressed to realize damage-controlled metal forming processes.     

Surface roughening of metal–polymer systems during plastic deformation

This paper concentrates on the evolution of roughness at the surface of a glassy polymeric coating that co-deforms with a metal under uniaxial strain. In experiments and simulations the roughness is described by three parameters: the rms roughness amplitude w, a correlation length ξ, and a Hurst exponent H. In the plane strain simulations, the three stages (elastic, softening and hardening) in the stress–strain behavior of the polymer can be distinguished in their effect on the rms roughness amplitude w(ε). w(ε) decreases as a function of the thickness d of the coating for strains in the elastic and hardening regime. In the softening regime, shear bands originating at the interface intersect at a distance above the interface. In simulations, this leads to a distinct non-monotonous behavior of w(ε) as a function of thickness, with w(ε) reaching values above that at the interface at some thicknesses. In both experiments and simulations, it is found that the Hurst exponent H increases with increasing d. The correlation length ξ at the polymer surface increases with increasing d in the simulations, whereas in the experiment an increase is observed only above a certain value of d.     

Multi-scale modeling to predict sub-surface damage applied to laser-assisted machining of a particulate reinforced metal matrix composite

A multi-scale finite element model (FEM) is developed to predict the post machined sub-surface damage in a particle reinforced metal matrix composite (MMC) subjected to laser-assisted machining (LAM). The MMC studied is an A359 aluminum matrix composite reinforced with 20% by volume fraction silicon carbide particles. In this model, molecular dynamics (MD) simulations are carried out to parameterize traction–separation laws for the aluminum–silicon carbide interface. The parameterized traction–separation laws are then input into a finite element model, in the form of a cohesive zone model to subsequently simulate the sub-surface damage. In this manner, the multi-scale hierarchical model successfully bridges the atomic, micro and macro scales. Average values of the predicted quantities are compared with experimental results, and the favorable agreement confirms the validity of the multi-scale FEM.     

Temperature-dependent anisotropic material modeling of the sheet metal component within the polymer injection forming process

In the course of this work, an extended material model for a carbon steel sheet metal has been developed based on Hill’48 yield criterion, considering temperature-dependent plastic anisotropy coefficients. This material model is applied on a polymer injection forming process in which the sheet metal heats up to a critical forming temperature through the contact with the plastic melt. At this temperature range blue brittleness occurs. The elastic properties, the yield stress as well as the plastic anisotropy coefficients of the sheet material become significantly different compared to those at room temperature. It should be emphasized that especially temperature-dependent anisotropy coefficients are not yet considered in most common material models. With the help of the presented modelling approach a more precise modelling of the temperature-dependent carbon steel material behavior can be realised.     

Bulk forming of sheet metal

Ever increasing demands on functional integration of high strength light weight products leads to the development of a new class of manufacturing processes. The application of bulk forming processes to sheet or plate semi-finished products, sometimes in combination with conventional sheet forming processes creates new products with the requested properties. The paper defines this new class of sheet-bulk metal forming processes, gives an overview of the existing processes belonging to this class, highlights the tooling aspects as well as the resulting product properties and presents a short summary of the relevant work that has been done towards modeling and simulation.     

夹层钢板冲压的成形机理与缺陷分析

介绍了夹层钢板的材料结构、夹层钢板的冲压成形性及在成形过程中容易产生的缺陷,总结了影响夹层钢板成形性能的因素。介绍了夹层钢板在汽车行业中的应用情况及国内外的研究现状,并指出了当前车用夹层钢板研究的热点难点,对夹层钢板在此行业中应用发展做了展望。