多点复合渐进成形与单点渐进成形的对比分析

为提高金属板材渐进成形的成形质量、成形精度、成形效率和成形极限,了解不同渐进成形工艺对制件成形性能的影响,本文以典型方锥台制件为研究对象,利用有限元软件MSC.Marc对2种渐进成形工艺进行了三维建模,对比分析了单点渐进成形和多点复合渐进成形对制件等效塑性应变、厚度分布和成形精度的影响.数值模拟结果表明:单点渐进成形的等效塑性应变和厚度减薄主要集中在制件相邻侧壁间的拐角处,而多点复合渐进成形的等效塑性应变和厚度减薄均匀地分布在制件成形区;相同成形工艺参数下,相比单点渐进成形,多点复合渐进成形更有利于制件的成形效率、成形质量、成形精度和成形极限的提高,更有利于抑制破裂等失稳现象的产生.2种渐进成形工艺的成形试验表明,数值模拟结果与试验相符.     

Single point incremental forming: state-of-the-art and prospects

Incremental sheet metal forming in general and Single Point Incremental Forming (SPIF) specifically have gone through a period of intensive development with growing attention from research institutes worldwide. The result of these efforts is significant progress in the understanding of the underlying forming mechanisms and opportunities as well as limitations associated with this category of flexible forming processes. Furthermore, creative process design efforts have enhanced the process capabilities and process planning methods. Also, simulation capabilities have evolved substantially. This review paper aims to provide an overview of the body of knowledge with respect to Single Point Incremental Forming. Without claiming to be exhaustive, each section aims for an up-to-date state-of-the-art review with corresponding conclusions on scientific progress and outlook on expected further developments.     

Efficient implicit simulation of incremental sheet forming

In single point incremental forming (SPIF), the sheet is incrementally deformed by a small spherical tool following a lengthy tool path. The simulation by the finite element method of SPIF requires extremely long computing times that limit the application to simple academic cases. The main challenge is to perform thousands of load increments modelling the lengthy tool path with elements that are small enough to model the small contact area. Because of the localised deformation in the process, a strong nonlinearity is observed in the vicinity of the tool. The rest of the sheet experiences an elastic deformation that introduces only a weak nonlinearity because of the change of shape. The standard use of the implicit time integration scheme is inefficient because it applies an iterative update (Newton–Raphson) strategy for the entire system of equations. The iterative update is recommended for the strong nonlinearity that is active in a small domain but is not required for the large part with only weak nonlinearities. It is proposed in this paper to split the finite element mesh into two domains. The first domain models the plastically deforming zone that experiences the strong nonlinearity. It applies a full nonlinear update for the internal force vector and the stiffness matrix every iteration. The second domain models the large elastically deforming zone of the sheet. It applies a pseudolinear update strategy based on a linearization at the beginning of each increment. Within the increment, it reuses the stiffness matrix and linearly updates the internal force vector. The partly linearized update strategy is cheaper than the full nonlinear update strategy, resulting in a reduction of the overall computing. Furthermore, in this paper, adaptive refinement is combined with the two domain method. It results in accelerating the standard SPIF implicit simulation of 3200 shell elements by a factor of 3.6. Copyright © 2011 John Wiley & Sons, Ltd.     

Polymer incremental sheet forming process: Temperature analysis using response surface methodology

To reduce costs associated with the manufacturing of customized products, several innovative forming processes have been developed. Incremental sheet forming (ISF) is one of these new technologies, becoming, in the past decade, more interesting for the academic and industrial community. The influence of main process parameters, namely, tool diameter, spindle speed, feed rate, and step down, is studied in depth in this paper. The maximum temperature achieved during the forming process of a truncated pyramid frustum with a circular generatrix using three nonbiocompatible and two biocompatible polymer materials is measured. Box–Behnken design of experiments and the response surface methodology have been utilized to statistically analyze the results and to provide models able to predict the maximum temperatures.     

工艺参数对多点复合渐进成形厚度减薄的影响

为提高成形质量、预防破裂等缺陷,在金属板材多点复合渐进成形的基础上,通过建立三维有限元模型,对不同工艺参数成形方锥台制件进行了数值模拟和分析,探讨了制件成形过程中厚度分布和变化情况及不同工艺参数对厚度减薄率的影响.数值模拟结果表明,制件成形区对角线上的厚度减薄相比中线上的更严重,工具头直径和板材初始厚度越小、成形角和进给量越大,制件所能达到的最大厚度减薄率越大,制件越易破裂.多点复合渐进成形试验表明,数值模拟结果与实验相吻合.     

Critical analysis of necking and fracture limit strains and forming forces in single-point incremental forming

Single-Point Incremental Forming (SPIF) is an emerging manufacturing process especially suitable to produce small batches of metal parts. Moreover, the enhanced formability of metal sheets deformed by SPIF makes this technology useful to those industrial applications requiring high deformation levels. In this sense, the precise setting of limit strains in SPIF in relation to the conventional formability limits of the material, as well as the influence of the process parameters on these strains, are essential variables to understand how and how much can be deformed the metal sheets in real production. On the other hand, the forming force in SPIF is an essential variable, especially for the design of dedicated equipment or for the safe use of adapted machinery. This paper revisits failure in SPIF by means of an experimental analysis of the influence of process parameters, such as the tool diameter, the spindle speed and the step down, on the formability in SPIF (spifability) of AISI 304 metal sheets, studied in the light of circle grid analysis. The work also involves the independent determination of conventional formability limits by necking and fracture under laboratory conditions by using stretching tests (Nakazima tests), in conjunction with stretch-bending tests performed in order to quantify the influence of the bending induced by the tool radius. Failure strains are experimentally obtained and compared in stretch-bending and SPIF tests, being the failure mode discussed in each case. Finally, the axial forming force evolution was recorded with the aim of analyzing the range of process parameters that would guarantee the safely utilization of the non-dedicated process equipment.     

板料渐进成形数值模拟与实验研究

为提高渐进成形的成形效率和成形质量,了解板料渐进成形的变形规律及工艺参数对成形的影响,采用有限元方法对板料渐进成形过程进行了数值模拟研究,分析了斜壁盒形件渐进成形过程应力分布和厚度变化趋势,通过对不同进给量和不同成形路径进行数值模拟,分析了工艺参数对成形的影响.结果表明,斜壁盒形件最大应力和最大厚度减薄发生在底面拐角处;成形过程中工具头运动轨迹应尽量采用走螺旋线的方式,可以提高成形件的成形能力和成形质量.渐进成形实验表明,数值模拟结果与实验结果基本吻合.     

Stress gradient due to incremental forming of bonded metallic laminates

The residual stress and associated gradient can affect the performance of a material/component during service. Sheet-metal in incremental sheet forming (ISF) due to missing back support may experience high stress gradient across the thickness. The current work is aimed at experimentally analyzing the through-thickness stress gradient in the Cu/steel bonded laminates after ISF deformation. It is found that ISF induces compressive stress gradient, which can be a way greater (about 18 times) than that the rolling process induces in the parent laminates while bonding, specifically when the deformation angle is high. Further, the tool imposes more stress gradient (1–50% depending on the forming conditions) in its motion direction than that in the transverse (or stretching) direction. Moreover, un-strained Cu/steel laminated sheet experiences higher (25%–68%) gradient than that the pre-strained/rolled sheet endures. Regarding the role of technological parameters, high angle, small tool, average step-size and spindle rotation, and low flow-stress induce high stress gradient. The tension tests of the ISFed samples reveal that the post-ISF tensile strength of laminated sheet increases as the stress gradient increases, thus showing a direct relationship between stress gradient and strain hardening in ISF. Finally, models are proposed to predict the stress gradient in the ISFed Cu/steel components.     

大幅面板材渐进折弯成形的本构建模及模拟

为了提高大幅面板材成形的模拟精度,在板材折弯平面应变假设条件下,推导出基于Hill各向异性屈服准则的弹塑性本构方程.借助ABAQUS有限元软件本构模块用户子程序接口,通过编程将上述推导的应力-应变本构关系显示表达式嵌入ABAQUS分析平台.以超长大开口半椭圆形工件成形为例,建立了大幅面钢板渐进折弯的三维弹塑性有限元模型,并数值模拟了多道次渐进折弯成形及回弹全过程.模拟效果和工程应用结果表明,与传统的基于平面应力假设的本构关系模型相比,采用平面应变假设的本构关系模型的模拟结果更接近实验值.     

渐进成形A3003铝板减薄带分析及数值模拟研究

研究渐进成形过程中板料减薄带的变化,可以提供合理的加工参数,提高板料的成形性能和加工利用率,减少零件破裂失效.基于渐进成形过程中金属板料轮廓的变化与理想情况下轮廓的区别,对渐进成形初始成形阶段A3003铝板减薄带的产生原因和剪切力的变化过程进行了理论分析,并通过有限元模拟分别从未变形区金属板料的长度和强度两个角度对板料渐进成形过程中未变形区下沉的影响,以及成形角度和杨氏模量对变形区回弹的影响两个方面,对减薄带的产生原因进行研究.结果表明:板料未变形区的下沉和变形区的回弹使板料在初始加工阶段形成一段平缓区域,工具头在平缓区域的变形性质发生了变化,平缓区域发生剪切变形导致了板料在初始加工阶段形成了减薄带;渐进成形时减小板料未变形区的长度,增大板料与垂直方向的角度可以一定程度上阻碍减薄带的产生,模拟结果与理论分析相符合.     

Finite element analysis of the superplastic forming of thick sheet using the incremental flow formulation

The paper discusses the finite element analysis of the superplastic forming of thick sheet components. The incremental formulation proposed is based on a geometrical approximation of the flow type of constitutive equations that describe the behaviour of the alloy during forming. The spatial discretization is achieved using eight-noded finite elements. An algorithm capable of predicting the correct forming pressure is also presented in a form consistent with the incremental flow formulation. Some experimental validation of these techniques will be shown together with a number of more realistic applications which will illustrate the generality of these techniques and their ability to simulate the forming of complex components. Most of the material in this section is standard but has been included for the purpose of completeness and to introduce the reader to the notation used in the paper. © 1997 John Wiley & Sons, Ltd.     

板厚对08Al薄板单点渐进成形中成形极限的影响

目的 针对渐进成形中成形极限测量难的问题,提出一种新的评定成形极限方法.方法 选用08Al为实验材料,通过模拟和实验相结合的方法,研究不同板厚下成形极限角和减薄率的关系,提出利用成形极限角和最大减薄率2个参数组合的方法判断薄板的成形极限,并通过数控实验验证提出方法的准确性,分析板厚对单点渐进成形工艺成形极限的影响.结果...     

工艺参数对AZ31B镁合金单点渐进翻边精度的影响

目的 以AZ31B镁合金板为研究对象,研究初始成形角、工具直径、成形温度及层间距对单点渐进圆孔翻边精度的影响规律。方法 使用有限元软件对2 mm厚的镁合金板材进行数值模拟,通过计算翻边直壁处的平均回弹量,得出不同工艺参数对单点渐进圆孔翻边直壁轮廓的影响规律。通过正交实验分析了交互作用下工艺参数对圆孔翻边直壁处平均回弹量的影响,通过极差分析确定了最优工艺参数组合,并通过实验对所得结果进行了验证。结果 随着初始成形角的增大、工具直径的增大、成形温度的升高及层间距的减小,圆孔翻边制件直壁处的成形精度提高,各因素按影响程度由大到小的顺序依次为:成形温度、初始成形角、工具直径和层间距。成形精度最高的工艺参数组合如下:初始成形角为30°、工具直径为10 mm、成形温度为275 ℃、层间距为0.5 mm。结论 采用仿真模型模拟单点渐进圆孔翻边过程具有较高的准确性,使用优化后的工艺参数得到翻边零件直壁区域的最小厚度以及平均回弹量与仿真结果误差均在3%以内,升高温度可以明显提高单点渐进圆孔翻边的制件精度。     

单点渐进成形工艺参数对正五边锥形件壁厚的影响

目的 利用数值模拟方法研究单点渐进成形工艺参数对制件成形区最小壁厚的影响规律,得出最优工艺参数组合,提高制件的成形质量。方法 在对2024铝合金正五边锥形件建立有模单点渐进成形数值仿真模型的基础上,对进给率、层间距、成形工具头直径和摩擦因数对制件成形区最小壁厚的影响进行单因素和正交试验分析,并通过物理试验对仿真优化后的工艺参数组合进行验证。结果 正五边锥形件单点渐进成形加工过程中,最小壁厚与进给率、层间距成反比,与成形工具头直径成正比,而摩擦因数对最小壁厚的影响较小;各工艺参数对最小壁厚的影响程度为进给率＞层间距＞成形工具头直径＞摩擦因数;最佳工艺参数为成形头直径9 mm、进给率200 mm/min、加工层间距0.2 mm和摩擦因数0.1。结论 通过有限元仿真得出了单点渐进有模成形工艺对制件最小壁厚的影响规律,通过正交试验分析得出了正五边锥形件单点渐进有模成形最佳工艺参数组合,利用该参数组合可以得到壁厚较为均匀的正五边锥形件。     

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.     

High speed steel produced by spray forming

In this paper, ASP2030 (A30) high speed steel (HSS) was produced by spray forming and the microstructure was studied by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The spray formed A30 (SF A30) steel exhibited a very uniform and fine microstructure consisting of martensite, retained austenite and uniformly distributed network carbides. Microstructure refining can be explained in terms of the rapid solidification of spray forming. M₂C, MC and M₆C type carbides were found in the as-sprayed A30 HSS by XRD and TEM. A uniform distribution of carbides was obtained after forging and annealing. The microstructure properties of SF A30 steel indicate that spray forming can be considered as a cost-effective route for the production of A30 steels and other highly alloyed steels.     

Prediction model for determining the optimum operational parameters in laser forming of fiber-reinforced composites

Composite materials are widely employed in various industries, such as aerospace, automobile, and sports equipment, owing to their lightweight and strong structure in comparison with conventional materials. Laser material processing is a rapid technique for performing the various processes on composite materials. In particular, laser forming is a flexible and reliable approach for shaping fiber-metal laminates (FMLs), which are widely used in the aerospace industry due to several advantages, such as high strength and light weight. In this study, a prediction model was developed for determining the optimal laser parameters (power and speed) when forming FML composites. Artificial neural networks (ANNs) were applied to estimate the process outputs (temperature and bending angle) as a result of the modeling process. For this purpose, several ANN models were developed using various strategies. Finally, the achieved results demonstrated the advantage of the models for predicting the optimal operational parameters.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00304-3     

合金非晶形成能力的研究进展

在描述合金非晶形成能力的各种参数中，过冷液相区的范围△Tx和约化玻璃转变温度Trg是两个最重要最常用的参数，然而在实际应用过程中，仅用这两个参数并不能完全解释所得到的一些实验现象。于是，用来表征合金非晶形成能力的各种参数被相继提出。本文综述了各种表征合金非晶形成能力的有关参数，在这些参数中，每一参数都有其合理性与局限性，但都不能应用于所有合金系，因此，寻求一个更为合理和通用的参数以表征不同合金非晶形成能力就显得尤为迫切。     

Research on deformation characteristics of JCOE forming in large diameter welding pipe

In the present work, the JCOE forming is investigated using the finite element (FE) method. A twodimensional FE model is established for the plane strain condition by FE code ABAQUS, and the FE model is validated by experiments. The aim of this research is to investigate forming quality states in the JCOE forming process; in particular, the effects of technological parameters on forming quality are evaluated. Taking the JCOE forming process of X80 steel φ1 219 mm×22 mm×12 000 mm welding pipe for instance, the deformation characteristics of JCOE forming are analyzed, in which the geometry of the formed pipe, residual stress distributions and effects of process parameters on JCOE forming quality can be obtained. Thus, the presented results of this research provide an effective approach to improve welding pipe forming quality.     

用FEM/FIM研究单壁碳纳米管束

利用范氏力将单壁碳纳米管样品组装到钨针尖上 ,用FEM/FIM对同一碳纳米管样品用热处理方法和场脱附方法进行了研究。场离子显微镜是具有原子级分辨能力的尖端表面分析工具 ,由场离子像推测这次组装的样品是由三根单壁碳纳米管突起组成的碳纳米管束。清洁碳纳米管束样品的场发射像和场离子像有极好的对应关系。场脱附后的碳纳米管束的场发射特性较好地符合Fowler Nordheim场发射模型。通过比较碳纳米管束吸附态和热处理后以及场脱附后的Fowler Nordheim曲线的斜率变化 ,得出碳纳米管束样品逸出功的变化 ,再结合场发射像的变化推断出场脱附与热处理结合是一种较理想的获得清洁碳纳米管表面的方法