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.     

基于随动支撑的板料渐进成形数值模拟

目的 提出了基于随动支撑的板料渐进成形方法,研究基于随动支撑的渐进成形在刀具与随动板之间距离不同时成形精度、厚度、轴向力、等效应变和等效应力的变化情况。方法 通过对厚度为1 mm的6061铝合金板料分别进行普通渐进成形数值模拟、刀具与随动支撑板距离为1 mm和0.8 mm的随动支撑渐进成形数值模拟,分析了板料在成形过程中成形精度、厚度、轴向力和等效应变的变化情况,并将普通渐进成形数值模拟的结果与刀具和随动支撑板距离为1 mm和0.8 mm的基于随动支撑渐进成形数值模拟结果进行对比分析。结果 与普通渐进成形相比,随动支撑渐进成形能够提升成形精度,但当刀具与随动板之间的距离较小时,成形精度较差;随动支撑渐进成形板料侧壁厚度更薄,轴向力的数值及波动范围都更大,且随着刀具与随动支撑板之间距离的减小而增大。此外,当刀具与随动支撑板之间的距离为0.8 mm时,随动支撑渐进成形板料的等效应变会明显增大。结论 基于随动支撑的板料渐进成形在一定程度上可以提高板料成形精度。     

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...     

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.     

LY12超塑性成形有限元分析

基于LY12铝合金超塑性材料属性建立了弹-粘塑性本构模型.利用该本构模型并结合最大等效应变速率控制压力变化算法对LY12铝合金板超塑性圆杯成形进行数值模拟,得到圆杯变形过程中的应力应变分布、板料厚度变化及所需成形时间.根据模拟获得的优化压力时间曲线对圆杯进行超塑性气压胀形加载实验,制件厚度分布与模拟结果非常接近.     

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。     

金属板材单点渐进塑性成形过程的计算机模拟

研究了金属板材单点渐进塑性成形的成形机理,通过建立渐进成形的变形模型,详细分析了变形过程中受力的情况及成形过程,利用ANSYS软件对成形过程进行了计算机模拟.     

金属板材数控渐进成形工艺的研究进展

为了总结过去十几年国内外学者对板材数控渐进成形工艺技术的研究进展,对渐进成形工艺成形机理方面的研究成果进行了综述,分析了其材料变形的特点;全面概述了近年来国内外学者有关成形工艺参数对成形极限、成形精度、表面质量及能耗和效率的影响方面的研究成果,并介绍了国内外金属板材渐进成形装备的研究进展,最后对新兴的板材渐进成形工艺进行了总结概括。现有研究表明,成形件几何精度、表面质量和成形效率等方面的不足仍然是制约该技术广泛工业化应用的关键问题,同时渐进成形件的形性协同控制机理也亟待研究。     

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。     

铝合金双曲率薄壁件电磁渐进辅助拉伸成形工艺方案设计与开发

目的 针对铝合金双曲率薄壁件传统拉伸成形工艺成形均匀性差的问题,提出一种采用电磁渐进辅助拉伸成形的高精度成形工艺。方法 设计电磁渐进辅助拉伸成形工艺方案,基于有限元仿真软件LS-DYNA R13.0,建立拉伸成形和电磁成形有限元模型。通过数值仿真研究线圈移动路径和放电电压组合对成形质量的影响以及薄壁件的整体贴模成形过程和等效塑性应变。结果 与单程放电相比,双程放电能够大幅度提高板材变形均匀性。与以中间值电压连续放电以及先大电压后小电压的放电电压组合相比,在先小电压后大电压的放电电压组合下,板材的成形质量更高。选择线圈双程顺序移动路径和7 kV-10 kV放电电压组合,通过10次拉伸和9层54次放电,得到了减薄率仅为3%的贴模性良好的双曲率薄壁件。变形量基本呈现随着放电层数的增加而不断降低的趋势。电磁放电仅扩展更大的塑性应变区域,不改变已贴模区板材的塑性应变值。结论 与拉伸成形相比,电磁渐进辅助拉伸成形工艺有效提高了板材的塑性变形程度并极大控制了回弹的发生。     

Finite element modelling and experimental investigation of single point incremental forming process of aluminum sheets: influence of process parameters on punch force monitoring and on mechanical and geometrical quality of parts

New trends in sheet metal forming are rapidly developing and several new forming processes have been proposed to accomplish the goals of flexibility and cost reduction. Among them, Incremental CNC sheet forming operations (ISF) are a relatively new sheet metal forming processes for small batch production and prototyping. In single point incremental forming (SPIF), the final shape of the component is obtained by the CNC relative movements of a simple and small punch which deform a clamped blank into the desired shape and which appear quite promising. No other dies are required than the ones used in any conventional sheet metal forming processes. As it is well known, the design of a mechanical component requires some decisions about the mechanical resistance and geometrical quality of the parts and the product has to be manufactured with a careful definition of the process set up. The use of computers in manufacturing has enabled the development of several new sheet metal forming processes, which are based upon older technologies. Although standard sheet metal forming processes are strongly controlled, new processes like single point incremental sheet forming can be improved. The SPIF concept allows to increase flexibility and to reduce set up costs. Such a process has a negative effect on the shape accuracy by initiating undesired rigid movement and sheet thinning. In the paper, the applicability of the numerical technique and the experimental test program to incremental forming of sheet metal is examined. Concerning the numerical simulation, a static implicit finite element code ABAQUS/Standard is used. These two techniques emphasize the necessity to control some process parameters to improve the final product quality. The reported approaches were mainly focused on the influence of four process parameters on the punch force trends generated in this forming process, the thickness and the equivalent plastic deformation distribution within the whole volume of the workpiece: the initial sheet thickness, the wall angle, the workpiece geometry and the nature of tool path contours controlled through CNC programming. The tool forces required to deform plastically the sheet around the contact area are discussed. The effect of the blank thickness and the tool path on the punch load and the deformation behaviour is also examined with respect to several tool paths. Furthermore, the force acting on the traveling tool is also evaluated. Similar to the sheet thickness, the effect of wall angle and part geometry on the load evolution, the distribution of calculated equivalent plastic strain and the variation of sheet thickness strain are also discussed. Experimental and numerical results obtained allow having a better knowledge of mechanical and geometrical responses from different parts manufactured by SPIF with the aim to improve their accuracy. It is also concluded that the numerical simulation might be exploited for optimization of the incremental forming process of sheet metal.     

An investigation into thickness distribution in single point incremental forming using sequential limit analysis

Single point incremental forming (SPIF), needing no dedicated tools, is the simplest variant of incremental sheet metal forming processes. In the present work, a simplified model of SPIF of a truncated cone, capable of predicting the thickness distribution, has been developed using sequential limit analysis (SLA). The obtained results were validated experimentally and compared with thickness predictions obtained from an explicit shell FE model implemented in Abaqus. It is shown that SLA is capable to solve the thickness prediction problem more accurately and efficiently than the equivalent FEA approach. As an application of the proposed model, the effect of the diameter of the hemispherical tool tip and the step down on the thickness distribution and the minimum thickness in a 50° cone is studied using SLA. By introducing bending and stretching zones in the wall of the cone, variations of the minimum thickness by changing the tool diameter and the step down are discussed.     

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.     

An assessment of various process strategies for improving precision in single point incremental forming

Single point incremental forming (SPIF) is a process with the capability to form complex geometries using a tool of very simple geometry, without the need for a matching die. However, large elastic springback resulting from the die-less nature of the process can cause problems if high levels of accuracy are required. The aim of this investigation is to use numerical modelling to investigate different strategies to improve the process precision. A finite-element (FE) model has been used to investigate the effects of adding a backing plate, a supporting kinematic tool and modifying the final stage of the tool path. The results show that the backing plate will minimise the sheet bending near to the initial tool contact location; the additional kinematic tool will reduce springback; and the extension of the tool path across the base of the sheet will eliminate the pillow effect. The cumulative effect of introducing these features to the process shows an improvement in the overall accuracy of the profile and in the thickness distributions of the final product. The results contribute to a better understanding of springback in SPIF.     

Microstructure and texture evolution during incremental sheet forming of AA1050 alloy

In incremental sheet forming higher limiting strain can be achieved compared to the conventional sheet metal forming process, which results in increased formability. The higher level of strain may be accompanied by non-uniform thinning. Thus, the different sections in a component may undergo different levels of deformation. In the present work a truncated cone of AA1050 H14 alloy was formed using the incremental sheetmetal forming (ISF) technique. The deformation mechanism during ISF was studied by investigating the microstructural and texture evolution in the truncated cone along the thickness of the cone wall. High resolution electron backscatter diffraction was performed at different sections of the formed truncated cone. The results show the formation of subgrains in different sections of the cone. At higher strains, grains become thin and elongated which results in grain fragmentation and formation of small grains. These small grains undergo complete recovery process and new grain boundaries (low and high angle) are formed within the thin elongated grains. Further, the evolution of shear texture shows the evidence of shear mode of deformation during incremental sheet forming. Thus, the presence of through thickness shear could be used for understanding the higher forming limit in the ISF process.