板料单点渐进成形中成形角对成形影响的模拟分析

介绍了金属板料单点渐进成形的基本原理;利用有限元软件LS_DYNA分析了板料渐进成形中当工具头压下时,不同成形角条件下,工具头与板料接触区域的应力分布;根据对模拟数据的分析比较,讨论了不同成形角对板料成形时的影响;就提高成形直壁件的高度提出了改进意见,并在试验中得到证实。     

单点渐进成形工艺参数对激光拼焊板圆锥台件回弹影响研究

激光拼焊板单点渐进成形回弹是影响成形精度的重要因素。使用回弹角来度量板料回弹大小,并使用正交试验设计对工具头直径、成形高度、下压量、半顶角等因素进行实验研究,得到各因素对回弹的影响程度。得出影响板料回弹因素的大小依次为:成形高度、下压量、半顶角和工具头直径;工具头直径变化对回弹影响不大;成形高度对回弹影响显著,成形高度越高,回弹量越小;在一定范围内,回弹角的大小取决于下压量的大小,下压量越大回弹角越小;过大或过小的半顶角都会导致显著的回弹现象,合适的半顶角设计能够有效减少回弹的出现,从而保证成形精度。最后通过实验验证了正交试验得出的最优工艺参数。     

单点渐进成形中成形角对成形极限的影响

在单点渐进成形中,成形零件的厚度满足正弦定律,成形极限用最大成形角表示.本文设计了测定板料最大成形角的试验装置并通过两组试验来测定LY12M的最大成形角.首先用曲线斜率为变量的旋转类零件初步确定最大成形角范围,然后再用曲线斜率为定值的旋转类零件确定真实最大成形角.经测定,铝板LY12M的真实最大成形角为65°.该方法用来测定板料的最大成形角是简单、可行的.     

有模单点渐进成形工艺参数对1060铝合金成形性能的影响

为了研究各工艺参数对有模单点渐进成形直壁筒形件成形性能的影响,采用正交实验法,对层间距、工具头半径、进给速度和成形道次4个工艺参数进行优化设计,对板料变形区厚度进行仿真研究,并通过极差分析,得出各工艺参数对成形后板料最小厚度的影响。研究结果表明:各工艺参数中,成形道次数对板料成形最小厚度影响最大,工具头半径影响最小;对1 mm厚的1060铝合金板进行优化后,最小成形厚度为0.389 mm,比2道次成形后的最小厚度0.242 mm提高了60%。因此,在有模单点渐进成形直壁筒形件过程中,成形时间允许时,可适当增加成形道次,提高成形质量。     

正十二边形锥件单点渐进成形工艺参数研究

影响正十二边形锥件多道次单点渐进成形壁厚均匀度的因素有很多,其中工艺参数的影响较显著。在确定冷却润滑方式的基础上,采用数值模拟与物理试验相结合的方法,对下压量、工具头直径、进给量等因素对成形制件壁厚均匀度的影响进行分析,得出了各影响因素对正十二边形锥件壁厚均匀度的影响大小依次为:工具头直径、进给量、下压量。通过试验验证了正交试验所得最优工艺参与数值模拟结果的一致性。     

多道次单点渐进成形多参数交互影响

以成形角度为70°的锥形件为研究对象,研究了多道次渐进成形中每个道次的角度间隔、刀具半径和轴向进给量3个成形参数对制件壁厚的交互影响。首先,研究了单个参数在不同道次中变化对制件截面厚度的影响,然后设计正交试验分析了3组参数的交互作用对制件厚度的影响,并获得了成形参数的最优组合。最后进行数控试验验证了仿真结果的准确性。结果表明,3个参数影响的主次顺序为刀具半径、轴向进给量及道次角度间隔,最优组合为刀具半径4 mm,轴向进给量分别为0.5、1.0和1.5 mm,道次角度间隔分别为50°、60°和70°。通过选取合适的成形参数,成形质量和成形效率得到了提高。     

钛板材单点渐进成形工艺数值模拟分析

单点渐进成形技术可以明显地缩短新产品的生产周期,对于加工小批量、多品种、形状复杂的薄板成形件有着一定的优势.运用有限元分析软件ANSYS/LS-DYNA对钛板材的有模单点渐进成形过程进行了数值模拟,分析了不同板厚的钛板材对成形性能的影响,为后续实验研究奠定基础.     

板材单点渐进成形工艺数值模拟与成形缺陷研究

工具头运动轨迹的动态加载是建立板材渐进成形有限元模型的难题。首先基于DYNAFORM建立基本的有限元模型,而后直接提取数控代码中工具头的位移坐标信息并添加至关键字文件,从而实现任意复杂运动曲线的加载;数控代码规划的加工轨迹存在起刀区域集中和加工方向单一的问题,容易造成破裂和失稳缺陷。起刀区域塑性变形大,累积效应使该区域板材严重减薄,采用均布策略,并保证均布后相邻起刀点的空间距离大于塑性变形区的最大半径可避免此缺陷。同时,运用顺逆相间的加工方式避免了单一方向加工方式存在的材料堆积引起的形状失稳和棱纹缺陷。     

单点渐进成形装置研制

单点渐进成形是一种基于分层逐步成形的原理,每一层采用局部塑性变形,最终达到产品目标形状的先进工艺.在加工小型板材三维零件时只需要简单工装即可实现成形,但对于中、大型覆盖件则需要精度高的装置以保证工件的成形质量.利用数控铣床提供的X、Y、Z方向移动定位等功能,开发制造了适于数控铣床的单点渐进成形加工的专用装置.通过大量实...     

A new formability indicator in single point incremental forming

Material properties play an important role in determining the sheet fracture in metal forming processes. However, the degree of influence of a material property on the forming extent depends on the nature of the forming process employed. In the current study, the effect of various material properties on the formability in SPIF has been investigated. Correlations of the formability with material properties under investigation were developed in order to establish a new formability indicator. An empirical model describing the effect of the newly introduced formability indicator has also been proposed.     

Influence of mechanical properties of the sheet material on formability in single point incremental forming

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 single point incremental forming operations, in which the final shape of the component is obtained by the relative movement of a simple and small punch with respect to the blank, appear quite promising.In the paper, material formability issues in incremental forming were studied. Some relevant correlations among material formability and other mechanical properties of the material were analysed. The FLD₀ value, i.e. the major strain at fracture in plane strain conditions, was determined for different materials and the influence of the main material parameters on formability was accurately investigated through a statistical analysis.     

Theory of single point incremental forming

This paper presents a closed-form theoretical analysis modelling the fundamentals of single point incremental forming and explaining the experimental and numerical results available in the literature for the past couple of years. The model is based on membrane analysis with bi-directional in-plane contact friction and is focused on the extreme modes of deformation that are likely to be found in single point incremental forming processes. The overall investigation is supported by experimental work performed by the authors and data retrieved from the literature.     

Mechanics of fracture in single point incremental forming

Single point incremental forming (SPIF) is a sheet metal forming technique which has gained considerable interest in the research community due to its enhanced formability, greater process flexibility and reduced forming forces. However, a significant impediment in the industrial adoption of this process is the accurate prediction of fracture during the forming process. This work uses a recently developed fracture model combined with finite element analyses to predict the occurrence of fracture in SPIF of two shapes, a cone and a funnel. Experiments are performed to validate predictions from FEA in terms of forming forces, thinning and fracture depths. In addition to showing excellent predictions, the primary deformation mechanism in SPIF is compared to that in conventional forming process with a larger geometry-specific punch, using the deformation history obtained from FEA. It is found that both through-the-thickness shear and local bending of the sheet around the tool play a role in fracture in the SPIF process. Additionally, it is shown that in-spite of higher shear in SPIF, which should have a retarding effect on damage accumulation, high local bending of the sheet around the SPIF tool causes greater damage accumulation in SPIF than in conventional forming. Analysis of material instability shows that the higher rate of damage causes earlier growth of material instability in SPIF. A new theory, named the ‘noodle’ theory, is proposed to show that the local nature of deformation is primarily responsible for increased formability observed in SPIF, in-spite of greater damage accumulation as compared to conventional forming.     

主轴转速对单点渐进成形工件表面粗糙度的影响

表面粗糙度是单点渐进成形技术的主要指标之一。在单点渐进成形机上对2A12铝合金薄板进行单点渐进成形实验,研究了主轴转速对成形工件表面质量的影响。实验表明:随着主轴转速的增大,粗糙度总体趋势是逐步减小,速度达到一定值时,粗糙度趋于平稳;转速低时,表面有类似鱼鳞纹的刀路,随着转速的变大,鱼鳞纹越来越小,直至消失,表面也越来越光亮。     

主轴转速对单点渐进成形精度的影响

研究了不同主轴转速条件下的成形件的回弹量大小,结果表明:在较低的主轴转速范围内,回弹量随主轴转速的增加而增大;在中等主轴转速范围内,回弹量随主轴转速的升高而减小,但变化幅度不大;在较高的主轴转速范围内,回弹量随主轴转速的增加而增大,且变化幅度较大。同时,分析了不同主轴转速范围下成形件的表面质量,结果表明:在低速和高速主轴转速下,成形件表面几乎没有鱼鳞纹,质量较好;在中间主轴转速范围内,成形件的表面质量较差,且鱼鳞纹较多。并且运用负补偿的方法研究了不同补偿值条件下的回弹量大小,结果表明:采用负补偿的方法能够减小成形件的回弹量。     

Mechanism investigation for the influence of tool rotation and laser surface texturing (LST) on formability in single point incremental forming

Single point incremental forming (SPIF) is a new sheet metal forming process which achieves higher formability, greater process flexibility and reduced forming force compared to conventional sheet forming operations due to its characteristic of localized deformation. In recent years, a novel SPIF process assisted by localized friction heat is developed to further improve the material formability. Physically, the frictional heat is generated by the high relative motion at tool–workpiece interface resulted from tool rotation. However, the mechanisms behind formability difference induced by tool rotation at both low and high speed ranges are required to investigate in detail. In this paper, a series of experiments with an increase of tool rotation speeds ranging from 0 to 7000 rpm are conducted to form AA5052-H32 aluminum alloy sheets into a truncated funnel. Additionally, the obtained results are analyzed in terms of formability, forming forces and temperature trends to find out the different roles of friction and heat during the forming process. As a result, the formability behaviors at varying tool rotation speeds can be categorized into four stages according to different reasons. It indicates that friction is the dominant factor in low tool rotation speed range (0–1000 rpm) but will be substituted by thermal effect and potential dynamic recrystallization in high tool rotation speed range (2000–7000 rpm). Furthermore, due to the proved lubrication enhancement and hydrodynamic enhancement generated by surface textures, a laser surface textured forming tool is also utilized to show its influence on forming forces, measured temperatures and the corresponding formability. Finally, it demonstrates that the fabricated laser surface texturing (LST) is capable to reduce the friction at tool–workpiece interface and change the magnitude of heat generation.     

Twist revisited: Twist phenomena in single point incremental forming

Twist phenomena in incrementally formed parts have been observed both in the domain of single and two point incremental forming. In the reported experiments the resulting twist direction typically corresponds to the toolpath direction and can be explained by the monotonous tangential force component exerted on the workpiece when using unidirectional toolpaths. When processing parts with high drawing angles, however, twist deformations corresponding to in-plane shear in opposite toolpath direction have been observed by the authors. In this paper this phenomenon is documented and explained by means of strain measurements and FEA results. The role of asymmetric, cumulative, extended strain effects, resulting in severe thinning, and reinforced when stiff, semi-vertical rib features are present in the part geometry, is demonstrated by means of a detailed deformation analysis.