板料凸起成形的底部压缩拉深法

介绍了凸起成形的一种新加工方法--底部压缩拉深法.利用有限元软件Deform-3D对薄板上凸起成形过程进行了数值模拟,分析了初始板厚、摩擦条件、背压对加工载荷和凸起高度的影响.结果表明:初始板厚、摩擦条件、背压对加工载荷和凸起高度有明显影响.初始板料越厚,极限凸起高度越高,缩孔缺陷越难发生;摩擦系数越小,极限凸起高度越高,越容易产生缩孔缺陷;施加的背压越大,极限凸起高度越高,越容易产生缩孔缺陷.选取合适的加工条件,可避免缩孔缺陷.     

摩擦系数对DP780钢拉深成形极限的影响

首先对DP780试样进行圆杯拉深试验,获得DP780试样的极限拉深深度。然后建立圆杯拉深试验的有限元模型,定量分析摩擦系数变化对DP780钢拉深成形应力应变演化的影响规律。最后将拉深试验和有限元仿真相结合,利用CockcroftLatham准则对不同摩擦系数下的DP780钢拉深成形极限进行预测和比较,定量获得摩擦系数对极限拉深深度和极限应变的影响规律。结果表明,极限应变不能用于评价拉深成形极限,应采用极限拉深深度。板料与凹模和压边圈间的摩擦系数越大,DP780钢的极限拉深深度越小,板料与凸模间的摩擦系数对极限拉深深度影响较小。为了提高DP780钢的拉深成形极限,应尽量减少板料与模具间的摩擦系数,且重点关注板料与凹模和压边圈间的摩擦系数。     

材料参数对斜壁矩形盒件多点拉深成形性能的影响

多点成形技术是一种用于三维板类件成形的柔性加工技术.本文采用数值模拟方法研究了三个重要的材料力学性能参数──各向异性指数、应变硬化指数和屈服强度对斜壁矩形盒件多点拉深成形性能的影响.结果表明,与传统的模具拉深成形一样,板料的成形性能参数对多点拉深成形结果有着十分重要的影响;并且在一定的范围内,材料的各向异性指数越大,硬化指数越大,屈服强度越低越有利于斜壁矩形盒件的多点拉深成形.     

单点渐进成形时工艺参数对成形能力的影响

采用2A12铝合金作为试验材料,以成形极限角作为衡量工艺参数对板料单点渐进成形的成形能力影响的标准。试验中研究对成形能力影响的工艺参数有:工具头半径、加工步长、进给速度和主轴转速。采用正交试验法对板料在单点渐进成形中的成形极限进行研究。试验结果表明,对板料单点渐进成形的成形能力影响最大的因素是加工步长,其次是进给速度、主轴转速和工具头半径。     

不同层间距对板料渐进成形影响的数值模拟与试验研究

采用有限元法对板料成形过程进行数值模拟,分析了圆锥台件渐进成形过程中不同层间距对等效应变、应力和厚度变化趋势的影响。试验表明,层间距越小,最终等效应变量越大,成形极限越高,较小的层间距有利于减少局部应力集中,数值模拟结果与试验结果基本吻合。     

基于CAE的铝合金板料冲压成形中摩擦特性研究

依据摩擦理论和有限元仿真理论,通过数值仿真计算的方法,将有限元计算出的摩擦力与实际生产中的摩擦力对应起来,分析了不同摩擦系数下铝合金板料在冲压成形过程中的摩擦特性。研究了铝合金板料在冲压成形过程中的摩擦力变化规律以及不同摩擦系数对摩擦特性和成形质量的影响。研究表明:铝合金板料冲压成形后期摩擦力随着摩擦系数增大而迅速增加,但板料成形质量评价指标升高,板料厚度更加均匀;通过研究不同节点摩擦力随时间的变化曲线,板料减薄区和起皱区的摩擦力变化规律完全不同。     

差厚拼焊板拉深方盒形件成形极限及焊缝移动

采用Dynaform专业板料成形软件,对差厚异质激光拼焊板拉深方盒形件的成形过程进行了研究.结果表明:母材厚度差对压边力的合理范围以及盒形件的成形极限和焊缝移动量有很大的影响;两种母材所占比例不同(焊缝位置变化)时,比例差别越大,成形极限越小,薄侧材料所占比例越大,焊缝移动量也越大.并根据两种母材在成形过程中的应力状态和应变状态分析了这些现象.     

SLS的成形工艺参数对木塑复合材料烧结性能的影响

以木粉、热熔胶及聚丙烯等为原料,制备木塑复合材料,在HRPS—Ⅲ激光快速成形机上成形试件,试验采用正交优化设计方法,对木塑复合材料采用不同工艺参数(激光功率、激光束扫描速度、扫描间距及预热温度)进行烧结,以烧结密度为主要性能指标,采用方差分析法分析,得出一组既保证烧结质量与加工效率,又合理匹配的优化成形工艺参数.结果表明,扫描速度越低、激光功率越大、扫描间距越小和预热温度越高,烧结密度越大.     

1060铝板渐进成形极限及影响因素

目前,渐进成形极限曲线(FLC)主要采用实验方法获得,耗时、耗材,且无统一的制作标准。针对理论预测方法较少的问题,借助少量实验,采用Lemaitre韧性断裂准则,预测1060铝板渐进成形极限曲线,进而将预测曲线与实验曲线进行对比,研究工艺参数对渐进成形极限曲线的影响。结果表明,Lemaitre韧性断裂准则能较好地预测1060铝板渐进成形极限曲线,该方法可运用于渐进成形极限曲线的预测。渐进成形中,层间距越小,工具头转速越高或进给速度越低,板料成形极限曲线越高,板料越不容易开裂,成形性能越好。工具头半径在一定条件下,对成形极限曲线的高度影响并不明显。     

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。     

成形轨迹对数控渐进成形质量的影响

为了研究数控渐进成形过程中不同的成形轨迹对成形质量的影响,在给出下压点集中的等高线轨迹、下压点分散的等高线轨迹、等螺距螺旋线轨迹和不等螺距螺旋线轨迹这4种成形轨迹的生成方法的基础上,采用ANSYS/LS-DYNA软件,对基于这4种成形轨迹的数控渐进成形过程进行数值模拟,并根据数值模拟结果,对比分析了基于这4种成形轨迹的...     

数控渐进正/反向复合成形中成形顺序对成形质量的影响

对于数控渐进成形中装夹面上下两侧都具有形体特征的复杂钣金件,仅利用单一的数控渐进反向成形或正向成形无法完成其成形。针对此问题,提出了一种基于正向成形与反向成形相结合的数控渐进复合成形方法,并给出了3种复合成形策略即正向成形与反向成形的3种成形顺序:反向-正向成形、正向-反向成形、正向/反向并行成形。同时利用数值模拟和实际成形实验对比分析了上述3种成形顺序对成形质量的影响。研究结果表明,采用正向-反向成形和正向/反向并行成形的成形效果优于反向-正向成形;在3种复合成形方式中,采用正向-反向成形的成形质量与成形效率最高。     

管材流体压力成形三维成形极限图

成形极限图是一种评估单向拉伸到双向等拉应力范围内板料成形性能的有效手段。传统板料成形中,法向受到的应力远小于面内应力,所以,传统成形极限图是基于忽略法向应力而简化为平面应力状态的理论计算。该文论述了传统成形极限图以及现有的考虑法向应力影响的二维成形极限图在研究液压成形中流体压力影响时存在的缺陷与不足;同时,在二维成形极限图以及固体现实应力空间的基础上,建立了以法向流体压力p的函数f(p)为第三轴的三维成形极限图。该三维成形极限图不仅可以考虑液压成形中流体压力的影响,而且能够形象直观呈现出成形极限随流体压力的变化速率。     

基于冲压与数控渐进成形的复合成形

针对冲压工艺难以成形形状复杂板材件、冲压模具难以制造或加工成本高以及单独采用数控渐进成形加工效率低的问题,提出基于冲压工艺与数控渐进成形工艺相结合的复合成形方法,并给出了基于冲压与数控渐进成形的复合成形的数值模拟方法。采用冲压成形、数控渐进成形和复合成形3种成形方式,以有限元分析软件数值模拟分析同一形状板材件,对比分析数值模拟后的板材件的轮廓尺寸精度与厚度分布。结果可知,采用复合成形得到的板材件轮廓尺寸精度与厚度分布能够满足实际应用,所提出的复合成形方法具有可应用性。     

Investigation into a new hybrid forming process: Incremental sheet forming combined with stretch forming

Asymmetric incremental sheet forming (AISF) is a process for the flexible production of sheet metal parts. In AISF, a part is obtained as the sum of localised plastic deformations induced by a simple forming tool that moves under CNC control. Three main problems exist in AISF: material thinning, geometric accuracy and the process duration. These limits restrict the range of applications of AISF. This paper focuses on a new hybrid process, the combination of AISF and stretch forming. First results are presented that show the positive impact of this hybrid process on the process limits.     

薄板多点成形与模具成形过程数值模拟及成形性比较

基于动力显式有限元方法,针对不同工艺参数对带压边薄板类零件的多点成形和模具成形过程的影响进行了数值模拟与比较分析。由于成形方式的不同,各参数对起皱、破裂等成形缺陷的影响也不尽相同。通过对比分析发现,相同条件下多点成形对破裂的抑制效果优于模具成形;只要参数选取适当,板材在多点成形方式下的成形质量可以达到或超过模具成形方式。这些结果对于认识多点成形方法的塑性变形特点、合理设置多点成形工艺参数具有指导作用。     

Experimental study of forming and tightening processes with thread forming screws

Thread forming screws are being increasingly used, particularly in the automobile industry. They are designed to directly assemble two parts by displacing material to form their own thread. This specificity implies knowledge of the screwing torque needed for the thread to be formed in the lower plate of the assembly and of the tightening torque necessary so as to establish the preload in the assembly. The experimental study presented in this paper is divided into two parts.The first concerns the thread forming process and shows the influence of the geometrical parameters of the thread forming screw and of the work-piece, and the influence of the process parameters on the maximum forming torque. A compromise can be proposed for the choice of the lead hole diameter, which is the most important parameter to be considered in order to keep a reasonable forming torque while obtaining threads deep enough to avoid stripping problems.The second part concerns the tightening process. An original experimental device is used to enable an empirical formula to be proposed, based on the ISO standard screw formula giving the tightening torque according to the preload applied inside the assembly.     

A review of spinning, shear forming and flow forming processes

In the last two decades or so, spinning and flow forming have gradually matured as metal forming processes for the production of engineering components in small to medium batch quantities. Combined spinning and flow forming techniques are being utilised increasingly due to the great flexibility provided for producing complicated parts nearer to net shape, enabling customers to optimise designs and reduce weight and cost, all of which are vital, especially in automotive industries.In this paper, process details of spinning and flow forming are introduced. The state of the art is described and developments in terms of research and industrial applications are reviewed. Also, the direction of research and development for future industrial applications are indicated.     

Electro-hydraulic forming of sheet metals: Free-forming vs. conical-die forming

This work builds upon our recent advances in quantifying high-rate deformation behavior of sheet metals, during electro-hydraulic forming (EHF), using high-speed imaging and digital image correlation techniques. Aluminum alloy AA5182-O and DP600 steel sheets (1 mm thick, ∼152 mm diameter) were EHF deformed by high-energy (up to ∼34 kJ) pressure-pulse in an open die (free-forming) and inside a conical die. The deformation history (velocity, strain, strain-rate, and strain-path) at the apex of the formed domes was quantified and analyzed. The data shows that the use of a die in the EHF process resulted in an amplification, relative to free-forming conditions, of the out-of-plane normal velocity and in-plane strain-rate at the dome apex. This amplification is attributed to the focusing action of the die on account of its conical geometry. Further, while the strain-path at the dome apex was generally linear and proportional, the use of a die resulted in greater strain at the apex relative to the strain during free-forming. The sheet deformation profile in the EHF process was found to be different from that previously observed in electromagnetic forming (EMF) and, thus, the two processes are expected to result in different strain-paths and formability. It is anticipated that quantitative information of the sheet deformation history, made possible by the experimental technique developed in this work, will improve our understanding of the roles of strain-rate and sheet-die interactions in enhancing the sheet metal formability during high-rate forming.