圆锥形凹模径向分块压边拉深工艺实验研究

采用圆锥形凹模拉深工艺可以提高成形极限,但需要用压边圈将板坯先压成与凹模面吻合的形状,当变形程度较大时,板坯很容易起皱。为了克服这一缺点,提出了将圆锥形凹模与径向分块压边方法结合的工艺,该工艺可有效改善压边圈与板坯的约束状态,从而达到抑制起皱的目的。对圆筒形件的拉深成形,采用了刚柔复合的径向分块压边圈结构,设计了圆锥形凹模径向分块多压边圈拉深模,取不同凹模半锥角的圆锥形凹模进行了圆筒形件的拉深成形实验。实验表明,新的压边方法能有效克服初始成形过程的起皱,可与锥度较小的凹模一起使用。采用凹模半锥角为45°的凹模,得到AA5754、AA6061和08Al三种板材的极限拉深系数分别为0.410、0.431、0.373,显著提高了成形极限。对圆锥形凹模的拉深成形,给出了理论计算成形极限的方法,理论与实验结果非常接近。     

基于多点成形的液压成形工艺关键技术的研究

介绍了基于液压成形和多点成形原理的板材成形新工艺.该工艺凸模用液体代替,凹模采用多点基本体调形而成.并用凹模垫技术提高多点成形技术中板材面轮廓度形状精度.对该工艺的液压系统、基本体的调形及压边圈等关键技术问题进行了深入研究.研制出了成形装置,并进行模拟试验.     

L2Y2铝板3维曲面的无模成形试验研究

针对板材的无模曲面成形,在自制的多点无模试验装置上对马鞍形曲面的成形进行了研究。结果表明,逐次成形有利于提高曲面的成形极限,变形增量对成形极限有一定的影响。     

阶梯形件液压凸模拉深成形装置的设计及试验

针对阶梯形件在刚模拉深成形中易出现起皱、破裂、壁厚偏差大等缺陷以及普通液压拉深易出现的变形不均匀、不充分等问题，开发了一种简单实用、在拉伸机上就能实现板材预胀充液拉深试验的液压凸模拉深成形装置，该装置采用了液压凸模、刚体凹模的拉深方法。通过不同高度的垫板控制移动凹模的位置，并以1060-O态铝板为材料进行相关试验，利用预胀充液拉深原理，得到阶梯形件。结果表明：该装置可合理匹配预胀压力和凹模预胀位置并显著的提高零件的成形高度和成形质量。     

基于对向液压拉深的高精度拉深件的应用研究

对向液压拉深是在凹模兼液压室的型腔内充满液体,利用凸横带动板料进入凹模后建立的反向液压而使板料成形的方法。对向液压拉深方法可提高拉深时的成形极限、抑制侧壁起皱．使零件具有很高的尺寸、形状精度及表面质量。可实现零件的一体化成形,在精度要求高的拉深件中可得到广泛应用。     

大角度锥台单道次渐进成形工艺的研究

以大角度锥台为研究对象,通过单道次渐进成形试验,分析了工具头半径、轴向进给量、进给速度和主轴转速等对用成形角表示的成形极限的影响;分析了板材厚度对板材减薄率的影响。试验结果表明,影响该类零件成形极限的主要因素依次是轴向进给量、进给速度、主轴转速和工具头半径。板料初始厚度越大,允许的变形区厚度减薄越大。     

筒形件颗粒软凹模拉深成形试验研究

分析了颗粒软凹模成形的工艺特点,设计了筒形件颗粒软凹模拉深成形试验模具,对筒形件颗粒软凹模拉深成形进行了试验研究,成形出了质量良好的圆筒零件.颗粒软凹模拉深成形零件各部分的厚度均减小,而且随着拉深高度的增加,减薄量增大.与刚性模具拉深工艺相比,该工艺可有效提高板材的拉深成形极限.颗粒软凹模拉深成形和刚性模具拉深筒形件各部位表面微观形貌的对比分析表明:颗粒软凹模成形可抑制凸模圆角区域微裂纹的产生.     

复合变形路径下的板材冲压成形极限应变(Ⅰ)——冲压成形极限应变的立论与解析

从4个方面就变形路径对成形极限图影响的研究现状进行综述,并进一步论述了复杂变形路径和单一变形路径的概念,以及基于Hill'48屈服准则的塑性应变几何关系.为了在任意复杂变形路径下计算冲压板材的失稳极限应变,提出"任意复杂变形路径均可简化为线性复合变形路径"、"板材的冲压成形能力亦即板材允许的极限厚度应变",以及"板材在线性复合变形路径下的冲压成形能力取决于其最终变形路径的应变比值"等3个工程简化假设,并对它们进行立论和诠释.同时基于这些假设,在板材承受线性复合变形路径和前后变形路径的应变主轴发生转动的条件下,解析和推导出计算冲压成形极限应变的理论公式.利用这些简化假设和理论公式,可以在任意复杂变形路径下计算板材的冲压成形极限应变并绘制其冲压成形极限图.     

电磁力作用下平板变形的实验研究

通过平板件的电磁无底凹模成形、有底凹模成形的实验研究，发现不同形式的压边圈可以导致不同的工件变形高度。有底凹模成形时，在设备能量足以使工件变形达到凹模底部的情况下，工件的最大变形高度小于凹模深度，并且电压越大，工件的变形高度越小，而且在较大电压的情况下，工件底部还会出现反向变形。对实验现象进行了分析，认为不同形式的压边圈，板料所受径向拉深力不同，导致不同的工件变形高度；板料受撞击产生的反向运动是导致工件最大变形高度小于凹模深度的主要原因。     

直缝焊管液压成形极限理论预测模型

直缝焊管广泛应用于汽车车身管状零件液压成形中,焊接区影响着焊管塑性变形规律,准确评价焊管缩颈或破裂现象是工程上倍受关注的问题。基于金相分析法和显微硬度测量法分析高频感应焊管的结构特征,并根据液压成形条件下高频感应焊管的变形特点,提出一种用于计算直缝焊管液压成形极限的理论方法。基于该方法,选用Swift硬化方程和Hill屈服准则推导出直缝焊管液压成形极限理论预测模型,在已知焊管(包含焊接区和基体区)材料性能参数条件下可获得直缝焊管液压成形极限图。运用此理论预测模型,计算出QSTE340高频感应焊管的液压成形极限图。成形极限的计算结果与试验对比表明,二者吻合较好,这证明所建立的直缝焊管液压成形极限的理论预测模型是正确的。     

航空铝合金复杂构件充液柔性成形过程及质量控制研究

针对某型号飞机铝合金复杂构件充液成形的失效形式,采用有限元数值模拟和试验的手段,研究了毛坯形状、液室压力等关键工艺参数对成形失效的影响,给出了铝合金复杂构件充液成形质量控制的措施,为此类型航空复杂构件的充液成形提供了技术指导。     

One step positive approach for sheet metal forming simulation based on quasi-conjugate-gradient method

In one step inverse finite element approach, an initial blank shape is normally predicted from the final deformed shape. The final deformed shape needs to be trimmed into a final part after stamping, the trimmed area, therefore, needs to be compensated manually before using one step inverse approach, which causes low efficiency and in consistency with the real situation. To solve this problem, one step positive approach is proposed to simulate the sheet metal stamping process. Firstly the spatial initial solution of one step positive method is preliminarily obtained by using the mapping relationship and area coordinates, then based on the deformation theory the iterative solving is carried out in three-dimensional coordinate system by using quasi-conjugate-gradient method. During iterative process the contact judgment method is introduced to ensure that the nodes on the spatial initial solution are not separated from die surface. The predicted results of sheet metal forming process that include the shape and thickness of the stamped part can be obtained after the iterative solving process. The validity of the proposed approach is verified by comparing the predicted results obtained through the proposed approach with those obtained through the module of one step inverse approach in Autoform and the real stamped part. In one step positive method, the stamped shape of regular sheet can be calculated fast and effectively. During the iterative solution, the quasi-conjugate-gradient method is proposed to take the place of solving system of equations, and it can improve the stability and precision of the algorithm.     

The effect of upper sheet on wrinkling and thickness distribution of formed sheet part using double-layer sheet hydroforming

In the hydroforming of curved sheet parts with a small thickness-diameter ratio, qualified parts are difficult to be manufactured when using the traditional hydroforming process. To solve this problem, double-layer sheet hydroforming was proposed and the wrinkle-free sheet parts were obtained in the authors’ previous study, but the inhibition mechanism of forming defects is far from perfection. Therefore, in this paper, the inhibition mechanism of forming defects is investigated by the combination of FE simulations and technological experiments. Different from the previous research, 2198 Al-Li alloy sheet was selected as the lower sheet. Other conditions such as heat treatment status and thickness are the same as before. The principle of wrinkle elimination can be concluded into the following two aspects. On the one hand, the upper sheet cannot be wrinkled during hydroforming, On the other hand, the surface blank holder pressure is applied in the suspending area. In addition, the beneficial friction between this two sheets changes the radial stress state of the lower sheet and makes the radial strain at some specific area (punch contact area and die corner area) decreased. In conclusion, qualified sheet parts can be manufactured by double-layer sheet hydroforming.     

Experimental and numerical analysis of titanium/aluminum clad metal sheets in sheet hydroforming

Clad metals are becoming increasingly emphasized in sheet metal applications. In this research, sheet hydroforming process (SHF) was adopted to improve the formability of Ti/Al clad metal sheets and SUS 304 metal sheets used in computer, communication, and consumer product housings. Both finite element simulation and experimental verification were carried out to investigate the deformation of blanks. Several significant process parameters, such as holding force, friction, counter pressure history, and blank dimensions, were discussed for improving the formability of the two metal sheets. In SHF simulation, a virtual film technique was proposed to realistically approach the hydraulic loading condition during SHF. Finally, the deformed shape and thickness distribution of parts manufactured with SHF were compared with the results of simulation. Good agreements were obtained.     

Development of a hydroforming setup for deep drawing of square cups with variable blank holding force technique

Sheet hydroforming is a process that uses fluid pressure for deformation of a blank into a die cavity of desired shape. This process has high potential to manufacture complex auto body and other sheet metal parts. Successful production of parts using hydroforming mainly depends on design aspects of tooling as well as control of important process parameters such as closing force or blank holding force (BHF) and variation of fluid pressure with time. An experimental setup has been designed and developed for hydroforming of square cups from thin sheet materials. Square cups have been deep drawn using constant and variable BHF techniques. A methodology has been established to determine the variable BHF path for successful hydroforming of the cups with the assistance of programmable logic controller and data acquisition system. Finite element (FE) simulations have also been carried out to predict formability with both of these techniques. It has been found that it is possible to achieve better formability in terms of minimum corner radius and thinning in the case of variable BHF technique than in the case of constant BHF technique (constant force during forming and calibration). The results of FE analysis have been found to be in good agreement with experimental data.     

Improvement of formability for the incremental sheet metal forming process

In order to obtain competitiveness in the field of industrial manufacture, a reduction in the development period for the small batch manufacture of products is required. In order to meet these requirements, an incremental sheet metal forming process has been developed. In this process, a small local region of a sheet blank deforms incrementally by moving a hemispherical head tool over an arbitrary surface. In this work, an incremental sheet metal forming process controlled three dimensionally by a computer has been accomplished. It has been shown by the experiments that a sheet blank is mainly subject to shear-dominant deformation. Therefore, the final thickness strain can be predicted. The uniformity of thickness throughout the deformed region is one of the key factors to improve the formability in the sheet metal forming processes. Using the predicted thickness strain distribution, the intermediate geometry is decided in the manner that a shear deformation is restrained in the highly shear-deformed region and vice versa. This double-pass forming method is found to be very effective so that the thickness strain distribution of a final shape can be made more uniform.     

Blank optimization for sheet metal forming using multi-step finite element simulations

The present study aims to determine the optimum blank shape design for deep drawing of arbitrary shaped cups with a uniform trim allowance at the flange, i.e., cups without ears. The earing, or non-uniform flange, is caused by non-uniform material flow and planar anisotropy in the sheet. In this research, a new method for optimum blank shape design using finite element analysis is proposed. The deformation process is first divided into multiple steps. A shape error metric is defined to measure the amount of earing and to compare the deformed shape and target shape set for each stage of the analysis. This error metric is then used to decide whether the blank needs to be modified. The blank geometry change is based on material flow. The cycle is repeated until the converged results are achieved. This iterative design process leads to optimal blank shape. To test the proposed method, three examples of cup drawing are presented. In every case converged results are achieved after a few iterations. The proposed systematic method for optimal blank design is found to be very effective in the deep drawing process and can be further applied to other sheet metal forming applications such as stamping processes.     

先进充液柔性成形技术及其关键参数研究

基于所提出的具有均匀压边力并轴向加压的板材充液柔性成形技术,面向板材液压柔性成形技术的普遍规律,成形出拉深比较高的铝合金筒形件以及其他复杂形状的零件如方锥盒形件、方盒形件、轴对称锥形件等,对其中的关键技术如初始液压加载状态、液压加载最优路径、破裂控制等一些关键参数进行了研究和优化;考虑板平面方向性系数的影响,利用数值模拟的手段对其成形过程进行了分析,指导实验研究,得出了有益的结论。     

Wrinkling control in aluminum sheet hydroforming

In this paper, the wrinkling behavior of 6111-T4 aluminum alloys during sheet hydroforming process was numerically and experimentally investigated. In sheet hydroforming, one or both surfaces of the sheet metal are supported with a pressurized viscous fluid, while a punch forms the part. In sheet hydroforming the use of a matching female die is not needed. The use of the pressurized fluid delays the onset of material rupture (International Journal of Mechanical Science 2003;45:1815–48) and also acts as an active blank-holding force to control wrinkling in the flange area. To form a wrinkle-free deep-drawn hemispherical cup with sheet hydroforming, a theoretical analysis based on the work of Lo et al. (Journal of Materials Processing Technology 1993;37:225–39) was initially used to predict the optimum fluid pressure profile. Simplifying geometrical assumptions and Tresca material model used in the theoretical analysis provided a fluid pressure profile that resulted in premature rupture of the sheet metal. However, an optimum fluid pressure profile generated by the finite element method, using Barlat's anisotropic yield function (Journal of Mechanical Physics and Solids 1997;45(11/12):1727–63), was successfully applied in sheet hydroforming to make the deep-drawn hemispherical cup without tearing and with minimal wrinkling in the flange area. The finite element model was also capable of accurately predicting the location of the material rupture in pure stretch, and wrinkling characteristics of the aluminum alloy sheet in the draw-in process.     

Modelling Deformation of Hydroformed Circular Plates Using Neural Networks

The process of applying fluid pressure to form metal sheets into desired shapes is widely used in the industry and is known as hydroforming. Similar to most other metal forming processes, hydroforming leads to non-homogeneous plastic deformation of the workpiece. Predicting the amount of deformation caused by any sheet metal forming process leads to better products. In this paper, a model is developed to predict the amount of deformation caused by hydroforming using an artificial intelligence technique known as neural networks. The data used to design the neural network model is collected from an apparatus that was designed and built in our laboratory. The neural network model has a feedforward architecture and uses Powell’s optimisation techniques in the training process. Single- and two-hidden-layer feedforward neural network models are used to capture the nonlinear correlations between the input and output data. The neural network model was able to predict the centre deflection, the thickness variation, and the deformed shape of circular plate specimens with good accuracy. ID="A1"Correspondance and offprint requests to: Dr M. Karkoub, Mechanical and Industrial Engineering Department, College of Engineering and Petroleum, Kuwait University, PO Box 5969, Safat 13060, Kuwait