板条多点成形中曲率分布及回弹控制的研究

分析了板条在整体模具成形与多点成形过程中的受力状态,指出　整体模具成形和多点成形的实质均为多点弯曲成形;通过有限元分析揭示了采用不同成形方式,如：多点模具成形、多点压机成形和整体模具成形时,板条柱面弯曲曲率分布及回弹规律,从而提出了有效抑制回弹及均布曲率的反复多点成形方法;利用有限元法对反复成形抑制回弹的机理进行了分析,考查了反复成形次数对曲率分布及回弹控制的影响。     

板材多点成形使用弹性垫后回弹的数值模拟

利用有限元软件LS-DYNA对板材冲压成形的回弹进行数值模拟。使用3mm厚的弹性垫抑制板材成形产生的压痕,但弹性垫的使用加上板材的回弹会导致成形误差的增大。基于数值模拟的结果,提出了修正基本体群成形面补偿回弹。经过两次补偿,精度得到了很好的提高,证明该方法可以很好地补偿多点成形中的回弹。     

多点拉形工艺及其数值模拟研究

介绍了多点拉形工艺的基本原理;利用非线性有限元软件进行了多点拉形过程的数值模拟,并对多点拉形中出现的压痕缺陷的产生原因及抑制方法进行了研究.结果表明:多点拉形工艺产生的压痕主要表现为凹凸压痕;采用弹性垫技术能够有效抑制压痕的产生;选择适当厚度弹性垫,可以得到表面光滑、成形误差较小的工件.     

船用钢板多点成形试验研究

使用多点简易模具对不同材料、厚度的各种规格船用钢板多点冷成形过程进行试验研究。试验结果表明：船用钢板能够通过多点冷成形的方式成形;船用钢板在多点成形过程中的主要缺陷为压痕和起皱;船用高强钢板比低强度钢板更容易产生褶皱缺陷。在钢板上面加垫聚氨脂弹性垫,在钢板下面加垫B级钢板可有效抑制压痕及起皱缺陷的产生。     

压气机叶片辊轧模具型腔回弹补偿方法研究

航空发动机高压压气机叶片在辊轧成形过程中会沿着弦长方向发生回弹,直接影响叶片的成形精度进而影响其气动性能。为实现航空发动机压气机叶片无余量辊轧成形,提出并研究基于截面线回弹补偿的叶片辊轧模腔优化设计方法。分析钣金件弯曲变形过程并基于钣金件的几何结构和材料特性建立回弹前后中心角的变化模型。在此基础上提出叶片截面回弹补偿模型,并对辊轧叶片工艺模型截面进行回弹误差补偿。将回弹补偿后的叶片工艺模型截面线族绕轧辊轴线进行扇态分布并重构辊轧模具型腔。基于数值计算方法使用几何映射和回弹补偿设计的型腔对叶片辊轧成形过程进行模拟,并获得了相应的轧制成形叶片模型。结果表明,回弹补偿后的模具型腔能够有效提高叶片型面的成形精度,叶片成形误差缩小到原来的16.7%。本文研究内容为压气机无余量辊轧成形模具设计提供理论支撑,同时对不规则薄壁类结构塑性成形精度控制具有参考价值。     

铝合金整体壁板时效成形模具型面构造

时效成形是飞机整体壁板的主要成形工艺之一,由于成形过程中回弹量大的特点,需要对模具进行补偿以消除回弹对零件成形精度的影响。为了有效消除回弹影响,提出一种有限元模拟与物理试验相结合的思路,基于有限元模具型面回弹补偿—试验迭代的频域模具型面修正方法。以2124铝合金材料为例,以零件理论外形作为初始模具型面对整体壁板进行仿真回弹补偿迭代,经过6次补偿,零件成形误差减小到0.47 mm,把有限元迭代所得模具型面进行工艺试验,验证结果表明,仿真迭代所得模具型面成形零件的误差为0.63 mm;达不到0.5 mm的外形误差要求。进一步采用模具"频域"修正算法对时效成形模具型面进行修正,经过2次修正,成形零件误差降低至0.484 mm,满足使用要求,结果表明该方法可行。     

圆柱面多点成形中弹性垫对压痕抑制的数值模拟

压痕是板材多点成形中特有的成形缺陷,是多点成形必须解决的问题。通过ANSYS软件对板材进行圆柱面的多点成形仿真分析,并针对分析的结果提出了抑制压痕的方法,进一步数值模拟说明了一定厚度的弹性垫技术消除压痕缺陷的有效性。     

RSM优化冲焊型液力变矩器叶片冲压工艺及回弹抑制

冲焊型液力变矩器性能与叶片形状密切相关，为提高叶片成形精度，减小回弹对性能的影响，以摩擦系数、模具间隙、冲压速度为试验因素，以叶片最大减薄率和最大回弹量为优化目标，基于优化拉丁超立方试验方法，通过Dynaform对涡轮叶片冲压过程及回弹变形进行模拟获得样本数据，研究不同工艺参数对叶片成形质量的影响，并得到关于优化目标的多项式回归响应面模型。结合多目标优化算法对冲压工艺进行优化求解，获得最优解集，选取最优冲压工艺参数组合。最后对所选优化工艺参数进行仿真验证，结果显示，优化后叶片成形质量良好，减薄率和回弹均得到优化。     

基于快速回弹补偿的橡皮囊液压成形模面设计方法

橡皮囊液压成形工艺(简称"橡皮成形")是航空钣金成形的主要方法之一,而回弹是影响其产品制造精度的主要缺陷.回弹补偿技术可有效地消除钣金件回弹误差,但其依赖的数值模拟耗时极长,目前不易于大范围推广.提出一种考虑回弹误差修正的模面设计方法,即在完成模具设计后,直接进行模面的调整,无须单独对零件进行数值模拟.针对橡皮成形零件的特点,提出基于特征的模面快速设计方法.研究曲弯边特征的回弹规律,并建立针对曲弯边的回弹分布函数,以实现回弹角快速预测.基于位移调整法,将回弹角转化为模面网格的调整量,可完成模面的补偿.将该方法应用于某飞机零件的模面设计中,通过数值模拟对补偿后的模具成形效果进行验证,结果表明该方法能明显地减少回弹误差.     

基于几何补偿的高强板汽车覆盖件回弹优化控制

利用板料成形CAE软件DynaForm对高强板汽车覆盖件地板中通道进行回弹仿真分析,结合模具几何补偿,通过对成形工艺参数的正交优化,找到了最优参数组合及各因素对回弹的影响程度,有效地控制了零件在多工序冲压成形过程中产生的回弹.     

Principles and apparatus of multi-point forming for sheet metal

As a flexible forming method for sheet metal part, multi-point forming (MPF) technology is discussed in the paper. It employs two reconfigurable element groups to approximate the continuous upper and lower solid dies. With the technique, rapid fabrication of 3D sheet metal part is realized. The principles of multi-point die forming (MPDF) and multi-point press forming (MPPF) are described and then the rules to determine the size of the element are given. For any spatial shape surface to be formed, all elements’ height can be calculated through the contacting point calculation equation. On the computer control, the shape of the two element groups can be adjusted by serial adjusting mode or parallel adjusting mode. MPDF apparatus that includes CAD software, computer control system, two element groups, hydraulic press and laser CMM is developed. Following the given MPF procedure, 3D sheet metal part was formed without failure. Due to the rapid change characteristics of the two element groups, several special MPF forming techniques that are impossible in conventional sheet forming have been investigated in detail. By flexible blank holder technique, thin sheet MPDF is realized. With sectional MPF, large size sheet would be formed on small scale MPF apparatus. Through closed loop MPF, spring-back would be compensated cycle by cycle, and large deformation part is obtained with incremental MPDF successfully.     

多点成形压力机及成形工艺的最新进展

多点成形技术是金属板材三维曲面成形的新技术 ,与传统的整体模具板材成形工艺相比 ,多点成形压力机有许多优点 ,可以实现三维板类件既经济又快速的柔性成形。本文介绍了多点成形压力机系列规格参数、设备构成原理及其成形工艺。重点论述了几个现有的多点成形压力机的技术参数、调形方式的重大改进及多点成形技术应用领域的不断扩大。     

Numerical investigation of the influence of punch element in multi-point stretch forming process

Multi-point stretch forming (MPSF) technology is a flexible forming method, and it eliminates the need to the traditional fixed shaped-stretching die and, therefore, is a suitable method for forming small batch quantities of aircraft outer skin parts. Multi-point stretch die (MPSD) is composed of a punch element matrix, the size of punch elements and the radius of the hemispherical end of elements are the two important geometrical parameters of MPSD and they are major factors to influence the shape accuracy of MPSF parts. The smaller size of punch elements makes the punch element number of MPSD larger in the same area. MPSDs with different element numbers and different hemispherical end radii are used for stretch spherical and toroidal saddle-shaped parts. The dimples and the shape error of MPSF parts were analyzed, and the results show the influences of punch element number and element hemispherical end radius on forming results. MPSF tests show that the forming effect of MPSF is excellent.     

Numerical simulation on the local stress and local deformation in multi-point stretch forming process

Multi-point stretch forming (MPSF) is a new flexible forming technique to form aircraft outer skin parts. The multi-point stretching die (MPSD) replaces the traditional fixed shape stretching die, and the sheet metal is formed over a MPSD composed by the punch element. The MPSD is a discontinuous surface of discrete stretching die, and the stress concentration and local strain occur on formed parts. These lead to generate dimples on the surface of formed part. In this paper, a series of numerical simulations on MPSF processes for stretching parabolic cylindrical, spherical, and saddle-shaped parts were carried out. The local stress and local strain in thickness distribution of MPSF part were analyzed by dispersed the blank into solid elements. The forming results of MPSF were compared with those that use traditional stretch forming, and the influences of thickness of elastic cushion and the size of punch element on the stress concentration and local strain were surveyed. The simulation results show the distribution of local stress and local deformation in different layers, and the elastic cushion and the small size of punch element can reduce the stress concentration and local deformation. The results may understand the stress distribution on the sheet and prevent the defect of dimple.     

防皱多点成形及其误差分析

防皱多点成形是一种在调形单元之间布置防皱单元,使防皱单元与调形单元交错排列,从而在成形区内对板料表面进行约束,无需压边圈就可以产生防皱效果的多点成形方法。以球形件为例,运用有限元法针对起皱问题比较防皱多点成形和多点模具成形的成形效果。分析防皱多点成形在采用不同工艺参数时的成形误差,并探讨防皱多点成形对成形较小尺寸件的成形质量。研究发现,防皱多点成形方法能够很好地抑制板料在成形过程中的起皱现象;防皱多点成形时的球形件边缘的成形误差大于其内部区域的成形误差,减小防皱单元压力能够减小成形误差,但同时也会相应降低防皱单元的防皱能力;防皱多点成形采用头部具有转动自由度的单元能够增大单元与板料的接触面积,降低其成形误差;当防皱多点成形采用具有转动自由度的单元,并保证板料边缘外侧多设置一排单元时,成形件具有较高的成形质量。     

Generation and suppression of local severe plastic deformation in sectional multi-point forming

Sectional multi-point forming (SMPF) technology provides a new solution for forming large-size sheet metal. With this technique, large-size parts of sheet metal can be manufactured on a smaller multi-point forming press. But the force status and deformation of the workpiece are complicated in SMPF; the local severe plastic deformation will be produced easily in the transition region, and strain-hardening will be commonly produced subsequently. The hardening is difficult to eliminate in subsequent processes, which will largely affect the final deformation quality. In this paper, the generation of local severe plastic deformation was discussed; NURBS-based modeling method was used to construct the shape of the assortative region to suppress the defect. Experiments proved that the method is fairly effective. Finally, a plan was suggested to raise further the forming limit of materials and enhance the work efficiency by combining multi-point press forming with assortative region method.     

Analysis and Optimization on Factors Affecting Forming Quality of Half Axle Gears Warm Precision Forging

Half axle gears is produced by precision forging popularly because of the advantages in minimum machining allowances, lower material consumption and good service properties. But the forming quality of precision forging is difficult to control. Many simulations and analysis of precision forging process were taken by previous researchers. But no concrete method is proposed to evaluate and optimize the forming quality of half axel gears. The primary purpose of this work is improving the forming quality of half axel gears by analyzing and optimizing the affected factors of forming quality. The enclosed-die warm forging process of half axle gears was developed, and a new type of die-set used on double action hydraulic press was brought forward. The main influential factors of precision forming quality were analyzed after the forming process had been simulated by using finite element method(FEM). These factors include die structure, web thickness and web position. A method used to evaluate the forming quality was established, which investigated the maximal forming load, the metal filling rate and the material damage factor. The FEM simulations of half axle gears precision forging were evaluated by this method. The results show that the best forming quality can be achieved when the punches were added with bosses, the web located at the middle plant of the gear, and the web thickness was 30 percent of the inner hole diameter. Verification experiments taking the above optimized parameters were performed on a 7.8 MN double action hydraulic press. The trial products were formed well. And their geometric precision meets the demand. The verification result shows that the optimization of the influential factors, according to the simulations and the evaluation method, can improve the forming quality. The new structure of precision forging die-set and the new evaluation method guarantee a high forming quality of half axel gears.     

汽车覆盖件拉延模具虚拟调试的研究

以汽车覆盖件拉延模具为研究对象,根据板料成形及回弹的数值算法,进行了基于Autoform软件的覆盖件拉延模具设计、成形性分析及回弹计算,并实现了对模具的参数化虚拟调试,使得模具在制造前就消除了成形缺陷,极大地提高了模具的整体制造水平。     

Prediction of dimensional errors in 3D complex shapes due to press elasticity

This paper presents an approach to predict dimensional errors in 3D complex shapes due to press geometry errors and elasticity. Using a press stiffness matrix formulation for the press deflections in forging operation, a quantitative relationship between forging die deviations and the press geometry errors and elastic deflections is developed, which is a function of the forging force, press stiffness and the spatial relationship between the forging dies and the press table. The stiffness matrix of a screw press is obtained using finite element analysis. To evaluate the effect of the press elasticity on dimensional errors of 3D components, a case study of forging for aerofoil shapes is carried out based on the results from physical modelling experiments. With the representative information of the tool shape and forging force data, numerical results of the forging die deviations as a source of dimensional errors for the aerofoil shape are obtained and evaluated. It is demonstrated that this approach is applicable to forging and other metal forming processes for complex shapes.     

NUMERICAL METHOD FOR PREDICTION OF NET-SHAPED BLANK IN MULTI-POINT FORMING OF SHEET METAL

A new numerical method to predict the initial blank geometry from the desired objective shape of parts is presented. Based on the conditions that the deformations in material are most evenly distributed and that the volume remainsconstant, a positive definite functional for blank design is constructed. The functional is minimized by an iterative schemeof finite element, and then the optimal initial configuration is obtained. The method is easy and expedient to use. The results of numerical simulation of forming process and multi-point forming experiments for sheet metal demonstrate thatgood precision is achieved by the proposed method.