Research on three-dimensional surface parts in multi-gripper flexible stretch forming

Multi-gripper flexible stretch forming (MGFSF) is a novel flexible forming process of sheet metal based on the multi-point forming principle. The straight jaws in traditional transverse stretch forming (TSF) are replaced by several discrete clamping mechanisms on both sides. To help understand the forming characters of MGFSF, spherical and concave–convex parts were selected as the research objects and finite element analyses on TSF and MGFSF were implemented using an explicit nonlinear finite element code. The influence of the transition length on the forming results in MGFSF was also taken into account in the present work. The simulation results reveal that a shorter transition length in MGFSF would result in an easier conformability of the sheet metal to the desired shape as well as a smaller strain variation in the forming zone. It is also found that, compared to TSF, the sheet metal can be formed without transition zone by utilizing MGFSF, which could significantly improve the material utilization and save the manufacturing costs. Finally, experimental validations were conducted on the self-developed MGFSF apparatus and the experimental results show a good agreement with the numerical results.     

激光拼焊板成形过程数值模拟技术现状及趋势

由于焊缝性能与母材存在较大的差异以及焊缝自身形状的特点,激光拼焊板在成形过程中的数值模拟分析可以采用不同的建模方法。介绍了国内外对激光拼焊板数值模拟采用的不同建模方法,比较了不同焊缝模型对计算结果的影响,并利用ABAQUS／Explicit动力显示积分模块分别采用忽略焊缝以及考虑焊缝采用壳单元时的建模方法对U形件的弯曲成形过程进行了数值仿真,结果显示焊缝模型对模拟结果影响较大,采用忽略焊缝的建模方法得到的焊缝移动量较小。     

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.     

Application of flexible forming process to hull structure forming

The conventional line heating method has been applied for the manufacture of various curved blocks used for hull structures in the ship-building industry. However, it has low economical efficiency and productivity because most of its processes are based entirely on the skillful experience of experts. In this study, a flexible forming process is proposed and utilized to substitute for the conventional manual process. In the proposed process, numbers of punches which have round shapes on the contact tip are adopted to configure an equivalent forming surface according to the arbitrarily curved objective surface. A simple punch height determination algorithm that considers the discrete surface and its spatial planar equations is applied to determine the discrete forming surface composed of the adjusted punches. Punch height data are transferred to a numerical simulation model using ANSYS parametric design language, and finite element analysis is conducted to check the formability of the process. Further, experimental investigations are carried out to verify the feasibility of the process using a flexible forming apparatus. Consequently, it is confirmed that a double-curved thick plate could be obtained by the flexible forming process.     

板料拉深成形数值模拟中动态边界条件的处理

针对板料拉深成形过程中工件与模具接触边界的动态变化,将模具表面离散为若干个三角形单元,并用参数方程来描述工件节点及模具三角形单元的运动情况,将工件与模具的接触问题转化为空间直线与平面的动态求交问题。在此基础上,通过实际的模拟分析,证明该处理方法的可行性。     

空心工字钢冷弯成型过程的数值模拟

空心工字钢是一种新型断面型材,它由铜板经冷弯成型机组在室温下冷弯成两块近似M形型钢后再焊接在一起而成.设计了一种冷弯成型孔型系统,并利用Pro/E软件建立了空心工字钢冷弯成型机的虚拟样机.采用三维有限元方法,利用ANSYS-LS/DYNA软件对冷弯成型过程中的弹塑性变形过程进行了数值模拟,系统地分析了成型过程中的应力变化规律.研究结果对于冷弯型钢产品的开发、孔型系统的设计具有参考价值.     

等效拉延筋模型及其在板料成形数值模拟中的应用

讨论等效拉延筋的建模方法、常用模型及其在板料成形数值模拟中的应用情况,并指出研究中仍存在的问题及今后的发展方向。     

Continuous flexible roll forming for three-dimensional surface part and the forming process control

Continuous flexible roll forming (CFRF) is an effective sheet metal-forming process used to manufacture three-dimensional surface parts. To obtain a final part with desired shape, the CFRF process should be systematically and accurately controlled in the longitudinal and transverse directions simultaneously. The major purpose of the present work is to establish a system of methods for controlling the continuous forming process. The target surface of desired part is represented by triangular mesh; the transverse control model for adjusting the shape of flexible roll is proposed based on the cubic B-spline curves; and the formulations to determine the downward displacement of upper roll is presented. Finally, the software for controlling CFRF process is developed, and the validity of the presented methods and the effectiveness of the developed software are demonstrated by CFRF test for a typical surface part.     

Numerical simulation of multi-point stretch forming and controlling on accuracy of formed workpiece

A finite element model was built for the sheet metal multi-point stretch forming (MPSF), and the model was applied to the MPSF of a typical part. The numerical simulation of the MPSF for a saddle and cylindrical surface workpiece was performed. The effects of non-uniform deformation of elastic cushion and spring back after unloading on the precision of formed workpiece were investigated. The simulation results show that using elastic cushion can effectively suppress generation of dimples, but have an effect on precision of formed workpiece. In addition, the amount of spring back after unloading is small, and the effect of the non-uniform deformation of the elastic cushion on the precision of the MPSF workpiece is larger than that of the spring back. A method based on the iterative corrections according to the numerical simulation results was proposed to compensate the non-uniform deformation of elastic cushion and the spring back to enhance the accuracy of MPSF.     

多道次双点渐进成形数值模拟与实验研究

针对多道次双点渐进成形中材料变形规律问题,建立了典型圆锥台件双点渐进成形有限元模型,采用螺旋轨迹对其多道次成形规律进行了数值模拟,对模拟结果中节点坐标和位移、单元应变和壁厚数据进行了提取,分析了成形过程中节点流动、单元应变及壁厚分布规律,并通过在实验板料表面印制圆形网格和制作标记点进行了多道次双点渐进成形实验,对成形零件网格变化、标记点径向移动和零件壁厚进行了测量分析,验证了模拟结果的正确性。研究结果表明,多道次双点渐进成形中材料产生明显的径向流动,且随着成形道次增多而增大,同时,成形道次越多零件壁厚均匀性越好;另外,采用变间隔角度设计方法,可改善多道次双点渐进成形零件壁厚分布均匀性,且随着成形道次增多作用越明显。     

Pressure-control algorithms for the numerical simulation of superplastic forming

Superplastic forming is a manufacturing process whereby certain materials under the correct conditions of temperature and strain rate exhibit high ductility and can be blow-formed into a die to produce components that are typically very light and strong. It is crucially important, in the process, to be able to control the pressure cycle in order to obtain the optimum strain rate. This paper considers methods for calculating the pressure cycle which may be incorporated into a finite element program for simulating the forming process.     

数值模拟技术在汽车覆盖件成形中的应用

综合论述了数值模拟技术的发展概况,介绍了几种典型的专用板材成形模拟软件的特征,以Dynaform为例重点介绍了其在汽车覆盖件成形中的应用,阐述了数值模拟技术的应用前景,并指出了其研究方向。     

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.     

数控弯管机机构运动学建模与加工过程仿真技术

针对现有数控弯管加工过程仿真方法通用性差的问题,提出一种基于机构运动学模型的数控弯管加工过程仿真方法。在运用多体系统运动学理论对数控弯管机进行机构运动学分析的基础上,建立了描述数控弯管机运动特征和结构参数的信息模型及机构运动学模型,采用Newton-Raphson迭代法对数控弯管机机构运动学方程进行求解,给出了数控弯管机运动和导管动态成形的运动规划算法,实现了任意结构单头数控弯管机的加工过程仿真。最后开发了原型系统,以SWING和VB200HP两种数控弯管机为例对所提方法进行了验证。     

Analytical modeling and numerical simulation for three-roll bending forming of sheet metal

The three-roll bending forming of sheet metal is an important and flexible manufacturing process due to simple configuration. It is suitable for forming large sheet parts with complex, curved faces. Most researches on roll bending forming of large workpiece are mainly based on experiments and explain the process through macroscopic metal deformation. An analytical model and ABAQUS finite element model (FEM) are proposed in this paper for investigating the three-roll bending forming process. A reasonably accurate relationship between the downward inner roller displacement and the desired springback radius (unloaded curvature radius) of the bent plate is yielded by both analytical and finite element approaches, which all agree well with experiments. Then, the three-roll bending forming process of a semi-circle-shaped workpiece with 3,105 mm (length)?×?714 mm (width)?×?545 mm (height) is simulated with FEM established by the optimum tool and process parameters. Manifested by the experiment for three-roll bending forming of this workpiece, the numerical simulation method proposed yields satisfactory performance in tool and process parameters optimization and workpiece forming. It can be taken as a valuable mathematical tool used for three-roll bending forming of large area sheet metal.     

玻璃成形数值模拟技术研究概述

玻璃成形模拟技术的研究既具有重要的理论意义又具有广阔的应用前景,经过长期的研究和探索,人们对它的认识不断加深,研究范围不断扩大。但总体来说,目前对玻璃成形模拟技术的研究还较为薄弱,不够系统和深入,还需作更进一步的研究。这里对玻璃成形模拟技术的研究现状进行了综述。     

优化方法在注塑成型数值模拟中的应用

注塑成数值模拟技术,可通过计算机对设计方案进行分析计算,在模具制造之前,预测设计中存在的问题,为模具设计与注塑成型工艺优化提供定量依据。针对注塑成型数值模拟技术智能化、自动化的发展趋势,在此给出了注塑模冷却系统、塑件厚度尺寸、浇口位置、一模多腔的浇道布置及注塑成型鲁棒（稳健性）设计的优化模型,说明了优化方法在注塑成型数值模拟中的应用情况。