Development of a Highly Flexible Incremental Roll Forming Process for the Manufacture of a Doubly Curved Sheet Metal

A flexible incremental roll forming process has been developed by adopting the advantages of the incremental forming process and the roll forming process: i.e., inherent flexibility of the incremental forming process and continuous bending deformation of the roll forming process. It has an adjustable roll set as a forming tool composed of one upper center roll and two pairs of lower support rolls, which plays a key role. Through the experiments, it is shown that the improved forming method of the proposed process is effective in the manufacture of various doubly curved sheet metals, and the proposed relationship of the experimental parameters and the radius of curvature of the formed sheet boundary is useful to control the final shape     

Numerical and experimental investigation into cold incremental rolling of doubly curved plates for process design of a new LARS (line array roll set) rolling process

The line array roll set (LARS) rolling process is a new incremental sheet metal rolling process for effective manufacture of doubly curved metal plates. In this study, design equations were developed to predict the curvatures of formed plate shapes with complex curvatures using the experimental data. A series of experiments with various curvatures have been performed. The comparison of the finite element computation results with the design equations has shown that the design equations can be effectively used for process design of forming processes in forming of doubly curved plates over a wide range of input curvatures.     

Investigation into forming sequences for the incremental forming of doubly curved plates using the line array roll set (LARS) process

The line array roll set (LARS) process [7] proposed by the authors is an effective metal forming process used to manufacture doubly curved metal plates. To obtain a final shape with the desired bend radii and to minimize any possible defects, the process for forming the desired shape should be systematically and accurately designed. The major purpose of the present work is to analyze the effect of the forming sequences in the LARS process. The experiments are conducted using three types of forming sequences, and the final bend radii and the quality of the formed plates produced by the LARS process are evaluated. It is found that it is more effective to form a doubly curved plate through a singly curved shape in order to improve the quality of the formed plate. A series of forming experiments with various bending radii are conducted and the interaction phenomena in double curvature bending are observed.     

基于有限元仿真的金属板材单点渐进成形分析

目前对板材单点渐进成形新型工艺的研究多是通过物理试验,从金属宏观位移的角度分析成形过程的一般规律,研究成形参数对成形能力的影响,而无法获得成形过程中真实的变形过程。文章基于刚粘塑性有限元法,应用实体单元,对渐进成形中在直线轨迹和曲线轨迹下的板材成形过程进行数值模拟,分析成形过程中各部分应力、应变的特点,并深入探讨了渐进成形过程的成形机理。研究表明,成形过程中,变形区可以划分为4个具有显著差异的区域考察变形特点;在工具头局部成形时,变形金属在压应力的作用下变形,具有更高的成形极限。     

液体介质传热渐进温成形研究

由于液体介质的存在,在以导热油直接作为传热介质加热板料实现板料温热渐进成形中,成形初始的预胀以及成形过程中存在的背压是区别于其他渐进成形方法的显著特征。在数控渐进机床上,首先以2A12铝合金板料对成形过程中液体压力产生的板料预胀和过程背压的影响进行了研究,然后采用SUS304不锈钢板料对成形过程中的导热油温度影响进行了研究。研究结果表明：液体介质较小的压力产生的预胀和背压对成形过程没有显著影响,成形过程中为了保证导热油和板料充分接触,导热油可以保持一定的系统压力;采用液体介质直接作为传热介质加热板料进行板料温渐进成形是可行的;温度对SUS304不锈钢板渐进成形性能影响显著。     

金属板材数控渐进成形技术及加工轨迹坐标对位研究

金属板材数控渐进成形技术，是一种通过三轴数控成形机对金属板材进行逐层辗压而成形工件的柔性加工技术。本文探讨了金属板材数控渐进成形技术的过程、原理，同时，为了有效地排除成形过程中坐标对位对零件上出现的拉裂、材料堆积、材料硬化等现象的影响，本文提出了一种基于机器视觉的非接触式加工轨迹坐标对位方法，完成了金属板料数字化渐进成形中支撑模型的非接触式高精度快速定位。     

Study on the continuous roll forming process of swept surface sheet metal part

Continuous roll forming (CRF) is an effective process to manufacture swept surface parts of sheet metal. The forming tool in CRF is a pair of small-diameter bendable forming rolls, a swept surface is formed continuously after the rotating rolls sweep out the whole sheet metal blank. The two bent rolls and the non-uniformly distributed roll gap along the rolls’ length make the sheet metal bent in longitudinal and transverse directions simultaneously, the cross-section curve of the formed swept surface is controlled by the curved profile of the forming rolls and the spine curve is controlled by the differential elongations of sheet metal generated by roll gap. In this paper, a necessary condition for the formation of a swept surface is proposed and analyzed, the parametric equations of the formed surface in CRF are derived and the method to determine the roll gap for forming a given swept surface is presented. The numerical simulations and analyses on the CRF processes demonstrate the validity of the presented theoretical models. The experimental and measured results show that the formed surfaces are in good agreement with the desired surfaces, and swept surface parts with good forming precision can be obtained by CRF process.     

Three-dimensional sheet metal continuous forming process based on flexible roll bending: Principle and experiments

To effectively manufacture three-dimensional sheet metal parts with various curvatures produced in small batch quantities, continuous sheet metal forming, a new flexible forming technology is being developed. This process employs an upper flexible roll and two lower flexible rolls as a forming tool, and the shape of a flexible roll can be changed in vertical direction. With the rotation of flexible rolls, the sheet metal is bent in longitudinal and transverse directions simultaneously and is formed continuously. In the present study, the three-dimensional surface of formed part is described by sweep surface based on the characteristic of the forming process and the arc-length parametric equation for describing continuous forming part is developed. The three-roll bending deformation of sheet metal in longitudinal direction is analyzed and the longitudinal curvature equation of the formed part is derived. The shape of flexible roll axis controlled at a number of points is represented by the cubic spline curve and the transverse curvature of the formed part after springback is then calculated piecewise. Typically experiments for forming concave shape surface and saddle-type surface have been performed, the experiment results are measured and analyzed by a binocular stereo vision measurement system, it is demonstrated that the formed surfaces are in good agreement with the desired shapes and the presented equations are useful for the continuous forming process design.     

Autonomous on-line system for fracture identification at incremental sheet forming

Before starting, the production forming processes require real experiments in order to accurately define forming limits. For this reason and because incremental sheet metal forming technology requires a relatively long production time, an autonomous on-line system for fracture identification has been developed. The system is a versatile tool for the identification of the location and time of the occurrence of the fracture, without human influences or oversight. The system is based on an investigation of the forming forces, responsive to very small variations, appearing during the forming process, and works effectively with different material types, material thicknesses and product shapes.     

基于金属板材数控渐进技术的汽车座椅成形工艺

金属板材数控渐进成形工艺不需要专用的模具,是一种柔性的成形工艺.在工艺规划中,通过零件的数字模型来调节成形工具的运行轨迹,达到渐进成形零件形状的目的.由于汽车座椅形状复杂,金属板材渐进成形较困难.本文对其数控渐进成形工艺进行了分析,提出由建模、工艺分析、轨迹生成、HrpDSF处理、安装定位、加工润滑、后处理等组成的金属板材数控渐进成形工艺规划方法,成功地应用于汽车座椅的数控渐进成形中.并对汽车座椅数控渐进成形加工中,通常出现的破裂、回弹、起皱等严重影响成形质量的缺陷原因进行分析,采取不同的处理防范措施,取得满意的效果.为今后完善和发展金属板材数控渐进成形技术起到重要作用.     

金属薄板直壁件数字化渐进成形过程的实验研究

金属薄板直壁件的成形是数字化渐进成形技术中的热点和难点之一。本文基于数字化渐进成形的基本原理提出了一种加工金属直壁件的方法,在实验中研究金属薄板直壁件的成形过程,了解直壁成形机理和控制成形过程的工艺措施。     

金属板材数控渐进成形加工轨迹交互修改及优化

金属板材数控渐进成形技术,是一种利用快速原型分层制造的思想对金属板材进行逐层挤压而成形金属覆盖件的柔性加工技术。本文介绍了金属板材数控渐进成形技术的过程、原理,同时,主要针对加工过程中发生的破裂、凹陷等缺陷,提出了一种基于NURBS的加工轨迹人机交互修改和优化的方法,解决了复杂曲面零件无法加工的难题,实现了金属板材数控渐进成形加工过程的快速响应。     

模型姿态按给定成形方向定向定位方法

在金属板材数控渐进成形中模型姿态决定着成形半锥角,因而对成形件的厚度减薄率和分布具有较大的影响。为了按照能使板材件厚度均匀化的最佳方向或防止某一局部区域板材减薄量过大的方向成形,需要将待成形件CAD模型通过模型变换的方法,按照所希望的成形方向重新定向和定位。提出待成形件CAD模型的三维变换算法和定位算法,使用户能够根据自己所希望的方向进行成形加工。     

板料零件数控渐进成形工艺研究

板料零件数控渐进成形工艺是一种通过数字控制设备 ,采用预先编制好的控制程序逐点成形板料零件的柔性加工工艺。本文就板料零件数控渐进成形工艺的成形过程、变形机理、极限半顶角等方面进行了探讨。认为 ,板料零件数控渐进成形是使板料的厚度减薄 ,表面积增大 ,靠逐次的变形累积产生整体的变形。变形区厚度的变化与成形半顶角有关 ,其中 ,成形极限半顶角是数控渐进成形能否成功的关键 ,它不仅与材料有关 ,而且与板料厚度有关。     

Analytical and experimental investigations on deformation mechanism and fracture behavior in single point incremental forming

Incremental sheet forming (ISF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. The characteristic of localized deformation is significantly different from conventional sheet metal forming process. To understand the fundamental material deformation mechanism during the ISF process is of great importance for ISF process design and optimization in achieving improved material formability, accuracy and more uniform thickness distribution. In this paper, an analytical model for single point incremental forming (SPIF) process has been developed to describe the localized deformation mechanism. With the consideration of both bending effect and strain hardening, the stress and strain states in the deformation zone are described. Analytical evaluation reveals that the deformation occurs not only in the contact zone, but also in the neighboring wall which has been already formed in the vicinity of the contact zone. In addition, the results also suggest that the fracture tends to appear at the transitional zone between the contact area and the formed wall. In order to validate the analytical results, SPIF simulation and experiments both have been conducted with good agreement obtained.     

Review on the development of a hybrid incremental sheet forming system for small batch sizes and individualized production

Asymmetric Incremental Sheet Forming (AISF) has been developed as a flexible process for low-volume production of sheet metal parts. In AISF, a part is obtained as the sum of localized plastic deformations produced by a simple forming tool that moves under CNC control. In spite of about 20 years of research and development, AISF has not had much industrial take-up yet. The main reason for this is that attempts to improve, among other limitations, the accuracy, speed and range of feasible geometries of the process by adapted process strategies has not brought about general solutions. This paper presents an overview of the current state of development of hybrid asymmetric incremental sheet forming processes at RWTH Aachen University. The goal of the development of hybrid ISF processes is to allow for a quantum leap of the capabilities of AISF in order to enable a broader industrial use of AISF. Two hybrid process variations of AISF are presented: stretch forming combined with ISF and laser-assisted AISF. It is shown that the combination of stretch forming and AISF can improve the time per part, sheet thickness distribution and accuracy of the final part. Laser-assisted AISF is shown to enable the flexible forming of non cold-workable materials such as magnesium and titanium alloys when the forming conditions are adapted to the temperature and strain rate dependent formability of the sheet metal. In addition, first results of the forming of hybrid aluminum-steel sheet metal are shown.     

New incremental methods for springback compensation by stress superposition

In forming technology, the principle of stress superposition is well known for a controlled influencing of the forming zone. The aim of stress superposition is to reach an additional plastification of the material, which can be used to compensate the springback effect, e.g. of bending angles or bending radii, to extend the forming limits of the material and to reduce the forming forces. The paper deals with two new forming process variants invented by the authors, which are based on the principle of stress superposition. The first is an air bending process using an additional roll for the incremental superposition of compressive stresses along the tensile zone of a bent sheet metal. The second is the new process of incremental tube forming, which is suitable for bending tubes two- and three-dimensionally to arbitrary contours. It is based on the combination of a spinning process with the free forming of tubes.     

液压油箱成型机设计及工艺参数控制

针对现有围板成型方式的不足,提出一种伸缩式的支撑方式,极大地提高了工作效率。基于金属塑性成型理论,根据板料成型过程中的塑性条件和板料卸载原理,推导出塑性成型弯曲回弹规律。基于材料力学小变形叠加原理,进行折弯辊挠度推导,应用Workbench仿真设计,得到折弯辊最小挠度尺寸。通过以上计算与仿真得出的围板成型工艺参数,保证了产品质量。     

金属板料渐进成形工艺过程有限元模拟

介绍了金属板料分层渐进成形过程有限元模拟。在金属板料渐进成形过程中,材料的弹塑性变形十分复杂,影响成形过程的因素很多,同时各个工艺参数对成形过程的影响又很难确定。为此,根据金属板料分层渐进成形为多工步成形的技术特点,建立一种有限元模拟方案,对板料渐进成形过程进行了模拟分析。     

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...