【作者】 韦红余；

【导师】 高霖；

【作者基本信息】 南京航空航天大学 ， 航空宇航制造工程， 2010， 博士

【摘要】 渐进成形工艺是一种新兴的金属板料柔性快速成形技术,由于不需要模具或仅采用简单模具支撑,即可按照预先编制的加工程序,通过专用数控设备造出成形极限较大,形状复杂的板金零件,因此渐进成形技术特别适合于板金类产品的单件、小批量生产及产品试制。成形质量较差与成形效率不高是困扰当前渐进成形工艺应用与推广的两大主要问题,本文首次针对金属板料渐进成形质量及其控制问题,系统深入的研究了成形零件质量缺陷产生的基本原理、关键工艺及改善措施,主要包括成形工艺与成形机理、渐进成形工艺条件下的材料流动规律与零件回弹、成形补偿技术及渐进成形自动编程技术。本文的主要研究内容和成果可概括为:深入研究了金属板料渐进成形过程及成形机理。渐进成形工艺大致可分为工艺模型建立,工艺准备及成形三个步骤,针对其成形过程,提出了成形过程划分模型,将整个过程划分为初始成形,稳定成形及终了成形三个主要阶段;为研究成形阶段材料变形机理,建立其受力分析模型,提出了变形区划分方案,进而提出了可能存在的失稳形式及危险失稳点的判断方法;综合各成形阶段材料可能存在的变形方式,提出了渐进成形最终变形行为的判断方案。深入研究了金属板料渐进成形过程中材料流动规律,提出了材料流动的基本规律—余弦规律,即在理想条件下,由于简单夹具及成形零件自身的约束作用,材料仅在成形轴向发生剪切滑移变形,其变形属于平面应变;基于平面应变原理,提出了壁厚分布计算公式,并以此为基础自主开发了渐进成形零件厚度计算软件模块。对于拉深类渐进成形,由于没有简单夹具的约束作用,成形时,金属板料处于自由状态,边缘材料发生径向补充流动,其变形不符合余弦基本规律,为此,提出了一种基于“虚拟靠模导向法”的壁厚分布有限元估算方法。深入研究了回弹对金属板料渐进成形零件质量的影响,提出了成形误差补偿回弹评价方法,即通过确定测量方向上的理论补偿量与实际补偿量之间的差异来衡量回弹大小;按照成形误差补偿回弹评价原理,设计试验方案,进行成形试验,研究表明:成形零件平均回弹量δE值很小,采取误差补偿措施可显著提高零件成形精度;进而基于主变形区材料的双拉应力状态,提出了该变形区材料基本不发生回弹的假设。为使用有限元方法对成形零件回弹进行研究,自主开发了渐进成形有限元分析加载路径自动生成软件模块,在此基础上将弹塑性有限元求解的显式算法和隐式算法联合使用,采用显式算法模拟成形过程,采用隐式算法模拟回弹过程。模拟结果表明:材料主要变形区的回弹很小,且随着成形角的增大,零件在接触变形区的最大回弹量逐渐减小,且呈近似线性关系。深入研究了渐进成形补偿技术。为研究精度对成形质量的影响,提出了成形精度位移误差评价方法,即通过确定测量方向上的变形位移误差来衡量零件成形精度。为进行成形补偿,提出了成形力理论计算与修正计算模型。成形过程中,成形工具系统可简化为一个悬臂梁系统,在成形力的作用下,容易发生弹性变形,造成成形不足,引起精度下降。分析成形工具与金属板料的接触关系,简化其过程,借助几何作图法建立了成形力理论计算公式,进而通过试验途径建立成形力修正公式。在此基础上,按照几何补偿原理,建立渐进成形补偿方案。研究表明,采取补偿措施后,成形精度显著提高,各项指标均满足设计要求。深入研究了渐进成形加工自动编程技术。自主开发了自动编程系统,主要实现零件可成形性分析,成形轨迹生成与优化,成形加工仿真三个主要功能。以厚度减薄为依据,设置阀值,以判断板料是否会破裂,进而判断成形可否顺利进行。处理导入的模型数据以生成成形工具加工轨迹;根据螺旋线及贝塞尔曲线等具备的优良性质,针对加工路径设计优化算法,以光顺加工轨迹,减轻振动;采用离散的思想,用细分网格表示毛坯模型,实现成形过程动态仿真。文中提出的各种分析模型、分析方案、计算模型和软件功能均进行了翔实的理论分析,实验对比,并将研究成果应用到实际产品制造中,效果良好。更多还原

【Abstract】 Incremental forming is an innovative and flexible forming process which belongs to rapid prototyping of sheet metal, with the support of simple die or without it,Also the sheet metal part with higher forming limit and more complex shape can be manufactured using NC machine according to the pre-programme. And incremental forming technology is particularly suitable for sheet metal manufacturing during the period of single or small batch production and product trial. Currently, poor forming quality & low forming efficiency, especially the poor quality, are the most two important defects that can be hindered the popularization & application of sheet metal incremental forming process. The target of the present work was to solve the quality problem of sheet metal incremental formed parts, and the principle of defects arising, key processes and improving measures including the forming process & mechanism, material flow law, springback, forming compensation technology and automatic programming technology were studied. The main contributions of the present thesis in details are as follow:Sheet metal incremental forming process & mechanism was studied in details. (The process of incrental forming can be roughly divided into three processing: modeling process, technological preparation process and forming process. Also the forming process can be devided into three divisions: initial forming, stabilize forming and end forming) which was suggested in the present research. Indeed mechanical analysis model was established for the study of material deformation mechanism, and deformation area division method was advanced firstly, also the possible existence of instability forms and dangerous instability point of judgment method were proposed, finally the eventually deformation behaviors of judgment scheme was proposed according to comprehensive deformation styles during each forming stage.Researchs which were based on material flow law during sheet metal incremental forming were carried out. A basic law of material flow, cosine rule also was proposed. Under ideal conditions, due to simple fixture and forming parts own restriction, material flow takes place along the axial direction, and its deformation belongs to slip at plane strain. Based on the plane strain principle, a general thickness distribution calculation formula was suggested, and then thickness calculation software modules for incremental formed parts were also developed independently. It’s was be noticecd that material flow would not meet the law of basic flow because of the sheet was in a free state without simple fixture restriction effect, and the edge of material could be flow inside during tensile style incremental forming. Also the thickness distribution estimation using FEM method based on "virtual modeling orientation method" was proposed in the present research.Research based on springback of incremental formed parts was considered. The springback evaluation method based on forming error compensation also was proposed, which it can be defined as the difference between theory and the actual amount of compensation along the measured direction. According to forming error compensation evaluation method, expiments was designed and implemented. And from the results that obtained it can be show, the magnitude of springback average (δE) of formed parts was very small, and the forming precision could be significantly improved by adopting compensation method. Based on double tensile stress state in the main deformation area, the hypothesis and springback could not be occured on the formed parts that have been proposed.In order to study the springback by FEM, loading path automatically generation software module which be used for incremental forming simulation, was developed independently. With the help of the software module, elastic-plastic finite element solution based explicit & implicit algorithm could be used in combination, and it can be noticed that forming process simulated using explicit algorithm and springback simulated using implicit algorithm. The simulation results showed that small springback would be taken place in the main deformation area, and springback would be decreased linerly gradually as the forming angle increased.Research based on incremental forming compensation technology was studied. In order to study the quality of formed parts that influenced by forming precision, the forming precision displacement error evaluation method was proposed, which it can be defined as the deformation displacement error along the measured direction. Also the theoretical calculation & correction calculation model of forming force has been advanced. The forming tool system could be simplified as a cantilever beam system during the forming process, indeed elastic deformation on the forming tool was taken place under the action of the forces, and then the insufficient forming would be occurred, and the forming precision would be declined. Contacting relationship between the forming tool and sheet metal was analysed, theoretical formula of forming force was established with the aid of process simplification using geometric graphic method, and the modified computing formula of forming force was established with the aid of experiment. On theses basises, according to the principle of geometrical compensation, forming compensation plan was established. Studies showed that the forming precision could be improved significantly adopting compensation method.Automatic programming technology that used for incremental forming was studied. The three functions, such as parts formability analysis, forming path generation & optimization and forming simulation, were mainly realized in automatic programming system which was be developed independently. Based on the law of thickness thinning, threshold value was setted to determine whether the sheet metal forming could be carried out. The import data from the CAD model was handled to create tooling path using automatic programming system. Smooth of tooling path, vibration reduction, and optimization algorithms were designed according to the spirals and Bessel criteria. Based on the discretization thoughts, the dynamic simulation of forming process could be carried using triangle mesh said blank model.Various analytical models, analytical solutions, calculating model and software functions, which proposed in the present research, were analysed by abundant theoretical, comparative experiments. Also good results were obtained and it can be used these research results in real manufacturing products.更多还原