高柔性拉伸成形过程有限元分析及工艺优化研究

发布时间：2018-05-16 14:53

本文选题：柔性成形 + 拉伸成形　；参考：《吉林大学》2017年博士论文

【摘要】：拉伸成形是大尺寸、小曲率蒙皮类件的主要成形方法,与传统模具冲压成形比较,具有零件回弹小、成形精度高的优点,但设备研制成本高,一般只用于航空、航天领域。随着航空、航天工业的快速发展,蒙皮的生产周期要求越来越短,形状更是向着个性化、复杂化的方向发展,这对传统拉伸成形方法提出了新的挑战。传统拉伸成形存在两方面弊端:一方面整体模具体积大、数量多,生产周期长,储运成本高,重复利用率低;另一方面拉伸成形机柔性程度低,成形过程板料不易贴模,材料利用率低,变形不均匀,易出现拉裂、起皱等缺陷。可见,沿用传统拉伸成形技术已经无法满足新形式下的蒙皮生产需要。此外,国内拉伸成形设备以进口为主,欧美等发达国家掌控设备制造的核心技术,高昂的设备售价令中小企业难以承受。因此,生产具有自主知识产权的柔性化拉伸成形设备已经成为我国工业发展的迫切需求。高柔性拉伸成形设备是由我国自主研发的新型拉伸成形设备,包括高柔性模具和高柔性拉伸成形机。高柔性模具使用多点数字化模具代替传统的整体模具,可以一模多用、降低模具制造成本和缩短模具生产周期。高柔性拉伸成形机通过离散夹钳的自协调作用实现板料贴模,能够提高成形质量、材料利用率和生产效率。另外高柔性拉伸成形设备简化了控制系统,制造成本降低,价格便于中小企业接受,有利于该技术在其它领域的应用推广。本课题以多点模具和高柔性拉伸成形机为主线展开研究,采用有限元数值模拟和试验相结合的方法分析板料拉伸成形过程,旨在优化加工工艺、提高零件的成形质量,同时也为工业生产和新型拉伸成形设备的研制提供科学的指导。本文的主要内容和结论如下:1.高柔性拉伸成形原理及成形过程力学分析对高柔性拉伸成形原理、技术特点及成形过程进行分析;分析高柔性拉伸成形时板料内部的应力、应变变化过程;对板料内部拉力以及卸载回弹量进行推导计算;给出毛坯尺寸的选择依据和成形质量的评定标准。2.建立高柔性拉伸成形有限元模型对有限元数值模拟的动力显式、静力隐式的求解算法以及材料的弹塑性本构关系进行探讨;建立高柔性拉伸成形有限元模型及板料回弹模型。3.拉伸成形机的结构分析及数值模拟对高柔性拉伸成形机的主要部件(夹料机构、拉料机构、万向结构)进行结构分析;采用有限元数值模拟方法分析夹钳离散化程度、夹钳间隙、加载幅值对成形结果的影响。分析表明:随着夹钳数量的增加,板料贴模效果逐渐变好,成形质量提高;随着夹钳间隙的增加,成形件的应力、应变分布均匀程度先提高后降低,间隙过大,成形区出现起皱现象,在板料宽度为1200mm,10个夹钳的工况下,夹钳间隙为其宽度的1/9时,成形效果最佳;成形力按合理的幅值加载能够提高成形质量。4.高柔性拉伸成形时基本体排列方式的研究对高柔性拉伸成形件的压痕形式及其产生原因进行分析,提出了通过改变基本体排列方式抑制成形件表面缺陷的方法。以球形件、鞍形件为研究对象,采用有限元数值模拟和拉伸成形试验相结合的方法比较了常规排列、倾斜交错排列、平行交错排列的多点模具对成形结果的影响。结果表明:球头压窝和拉伸沟是成形件表面的主要缺陷,交错排列的多点模具能够有效地抑制压痕缺陷,提高成形件的表面质量和成形精度,比常规排列的多点模具成形效果更好。5.研究基本体球头形式对成形结果的影响推导出球头与板料相切的几何条件,基于摆动球头多点模具建立拉伸成形有限元模型,采用有限元数值模拟和拉伸成形试验相结合的方法分析摆动球头对成形结果的影响。分析表明:基本体球头半径小于与板料相切的临界半径时,随着球头半径增加,成形质量提高,球头半径大于临界半径时,随着球头半径增加,表面质量下降。摆动球头模具代替固定球头模具能够有效抑制成形件表面压痕,降低回弹,提高了成形质量。交错排列的多点模具使用摆动球头的成形效果优于常规排列的多点模具。6.研究摩擦条件对成形结果的影响通过摩擦试验测定不同摩擦接触对在干摩擦和油润滑条件下的摩擦系数;采用有限元数值模拟方法研究板料与模具之间的摩擦条件对成形结果的影响;通过有限元数值模拟和拉伸成形试验相结合的方法研究多点模具和弹性垫、弹性垫与弹性垫之间的摩擦条件组合对成形结果的影响。结果表明:板料与模具之间为干摩擦时,成形件有效成形区成形效果更好,但过渡区的应力、应变较大,用油润滑的方法可以有效降低过渡区的应力、应变;在存在多个接触对时,保持各接触对之间为干摩擦,有效成形区成形效果更好,弹性垫与弹性垫之间使用油润滑时,成形效果较差。7.研究弹性垫对高柔性拉伸成形的影响以球形件为研究对象,采用有限元数值模拟方法分析弹性垫厚度、硬度、层数对成形件表面质量和成形误差的影响;对板料贴模的判定方法和误差补偿的实现方法进行探讨。结果表明:弹性垫厚度增加,成形件表面质量提高,但成形误差增大;弹性垫硬度越大,成形件表面质量和成形精度越高;相同厚度的弹性垫,随着层数增加,成形件表面质量和成形精度降低,但回弹量同时减小;使用剖面法判断板料贴模更简单;多点模具通过模具型面修正法可以快速实现误差补偿。
[Abstract]:Tensile forming is the main forming method of large size and small curvature skin parts. Compared with traditional die stamping, it has the advantages of small springback and high forming precision. But the cost of the equipment is high, and the equipment is usually used in aviation and space industry. With the rapid development of aerospace industry, the production cycle of the skin is shorter and more shaped. In the direction of individualization and complicating, it poses a new challenge to the traditional drawing method. There are two disadvantages in traditional drawing forming. On the one hand, the whole mold has large volume, large quantity, long production cycle, high cost of storage and transportation, low reuse rate, low flexibility of the other side stretch forming machine, and the forming process is not easy to paste. The material utilization rate is low, the deformation is not uniform, it is easy to crack, wrinkle and so on. It can be seen that the traditional drawing technology has been unable to meet the needs of the skin production in the new form. In addition, the domestic tensile forming equipment is mainly imported, the European and American developed countries control the core technology of the equipment manufacturing, and the high price of the equipment makes the small and medium enterprises. It is difficult to bear. Therefore, the production of flexible tensile forming equipment with independent intellectual property has become an urgent demand for the development of China's industry. The high flexible stretch forming equipment is a new type of tensile forming equipment developed by our country, including high flexible die and high flexible stretch forming machine. For the whole traditional mold, can use the first mock exam, reduce the manufacturing cost and shorten the manufacturing cycle of the mould. High flexible stretch forming machine by discrete clamp self coordinating role in the process of sheet metal punch, can improve the forming quality, material utilization and production efficiency. In addition high flexible stretch forming device simplifies the control system. Manufacturing cost The price is easy to be accepted by small and medium enterprises and is beneficial to the application and popularization of the technology in other fields. This subject is to study the main line of multi point die and high flexible stretch forming machine, and analyze the drawing process by combining the finite element numerical simulation and experiment. The aim is to optimize the processing technology and improve the forming quality of the parts. At the same time, it also provides scientific guidance for the development of industrial production and new type of tensile forming equipment. The main contents and conclusions of this paper are as follows: 1. the principle of high flexible tensile forming and the analysis of the mechanical analysis of the forming process, the technical characteristics and the forming process of the high flexible stretch forming, and the analysis of the internal stress in the sheet material during the high flexible stretch forming. The strain change process is derived, and the internal tension of the sheet material and the unloading and rebound are derived and calculated. The selection basis of the blank size and the evaluation standard of the forming quality.2. are given to establish the dynamic explicit formula of the finite element model for the finite element numerical simulation, the static implicit solution algorithm and the elastoplastic constitutive relation of the material. The structure analysis and numerical simulation of the high flexible stretch forming finite element model and the springback model.3. stretch forming machine are set up to analyze the main components of the high flexible stretch forming machine (the clamping mechanism, the pulling mechanism, the universal structure), and the finite element numerical simulation method is used to analyze the degree of the clamp discretization, the clamp gap, and the loading. The effect of the amplitude on the forming result shows that with the increase of the clamp number, the effect of the sheet material is gradually better and the forming quality is improved. With the increase of the gap of the clamp, the stress and strain distribution uniformity of the forming part first increases and then decreases, the gap is too large, the forming area is wrinkled, the width of the sheet is 1200mm, and the working conditions of the 10 clamps are on the sheet. The forming effect is the best when the gap of the clamp is 1/9 of its width. The forming force according to the reasonable amplitude can improve the forming quality of the forming mass.4. in the high flexible stretch forming. The method of surface defect is studied with spherical and saddle parts as the research object. The method of finite element numerical simulation and tensile test are used to compare the influence of the conventional arrangement, the inclined staggered arrangement and the parallel interlaced multi point die on the forming result. The interlaced multi point die can effectively restrain the indentation defect, improve the surface quality and forming precision of the forming parts, and better than the conventional multi point die forming..5. studies the influence of the form of the basic body ball on the forming result, and derives the geometric strip tangent to the ball head and the sheet material, and builds the drawing based on the multi point die of the swinging ball head. The finite element model is used to analyze the influence of the swinging ball head on the forming result by combining the finite element numerical simulation with the tensile test. The analysis shows that when the radius of the ball head is less than the critical radius of the tangent, the forming quality is higher and the radius of the ball head is larger than the critical radius when the radius of the ball head is increased, with the ball head half the radius, with the ball head half the head. The shape of the swinging ball head die instead of the fixed ball head can effectively restrain the surface indentation of the forming parts, reduce the springback and improve the forming quality. The forming effect of the multi point die with swinging ball is superior to that of the conventional multi point die.6.. The friction coefficient of different friction contact pairs under dry friction and oil lubrication is tested. The effect of friction conditions between sheet and die is studied by finite element numerical simulation. Multi point die and elastic cushion, elastic cushion and elastic cushion are studied by the combination of finite element numerical simulation and tensile forming test. The effect of the combination of friction conditions on the forming results is shown. The results show that the forming effect of the forming part is better in the dry friction between the sheet and the die, but the stress and strain of the transition zone are large. The method of oil lubrication can effectively reduce the stress of the transition zone and should be changed; in the presence of multiple contact pairs, the contact pairs can be kept between each contact pair. For dry friction, the forming effect of the effective forming area is better. When oil lubrication is used between the elastic cushion and the elastic cushion, the forming effect is poor.7.. The effect of the elastic cushion on the high flexible stretch forming is studied by the spherical parts. The finite element numerical simulation method is used to analyze the thickness of the elastic cushion, the hardness and the number of layers on the surface quality and forming error of the forming parts. The results show that the thickness of the elastic cushion increases, the surface quality of the forming part increases, but the forming error increases; the greater the hardness of the elastic pad, the higher the surface quality and the forming precision of the forming parts; the elastic cushion with the same thickness increases with the number of layers, the surface quality of the forming parts. And the forming precision is reduced, but the rebound amount is reduced at the same time; it is simpler to use the section method to judge the sheet material. The error compensation can be realized quickly by the mould surface correction method of multi point die.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG306

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