【作者】 曲洪伟；

【导师】 徐文骥；

【作者基本信息】 大连理工大学 ， 机械制造及其自动化， 2004， 硕士

【摘要】 金属板材弯曲成形技术在航空航天器、汽车、船舶、化工容器等制造业中应用广泛，传统的成形技术通常需要根据板件形状，花费大量时间和资金制造相应的工模具，在大型板件成形中，这些费用更为昂贵。研究无模具柔性成形理论与技术，对减少新产品开发成本、缩短开发周期都有重要意义，在大型板件多品种小批量成形生产中具有极大的潜在优势。尤其在汽车制造领域，利用等离子体弧柔性成形技术可以对汽车覆盖件进行柔性校正及其它异形件的成形，特别是在新款式样车的试制中，可以充分发挥其适合于单件及小批量生产的优势。 分析金属板件无模具柔性成形技术的研究现状可以发现，利用热应力和热应变来实现板材成形在国内外逐渐成为研究的热点。因为等离子体弧与其它热源相比更经济、安全、灵活、实用，所以最近三年来等离子体弧板材柔性成形技术也引起了研究者的重视。但是目前相关工作只限于利用不锈钢板定性研究工艺参数与弯折角度的关系，考察弯折区域金相组织的变化等问题，扫描路径还局限于直线扫描，但对于具有复杂曲面(如非直线展成面)的零件，仅靠目前的直线扫描研究结果显然还难以达到要求。所以本文在直线扫描的基础上做了如下问题的研究： 1．探讨了薄板等离子体弧柔性成形技术的成形机理，分析了温度梯度机理、屈曲机理和镦粗机理诱发原因及作用过程。 2．建立了等离子体弧柔性成形过程的有限元热应力分析模型，并根据成形过程的热源移动的特点，将等离子体弧处理成小步距间歇跳跃式移动热源进行加载，解决了成形过程中板材的弹塑性大变形瞬态热应力问题，计算出了包括温度场分布、应力状态以及形变规律等结果。 3．以矩形板、环形板、扇形板为例，在模拟分析的基础上，以实验的方法探索了直线扫描和曲线扫描的差异以及板材的几何形状对成形结果的影响。 4．在大量实验研究的基础上，探索出由圆形板材加工球冠的等离子体弧扫描路径及其加工工艺方法。 5．针对不同几何形状的板件采用不同的扫描路径对等离子体弧柔性成形规律进行了实验研究。 综合本文以上研究结果可以发现，等离子体弧柔性成形技术不仅可以应用于板材的直线弯曲成形中，还可以应用于板材三维复杂曲面成形生产中。随着研究的不断进行，等离子体弧柔性成形技术必将在板材成形应用领域产生巨大的经济效益。更多还原

【Abstract】 Flexible forming of sheet metal is a technique applied widely in manufacturing such as in the aerospace, automobile, shipbuilding, and chemical container industries. In traditional manufacturing field of forming for sheet metal, a lot of time and money are usually cost to produce the mould and die according to the desired shape of the product. Especially, the cost for larger sheet metal will be higher. Investigating theory and technology of flexible forming without the need for mould and die contributes to significantly decreasing the high cost and long lead-time. In the versatile varieties and small-batch production, this technique has greatly potential advantages. Especially, in automobile industry, this technique can be used in flexible repair and modification for sheet metal of automotive or shaped objects. It can play important role in trial-manufacture of new type automotive.By analyzing the recent investigation on flexible forming of sheet metal without mould and die, it can be found that the technology of forming for sheet metal induced by thermal stress-strain gradually become a focus of research. Compared with another heating source, plasma arc is more economical, safe, agile and practical. So in recent three years, flexible forming technology using plasma arc gradually catch investigator’s attention. However, present researches on flexible forming of sheet metal using plasma arc are still limited to investigate the relationship between various process parameters and bending angle, and the microstructure development and transition in heat affecting zone of sheet metal. The scanning path is limited in straight line. However, it is difficult to obtain complex shapes such as nonlinear prolonged surface only by linear scanning. Therefore, the following issues have been investigated at the base of linear scanning in this paper:1. The mechanisms and characteristics of flexible forming for sheet metal using plasma arc are discussed. Temperature gradient mechanism, buckling mechanism and upsetting mechanism and causes induced are analyzed.2. Finite element method analytical model of thermo-elastoplastic stress during plasma arc scanning is established. The plasma arc is treated as a jumping heat source with small steps, which is loaded on sheet metal, according to its process of floating scanning. Transient response of stress and elasto-plastic large deformation are solved. Distribution of temperature field, stress state and result of deformation are calculated.3. At the base of simulation, the differences between linear and curved scanning, also the influences of sheet metal geometry on deformation are investigated by means of experiments, in which rectangle, ring segment and circle segment are served as specimens.4. The processing method and scanning path, by which circular plate is transformed intospherical cap using plasma arc, have been explored at the base of considerable experiments.5. Behaviors during forming by different scanning paths corresponding to different shape of sheet metal are investigated by means of experiments.In summary, it can be found that the flexible forming technology using plasma arc can be employed not only in linear bending but also in 3D complex curved surface forming for sheet metal. The technology of flexible forming for sheet metal using plasma arc will bring enormous economic benefit in the field of sheet metal forming with the development of investigation.更多还原