【作者】 石永军；

【导师】 姚振强；

【作者基本信息】 上海交通大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 在航空航天、舰船、汽车及微电子的零部件中,成形件所占比重较大,品种多,批量小,成形工艺过程复杂,尤其是钛镍合金等难成形材料零件。采用常规整体加热后冲压的方法需要制作大量的耐高温模具,成本高且周期长;部分零件由于受到加热炉尺寸的限制,不能使用该方法进行成形加工。激光热成形利用高能激光束对工件局部加热诱发不均匀热应力,使板材产生塑性变形,以获得所需要的目标形状。作为一种基于热态积累的成形方法,激光热成形无需模具与外力,是一种柔性成形技术,特别适合高硬脆性材料的成形与小批量零件的生产。本课题针对复杂曲面激光热成形工艺规划研究中存在的问题,采用实验测试、数值仿真和理论分析相结合的方法,通过对不同工艺参数条件下板材变形行为的研究,深入分析了激光热变形过程中板材的成形机理、温度场和变形场规律、成形精度控制方法、路径规划与工艺参数的确定方法,为实现金属板材的快速精确成形提供理论基础。论文的主要研究工作和创新成果如下:(1)机理分析和板材弯曲方向控制。论文分析了温度梯度机理、屈曲机理与增厚机理等主要的成形机理,从板材弯曲变形和增厚等角度探讨了不同工艺参数条件下板材的变形行为。针对复杂型面板材成形应变场的要求,根据激光热成形后板材的应变分布规律,论文重新探讨了温度梯度机理与增厚机理,使其分别对应于弯曲应变与平面应变,并提出了一种包含着温度梯度机理和增厚机理条件下板材变形特征的热成形机理——耦合机理。同时发现了在温度梯度机理、屈曲机理与耦合机理条件下,板材既产生绕x轴弯曲也产生绕y轴弯曲变形的现象。此外,为了实现板材弯曲方向的精确控制,论文对屈曲机理条件下板材的温度分布与屈曲条件进行了理论分析,推导出屈曲机理适用范围判断准则,根据Fbuckling值可判断板材的弯曲方向,并探讨了加热起始点以及加热线位置对弯曲方向的影响规律,为激光热成形工艺规划中参数选择提供理论基础。(2)激光热成形温度分布与变形行为的扩展性规律。为了减少小批量和大尺寸成形件的研究周期和成本,找出不同尺寸、材质板材激光热成形行为之间内在联系,论文对激光热成形温度分布与变形规律的可扩展性进行研究。首先,通过定义转化温度,对激光能量、扫描速度和光斑直径等单一工艺参数调整时温度场变化的规律进行研究,进而揭示出不同加工工艺参数之间温度场的映射关系。基于工艺参数与温度分布之间映射规律,可以有效地通过已知工艺参数的温度场预测出不同工艺参数条件下板材的温度分布。其次,通过定义无量纲温度和坐标转化,研究了板内任一平行于上表面的更多还原

【Abstract】 Forming parts account for much bigger proportion in the fields of the aerospace, shipbuilding, automobile and microelectronics. However, due to complex process, various products and low volume production and difficult to form materials like titanium alloy, nickel alloy, etc, the traditional whole heat forming needs a large number of high temperature resistant dies, which leads to a high expense and long times. In addition, some workpieces can not be processed because they are confined by the size of heating furnace. Laser forming is a flexible forming technology which forms sheet metal by means of laser-induced non-uniform thermal stress. As a forming method of hot accumulation, in comparison with conventional metal forming process, it requires no dies and external forces, especially, it is suitable for the hard and brittle materials forming and low volume production.In order to solve the associated problems in the process planning of complicated shape workpiece, the forming mechanism, the temperature and deformation rules, the method of forming accuracy control as well as process planning of complex shapes in the laser forming process are studied profoundly in the dissertation by experiment, numerical simulation and theoretical analysis. These investigations can provide theoretical basis for the rapid and precise forming of metal plate on the basis of the research of deformation behavior of plate under the different process parameters. The main research contents and original findings are as follows:(1) Research on forming mechanisms and the bending direction of plate. Firstly, the bending deformation and upsetting of plate under the temperature gradient mechanism, buckling mechanism and upsetting mechanism are analyzed. According to the strain field requirement of complicated shape forming, the temperature gradient mechanism and the upsetting mechanism are discussed further based on the strain distribution after laser forming, under which the plate produce the bending strain and plane strain, respectively. At the same time, a new mechanism, named as the coupling mechanism by the author is proposed, which is the combination of the temperature gradient mechanism and the upsetting mechanism. Moreover, it can be observed that the plate bends not only about the x-axis but also about the y-axis under the process conditions of the temperature gradient mechanism, the buckling mechanism and the coupling mechanism. To achieve the precise control of bending direction更多还原