| 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. |
