Development of a flexible forming system using the incremental roll forming process for the manufacture of a doubly curved sheet metal

Abstract

Bodies of automobiles, ships and airplanes are composed of doubly curved sheet metals. Even though various processes are available for manufacturing doubly curved sheet metals, such as stamping, stretch-bending, roll forming, etc., the high setup cost and long setup time make them unsuitable for manufacturing small batches of doubly curved sheet metal components. On the contrary, incremental forming processes, which have attracted renewed attentions, do not require expensive conventional equipment and time-consuming setup operations. Thus, it is suitable and efficient for the small volume production of doubly curved sheet metals. A new sheet metal forming process has an adjustable roll set as a forming tool instead of the formerly proposed incremental process by incremental press-bending technique. The roll set composed of one upper center roll and two pairs of lower supporting rolls plays a key role in this process. The motor-driven center roll rotates about a fixed axis and its rotation guides the workpiece movement. That is, after being pressed by the rolling center roll, the workpiece is moving in the tangential direction of the rotation of the center roll by the friction between the center roll and the workpiece. Each supporting roll rotates freely like a ball bearing so that it can help the workpiece move along the forming pass and be deformed by continuous bending. In this process based on the incremental sheet metal forming, since bending deformation occurs within a local contact region of a sheet just beneath the center roll, it is incrementally deformed as deformation proceeds throughout its whole region by continuous rolling movement. According to the forming schedule, the sheet can be formed repeatedly to attain further depth in shape. The process is characterized by high flexibility as compared with the typical incremental forming processes because it does not require any complex die and the loss of material is minimized without any need for ...