Cylindrical Stretch-Expanding of Sheet Metal by CNC Incremental Forming Process.

Abstract

The process of CNC incremental forming enables us to suitable for small-lot production of thin shell parts, since a variety of forming configurations can be achieved by changing only the tool-path contour. A suitable tool-path shedule has been found for some shells, such as conical and spherical shells, but has not been illuminated previously for a cylindrical shell. In this study, a cylindrical stretch-expanding process in which a cylindrical shell is formed from a flat blank by means of conical stretch-expanding and subsequent reverse stretch-expanding in two continuous tool-path schedules has been proposed and its feasibility has been experimentally investigated. Hard and soft aluminum sheets were stretch-expanded to cylindrical shells with various diameters and heights, and the deformation behavior was examined. It was found that cylindrical shells could be formed from a flat blank by means of the proposed process. Experimental results also showed that half apex angle and height of the conical shell at the first stage, moving direction of tool at the second stage and original thickness of sheet metal had significant influences on the thickness and height of the cylindrical shell. Although the wall thickness of the conical shell at the first stage decreased to a value of the Sine law, the wall thickness of the cylindrical shell at the second stage was greater than that of the conical shell at the first stage except for the part near the root of the cylindrical shell. By measuring the strain increments, it was clarified that the cylindrical shell was incrementally drawn from the conical shell at the second stage. From the incremental drawing at the second stage, it was concluded that the cylindrical shell could be seemingly stretch-expanded from the flat blank.