Hemi-ellipsoidal stretch-expanding of aluminum sheet by CNC incremental forming process with two path method

Abstract

For incremental stretch-expanding of sheet metal, the reduction of tool-path schedule is recognized because numerous tool-paths are generally necessary for producing the required profile. A suitable tool-path schedule has been found for hemispherical shells, but the tool-path schedule for hemi-ellipsoidal shells has not been solved yet. In order to reduce the tool-path schedules for producing the hemi-ellipsoidal shells, a possibility of two path method in which a hemi-ellipsoidal shell is formed from a flat blank by means of conical stretch-expanding at first stage and subsequent hemi-ellipsoidal stretch-expanding at second stage was experimentally investigated using blanks of 1100 commercially pure aluminum sheet. Experimental results showed that the occurrence condition of unfavorable deformation modes, such as rupture and rising, depended much on the condition of conical shell height at first stage; by selecting suitable condition of the height, the hemi-ellipsoidal shell could be formed from the aluminum blank.