抄録
It is well known that the sheet metal can be stretched under the incremental forming with CNC machine tools. The deformation mechanism is studied by 3D-FE analysis. It is numerically presented that the thickness of the sheet metal is decreased under "the Sine rule", the deformation of which is subjected to the bending and unbending with the stretching along the meridian line and also the shear in the circumferential direction. In addition it is formed under the condition that the necking is generated on the part of the sheet metal on the contact with the punch and that it is stopped after the punch passes through the necking point. This deformation is repeated as the punch travels on the sheet metal, which stretches the sheet metal so much.
