Abstract: Wrinkling caused by plastic instability and bifurcation is a common phenomenon in the material forming process, which can affect the forming quality and performance of the parts. Existing work mainly focuses on one or two dimensional wrinkling. Actually, three dimensional wrinkling will be found in the early stage of open extrusion process or assembling process for some low-stiffness materials. Combining the feature of drawing and extrusion, a new experiment program is proposed to detect wrinkling characteristic through changing the mould angle. The wrinkling features in each direction are described and the influences of the angle of conical die and the grain size of specimen on the wrinkling are analyzed systematically. The result shows thatthe height and distance of protrusion on the cylindrical surface and the extension length of wrinkling wave all increase with the increase of extrusion angle. Different from that, when the angle goes up, the height of protrusion, the wavelength and the extension length of the wrinkling on the bottom surface first increase and then decrease, and the protrusion distance on that surface only decreases. The longer the wavelength is, the farther the corresponding wrinkling extension will be. The larger the grain size of specimen surface is, the greater the wrinkling wavelength and the extension distance, and the more obvious the wrinkling morphology will be.

Key words: Cylinders, Extrusion, Plastic deformation, Stress concentration, Wrinkling