Automatic re-lubrication by pulsating motion with punch having dimple bottom in backward extrusion of cylindrical cup

Abstract

To utilise liquid lubricants for cold forging and extrusion operations causing severe deformation without phosphate-conversion coatings, automatic re-lubricating using pulsating motion of a servo press was enhanced. Although in spline forming, there is a gap between the punch and the billet, in the extrusion of a cylindrical cup, there is almost no-gap and it is difficult to feed the lubricant. To apply the automatic re-lubrication by pulsating motion in the extrusion of cylindrical cup, a punch having dimple bottom was utilised. The lubricant is trapped in the dimples at the punch bottom. While the punch is downstrokes, the lubricant remains in the dimple, while the punch is upstrokes slightly, the lubricant in the dimple is feed to the bottom of the billet. The effects of the dimple punch were compared with the result of the flat punch. The behaviour of the re-lubrication during forging was also investigated.